Using the 'tracer' technique, the distribution with depth of generated X-rays, the φ(rhoz) curve, has been measured for carbon, aluminium and gold over a range (5-29 kV) of probe voltages. The measurements were carried out at three specimen tilt angles ( tau = 90°, 60°, and 40°), where tau is the angle between the incident electron beam and the specimen surface). φ(rhoz) profiles have also been calculated for the same experimental conditions using the simplified Monte Carlo method of Love et al. (1977). Comparison with the tracer data showed that the Monte Carlo method predicted a reasonable shape to the φ(rhoz) curve, but it gave too high a peak, discrepancies becoming worse at lower overvoltages. A new absorption correction for quantitative electron-probe microanalysis has been developed, based upon the representation of the φ(rhoz) profile by a quadrilateral shape. This simple shape can be characterised by three parameters, the position and relative height of the peak and the mean depth of Z-ray generation. Analytical expressions for the parameters as a function of overvoltage ratio, atomic number and backscatter coefficient have been derived using the experimental φ(rhoz) data. The performance of the Quadrilateral model absorption correction has been tested using a collation of microanalysis data obtained from samples of known composition. The findings have been compared with those given by some other correction methods and the Quadrilateral model shown to give better results for both heavy and light element analysis. Finally, specimen tilt factors have been developed for the new correction, so that it can deal with specimens inclined to the incident electron beam direction.
|Date of Award||1984|