Lens aberrations and Scanning Electron Microscope

Topic : Scanning Electron / Ion / Probe Microscopy in Materials  Characterization(SEIPM) 

Concepts Covered

ØLens aberrations

ØHistory on electron microscope

ØLight versus electron

ØWhat is a scanning electron microscope (SEM)?

Early History of Electron Microscope

 •1931 - The German physicist Ernst Ruska and the electrical engineer Max Knoll constructed the first transmission  electron microscope (TEM). •1935 - Knoll built a first “scanning microscope” The resolution limit was ~100 mm. •1937/1938 - Manfred von Ardenne pioneered the scanning electron microscope by adding scan coils to a transmission electron microscope. It is actually a STEM. •1938 - Ruska and Bodo von Borries improved the resolution of TEM to 10 nm. •1938 - The first practical electron microscope was constructed at the University of Toronto, by Eli  Franklin Burton and students Cecil Hall, James Hillier, and Albert Prebus •1939 - Siemens produced the first commercial TEM •1942 – The first true SEM was developed by Vladimir Zworykin, who showed topographic contrast  using secondary electrons. •1952 – Oatley and McMullan achieved a resolution of 50 nm using the SEM built by them. •1960 – Everhart and Thornley improved secondary electron detection. •1963 – Pease and Nixon combined previous improvements in one SE M  with three magnetic lenses  and a E-T detector

•1965 – The first commercial SEM, the Cambridge Scientific Instruments Mark I “Stereoscan”

 

 Light versus Electron

 •Wavelength •Scattering  •Charge •Type of lens can be used

  

1. Wavelength of electron in an electron microscope

2. What is a SEM?

The S  E  M   is an instrument that scans a sample surface with a finely converged electron beam under vacuum, detects the information (signals) produced at that time from the sample, and  presents an enlarged image of the sample surface on the monitor screen.

 

Conclusions 

 

ØElectron can have small wavelength – thus can produce higher resolution image

ØDue to its charge, we can use electromagnetic lenses in microscope

ØLens aberrations reduce the performance of a microscope

 

References

 ØElectron Microscopy and Analysis by Goodhew and Humphreys, 1988, Taylor & Francis ØScanning Electron Microscopy and X-ray Microanalysis by Joseph Goldstein et al., 3rd  edition, 2003, Springer Science + Business Media

 

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