11:00-12:00
X-Ray Microanalysis in the Low Voltage Field Emission Scanning Electron Microscope and in the Variable Pressure Scanning Electron Microscope
Prof.Raynald Gauvin(Department of Mining, Metals & Materials Engineering, McGill University)
- With the advent of high resolution field emission scanning electron microscopy (FE-SEM), low voltage scanning electron microscopy (LV-SEM) becomes possible. Field emission sources are shown to have an increased brightness on the order of 1000 times to that of conventional W filaments, which leads to an overall increase in performance. Resolution is said to be on the order of 2-3 nm at 1 keV and 1.5 nm at 15 keV. The decrease in interaction volumes with this microscope when working at low beam energy yield results closer to the TEM, with the advantage of limited or no sample preparation. Furthermore, analysis of bulk samples provides better counting statistics than the TEM because the area that is transparent in a thin foil is a few orders of magnitude smaller than the surface area of typical bulk SEM samples. Electron optics in the column has come a long way in maintaining the small spot size on the sample surface, which allows a wide range of applications to be explored. This seminar aims at describing the pros and cons of LV-SEM work for imaging and with emphasis on microanalysis. Recent applications of LV-SEM will be explored in brief in order to show the overall effectiveness of this technique for material characterization. Also, results of STEM imaging of carbon nanotubes in dark and bright field will be covered.
Of course, this seminar will present how Monte Carlo simulations can be used in advance to determine the best experimental conditions for performing x-ray microanalysis and electrons backscattered imaging in a field emission scanning electron microscope. The Monte Carlo free software, Casino [1] and Win X-Ray [2] will be presented. These two Monte Carlo programs can be downloaded at http://www.montecarlomodeling.mcgill.ca/ . These programs can be used to perform quantitative x-ray microanalysis as well as to find optimum conditions to analyse and image various types of materials. The utility of Monte Carlo simulations to characterize non homogeneous materials in the SEM will also be covered. Finally, Monte Carlo simulations for the effect of the skirt on X-Ray microanalysis in the variable pressure scanning electron microscope (VP-SEM) will be discussed. Problems and corrections methods for quantitative x-ray microanalysis in the VP-SEM will be addressed.
References
1. P. Hovington, D. Drouin and R. Gauvin (1997), "Casino: A New Era of Monte Carlo Code in C Language for Electron Beam Interaction, Part I: Description of the Program", Scanning, Vol.19, pp. 1-14.
2. R. Gauvin, E. Lifshin, H. Demers, P. Horny and H. Campbell (2003), "Win X-ray, a new Monte Carlo Program that Computes X-ray Spectrum for X-ray Microanalysis in the Scanning Electron Microscope", Microscopy & Microanalysis, in press.
