Electron Probe X-Ray Analysis of Nano-Films at Off-Normal Incidence of the Electron Beam
The frontier of electron probe x-ray method in determination of the trace quantities of metal on a silicon substrate is studied. Experimental data are obtained for ultra-thin chromium films on a silicon substrate. It is shown that the signal - noise ratio significantly increases at a strong inclination of the sample (80°) which provides determination of extremely low (for this method) chromium content. Calibration curve for inclined sample position is obtained using Monte Carlo method. Surface concentration of chromium atoms (2.2 ± 0.5) × 1014 cm-2 and chromium detection limit (5 × 1013 cm-2) are determined experimentally for the given configuration of the experiment. For electron-probe microanalysis of bulk samples this is a record value. The equivalent mass of chromium at aforementioned value of the surface concentration is approximately 4 × 10-18 g. Implementation of the method does not require changes in the of the device design.