This article was downloaded by: [Pennsylvania State University]On: 25 September 2013, At: 06:22Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office:Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Contemporary PhysicsPublication details, including instructions for authors and subscriptioninformation:http://www.tandfonline.com/loi/tcph20

Thin film analysis with nuclear methodsKlaus-Peter LiebPublished online: 08 Nov 2010.

To cite this article: Klaus-Peter Lieb (1999) Thin film analysis with nuclear methods, Contemporary Physics,40:6, 385-413

To link to this article: http://dx.doi.org/10.1080/001075199181297

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”)contained in the publications on our platform. However, Taylor & Francis, our agents, and ourlicensors make no representations or warranties whatsoever as to the accuracy, completeness, orsuitability for any purpose of the Content. Any opinions and views expressed in this publication arethe opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis.The accuracy of the Content should not be relied upon and should be independently verified withprimary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoevercaused arising directly or indirectly in connection with, in relation to or arising out of the use of theContent.

This article may be used for research, teaching, and private study purposes. Any substantialor systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, ordistribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use canbe found at http://www.tandfonline.com/page/terms-and-conditions

Thin ® lm analysis with nuclear methods

KLAUS-PETER LIEB

Nuclear physics provides a number of unique methods to analyse thin ® lms in the range of

tens to hundreds of nanometres thickness. This article ® rst describes the basics and recent

applications of the most prominent ion-beam analysis techniques, such as Rutherford

backscattering, nuclear reaction analysis, elastic recoil detection, ion channelling, and

particle induced X-ray emission. The use of microbeams in thin- ® lm analysis will be

sketched. In addition, some nuclear techniques using (implanted ) radioactive probe nuclei

will be shortly described, such as emission channelling, conversion electron MoÈ ssbauer

spectroscopy and perturbed gamma-ray angular correlations. Mainly, such examples have

been selected where combinations of these analysing techniques illustrate their respective

power and limitations.

1. Introduction

The decade leading into the next millenium is that of thin

® lms, be they optical, hard or wear- and corrosion-resistant

coatings, multilayer electronic chips, magnetic or chemical

sensors, nanometre-to-micrometre biological structures,

just to mention a few examples. Such modern materials

are often too complicated in their compositions and

structures so that a single method rarely allows one to

fully characterize their properties and to monitor wanted or

unwanted changes of them during manufacturing or use.

For that reason, the full arsenal of solid-state spectroscopic

tools is being tested to provide the `best’ (most sensitive,

most direct, non-destructive, cheapest ) ways of analysis.

Nuclear physics along its way to investigate subatomic

structures, has developed and optimized a number of rather

simple analysing methods in thin ® lm technology which are

particularly sensitive to properties such as element compo-

sition, crystallinity, lattice locations, defect structures, and

phases. These methods can be used, to monitor the ® lm

properties during manufacturing (quality control ), but also

to investigate changes of the ® lms due to external

in¯ uences, as for example wear, corrosion, ion impact or

laser treatments. It is the aim of the present article to

describe in section 2 the most common nuclear and ion-

beam analytical methods such as Rutherford backscatter-

ing (RBS ), nuclear reaction analysis (NRA ), elastic recoil

detection analysis (ERDA ), channelling, and particle

induced X-ray emission (PIXE ). The basics, advantages

and limitations, as well as some recent applications will be

reviewed in section 2. This section also highlights develop-

ments in microbeam analysis. In section 3, shorter accounts

will be given, concerning methods using implanted radio-

active tracer ions, such as emission channelling, perturbed

gamma-ray angular correlations (PAC ) and conversion

Electron (or X-Ray ) MoÈ ssbauer spectroscopy (CEMS,

CXMS ). Among the powerful and widely used `nuclear’

methods of analysis in thin ® lms, we also have to mention

radiotracer diŒusion, neutron diŒraction, scattering and

capture, nuclear magnetic resonance, positron annihilation,

accelerator mass spectrometry, or muon spin resonance,

which are not the focus of the present survey.

As the ® eld to be covered in this rather short article has

become very broad, care has been taken to ® rst introduce,

for each method, the basic idea, to highlight its application

in one or several examples (many of them selected from

very recent work carried out at GoÈ ttingen University ), and

to ® nally summarize its bene® ts and shortcomings. We

hope that readers having specialized in one ® eld, ® nd this

presentation useful to consider supplementary analysing

methods. For more detailed information they should refer² Author’ s address: II. Physikalisches Institut, UniversitaÈ t GoÈ ttingen,

Bunsenstr. 7-9, D-37073 GoÈ ttingen, Germany.

Contemporary Physics, 1999, volume 40, number 6, pages 385± 413

Contemporary Physics ISSN 0010-7514 print/ISSN 1366-5812 online Ó 1999 Taylor & Francis Ltdhttp://www.tandf.co.uk/JNLS/cph.htm

http://www.taylorandfrancis.com/JNLS/cph.htm

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

to [1-6] and to the original papers listed at the end of this

article.

2. Ion beam analysis with stable projectiles

Modern thin-® lm materials are often made up of many

components and tailored in complicated (multilayer )

geometries. For that reason, combinations of ion-beam

analytical and other methods are being employed to

characterize the materials. Figure 1 illustrates a typical

multi-purpose experimental equipment for ion-beam ana-

lysis: the high-vacuum or UHV target chamber is connected

to an ion-accelerator beam and equipped with detectors

suitable for RBS, NRA, ERDA and PIXE and possibly

also ion channelling. In most cases, the accelerator will be

either a Cockcroft± Walton machine, a single-ended or a

tandem van de GraaΠaccelerator, or a cyclotron which

provides well focused, mono-energetic beams of light

particles (protons, deuterons, a -particles ) and possibly

heavy ions (6 ,7Li,

12C,

16 ,1 8O,

35Cl,

40Ar,

58Ni,...).

2.1. Rutherford backscattering spectroscopy (RBS )

2.1.1. Principle. RBS is the most commonly used

nuclear method for elemental depth analysis of nm-to- l m

thin ® lms [6, 7]. It is based on the elastic scattering of a

beam of monochromatic ions (typically 1 ± 3 MeV a -

particles ) at the Coulomb potential of the target nuclei,

and the known energy loss of the beam, D E in , and of the

scattered projectiles, D Eout, on their way into and out of the

target. The principle of RBS is sketched in ® gure 2 (a ): the

beam of projectile ions (nuclear mass M 1 , element number

Z1 , ion energy E1 ) hits the sample at normal incidence. If

the scattering occurs at the depth x from the surface, the

energy E f of the backscattered particles measured at the

angle h relative to the direction of the incoming beam, is

given by

E f 5 k [E 1 2 D E in (x) ] 2 D E out (x) . (1)

The kinematical factor

k 5 [M2 cos h 1 (M 22 2 M 2

1 sin2h )

1 /2]2/[M1 1 M2]

2(2)

depends on the mass (es ) M 2 of the target nuclei. Knowing

the stopping power dE1/dx of the projectile in the material,

the combined energy loss D E in (x )+ D Eo ut (x ) is a measure of

the depth x. The diŒerential cross-section for Rutherford

scattering in a laboratory system for the projectile energy at

depth x, E1 ¢ = E1- D E in (x )= E1-o & X (dE1/dx ¢ ) dx ¢ ,

d r /d R 5 [Z1Z2e2/2 E 1 sin2

h ]2 D x , (3)

depends on the nuclear charge (s ) Z 2e of the target nuclei.

Here multiple scattering and energy straggling of the

Figure 1. Typical experimental set-up for ion beam analysis

providing detectors for charged particles (Rutherford back-

scattering spectrometry= RBS, elastic recoil detection analysi-

s= ERDA, nuclear reaction analysis= NRA ), X-rays (PIXE:

Si ± Li detector ) and c -rays (PIGE: Ge-HP ). The acronym PIGE

stands for proton-induced gamma-ray emission, Ge-HP for high-

purity germanium detector. The analysing beam enters from the

right.

Figure 2. (a ) Geometry of RBS analysis. (b ) Geometry of

RNRA analysis using a proton beam and a Ge detector.

K.-P. Lieb386

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

projectiles have been neglected. The factor

D x 5 [(1 2 (M1 sin h /M2)2)1 /2 1 cos h ]

2/

[1 2 (M1 sin h /M2)2) ]

1 /2(4)

approaches 4 cos4 (h /2 ) in the limit M 1 < < M 2 , in which

case one obtains k ® 1 and

d r /d R 5 [Z1Z2e 2 /4 E ¢1]2

sin 2 4( h /2) . (5)

For a given number of projectile ions, the yield and energy

spectrum of the backscattered particles (RBS spectrum dN /dE f ) depend on the concentration pro® le of the target

atoms, c2 (x ). Several computer codes are available [8,9] to

deconvolute RBS spectra. Evidently, the dependence of the

cross-section on Z22

enhances the detection sensitivity to

heavy elements, while the dependence of the kinematical

factor k on M 2 shifts the signals from the heavy elements to

the upper part of the spectrum where they overlap least

with the lighter mass components.

2.1.2. Examples. The ® rst example selected refers to the

analysis of polycrystalline Ag± Fe bilayers deposited onto Si

wafers and their behaviour under irradiation with Xe ions

(ion beam mixing ). This system oŒers a high dynamic

contrast, due to the large diŒerence in mass and element

numbers of the three components (Ag: Z2 = 47, M 2 »108 amu; Fe: Z2 = 26, M 2 » 56 amu; Si: Z2 = 14; M 2 »28 amu ). The signals from all three components are well

separated in the backscattering spectra taken with 0.9 MeV

a -particles as shown in ® gure 3 (a ). When irradiating such

multilayers with 750 keV Xe+ +

-ions at 77 K, one notes

that the edges of the concentration pro® les at the Ag± Fe

interface get less and less steep with the increase of the ion

¯ uence U . From this observation, one was tempted to

conclude that the Ag± Fe interface roughens, due to the

mutual ion-induced transport of Ag atoms into the Fe layer

and vice versa (ion beam mixing ). However, on the basis of

STM analyses of the Ag surface, Crespo-Sosa et al. [10,11]

realized that the ion irradiation roughens the surface and

leaves the Ag ± Fe ¯ at! Indeed as shown in ® gure 3 (b ), the

diŒerence of variances measured via RBS and STM,

d r 2 (U ) º D r R BS2 (U )- D r S TM

2 (U ), is consistent with zero.

This phenomenon can be understood if we assume that

the elements in the ballistically mixed Ag± Fe interface zone

segregate as a consequence of local thermal spikes initiated

Figure 3. Athermal mixing of an Ag ± Fe bilayer via a 750 keV

Xe+

-ion beam [10, 11]. (a ) RBS spectra taken with a 0.9 MeV

a -particle beam before and after a Xe irradiation at 77 K. Note

the reduction of the thickness of the Ag top layer due to

sputtering and its increase of the variance of the Ag layer

thickness. (b ) DiŒerence of the ion-induced variances in the Ag

layer thickness obtained via RBS and STM, d r 2= D r R B S

2±

D r S T M2, as a function of the ion ¯ uence U . The three curves refer

to sequential (top ) or single irradiations (middle ) at 77 K and

single irradiations at 300 K (bottom ). As d r 2is consistent with

zero and less than the prediction of the ballistic model (dashed

lines ), it must be concluded that the Ag/Fe interface stays ¯ at

and that the Ag surface roughens.

Thin film analysis with nuclear methods 387

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

by the energetic Xe ions [12 ± 14]. Note that Ag and Fe are

not thermally miscible. The increase of the variance

D r ST M2 (U ) indicates an ion-induced roughening and grain

growth at the surface of the Ag layer [11].

The second example refers to a recent study by Schaaf

and co-workers [15 ± 18] on the laser nitriding of armco iron

via short pulses of a XeCl excimer laser (pulse duration

55 ns, average energy density 2 ± 8 J cmÐ 2 ). Many facets of

this complicated and technically important process have

been understood on the basis of nuclear techniques such as

RBS, RNRA and MoÈ ssbauer spectroscopy (see [18] and

below ). The high energy density of the laser beam melts

about a 1 l m thick surface layer and may lead to several

transport processes such as turbulent ¯ ow, ablation and

ejection of the melt by the plasma pressure. These transport

properties have been made visible through RBS by

introducing a 10 nm thin Au layer into the Fe sample at a

depth of 60 nm below the surface, before laser irradiation.

Figure 4 illustrates RBS spectra taken at 0.9 MeV a -particle

energy before and after applying 1 and 4 laser pulses:

clearly, already the ® rst laser pulse fully dissolves the Au

marker layer and leads to a uniform distribution of the

marker, as can be seen by the ¯ at Au distribution between

690 and 830 keV a -energy in the RBS spectrum [15].

2.1.3. Depth and mass resolutions, eŒects of roughness.

The depth resolution D x » D E (dE/dx )Ð 1

to be achieved in

RBS depends on the energy precision of the primary beam,

r 12, the energy straggling of the beam on its way into and

out of the target, r S2, the variation of the backscattering

energy due to the ® nite solid angle of the detector, r X2, and

the energy resolution of the detector, r det2:

D E » ( r 21 1 r 2

S 1 r 2 1 r 2de t)

1/2. (6)

For a well-stabilized, low-energy Cockcroft± Walton accel-

erator, r 1 is of the order of 0.05 ± 0.15 keV at E1 < 0.5 MeV

[19], while for a 2 ± 5 MeV van de GraaŒ or tandem

accelerator, r 1 » 1 keV. Electronic straggling, r S2, can be

estimated via Bohr’ s expression [20],

r2S » 4p e 2

Z21 Z2 N2 x(1 1 1 /cos h ) , (7)

where N2 denotes the atomic density of target atoms and x

the depth of the scattering process in the ® lm; the quantity

x (1+ 1/cos h ) is then the full path length traversed by the

projectile. For a -backscattering from a Fe ® lm (Z2 = 26,

M 2 » 56 amu, h = 165 8 ), r S increases as 12 from about

2 keV for x = 10 nm to some 10 keV at 200 nm.

The main contribution to the depth resolution there-

fore is usually derived from the energy resolution of the

detector, r d et. For the most commonly employed Si

surface barrier detectors having a very thin ion-

implanted Au top layer towards the target, r det = 11 ±

13 keV. Alternative solutions to improve the detector

resolution have been developed by using electrostatic or

magnetic spectrometers [21,22]. In the best cases, an

energy resolution as small as < 1 keV has been achieved

Figure 4. RBS spectra and deduced Au depth distributions of an armco Fe sample containing a 10 nm Au marker layer at a depth of

60 nm and irradiated with 1 or 4 pulses of a XeCl excimer laser [15].

K.-P. Lieb388

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

using a magnetic analyser, which leads to a depth

resolution of about a monolayer at the surface of the

sample [22,23].

RBS averages with respect to the ¯ uctuations in ® lm

thickness and density over the spot size of the analysing

beam (typically 1 ± 5 mm2

if no microbeam is used ). As a

consequence, the tails of the edges in the RBS spectrum

directly re¯ ect these ¯ uctuations, but they do not allow one

to distinguish between surface roughness and interface

roughness if the thin ® lm is deposited on another thin ® lm

or on a substrate. The eŒect of surface roughness has

recently been studied by Metzner et al. [24,25] for

polycrystalline, 10 ± 500 nm thick In ® lms deposited via

evaporation from a Knudsen cell onto nanometre smooth

Si wafers. Figure 5 illustrates RBS spectra obtained at 0.9

a -energy for two rather thick samples. A scanning electron

microscopy (SEM ) analysis showed the presence of In

droplets of several hundred nanometre diameter on the

surface of sample #12. An analytical description of this

surface topography has been inferred by assuming a height

probability function p (h ) which is composed of two

fractions: the droplet part pD (h ) is represented via hemi-

spheres of radius R , pD (h )= (4fD / p R2 ) (R

2± h

2 )12, while the

non-structured part of the ® lm is approximated by a

Gaussian distribution (fraction fG = 1 ± fD , average thick-

ness < h> , variance r h2 ). Fits to the RBS spectra gave the

parameters listed in table 1. A comparison of the spectra

taken at 0.9 and 2.0 MeV a -energy and the errors given in

table 1 shows that the lower a -energy provides better depth

resolution, while the higher a -energy provides better mass

resolution. This diŒerence is due to the variation of the a -

particle stopping power.

Figure 5. RBS spectra obtained at 0.9 MeV a -particle energy from two thick In ® lms deposited via evaporation onto Si substrates. The

inserts illustrate the height distributions p (h ) whose parameters are listed in table 1 [25].

Thin film analysis with nuclear methods 389

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

2.2. Nuclear reaction analysis (RNRA )

2.2.1. Principle. While Rutherford scattering enhances

the heavy components of the target to be analysed, nuclear

reaction analysis (NRA ) induced by protons or a -particles

of some 100 keV up to several MeV is most useful for depth

pro ® ling the light components of ® lms. Since almost all

modern ceramic materials contain carbon, nitrogen and

oxygen, NRA, in particular in combination with proton-

induced resonance reactions (RNRA ), has become very

popular for depth pro® ling these light components. Since

RNRA is not only depth sensitive, but selects particular

target isotopes, this technique opens the way to detailed

isotope-sensitive studies (we mention corrosion in18

O-

enriched gases or ¯ uids [26] and nitriding in15

N-enriched

atmospheres [27] ).

In ® gure 2 (b ), the basic principle of RNRA is sketched

for a reaction having a narrow resonance at energy ER and

total resonance width C , in the laboratory frame. Neglect-

ing any non-resonant processes and the dependence of the

resonance width parameters on the beam energy, the cross-

section over the resonance follows the Breit± Wigner

formula

r (E 1) 5 r 0 G in G out /[(E 1 2 E R )2 1 G 2 /4], (8)

where r 0 is a constant and C in and C out denote the partial

widths of the entrance and exit channel of the resonance,

respectively. The yield of the resonance reaction can be

monitored by measuring the emitted charged particles and/or subsequent c -radiation of the ® nal nucleus. Generally,

the analysing beam (say protons at energy E1 ) hits the

sample at normal incidence. In ® rst approximation, if

E1 = ER , the resonance reaction evidently selects nuclei

located at the surface. If E1 > ER , the resonance occurs at

the depth x = (E 1 ± ER ) (dE 1/dx )Ð 1

. By measuring the yield

function Y (E1 ) for constant projectile number (accumu-

lated charge ) and varying the beam energy E1 in small

steps, the yield function Y (E1 ) can be deconvoluted into the

desired concentration pro® le c2 (x ). Of course, the ® nite

resonance width C , the beam spread of the accelerator and

the energy straggling of the projectiles in the target have to

be considered in the analysis. A survey of reactions suitable

for NRA is given in [28 ± 30]. Table 2 lists some useful low-

energy proton-induced resonance reactions (E 1 < 0.5 MeV )

whose resonance parameters ER and C have been measured

at the GoÈ ttingen high-resolution implanter IONAS and

which are appropriate for depth-pro® ling the isotopes14 ,1 5

N,18

O,19

F,23

Na,24 ± 26

Mg and27

Al [19].

2.2.2. Examples. Important details of the laser nitriding

process [16, 18] already discussed in section 2.1 have been

revealed by RNRA using the prominent15

N (p, a c )12C

resonance at 430 keV for depth-pro® ling the nitrogen

isotope15

N (see table 2 ). The 4.43 MeV c -radiation in12

C emitted in this reaction is recorded in a 12 cm long,

16 cm wide NaI detector and the 2.0 l A proton beam is

scanned in 5 keV steps over the resonance. When

deconvoluted, the c -ray yield curve Y c (E1 ) provides the

desired15

N concentration pro® le. Usually, the 0.37%

abundance of the isotope15

N present in natural nitrogen

is su� cient for such analyses. If the laser nitriding process

is carried out in atmospheres of enriched15

N content, the

eŒect of single laser pulses within a series of multiple

irradiations can be highlighted [15,17,27]. Figure 6 illus-

trates nitrogen depth pro® les obtained when irradiating the

Fe sample with up to 256 pulses of a homogeneous XeCl

excimer laser beam at an average energy density of

4.0 J cm2

[17]. While the ® rst pulse induces a more or less

exponential nitrogen pro® le and very little nitriding, each

subsequent pulse increases the nitrogen content at depths

larger than 20 nm, until a saturation pro® le develops after

some 128 pulses, equivalent to cN (x )= 12 at.% at depths

x> 100 nm. At the surface, saturation is already reached

Table 1. Fit parameters of rough In layers deposited onto Si

wafers and covered with hemispherical in droplets [25].

Sample Ea

(MeV )

fD

(% )

R

(nm )

< h>

(nm )r h

(nm )

hm

(nm )

#11

#12

#12

0.9

0.9

2.0

58 (2 )

68 (1 )

68 (3 )

460 (12 )

217 (1 )

208 (4 )

614 (1 )

277 (1 )

261 (4 )

71 (1 )

54 (2 )

54 (4 )

492 (1 )

224 (1 )

205 (4 )

Table 2. Useful proton resonances for RNRA below

E1= 500 keV.

Reaction ER (keV )a G (eV )a W (eV )b Reference

14N (p, c )1 5

O15

N (p, a c )12C

18O (p, a )15

N19

F (p, a c )16O

23Na(p, c )24

Mg24

Mg (p, c )25Al

24Mg (p, c )26

Al

26Mg (p, c )27

Al27

Al (p, c )28Si

277.60 (27 )

429.57 (9 )

150.97 (26 )

223.99 (7 )

340.46 (4 )

483.91 (10 )

308.75 (6 )

222.89 (8 )

316.16 (11 )

389.24 (11 )

434.85 (12 )

496.75 (12 )

292.06 (9 )

222.82 (10 )

293.08 (8 )

326.97 (5 )

405.44 (10 )

446.75 (15 )

1115 (15 )

125 (16 )

178 (30 )

985 (20 )

2340 (40 )

903 (30 )

< 36

< 32

< 37

< 4

< 44

< 51

< 37

< 34

59

< 38

< 42

40 (5 )

60 (5 )

53 (5 )

48 (5 )

62 (5 )

72 (5 )

64 (5 )

52 (5 )

68 (5 )

82 (5 )

85 (5 )

95 (7 )

69 (5 )

57 (5 )

70 (5 )

73 (5 )

87 (5 )

96 (6 )

c

[31]c

[19]

[19]

[32]

[19]

[19]

[19]

aEnergies ER and G in the laboratory system.

bBeam ripple and Doppler broadening at room temperature.

cK. P. Lieb, private communication.

K.-P. Lieb390

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

after 8 laser pulses. On the basis of the depth and lateral

nitrogen pro® les and other quantities like surface pro® le

and hardness, Schaaf and co-workers [15, 16] developed a

scenario which accomodates various aspects of the laser±

plasma± melt± solid interactions, the nitriding eŒect and

other transport processes due to laser irradiation.

The second example presented refers to the analysis of

magnetron-sputtered FeN layers, a recently identi ® ed phase

in the otherwise well-documented Fe± N phase diagram

[33,34]. This system can be ideally analysed by combining

RBS, which is sensitive to the Fe concentration pro® le,

and RNRA, again using the15

N (p, a c )12C resonance

reaction for depth pro® ling the N concentration. Figures

7 (a ) and (b ) illustrate the N and Fe depth pro® les

obtained in this way [35], together with the depth pro® les

of all elements deduced from an ERDA analysis (® gure 7

(b ), see section 2.3 ). The relative calibrations of the two

methods pose a certain problem. In the case of RNRA

one may use stoichiometric CrN or TiN ® lms. As long as

only Fe and N are present in the ® lms, this combination

of methods works very well and the typical error of

stoichiometry amounts to 1 ± 2% . If additional (light )

elements such as carbon or oxygen are present in the

® lms, one cannot quantitatively determine their contents

via RBS, while RNRA would require appropriate

resonance reactions for each element. Under such condi-

tions, ERDA oŒers an elegant alternative for multi-

element analysis (see ® gure 7 (b ) and section 2.3 ).

2.2.3. Depth resolution and sensitivity. The depth resolu-

tion of RNRA, D x » D E (dE /dx )Ð 1

, depends on similar

quantities as for RBS. The achievable energy resolution D E

is again in¯ uenced by the energy precision of the beam, r 1 ,

and the straggling of the projectile, r S, on its way from the

surface to the depth x, where the nuclear reaction takes

place. In addition, the Doppler broadening due to the

thermal motion of the capturing target nuclei, r D op p, and

the resonance width C in¯ uence the energy resolution:

D E » ( r 21 1 r 2

Dopp 1 G 2 1 r 2S )

1/2. (9)

Using a highly stabilized proton beam (e.g. that of IONAS )

and the very narrow resonances listed in table 2, the energy

ripple of the beam and the Doppler broadening at room

temperature, W = (r 12+ r D o pp

2 )12 increase from 50 eV to

100 eV for E 1 = 100 ± 500 keV [19]. Therefore, the energy

resolution D E mainly re¯ ects the energy straggling r S of the

proton beam in the target, leading to depth resolutions of

some 10 ± 20 nm at x » 100 ± 300 nm. If straggling can be

avoided, i.e. when using RNRA at the surface, the depth

resolution can be reduced to less than 1 nm and RNRA has

even been used to study, e.g. atoms adsorbed at surfaces

[37].

Figure 6. Laser nitriding of armco iron by a XeCl excimer laser

beam. The curves represent the nitrogen depth pro® les for n= 1

up to n= 256 laser pulses obtained via RNRA by means of the

reaction15

N (p, a c )12C [17].

Figure 7. Analysis of magnetron-sputtered FeN ® lms on Si

substrates highlighting the depth pro® les of various elements in

the sample [35,36]. (a ) N depth pro® le obtained from RNRA and

the reaction15

N (p, a c ); (b ) TOF-ERDA analysis using a 37 MeV197

Au beam and glancing geometry. Note the contents of carbon

and oxygen not observed in (a ) nor in (c ); Fe depth pro® le

obtained from RBS using 0.9 MeV a -particles.

Thin film analysis with nuclear methods 391

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

2.3. Elastic recoil detection analysis (ERDA )

2.3.1. Principle. This ion-beam technique, which was

pioneered in the seventies mainly for the purpose of

hydrogen pro® ling [38 ± 42], has very much developed in

thin-® lm analysis during the last decade, especially for

depth pro® ling of light and medium-mass elements, and

some very sophisticated instrumentation has been designed.

The recent review by Tirira et al. [43] covers these

developments. The main diŒerence between ERDA and

RBS and NRA is the use of heavy projectiles M 1 > M 2 . Due

to energy and momentum transfer during the nuclear two-

body collision with the target nucleus (scattering or

reaction ), a pair of energetic ions is produced and either

the scattered ion (Z1, M 1 ) or the ejected recoil atom (M 2 ,

Z2 ), or both, may leave the sample and are analysed. In the

case of an appropriate geometry (see ® gure 8 ), both

particles may be measured in coincidence. Again, the

energy losses of the projectile before, during and after the

collision and the stopping of the associated recoil atom on

the way out of the sample determine site x of the reaction

within the target.

Figure 8 illustrates the two basic experimental set-ups

used in ERDA [44]. In order that both particles can be

observed, the technique is either used for thin, self-

supporting ® lms (transmission geometry ) or at very small

incidence and ejection angles with respect to the ® lm

normal (glancing geometry ). For pure Rutherford scatter-

ing, the diŒerential cross-section for recoil mass M 2 at an

angle / with respect to the direction of the primary beam is

given in the laboratory frame as

d rrec

/d R 5 [Z1Z2e 2 /2E ¢1 ]

2[M1 1 M2) /M2]

2cos 2 3 u ,

(10)

where E1 ¢ again denotes the projectile energy just before the

collision.

As in RBS, the simplest way to use ERDA is the

measurement of the projectile and/or recoil energy spec-

trum Y (E f ) which contains information about the concen-

tration depth pro® les c2 (x ) within the analysed ® lm and can

be deconvoluted in a similar manner. However, as long as

one does not diŒerentiate between the projectile and the

ejected (recoil ) species, there exists an ambiguity concerning

the fractions of energy shared between both partners.

Depending on their masses M 1 and M 2 , particles from

diŒerent depths can have the same energy. This leads to a

mass± depth ambiguity or, in the forward direction, to a

recoil± projectile ambiguity [44].

Several remedies have been tested to solve this problem.

The simplest solution is the use of absorber foils in which

the diŒerent ions experience diŒerent energy losses,

depending on their mass, element number and energy.

High-resolution magnetic spectrometers, combinations of

Figure 8. Typical set-ups of ERDA in glancing and transmission geometry used to depth-pro® le hydrogen via impact with a4He beam

[43].

K.-P. Lieb392

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

electric and magnetic ® elds (ExB ® lters ) or a gas ionization

chamber in conjunction with the silicon surface barrier

energy detector have also been used for particle identi ® ca-

tion [45 ± 47]. A quite universal and experimentally still

straightforward version of ERDA which oŒers mass and

element identi ® cation, is sketched in ® gure 9. Via a time-of-

¯ ight spectrometer (mass ), combined with a D E -E telescope

(element number, energy ), all three quantities can be

determined. This technique is called TOF-ERDA. The

¯ ight path is de® ned by an electrostatic start detector,

usually a thin carbon foil emitting secondary electrons

during the very short passage time of the ion. These

electrons are collected via an arrangement of electric ® elds

and mirrors and guided to a microchannel plate where they

produce a nanosecond sharp time mark. As stop detector,

one can either use a similar electrostatic detector or directly

the thin D E surface barrier Si detector of the telescope.

2.3.2. Examples. The example for ERDA with coinci-

dence spectroscopy shown in ® gure 10 refers to the analysis

of self-supporting polycarbonate foils (C16O3H14 ) by means

of a 2 MeV a -beam [49]. In order to remove the projectile ±

recoil ambiguity, coincidences were required between the

forward-scattered a -particles (h = 70 8 ) and the O and C

recoil atoms (/ = 48 8 ). Figures 10 (a ) and (b ) illustrate the

3-dimensional energy± energy-intensity histogram, and a

projection of it onto the energy± energy plane, which the

distribution of oxygen and carbon in the foil can be

deduced from.

The properties of magnetron-sputtered FeN layers have

been studied by Rissanen et al. [35, 36] via glancing ERDA

(as well as RBS, RNRA and MoÈ ssbauer spectroscopy, see

sections 2.2 and 3.2 ). The stoichiometries of the ® lms and

the occurrence of contaminants were investigated, depend-

ing on the deposition parameters in the HF magnetron (gas

mixture, substrate temperature, HF power ). The analysis of

light elements was carried out by means of a TOF-ERDA

spectrometer [48] set up at the University of Helsinki

tandem accelerator using a 37 MeV197

Au beam (see ® gure

9 ). The element depth pro® les of a nearly stoichiometric

FeN ® lm on a Si substrate containing very few contami-

nants of carbon and oxygen are plotted in ® gure 7 (b ). When

comparing the bene® ts and limitations of RBS, RNRA and

ERDA in this particular example, one clearly would prefer

ERDA as long as depth resolution is not the critical

parameter.

2.3.3. Depth and mass resolution, sensitivity, limitations.

The wide range of target± projectile combinations and

geometries in ERDA usually does not provide a general

estimate of the achievable depth and mass resolutions [43].

With 3 MeV a -particles, depth resolutions of 10 ± 40 nm

have been reported for H-pro® ling in silicon [50, 51]. Using

a 60 MeV12

C beam of the Munich tandem accelerator and

a Q3D magnetic spectrograph, Dollinger et al. [45] recently

achieved atomic resolution for the (0002 ) layers of a highly

oriented pyrolytic graphite (HOPG ) crystal, in glancing

geometry (h = 96 8 ). As mentioned before, one can orient

the sample in such a way as to allow both the projectile and

recoil to travel out of it so that their energies (and masses )

can be measured in coincidence. Whenever the sample can

be manufactured as a self-supporting thin foil, the

transmission geometry is preferred for the following

reasons [44].

(a ) It facilitates coincidence measurements with large

detector solid angles.

(b ) The maximum probing depth is larger than in

glancing ERDA, since the analysing beam enters at

normal incidence.

(c ) The depth resolution does not depend on the surface

roughness (which is a very important limitation in

glancing geometry ), but rather on the homogeneity

of the ® lm.

(d ) The mass resolution d = d E2/ d M2 of the device is

de ® ned via the energy diŒerence d E2 of recoil atoms

after the collision, when two types of atoms diŒer by

the quantity d M 2. The calculated mass resolution din transmission ERDA [43] as a function of M 2 is

plotted in ® gure 11 for the four projectile beams4He,

16O,

35Cl and

58Ni, which all are easily available

at tandem accelerators. One notes the poor resolu-

tion for M 1 = M 2 . This graph shows that4He beams

are best suited to diŒerentiate between the hydrogen

isotopes and in the mass range M 2 = 10 ± 30 amu,

while16

O ions are recommendable for pro® ling

heavier nuclei (M 2 = 30 ± 80 amu ).

2.4. Ion channelling

2.4.1. Principle. While RBS, NRA and ERDA generally

determine the concentration pro® les of elements or isotopes

in thin ® lms, channelling uses well focused ion beams for

getting information on the crystallinity of the sample and/

Figure 9. Time-of-¯ ight ERDA arrangement [48].

Thin film analysis with nuclear methods 393

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

or the lattice locations of dopants or self-atoms. Channel-

ling rests on the intuitive idea that positive ions, mostly

protons, a -particles and other light ions, travelling along an

`open’ (axial or planar ) channel in a crystal experience

fewer collisions and therefore a reduced energy loss. What

is more important, the channelled ions are focused by the

ion cores aligned along the boundary atomic rows of the

channels. Any atom located within the channel therefore

constitutes a collision centre (for reactions or backscatter-

ing ) and in this way adds to the stopping process [52 ± 56].

The theory of channelling was ® rst worked out, for

example, by Lindhard and by Leibfried [56] in the limit of

the `continuum channel potential’ (see ® gure 12 )

Ua (r ) » (Z1Z2e 2 /d) ln (3a /r )2 1 1]. (11)

Here the quantity d denotes the distance of neighbouring

Figure 10. Coincidence ERDA analysis of a self-supporting polycarbonate ® lm with a 4 MeV4He

+ +beam in transmission geometry

[49]. (a ) Histogram of the energies of recoil atoms (Ereco il ) and scattered He-projectiles (EH e ). (b ) Projection of the histogram shown in(a ) onto the Erec o il-EH e plane.

K.-P. Lieb394

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

atoms in the row, a the Thomas± Fermi screening length

and r the distance of the moving ion Z 1 from the row. This

potential gives rise to a critical tilt angle w c (relative to the

channel direction ) up to which the incoming ions are being

axially guided (transmitted ) within the channel:

c 5 (Z1Z2e 2/E

¢1 d )

1 /2|ln [3a / q )2 1 1]|1 /2

. (12)

The quantity q is approximately 2/3 of the mean square,

lattice vibrational amplitude and E1 ¢ is the energy of the

impinging ion inside the crystal:

E ¢1 5 Ua (r ) 1 (p1^ 2 /2M1) 1 (p15

2 /2M1) , (13)

where p1 ^ and p1 | | denote the transversal and long-

itudinal components of the projectile momentum relative

to the channel axis. For 1.0 MeV a -particles incident

onto Si < 110> at room temperature, the calculated

critical tilt angle is w c = 0.65 8 which compares fairly

well with the measured value w c = 0.55 8 [55]. Similar

Figure 11. Mass resolution d j /dM 2 calculated as function of M 2 , for analysing beams of4He,

16O,

35Cl,

58Ni and

63Cu [43].

Figure 12. The ion beam entering from the left is partly transmitted through the crystal channel and partly rescattered from surface

atoms (shadow cone ).

Thin film analysis with nuclear methods 395

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

expressions have also been derived for planar ion

channelling conditions.

2.4.2. Examples. Figure 13 shows an example illustrat-

ing the lattice locations of Yb impurity atoms in silicon which

have been implanted at 60 keV and 450 8 C, at a ¯ uence of

5 ´ 1014

ions cmÐ 2

. The normalized backscattering yield of

1.0 MeV a -particles is plotted versus the tilt angle h relative

to the < 110> channel. The Si signal (full line ) shows the

expected channelling dip proving the crystalline structure of

the matrix after implantation, while the Yb signal (broken

line ) indicates a ¯ ux peaking eŒect arising from the

interstitial lattice location of the implanted Yb ions [52].

The second example refers to the solid phase epitaxial

regrowth (SPEG ) of ion-irradiated SiO2 (a -quartz ) sam-

ples. Even small ion ¯ uences are known to damage

monocrystalline SiO2 to such an extent as to destroy the

long-range crystalline order. For instance, 50 keV20

Ne

ions produce a coherent amorphized layer at a ¯ uence of

only 1 ´ 1014

ions cm2

[57]. On the other hand, the short-

range order of Si and O atoms, i.e. the degree of

connectivity, is usually preserved up to much higher ion

¯ uences and even for ions as heavy as Xe. For this reason,

the conventional method of solid-phase epitaxial regrowth

via post-annealing of the irradiated samples in vacuum has

never been successful [58, 59]. Bolse and co-worker [60 ± 62]

have recently solved this longstanding problem and, indeed,

succeeded in preserving or achieving full recrystallization of

ion-beam amorphized SiO2. In all these studies, RBS

channellng was the key method of investigation of the

crystalline structure of the amorphized and recrystallized

SiO2 surface layers.

Dahr et al. [60] investigated SPEG of Ne-irradiated a -

quartz via dynamic annealing up to 980 K, by searching for

the balance between damage accumulation and annealing,

as a function of the ion ¯ uence U and the sample

temperature T. Figure 14 illustrates RBS-channelling

spectra taken after implanting 1 ´ 1015 20

Ne ions cmÐ 2

at

50 keV and for the substrate temperatures indicated. One

notes that the damage (degree of amorphization ) decreases

for increasing substrate temperature and that all damage

completely disappears at the critical temperature

Tc » 970 K. If one applies lower ion ¯ uences, SPEG can

be achieved at lower temperatures. Figure 15 displays the

temperature dependence of the critical ¯ uence U c , i.e. that

of Ne-ion ¯ uence at which defect production accumulates

to form an amorphous layer. One notes that at T » 980 K,

F c steeply increases, indicating that SPEG wins over

amorphization at any ion ¯ uence. The temperature

dependence of the critical ¯ uence U c can be parametrized

by the defect out-diŒusion model by Morehead and

Crowder [63] and is compatible with an activation energy

of Ea = 0.28 (2 ) eV. (In passing we note that the back-

scattering spectra from both the virgin and fully recrys-

tallized samples show a small peak at the surface. This peak

arises from the non-channelled scattering of the a -particles

at the surface Si atoms; it depends on the propeties of the

bulk surface and contains information about reconstruc-

tion and relaxation of the surface and adsorbed atoms or

molecules. )

While dynamic annealing tries to avoid damage accu-

mulation during the process of implantation, Roccaforte

and cok-workers [61, 62] studied the epitaxial recrystallisa-

tion of alkaline-ion irradiated a -quartz in air. In these

experiments, single-crystalline (0001 ) a -quartz samples were

irradiated at 77 K with 250 keV Cs+

ions to a ¯ uence of

2.5 ´ 1016

ions/cm2. The c axis of the crystal was misaligned

Figure 13. Channelling analysis of a Si sample doped with

5 ´ 1014

Yb-ions cmÐ 2

via 60 keV ion implantation at 450 8 C.

The a -particle backscatter yields from Si and Yb as function of

the tilt angle relative to the < 110> channel direction in the Si

matrix are shown. The yield functions demonstrate that the Yb

implants are located on intersitial sites, while the Si matrix has

stayed single-crystalline [52].

K.-P. Lieb396

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

by 6 8 relative to the beam direction to prevent channelling

eŒects during implantation. Isochronal annealings (1 h )

either in an air furnace or in vacuum at 2 ´ 10Ð 6

mbar were

carried out at 500 ± 900 8 C. An important result of these

measurements is illustrated in ® gure 16, which shows RBS-

channelling spectra of Cs-irradiated samples individually

heated in air to the temperatures indicated: the recrystalli-

zation process starts around 800 8 C and is fully completed

at 875 8 C where the backscatter spectrum cannot be

distinguished any more from that of a virgin single crystal.

As shown in ® gure 16 (bottom ), the recrystallization speed

v (T ) follows an Arrhenius dependence governed by an

activation energy of Ea = 2.83 (20 ) eV. Also indicated in

® gure 16 (top ) is the RBS signal of the pro ® le of the

implanted Cs which shows its migration during annealing:

the as-implanted Gaussian pro® le broadens to a box-like

shape at 700 8 C, with Cs penetrating deeper into the sample

until reaching the amorphous± crystalline interface around

800 8 C. Finally, all Cs migrates to the surface and leaves the

sample at 875 8 C, where complete recrystallization of the

matrix was achieved. Previously, SPEG of Si- and O-

irradiated Brasilian quartz was observed by Devaud et al.

[64] to occur around 1050 8 C under air. Similar self-

implantation experiments in a -quartz did not show any

recrystallization up to 875 8 C [61]. Control experiments

were also carried out with132

Xe,23

Na and7Li ions. While

annealing in air of the alkali-ion irradiated samples resulted

in SPEG, no epitaxial recrystallization was observed after

the Xe implantations nor after annealing in vacuum.

The peculiar in¯ uence of Cs (or other alkali ions studied

such as Li and Na ) on the recrystallization process of a -

quartz can be explained by topological arguments. Amor-

phous and crystalline SiO2 consist of networks of corner-

Figure 14. RBS-channelling spectra from single-crystalline SiO2 samples obtained after 50 keV Ne+

implantations at a ¯ uence of

1 ´ 1015

ions cmÐ 2

, measured at the substrate temperatures indicated [60].

Figure 15. Temperature dependence of the critical ¯ uence U c

for amorphization of SiO2 (a -quartz ) via 50 keV20

Ne ion

bombardment [60]. At 970 K, recrystallization balances amor-

phization at any ¯ uence. The ® t to the data is based on the model

of Morehead and Crowder [63] and corresponds to the values of

the activation energy Ea and critical temperature Tc indicated.

Thin film analysis with nuclear methods 397

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

sharing [SiO4] tetrahedra, having four oxygen vortices, each

of them common to two adjacent [SiO4 ] tetrahedra. Recent

theoretical modelling of the network structure [65] suggests

that SiO2 is fully connected in the ordered and in the

amorphous phase. The ability of a random network to

epitaxially recrystallize strongly depends on the connectiv-

ity of the tetrahedra. The introduction of alkali ions into

the SiO2 matrix, regarded as network modi® ers, breaks up

the network, generates non-connected tetrahedon corners

and increases the recrystallization probability. Most likely,

the role of oxygen during annealing relies on the formation

and disintegration of alkali oxides. This hypothesis can be

checked by annealing the samples in enriched18

O and

measuring the18

O concentration pro® les, via ERDA or the18

O (p, a ) resonance reaction [62].

2.5. Particle induced X-ray emission (PIXE )

2.5.1. Principle. In the true sense, PIXE is not a

nuclear technique, since the ionization of the atoms of a

thin-® lm sample by charged-particle impact (electrons,

protons, ions ) and the subsequent emission of character-

istic X-rays are purely atomic electromagnetic processes.

Furthermore, only under very special conditions PIXE

provides information on depth pro® les of the elements

within the sample. Nonetheless, PIXE ranges among the

most common ion-analytical methods of thin ® lms, as it

provides detailed information about the (generally aver-

age ) element composition of the sample and is able to

detect elements at the sub-ppm concentration level. For

that reason a short outline of PIXE is being included in

this article.

PIXE has been widely documented, and we refer to some

recent survey articles [66 ± 69]. In general, one uses a proton

beam at an energy E1 close to the Coulomb barrier EC » Z 2/M 2

1 /3 of the lightest element (Z 2 ,M 2 ) to be detected in order

to avoid nuclear reactions taking place. A more recent

development of PIXE in thin ® lm analysis, called diŒer-

ential PIXE [31], uses the strong decrease of the K-hole

production cross-section r K toward smaller proton energies

which restricts X-ray emission to the top layer of the ® lm or

substrate. Figure 17 (a ) shows the normalized K-ionization

cross section r K (EK 2/Z1 )2 as a function of the proton

energy E1/EK 2 [67], normalizd to the K-shell binding energy

EK 2 of the matrix atom. As the K a X-ray emission strongly

competes with the emission of Auger electrons in low-Z2

substrates and therefore gives a ¯ uorescence yield x X < 1,

the K a X-ray yield rises sharply with the proton energy, but

Figure 16. Solid state epitaxial recrystallisation of SiO2

irradiated with 250 keV Cs+

ions at ¯ uences of

2.5 ´ 1015

ions cmÐ 2

and 77 K [61]. (a ) RBS-channelling spectra

after 1 h annealings at the temperatures given; (b ) Arrhenius plot

of the recrystallization speed v (T ).

Figure 17. Normalized K-hole production cross section r (EK 2/Z1 )2 after proton bombardment of light and medium-mass

elements (Z2= 6 ± 28 ), plotted versus the reduced proton energy

E1/EK 2 . The quantity EK 2 denotes the K-shell ionization energy

of the target. The full line is the prediction of the binary

encounter theory [67].

K.-P. Lieb398

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

then decreases at higher proton energies. Figure 17 (b )

illustrates the energy dependence of the K a X-ray emission

cross-section r K x X for various elements [69].

2.5.2. Examples. The ® rst example selected illustrates

the use of diŒerential PIXE in analysing TiN coatings on

steel [31, 70]. Figure 18 (a ) shows the X-ray spectrum taken

for a 500 keV proton beam impinging onto a 30 nm thin

TiN layer deposited on 1 mm stainless steel. One discerns

the K a and K b X-ray lines of the elements Ti, Cr, Fe, and

Ni. The relatively large yield of the Ti K-radiation is due to

the fact that the cross-section for K-hole production rises

steeply with the proton energy (see ® gure 17 (a )), thus

enhancing X-ray emission in the top (TiN ) layer of the

sample relative to the deeper (steel ) layers. For that reason,

even modi® cations of the top TiN layer, e.g. by ion-induced

sputtering, can be measured: ® gure 18 (b ) illustrates a scan

of the Ti X-ray yield over the implantation spot of 1016

Kr

ions cmÐ 2

. The reduction in the Ti K a yield in the

implantation spot illustrates the reduction of the TiN layer

thickness, due to sputtering, and can be used to measure the

sputtering coe� cient.

Measurements of trace elements in tree rings illustrate

the power of the PIXE method in analysing biomaterials

[71]. Figure 19 (a ) illustrates the X-ray spectrum obtained

in a Si (Li ) detector when bombarding a sample of kaki

wood with a 4 ´ 4 mm2

proton beam at 2.0 MeV energy

and 20 ± 50 nA current. The detector was covered with

two absorbing foils, 16 l m mylar and 58 l m Al, in order

to enhance the signals of the heavier elements in the

spectrum. One discerns the K a lines from elements

between potassium and strontium. Figure 19 (b ) shows

the variations of the Cu, Zn, Rb and Sr contents in the

rings of a sugi stem over the years 1920 ± 1991 ; the

concentrations run between 1 and 20 ppm. While the

measurement and analysis of such spectra are quite

simple, their calibration concerning sub-ppm concentra-

tions can pose some problems. In the presented case, ® lter

papers were prepared which had absorbed standard

element solutions before drying.

2.6. Microbeam Analysis

So far, we have stressed the capacities of nuclear and/or

ion-beam analytical methods concerning their depth

resolution (RBS, NRA, ERDA ), their isotope and/or

element sensitivity (RNRA, ERDA, PIXE ), and their

sensitivity to lattice structures or immediate atomic

surroundings (ion channelling ). The choice of some of the

examples has highlighted that the combination of several

analysing techniques (in addition to conventional surface

and solid state methods ), indeed, can provide detailed

information on rather complicated processes and structures

in thin ® lms. At the end of this section, the ever growing use

of microbeams in thin ® lm analysis will be documented

brie¯ y. These techniques oŒer high lateral resolution in the

l m or sub- l m range [72 ± 74] .

2.6.1. Principle. When keeping the current density at a

`reasonable’ level, only analysing methods having an

`atomic’ cross-section (> 10Ð 20

cm2 ) appear to be useful

for microprobe analysis, i.e. PIXE, RBS, ERDA, and

possibly also RBS-channelling. For these applications,

microbeams in the 100 pA domain are considered to be

standard. For much lower beams in the 1 pA range, novel

techniques such as ion beam induced charge (IBIC ) [75] and

scanning transmission ion microscopy (STIM ) [76] have

Figure 18. PIXE analysis of a 30 nm TiN/steel bilayer sample

irradiated with 2.1 ´ 1017

Kr+

ions cmÐ 2

and analysed with a

0.4 MeV proton beam [70]. (a ) X-ray spectrum showing the K a

and K b radiations of the layer elements Ti, Cr, Fe and Ni; (b ) If

the radiations from the layer elements are partly absorbed in a

0.2 mm Al absorber, one also discerns the K a and K b lines of the

implanted Kr; (c ) Lateral scan of the Ti K-line intensity over the

Kr implantation spot showing the reduction of the TiN ® lm

thickness due to sputtering [70].

Thin film analysis with nuclear methods 399

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

been invented which are able to create direct pictures of

thin ® lm structures.

A comparison of X-ray microprobe methods using

synchrotron radiation, electrons or ions (including their

bene® ts and shortcomings ) has been given by Butz and

Legge [77] (see table 3 ). Watt et al. [78] recently surveyed

the state of the art performance of nuclear microprobe

analysis using proton and a beams; their results are

summarised in table 4. With the most widely used MeV

proton beams, the best high-current (> 100 pA ) and low-

current (< 0.1 pA ) performances were achieved at 2 ±

3 MeV giving lateral resolutions in the 50 ± 400 nm range.

Similar ® gures have also been reached with beams of few

MeV a -particles. Watt et al. [78] also discussed the various

limitations aŒecting the attainment of small spot sizes: in

the case of PIXE and RBS, the major factors in focusing

Figure 19. PIXE elemental analysis of kaki and sugi tree rings [71]. (a ) X-ray spectrum obtained from a 1 mm thick sample of kaki

wood. (b ) Distribution of the elements Cu (h ), Zn (j ), Rb (o ) and Sr (· ) in a sugi stem.

K.-P. Lieb400

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

the beam are the quality of the lens system and optimiza-

tion of system aberrations.

2.6.2. Examples. The two examples selected for microp-

robe element analysis illustrate the performance of a proton

beam for PIXE [84] and of an a -particle microbeam for

RBS [85]. Furthermore, we illustrate the use of a focused

proton beam for maskless micro-machining in three

dimensions [86].

The Oxford group recently contributed to medical

diagnosis by performing a PIXE microprobe study on hair

which was taken from a patient known to have clinical

symptons of lead poisoning [84]. The 3 MeV and 200 pA

proton microbeam was used to create elemental maps

across the section of the sample, a 42 l m thick hair. In

® gure 20 concentration scans of sulphur (which is a major

component of the base material, keratin ) and lead are

shown. The non-uniform pro® le of the latter element,

showing pronounced maxima at the perimeter, may be

associated with the metabolic transcellular transport

mechanism of heavy metals.

Intercalating of Ag into a layered crystal of TiS2

schematically explained in ® gure 21 (a ) was recently studied

by Heitmann and collaborators, using the 2 MeV He+

microbeam of the MARC scanning microprobe facility at

the University of Melbourne [85]. The ion beam was

focused to a 4 l m beam spot and the backscattered ions

were detected in a telescope positioned at 35 8 to the beam.

The samples were scanned in three dimensions by mapping

the Ag content after electrolytic intercalation. Figure 21 (b )

illustrates an Ag map obtained after 2.5 h, which indicates

regions diŒering in their Ag content (A, B, C ). The

corresponding RBS spectra of these regions shown in

® gure 21 (c ) exhibit the Ag, Ti and S pro® les (for decreasing

channel number ). The large kinematical contrast of the

Table 4. High-performance nuclear microprobe facilities [78].

Site Beam Resolution Reference

Oxford SPM Unit

National University, Singapore

Max Planck Institut, Heidelberg

TIARA, Takasaki

MARC, Melbourne

3 MeV protons , 100 pA

2 MeV protons , < 0.1 pA

2 MeV proton s

2 MeV a -particles, 100 pA

2 MeV a -particles

400 nm

100 nm

400 nm

70 nm

[79]

[80]

[81]

[82]

[83]

Table 3. Comparison of features of X-ray microprobes using

ions, electrons and synchrotron radiation [77].

Property Ions Electrons Synchrot ron

radiation

Depth sensitivity

Element speci® c

Quantitation

Background

Sensitivity

Depth resolution

Versatility

Cost

yes

yes

good

low

very good

100 nm± 1 l m

high

high

poor

yes

moderate

high

good

1 nm ± 1 l m

moderate

intermediate

no

yes

good

very low

very good

few l m

limited

very high

Figure 20. Relative X-ray yields of S and Pb measured with a

proton microbeam across a hair of a person showing symptons of

lead poisoning [84].

Thin film analysis with nuclear methods 401

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

three elements involved makes RBS analyses particularly

sensitive in this case.

The use of microbeams is not restricted to resolving

lateral structures in thin ® lm analysis, but can be extended

to fabricate 3-dimensional microstructures. A very ® ne

example was recently communicated by de Kerckhove et

al. [86] who etched microturbines in polymethylmethacry-

late (PMMA ). The spot size of the Oxford SPM Unit

3 MeV proton beam was about 1 l m and the range in

PMMA some 125 l m; the necessary dose was 1 pC l mÐ 2

.

Figure 22 shows a microturbine manufactured with the

proton beam tilted by 10 8 with respect to the sample

normal, for every blade. The three photographs were taken

with increasing spatial resolution and illustrate the micro-

turbine, details of a blade and further details of one of the

edges of a blade.

Figure 21. (a ) Intercalation of Ag into layers of TiS2 [85]; (b ) Map of the Ag content after a 2.5 h electrolytic intercalation; (c ) RBS

spectra taken with a 4- l m wide 2-MeV4He microbeam in the regions A, B and C shown in (b ).

K.-P. Lieb402

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

2.7. Synopsis of ion beam analytical method

At the end of this section, we present a synopsis of the

various methods discussed so far and summarize their

advantages and disadvantages.

2.7.1. Rutherford backscattering spectroscopy. RBS with

1 ± 3 MeV a -particles is a precise, simple and rather

convenient depth pro® ling method in thin-® lm technology

of nanometre depth resolution, mainly for heavy elements.

It is best applicable whenever the multi-element composi-

tion of the ® lm (s ) shows a large contrast in mass number

M 2 which means that the mass resolution of RBS is rather

limited. In most applications, the depth and mass resolu-

tion are limited by the energy resolution of the detection

system. Monolayer depth resolution at surfaces has been

achieved when using an appropriate magnetic or electro-

static analyser for the scattered particles. In the case of bi-

or multilayers, RBS determines the eŒective ® lm thick-

ness (es ) and requires surface-sensitive methods such as

STM, AFM or SEM to distinguish between surface and

layer interface properties. RBS is non-destructive in most

cases, due to the low analysing beam current required.

2.7.2. Resonant nuclear reaction analysis. RNRA is a

depth- and isotope-sensitive pro® ling method of high

resolution at or near the surface (< 1 ± 10 nm ), and still

rather good depth resolution in the interior of the ® lm.

Besides depth resolution, its main advantage is the high

isotope sensitivity which facilitates the detection of isotope

concentrations as low as 100 ppm for strong nuclear

resonances. The disadvantages of this technique to be

mentioned here are that it is rather time-consuming, due to

the small nuclear cross-sections, and that it is not always

non-destructive in the strict sense. In the case of proton

resonances, large amounts of hydrogen are injected into the

sample which may modify some properties of the ® lms.

Possible ® lm deterioation during particle bombardment

may be due to defect production, surface sputtering, or

surface deposition of contaminants under non-UHV

irradiation conditions.

2.7.3. Elastic recoil detection analysis. The main advan-

tage of ERDA in thin-® lm analysis arises from the

possibility to depth pro® le simultaneously many or even

all (light and medium-mass ) elements within the ® lms. For

small Z 2, one even may distuinguish between the diŒerent

isotopes, in particular when selecting beams of diŒerent

masses M 1 . For elastic scattering, the cross-section d rrec

/d X R scales with (Z1 Z2 )2 cos

Ð 3/ (see equation (10 )) and

can therefore be quite high at large angles / and for

appropriate projectiles Z 1, even for low values of Z 2. For

pro® ling medium-mass elements, the use of energetic heavy

projectiles of tens of MeV often still guarantees pure

Coulomb interactions, due to the large mass ratio M 1/M 2

and the correspondingly reduced projectile energy in the

centre-of-mass system. The main disadvantage of ERDA

with heavy ions appears to be that it may in¯ ict radiation

damage in the samples, in particular in insulators and

semiconductors.

Figure 22. Microturbine etched with a 3 MeV proton microbe-

am in PMMA [86]. The blades are tilted by 10 8 relative to the

normal of the sample. (a ) Micrograph taken at 45 8 ; (b )

Micrograph showing the tilt on a blade; (c ) Details of the blade.

The scale bar in each ® gure is 10 l m long.

Thin film analysis with nuclear methods 403

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

2.7.4. Ion channelling. Ion channelling (in connection

with RBS ) is a very useful ion beam analytical method for

testing the crystallinity of thin ® lms and to identify lattice

locations of (mainly interstitial ) self-atoms or dopants. The

sensitive depth is up to several hundred nanometres, the

precision in lattice locations down to a few picometres. The

method is also accessible to NRA to analyse light elements

using strong nuclear resonance reactions.

2.7.5. Particle-induced X-ray emission. Over the last

decade, the ever growing importance of PIXE for elemental

analysis in thin coatings on archeological objects (pottery,

metals, ¯ ints ), antiques (paintings, laquers, vases, hand-

written manuscripts ), biological and medical samples

(tooth inlays, tree-ring dating ), environmental pollution

(aerosols, limnology ) etc. has led to an enormous expansion

and re® nement of this technique [68]. The use of microbe-

ams and the combination of PIXE with RBS and NRA will

further promote this versatile method.

3. Methods using implanted radioactive probes

The methods presented in section 2 all use scattering or

reactions induced by well focused beams of stable isotopes.

The somewhat more exotic, but still manageable analysing

methods which will be sketched in section 3, use radio-

tracers. In the case of emission channelling and perturbed

c -ray angular correlations (PAC ), the radiotracers are ion-

implanted, diŒused or deposited in the ® lms to be analysed,

while MoÈ ssbauer spectroscopy generally uses radioactive

sources outside the samples. The information obtained

from the last two methods is complementary to that gained

in ion beam analysis insofar as they give access to phases

and defect structures, within thin layers, surfaces and

interfaces.

3.1. Emission channelling

3.1.1. Principle. Depth pro® ling of the constituents of

thin ® lms via elastic scattering or nuclear reactions with

beams of stable isotopes, mainly protons and a -particles, is

the most common method. The information obtained

relates to the concentration pro® les and, if used under

channelling conditions, to the crystalline order or disorder

of the samples. Lattice site locations can also be determined

from channelling measurements of a -decay particles or b -

decay positrons and electrons emitted from implanted

radioactive sources. These measurements, in addition to

radiotracer diŒusion measurements, have become quite

important nuclear techniques of thin-® lm analysis.

Emission channelling is, cum grano salis, the reverse of

ion-beam induced channelling described in section 2.4. If

the source nucleus emitting a positively charged particle

(positron, a -particle ) is located at a substitutional lattice

site, the corresponding channel directions and planes are

blocked and one will observe minima of the channelling

yields. If on the other hand, the source nucleus emits its

positive particle from an interstitial site, the corresponding

emisson directions will show channelling peaks. For the

emission of b -decay electrons, the very opposite is true: the

ion cores along the lattice rows will guide and focus

electrons emitted from a substitutional source nucleus

along these lattice directions and produce channelling

peaks, but will not do so if the source is situated within a

channel. The analytical treatment of emission channelling

of massive particles very much follows the line of

argumentation presented in section 2.4 [87, 88].

3.1.2. Example. The example chosen describes work by

HofsaÈ ss et al. [89] who investigated the role of Li doping of

III ± V semiconductors. In particular, the lattice locations of8Li-ions in InSb single crystals were studied in that work.

8Li b -decays with a half-life of 0.84 s to a state of

8Be,

which breaks up, within 4 ´ 10Ð 22

s, into two mono-

energetic a -particles and can thus be used for a channeling

analysis. The emitted a -particles were recorded in a two-

dimensional, position-sensitive Si-detector having a

10 ´ 10 mm2

active area centred under 28 8 to the implanta-

tion direction.

The aim of the study was to identify the original

implantation site (s ) and their changes due to thermal

transport up to room temperature. Figure 23 illustrates

two-dimensional a -particle yield patterns taken around

< 211 > at substrate temperatures of 110 K, 170 K and

295 K during 60 keV implantation into n-InSb. Evidently

the pattern obtained at 295 K indicates that both the {111}

and {110} channel planes are blocked, visible in the low a -

particle yields in these directions. It must be concluded that8Li has reached substitutional positions in the zincblende

structure of InSb, possibly by migrating to and combining

with an In-vacancy within its 0.84 s lifetime. At the

implantation temperature of 110 K, the emission channel-

ling pattern is quite diŒerent: only the {110} plane is

blocked, while yield maxima are seen along the {111} and

{311} planes, indicating that the8Li atoms are implanted

on tetrahedral interstitial lattice sites. The 170 K channel-

ling pattern is typical for an intermediate situation, i.e.

{110} blocking, but neither blocking nor channelling along

the other planes [89].

3.1.3. Summary. The example presented refers to the

rare case of a -particle emission channelling [90], while the

majority of such studies deals with emission channelling of

positrons or electrons following the b -decays of implanted

radioactive nuclei. Fortunately almost all elements have

such b -decaying isotopes which have proper lifetimes and

can be produced abundantly via nuclear reactions (® ssion,

proton spallation, heavy-ion reactions ). These tracer

K.-P. Lieb404

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

isotopes can be either recoil-implanted during the nuclear

reaction itself or implanted oŒ-line by means of an ion

implanter (ISOLDE [87, 88] ). In this respect, emission

channelling is quite versatile. Furthermore, the necessary

number of radioactive tracer usually is quite small, typically

1011

tracers cmÐ 2

. On the other hand, the need of precise

goniometers and position-sensitive two-dimensional detec-

tors and the doping of the ® lms with appropriate sources

makes emission channelling a rather delicate method.

3.2. MoÈ ssbauer spectroscopy

Through the hyper® ne interactions of radioactive isotopes,

important information can also be gained on defect

structures, phases and interface properties in thin ® lms.

For that reason, we illustrate here a few applications of

conversion electron (and X-ray ) MoÈ ssbauer spectroscopy

(CEMS, CXMS ) and, in section 3.3 of perturbed angular

correlation (PAC ) spectroscopy in the analysis of nano-

metre ® lms. These techniques often complement (and

a emission channeling spectrafrom 8Li-implanted p-InSb T = 110K

Tilt angle / deg-2

-1

0

1

2

Tilt an

gle / d

eg

-2

-1

0

1

2

0.6

0.8

1.0

1.2Norm

alized yield

T = 170 K

-2

-1

0

1

2

Tilt an

gle / d

egTilt angle / deg

-2

-1

0

1

2

0.6

0.8

1.0

1.2Norm

alized yield

-2

-1

0

1

2

Tilt an

gle /

degTilt angle / deg

-2

-1

0

1

2

0.6

0.8

1.0

1.2Norm

alized yield

T = 295 K

{111}

{311}

{110}{311}

{111} {110}

{111}

{311}

{110}

{311}

Figure 23. a -emission channelling yields from the decay of8Li which was implanted at 60 keV and 110 K, 170 K and 295 K in p-InSb.

For details see text [89].

Thin film analysis with nuclear methods 405

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

compete with ) transmission electron microscopy and X-ray

diŒraction.

3.2.1. Principle of CEMS and CXMS . The principles

and applications of MoÈ ssbauer investigations have been

described extensively [91 ± 93], and there is no need to give a

general introduction here. Resonant c -ray excitations of

nuclear levels can be used for thin ® lm analysis through the

observation of conversion electrons and/or characteristic

X-rays following the electromagnetic decays of the

MoÈ ssbauer state. In the case of the 14.4 keV 3/2 ® 1/2transition in

57Fe, populated in the electron capture decay

of57

Co with a hal¯ ife of 270 d, the electron conversion

coe� cient is a = 8.2. The conversion electrons have an

initial kinetic energy of 0.6 ± 14.3 keV, while the photon

energy of the emitted K a -radiation is 6.4 keV. These two

energies determine the sensitivity range of CEMS to

roughly 150 nm and that of CXMS to the absorption

length of the K a X-rays of some 10 l m. Without any

additional energy selection of the conversion electrons,

CEMS and CXMS therefore are able to distinguish

properties of the ® lms on these length scales. In thin-® lm

MoÈ ssbauer analysis, the simultaneous recording of trans-

mission (TM ), conversion electron (CEM ) and X-ray

(CXM ) spectra may be desirable, and spectrometers have

been designed to allow such measurements. Figure 24

illustrates the design of a triple-beam MoÈ ssbauer spectro-

meter [94]. The conversion electrons are recorded in a gas-

® lled proportional chamber in which the sample is housed,

while the X-rays are detected in a toroidal gas detector

adjacent to it and separated by a thin window.

Being a hyper® ne interaction method, MoÈ ssbauer

spectroscopy provides information on the isomer shift

(IS, electric monopole interaction ), magnetic hyper® ne

® elds B~

h f and electric ® eld gradient tensors V ik (electric

quadrupole splitting QS ) of the probe nuclei in the matrix

[91]. Typical CEMS spectra for57

Fe are sketched in ® gure

25. Usually, one needs good calibrations to interpret these

hyper® ne parameters and to associate them with de® nite

microsurroundings.

3.2.2. Examples. MoÈ ssbauer eŒect studies in thin ® lms

or multilayers are quite common and there are many

examples for their power and versatility [95,96]. Our ® rst

example selected refers to a CEMS experiment performed

by Sauer et al. [97]. It aimed at measuring the variation of

the magnetic hyper® ne ® eld B~

hf within a Fe/Cr bilayer, as a

function of the distance from the interface. As shown in

® gure 26, an isotopic57

Fe marker ® lm of 2 monolayers

(MLS ) thickness (in order to enhance the sensitivity ) was

placed within a Fe± Cr bilayer epitaxially grown on GaAs;

the57

Fe marker layer was embedded within the Fe ® lm, at a

distance d from the Fe ± Cr interface. The hyper® ne ® eld B~ hf

as measured via CEMS and extrapolated to T = 0 K, was

found to increase to Ð 35.0 T at d » 2 ML from the

interface and to reach the bulk value of B~

h fbulk

= Ð 33.3 T

already at the fourth ML.

Returning to laser nitriding of armco iron, CEMS and

CXMS helped to identify the phases developing near the

surface during the multiple-pulse excimer laser irradiations

Figure 24. Sketch of an apparatus for transmission (TM ),

conversion electron (CEM ) and conversion X-ray (CXM )

MoÈ ssbauer spectroscopy [94] and typical spectra obtained for

each mode of operation. The sample is contained in the

proportional chamber for electron detection (CEMS ), while X-

rays are recorded in a toroidal proportional counter (CXMS ).

Figure 25. The hyper® ne eŒects in the CEM spectra due to the

isomer shift, quadrupole and magnetic splitting are indicated.

K.-P. Lieb406

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

[16,18]. Figure 27 shows CEM and CXM spectra taken

after 64 pulses of a XeCl excimer laser hit the surface at an

average energy density of 4 J cmÐ 2

and at a nitrogen

pressure of 1.5 bar. While the CXM spectrum closely

resembles that of pure Fe showing mainly the a -phase and

little c -Fe (N ), the CEM spectrum is very diŒerent and

con® rms the formation of various iron nitrides in the top

150 nm layer (a ¢ -FeN, c -Fe (N ), e -Fe2N 1-x ). Since the laser-

molten and nitrided coating is roughly 1 l m thick and the

nitrogen content decreases within the ® rst 300 nm (see

® gure 6 ), the two MoÈ ssbauer spectra complement each

other as well as the nitrogen pro® les obtained via RNRA

(see section 2.2 ). Table 5 lists the hyper® ne parameters and

phase fractions deduced from both spectra.

3.2.3. Summary on bene® ts and limitations. The greatest

bene® t of MoÈ ssbauer spectroscopy is possibly the simple

investigation of stable, non-radioactive samples without the

need for special sample preparation. The high resolution

allows easy phase and site analysis via distinct ®̀ nger-

prints’ . Information on the magnetic orientation, magnetic

moments, site occupations, ordering of substitutional and

interstitial sites, etc. can be gained from MoÈ ssbauer spectra.

Even dynamic processes such as superparamagnetism,

diŒusion, or site hopping, can be investigated. The isomer

shifts allow one to diŒerentiate between various cubic non-

magnetic phases which is not possible with most other

hyper® ne methods. More than 100 MoÈ ssbauer isotopes can

be used for the analysis of almost any material. In thin-® lm

analysis, diŒerential CEMS, which selects the conversion

electrons according to their energies, has been developed to

sub-nanometre resolution. The biggest problem of MoÈ ss-

bauer spectroscopy is the Debye± Waller factor, which is

generally not known and assumed to be equal for all phases

and sites. Its strong decrease with increasing temperature

hinders measurements at higher temperatures (up to

1200 K in Fe and up to 100 K in Ni ).

3.3. Perturbed c -ray angular correlations (PAC )

3.3.1. Principle. The application of the perturbed angu-

lar correlation technique in thin ® lm and surface analysis is

rather novel, but may have high potential for further

Bh

f / T

No. of Molecular Layers

Figure 26. Magnetic hyper® ne ® eld Bh f of a stack of 30 nm56

Fe/2 ML57

Fe/d ML56

Fe/4 nm Cr, epitaxially grown on

GaAs < 110> , measured as function of the distance d (in

monolayers ) between the57

Fe marker and the Fe ± Cr interface

[97].

Figure 27. CEM (a ) and CXM (b ) spectra of an armco Fe

sample after laser nitriding with 64 pulses of a XeCl excimer

laser beam. The diŒerences between the two spectra highlight the

formation of the iron nitride phases a ¢ -Fe, c -Fe (N ) and e -Fe2N1 -x

near the surface (a ), while the a -Fe phase in the deeper layers is

not aŒected (b ) [17].

Thin film analysis with nuclear methods 407

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

developments. In PAC, a radioactive nucleus b -decays to a

daughter probe nucleus which contains a c -ray cascade

populating and de-exciting the intermediate, hyper® ne-

sensitive nuclear level. If this nuclear state has a known

magnetic dipole and/or electric quadrupole moment and a

lifetime of the order of ns to l s, one is able to time-

diŒerentially measure the precession of the c -ray angular

correlation, due to the magnetic hyper® ne ® eld (s ) and/or

electric quadrupole tensor (s ) acting on the probe nucleus in

its sensitive state. Extensions of the method to time-integral

PAC measurements for shorter-lived states (down to a few

picoseconds ) are also known. Time-diŒerential or time-

integral measurements of in-beam perturbed c -ray angular

distributions (PAD ), in which the probe nuclei are directly

produced and recoil-implanted into the matrix via a nuclear

reaction, are other important extensions of the PAC

method.

The basic theoretical concept of PAC has been presented

in many treatises [91, 98, 99], and numerous applications to

various situations have been worked out (static magnetic or

electric interaction, superpositions of static magnetic or

electric interactions, superposition of both interactions,

time-dependent hyper® ne ® elds ). In order to enhance the

sensitivity of the experimental set-up, one uses 4 or 6 c -ray

detectors (mainly NaI or BaF2 scintillators ) arranged in a

symmetric planar (4 ) or cube (6 ) geometry and facing the

source which is placed in the centre. For a two-step c -ray

cascade, each detector can record either the start or stop c -

ray, giving a total of 12 or 30 coincidence combinations in

the planar or cube geometry, respectively. Each event of

these combinations is electronically labelled by the two c -

ray energies, detector numbers/positions and the time

diŒerence between the start and the stop signal and thus

provides the (perturbed ) correlation function R (t ). Its

Fourier transform contains the desired hyper® ne interac-

tion (s ). In the case of a static distribution of magnetic

hyper® ne ® elds B~ hf, one derives the ® rst two moments,

namely the centre Larmor precession frequency < x L >and the width d x L , and possibly the orientation of B

~h f

relative to the detectors and/or the sample.

3.3.2. Examples. The ® rst example presents the result of

PAC measurements concerning the magnetic hyper ® ne

interaction of111

Cd nuclei in iron ® lms. The 130 nm thin

Fe ® lm was deposited on either a Si or a SiO2 backing and

doped with a total of some 1012

radioactive111

In tracer

atoms via ion implantation at 280 keV [100]. The111

In

nuclei decay, with a hal¯ ife of 2.8 d via electron capture to

the daughter nuclei111

Cd. Each such decay is followed by

the emission of a two-step c -ray cascade of 171 and

245 keV photon energy and involves an intermediate state

in111

Cd having a hal¯ ife of 85 ns and a magnetic moment

of Ð 0.7656 (25 ) nuclear magnetons (see ® gure 28 ). Figure

29 shows two perturbation functions

R (t) 5 [N ( p , t) 2 N ( p /2, t) ] /[N ( p , t) 1 N ( p /2, t) ], (14)

where N (h , t ) denotes the coincidence rate with the two

detectors forming an angle h , and t being the time diŒerence

between the start and stop signals. The two peaks in each

Fourier spectrum A (x ) of this ® lm (right-hand side )

correspond to the Larmor frequency x L = 0.53 GHz and

its ® rst harmonic, 2 x L , of111

Cd tracer nuclei on substitu-

tional Fe sites. The data in ® gure 29 (a ) reveal that the

magnetic polarization is distributed uniformly within the

plane of the Fe foil. If one now irradiates this foil with

6 ´ 1015

Xe+

-ions cmÐ 2

at 450 keV (having an ion range

Table 5. Hyper® ne parameters of a laser-nitrided Fe sample

measured via CEMS and CXMS [17].

IS

(mm s± 1 )

QS

(mm s± 1 )

B~

h f

(T )

G ¢(mm s

± 1 )

Fraction

(% )

Phase

CEMS

± 0.04 (2 )

0.12 (2 )

0.37 (2 )

0

0.21 (4 )

0.40 (3 )

0.33 (6 )

0.37 (1 )

0.30 (1 )

0

0

0.10 (2 )

± 0.11 (1 )

32.9 (2 )

26.6 (3 )

19.9 (2 )

12.8 (3 )

0.36 (1 )

0.36 (1 )

0.33 (2 )

0.66 (4 )

0.80 (6 )

0.80 (6 )

0.80 (6 )

13 (2 )

12 (2 )

9 (3 )

20 (4 )

15 (2 )

23 (2 )

8 (1 )

cce

a , a ¢eee

CXMS

0.05 (3 )

0.11 (4 )

0

0.40 (5 )

0 33 (2 )

0.33 (1 )

0.33 (1 )

0.33 (1 )

4 (1 )

7 (1 )

89 (2 )

cca

IS= Isomer shift, relative to a -Fe.

QS= Quadrupole splitting.

B~

hf= magnetic hyper® ne ® eld.

G ¢ = line width.

Figure 28. Properties of the PAC source111

In/111

Cd. The

perturbation of the 171/245 keV c -ray cascade in111

Cd involving

the isomeric 245 keV state serves to measure the hyper® ne

interaction (s ) (see [91], chap. 5 ).

K.-P. Lieb408

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

about half the thickness of the Fe ® lm ), a dramatic

polarization of the magnetic hyper® ne ® eld can be

observed, since now the 2 x L component is much stronger

than the x L component (® gure 29 (b )). The origin of this

strong polarization eŒect is not fully understood.

An important information on the athermal ion-mixing

processes in Ag/Fe bilayers has been gained by PAC. As

deduced from the combined RBS and STM analyses and

discussed in section 2.1, the Xe-irradiations at 77 K lead to

a roughening of the Ag surface and induce very little net

atomic transport across the Ag± Fe interface (ion-beam

mixing ). This observation was explained by the existence of

local thermal spikes which produce segregation of Ag and

Fe in the interface zone, after the ballistic intermixing

processes in the collision cascade have taken place. By

means of PAC, Neubauer et al. [101 ± 103] recently

obtained a detailed picture of the stages of the interface

mixing process in this system and were even able to

estimate the average size of the local spikes. In these

studies,111

In tracer ions were introduced either by ion

implantation or deposited as marker layers in the samples

[104].

For measuring the average size of thermal spikes, the

trick was to deposit a submonolayer of111

In tracer atoms

[104], at a variable distance x from the Ag± Fe interface

(x = 0 ± 17 nm ), and to monitor the fraction fA g of111

In

tracers being transferred into Ag during the Xe irradiation

via PAC. Hence, the fraction fA g is characterized by the

absence of any hyper® ne perturbation, due to the fact that

probe nuclei on substitutional, defect-free lattice sites in the

fcc structure do not experience any electric ® eld gradient.

Figure 30 (c ) illustrates the layer geometry, while ® gures 30

(a ) and (b ) display two PAC spectra and their Fourier

transforms taken at the distances x = 0 and x = 1.4 nm

before the ion irradiations. The two sharp peaks in the

Fourier spectrum for x = 1.4 nm again correspond to the

Larmor frequency x L and its ® rst harmonics, 2 x L , of111

Cd

tracer nuclei on substitutional, defect-free Fe sites in Fe

bulk. The Fourier spectrum taken at x = 0, on the other

hand, exhibits two broad distributions of Larmor frequen-

cies centred around x L /2 and x L , which are due to the

smaller magnetic hyper® ne ® elds (and to the possible

existence of electric ® eld gradients ) acting on111

Cd probe

nuclei at the Ag± Fe interface [103,105]. The unperturbed

fraction fA g vanishes in both cases, as no111

In atoms are

located in the Ag layer.

After irradiating these bilayers with 450 keV Xe ions at

¯ uences of 3 ´ 1015

and 6 ´ 1015

ions cmÐ 2

at 77 K, the

fraction fA g is seen. This fraction, which is plotted in ® gure

31 as a function of the distance x, decreases exponentially

on a length scale of about 2.5 nm. However, as shown in

the inset of ® gure 31 (a ), its amount is not reproduced by

the ballistic model. On the other hand, we can apply the

concept of local thermal spikes to explain it: on the basis of

Figure 29. Perturbation functions R (t ) and Fourier transforms A (x ) of111

Cd on substitutional, defect-free sites in Fe, exhibiting the

Larmor frequency x L and twice its value, (a ) in an as-deposited Fe ® lm; (b ) after implanting 6 ´ 1015

450 keV Xe ions cmÐ 2

at 80 K.

Note the change of the relative fractions at the two frequencies indicating a strong net polarization of the magnetic hyper® ne ® eld Bh f in

the ® lm [100].

Thin film analysis with nuclear methods 409

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

tracer diŒusion data and the energy distribution in the

spike, one can estimate the time tS and the mean

temperature TS of the spike necessary to achieve a

su� ciently large diŒusion coe� cient for111

In atoms to

migrate into the Ag layer (see ® gure 30 (c )). It is an

interesting observation that for TS » 2000 K, i.e. just above

the melting temperature of Fe, the experimental and

calculated diŒusion lengths < xD > agree with each other

and with the average spike radius < rS > » 2.5 nm. This

series of experiments constitutes a direct experimental

estimate of the size of ion-induced thermal (droplet ) spikes

[10, 14, 101, 103].

Nonetheless, a small fraction of Ag atoms stays in the Fe

matrix after Xe-irradiations and their microsurroundings

have also been identi ® ed using PAC. As the111

In tracers

occupy substitutional Fe sites, any replacements of Fe

atoms in the neighbourhood of the111

In tracers by injected

Ag atoms lead to decreasing hyper® ne ® elds B~

h f, relative to

that of an inert Fe surrounding. According to calibration

measurements in laser-deposited AgzFE1 -z ® lms (z < 30

at.% ), B~

hf decreases linearly with the number of Ag atoms

in the nearest and next-nearest neighbourhood [106]. PAC

(and CEMS ) measurements of ion-mixed bilayers indicate a

stochastic occupation probability of the Fe lattice sites with

1 or 2 Ag atoms after ion-beam mixing. Athermal ion beam

mixing of Ag± Fe bilayers thus oŒers a particularly

convincing example of the power of nuclear methods

(RBS, PAC, CEMS ) to characterize a complicated ion-

beam induced transport process with nanometre resolution.

3.3.3. Bene ® ts and limitations. As in MoÈ ssbauer spectro-

scopy, the bene® ts of PAC lie in the high local sensitivity of

this method which can give access to structures on an

atomic scale. As long as the hyper® ne interaction is static

during the observation time, i.e. within the lifetime of the

nuclear level chosen, PAC depicts this interaction and is

able to resolve diŒerent static probe surroundings. The

method can be extended to dynamic processes on the

nanosecond time scale [107]. PAC is able to distinguish

between (static ) magnetic hyper® ne ® elds, electric ® eld

gradients and superpositions of both. Moreover, it provides

information about the orientation of such internal vector or

Figure 30. The two PAC spectra shown in (a ) and (b ) refer to

distances of x= 0 and 1.4 nm between the111

In marker layer and

the Ag ± Fe interface. The spectra were accumulated before the

Xe-ion irradiation. (c ) Layer geometry of the samples [103].

Figure 31. Top: fraction fA g of111

In probe atoms which have

migrated to substitutional, defect-free lattice sites in Ag,

measured as function of the distance x between the111

In marker

layer and the Ag ± Fe interface, after 450 keV Xe+

irradiations

at 77 K and for ¯ uences of U = 3 ´ 1015

and 6 ´ 1015

ions cmÐ 2

.

Note that the ballistic model does not reproduce this fraction(inset ). Bottom: spike temperature TS (a ) and experimental and

calculated eŒective diŒusion length < xD > (b ) as function of the

spike radius rS [103].

K.-P. Lieb410

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

tensor ® elds relative to crystallographic axes. In compar-

ison with MoÈ ssbauer spectroscopy, PAC is more favour-

able at higher temperatures, since it does not depend on a

Debye± Waller type factor. A further advantage of PAC is

the very small number of radiaoctive tracer atoms

necessary which, in general, do not in¯ uence the (macro-

scopic ) properties of the matrix.

The limitations of PAC derive from

(1 ) the small number of appropriate nuclear probe

nuclei available;

(2 ) the necessity to introduce the radioactivity into the

sample to be studied;

(3 ) the need to calibrate the observed hyper® ne ® elds;

(4 ) the modi® cations which the probe atoms (which

usually are impurities ) may exert onto the local

environment, either due to the chemical nature of the

probe atoms or, in the case of implantation, the

radiation damage.

3.3.4. Summary. Perturbed angular correlation spectro-

scopy bene® ts from the fact that, when using modern, large-

solid-angle gamma detector arrays, a large fraction of the

nuclear decays gives access for investigating the hyper® ne

interaction. Therefore, the density and total number of the

radioactive tracers necessary can be very small (< 1 ppm,

some 1012

tracer nuclei in total ). The short-range nature of

hyper® ne interactions makes this method very sensitive to

local structures such as point defects, atomic con® gurations,

local chemical reactions and phase transitions. The poten-

tial of PAC in thin-® lm analysis has not been fully exploited

yet, but despite the disadvantages mentioned above, PAC

oŒers some unique possibilities.

Acknowledgements

It is a pleasure to thank Tilmann Butz, Sankar Dhar, Lucie

Hamdi, Hans HofsaÈ ss, Andrea Jungclaus, Diane de

Kerckhove, Felix Landry, Momir Milosavljevic, Fabrizio

Roccaforte, Peter Schaaf and Michael Uhrmacher for their

suggestions and comments or for allowing me to quote

some unpublished results. This work was supported by

Deutsche Forschungsgemeinschaft (DFG ).

References

[1] Tesmer, J. R., and Nastasi, M., 1995, Handbook of Modern Ion Beam

Material Analysis (Pittsburgh: Material Science Society ).

[2] Feldman, L. C. and Mayer, J. W., 1986, Fundamentals of Surface and

Thin Film Analysis (Englewood CliŒs, NJ: Prentice Hall ).

[3] Nastasi, M., Mayer, J. W., and Hirvonen, J. K., 1996, Ion-Solid

InteractionsÐ Fundamentals and Applications (Cambridge: Cambridge

University Press ).

[4] H. Oechsner, 1984, Thin Film and Depth Pro® le Analysis, Topics in

Current Physics, Vol. 37 (Berlin: Springer-Verlag ).

[5] Mayer, J.W., and Rimini, E., 1977, Ion Beam Handbook for Material

Analysis (New York: Academic Press ).

[6] Meyer, O., et al. (eds ), 1976, Ion Beam Surface Layer Analysis (New

York: Plenum ).

[7] Chu, W. K., Mayer, J. W., and Nicolet, M. A., 1978, Backscattering

Spectrometry (New York: Academic Press ).

[8] Doolittle, L. R., 1985, Nucl. Instr. Meth., B9, 344; 1986, ibid ., B15,

227.

[9] Saarilahti, J., 1992, Nucl. Instr. Meth., B64, 734.

[10] Crespo-Sosa, A., Schaaf, P., Bolse, W., Lieb, K. P., Gimbel, M.,

Geyer, U., Tosello, C., 1996, Phys. Rev., B53, 734.

[11] Crespo-Sosa, A., Bolse, W., Geyer, U., Gimbel, M., Lieb, K. P., 1997,

Applications of Accelerators in Research and Industry, edited by J. L.

Duggan and I. L. Morgan (New York: AIP Press ), p. 945.

[12] Averback, R. S., 1986, Nucl. Instr. Meth., B15, 575.

[13] Johnson, W. L., Cheng, Y.-T., Van Rossum, M., and Nicolet, M. A.,

1985, Nucl. Instr. Meth., B7/8, 657; Cheng, Y.-T., 1990, Mater. Sci.

Eng., R5, 45.

[14] Bolse, W., 1994, Mater. Sci. Eng., R12, 53; 1998, ibid ., A253, 194.

[15] Schaaf, P., Landry, F., and Lieb, K. P., 1999, Appl. Phys. Lett., 74, 153.

[16] Illgner, C., Schaaf, P., Lieb, K. P., Queitsch, R., Barnikel, J., 1998, J.

Appl. Phys., 83, 2907.

[17] Landry, F., Lieb, K. P., Schaaf, P., 1999, J. Appl. Phys. 86, 168.

[18] Schaaf, P., 1999, Habilitationsschrift, GoÈ ttingen (in the press ).

[19] Uhrmacher, M., Pampus, K., Bergmeister, F. J., Purschke, D., Lieb,

K. P., 1985, Nucl. Instr. Meth., B9, 234.

[20] Ziegler, J. F., Biersack, J. P., and Littmark, U., 1985, The Stopping

and Range of Ions in Solids (New York: Pergamon Press ).

[21] Feuerstein, A., Grahmann, H., Kalbitzer, S., and Oetzmann, H., 1996,

Ion Beam Surface Layer Analysis, edited by O. Meyer et al. (New

York: Plenum ). T. Enders, M. Rilli, and H. D. Carstanjen, 1992,

Nucl. Instr. Meth., B64, 817.

[22] Arnoldbik, W. M., et al., 1996, Nucl. Instr. Meth., B118, 566; 1998,

Nucl. Instr. Meth. , B136 ± 138, 540.

[23] Kimura, K. and Mannami, M., 1996, Nucl. Instr. Meth., B113, 270.

[24] Metzner, H., Gossla, M., and Hahn, T. H. 1997, Nucl. Instr. Meth.,

B124, 567.

[25] Metzner, H., Hahn, T., Gossla, M., Conrad, J. and Bremer, J.-H.,

1998, Nucl. Instr. Meth., B134, 249.

[26] Kacsich, T., Lieb, K. P., Schaper, A., and Schulte, O., 1996, J. Phys.:

condens. Matter, 8, 10703.

[27] Illgner, C., et al., 1997, Appl. Surf. Sci., 109/110, 150.

[28] Demortier, G., 1992, (ed ), Nucl. Instr. Meth., B66, 1.

[29] Bethge, K., Nuc. Instr. Meth., B66, 146.

[30] See 2 Feldman, L. C., and Mayer, J. W., 1986, Fundamentals of

Surface and Thin Film Analysis (Englewood CliŒs, NJ: Prentice Hall ),

Table 12.2, p. 307.

[31] Osipowicz, T., Lieb, K. P., BruÈ ssermann, S., 1987, Nucl. Instr. Meth.,

B18, 232.

[32] Bergmeister, F. J., Lieb, K. P., Pampus, K., Uhrmacher, M., 1985, Z.

Phys., A320, 693.

[33] Wriedt, H.A., Gokzen, N. A., and Nafziger, R.H., 1987, Bull. Alloy

Phase Diagrams, 8, 355; Kunze, J., 1990, Nitrogen and Carbon in Iron

and Steel (Berlin: Akademie-Verlag ).

[34] Niederdrenk, M., Schaaf, P., Lieb, K. P., and Schulte, O., 1996, J. All.

Comp ., 237, 81; Schaaf, P., Illgner, C., Niederdrenk, M., Lieb, K. P.,

1995, Hyp. Int., 95, 199.

[35] Rissanen, L., Neubauer, M., Lieb, K.P., and Schaaf, P., 1998, J. All.

Comp ., 274, 74.

[36] Rissanen, L., Schaaf, P., Neubauer, M., Lieb, K. P., Keinonen, J.,

Sajavaara, T., 1999, Appl. Surf. Sci., 138/139, 261.

[37] Damjantschitsch, H., Weiser, M., Heusser, G., Kalbitzer S. and

Mannserger, H., 1983, Nucl. Instr. Meth., 218, 129.

[38] Cohen, B. L., Fink, C. L., and Degman, J. H., 1972, J. appl. Phys., 43, 19.

[39] Smidt, F. A., and Pieper, A. G., 1974, J. Nucl. Mater., 51, 361.

Thin film analysis with nuclear methods 411

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

[40] Moore, J. A., et al., 1975, J. Appl. Phys., 46, 52.

[41] Ecuyer, J. L., et al., 1976, J. Appl. Phys., 47, 381.

[42] Terrault, B., Martel, J. G., St.-Jacques, R., and Ecuyer, J. L ¢ , 1977, J.

Vac. Sci. Technol., 14, 492.

[43] Tirira , J., Serruys, Y., and Trocellier, P., (eds ), 1996, Forward Recoil

Spectrometry (New York, & London: Plenum Press ).

[44] HofsaÈ û , H., 1996, Forward Recoil Spectrometry, edited by J. Tirira, Y.

Serruys, and P. Trocellier, (New York, London: Plenum Press, p. 127

Œ; p. 209 Œ.

[45] Dollinger, G., Frey, C. M., Bergmaier, T., and Faestermann, A., 1998,

Nucl. Instr. Meth., B136 ± 138, 603; Dollinger, G., et al., 1996, Nucl.

Instr. Meth., B118, 291.

[46] Ross, G. G., et al., 1984, J. Nucl. Mat., 128/129, 730.

[47] Ross, G. G. and Leblanc, L., 1992, Nucl. Instr. Meth., B62, 17.

[48] Jokinen, J., Keinonen, J., Tikkanen, P., Kuronen, A., Ahlgren, T. and

Nordlund, K., 1996, Nucl. Instr. Meth., B119, 533.

[49] HofsaÈ ss, H., Parikh, N. R., Swanson, M. L., and Chu, W. K., 1990,

Nucl. Instr. Meth., B45, 151; 1991, Nucl. Instr. Meth., B58, 49.

[50] Paszti, F., Szilagyi, E., and Kotai, E., 1991, Nucl. Instr. Meth., B54,

507; Szilagyi, E., Paszti, F., and Amsel, G., 1995, Nucl. Instr. Meth.,

B100, 113.

[51] Nagata, S., Yamaguchi, S., Fujino, Y., Hori, Y., Sugiyama, N. and

Kamada, K., 1985, Nucl. Instr. Meth., B6, 533.

[52] Anderson, J. U., Andreason, O., Davies, J. A., and Uqgerhoj, E.,

1971, Rad. EŒ., 7, 25.

[53] Gemmell, D. S., 1974, Rev. Mod. Phys., 46, 129; Feldman, L. C.,

Mayer, J. W., and Picraux, S. T., 1982, Materials Analysis by Ion

Channeling (New York: Academic Press ).

[54] See Chap. 5. Feldon, L. C., and Mayer, W., 1986, Fundmentals of

Surface and Thin Film Analysis (Englewood CliŒs, NJ: Prentice Hall ).

[55] Appleton, B. R., and Foti, G., 1977, Ion Beam Handbook for Material

Analysis , edited by J. W. Mayer, and E. Rimini, (New York:

Academic Press ).

[56] Lehmann, C., and Leibfried, G., 1963, J. appl. Phys., 34, 2821;

Lindhard, J., 1965, Mat. Fys. Medd. Dan. Vid. Selsk., 34, 1.

[57] Harbsmeier, F., and Bolse, W., 1998, J. appl. Phys., 83, 4049; Bolse,

W., 1999, Nucl. Instr. Meth., B148, 83.

[58] GoÈ tz, G., 1987, Ion Beam Modi® cations of Insulators, edited by P,

Mazzoldi, and G. W. Arnold, (Amsterdam: Elsevier ), p. 412; Arnold,

G. W., 1992, Nucl. Instr. Meth. B65, 213.

[59] Marians, C. S., and Hobbs, L. W., 1990, J. non-cryst. Solids, 124, 242.

[60] Dhar, S., Bolse, W., and Lieb, K. P., 1999, Nucl. Instr. Meth., B148,

683; 1999, J. Appl. Phys., 85, 3120.

[61] Roccaforte, F., Bolse, W., Lieb, K. P., 1998, Appl. Phys. Lett., 73,

1349; Nucl. Instr. Meth., B18, 692; 1999, Appl. Phys. Lett., 74,

1992.

[62] Roccaforte, F., Gustafsson, M., Bolse, W., Keinonen, J., Lieb, K. P.,

1999, Nucl. Instr. Meth., B (submitted ).

[63] Morehead, F. F., and Crowder, B. L., 1970, Rad. EŒ., 6, 27.

[64] Devaud, G., Hayzelden, C., Aziz, M. J., and Turnbull, D., 1991, J.

non-cryst. Solids, 134, 129.

[65] Hobbs, L. W., 1994, Nucl. Instr. Meth., B91, 30.

[66] Johansson, S.A., Campbell, J. L., and Malmquist, K. G., 1995, Particle

Induced X-Ray Emissio n Spectroscopy (New York: Wiley & Sons ).

[67] Garcia, J. D., Bambynek, W., Crasemann, B., Fink, R. W., Freund,

H. U., Mark, H., Swift, C. D., Price, R. E. and Rao, P. V., 1972, Rev.

Mod. Phys., 44, 716.

[68] da Silva, M. F., Soares, J. C., and Breese, M., 1998, (eds ), 1998, Nucl.

Instr. Meth., B136 ± 138, Proceedings of the International conference

on Ion Beam Analysis, Chapter XII.

[69] Cahill, T. A., 1980, Ann. Rev. Nucl. Part. Sci., 30, 320.

[70] Osipowicz, T., Lieb, K. P., Bolse, W., Uhrmacher, M., 1990, Nucl.

Instr. Meth., B50, 10.

[71] Aoki, T., Katayama, Y., Kagawa, A., Koh, S. and Yoshida, K., 1994,

Nucl. Instr. Meth., B85, 708.

[72] Llabador, Y., and Moretto, P., 1998, Applications of Nuclear

Microprobes in the Life Sciences (Singapore: World Scienti® c Publ. ).

[73] Breese, M. B. H., Jamieson, D. N., and King, P. J. C., 1996, Material

Analysis with Nuclear Microprobe (New York: Wiley & Sons ).

[74] Watt, F., and Grime, G. W., 1987, Principles and Applications of High

Energy Ion Microbeams (Bristol: Hilger ); Mutsaers, H. A., 1996,

Nucl. Instr. Meth., B113, 323; Takai, M., 1996, ibid ., B113, 330; G.

Demortier 1996, ibid. , B113, 347.

[75] Breese, M. B. H., Grime, G. W., and Watt, F., 1993, Nucl. Instr.

Meth., B77, 301; Sexton, F. W., Horn, K. M., Doyle, B. L., Laird, J.

S., Cholewa, M., Saint, A. and Legge, G. J. F., 1993, Nucl. Instr.

Meth. B79, 436; Sakai, T., Hamano, T., Hirao, T., Kamiya, T.,

Murozono, K., Inoue, J., Matsuyama, S., Iwasaki, S. and Ishii, K.,

1998, Nucl. Instr. Meth. B136 ± 138, 390.

[76] Sealock, R. M., Mazzolini, A. P. and Legge, G. J. F., 1983, Nucl.

Instr. Meth., 218, 217; Overley, J. C., et al., 1983, Nucl. Instr. Meth.,

218, 337; van Maanen, F., Mutsaers, P. H. A., Verhoef, B. A. W., and

de Voigt, M. J. A., 1996, Nucl. Instr. Meth., B113, 382.

[77] Butz, T., and Legge, G. J. F., 1996, Nucl. Instr. Meth., B113, 317.

[78] Watt, F., Osipowicz, T., Choo, T. F., Orlic , I. and Tang, S. M., 1998,

Nucl. Instr. Meth., B136 ± 138, 313.

[79] Grime, G. W., and Watt, F., 1993, Nucl. Instr. Meth., B75, 495.

[80] Watt, F., Orlic , I., Loh, K., Sow, C. H., Thong, P., Liew, S. C.,

Osipowicz, T., Choo, T. F. and Tang, S. M., 1994, Nucl. Instr. Meth.,

B136-138, 313; Watt, F., Choo, T. F., Lee, K. K., Osipowicz, T.,

Orlic , S. M. and Tang, S. M., 1995, Nucl. Instr. Meth., B104, 101.

[81] Traxel, K., Arndt, P., Bohsung, J., Braun-Dullaeus, K. U., Maetz, M.,

Reimold, Schiebler, H. and Wallianos, A., 1995, Nucl. Instr. Meth.,

B104, 19.

[82] Kamiya, T., Suda, T., and Tanaka, R., 1995, Nucl. Instr. Meth., B104,

43.

[83] Bench, G. S., and Legge, G. L. F., 1989, Nucl. Instr. Meth., B40/41, 655.

[84] Malmquist, K. G., 1996, Nucl. Instr. Meth., B113, 336; Watt, F., and

Landsberg, J. P., 1993, Nucl. Instr. Meth., B77, 249.

[85] Heitmann, J., McCallum, J., TroÈ ger, W., and Butz, T., 1999 (in the

press ).

[86] Kerckhove, D. G., Breese, M. B. H., Marsh, M. A., and Grime, G.

W., 1998, Nucl. Instr. Meth., B136 ± 138, 379.

[87] HofsaÈ ss, H., and Lindner, G., 1991, Phys. Rep., 201, 121.

[88] HofsaÈ ss, H., 1996, Hyp. Int., 97/98, 247.

[89] HofsaÈ ss, H., Wahl, U., Restle, M., Ronning, C., Recknagel, E. and

Jahn, S. G., 1994, Nucl. Instr. Meth., B85, 468.

[90] Wahl, U., 1997, Phys. Rep., 280, 145.

[91] Schatz, G., and Weidinger, A., 1985, Nukleare FestkoÈ rperphysik

(Stuttgart: Teubner ), Chap. 4.

[92] Sawicki, J. A. and Sawicka, B. D., 1983, Hyp. Int., 13, 199; Sawicki, J.

A., 1986, Industrial Applications of the MoÈ ssbauer EŒect, edited by G.

J. Long, and J. G. Stevens, (New York: Plenum Publ. Corp. ) p. 83.

[93] Gonser, U., (ed ), 1975, MoÈ û bauer Spectroscopy, Topics in Applied

Physics, Vol. 5 (Heidelberg: Springer-Verlag ).

[94] Schaaf, P., KraÈ mer, A., Blaes, L., Wagner, H., Aubertin, F. and

Gonser, U., 1991, Nucl. Instr. Meth., B53, 184.

[95] Sauer, C. H., and Zinn, W., 1993, Magnetic Multilayers, edited by L.

H. Bennett, and R. E. Watson, (Singapore: World Scienti® c ).

[96] Gonser, U., and Schaaf, P., 1991, Fresenius J. Anal. Chem ., 341, 131.

[97] Sauer, C. H., Landes, J., Zinn, W., and Ebert, H., 1992, Mat. Res.

Soc. Symp. Proc., 231, 153.

[98] Recknagel, E., Schatz, G., and Wichert, T. H., 1983, Hyper® ne

Interactions of Radioactive Nuclei, edited by J. Christiansen, (Berlin:

Springer-Verlag ), p. 133.

[99] Langouche, G., (ed ), 1992, Hyper® ne Interactions of Defects in

Semiconductors, (Amsterdam: Elsevier ); Sielemann, R., 1998, Nucl.

Instr. Meth., B146, 329.

[100] Neubauer, M., Reinecke, N., Uhrmacher, M., Lieb, K. P., MuÈ nzen-

berg, M., Felsch, W., 1998, Nucl. Instr. Meth., B139, 332.

K.-P. Lieb412

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013

[101] Neubauer, M., Schaaf, P., Uhrmacher, M., and Lieb, K.P., 1996,

Phys. Rev., B53, 10237.

[102] Neubauer, M., Wodniecki, P., StoÈ rmer, P., Bolse, W., Krebs, H. U.,

Uhrmacher, M., Lieb, K. P., 1997, XXXII Zakopane School of

Physics, edited by E. A. GoÈ rlich, and K. Latka, (Krakow ), p. 56.

[103] Neubauer, M., Lieb, K. P., Uhrmacher, M., and Wodniecki, P., 1998,

Europhys. Lett., 43, 177.

[104] Uhrmacher, M., Neubauer, M., Bolse, W., Ziegeler, L., Lieb, K. P.,

1998, Nucl. Instr. Meth., B139, 306.

[105] Runge, B. U., Dippel, M., FilleboÈ ck, C., Jacobs, K., Kohl, U. and

Schatz, G., 1997, Phys. Rev. Lett., 79, 3054.

[106] Neubauer, M., Reinecke, N., Kulinska, A., Lieb, K. P., Uhrmacher,

M., Wodniecki, P., StoÈ rmer, M., Krebs, H. U., 1998, J. Magn. Magn.

Mat., 189, 8.

[107] Lupascu, D., Habenicht, S., Lieb, K. P., Neubauer, M., Uhrmacher,

M., Wenzel, T. and ISOLDE-Collaboration, 1996, Phys. Rev., B54,

871; Lupascu, D., Neubauer, M., Wenzel, T., Uhrmacher, M., Lieb,

K. P., 1996, Nucl. Instr. Meth. B113, 507.

Klaus-Peter Lieb was born 1939 in Germany. He

studied physics in Basel and Freiburg (1958± 67 ).

He holds diploma and doctoral theses (1964,

1966 ) in experimental nuclear physics, Universi-

taÈ t Freiburg. He has held postdoctoral position s

at the Universities of Freiburg (1966± 67 ), Texas

at Austin (1967± 69 ), Bogota/Colom bia (1969± 71 )

and KoÈ ln (1971± 73 ) and Associate Professor

UniversitaÈ t zu KoÈ ln (1973± 79 ). He currently hold

the position Full Professor UniversitaÈ t GoÈ ttingen

(since 1979 ). His research topics include: nuclear

spectroscopy of neutron and heavy ion reactions;

measurements of lifetimes and magnetic mo-

ments; EUROBALL spectrometer; applied nucle-

ar physics: ion beam implantation, mixing and

analysis, hyper® ne interactions, thin ® lms, laser

nitriding and corrosion . He has authored some

420 refereed articles in journals and books: editor

and author of textbook Experimental Physics:

Atoms, Molecules, Nuclei, Particles (1997 ).

Thin film analysis with nuclear methods 413

Dow

nloa

ded

by [

Penn

sylv

ania

Sta

te U

nive

rsity

] at

06:

22 2

5 Se

ptem

ber

2013