Slide 1
A PRESENTATION ONElectron Spectroscopy for Chemical
Analysis(ESCA)
[Session 2012-13] Presented by:- Usha sharma
(Nanotechnology)contentsIntroductionphotoelectric effectPrinciple
of ESCA(XPS)ComponentsElectron Energy AnalyzerX-ray
MonochromatorAnalysis Capabilities ApplicationsAdvantage &
disadvantages1. IntroductionElectron Spectroscopy for Chemical
Analysis (ESCA), also known as X-ray Photoelectron Spectroscopy
(XPS) is a widely used technique to investigate the chemical
composition of surfaces.XPS which makes use of the photoelectric
effect, was developed in the mid 1960s by Kai Siegbahn .ESCA is
based on the photoelectric effect.
2. photoelectric effectIn the photoelectric effect,electronsare
emitted from solids, liquids or gases when they absorb energy from
light. Electrons emitted in this manner may be called
photoelectrons.
ContdPhotoelectron spectroscopy uses monochromatic sources of
radiation (i.e. photons of fixed energy). In XPS the photon is
absorbed by an atom in a molecule or solid, leading to ionization
and the emission of a core (inner shell) electron.
The kinetic energy distribution of the emitted photoelectrons
(i.e. the number of emitted photoelectrons as a function of their
kinetic energy) can be measured using any appropriate electron
energy analyzer and a photoelectron spectrum can thus be recorded.
ContdElectrons ejected from a solid via the photoelectric effect
will be of two types: 1. Elastically scattered electrons which have
ejected from the solid without suffering an energy loss. 2.
Inelastically scattered electrons which have lost kinetic energy on
their way out of the solid.
4. ComponentsSource of fixed-energy radiation (an x-ray source
for XPS ).An electron energy analyzer (which can disperse the
emitted electrons according to their kinetic energy, and thereby
measure the flux of emitted electrons of a particular energy).High
vacuum environment (to enable the emitted photoelectrons to be
analyzed without interference from gas phase collisions).
Setup diagram of XPS system
Hemispherical electron energy analyzer
5. Electron Energy AnalyzerConcentric hemispherical analyzer
(CHA)
FactorsAnalyzer radius Slit width Elements in the transfer lens
Energy of the photoelectrons6. X-ray Monochromator
n = 2dsinFor Al K = 8.3 use (1010) planes of quartz crystald =
4.25 = 78.5Advantages of using X-ray mono chromator Narrow peak
width Reduced background No satellite & Ghost peaks What
information can we obtain from ESCA?Identification of elements near
the surface and surface compositionLocal chemical
environmentsOxidation states of transition metalsValence band
electronic structureMorphology of thin films
7.Analysis capabilitiesElemental Analysis: atoms have valence
and core electrons: Core-level Binding energies provide unique
signature of elements.
Quantitative analysis: measure intensities, use standards or
sensitivity factor8. ApplicationsSurface contaminationFailure
analysisEffects of surface treatmentsCoating, filmsTri biological
effectsDepth Profiling (Ar+ sputtering)
Advantages 1. surface sensitive (top few mono layers) 2. wide
range of solids 3. relatively non-destructiveDisadvantages 1.
expensive 2. slow, poor spatial resolution 3. requires high
vacuum
9. Advantages & Disadvantages
Thank you
