Inelastic Scattering - Introduction

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Inelastic Scattering - Introduction
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Quasiparticle Property Measurements
Two reasons why we can generate and detect 1)
Since the fast electrons passing through a
material can create plasmons, phonons, magnons,
etc., i.e, signal generating, their resulting
energy-loss electrons (used for signal detecting)
carry the information of their properties. 2)
Every electron that scatters off the same
quasiparticle mode picks up the same scattering
phase. - if an electron scatters off the
quasiparticle, this electron carries information
about the quasiparticle. e.g., the phonon
gluing Cooper pair electrons together to make
the superconducting fluxon.
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Inelastic Scattering - Introduction
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Electron Scattering
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Inelastic Scattering - Introduction
We will focus on the collective interactions
produced by inelastic scattering since no new
information concerning x-rays and secondary
electrons is available in Williams and Carter.
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Electron Energy Loss Spectrum (EELS)
Elastically scattered electrons Bragg
diffracted and diffuse elastically scattered
electrons
Zero-loss phonon loss
Low-energy, diffuse inelastically scattered
electrons
, I
(Bulk Plasmons)
(Surface Plasmons)
(excitons, bandgap, dopants, defects)
, E
000 beam
Diffracted beam
EELS spectrum of elastically inelastically
scattered electrons
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Zero-loss Phonon-loss Intensities for GaAs
Aplanatic STEHM required
total
Intensity
Zero-loss
atomic planes
444
222
666
Phonon-loss
s (1/Å)
0 10 20
f (mrad)
Similar intensity loss for plasma loss electrons
Doyle and Turner Acta Cryst. (1968). A24, 390
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Inelastic Scattering - Introduction
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Plasmons and Phonons
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Plasmons and Phonons
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for bulk plasmons, which exist inside the
material. There is also a surface plasmon, which
can be delocalized on the surface and exist for
micro-seconds
Longitudinal Waves
Recall the electron emitted from the source is a
transverse wave.
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Bulk Plasmons
If the specimen is gt100 nm, then another bulk
plasmon can be created. The diffracted beams can
also produce bulk plasmons.
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Surface Plasmons
The surface plasmon energy is equal to the bulk
plasmon energy (10s of eV) divided by square root
2. For some specimen and certain conditions,
surface plasmons can have a high intensity, e.g.,
gold nanoparticles, carbon nanotubes, etc.,
anything where the surface dominates over the
volume of the specimen. Their creation by the
electron beam creates a high intensity of surface
plasmon loss electrons.
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Plasmons
1. Localized Surface Plasmons
Surface Plasmon
2. Propagating Surface Plasmons
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Localized Surface Plasmons
Simple semi-classical model
electron wave
Surface plasmon densities around differently
shaped nanoparticles
A.J. Haes, C.L. Haynes, et al, MRS BULLETIN, 30
368 (2005)
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Surface Plasmon Polariton
The smaller the wavelength of surface plasmon,
the shorter length it travels or propagates over
the surface!
H.A. Atwater, S. Maier, et al, MRS BULLETIN, 30
385 (2005)
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Plasmons Loss Electrons
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Phonon Loss Electrons
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Interband and Intraband Loss Electrons
plus the presence of dopants and defects
(electronic and photonic defects) in the band gap
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Elastically Inelastically Scattered Electrons
Elastically scattered electrons Bragg
diffracted and diffusely scattered
Zero-loss phonon loss
, I
(Bulk Plasmons)
(Surface Plasmons)
(excitons, bandgap, dopants, defects)
, E
000 beam
Diffracted beam
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What is the better electron source that
represents elastically and inelastically
scattered electron coming from material specimens?
Lorentzian Represents electrons from specimen
that have lost energy such as inelastically
scattered electrons including plasmon loss
electrons and phonon loss electrons.
Gaussian Represents electrons from electron
emitter plus Bragg diffracted beams, which have
no energy loss.
Gaussian
Lorentzian
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Primary Beam
Lateral coherence enables continued interfere of
beams as they are separated by changing voltage
on electron biprism. New position on source, RS1
and RS2 enable the source size, shape and
coherence to be determined. Perhaps, first time
to measure properties of electron source coming
from specimen.
Condenser Aperture
ac
Crystal Specimen
RS1
RS2
2qB
Apparent Sources, Rs (virtual sources)
Electron Biprism ( )
aB
Main Beam
Diffracted Beam
Region 1
Region 2
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Fringe Contrast versus Beam Separation
86V
82V
The Lateral spatial coherence, do, is given as a
function of electron source size, Rs, to be
a)
b)
79V
74V
2
The reduced fringe contrast as the beams separate
gives a measure of the shape of the electron
sources.
1
2
c)
d)
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Beam Damage
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Beam Damage
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Beam Damage
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Beam Damage - Heating
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Beam Damage - Heating
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Beam Damage Polymers
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Beam Damage - Polymers
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Beam Damage Covalent Ionic Materials
cathodoluminescence

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Beam Damage in Metals
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Beam Damage
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Beam Damage
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Beam Damage
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Inelastic Scattering - Sputtering
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Inelastic Scattering - Summary
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Surface Plasmon Polariton
Propagating Surface Plasmons Surface Plasmon
Polaritons (SPPs)
SPP are electromagnetic modes bound to
metal/dielectric interface which propagates as a
longitudinal wave along the surface.
Localized Surface Plasmons Surface Plasmon Polaritons
Nanoparticles size 10-200 nm Metal thickness 10-200 nm
Field enhancement 100-10,000 times 10-100 times
Field spatial range 10-50 nm 1000 nm
A.J. Haes, C.L. Haynes, et al, MRS BULLETIN, 30
368 (2005)
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Plasmon Polariton Propagation in Gold Rod
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Plasmon Polariton Propagation in stripe with d lt ?
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Surface Plasmon Bio Sensors (SPR-like experiment )
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Bandgap Engineering
Figure 9 Energy band diagram versus lattice
constant.