Medium-energy ion scattering spectroscopy with a position-sensitive and time-resolving detector

Abstract

A Si (1 0 0) sample covered with a thin Ho layer was measured with a three-dimensional medium-energy ion scattering spectrometer. The spectrometer is an extended version of a time-of-flight spectrometer for medium-energy ion scattering, equipped with a large position-sensitive detector. The device is used for composition depth profiling and crystal structure determination. The intensity distribution of detected particles was visualized to present medium-energy scattering phenomena. Circular shapes were observed in images created with part of the data containing particles scattered from the surfaces of the sample layers. Images show leading edges of “clouds” of arriving scattered particles were detected using the flat surface of the detector, integrated over 2 ns intervals. The center positions of shapes produced by particles scattered on Ho and Si atoms are different. This is explained by the different kinematic-factor dependences on scattering angle of particles scattered on Si and Ho atoms. The depth resolution of the time-of-flight spectra acquired with the full solid acceptance angle of the detector is limited by the kinematic spread. Using position information of detected particles from the detector, corrections for the kinematic spread and variations of flight path lengths were applied to spectra, increasing the depth resolution.