Surface Analysis: X-ray Photoelectron Spectroscopy and Auger Electron Spectroscopy

First-Principles Estimation of Core Level Shifts for Hf, Ta, W, and Re

A simple first-principles approach is used to estimate the core level shifts observed in X-ray photoelectron spectroscopy for the 4f electrons of Hf, Ta, W, and Re; these elements were selected because their 4f levels are relatively close to the Fermi energy. The approach is first tested by modeling the surface core level shifts of low-index surfaces of the four elemental metals, followed by its application to the well-studied material TaSe2 in the commensurate charge density wave (CDW) phase, where agreement with experimental data is found to be good, showing that this approach can yield insights into modifications of the CDW. Finally, unterminated surface core level shifts in the hypothetical MXene Ta3C2 are modeled, and the potential of XPS for the investigation of the surface termination of MXenes is demonstrated.

Study on the atmospheric cold plasma (ACP) treatment of zein film: Surface properties and cytocompatibility

The cell adhesion and proliferation of zein-based biomaterials in cell culture application are limited by the strong hydrophobic surface with low surface energy. In this study, atmospheric cold plasma (ACP) was developed as a modification approach in enhancing the surface hydrophilic and cytocompatibility of zein films. The results indicated that water contact angles decreased from 72.85° (untreated) to 47.43° under the voltage of 100 V. The improvement of the surface free energy (SFE) was mainly attributed to the polar component rather than dispersive component. X-ray photoelectron spectroscopy (XPS) results indicated the change of surface physicochemical properties was mainly due to the partially transformation of long-chain aliphatic hydrocarbons (CH and/or CC) to oxygen- and nitrogen-containing bonds (CO, CO and CN). Furthermore, the content of secondary structure demonstrated β-turn and α-helix were transformed into β-sheet and random coil after ACP treatment. Combining with the cell experiment results, plasma treatment could significantly improve the adhesion rate and proliferation activity of C2C12 cells on zein films. With better cytocompatibility, the potentials of zein in tissue engineering scaffold could be readily exploited.

Monodisperse samarium and cerium orthovanadate nanocrystals and metal oxidation states on the nanocrystal surface

A new solvothermal method has been developed for the synthesis of monodisperse SmVO4 and CeVO4 nanocrystals with controlled size and shape. The obtained materials were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) techniques. The results reveal that uniform nanocrystals and pure tetragonal phase of SmVO4 and CeVO4 can be achieved. To investigate the oxidation states of the metals on the mixed oxide nanocrystal surface, the XPS technique was employed. The results exhibit that only one oxidation state of samarium, cerium, and vanadium for each metal (e.g., Sm3+, Ce3+, V5+) was surprisingly well stable on the particle surface at the nanoscale, even after calcination, while the existence of two oxidation states of these metals is observed (e.g., Sm3+/Sm2+, Ce4+/Ce3+, V5+/V4+) in the corresponding single metal oxide nanocrystals.