Sensitive multi-element profiling with high depth resolution enabled by time-of-flight recoil detection in transmission using pulsed keV ion beams

Abstract

The potential of time-of-flight recoil detection for sensitive multi-element profiling of thin membranes and quasi-2D systems in transmission geometry using pulsed keV ion beams is assessed. While the time-of-flight approach allows for simultaneous detection of multiple elements, to the largest extent irrespective of recoil charge states, the keV projectile energies guarantee high recoil-cross sections yielding high sensitivity at low dose. We demonstrate the capabilities of the approach using 22Ne and 40Ar as projectiles transmitted through thin carbon foils featuring optional LiF-coatings and single-crystalline silicon membranes for different sample preparation routines and crystal orientations.Using a large position-sensitive detector (0.13 sr), a depth resolution below 6 nm and sensitivity below 1014 atoms/cm2 was achieved for H in a 50 nm thick silicon membrane. For crystalline targets, we show how the probability of creation and detection of recoils and their observed angular distribution depend on sample orientation.