The first commercial SEM became available in 1965. Over the past four decades, the SEM has become an indispensable tool in both advanced research and routine analysis for science and industry. It has also become perhaps the best known and most widely-used of the surface analytical techniques.
SEM, accompanied by X-ray analysis, is a relatively rapid, inexpensive, and basically non-destructive approach to surface analysis. It is often used to survey surface analytical problems before proceeding to techniques that are more surface-sensitive and more specialised.
The electron microscope can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. The SEM produces images by detecting secondary electrons which are emitted from the surface due to excitation by the primary electron beam.
The
ERI SEM is equipped with Energy dispersive X-ray analysis ( EDXA). EDXA
allows elemental analyis on the specimen being viewed using the SEM..
Analysis may be performed on an area, along a line or on a single point.
This allows qualitative elemental analysis and/or element localization
on the specimen being viewed.
.The SEM EDXA system at the ERI has been used to analyze a variety of
elements in a variety of specimens e.g. elemental composition of corrosion
samples and the distribution of materials on biological samples (see below)
Variable
pressure or ‘wet’ SEM.
Using
traditional SEM, wet and non-conductive samples have to be prepared
to withstand the high pressure vacuum and to conduct the electron beam.
This involves dehydration and gold coating of samples, processes that
can create artefacts that do not reflect the original state of the sample.
The variable pressure SEM allows wet and non-conductive samples to be
viewed in their original state. As such, fresh biological specimens
such as algae and non-conductive materials such as crab carapace can
be studied without pre-treatment.
Topcon SM-300
SEM:
SEMICAPS Imaging Analysis System
EDXA Detector (low element)
WinEds EDX Analysis System
Interface MICA Mapping Tool
Cressington 108 Sputter Coater
Cressington MTM-10 High Resolution Thickness Monitor
The following links provide further information on SEM:
http://www.chems.msu.edu/curr.stud/mse.sops/sem.intro.htm
http://www.unl.edu/CMRAcfem/em.htm
http://www.jeol.com/sem/docs/sem_guide/tbcontd.html
Sputter Coater
The sputter coater (Cressington 108) is designed primarily for sputtering conducting gold layers on to samples to prevent charging effects in the scanning electron microscope.
The Cressington 108 is designed as an integrated vacuum system with it's desktop pumping system matched to the coating unit for optimum performance. The quality of coatings produced by the system relies on the gas handling characteristics in the range 0.01mb to 0.1mb. The high pumping speed of the system in this pressure range naturally results in rapid pumpdown performance from atmosphere and short cycle times.
In the past, sputter coaters for SEM have used the gas pressure control valve to adjust the sputtering current. This model does not opperate in this way:- gas control and current control functions have been seperated. This allows the user to independently adjust operating pressure (mb) and sputter current (mA) to obtain the best sample conformity and minimum grain size.
