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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.