1. Electron microscopy techniques like SEM and TEM use electrons accelerated to high energies to interact with and provide information about samples on the nanometer scale. 2. SEM can be used to provide information on surface topography, crystalline structure, chemical composition and electrical behavior of the top 1um of a sample through detection of signals like secondary electrons, backscattered electrons, and x-rays. 3. Different signals provide different types of information - secondary electrons provide topographic information at high resolution while backscattered electrons provide compositional information and can also provide crystallographic data through electron channeling effects.

1. Application of Diffraction to Texture Analysis 71
Incident
electron beam
Back reflection
(SEM)
Secondary electrons
(imaging)
Auger electrons
(surface analysis)
Backscattered electrons
(EBSD-, SAC-pattern,
imaging)
X-rays
(Kossel technique,
chemical analysis)
Sample
Transmission
(TEM)
Absorbed electrons
X-rays
(Kossel technique,
chemical analysis)
Elastically scattered electrons
(SAD point diagrams,
dark field imaging)
Inelastically scattered electrons
(Kikuchi diagrams)
FIGURE 3.14
Transmitted electrons
(bright field imaging)

2. Application of Diffraction to Texture Analysis 71
Summary of the various signals obtained by interaction ofelectrons with matter in an electron microscope.
surf
1.In electron microscopy the electrons are usuallyaccelerated
to high energies of between 2 and 1000 keV (i.e. wavelengths
0.027-0.0009 nm).
2. SEM can provide information on surface topography,
crystalline structure, chemical composition and electrical
behaviourof the top 1 urn or so of specimen.
3. If the specimen is very thin, then electrons may be
transmitted through it unabsorbed and used to form the image
in TEM. If the specimen is thicker, then electrons are no longer
transmitted so only particles (e.g.electrons, x-rays and photons)
emerging from the surface can give us information.Theseare
the signals used in a conventional SEM.
4. SEM can provide information on surface topography,
crystalline structure, chemical compositionand electrical
behaviourof the top 1 urn or so of specimen.

3. Application of Diffraction to Texture Analysis 71
5. Much higher magnificationscan be achieved(up to
1,000,000x), with an ultimateresolution of 1 nm.
6. SEM benefits from a large depth of field so most of the
specimen surface is simultaneouslyin focus
whatever the surface roughness.
7. Advantages of SEM over TEM include:
1. Large specimens (200 mm diameter wafers, or even larger in
speciallyadapted SEMs), compared to just 2.3 mm or 3 mm in
diameter for TEM.
8. SEM permits non-destructive evaluationof the specimen
(TEM is effectively a destructive techniquebecause of the
specimen preparationrequired).
9.Very short specimen preparationtime (maybe only a few
seconds) while the specimen is attached to a “stub” (specimen
holder).TEMspecimen preparationis more complex and
timeconsuming
10. In an SEM the incident electrons (from an electron gun)
typicallyhave energies of 2-40 keV
11. the 1)tungsten hairpinfilament which is heated (by passing
a current through it) to over 2500°C to produce
thermal emission of electrons from its tip. 2)Lanthanum
hexaboride (LaBG), 3)Field emission guns.

4. Application of Diffraction to Texture Analysis 71
12. Two or three electromagnetic condenser lenses demagnify
the electron beam into a fine probe which is scanned across a
selected area of the specimen surface in a raster by scan coils.
Secondary Electron (SE) images: “Secondary electrons” are
those that escape from the specimen with energies below 50
eY mainly knocked out of their orbits around an atom by an
incidentelectrons.
2. These provide the highest spatialresolution images, they can
only escape from a very shallow, near-surface layer of material
and the signal comes from an area about the size of the
electron probe. Primarily, they give topographicinformation
Backscattered Electron (BSE) images:Backscattered electrons
are those incident electrons that approach the nucleusof an
atom sufficiently closely to be scattered through a large angle
and reemerge from the surface.
2. Images have slightly less resolutionthan secondary electron
images because they come from slightly deeper in the
specimen, so the area giving rise to the signal is larger than the
probe size. Mostly, they provide compositional
information;elementsof higher atomic mass give brighter
contrast. Backscattered electrons can
also provide crystallographic information,as electron
channellingoccurs (similar to ion channelingduring ion
implantation).

5. Application of Diffraction to Texture Analysis 71
3. Electron backscattered diffraction pattern analysishas been
used for strain measurements in semiconductors,
and its use in studying the epitaxy(Epitaxy refers to a type of crystal growth
or material deposition in which new crystalline layers are formed with one or more well-
defined orientations with respect to the crystalline substrate. ) of GaN on
sapphire is being explored.
Auger electrons and x-rays: Auger electrons are emitted from
atomic layers very close to the surface and give valuable
information about the surface chemistry. Because of the low
numbers of Auger electrons and the need to measure their
energies with precision, Auger electron imaging is usually
performed in dedicatedinstruments and requires advanced
detectors and instrumentation.
2. Characteristic x-rays are generated by atoms when the
incidenthigh-energy particle knocks out an inner shell electron
and an outer- shell electron moves into the empty orbit. There
is now a progression of electron jumps from higher to lower
energy states (e.g. from L to K, then M to L etc) until all the
electron states are refffled.At each stage, x-rays are emitted to
conserve energy.
3. Measurement of the energies (or wavelengths) of these x-
rays gives informationabout the chemical
compositionof the specimen.
4. The x-rays are detected by either an energydispersive or a
wavelengthdispersivespectrometer. Energy dispersive x-ray

6. Application of Diffraction to Texture Analysis 71
spectroscopy (EDS or EDX) is the more common attachment to
SEMs as it provides rapid qualitative analysisof the specimen.