April 13, 2012 - 12:00pm
PINSE User Meeting – to be discussed: the Annual Report, NFCF Survey Results, Policy Updates, and an introduction to the new EPMA with keynote speaker Peter McSwiggen. Title: Electron Microprobe Basics and Low Accelerating Voltage, X-ray Microanalysis - Benefits and Challenges.
Abstract: The development of the field emission (FE) electron gun has made it possible to generate extremely high, electron densities and as a result, an electron beam that is one-half to one-tenth the diameter of the conventional thermionic emission electron gun using a W filament or a LaB6 tip. In addition, with a Schottky thermal, field emission (TFE) electron gun, sufficient beam currents can be provided for trace element microanalyses. Now the challenge is to be able to take advantage of this smaller electron beam to provide X-ray analyses of comparable size areas. Using the typical operating conditions for X-ray microanalyses (15-20kV accelerating voltage), the electron beam scattering within the sample results in an analysis area that is much larger than the diameter of the beam. Working at a low accelerating voltage, the amount of scatter is greatly reduced, resulting in an analytical area that can be about the size of the electron beam. The optimum accelerating voltage that will produce the smallest analytical volume is typically around 5-8 kV (Fig. 1). At lower accelerating voltages, the size of the analytical area is controlled by the size of the electron beam, which increases with decreasing accelerating voltage. Using a TFE electron gun at low accelerating voltages means it is possible to analyze areas in the range of 0.1 mm. However, working at low accelerating voltages can produce a new set of challenges when trying to obtain the best quality quantitative analyses. These include (1) sample preparation, (2) surface coatings, like carbon coatings or oxide films (3) fewer X-rays lines are generated, (4) lower X-ray count rates, and (5) problems with the matrix corrections. Each of these issues can be satisfactory addressed.
Location and Address
104 Thaw Hall-Lunch will be provided
Speakers
Peter McSwiggen-a consultant for JEOL