Comparison of TEM and SEM
PJL 11/16/98 rev. 11/22/05
definitions: e- = electron
GFPC = gas filled proportional counter
PMT = photomultiplier tube
SCD = semiconductor detector (Si or Ge)
Invented: Zworykin et al., 1942 Ruska, 1933
Available: Cambridge Instr., 1965 Vickers, 1936
Design: 2 CRTs, with synchronized e- 1 CRT, raster scan not essential.
beams scanning raster patterns.
Electron Electron gun, 2 lenses Electron gun, 4 lenses, 2 apertures,
column: 1 aperture, sample and sample & movable stage. Half the
(CRT #1) movable stage, various lenses & apertures are above & half
detectors. See below. below the sample.
Sample Large. Allows for sample Small. Allows for sample tilt and
Chamber: tilt & rotation. May also rotation.
allow electrical connections
and mechanical test apparatus.
Typical 1 to 50 kV 50 to 300 kV, even a million volts!
Voltage & 30 Ang. or more, depends on 10 Ang. or more. atomic planes visible
Resolution: sample. Great depth of field.
Display: CRT #2 provides a TV-like A fluorescent screen inside the
display. Display brightness electron column at the bottom.
is determined by detector
output, adjusted for ... or an area detector
brightness & contrast.
Photog- Take photo of the CRT display Load film cartridge inside the e-
raphy: or capture image digitally column under the fluorescent screen.
for analysis. Flip up screen to expose the film.
Standard Secondary e- (<50 eV) uses Just the fluorescent screen and
Detector: scintillator & PMT. Gives photographic film.
good topographical contrast.
Optional Backscattered e- (same energy Electron energy loss spectrometer
Detectors: as incident beam) uses SCD detects lighter elements using
or scintillator & PMT. Gives quadrupole magnetic detector in
good compositional contrast. the transmitted beam.
Energy dispersive X-ray uses
SCD, detects heavy elements. Energy dispersive X-ray.
Wavelength dispersive x-ray
uses crystal diffractometer Secondary e- detector, plus raster
with GFPC. Detects lower scan capability.
elements and avoids peak
convolution. Works slow.
Photoemission (a.k.a. cathodolumin-
escence) uses a mirror & PMT.
Good for non- or semi-conductors.
Specimen current to ground
= beam - secondary - backscatter.
Voltage contrast uses a slightly
modified secondary e- detector
to image regions of varying
potential. Ideal for IC chips.
Strobe the beam off & on to
"freeze" periodic signals.
Electron beam induced current,
flows between two contacts
to the sample, not to ground.
Good for semiconductors.
Thermal wave uses a piezoelectric
microphone to detect acoustic
noise generated in sample by
pulsing (blanking) the e- beam.
Good for imaging features which
conduct heat poorly.
Sample Almost any clean solid. Foil or powders < 1000 Ang. thick.
form: Big, thick samples are OK. or surface replicas.
Sample First clean off dirt & grease. Use ion mill, focused ion beam,
prep: Insulators must be coated electropolishing, jet polishing,
with a conducting layer dimpling, etc. Sample prep is
~100 Ang thick. Sputter or usually a lot of work and may
evaporate metal or C. irreversibly change the material.
Sample prep is usually simple.
Most Fracture, wear or corrosion Selected area e- diffraction,
useful surfaces, powders, polished imaging of dislocations, tiny
for: & etched microstructures, precipitates, grain boundaries
IC chips, chemical segrega- and other defect structures in
Both SEM and TEM are useful in biology and geology, as well as in materials science.
1) Goldstein, Newbury, Echlin, Joy, Fiori & Lifshin; Scanning Electron
Microscopy and X-Ray Microanalysis, Plenum, 1984
2) Hirsch, Howie, Nicholson, Pashley & Whelan, Electron Microscopy of
Thin Crystals, Krieger, 1977
3) ASM, Metals Handbook, 9th Edition, vol. 9, p. 89-122, Scanning Electron
Microscopy and Transmission Electron Microscopy.
4) ASM, Metals Handbook, 9th Edition, vol. 10, p. 427-546, Electron