Hibernia Electron Beam Facility
Scanning electron microscopy (SEM) is an analytical tool that utilizes a highly focused beam of electrons to scan a sample surface and produce detailed images of that surface at high magnification. Different interactions between the incident electron beam and the sample yield different signals for viewing. These include: (1) secondary electron (SE) imaging, the resulting images showing 3D structure of a surface, (2) backscatter electron (BSE) imaging, the resulting images reflecting differences in mean atomic mass from one area to another, (3) cathodoluminescence (CL) imaging, the resulting images being a complex function of chemistry (presence or absence of CL “emitters” – elements that enhance CL), lattice structure and structural defects and (4) chemical analysis using energy dispersive spectrometers (EDS) to measure characteristic x-rays. EDS is a quick and easy means of identifying elements in a sample but it is considered a semi-quantitative analysis.
Electron probe microanalysis (EPMA) is an analytical technique combining the strengths of SEM with the resolution and precision of wavelength dispersive spectrometers (WDS) to provide qualitative and quantitative elemental information of very small spots (ca. 1 um) on a sample. Imaging (SE and BSE), mapping (x-ray and CL) and quantitative analyses with detection limits down to the tens of ppm are available. It can detect all elements between C – U on the periodic table.
EPMA is commonly used by geologists but can be used for any solid sample that is flat and polished to a high “mirror-like” degree. Samples are prepared either as standard 27 mm x 26 mm rectangular thin sections or as 1-inch round pucks. The SEM can accommodate a wider variety of sample sizes, shapes and surface roughness and therefore it is used in many disciplines – geology, chemistry, physics, biology and engineering.
All sample preparation, included cutting and polishing of samples, are the responsibility of the users. In cases where suitable standards are not available in the lab, users may be asked to provide their own standards