Implantation of sapphire by Zr and Zr plus O: threshold fluence for amorphization and optical properties

(a) Materials Science and Engineering Department, University of Tennessee, Knoxville, TN 37996 (b) University of Sussex, Brighton, BN1 9QH, United Kingdom (c) Center for Materials Processing, University of Tennessee, Knoxville, TN 37996-0750 (d) Instituto Tecnológico e Nuclear (ITN) Ion Beam Laboratory, Sacavém, Portugal

Younes Sina a, Peter D. Townsend b, Carl J. McHargue a,c, Edvardo Jorge da Costa Alves d

Important factors for amorphization during ion implantation: Sample temperature Ion mass Ion energy Fluence Ionicity degree Chemical effect Thermodynamic stability Topology of the atomic scale structure Physical properties Ease of glass formation

Background

During ion implantation: The ions displace atoms from lattice sites They create vacancy-interstitial pairs and other associated defects At higher fluences: Recombination of defects can occur at the same rate as their

production In other cases: • Amorphization is the result of damage accumulation during ion

bombardment, especially at low temperatures

Background

4

Zr amorphizes sapphire at relatively low damage.

Background

0

0.2

0.4

0.6

0.8

1

1.2

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ΧA

l

dpa

Zr

Fe

Ti

Nb

Cr

5

-1

0

1

2

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9

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0 500 1000 1500 2000 2500 3000

E= 175 keV Φ= 4E16 Zr+/cm2

dpa Zr%

Depth [Å]

Buried amorphous layer suggest concentration of Zr may be controlling factor

Crystal Systems, Inc. (Salem, MA)

α-Al203

1) 120 h at 1450⁰C

Oxygen

To remove any residual polishing damage or surface contamination

α-Al203

I. Sample Preparation

2) slow cool

Zr (175 keV, 2x1015 -2x1016 /cm2) Room Temperature

α-Al203 Zr implanted α-Al203

RBS

OA, PL

O (55 keV, 1.1x1016 -2.3-x1016 /cm2) Room Temperature

Zr+ O implanted α-Al203

RBS

OA, PL Zr implanted α-Al203

7◦-off

7◦-off

I. Sample Irradiation

Zr

O

Rutherford backscattering/ Channeling (RBS-C) Disorder on the Al-sublattice Distribution of implanted species Verification of presence (or absence) of an amorphous phase Zr depth profiling Optical absorption (OA) Photoluminescence (PL) Verification of presence (or absence) of oxygen vacancies Check for F type color centers

III Characterization

8

IV Calculation of color centers concentration

Using Smakula’s equation for calculation of F+ F+ centers concentration

Results and discussion

1) Threshold fluence of amorphization 2) Effect of oxygen implantation on pre-Zr- implanted samples 3) Optical properties of the irradiated samples with Zr and Zr+ O 4) Calculating of true absorption coefficient of the induced bands 5) Concentration of F centres using Smakula’s equation

100 200 300 400 500 600 7000

400

800

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1600

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2800

3200

Yie

ld

channel

<0001>

random =4º

ZrAl

Ox10

Sample 2x1015

Zr+.cm

-2

100 200 300 400 500 600 7000

400

800

1200

1600

2000

2400

Sample 7.5x1015

Zr+.cm

-2

Yie

ld

channel

<0001>

random =3º

ZrAl

O

x3

Fluence below the amorphization threshold

Fluence on the verge of amorphization

Rutherford backscattering spectrometry along a channeling direction (RBS-C) using 2.0 MeV He+

100 200 300 400 500 600 7000

400

800

1200

1600

2000Sample 1.5x10

16 Zr

+.cm

-2

<0001>

random

Y

ield

channel

ZrAl

O

Zr fluence just above amorphization threshold

175 keV

40 nm

0

0.5

1

1.5

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0 50 100 150 200 250 300

Zr%

dp

a

Depth [nm]

dpa @ E=175keV, Φ=1.5E16

40 dpa

Φ=1.5×1016

Rutherford backscattering spectrometry along a channeling direction (RBS-C) using 2.0 MeV He+

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Yie

ld

channel

<0001>

random

Sample A

Zr (x3)Al

O

7.5 x1015

Zr+/cm

2 +1.1x10

16 O

+/cm

2

Oxygen implantation into a pre-Zr- implanted sample

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25001.5 x10

16 Zr

+/cm

2 + 2.3x10

16 O

+/cm

2

Yie

ld

channel

<0001>

random

ZrAl

O

Sample IR

Effect of oxygen in pre-Zr implanted samples

Low fluence-damaged Not amorphous

Higher fluence-damaged amorphous

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Yie

ld

Energy [keV]

2E15 Aligned

7.5E15 Aligned

1.5E16 Zr+/cm2 Aligned

By increasing Zr fluence damage in Al and O- sublattices increase

By implantation of O in pre-implanted Zr samples, damage in Al sublattice increases and in O sublattice decreases

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Yie

ld

Energy [keV]

1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 Aligned

7.5E15 Zr+/cm@ & 1.1E16 O+/cm2 Aligned

---- ----

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1500 1550 1600 1650 1700 1750 1800

Yie

ld

Energy [keV]

7.5E15 Zr+/cm2 Random 1.5E16 Zr+/cm2 Random 7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 Random 1.5E16 Zr+/cm2 & 2.3 E16 O+/cm2 Random

b

2) Effect of oxygen implantation on pre-Zr- implanted samples

Zirconium profiles in sapphire implanted with oxygen subsequent to implantation with Zr: (a) below and (b) at the threshold for amorphization.

The subsequent implantation of oxygen produces a slight broadening of the zirconium distribution, probably due to collisional mixing

a

Zr distribution

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3 4 5 6 7

Inte

nsi

ty [

Arb

it.

Un

it]

Energy [eV]

1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 , RT

2E16 Zr+/cm2 , RT

1.5E16 Zr+/cm2 ,RT

7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 , RT

2E16 Zr+/cm2 & 4E16 O+/cm2 , RT

7.5E15 Zr+/cm2 , RT

Optical absorption spectra with the absorption from a virgin crystal subtracted

F+

F+F+

Optical properties of the irradiated samples with Zr and Zr+ O

F+

F

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300 320 340 360 380 400 420 440 460 480

Inte

nsi

ty

nm

1.5E16 Zr+/cm2 & 2.3E16 O+/cm2

7.5E15 Zr+/cm2 & 1.1E16 O+/cm2

7.5E15 Zr+/cm2

1.5E16 Zr+/cm2

VIR

2E16 Zr+/cm2

Photoluminescence spectra obtained with 4.86 eV confirm that both types of oxygen vacancies are present in all implanted samples.

Concentration of retained simple oxygen defects (F-type centers) can be estimated by Smakula’s equation: NF= 0.87 x 1017 n µmax W1/2/f (n2 + 2)2

f is the oscillator strength and for the F band is ~1 n is the refractive index of implanted sapphire ~1.8 W1/2 is width (in eV) at half maximum of the optical absorption band characterized by a maximum optical density has a value of ~0.6 eV µm is maximum absorption coefficients of the induced bands

Important parameter in Smakula’s equation is absorption coefficient ( µm)

The absorption coefficient (µ) is given by log (I in/I out) = µt/2.3 where t is the path length

Calculated oxygen vacancy profiles produced by Zr and O irradiation in sapphire

The implant/damage depth, t, is only about 62 nm for the samples implanted with zirconium only and 68 nm for the dual implants

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0 500 1000 1500 2000 2500

Nu

mb

er/

(An

gstr

om

-Io

n)

Depth [A]

7.5E15 Zr 1.1E16 O

O Vacancies after Zr

O Vacancies after O

Number of O vacancies/Cm3 = [Number/Å × Ions].[Ions]. [Å/Cm3]

-

=

The implant/damage depth, t, is only about 62 nm for the samples implanted with zirconium only and 68 nm for the dual implants

I in I out

log (I in/ I out) = µt/2.3

Sample N (F+F+

) (cm-3)

7.5E15 Zr+/cm2 & 1.1E16 O+/cm2 , RT 3.00E+21

7.5E15 Zr+/ cm2 , RT 3.646E+21

1.5E16 Zr+/ cm2 , RT 3.5E+21

1.5E16 Zr+/cm2 & 2.3E16 O+/cm2 , RT 3.27E+21

2E16 Zr+/ cm2 , RT

3.89E+21

Concentration of retained simple oxygen defects (F-type centers) estimated by Smakula’s equation:

Implanted species Oxygen vacancies retained as F &F+ defects

( from Smakula’s equation)

Oxygen vacancies predicted by SRIM

(99% dynamically annealed)

Zr 1 - 2.5 % 6 -8 %

Zr + O 0.7 - 1.1 % 4 -5 %

Some of the displaced oxygen may reside in interstitial positions as O2- leaving a

vacancy without a trapped electron(s). This defect has an optical absorption band near

7.0 eV, outside the range of the instrument used here.

At the relatively high fluences used in this study, there is considerable overlapping of the displacement cascades that may give rise to extended defects such as interstitial dislocations, nanometer-sized clusters, defects trapped at dislocations, etc.

Conclusion

1. Threshold fluence of 175 keV Zr is approximately 1.5×1016 Zr+/cm2.

2. Subsequent implantation of oxygen produces slight broadening of damage region of low fluence and no apparent effect at fluence above amorphization threshold.

3. Number of oxygen vacancies retained as F and F+ centers is very low.

4. Implantation of oxygen in pre implanted samples reduced the number of F and F+ centers.

Thank you

These slides were prepared for an oral presentation for ICDIM 2012 Santa Fe, NM ( June 24-29/2012)

http://icdim.newmexicoconsortium.org/conference-agenda-clickable