Papers by Keyword: XPS

Abstract: Graphene was attended widely in recent years because of its excellent performance in electrical, mechanical, optical and magnetic applications. X-ray photoelectron spectroscopy (XPS) is commonly used tools for studying the chemical binding state, chemical modification, heteroatom dopants and quantitative chemical composition of graphene. In this work, XPS characterization of graphene films, obtained through reduction and then thermal treatment of graphene oxide films, was studied. The XPS of the graphene films are performed by direct testing, Ar⁺ etching, and direct peeling of the surface layer. The result shows that for graphene film, direct peeling is a simple and easy to use low-cost treatment, which can also be extended to XPS testing of other two-dimensional (2D) materials.

Abstract: Hydrogen absorption leads to redistribution of the components of the surface layer of the amorphous alloy Fe_73.8Si_12.7B_9.4Nb_3.2Cu noncontact side, while the amorphous structure of this layer is preserved. The type of the micro-groups Fe_y Si_x changes in such a way that the ratio y: x decreases (to less than 1) and the chemical bond polarity decreases, as well. After degassing, the surface layer composition becomes similar to those before hydrogenation. The loss of the mechanical stability of the amorphous ribbon is accompanied by the formation of the micro-groups Fe_y Si_x with a decreased ratio of y: x.

Abstract: The purpose of this study was to evaluate the effects of different polishing techniques on the topographical features and phase transformation of monolithic zirconia. Four brands of zirconia were ground and polished using one of four systems. All zirconia specimens were ground with a fine-grit diamond bur (GB) prior to polishing procedures. The surface roughness and phase transition (XRD) were evaluated, and surface characterizations (SEM and XPS) were performed. The highest roughness was obtained with the Tob system. The strongest diffraction peak in the obtained XRD patterns was at 2θ=30.246°. No monoclinic phase change was found in any group. The XPS analysis showed that the atomic percentages of yttrium in the specimens of Cercon before and after polishing were the highest of any sample. All the polishing systems tested may not adversely affect the phase transformation of monolithic zirconia. The Tob system resulted in the highest roughness. The XPS analysis showed that grinding and polishing had some effects on the properties of zirconia from a microscopic point of view.

Abstract: The effect of the formation and heat treatment modes of silicon-carbon coatings deposited by ion-beam sputtering of silicon carbide on their morphology, chemical and phase composition is determined. It has been established that an increase in the power of the ion source from 432 W to 738 W leads to a decrease in the sp³/sp² phase ratio by 1.7 times and an increase in the ratio of Si-C/Si-O bonds by 1.9 times. It is shown that doping of carbon coatings with silicon carbide increases their heat resistance.

Abstract: The goal of this work is to evaluate a common final sterilization technique with EtO by measuring its effect on the physicochemical properties of PVD deposited TiN/TiO₂ coatings on Ti-5Al-4V alloy. As the effectiveness of EtO sterilization corresponds to the operation parameters (temperature, duration, humidity, etc.), two different exposure cycles (cool (MS) at 37 °C for 220 min gas expose and warm (SS) at 55 °C for 100 min expose) were examined. SEM analysis revealed that the surface morphology of the coatings was not changed after both MS and SS treatments. In contrast to Ti 2p and O 1s peaks determined by XPS analysis, C 1s peak of TiO₂ layer decreased with increasing sterilization temperature while the percentage contribution of Ti-OH in O 1s increased. This affected the surface hydrophilicity and free energy that increased from 47.37 for the control sample to 50.77 mJ m^-2 in the case of SS specimen. Additionally, EtO sterilized samples demonstrated decreased values of corrosion and passivation current densities in simulated body fluid (pH 7.4) at 37 ± 0.05 °C as opposed to the control sample. The results indicate the suitability of both mild and severe EtO sterilization methods for improvement of the desired physicochemical properties of gradient TiN/TiO₂ coatings.

Abstract: We demonstrated an x-ray photoelectron spectroscopy (XPS)-based technique to reveal the detailed nitrogen profile in nitrided SiO₂/4H-SiC structures with sub-nanometer-scale-resolution. In this work, nitric oxide (NO)- and pure nitrogen (N₂)-annealed SiO₂/4H-SiC(0001) structures were characterized. The measured results of NO-annealed samples with various annealing duration indicate that preferential nitridation just at the SiO₂/SiC interfaces (~0.3 nm) proceeds in the initial stage of NO annealing and a longer duration leads to the distribution of nitrogen in the bulk SiO₂ within few nanometers of the interface. The high-temperature N₂ annealing was found to induce not only SiO₂/SiC interface nitridation similarly to NO annealing but also SiO₂ surface nitridation.

Abstract: The hydrolytic lignin (HL) derivatives have been prepared via its physical activation (high-temperature annealing in vacuum) followed by chemical modification (fluorination). It was found that the graphitized product of thermal activation up to 1000 °C at a low temperature gain rate of < 2 °C/min under high vacuum shows an enhanced specific surface area (215 m²/g), that makes it potentially useful as sorbent, catalytic substrate, or electrode material. It was revealed from the experimental data the manufactured graphitized material consists of nanometric structural blocks, possibly nanographites and/or few-layer nanographenes. The edges of graphenes in agglomerates in activated hydrolytic lignin (AHL) have armchair and zigzag shapes. The nontrivial electronic structure of the zigzag edges, along with the electronic conductivity and the ability of AHL to absorb oxygen, can cause an increase in the energy intensity of lithium battery (LB) manufactured using AHL.The carbon-fluorine bond of semi-ionic type was detected in HL and AHL fluorinated in the temperature range of synthesize 60 – 300 oC. The fluorinated forms of both HL and its thermally activated product show increased values of operating voltage due to the participation of fluorine bound to carbon in the electrochemical process.

Abstract: The information provided by different characterisation methods when measuring particle size varies depending on the chosen technique and analytical approach (e.g. light scattering, transmission electron microscopy, spectroscopy, x-ray scattering). This in turn has an impact on the accuracy of the results as well as comparability between methods and overall confidence on the analyses. The present study used a common sol-gel reaction to synthesise amorphous silica nanoparticles (aSiNPs) and characterised the product purity and homogeneity. The reaction involved hydrolysis and condensation of tetraethyl orthosilicate (TEOS) in the presence of lysine, which acted as catalyst for the silica production and also as a capping agent for particle size control in a suspension kept at pH 8-10. According to DLS data, the stock suspension was stable for at least 6 months in Milli Q water without surfactant when kept at 4°C. This study focused on multi-method size and shape characterisation of the aSiNPs, involving the following techniques: DLS, TEM, FTIR, STEM and SAXS. These techniques provided information on hydrodynamic diameter, core particle dimensions, sphere equivalent size, and radius of gyration. Our results show two particle populations, one around 2 nm and the other around 7 nm in diameter. Notably, these two populations are not resolved (i.e. “visible”) by all methods used.

Abstract: In order to improve the oxidation resistance of the ZrCoCe getter, highly porous Ni/ZrCoCe stack getter films were grown by the magnetron sputtering method. Scanning electron microscope (SEM) analysis indicate that the Ni/ZrCoCe stack film is composed of isolated columns. The film surface with cauliflower-like topography is formed among finely packed nanocrystals. Gas sorption investigation shows that the Ni/ZrCoCe stack film can be activated at 300 °C for 30 min and exhibits more favorable sorption capability than ZrCoCe bi-layered film. XPS results show that the Ni protective layer can play an important role in protecting the ZrCoCe film against oxidation. It can also improve the surface dissociation and diffusion of H₂.

Abstract: In order to study the activation process and mechanism of ZrCoCe, highly porous ZrCoCe getter films were grown by the DC magnetron sputtering method. The effect of activation temperature on the surface composition of the porous ZrCoCe getter films were studied by X-ray photoelectron spectroscopy (XPS). The results shows that the surface of air-exposed porous ZrCoCe film is covered with H₂O, CO₂ and hydrocarbons, both Zr and Ce exist in the oxidized state, and zirconium oxide starts to reduce at 300 °C. The activation process also results in a sizable Co segregation at surface. In addition, zirconium carbide can be found in the subsurface region of the film after thermal activation treatment.