A variable X-ray chopper system for phase-sensitive detection in synchrotron X-ray scanning tunneling microscopy

An ultra-high-vacuum compatible X-ray chopper system has been designed, constructed and integrated into the XTIP beamline at the Advanced Photon Source at Argonne National Laboratory. The XTIP beamline can operate at soft X-ray energies from 400   eV to 1900   eV while providing a focused beam down to about 10   µ m × 10   µ m into the synchrotron X-ray scanning tunneling microscopy (SX-STM) endstation instrument. The X-ray chopper is a critical component for separating topographic information from chemical information in SX-STM through phase-sensitive current detection. Depending on the experimental needs, the modulation frequency can be controlled from 100   Hz to 10   kHz. In addition, the chopper system is fully bakeable and can achieve a base pressure of 10 − 10   mbar. Facilities for active water cooling have been designed, but passive cooling through copper braids has been shown to be sufficient at standard chopping frequencies. Using an Fe/Al2O3/CoAl(111) sample, the separation of the SX-STM current into a chemical component and a stable feedback signal is demonstrated.
Source: Journal of Synchrotron Radiation - Category: Physics Authors: Tags: synchrotron X-ray scanning tunneling microscopy X-ray chopper X-ray absorption spectroscopy beamlines Source Type: research