Development of light-modulated XAFS spectroscopy

Abstract

The light-modulation method was applied to XAFS spectroscopy as a useful tool for electronic and structural studies of light-excited states. The visible light for electronic excitation was modulated by an optical chopper and the concomitant change in the X-ray absorbance was extracted by a lock-in amplifier. It is essential to reduce any noise arising from several sources, especially those generated by the X-ray monochromator. Fe and Co K-edge XANES and EXAFS spectra were measured using the present approach for spin transition compounds. The light-modulated XAFS method is found to be applicable to systems with an excited-state ratio of less than several percent. Detailed discussion is also given concerning quantitative measurements, including the signal amplitude and phase shift information.

Investigation of periodically driven systems by x-ray absorption spectroscopy using asynchronous data collection mode

“…This capability, implemented at the Inner Shell Spectroscopy (ISS) beamline of NSLS-II, is intended for studies of a variety of materials under modulated conditions, wherein materials exhibit dynamic response to external perturbation, such as electric, magnetic, temperature, pressure, gas composition, and electromagnetic radiation (e.g., UV or visible light). 1,7,9,25 In addition to the versatility of our setup, the data sorting algorithm used in post-processing of the time-dependent spectra is an alternative to a commonly used lock-in method, limited to the use with photon counting electronics providing analog signals. As we explain in greater detail below, pulsed experiments in which the time duration of X-ray scans and excitation pulse periods are fixed will suffer from non-uniform density of energy points within effective time intervals.…”

A new technique to measure the differential XAFS spectrum

“…Recently, it has been applied in XAFS experiments [6−10]. A periodic external perturbation, such as light [6], magnetic field [7], temperature [8], or high pressure [9,10], has been verified to enhance the XAFS signal of internal structure. In 2001, an energymodulation technique [11] for XAFS spectroscopy was first developed where another monochromator together with a piezo-driven oscillation stage were added to the beamline and used to modulate the energy.…”

Development of pressure-modulated EXAFS method

“…A modulated spectrum is used to detect small changes of optical reflection and absorption induced by the modulation of a given sample property. Many modulation techniques have been widely applied in the area of semiconductor spectroscopy, and some have been introduced into XAFS experiments, such as wavelength [1], light [2], magnetic field [3], temperature [4] and so on. In this paper the pressuremodulated Extended X-ray Absorption Fine Structure (EXAFS) is presented, measuring subtle changes in EXAFS signals caused by the modulation of high pressure.…”