O1s X-ray Photoelectron Spectroscopy Research Articles

Simulating temperature and tautomeric effects for vibrationally resolved XPS of biomolecules: Combining time-dependent and time-independent approaches to fingerprint carbonyl groups.

Carbonyl groups (C=O) play crucial roles in the photophysics and photochemistry of biological systems. O1s x-ray photoelectron spectroscopy allows for targeted investigation of the C=O group, and the coupling between C=O vibration and O1s ionization is reflected in the fine structures. To elucidate its characteristic vibronic features, systematic Franck-Condon simulations were conducted for six common biomolecules, including three purines (xanthine, caffeine, and hypoxanthine) and three pyrimidines (thymine, 5F-uracil, and uracil). The complexity of simulation for these biomolecules lies in accounting for temperature effects and potential tautomeric variations. We combined the time-dependent and time-independent methods to efficiently account for the temperature effects and to provide explicit assignments, respectively. For hypoxanthine, the tautomeric effect was considered by incorporating the Boltzmann population ratios of two tautomers. The simulations demonstrated good agreement with experimental spectra, enabling differentiation of two types of carbonyl oxygens with subtle local structural differences, positioned between two nitrogens (O1) or between one carbon and one nitrogen (O2). The analysis provided insights into the coupling between C=O vibration and O1s ionization, consistently showing an elongation of the C=O bond length (by 0.08-0.09Å) upon O1s ionization.

Growth of β-Ga2O3 nanostructures by thermal oxidation of GaN-on-sapphire for optoelectronic devices applications

Heterostructures of wide-bandgap semiconductors, like β-Ga2O3/ GaN, are being used in many high-power, high-frequency electronic and optoelectronic devices. This paper presents the growth of β-Ga2O3 thin film and nanostructures by thermally oxidizing (at 1000 °C) the planar and nano-structured GaN surfaces respectively. The nano-structures of GaN (having 300–500 nm long vertical nano-kinks) are fabricated by metal-assisted chemical etching of GaN surface for 1–2 hours. The thermally grown β-Ga2O3 samples are polycrystalline. The chemical analysis of the samples using X-ray photoelectron spectroscopy (XPS) showed enhancement of Ga-O peak intensity (at 20.21–20.3 eV) at the expense of the Ga-N peak intensity (at 19.2–19.7 eV) in the thermal oxidation process. The O1s XPS spectra of the oxidized samples exhibited prominent signature of O2- ions (530.7–530.9 eV) representing the formation of Ga2O3 with presence of adsorbed hydroxyl group at the surface (532.2 – 532.4 eV). The valance band XPS spectra disclosed the formation of an additional Ga(4 s)–O(2p) hybridization energy state, and the valence band maxima increased from 2.3 eV to 3.25 eV. The Raman spectra of the oxidized samples exhibited multiple Ag and Bg vibrational modes of β-Ga2O3 along with intense E2(high), A1(LO) modes of GaN. The time-resolved photoluminescence spectra of the samples demonstrated fast transition of charge carriers from excited state to ground state with 460–820 pico-seconds average career lifetime.

Oxidation state of cobalt oxide in thermal-cyclic atomic layer etching of cobalt by plasma oxidation and organometallization

Thermal-cyclic atomic layer etching of Co blanket film and a fine pattern by plasma oxidation and organometallization were investigated. To obtain a smoothly etched surface and self-limiting etching, a two-step temperature-etching process was used. Co was first oxidized using O2 plasma at a low temperature of 25 °C. Then, the Co oxide formed in the first step was organometallized with acetylacetone (acacH) and sublimed at a high temperature of 210 °C, which is appropriate for organometallization and sublimation. The etched amount per cycle was 0.6 nm. This value is the same as the saturated oxidation amount. The root-mean-square roughness after 20-cycle etching was 0.53 nm, and an atomically smooth etched surface was obtained. From the x-ray photoelectron spectroscopy (XPS) analysis, the oxidation state of Co oxide with a 530-eV O1s peak was dominant for organometallization with acacH. As the temperature increased, the O1s XPS peak of the Co oxide shifted lower to 529 eV and formed a columnar-shaped oxide. However, with acacH, oxide was organometallized when the O1s peak was at 530 eV.

Unveiling the effect of MnO/SiO2 ratios on the viscosity and structure of mold fluxes for high-Mn cryogenic steels

The serious reaction between Mn in molten steel and SiO2 in calcium silicate-based mold flux during continuous casting of Al-free high-Mn cryogenic steels could change the mold flux properties and in-mold performance. In this study, the combination of rotating viscometer, FTIR spectroscopy, Raman spectroscopy and O1s X-ray photoelectron spectroscopy (XPS) was employed to get a deep insight into the effect of the reaction levels characterized by MnO/SiO2 ratios on the viscosity and structure of mold fluxes. The results exhibit that the transformation of mold flux from Newtonian fluid to non-Newtonian fluid can be reflected by viscosity change with varying rotation speeds. The viscosity decreases continuously with increasing MnO/SiO2 ratio but the temperature dependence of viscosity decreases at high MnO/SiO2 ratio. Structural information from FTIR revealed the slag system is mainly a silicate structure. The deconvoluted results of Raman spectra show an increase in NBO/Si, amounts of Q0 ([SiO4]4–) and Q1 ([Si2O7]6–) units with increasing MnO/SiO2 ratio, whereas a decrease in amounts of Q2 ([SiO3]2–) and Q3 ([Si2O5]2–) units in the meantime, this indicates the depolymerization of the silicate structure with proceeding of the slag/steel reaction. According to semiquantitative analysis of XPS spectra, the relative proportion of bridge oxygen (O0) decreases at the cost of non-bridged oxygen (O–), which suggests that the silicate structure gradually depolymerizes. The structural analysis supports the change of viscous behavior of mold flux with slag/steel reaction.

Europium doped titanium dioxide nanocrystalline: synthesis, structure and optical properties

Abstract
 Uniform, spherical-shaped TiO2: Eu nanoparticles with different doping concentrations were synthesized using the sol-gel method. The structural, morphology, optical, luminescent, and surface properties of the samples were investigated at different Eu3+ concentration. The morphology, crystalline structure, and chemical composition of the samples were characterized by scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The X-ray diffraction results reveal that the obtained powder nanoparticles consist of a single phase tetragonal structure. The crystallite sizes calculated by utilizing Scherrer’s equation were found in the range of 18.94 – 7.77 nm for TiO2:Eu samples annealed at 550οC. The SEM images reveal an irregular agglomerated morphology indicating a decrease in particle size with an increase in Eu3+ concentration. X-ray photoelectron spectroscopy (XPS) high resolution spectra of the Ti-2p peak confirmed that Ti atoms were in a doubly ionized state, and the deconvolution of the O1s XPS peak show the presence of oxygen related defects in the sample. EDS results confirm a systematic increase of Eu content in the as-prepared samples with the increase of europium concentration. Incorporation of europium in the titania particles induces a structural deformation and a blueshift of their absorption edge. The luminescence intensity increases with Eu3+ concentration up to 3 mol% and then quenched. While the PL emission of the as-grown samples is dominated by the 5D0 - 7Fj transition of Eu3+ ions, the emission intensity reduces drastically after thermal annealing due to outwards segregation of dopant ions.
 Keywords: Titanium dioxide; Photoluminescence Spectroscopy; XPS; Nanocrystalline; Anatase; Rutile. 

Determining surface-specific Hubbard-U corrections and identifying key adsorbates on nickel and cobalt oxide catalyst surfaces.

NiO is a popular transition metal oxide (TMO) with high thermal and chemical stability and Co3O4 is a relatively more reducible TMO due to weaker metal-oxygen bonds. Both are often used as catalysts in a variety of chemical transformations. Density functional theory (DFT) and X-ray photoelectron spectroscopy (XPS) are used to investigate catalysis on TMO surfaces, yet both techniques have their own limitations. The accuracy of DFT highly depends on the choice of Hubbard U correction. The bulk-property optimized U value of 5.3 eV for NiO and different U values for Co3O4, without any consensus, are often used in the literature to simulate surface catalysis. However, U values optimized using bulk properties often fail to reproduce surface-adsorbate interactions on TMOs. Similarly, there exists arbitrariness in assigning observed XPS shifts to different surface species on these metal oxides. Hence, a synergistic application of XPS and DFT+U is implemented to determine the surface specific U values for NiO and Co3O4, and to identify adsorbed surface moieties corresponding to experimentally observed XPS shifts. For the NiO (100) surface, the U value of ∼2 eV is able to reproduce the experimentally observed XPS O1s core level binding energy shifts correctly, instead of the bulk property optimized and commonly used U value of 5.3 eV. Using this surface specific U value of 2 eV, the experimentally observed XPS shifts are assigned. Similarly, for Co3O4 (100) surface, ∼3 eV of U value could successfully predict the experimentally observed XPS shifts and corresponding adsorbates. The surface adsorbates and configurations suggested in this work will help analyze experimental XPS data and the surface specific U values will ensure accurate predictions of adsorption and reaction energetics on these catalysts.

BiO 2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO 2 Reduction to Formate

BiO _2-x Nanosheets with Surface Electron Localizations for Efficient Electrocatalytic CO ₂ Reduction to Formate

Promoting Photoelectrochemical Water Oxidation on Ti-Doped Fe2O3 Nanowires Photoanode by O2 Plasma Treatment

Surface electron traps on semiconductor photoanodes mediate surface recombination and deteriorate the photoelectrochemical (PEC) water oxidation performance of the photoanode. Developing convenient methods to reduce surface electron traps is therefore essential for high efficiency PEC water oxidation on semiconductor photoanodes, particularly for nanostructured photoanodes with large surface area. Herein, we employ a O2 plasma treatment to boost the PEC water oxidation performance of Ti-doped Fe2O3 (Ti-Fe2O3) nanowires photoanodes, aiming to reduce surface oxygen vacancies, the dominant electron traps on Ti-Fe2O3 surface. X-ray diffraction (XRD), scanning electron microscopy and spectroscopic analyses show that the oxygen plasma treatment changes the structural, morphological and optical properties negligibly, but it does reduce the content of surface oxygen vacancies, as estimated from O1s X-ray photoelectron spectroscopy spectra. An optimal O2 plasma treatment (200 W, 70 s) increases the photocurrent density of the Ti-Fe2O3 nanowire photoanode to 2.14 mA·cm−2 (1.23 V vs. RHE) under air mass 1.5G simulated solar light, which is 1.95 times higher than the pristine Ti-Fe2O3 nanowire photoanode. The surface hole transfer efficiency is also improved by 1.66 times due to the reduced surface recombination. The work suggests that O2 plasma treatment is a convenient but effective method to boost the PEC water oxidation performance of Ti-Fe2O3 photoanode and might be applicable to other semiconducting oxide photoanodes for high efficiency PEC water splitting.

Nitrogen, Sulfur Co-Doped Reduced Graphene Oxide: Synthesis and Characterization

Objective and Method: In this present research, a simple hydrothermal implantation technique for synthesizing N,S co-doped reduced graphene oxide (NS-r-GO) has been presented in which thiourea was used as a single-source precursor of N and S atoms. Results: Maximum N and S atoms, with an atomic percentage of 3.50 and 7.50 (at.%), were achieved in the GO matrix at the reaction temperature of 250°C. Introduction of N and S atoms into the GO lattice was confirmed by X-ray photoelectron spectroscopy (XPS). Different chemical bonds such as –C– S–C, C=O, N–O, and C–N–C have been suggested from the corresponding C1s, N1s, O1s, and S2p high-resolution XPS spectral analyses. Conclusion: FT-IR measurement also confirmed the presence of different functional groups as well as the formation of different bonds such as –OH, –N–H, –C=O, –C–OH, and C-S. XRD and Raman spectroscopy analyses confirmed the defects structures that arose from the penetration of N and S atoms into the GO lattice.

Graphene oxide as a radiation sensitive material for XPS dosimetry

The suitability of graphene oxide (GO) foils as radiation sensitive materials for soft X-ray irradiation is investigated by means of X-ray photoelectron spectroscopy (XPS). In particular GO micrometric foils have been irradiated by soft X-rays at a 1486.6 eV energy at high flux (>1012 photons/cm2s) in ultra-high vacuum. The XPS analysis of the carbon-carbon (CC) and the carbon-oxygen links (CO) characterizes the composition of the first layers of the GO foils. The CC/CO ratio of the high-resolution C1s XPS spectrum is used as dosimetric index. The incident X-ray photons, proportionally to their fluence, partially reduce GO foils decreasing the amount of oxygen groups chemically bonded to carbon network. This decrease causes an increase on the CC/CO ratio that is correlated to the irradiation time, i.e. to the dose absorbed by the GO foil, showing a linear increment with the dose. Our preliminary investigations indicate that GO can be employed to realize a thin foil dosimeter giving a linear response to the absorbed dose in the (275.76 kGy ÷ 8.02 MGy) range. The absorbed dose can be also evaluated by measuring the C/O ratio from the C1s and O1s XPS spectra analysis or with different techniques, as discussed in the paper.

Electronic structure, orbital symmetry transformation, charge transfer, and valence state studies on Fe3+ - substituted CaCu3Ti4O12 quadruple perovskites using X-ray photoelectron spectroscopy

Here, we report a detailed study on electronic structure of quadruple perovskite system, CaCu3-xTi4-xFe2xO12 (x = 0.0, 0.1, 0.3, 0.5 and 0.7), using the powerful X-ray photoelectron spectroscopy (XPS). The Ca2p and Ti2p XPS spectra indicate that Ca and Ti ions exist in the divalent and tetravalent state, respectively, and no visible change is observed in their valence states on Fe3+-substitution (x). The asymmetrically shaped peaks of Ti2p3/2 infer the significant orbital hybridization of Ti atoms with other metallic cations like Cu and Fe, i.e. the Ti2p-Cu3d-Fe3d mixed states, which shows an increment with the Fe3+-content. The spectra also indicate that the Fe-substitution causes an increase in the strength of CuFe3d-O2p hybridization while weakening the strength of TiFe3d-O2p orbital hybridization. The Cu2p spectra suggest that Cu ions exist in two valence states i.e. the Cu2+ and Cu3+ out of which Cu2+ is dominant. The XPS results show clear evidence of charge transfer amongst Ti–Cu ions and evolution of n-type charge carriers. The O1s XPS spectra indicate anti-bonding states of t2g and eg type molecular orbitals separated by an energy separation of ~1.6 eV. A systematic relative change in the intensity of t2g and eg peaks with Fe-substitution point towards a clear transformation of symmetry of the system from TiO6 octahedral to the square-planar.

Surface Contamination with Si and O Impurities for GaN Single-Crystalline Layers Grown by Ultra-High-Vacuum Sputter Epitaxy

Introduction GaN and related alloys have been extensively investigated for their potential applications in optoelectronic and high power electronic devices. The study on surface contamination with Si and O impurities is quite important for device fabrication, especially for Si, because Si is n-type impurity for GaN. In this work, we demonstrate the GaN surface contamination and cleaning technique focused on O and Si based compounds contaminated in air atmosphere. Experiment GaN single-crystalline layers were grown on sapphire (0001) substrates by ultra-high-vacuum radio-frequency sputter epitaxy technique. The thermal desorption spectroscopy (TDS) measurement was carried out for as-grown GaN layers at pressure of 10– 4 Pa, and the chemical etching was also carried out using buffered hydrogen fluoride (BHF) solution. The surface state of the GaN layer was analyzed by X-ray photoelectron spectroscopy (XPS) measurement. Results In the XPS measurements, O1s and Si2p XPS signals were detected from as-grown GaN layer surface. The thermal treatment was then carried out in order to remove these impurities, and the results on XPS measurements indicated the significant decrease of Ga–O bonds on the GaN layer surface. Moreover, from the TDS measurements, the signal of m/z = 70 corresponding to Ga (Figure 1(a)) and the signal of m/z = 32 corresponding to O2 (Figure 1(b)) indicated rapid increase at around 500 °C, which suggests that isolated Ga and O atoms were easily released from the GaN layer surface. On the other hand, the removal of Si compounds by the thermal treatment was quite difficult, because the thermally stable Si–N bonds which would be formed by nitrogen dangling bonds, were terminated with Si atoms during such thermal treatment. The chemical etching was very effective in order to remove the Si contamination, and after the BHF etching treatment the decrease of Si compounds on GaN layer surface was confirmed by the great decrease of Si2p/Ga3d XPS signal intensity ratio. After the chemical etching treatment, the GaN layer was then exposed in air atmosphere. Two kinds of methods were utilized for the air exposure; sample was put in open air (case 1), and also was put at the inside of closed narrow space (case 2) limiting the concentrations of impurities reaching onto the sample surface. Figure 2 shows the Si2p/Ga3d XPS signal intensity ratio depending on an elapsed time in air exposure. At the case 1, the rapid increase of the intensity ratio was observed within initial 120 minutes, and then it indicated the gradual increase. On the other hand, at the case 2, the intensity ratios were always lower than those at the case 1. Therefore, the storage of the sample in air atmosphere is the important factor for Si contamination. It seems that the grade of O contamination depends greatly on temperature and humidity in air atmosphere. The results in GaN layer grown by metal-organic chemical vapor deposition method will be also presented. Acknowledgement A part of this work was conducted at Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by "Nanotechnology Platform" of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. Figure 1

The effect of oxygen vacancies in ZnO at an Au/ZnO interface on its catalytic selective oxidation of glycerol

In catalytic reactions, the nature of the support has a major effect on the formation of active sites, especially in the case of catalysts with strong metal–support interactions. Two types of ZnO with different concentrations of oxygen vacancies (ZnO-U, produced by a hydrothermal procedure using urea, and ZnO-C, produced by a precipitation method using sodium carbonate) have been prepared and employed as supports for Au catalysts. The results of O1s X-ray photoelectron spectroscopy and positron annihilation spectroscopy showed that ZnO-U has fewer oxygen vacancies than ZnO-C. After the materials were loaded with Au, the formation of an Au/ZnO interface was demonstrated by high-resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Electron paramagnetic resonance spectroscopy and Au4f X-ray photoelectron spectroscopy showed that the formation of the materials involved electron transfer from Au to the ZnO support, resulting in the formation of positively charged Au species. A close correlation between the formation of the interface and the level of oxygen vacancies in the ZnO support was observed: low oxygen-vacancy concentrations result in an increase in the work function of ZnO, which facilitates electron transfer and makes the formation of the Au/ZnO interface more thermodynamically favorable. When they are used as catalysts in glycerol oxidation, the TOF of Au/ZnO-U (1159 h−1) was 1.47 times higher than that of Au/ZnO-C (786 h−1). The higher activity of Au/ZnO-U can be attributed to the abundance of positively charged Au sites, which strengthen the surface coverage of OH* and then promote H abstraction from an O–H bond in glycerol.

Surface Contamination with Si and O Impurities for GaN Single-Crystalline Layers Grown by Ultra-High-Vacuum Sputter Epitaxy

In this study, we demonstrated a GaN surface contamination and cleaning technique focused on O- and Si-based compounds generated by an exposure to the atmosphere. The GaN single-crystalline layers were grown on sapphire (0001) substrates using the ultra-high-vacuum radio-frequency sputter epitaxy technique. During X-ray photoelectron spectroscopy (XPS) measurements, O1s and Si2p XPS signals were detected on the as-grown GaN layer surface. Thermal treatment was performed in order to remove these impurities, and the results of the XPS measurements indicated a significant decrease in the O–Ga bonds on the GaN layer surface. Following the buffered hydrogen fluoride etching treatment, a decrease in the Si compounds on the GaN layer surface was confirmed by a significant decrease in the Si2p/Ga3d XPS signal intensity ratio.

Enhancement of ferromagnetic properties in (Fe, Ni) co-doped ZnO flowers by pulsed magnetic field processing

In this study, Zn0.97Fe0.01Ni0.02O diluted magnetic semiconductor (DMS) flowers were fabricated through hydrothermal method with 4 T (Tesla) pulsed magnetic field (PMF). Rietveld refinement of X-ray diffraction (XRD) patterns and Raman analysis indicated that the synthesized samples have the hexagonal wurtzite structure without any other secondary (impurity) phases. The O1s X-ray photoelectron spectroscopy (XPS) and Raman measurements of the synthesized samples showed the existence of oxygen vacancy (VO). The results indicated that PMF could increase the contents of VO and doped ions. The magnetic measurement showed that the room temperature ferromagnetic (RTFM) property of (Fe, Ni) co-doped ZnO is enhanced by PMF. The enhancement of RTFM is attributed to the intrinsic interaction of magnetic ions (Fe3+, Ni2+) via VO created by pulsed magnetic field processing.

Mixed protonic-electronic conducting perovskite oxide as a robust oxygen evolution reaction catalyst

Large-scale utilization of hydro, solar, or wind-based electrochemical water splitting relies on the availability of low cost, highly active oxygen evolution reaction (OER) catalyst. Transition metal-containing perovskite oxide is attractive in this regard. The OER on such perovskite oxide in an alkaline solution is nonetheless often limited by proton transfer step. To overcome such limitation, here we apply mixed protonic-electronic conductor BaCo0.8-xFexZr0.1Y0.1O3 (x = 0, 0.2, and 0.4) as an OER catalyst. Among these three, BaCo0.8Zr0.1Y0.1O3 (BC0.8ZY) in particular shows the lowest OER overpotential, the lowest Tafel slope, the highest OER mass activity, and the highest OER specific activity, which surpass those of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) benchmark. Using O2-temperature programmed desorption, impedance spectroscopy, and O1s X-ray photoelectron spectroscopy, we attribute such superior OER performance to the highest oxygen desorption capacity, the lowest charge transfer resistance, and the highest hydroxide species content for BC0.8ZY. We also demonstrate that the OER current of BC0.8ZY exhibits a first-reaction order dependence to the solution pH between 12.5 and 14, which confirms its proton transfer rate-determining step.

Exchange interactions and XPS O1s spectra in polynuclear lanthanide complexes with dibenzoylmethanide and 4-hydroxy-2,1,3-benzothiadiazole

Magnetic properties of tetra- and pentanuclear complexes, Ln4(dbm)4(O-btd)6(OH)2, Ln4(dbm)6(O-btd)4(OH)2 and Ln5(dbm)10(OH)5 (Ln = Er, Dy, Yb; dbm = dibenzoylmethanide, O-btd = 4-hydroxy-2,1,3-benzothiadiazole) were studied. The X-ray photoelectron spectroscopy (XPS) O1s spectra of the studied compounds were obtained and analyzed. The mechanisms of exchange interactions in these compounds are discussed.

Novel Method for Preparing Controllable Nanoporous a-Fe2O3 and its Reactivity to SCR De-NOx

ABSTRACTControllable nanoporous hematite (CNH, α-Fe2O3) was prepared by thermal treatment of α-FeOOH at different temperatures, and the SCR activity of the prepared α-Fe2O3 was evaluated. XRD (X-ray diffraction), HRTEM (high-resolution transmission electron microscopy), N2 adsorption-desorption, XPS (X-ray photoelectron spectroscopy), and NH3-TPD (NH3-temperature programmed desorption) were utilized to characterize the catalysts. The results indicated that after thermal treatment at less than 600°C, the α-Fe2O3 catalysts exhibited excellent NO conversion that was higher than 80% in a temperature range from 300 to 400°C. CNH400 with a relatively large surface area of 47.24 m2 g–1 and many surface hydroxyl groups did not exhibit a substantially improved SCR activity even though it exhibited the best SCR activity. Therefore, the L-H mechanism was not the main reaction route for SCR of NO by α-Fe2O3. The increasing crystallization of α-Fe2O3 decreased the SCR activity, indicating that a decrease in surface oxygen defects was important for the SCR of NO and fitting the E-R mechanism. The NH3-TPD and XPS (O1s) results confirmed this hypothesis. This study provides an approach for the design and preparation of a controllable nanoporous α-Fe2O3 catalyst for SCR of NO by NH3.

Thermally induced modification of the graphene oxide film on the tantalum surface

The interface chemical reactions, the deoxygenation and the overall thermal stability of the ex situ deposited graphene oxide (GO) thick film on the polycrystalline tantalum surface were studied by means of x-ray photoelectron spectroscopy (XPS) at room temperature and after annealing up to 600°С. The evolution of the Ta4f, C1s and O1s XPS core level spectra from the Ta/GO structure under study upon the increase of the annealing temperature was investigated with the reference to the uncovered Ta substrate surface. In the Ta/GO structure the Ta relative atomic concentration was about 1% at room temperature due to the low porosity of the GO layer while the thermal desorption of the overlayer at the elevated temperatures was accompanied by an increase of the Ta concentration up to 47% at 500°С. The C atoms relative concentration started decreasing after the annealing at 250°С accompanying the thermal desorption of the GO overlayer. The formation of the TaC compound starting from the 250°С annealing temperatures was determined. The relative oxygen concentration in the GO thick film was decreased upon increasing the annealing temperature accompanying both the thermal desorption of the GO material and the thermal reduction of the GO film.

Role of different plasma gases on the surface chemistry and wettability of RF plasma treated stainless steel

Vacuum radio frequency (RF) plasma treatment was conducted on electropolished and passivated 316 LVM stainless steel (SS) surface by using Ar and O2. Contact angle measurements revealed that both Ar and O2 plasma treatments significantly increased the wettability of the SS surface by water. The physical and chemical effects induced by Ar and O2 plasma on SS were investigated via Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). AFM analysis revealed that plasma process exerted similar effects on surface roughness and topography. Both Ar and O2 plasma treatments resulted in smoother surface when compared to reference electropolished sample. XPS investigations of the surfaces with respect to Fe2p, Cr2p, Mo3d and O1s XPS spectra showed that the main role of Ar plasma was thinning of the oxide-hydroxide layer along with the removal of contamination without any definitive difference on the valence states of metal compounds. On the other hand, O2 plasma treatment resulted in thickening of oxide layer along with oxidation of the species to their highest valence states (CrVI, FeIII and MoVI). After washing the plasma treated surfaces with water, contact angles for oxygen plasma treated samples increased dramatically indicating the substantial role of higher valent oxides on wetting process.