Department of Experimental Medicine

Università della“Magna Græcia” di Catanzaro, Italy

BIONEM Laboratory http:\\bionem.unicz.it

&

Nanobioscience lab at IIT (Italian Institute of Technology)

http:\\www.iit.it

Contact: difabrizio@tasc.infm.it

Application of Plasmons and fabrication methods

Enzo Di Fabrizio

Varenna 12 July 2010

Enzo Di Fabrizio group leader (BIONEM)

F. De Angelis, G. Das, C. Liberale,

R. Proietti, P. Candeloro, F. Gentile F. Mecarini,

M. L. Coluccio BIONEM group (Bio&Nano engineering for Medicine)

Department of Experimental Medicine,

University of Magna Græcia di Catanzaro, Italy

Acknowledgements

M. Lazzarino -TASC-Trieste, Alpan Beck- CBMM. Patrini, M. Galli, L.C. Andreani

Department of Physics “A. Volta”, University of Pavia, Italy

Contributors

Campus

“Salvatore Venuta”

University of Magna Graecia location

IIT-Genoa

Nanobioscience lab at IIT (Italian Institute

of Technology)

http:\\www.iit.it

Outline

• Combination of AFM & Raman Spectroscopy

• SENSe (Suface enhanced Nano SEnsor)

• Adiabatic nanocones on AFM cantilevers

• Self similar nanospheres for SERS

• Superhydrophobic devices

• Integration of Sup-hydro-dev and Plasmonics

Challenge 1:

combination of AFM-Raman spectroscopy

Main advantages of Raman

1. “Water-transparent”

2. Low damaging

3. Analysis vs temperature

4. Small samples (da 5 a 30 μl)

5. Fast measurements

Medical&biological applications

1. Molecular structure

2. Secondary structure observation

3. Amino-acidic composition

4. Protein-Protein interactions

Main disadvantage:

Low scattering cross-section

Structured surface

Challenge 1:

combination of AFM-Raman spectroscopy

Open challenge:

nanodevice on a cantilever efficiently

acting as AFM tip and as a nanontenna

for Raman scattering.

Plasmons

Scatt. eff. small sfere

Scattering efficiency from a small sfere of nobel metal

Enhanced Local Fields

in Proximity of Metal

Nanoparticle are

Nanoscale-Localized

Nanoplasmonics: ~10 nm

Field Enhancement or

Quality Factor:

10010~Im

Re

m

mQ

Nanoplasmonics in a nutshell

Lattice Electrons

Localized Surface Plasmon:

Skin depth, ~25 nm

Spatial dispersion/Nonlocality radius, ~2 nmFv

Mean free path, ~40 nm

Reduced wavelength, ~100 nm

Polarizability:

dm

dmR2

3

dm 2

Courtesy by M. Stockman

Padova 13-12-07

Padova 13-12-07

Surface plasmon polariton (SPP) in a planar layered medium is a TM wave where

in an i-th medium layer at a point (y, z) for a wave propagating in the y direction

Boundary conditions are continuity across the interface plane of

z

H

k

iEH x

yx

0

and

ckkk

zyiHk

zyiE

ikyzBzAk

zyiE

ikyzBzAzyiH

y

x

i

z

iiii

i

iy

iiiix

0

0

;

);,,(),,(

),exp()exp()exp(),,(

),exp()exp()exp(),,(

x

y

z

Courtesy by M. Stockman

Metal-Dielectric Interface

For a two-medium system, the SPP wave vector is found as a function of frequency

(dispersion relation):

Evanescent decay exponents in these two media are found as

21

21

ck

21

2

11

c21

2

22

c

From these, it follows that for the existence of SPPs, it is necessary and sufficient that

0 and 0 2121

Courtesy by M. Stockman

Dielectric permittivity for silver and gold in optical region

P. B. Johnson and R. W. Christy, "Optical-Constants of Noble-Metals," Physical

Review B 6, 4370-4379 (1972).

Courtesy by M. Stockman

SERS and nanoparticles

Local field depends mainly on:

1) The size and shape of metal

nanoparticles (about /10)

1) The distance between metal

nanoparticles (about /100)(Both difficult to control with colloidal

nanoparticle)

2

Concentration of optical (electromagnetic wave)

energy in free space: we cannot do better than /2

…

courtesy of M. Stockman

Problems in Nanooptics

Microscale

Delivery of energy

to nanoscale:

Adiabatically

converting

propagating EM

wave to local fields

Enhancement and

control of the local

nanoscale fields.

Enhanced near-

field responses

Generation of

local fields on

nanoscale

Far field

collection

(if possible)

courtesy of M. Stockman

Nanofabrication

Nanofabrication can generally be divided into two categories based on the approach:

“Top-Down”: Fabrication of device structures via monolithic processing on the nanoscale.

“Bottom-Up”: Fabrication of device structures via systematic assembly of

atoms, molecules or other basic units of matter.

Nanotech and Microfabrication• Microfabrication is a top-down technique utilizing the

following processes in sequential fashion:

– Film Deposition

• CVD, PVD

– Photolithography

• Optical exposure, PR

– Etching

• Aqueous, plasma

Many of these techniques are useful, directly or indirectly in

nanofabrication

L 'autoassemblaggio si verifica spontaneamente

quando molecole dotate di un apposito «gruppo

terminale»

(in giollo} si ancorano alIa superficie di un

substrato

Dip-pen litho: top down-bottom up Hybrid technique

Electrons to “write” small

The “miniaturized” Bible

Overall view of the sampleDetailed view. One line has 100nm

One of the typical defects encountered

Courtesy by R. Malureanu

Sample

CrossBeam® Operation

SE

M

Scan Generator SEM

Scan Generator

FIB

Monitor

Sync

SED

Both beams are scanned

completely independent from

each other and the SED

Signal is synchronised to the

SEM scan. This results in the

CrossBeam™ operation

feature:

The ion milling process

can be imaged using the

SEM in realtime!

Sync

Pattern

Generator

The Cross-Beam equipped by a good lithography pattern generator

tool became an excellent instrument for the micro and nano

fabrication

Gas Injection System

5 reservoirs for up to 5 different gases

5 separate injection lines (one per gas)

All reservoirs and injection lines can be heated separately

Fully software controlled

Pneumatic actuators

Crossbeam chamber flange3 axis micropositioner

Injection lines

NozzlesVacuum jar with

precursor capsules inside

1. Adsorption of the gas molecules on

to the substrate surface

2. Activation of an chemical reaction

of the gas molecules with the

substrate by the Ion- / E-beam

3. Generation of volatile reaction-

products :

GaCl3 SiCl4 SiF4

4. Evaporation of volatile species and

sputtering of non volatile species

Focused Ion Beam milling and gas assisted etch

Gas assisted etch

Available on LEO CrossBeas:

XeF2,

1. Adsorption of the precursor

molecules on the substrate

2. Ion beam / e-beam induced

dissociation of the gas

molecules

3. Deposition of the material

atoms and removal of the

organic ligands

Beam induced deposition

Available on LEO CrossBeams:

Metals: W, Pt

Insulator: SiO2

Tungsten wall

Tungsten deposition

How to make things small

Ions to sculpture

Focused Ion Beam - Applications

Diamond particle on

sapphire stalk

Focused Ion Beam - Applications

Microsculpture by FIB

Catanzaro 31-05-07

a-Si 2D Photonic Crys.

Coll. F. Pirri group

3D PH. Crys. By X-ray litho 2D Bragg reflector Si/SiO2 Coll. F. Priolo

2D-3D structures

INFM network LIF@TASC

Topographic lenses

Effects produced by electron bombardment of a

material.

Two major factors control which effects can be detected

from the interaction

volume. First, some effects are not produced from certain

parts of the interaction volume (Figure 2.1b).

Beam electrons lose energy as they traverse the sample

due to interactions with it and if too much energy is

required to produce an effect, it will not be possible to

produce it from deeper portions of the volume. Second,

the degree to which an effect, once produced, can be

observed is controlled by how strongly it is diminished by

absorption and scattering in the sample.

For example, although secondary and Auger electrons are

produced throughout the interaction volume, they have

very low energies and can only escape from a thin layer

near the sample's surface. Similarly, soft X-rays, which are

absorbed more easily than hard X-rays, will escape more

readily from the upper portions of the interaction volume.

Absorption is an important phenomenon and is discussed

in more detail below.

Figure 2.1b. Generalized

illustration of interaction volumes

for various electron-specimen

interactions. Auger electrons (not

shown) emerge from a very thin

region of the sample surface

(maximum depth about 50 Å) than

do secondary electrons (50-500 Å).

Interaction volumes

Volume of Excitation

Two factors limit the size and shape of the interaction volume: (1) energy loss through inelastic interactions

and (2) electron loss or backscattering through elastic interactions. The resulting excitation volume is a

hemispherical to jug-shaped region with the neck of jug at the specimen surface. The analyst must remember

that the interaction volume penetrates a significant depth into the sample and avoid edges where it may

penetrate overlapping materials. The depth of electron penetration of an electron beam and the volume of

sample with which it interacts are a function of its angle of incidence, the magnitude of its current, the

accelerating voltage, and the average atomic number (Z) of the sample. Of these, accelerating voltage and

density play the largest roles in determining the depth of electron interaction (Figure 2.2a).

Figure 2.2a. Schematic depiction of the variation of

interaction volume shape with average sample

atomic number (Z) and electron beam accelerating

voltage (Eo). The actual shape of the interaction

volume is not as long-necked since the electron

beam in microprobe analysis has a diameter of about

1 m (see Figure 2.1b).

Electron penetration generally ranges from 1-5 µm with the beam incident perpendicular to the sample. The

depth of electron penetration is approximately (Potts, 1987, p. 336):

For example, bombarding a material with a density of 2.5 g/cm3, about the minimum density for silicate

minerals, with Eo = 15 keV, gives x = 2.3 µm. The width of the excited volume can be approximated by

(Potts, 1987, p. 337):

Both of these are empirical expressions. A theoretical expression for the "range" of an electron, the straight line distance between where an

electron enters and its final resting place, for a given Eo is (Kanaya & Okayama, 1972):

The volume of interaction can be modeled by Monte Carlo simulation. In such models, the likelihood of incident electrons interacting with the

sample and scattering and the angle of deflection are determined probabilistically. X-ray generation depths depend strongly on density and

accelerating voltage (Figure 2.2b.). The results derived from Monte Carlo modeling yield a volume of interaction that is very similar to that

determined by etching experiments. The excited volume is roughly spherical and truncated by the specimen surface. The depth of the center of the

sphere decreases with increasing atomic number of the target.

Figure 2.2b. Comparison of electron paths (top) and

sites of X-ray excitation (bottom) in targets of

aluminum, copper, and gold at 20 keV, simulated in

a Monte Carlo procedure (after Heinrich, 1981).

■：ＥＢ uniform irradiation

■：ＥＢ uniform

irradiation

DD of a,b,c change due

to EB irradiation at d.DD of a,b,c change

again due to EB

irradiation at e.

a

b

aa

c

bb

d

cc

e

dd

ee

Dose Distribution (DD) Simulation

(2)

L/S(Line & Space)Resist Pattern

HV : 50keV

Dose : 140μC/cm2

L = 50nm P

=100nm

L = 90nm P

=200nm

L =150nm P

=300nm

L = 70nm P

=140nm

10 nm

10 nm Space Width Resist Pattern

HV: 50kV

Resist : ZEP520

Hexagonal Grating(by Spot Scan Writing)

500 dots/100μm- length

30kV

5×10-11A

40μs/dot

DualBeam concept

Electron Beam

Tilt axis

1. Electron Columnfor imaging

2. Ion column for micromachining(and imaging)

Confidential

FEI DualBeams

Quanta 3D and

Helios NanoLab

The Ion Beam

•For the same Beam Energy (as used in SEM) there are big differences in other critical parameters:

•Mass: Ga+ Ion = 128,000 times heavier than Electron

•Velocity: Ga+ Ion = 1/360 of Electron

•Momentum: Ga+ Ion = 360 times Electron

Typical beam parameters

Acceleration voltage (beam energy): 500 V-30 kV

Beam current: 1pA to 20-60 nA

Beam spot: 10 nm spot size at 1pA (300 nm @ 20nA)

Liquid Metal Ion Source (field emission)

The tungsten is wetted

with gallium which is

held in the spiral by

surface tension. The

vapour pressure is

about 10-7 mbar.

Frozen-in-shape LMIS

showing 49o

half angle.

The field emission area

is a 2-5nm across giving

current densities >108

Acm-2.

Electric

field

Taylor

cone of

gallium

Ion Column

Suppressor & LMIS

Extractor Cap

Beam Acceptance Aperture

Lens 1

Beam Defining Aperture

Beam Blanking

Deflection Octupole

Stigmator Lens

Final Lens (Focus)

Lens 2

55

Primary Ion Beam

Implanted Ion

Low energy sputtered

ions and neutralse-

e-e-

e-

e-Vacuum

Solid specimen

Primary ion penetration

depth 20 nm

SE - Secondary Electrons

Ion Beam - Sample Interactions

Ga+ mass is 105 times electron mass

ConfidentialGold particles on carbon Resolution ~6nm

Resolution ~ 5 nm @ 1pA Ion beam current

electrons/ions on target of Aluminium with different energy

30 keV electron

Penetration

depth

1 keV Ga+ ion

Stop Range

30 keV Ga+ ion

Stop Range

1 keV electron

Penetration

depth

6 u

m

50 n

m

30 n

m

6 n

m

58

Sputter Yield in Si as a function of angle and E

0

5

10

15

20

25

30

35

40

0 10 20 30 40 50 60 70 80 90

incidence angle (degrees)

sp

utt

er

yie

ld (

ato

ms/io

n)

Ga 1 keV

Ga 2 keV

Ga 5 keV

Ga 30 keV

channelling

59

Sputter Yield and target materials

Prenitzer et al., M&M 2003

Z=30

Z=14

Z=29

Z=13

Materials

Parameters:

- Atomic number or

mass

- Binding energy

- Crystal structure

(channelling)

- Re-deposition

60

Materials Have Different Sputter Yields

Zinc, Z=30

Copper, Z=29

Aluminum, Z=13

Silicon, Z=14

Gas assisted etch and deposition

Common gases available (etch):

Iodine (silicon)

xenon fluoride (oxide, nitride)

Water (resist, plastic)

Common gases available (depo):

Platinum, Tungsten,

Gold, Iron,

carbon

Silicon oxide…

1. Adsorption of the gas molecules on to the substrate surface

2. Activation of an chemical reaction of the gas molecules by the Ion- / E-beam

3. Generation of volatile reaction- products .

4. Evaporation of volatile species and sputtering of non volatile species

Focused Ion Beam milling and gas assisted etch

63

Iodine Enhanced Etch (IEE)

30 KeV Ion Beam on Silicon

Electron/ Ion Beam Induced deposition (EBID)

Common gases available (depo):

Platinum, Tungsten,

Gold, Iron,

carbon

Silicon oxide…

Confidential

Electron Beam Induced deposition (EBID)

Electron Beam Induced deposition (EBID)

Confidential

1. Adsorption of the precursor molecules on the substrate

2. Ion beam / e-beam induced dissociation of the gas molecules

3. Deposition of the material atoms and removal of the organic ligands

Available on CrossBeams:

Metals: W, PtInsulator: SiO2

Ion Beam Induced deposition

69

• Deposition is a delicate balance between decomposing the adsorbed gas and sputtering.

Ion Beam Induced deposition

Typical W deposition layer composition:

W: 60%Ga: 25%C: 15%

Comparing EBID and FIB deposition

FIB deposition EBID

Deposition rate high low

Substrate milling yes no

Deposition Ga yes no

Purity high lower, current dep

Min size 20 nm 10 nm

Confidential

Overview of DualBeam Applications

Cross Sectioning

Serial Sectioning for 3D reconstruction

Patterning / Micromachining

TEM Sample Preparation

Confidential

Cross SectioningWhat is a Cross section?

FIB removes some material from bulk leaving a trench with a vertical side wall (perpendicular to the surface) revealing the inner sample structure.

SEM collects images of the side wall, with a certain incidence angle

Electron beam

Confidential

A three-step process•1 - Pt Deposition

•2 - Rough Cut

•3 - Polish

1 2 3

Confidential

(Large) Cross Section – End Result

Confidential

Defect Analysis on coating

Confidential

Cross-section of a Hepe filter

Platinum protection strap

Any kind of material: Cellulose

Confidential

Delaminating of layers on helmet’s windshield (polycarbonate)

Any kind of material: Polymers

Defect on surface

Confidential

Cross Sectioning: Cryo mode

Cross section of petal’s

flower with the use of

Cryo stage.