SEM

About our SEM

The CamScan Series II SEM performs routine surface imaging using Secondary Electron techniques as well as Back-Scattered Electron quasi-compositional imaging. In addition, the CamScan is fitted with an automated American Nuclear Systems EDS system that allows rapid semiquantative chemical analysis of natural and synthetic materials. A recent addition to this instrument is a high-sensitivity GATAN Cathodoluminescence spectrometer that allows qualitative identification of luminescence patterns for study of mineral zoning as well as acquisition of quantitative spectral data from 200 to 900 nanometers.

What is SEM?

A scanning electron microscope (SEM) is a device that creates a focused beam of electrons, directs this electron beam onto a sample to be analyzed, and collects secondary radiation generated by the sample during analysis. This technique is analogous to the use of a visible light microscope aside from two major differences: 1) resolution, and 2) secondary radiation. First, electrons are smaller than visible light photons and can therefore be used to resolve features at a significantly smaller scale than visible light (0.5 micrometers for visible light vs 0.001 micron for SEM). Second, material being analyzed by an electron beam (when accelerated at 10s of kV) produces secondary radiation in the visible light range (cathodoluminescence) and X-ray range (X-ray fluorescence) -- both of which can be used to determine the chemical composition of the sample.

What kind of samples can be analyzed by SEM?

The SEM in this facility can be used to analyze most solid, inorganic material. Unlike a visible light microscope, the analyte observed by SEM must be loaded into a vacuum chamber to prevent air from interacting with the electron beam. Additionally, the analyte must remain solid (given that the SEM in the VT microprobe lab is not currently equipped with a cryogenic stage) and stable when irradiated by the electron beam (15 kV, 5 nA), which precludes analysis of most organic matter.

What kind of data can be obtained using the SEM?

• Secondary electron images (SEI)

• Backscattered electron images (BEI)

• Cathodoluminescence (CL) spectra and images

• Energy-dispersive x-ray spectra (EDS) and images