Electron channeling: a problem for x-ray microanalysis in materials science.

Electron channeling effects can create measurable signal intensity variations in all product signals that result from the scattering of the electron beam within a crystalline specimen. Of particular interest to the X-ray microanalyst are any variations that occur within the characteristic X-ray signal that are not directly related to a specimen composition variation. Many studies have documented the effect of crystallographic orientation on the local X-ray yield; however, the vast majority of these studies were carried out on thin foil specimens examined in transmission. Only a few studies have addressed these effects in bulk specimen materials, and these analyses were generally carried out at common scanning electron microscope microanalysis overvoltages (>1.5). At these overvoltage levels, the anomalous transmission effect is weak. As a result, the effect of electron channeling on the characteristic X-ray signal intensity has traditionally been overlooked in the field of quantitative electron probe microanalysis. The present work will demonstrate that electron channeling can produce X-ray variations of up to 26%, between intensity maxima and minima, in low overvoltage X-ray microanalyses of bulk specimens. Intensity variations of this magnitude will significantly impact the accuracy of qualitative and quantitative X-ray microanalyses at low overvoltage on engineering structural materials.