The Scanning Electron Microscope (SEM) is a microscope that uses electrons rather than light to form an image. There are many advantages to using the SEM instead of a light microscope including, a large depth of field, which allows a large amount of the sample to be in focus at one time, and also the ability to obtain images of high resolution, which means that closely spaced features can be examined at a high magnification.
Preparation of the samples is relatively easy since most SEMs only require the sample to be conductive.Non-conductive samples can be coated using a sputter coater to deposit a thin layer of silver, gold or other conducting material. The combination of higher magnification, larger depth of focus, greater resolution, and ease of sample observation makes the SEM one of the most heavily used instruments in research areas today.
To learn more detail about the technique of scanning electron microscopy at the college level, please use the URL provided below:
http://surf.eng.iastate.edu/~karie/Documentation/college.html
The Department of Geology and Geophysics and the Department of Mechanical Engineering, recently purchased a high quality Leo 430 SEM, from an NSF with matching funds provided by the University of California. The instrument is under the direction of H. R. Wenk and G. Johnson. The instrument is located in the Department of Geology, McCone Hall.
Electron Column
Resolution: 4.0nm
Acceleration Voltage: 300V to 30kV in 10V steps
Magnification: Range 15x to 300,000x
Probe Current: Continuously variable between 1pA and 500nA
Automation
Auto gun run-up
Auto column control
Auto focus - coarse and fine
Auto stigmation correction
Auto resolution
Auto contrast
Auto compensation for photo recording
Accessories
Electron Backscatter Pattern (EBSP) Imaging Fiber Optic Coupled
CCD Camera
A desktop sputter coater for non-conductive samples is available for both Ag (silver) and Au-Pd (gold-palladium) coating using an Ar (argon) inert gas plasma. Ag coating is prefered for samples that require that the coating be easily removed. This is accomplished by a very dilute nitric acid wash. Coating thickness varies but is usually in the 1 to 5 nm range.
The Leo 430 SEM, is a fully digital SEM which has the capability of controlling all instrument parameters, stage control and image acquisition from software. Stage automation and beam control is also provided through custom software running on an off-line computer through a Network DDE connection.
Image output is provided by a high resolution video printer on thermal paper and digital images may also be saved to disk in TIFF or BMP format at 1024 x 768 resolution in 256 gray levels.
Currently, the only electron imaging signal source is SE (secondary electron) imaging. By mid 1998, we should have completed the addition of both a backscatter (pole-face mounted) and front-scatter (tilt facing mounted) detectors for BSE (backscattered electron) imaging.
The instrument has a very large sample chamber capable of holding specimens up to 10 centimeters in size. Movement of samples using the 5 axis (x, y z tilt and rotation) stage joystick, is facilitated by a GW infra-red camera mounted normal to the tilt axis.
By the end of 1998, it is anticipated that we will also have a qualitative x-ray analysis system for demonstration and teaching of the x-ray fluorescence and spectrum techniques in undergraduate laboratory courses.
In addition, a state-of-the-art Peltier cooled fiber optic coupled camera has just been ordered that will provide for EBSP (electron-backscatter pattern) imaging of individual grains and OIM (orientation image mapping) for the purposes of texture analysis. The UC Texture Laboratory is a collaborative effort between the Department of Geology and Geophysics and the Department of Mechanical Engineering.
This CCD camera is a 1024 x 1024 large pixel format with frame transfer capability. Expected acquisition times are 0.2 to 1 seconds with a typical download time of 0.5 secs at 2 megapixels/per second at 14 bits image resolution depth. The camera will also be capable of arbitrary integer binning is both directions for reduced download times. The coupling of EBSP derived crystal symmetry and lattice spacing with qualitative x-ray intensity information should provide for rapid phase identification capability in the near future.
The Department of Geology and Geophysics offers Geology 402, a course in the operation and theory of the electron scanning microscope. This pass/fail course is available each quarter and must be taken by all graduate students who require the scanning electron microscope for their thesis work. Please contact John Donovan jdonovan@socrates.berkeley.edu for course details.
The SEM Laboratory is available on a re-charge basis for students and researchers at the University of California. The typical rate is approximately $44 per hour and a 50% overhead is charged for users outside the U.C. system. Please contact John Donovan jdonovan@socrates.berkeley.edu for details.
Electronic mail address
jdonovan@socrates.berkeley.edu
jdonovan@seismo.berkeley.edu
Web address
http://www.geo.berkeley.edu/geology/labs/sem/index.html
Telephone
(510) 642-5459 (Voice)
(510) 643-9980 (FAX)
The UCB SEM Laboratory is located in Room 408, McCone Hall on the Berkeley campus near North Gate. The lab manager, John Donovan, has an office in Room 455, McCone Hall.
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The mailing address is:
John Donovan
Room 301, McCone Hall
Department of Geology and Geophysics
University of California
Berkeley, CA
94720-4767
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The Department of Geology and
Geophysics
Room 301, McCone Hall
The University of California
Berkeley, CA 94720-4767
Copyright 1998, The Regents of the University of California.
Questions, comments and e-mail for this web-site: jdonovan@socrates.berkeley.edu
Last Updated 03/09/11