Measures for spectral quality in low-voltage x-ray microanalysis

Characteristic x-ray production with energetic electrons depends strongly o n the overvoltage, the ratio of the incident beam energy to the critical ex citation energy for the atomic species of interest. Low-voltage x-ray micro analysis (beam energy less than or equal to5 keV) is especially susceptible to artifacts due to sample charging because the overvoltage is low and eve n slight charging can strongly affect peak intensities. The Duane-Hunt brem sstrahlung limit is a good diagnostic to detect sample charging. Dynamic ch arging effects, however, can influence spectra despite an apparently satisf actory Duane-Hunt limit. Dynamic charging effects must be examined by time series experiments, or through use of dynamic energy windows continuously m easuring count rates placed across the spectrum. When charging is a problem , conductive surface coatings can eliminate the effects.. When pristine sur faces must be examined without coating, the use of a conductive grid can co ntrol charging so that, useful x-ray spectra can be obtained.