A scanning electron microscope is an electron microscope designed primarily for high magnification imaging, and may also be used for semi-quantitative analysis using an energy-dispersive spectrometer. It is capable of generally higher spatial resolution but inferior analytical sensitivity compared to the electron microprobe. This Camscan Series II SEM can acquire digital secondary-electron and backscattered-electron images, and digital energy-dispersive x-ray maps. Semi-quantitative energy-dispersive microanalysis can be performed as well. Most of the periodic table can in principle be analyzed (Beryllium through Uranium), subject to several important considerations and limitations related to measurement using an energy-dispersive spectrometer. The analytical sensitivity is typically 0.X% (i.e. several thousand ppm), but can be as high as several weight percent for problem elements. The volume sampled is typically a few cubic microns, corresponding to a weight of a few picograms. The quality of imaging and analyses performed depend on the quality of sample preparation, character of the sample material, and availability of appropriate primary and secondary calibration standards for the desired elements. A precision approaching a few percent relative and accuracy of 5-10% can be expected with this instrument. We have acquired a Cameca Series II Camscan SEM equipped with a LINK EDS detector. The instrument was installed in room 118 GS.
The instrument is a Camscan Series II Scanning Electron Microscope. The Camscan is capable of obtaining images over a wide range of accelerating potential (from about 2 KV to 30 KV), and probe current (from low picoamp to about 15 nanoamps), which can be used to study a variety of materials. It is equipped with an Everhart-Thornley secondary-electron collector for secondary-electron imaging, a Robinson-type backscattered electron detector for atomic-number-contrast imaging, and a relatively slow speed absorbed current imaging system. The backscattered detector is a large-solid-angle, low noise, high sensitivity detector that is capable of high atomic number contrast (less than 0.1 Z) at comparatively low probe current. The instrument is optimized for concurrent backscattered electron imaging and x-ray analysis at the same working distance. An on-board frame averaging system allows one to integrate several scan frames in order to reduce noise and obtain a cleaner image. Compensated brightness and contrast adjustments are automatically performed by the imaging system, and dynamic focussing is available for samples having a highly tilted surface. The working resolution for this instrument is dependent on the sample being studied, but is approximately of 100 nm.
The sample stage assembly is capable of motorized movements in the x-axis and y-axis directions, and manual adjustments can be made for z-axis, z' eucentric, rotation, and tilt. The sample chamber is capable of handling large samples, although it is usually preferable to minimize the sample size if possible. Sample holders are available for small samples via 1 cm pin-type mounts, 1 inch circular thin sections, 1 inch thick mounts, petrographic thin sections, and 1.25 inch metallurgical mounts.
The instrument is
outfitted with a Link Analytical pentafet SiLi energy-dispersive x-ray
spectrometer which has a turret control that allows either a Beryllium window
or a Boron Carbide window to be used for normal or light element x-ray
acquisition, respectively. The Link detector is interfaced to an
Digital imaging and x-ray mapping are performed using the 4Pi Systems Scanning Interface Unit for digital beam control. Digital images may be acquired at magnifications up to 15,000X, and a large number of x-ray maps may be acquired simultaneously, using the Link EDS detector.
Digital secondary-electron and backscattered-electron images and x-ray maps are acquired using special acquisition plug-ins that can be used by the NIH Image program. Digital images can be acquired using a range of pixel dwell times and image resolutions suited to the needs of the sample being studied. Image resolutions of about 2048x2048 pixels achieve the line resolution observed for Polaroid film micrographs. Digital images can be acquired typically in about 30 seconds (longer for high resolution, long-dwell images), and x-ray maps can be acquired in as little as 15-30 minutes, although mapping runs typically require several hours.
Once acquired, digital images can be processed either on-line or off-line using NIH Image, Adobe Photoshope, or a variety of digital image processing packages. NIH Image allows one to perform spatial and fourier transform image filtering, the application of a variety of color lookup tables, and can be used to generate binary images which are then used for feature sizing. Automated particle counting and sizing, morphometric feature analysis, and phase abundance determinations can be performed using NIH Image.
Quantitative results with a relative accuracy of better than 5% and detection limits of better than 0.5% can be readily obtained.
Your samples should be completely polished, coated, and mounted (if applicable and reasonable) before the beginning of your session.
SEM Checkout Procedure
The Camscan SEM is easy to use, and digital imaging and x-ray analysis are conveniently performed using the manuals. In order to use the SEM in an unsupervised capacity, you need to obtain an instrument checkout. You can do this as follows:
You can download most of the manuals that you need from this web page. These documents are in pdf format, so you will need Adobe Acrobat reader in order to read them. The Acrobat reader for your computer platform can be obtained from Adobe at this link.
Camscan SEM Manual
This manual covers the function and operation of the Camscan Series II Scanning Electron Microscope. It guides you step-by-step through the startup, sample exchange, filament saturation, imaging, and shutdown procedures. This manual is the first you should read before getting a checkout on the Camscan. Download the Camscan SEM Manual.
Digital Imaging and X-ray Mapping
This is the manual you need in order to do digital secondary-electron and backscattered-electron imaging and energy-dispersive x-ray mapping using the Camscan. It guides you through the step by step procedure for acquiring digital images and x-ray maps. It is the second manual you should read before using the Camscan. Download the Digital Imaging and X-ray Mapping Manual.
NIH Image Program and Manuals
The NIH Image program is public domain software, and is available for the MacIntosh and PC computers. You can download the software and documentation to run on your computer, and you can also find links to many other sources of digital image processing programs and related materials. The NIH Image web site is http://rsb.info.nih.gov/nih-image/, and you can also reach their ftp site at ftp://zippy.nimh.nih.gov.
The DTSA manual is a step-by-step guide to setting up the DTSA program for quantitative energy-dispersive analysis. This guide will show you how to set up an analytical experiment, how to acquire EDS spectra, how to set up the multiple linear least-squares fitting routine, and how to set up the CITZAF correction program. This manual assumes that you know the basics of EDS analysis. See the references section if you don't know anything about EDS. Download the DeskTop Spectrum Analyzer Guide.
For scheduling, prices and other details, contact Dr. Ducea at firstname.lastname@example.org or 621-5171.
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