MRI-R2: Acquisition of an X-ray photoelectron spectrometer (XPS)

University Of California-Riverside, Riverside CA

Investigators

Abstract

MRI-R2 0958796 Zaera This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5). Technical Abstract: This proposal requests funds for the purchase of a new analytical X-ray photoelectron spectrometer (XPS) for the University of California, Riverside (UCR). This will be the first instrument of its type at UCR. XPS provides vital information of the nature and composition of solid surfaces and has become an essential tool in materials science research. The new instrument, to be acquired from Specs, will be based on a mu-metal ultrahigh vacuum (UHV) spherical chamber turbopumped to pressures below the 10^-9 Torr range, and will be equipped with a twin anode X-ray source and a 150 mm hemispherical energy analyzer, an ion source for cleaning, depth-profiling, and low-energy ion scattering, and rasterable and flood electron guns for Auger electron spectroscopy and to compensate for sample charging, respectively. It will also include a sample manipulator with linear movements in the x, y and z directions, a preparation chamber, and a load-lock system for quick sample introduction. The instrument will be set for remote control and automation for cyber access, with capabilities that include motorization of UHV manipulator for all 4 axis (x, y, z and polar rotation), an interface for remote control of the X-ray source, a special modification of the power supply for remote control of the flood gun, and the SpecsControl software package for full measurement control, including sample positioning, analyzer control, X-ray source, flood gun and ion source. The new XPS will be maintained, operated and administered by the Analytical Chemistry Instrumentation Facility (ACIF) of UCR. It will be available for use to PIs, students, and postdoctoral fellows at UCR, and also to outside partners, including a number of local colleges (the California State University Los Angeles, San Bernardino and San Diego campuses, the University of La Verne, Westmont College). Layman Abstract: With the advance of new nanotechnologies and miniaturized microelectronics, the interfaces between the different elements that constitute those devices are becoming a larger part of their total volume, and the corresponding surface physics and chemistry is playing an increasing role in their performance. Surface chemistry is also prevalent in problems related to environmental issues, biological and analytical applications, catalysis, and tribology, to mention only a few. No modern materials-science laboratory is complete nowadays without appropriate analytical tools to study solid surfaces. X-ray photoelectron spectroscopy (XPS, also known as ESCA) in particular has become a ubiquitous tool in materials-science research. XPS relies on the detection of the photoelectrons ejected from solid samples upon excitation with X-rays. The approximate kinetic energies of the photoelectrons can be converted into electron binding energies and used to determine the elemental composition of a given sample, and more accurate measurements to obtain information on the chemical environment surrounding particular surface atoms, in particular their oxidation state. The photoelectron yield provides quantitative information on the composition. The power of XPS is that it relies on the detection of electrons, a fact that renders it quite surface sensitive. Most typical analytical techniques are based on the use of photons, which penetrate deep into solid samples and yield information about the bulk. The small free path of electrons through solids, by contrast, allows for the discrimination of the signal from the topmost layers. Combined with controlled sputtering for the removal of material over time, XPS can be set up to provide a depth profile of the composition and chemical nature of solid samples. At UCR, XPS will be used to study problems related to porphyrin-based molecular memories, grapheme derivatization, biomimetic-based solar harvesting devices, zeolite coatings and nanoparticles, atomic layer deposition of thin films, and catalyst development, among others.