Oxidation of Zircaloy-4 by H2O followed by molecular desorption

The interaction of H₂O with Zircaloy-4 (Zry-4) is investigated using Auger electron spectroscopy (AES) and temperature programmed desorption (TPD) methods. Following adsorption of H₂O at 150 K the Zr(MNV) and Zr(MNN) Auger features shift by ∼6.5 and 4.5 eV, respectively, indicating surface oxidation. Heating H₂O/Zry-4 results in molecular desorption of water at both low and high temperatures. The low-temperature desorption is attributed to ice multilayers, whereas, three overlapping high-temperature features are presumably due to recombinative desorption. This high-temperature desorption begins before the surface oxide is dissolved, continues upon its removal, and is atypical for water/metal systems. Unexpectedly, no significant desorption of hydrogen is observed near 400 K, as is typically observed following O₂ adsorption on Zr-based materials. However, we do observe that H₂O adsorption on Zry-4 surfaces roughened by argon ion sputtering results in H₂ desorption.     

Inhibition of initial surface oxidation by strongly bound hydroxyl species and Cr segregation: H2O and O2 adsorption on Fe-17Cr

The initial stages of surface oxidation of Fe-17Cr (ferritic stainless steel) were investigated at 323 K by X-ray photoelectron spectroscopy (XPS) and inelastic electron background analysis. The results indicated the formation of a mixed iron-chromium oxide layer upon O₂ exposure and the formation of a thin chromium oxyhydroxide layer upon H₂O exposure. The oxidation of Fe did not occur in the latter case. Moreover, it was found that pre-exposing the Fe-17Cr surface to H₂O significantly hinders subsequent oxidation by O₂, thus providing a way to control the formation of nanoscale oxides on stainless steel materials. It was concluded that the formation of strongly bound hydroxyl species together with adsorbate-induced segregation of Cr severely limits the reaction between O₂/H₂O and Fe from the alloy.     

Surface sprouting growth of Na2Nb2O6·H2O nanowires and fabrication of NaNbO3 nanostructures with controlled morphologies

The one-dimensional (1D) Sandia octahedral molecular sieves (SOMS) Na₂Nb₂O₆·H₂O nanowires were prepared by the reaction of Nb powder with NaOH via a one-step hydrothermal methods. The products were characterized by SEM, TEM, XRD, IR and EDX. A plausible sprouting growth mechanism is proposed for the formation of Na₂Nb₂O₆·H₂O nanowires based on the systematic investigation. Na₂Nb₂O₆·H₂O nanoribbons-based complex flowerlike structure were first grew on the metallic niobium surface, the growth process of SOMS nanowire is similar to the plant seed sprouting and growing, Na₂Nb₂O₆·H₂O nanowires were finally formed at the depletion of metallic niobium powder. In the end, we showed that Na₂Nb₂O₆·H₂O nanowires is hydrothermally synthesized in the 15 M NaOH solution at 423 K, which can be easily converted into NaNbO₃ nanowires by calcination, while the NaNbO₃ cubes were obtained through the same hydrothermal process at a higher temperature of 453 K.     

Si在水汽中氧化传质机制的H218O/H216O同位素示踪研究

采用同位素H₂¹⁶O/H₂¹⁸O接续氧化同位素示踪方法,研究了单晶硅在1100 ℃水汽中氧化的微观传质机制.在H₂¹⁶O,H₂¹⁸O分别氧化和H₂¹⁶O/H₂¹⁸O接续氧化处理后,研究氧化产物形态和结构.并用二次离子质谱仪(SIMS)研究了同位素 关键词： 同位素示踪 2¹⁸O')" href="#">H₂¹⁸O 替位扩散 硅     

Interaction of PH3 coadsorbed with H2, D2, O2 and H2O on Rh(100)

The coadsorption of PH₃ with H₂, D₂, O₂ and H₂O on Rh(100) has been studied using temperature programmed desorption (TPD), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). The adsorption and molecular desorption of PH₃ is not affected by preadsorbed H₂, D₂ and O₂. Preadsorbed PH₃ blocks H₂ desorption sites while postdosed PH₃ displaces H₂ (D₂₁) from the Rh(100). When D₂ and PH₃ are coadsorbed, no D appears in desorbed phosphine. Preadsorbed O₂ reduces the amount of H₂ desorption (from PH₃ decomposition) and increases the H₂ desorption temperature. There is also some reaction between O(a) and H(a) to form water. Preexposure to H₂O decreases the extent of PH₃ adsorption and of PH₃ decomposition.     

The initial interactions of beryllium with O2 and H2O vapor at elevated temperatures

In the 310-790 K temperature range, the mechanism of initial oxidation by O₂ is oxide island nucleation and growth. At the lower temperature range, oxygen is first chemisorbed and the oxide nucleates at coverage of ∼0.2. Increasing the temperature causes the oxide islands to nucleate at lower coverage and at 700 K and above, the oxide nucleates without any significant stage of chemisorbed oxygen. The temperature dependence shows that while the dissociation stage is not activated, the oxide nucleation and growth are thermally activated. Also, opposite to O₂ adsorption, the initial H₂O adsorption and oxidation rate was found to decrease with temperature. Opposite to the oxygen case, upon exposure to water vapor there is no noticeable stage of chemisorbed oxygen (or OH) and oxide is directly nucleated. Only after oxide coalescence, this tendency changes and the oxidation rate is increased with temperature.     

On the origin of electron stimulated desorption of H+ from metal surface

The emission of hydrogen ESD ions from polycrystalline Nb is studied experimentally. The results demonstrate clearly that no ESD emission of H⁺ occurs from a pure H adsorbate. However, adsorption of H₂O, present as an impurity in H₂, and H₂ adsorption on Nb preceded by O adsorption, produce strong H⁺ ESD emission. It is shown that Auger ionization of O can account for the increased H⁺ yield and it is postulated that similar effects also occur on other metal surfaces.     

Comparison of CH4/H2 and C2H6/H2 inductively coupled plasma etching of ZnO

CH₄/H₂-based discharges are attractive for dry etching of single crystal ZnO because of their non-corrosive nature. We show that substitution of C₂H₆ for CH₄ increases the ZnO etch rate by approximately a factor of 2 both with and without any inert gas additive. The C₂H₆/H₂/Ar mixture provides a strong enhancement over pure Ar sputtering, in sharp contrast to the case of CH₄/H₂/Ar. The threshold ion energy for initiating etching is 42.4 eV for C₂H₆/H₂/Ar and 59.8 eV for CH₄/H₂/Ar. The etched surface morphologies were smooth, independent of the chemistry and the Zn/O ratio in the near-surface region was unchanged within experimental error after etching with both chemistries. The plasma etching improved the band-edge photoluminescence intensity and suppressed the deep level emission from the bulk ZnO under our conditions, due possibly to removal of surface contamination layer.     

Oxidation of Al single crystal surfaces by exposure to O2 and H2O

The initial stages of oxidation of Al single crystals are studied by soft X-ray photoemission spectroscopy at photon energies hv = 30 eV and 111.13 eV using synchroton radiation. Both the valence band region and the substrate Al 2p core levels are measured with high resolution to clarify the differences between (a) the geometrical effects at different surfaces, (100) and (110), and (b) between the oxidation by pure O₂ and H₂O. There is a well established but not very dramatic differences in the O 2p induced band between the two crystal surfaces when oxidizing with O₂. The Al 2p spectra reveal an initial state of oxidation with less O atoms per Al atom than in Al₂O₃ate disappears at higher exposures with O₂ while it is absent when oxidizing with H₂O. Only about 1/4 of the exposure with H₂O is needed to obtain the same coverage as with O₂.     

Photon stimulated ion desorption of H+ ions from GaAs (110)/H2O

The photon stimulated ion desorption yield of H⁺ ions from a H₂O dosed GaAs (110) surface has been measured in the range 18eV ? hυ ? 30eV. There is a direct correspondence between the PSID H⁺ yield, reflectance, and the secondary electron yield spectrum of GaAs (110). The data provides evidence that the initial stages of PSID involve core level (Ga(3d), O(2s)) → conduction band excitation followed by Auger decay.     

Structure and composition of the segregated Cu in V2O5/Cu system

We have investigated segregation of copper at the surface of V₂O₅ films deposited onto Cu substrate by employing surface analysis techniques. X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) confirmed that the Cu is segregated at the surface and its chemical state is Cu₂O. According to secondary ion mass spectroscopy (SIMS) and glow discharge spectroscopy (GDS), the Cu concentration inside the deposited V₂O₅ layer is low. Ultraviolet photoelectron spectroscopy (UPS) and scanning tunneling spectroscopy (STS) revealed the segregation alters the surface local density of states. Surface analysis of deposited samples in ultra high vacuum (UHV) condition verified that the segregation occurs during the deposition. We have extended kinetic tight binding Ising model (KTBIM) to explain the surface segregation during the deposition. Simulation data approve the possibility of surface segregation during room temperature deposition. These results point out that on pure Cu substrate, oxidation occurs during the segregation and low surface energy of Cu₂O is the original cause of the segregation.     

Ion survival probabilities for 3 keV Ar+ scattering from La,Yb, and chemisorbed H2, O2, and H2O on La surfaces

TOF spectra of scattered primary and surface recoiled neutrals and ions for 3 keV Ar⁺ bombardment of clean La and Yb and H₂, O₂, and H₂O saturated La surfaces are presented. The spectra are analyzed in terms of single (SS) and multiple (MS) scattering of the primary ions and surface recoiling (SR) of adsorbate atoms. Measurement of spectra of neutrals + ions and neutrals alone allows determination of scattered ion fractions Y. The Y values for the SS event are high for clean La (37%) and lower for adsorbate covered La (32% for H₂, 13% for O₂, and 8% for H₂O); Yb exhibits a similar behavior, i.e. 16% for clean Yb and 5% for O₂ + H₂O covered Yb. Photon emission accompanying the scattering collision has been observed from clean La and Yb and adsorbate covered La. A preferential inelastic energy loss of 15 ± 3 eV for the SS event has been observed for scattered neutrals as opposed to ions for La and H₂ saturated La at 135°. These results are interpreted within the models for Auger and resonant electronic charge exchange transitions during approach or departure of an ion with a surface and the electron promotions occuring during close atomic encounters where the electron shells are interpenetrating.     

An examination of the initial oxidation of a uranium-base alloy (U–14.1 at.% Nb) by O2 and D2O using surface-sensitive techniques

The corrosion resistance of uranium is greatly enhanced by alloying with niobium. In this study the initial stages of corrosion of a specific uranium-base alloy (U–14.1 at.% Nb) by O₂ or D₂O have been examined using the surface specific techniques of X-ray photoelectron spectroscopy (XPS), thermal programmed desorption (TPD), static secondary-ion mass spectroscopy (SSIMS), and sputtered neutrals mass spectroscopy (SNMS). XPS studies of the U–14.1 at.% Nb surface following oxidation using O₂ at 300 K indicate production of a thin oxide overlayer of stoichiometric UO_2.0 intermixed with Nb₂O₅. The same stoichiometry is exhibited for uranium when the oxide is prepared at 500 K with O₂; although, niobium is much less oxidized exhibiting a mixture of NbO and Nb. Contrary to previous XPS literature, SNMS depth profiling studies reveal that oxidation by O₂ is much greater (as judged by oxide layer thickness) than that exhibited by D₂O. An oxide layer thickness of less than 20 Å was created using D₂O as an oxidant at 300 K with exposures >3500 L (oxide layers created from O₂ are significantly greater at much smaller exposures). Formation of a critical density of Nb₂O₅ is suggested to be responsible for the enhanced corrosion resistance by preventing diffusion of O⁻ (O²⁻) or OD⁻/OH⁻ into the oxide/metal interface region. The domains of stability of hydroxyl formation have also been followed using TPD, SSIMS and XPS. Maximal surface hydroxyl concentrations (Θ_rel=0.30) are obtained at a surface temperature of 175 K for these experimental conditions.     

Reactivities of ultrathin alumina films exposed to intermediate pressures of H2O: Substrate-mediated mechanism for growth and loss of surface order

The response of ordered ultrathin Al₂O₃ films on NiAl(1 1 0) and Ni₃Al(1 1 0) substrates to sequential exposures at varying pressures of H₂O between 10⁻⁷ Torr and 10⁻³ Torr, ambient temperature, was characterized by LEED, AES and density functional theory (DFT) calculations. In all cases, an increase in average oxide thickness, as determined by AES, was observed, consistent with a field-induced oxide growth mechanism. Ordered oxide films of initial average thicknesses of 7 Å and 12 Å grown on NiAl(1 1 0) achieved a limiting thickness of 17(1) Å, while films of initial thickness of 7 Å and 11 Å grown on Ni₃Al(1 1 0) achieved a limiting thickness of 12(1) Å. The LEED patterns for the thinner (7 Å) films were not observed after exposure to 10⁻⁵ Torr (NiAl(1 1 0)), or 10⁻⁴ Torr (Ni₃Al(1 1 0)). In contrast, LEED patterns for the films of greater initial thickness persisted after exposures to 10⁻³ Torr UHV. DFT calculations indicate an Al vacancy formation energy that is significantly greater (by ∼0.5 eV) on the surface that has the thicker oxide film, directly opposite to what may be naively expected. A simple coordination argument supports these numerical results. Therefore, the greater limiting oxide thickness observed on NiAl(1 1 0) demonstrates that the rate determining step in the oxide growth process is not Al removal from the metal substrate and transport across the oxide/metal interface. Instead, the results indicate that the determining factor in the oxide growth mechanism is the kinetic barrier to Al diffusion from the substrate bulk to the oxide/metal interface. The persistence of the LEED patterns observed for the films of greater initial oxide thickness indicates that the surface disorder generally observed for alumina films grown on aluminide substrates and exposed to intermediate pressures of H₂O is due to the growth of a disordered alumina layer over an ordered substrate, rather than to direct H₂O interaction with terrace sites.     

Oxidation of H2/CO2 mixtures and effect of hydrogen initial concentration on the combustion of CH4 and CH4/CO2 mixtures: Experiments and modeling

An experimental investigation of the oxidation of hydrogen diluted by nitrogen in presence of CO₂ was performed in a fused silica jet-stirred reactor (JSR) over the temperature range 800-1050 K, from fuel-lean to fuel-rich conditions and at atmospheric pressure. The mean residence time was kept constant in the experiments: 120 ms at 1 atm and 250 ms at 10 atm. The effect of variable initial concentrations of hydrogen on the combustion of methane and methane/carbon dioxide mixtures diluted by nitrogen was also experimentally studied. Concentration profiles for O₂, H₂, H₂O, CO, CO₂, CH₂O, CH₄, C₂H₆, C₂H₄, and C₂H₂ were measured by sonic probe sampling followed by chemical analyses (FT-IR, gas chromatography). A detailed chemical kinetic modeling of the present experiments and of the literature data (flame speed and ignition delays) was performed using a recently proposed kinetic scheme showing good agreement between the data and this modeling, and providing further validation of the kinetic model (128 species and 924 reversible reactions). Sensitivity and reaction paths analyses were used to delineate the important reactions influencing the kinetic of oxidation of the fuels in absence and in presence of additives (CO₂ and H₂). The kinetic reaction scheme proposed helps understanding the inhibiting effect of CO₂ on the oxidation of hydrogen and methane and should be useful for gas turbine modeling.     

High-density plasma etching of indium-zinc oxide films in Ar/Cl2 and Ar/CH4/H2 chemistries

The dry etching characteristics of transparent and conductive indium-zinc oxide (IZO) films have been investigated using an inductively coupled high-density plasma. While the Cl₂-based plasma mixture showed little enhancement over physical sputtering in a pure argon atmosphere, the CH₄/H₂/Ar chemistry produced an increase of the IZO etch rate. On the other hand, the surface morphology of IZO films after etching in Ar and Ar/Cl₂ discharges is smooth, whereas that after etching in CH₄/H₂/Ar presents particle-like features resulting from the preferential desorption of In- and O-containing products. Etching in CH₄/H₂/Ar also produces formation of a Zn-rich surface layer, whose thickness (∼40 nm) is well-above the expected range of incident ions in the material (∼1 nm). Such alteration of the IZO layer after etching in CH₄/H₂/Ar plasmas is expected to have a significant impact on the transparent electrode properties in optoelectronic device fabrication.     

Spectroscopically determined potential energy surfaces of the H2O, H2O, and H2O isotopologues of water

Adiabatic potential energy surfaces (PESs) for three major isotopologues of water, H₂¹⁶O, H₂¹⁷O, and H₂¹⁸O, are constructed by fitting to observed vibration-rotation energy levels of the system using the nuclear motion program DVR3D employing an exact kinetic energy operator. Extensive tests show that the mass-dependent ab initio surfaces due to Polyansky et al. [O.L. Polyansky, A.G. Császár, S.V. Shirin, N.F. Zobov, P. Barletta, J. Tennyson, D.W. Schwenke, P.J. Knowles, Science 299 (2003) 539-542.] provide an excellent starting point for the fits. The refinements are performed using a mass-independent morphing function, which smoothly distorts the original adiabatic ab initio PESs. The best overall fit is based on 1788 experimental energy levels with the rotational quantum number J = 0, 2, and 5. It reproduces these levels with a standard deviation of 0.079 cm⁻¹ and gives, when explicit allowance is made for nonadiabatic rotational effects, excellent predictions for levels up to J = 40. Theoretical linelists for all three isotopologues of water involved in the PES construction were calculated up to 26 000 cm⁻¹ with energy levels up to J = 10. These linelists should make an excellent starting point for spectroscopic modelling and analysis.     

High resolution pure rotational spectrum of water vapor enriched by H217O and H218O

The pure rotational spectrum of a mixture of H₂¹⁶O, H₂¹⁷O and H₂¹⁸O between 50 and 730 cm^?1 was recorded on the Fourier transform spectrometer at the University of Oulu. The resolution achieved was about 0.010 cm^?1 and the precision of the unblended lines was better than 0.001 cm^?1. About 1100 lines were assigned. The measured line positions of H₂¹⁷O and H₂¹⁸O were compared with the values derived from the rotation and distortion constants given in the literature.     

InP清洁表面上电子感应吸附氧的研究

用俄歇电子能谱观察清洁InP表面在电子束照射下与真空室中H₂O和O₂的相互作用,发现水蒸汽所引起的电子束感应吸附氧的作用比氧气要明显得多。在吸附氧的同时,In和P的俄歇信号也发生变化,分析其过程为一种氧化过程,氧一开始先同表面的In结合成为氧化铟,随后向表面以内透入,并不断同In和P结合,氧化层的厚度随时间几乎是线性地增加的。与InP的自体氧化层的俄歇深度分布相比较,二者极为相似,所不同的是,电子束感应吸附的氧不足以使表面层中的磷全部氧化,而ESO的氧化层中磷的 关键词：     

Adsorption of H2O on clean and on boron-contaminated Rh surfaces

The adsorption and dissociation of H₂O on Rh(111) and Rh foil surfaces have been studied in UHV using Auger electron, electron energy loss (in the electronic range) and thermal desorption spectroscopy. H₂O adsorbs weakly on clean Rh samples at 110 K. The adsorption is accompanied by the appearance of a broad loss feature at 14–14.5 eV. At higher exposures new losses appeared at 8.6 and 10.5 eV. The desorption of H₂O took place in two stages, with T_p = 183 K (β, chemisorption) and 158 K (α, multilayer formation). There was no indication of dissociation of H₂O on a clean Rh(111) surface. Similar results were obtained for a clean Rh foil. However, when small amounts of boron segregated on the surface of Rh, they exerted a dramatic influence on the adsorptive properties of this surface and caused the dissociation of H₂O. This was exhibited by the formation of H₂, by the buildup of surface oxygen, by the appearance of an intense new loss at 9.4 eV, identified as B-O surface species, and by the development of “boron-oxide”-like Auger fine structure.