Ultra-high vacuum compatible optical chopper system for synchrotron X-ray scanning tunneling microscopy

Abstract

High-speed beam choppers are a crucial part of time-resolved X-ray studies as well as a necessary component to enable elemental contrast in synchrotron X-ray scanning tunneling microscopy (SX-STM). However, many chopper systems are not capable of operation in vacuum, which restricts their application to X-ray studies with high photon energies, where air absorption does not present a significant problem. To overcome this limitation, we present a fully ultra-high vacuum (UHV) compatible chopper system capable of operating at variable chopping frequencies up to 4 kHz. The lightweight aluminum chopper disk is coated with Ti and Au films to provide the required beam attenuation for soft and hard X-rays with photon energies up to about 12 keV. The chopper is used for lock-in detection of X-ray enhanced signals in SX-STM.