Increasing the scan speed in high resolution, low energy electron diffraction measurements by presetting the gate time

Abstract

We report on a speed-up data acquisition routine for recording intensities in reciprocal space (k-space) with increased scan speed by a single point detector. It is designed for recording low energy electron diffraction (LEED) data with high resolution by a spot profile analysis LEED instrument. It counteracts the problem of long acquisition times that are encountered when larger areas in the reciprocal space are scanned. It exploits the fact that in typical LEED images of ordered surfaces, more than 90% of the data points in k-space belong to the low-intense background, which is often not of interest. Only about 10% of the data points are related to the relevant diffraction features, namely, the LEED spots. Often it is not necessary to measure the background with the same statistical significance as measuring those points that contain information. The data points belonging to the LEED spots can be discriminated from those of the background by their higher intensities. An acquisition routine that sets an increased gate time for the counting in response to higher intensities thus safeguards good statistics for data points of the LEED spots and saves measurement time when recording data points of the background with small gate times. For typical LEED images, a reduction of the total acquisition time by a factor of about 10 is obtained. We give examples of one- and two-dimensional scans from current experiments, recorded with and without the speed-up routine. We further discuss how the routine supports the measurement of energy dependent reciprocal space maps.