The Grassian group is involved in several research areas including surface chemistry of environmental interfaces, heterogeneous atmospheric chemistry, climate impact of atmospheric aerosols, and environmental and health aspects of nanoscience and nanotechnology.

Surface analysis - XPS, UPS and AES

Surface analysis - XPS, UPS and AES

We currently have a state-of-the-art, custom-designed surface analysis chamber for X-ray Photoelectron Spectroscopy (XPS), Ultraviolet Photoelectron Spectroscopy (UPS) and Auger Electron Spectroscopy (AES) (see schematic below). The instrument is capable of: XPS small area analysis (~10micrometers); two-dimensional elemental XPS and AES mapping; two-dimensional chemical state mapping; charge neutralization for the analysis of insulating samples; depth profiling; automated analysis of hundreds of samples or hundreds of different areas of the same samples and wide spot size UPS.

Schematic of the custom-designed Kratos Axis Ultra XPS system. The system consists of three chambers: a surface analysis chamber, transfer antechamber and reaction chamber. Each chamber is equipped with a pumping system and pressure gauges. The surface analysis chamber is equipped with X-ray sources, FE-SEM gun, SE detector, UPS source, ion gun and sample manipulator. (Note: TMP—turbomolecular pump; CCG—cold cathode gauge; LV—leak valve and; V—valve.)

 

Most novel is the reaction chamber can be used to react various atmospheric gases such as SO2, NO2 and water vapor on a interested surface. Photochemical reactions are studied using the Hg arc lamp to irradiate the samples in reaction chamber. Reacted surface will be transferred to the analysis chamber under vacuum condition for surface analysis. The below figure shows the XPS spectra of S2p binding energy region following TiO2 particle exposure to SO2 at 298 K under different conditions.

Figure showing XPS data in the S2p binding energy region following TiO2 particle exposure to SO2 at 298 K of (a) 100mTorr of SO2, (b) 100 mTorr of SO2 and 100 Torr of O2, (c) 100 mTorr of SO2 in the presence of irradiation (λ > 300 nm), (d) 100mTorr of SO2 and 100 Torr of O2 in the presence of irradiation (λ > 300 nm), and (e) 100mTorr of SO2, 13 Torr of H2O, and 100 Torr of O2 in the presence of irradiation (λ > 300 nm). The spectra are fit to two transitions; S2p3/2 and S2p1/2, for two species, adsorbed sulfite and sulfate. The individual components are shown in red (sulfite) and blue (sulfate) solid lines. The total peak fit is shown in green with circular markers.