UPS and XPS studies of the chemisorption of O2, H2 AND H2O on reduced and stoichiometric SrTiO3(111) surfaces; The effects of illumination

About one monolayer of Ti³⁺ species is detectable at the surface of reduced SrTiO₃(111) single crystals by XPS and UPS. O₂, H₂ and H₂O have been adsorbed in the dark and the decrease on the concentration of the Ti³⁺ species has been monitored as a function of the gas exposures. Subsequent band gap illumination partially restores the Ti³⁺ initial concentration in the cases of O₂ and H₂ exposures but not in the case of H₂O. The Ti³⁺ photogeneration on the oxygen covered surface is associated with oxygen photodesorption as indicated by XPS and UPS. UPS measurements give evidence for surface hydroxylation resulting from water and hydrogen adsorption. The activity of the stoichiometric SrTiO₃(111) crystal face for O₂ and H₂ adsorption is very low when compared with the reduced SrTiO₃ samples.     

Theoretical study of stereodynamics for the N+H2/D2/T2 reactions

The effects of isotopic variants on stereodynamic properties for the title reactions have been investigated using a quasi-classical trajectory method based on the first excited state NH2（I^2A＇） potential energy surface [Li Y Q and Varandas A J C 2010 J. Phys. Chem. A 114 9644]. The forward–backward symmetry scattering of the differential cross section can be observed, which demonstrates that all these reactions follow the insertion mechanism. Three angle distribution functions P（θr）, P（φr）, and P（θr, φr） with different collision energies and target molecules H2/D2/T2 are calculated. It is shown that the product rotational angular momentum is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The title reaction is mainly governed by the ＂in-plane＂ mechanism through the calculated distribution function P（θr, φr）. The observable influences on the rotational polarization of the product by the isotopic substitution of H/D/T can be demonstrated.     

The chemisorption of CO,CO2, C2H2, C2H4, H2 and NH3 on the clean Fe(100) and (111) crystal surfaces

The chemisorption of small molecules (CO, CO₂, C₂H₂, C₂H₄, H₂ and NH₃) has been studied on the clean Fe(110) and (111) crystal faces by low-energy electron diffraction (LEED) and thermal desorption. C₂H₄ and C₂H₂ yield the same sequence of surface structures that change with temperature and crystal orientation. CO and CO₂ chemisorption similarly results in the formation of the same types of surface structures that change with surface temperature and crystal orientation. Ammonia forms several ordered surface structures on both iron crystal faces. All of the molecules decompose as a function of temperature on the iron surfaces as indicated by the Auger and thermal desorption spectra.     

Adsorption of H2S,H2O and O2 on Si(111) surfaces

Electron energy-loss spectroscopy has been applied to the study of Si(111) surfaces covered with H₂S, H₂O and O₂ at room temperature and the surfaces annealed at ～ 600°C. The experimental results strongly suggest that H₂S and H₂O adsorb in the molecular states at room temperature. It is proposed that O₂ is first adsorbed in a molecular state, then adsorbs as atoms, and finally oxidizes forming SiO₂.     

H2 分子在Li3N(110)表面吸附的第一性原理研究

采用第一性原理方法研究了H₂分子在Li₃N(110)晶面的表面吸附. 通过研究H₂/Li₃N(110)体系的吸附位置、吸附能和电子结构发现: H₂分子吸附在N桥位要比吸附在其他位置稳定,此时在Li₃N(110)面形成两个-NH基,其吸附能为1.909 eV,属于强化学吸附;H₂与Li₃N(110)面的相互作用主要是H 1s轨道与N 关键词： 第一性原理 3N(110)')" href="#">Li₃N(110) 2')" href="#">H₂ 吸附和解离     

Selective adsorption of He,H2 on copper surfaces

The selective adsorption of helium and molecular hydrogen has been experimentally observed on various copper surfaces characterized by a quasi one-dimensional corrugation: Cu(110), (113), (115), (117). Four bound state energy levels for the He-Cu potential and six for H₂-Cu have been measured. They are independent of the surface crystalline structure. They are well fitted by a 9-3 potential from which the well depth is deduced: D = 6.35 meV for He-Cu and D = 22 meV for H₂Cu. The Van der Waals constant C₃ is also estimated from the data. The ratio is approximately the ratio of the static polarizabilities of He and H₂. The semi-empirical formula of Hoinkes is found to agree with the present data.     

H+5团簇离子及其中性团簇产物H3和H4

报道了H⁺₅的实验结果.分析讨论了H⁺₅的 形成和分解途径.根据理论分析，以稳定的H⁺₃为核心与一个或多个氢分子结合可能形成稳定的H^{+_n氢团簇离子.另一方面，在高频离子源中, 有发生H+₃与H₂反应的条件.实 验中，从高频离子源引出的离子束被静电加速器加速，然后用9 关键词： +}₅团簇离子')" href="#">H⁺₅团簇离子 3中性团簇')" href="#">H₃中性团簇 4中性团簇')" href="#">H_{4中性团簇}     

H2 and CO chemisorption on polycrystalline titanium studied by flash desorption mass spectrometry

We have used flash desorption mass spectroscopy to study the adsorption and desorption of H₂ and CO from clean titanium at room temperature. CO flash desorption occurs predominantly from a low temperature state whose binding energy is 20.3 kcal/mole. H₂ flash desorption is complex. Only one peak is observed; it is broader than flash desorption spectra normally corresponding to first or second order kinetics. The shift in the peak temperature to lower values with increasing coverage has been analysed using the isothermal desorption rate technique. The apparent order of H₂ desorption is 1.5 and is independent of temperature from 888 to 1077 K. The activation energy is 21 kcal/mole. These results will be discussed in terms of absorption of H₂ into titanium and thermal decomposition of a titanium hydride compound.     

RHEED and Auger study of the MoO3(010) surface interaction with H2S/H2 mixture and pure H2S

Pure single crystals of MoO₃ were carefully grown by physical vapor transport. The initial stages of the interaction of H₂S with a MoO₃ (010) surface were studied by RHEED and AES at low pressure p <133 Pa and at T < 700 K. Three main stages were found: (a) The formation of either a completely disordered sulphur adiayer (with pure H₂S) or a superstructure MoO₃(010)-[2 × 1]S (with H₂S/H₂). (b) A reduction of MoO₃ producing oriented three-dimensional MoO₂ islands, (c) An epitaxial overgrowth of MoS₂ from the MoO₂ three-dimensional crystallites.     

He—H2碰撞过程中的H2分子的振动激发

用半径典模型描述原子A与双原子分子B－C的共线碰撞,分子B－C的振动激发,近似用线性外场中的变频振子描述,应用不变量方法求出He和H2碰撞过程中H2分子从基态到所有振动激发态的跃迁几率。     

Magnetic susceptibility of the TaV2/H2 system

The magnetic susceptibility exhibited by the ordered (C-15) and random bcc allotropes of TaV₂ decreases linearly with increasing hydrogen content. However, the susceptibility exhibited by the (C-15) form is about four times more sensitive to hydrogen than that exhibited by the bcc form. The results are in qualitative accord with the thermodynamics of hydrogen solution.     

Immobilization of bovine serum albumin on TiO2 film via chemisorption of H3PO4 interface and effects on platelets adhesion

In the present study, bovine serum albumin (BSA) was successfully covalently immobilized on the surface of anatase TiO₂ film by a three-step method, i.e. application of H₃PO₄ chemisorption to increase surface -OH, which increases the amount of coupling 3-aminopropyl-triethoxylsilane (APTES), thus linking with BSA by imide bond using EDC/NHS/MES. There is no significant -OH group increase on rutile film when using the same method of phosphoric acid treatment, which suggest it is difficult for further chemical modification of the rutile film. After covalent immobilization of BSA on anatase film, an improved hemocompatibility of anti-platelet adhesion and aggregation in vitro could be recognized by LDH and SEM analysis. This study suggests BSA-immobilized anatase surface can serve as hemocompatibility material in vivo.     

The adsorption of CO,H2, H2, CO2 and H2O on carburized and graphitized Ni(110)

A study of the adsorption/desorption behavior of CO, H₂O, CO₂ and H₂ on Ni(110)(4 × 5)-C and Ni(110)-graphite was made in order to assess the importance of desorption as a rate-limiting step for the decomposition of formic acid and to identify available reaction channels for the decomposition. The carbide surface adsorbed CO and H₂O in amounts comparable to the clean surface, whereas this surface, unlike clean Ni(110), did not appreciably adsorb H₂. The binding energy of CO on the carbide was coverage sensitive, decreasing from 21 to 12 $\text{kcal}\text{mol}$ as the CO coverage approached 1.1 × 10¹⁵ molecules cm^?2 at 200K. The initial sticking probability and maximum coverage of CO on the carbide surface were close to that observed for clean Ni(110). The amount of H₂, CO, CO₂ and H₂O adsorbed on the graphitized surface was insignificant relative to the clean surface. The kinetics of adsorption/desorption of the states observed are discussed.     

Density functional theory study of the interaction of H2 with pure and Ti-doped WO3 (002) surfaces

Density functional theory (DFT) calculations are conducted to explore the interaction of H₂ with pure and Ti-doped WO₃ (002) surfaces. Four top adsorption models of H₂ on pure and Ti-doped WO₃ (002) surfaces are investigated respectively, they are adsorption on bridging oxygen O_1c, absorption on plane oxygen O_2c, absorption on 5-fold W_5c (Ti), and absorption on 6-fold W_6c. The most stable and H₂ possible adsorption structure in the pure surface is H-end oriented to the surface plane oxygen O_2c site, while the favourable adsorption sites for H₂ in a Ti-doped surface is not only an O_2c site but also a W_6c site. The adsorption energy, the Fermi energy level E_F, and the electronic population are investigated and the H₂-sensing mechanism of a pure-doped WO₃ (002) surface is revealed theoretically: the theoretical results are in good accordance with our existing experimental results. By comparing the above three terms, it is found that Ti doping can obviously enhance the adsorption of H₂. It can be predicted that the method of Ti-doped into a WO₃ thin film is an effective way to improve WO₃ sensor sensitivity to H₂ gas.     

Collision-induced simultaneous transitions in H2+CF4 and H2+SF6 mixtures

The simultaneous transitions of the v₃ fundamental vibrations of CF₄ and SF₆ with the fundamental Q branch and S(1) line of H₂ have been studied for various H₂+CF₄ and H₂+SF₆ mixtures at total pressures up to 185 bars. The integrated intensities are found to be proportional to the partial densities of the gas mixture components. The agreement between experimental and calculated intensities is generally better for the Kihara potential than for the Lennard-Jones potential.     

He原子与N2分子相互作用势的理论研究

用量子力学从头算方法深入研究了He原子与N2分子的相互作用势,用不同的方法和基组计算了该体系的各项异性相互作用势的单点能数据,得出了空间势能面的分布情况,并选定CCSD(T)/6-311++G(3df,2pd)方法和基组,同时采用了Boys和Bernardi提出的Full Couterpoise方法,消除了计算中的基组重叠误差,得出了较为准确的He-N2体系相互作用势的解析表达式.通过计算得到的微分截面与实验值符合较好,同时得出了不同碰撞能量时He原子与N2分子碰撞的微分截面的规律.     

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.     

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.