A Novel Spectrometer System For Hard X-Ray Interfacial Environmental Chemistry

A new high-precision spectrometer system has been developed and tested for measuring grazing-incidence XAFS spectra, x-ray reflectivity, and standing wave intensity data from adsorbates on oriented single crystals and flat polycrystalline samples. The instrument system was designed for routine, rapid installation and alignment in synchrotron experimental hutches utilized for XAFS measurements. Two major components comprise the system: (a) a strongback cradle on which flexor slits, sample positioners, and detectors are aligned, and (b) a multi-altitudinal detector support, which allows a 30-element Ge detector array to be positioned at vertical down-looking, horizontal side-looking, and intermediate observation angles. Motorized positioners provide seven axes of motion for samples, which allows accurate positioning of large sample cells and samples having uneven shapes. Precision slits located upstream of the sample provide aperture control to about 1 micron precision over a range of motion from zero to 1.5 mm, making possible measurements on mm-diameter samples at very small incidence angles (∼0.15 deg.). An ion chamber detector located downstream of the sample is mounted on a bearing arc to rotate about the sample eucentric for specular reflectivity measurements. This detector can be replaced with an analyzer crystal and proportional counter to provide high-rate counting with high angular/energy resolution. Results from recent measurements demonstrate the utility and precision of this instrument for molecular environmental interface science