Study of defects and thermal stability of ultrathin Cu films on Ta(110) and Ta(100) by thermal helium desorption spectrometry

Thermal helium desorption spectrometry has been used to study the interaction of helium with defects in Cu films (5-300 Å) deposited on Ta(110) and Ta(100) single crystals by ultrahigh vacuum electron beam evaporation. The thermal stability of the Cu films was also investigated. Cu films on Ta(110) and Ta(100) at room temperature are metastable and on heating, the films transform into islands. The temperature at which this takes place is strongly dependent on the Cu film thickness and for a given thickness (> 40 Å) occurs at a lower temperature on Ta(100) than on Ta(110). The activation energy for island formation is 1.6 ± 0.4 eV for 50 Å Cu/Ta(110) and 0.8 ± 0.1 eV for 100 Å Cu/Ta(100) obtained by Kissinger analysis. The geometry of the Cu islands resulting from annealing 50 Å Cu films at 1000 K for 10 s depends strongly on the Ta substrate orientation. There is evidence for the stressed states of both the Cu films and the Ta substrates. Helium release from monovacancies and vacancy clusters in Cu films (> 75 Å) on Ta(110) and Ta(100) was detected at ~ 750 K and ~ 800-1000 K respectively. The sublimation of the Cu films from the Ta substrates could be observed by the release of retained helium at ~ 1300 K.     

A comparison of the initial growth of metal layers on Mo(110) and W(110) surfaces

The growth of copper, silver and gold on Mo(110) is studied using low energy electron diffraction and Auger electron spectroscopy. The results are compared with previous results for the same metals on W(110). In spite of the nearly identical lattice constants and electronic structures of the two substrates, significant differences in the initial growth of copper and silver are found and are related to differences in the interaction between the substrate and the overgrowth.     

Effective CO2 activation of enriched oxygen vacancies for photothermal CO2 methanation

Oxygen vacancies have been widely concerned with the facilitation effects of CO2 activation for CO2 methanation.However,little attention has been paid to the generation of active intermediate species induced by enriched oxygen vacancies.Herein,we discovered that CeNiO3-δ catalyst enriched oxygen va-cancies can efficiently activate CO2 and realize high activity for photothermal CO2 methanation.In situ dif-fuse reflectance infrared Fourier transform spectroscopy(DRIFTS)proved that oxygen vacancies are bene-ficial to the formation of reactive intermediate species of polydentate carbonate over CeNiO3-δ,which is crucial for efficient CO2 methanation.These results revealed mechanistic insights into how effective CO2 activation induced by oxygen vacancies can be manipulated by adjusting the adsorption intermediate species.     

Experimental evidence on molecular interaction in desorption and adsorption of CO molecules on metal surfaces

Adsorption and desorption of CO on Ni(100) and Pt(111) surfaces are presented. At the thermodynamic equilibrium, the site occupation between the terminal and the bridged sites are described with the free energy of the system, including the vibrational entropy. Adsorption of CO onto a cold surface as 20 K has also been studied by infrared reflection absorption spectroscopy (IRAS). The occupation ratio of bridged CO to terminal CO species on Ni(100) at 20 K ranges from ～ 2·8 to 0·7 at the total coverage from 0·003 to 0·15 ML. Such strong coverage dependence of the occupation ratio even at small coverages suggests that the interaction between CO molecules operates at relatively long range (> 10 Å). The isotope experiments suggest that there is substantial interaction between preadsorbed (accommodated) CO species and incoming (mobile) CO species. Desorption process is also affected by the interaction between the adsorbed CO and the incoming species. The effect of temporal bimolecular CO interaction on the desorption kinetics is also discussed.     

MlNi_4Co_(0.6)Al_(0.4)储H_2合金表面吸H_2的TDS研究

用热脱附谱 (TDS)对不同表面处理的富La混合储H2 合金MlNi4 Co0 6Al0 4 粉末样品进行H2 气吸附和脱附特性的比较和研究。未经表面处理的粉末样品 ,只测到一个H2 脱附峰 (α峰 ) ,脱附温度在 40 0K左右 ;经 6molKOH溶液 ,在 80℃下处理 6h的MlNi4 Co0 6Al0 4 粉末样品 ,有 2个H2 热脱附峰 (β峰和γ峰 ) ,脱附温度分别在 5 40和 6 30K处 ;而用 6molKOH 0 0 2molKBH4 溶液处理后 ,则有 3个H2 热脱附峰 (α峰 ,β峰和γ峰 ) ,脱附温度分别在 40 0 ,5 30和 6 40K处。TDS研究表明 ,热碱加还原的处理使材料表面对H2 气吸附的活性和容量提高 ,并使各个吸附态的扩散和转变更加容易。     

Tunneling induced decomposition of Mo(CO)6 onto TiO2(110) surface

Tunneling induced decomposition of Mo(CO)₆ from the gas phase was studied on TiO₂(110) surface by scanning tunneling microscopy (STM) and spectroscopy (STS). The efficiency of the procedure was followed by measuring the dot volume as a proportional indicator of the amount of the decomposed precursor. It was found that below 1 × 10⁻⁵ Pa background pressure of Mo(CO)₆, there is no measurable effect and above 1 × 10⁻⁴ Pa, the nanodot size is too large compared to the curvature of the tip (20-40 nm). A threshold bias of +3.1(±0.1) V on the sample was measured for the decomposition of Mo(CO)₆ in gas ambient. In the absence of the precursor, dot formation was observed only above +3.7(±0.2) V, in good agreement with the results reported in our earlier work about nanolithography on clean TiO₂(110) substrate (E. Kriván, A. Berkó: J. Vac. Sci. & Tech. B 15(1) (1997)25). By applying voltages in the range of 3.1-3.5 V, a systematic enlargement of the created nanodots was found in the range of 2-20 s of duration and 0.01-1.0 nA of tunneling current. The I-V curves detected on the top of the nanodots have shown that the created features are of insulator character. This observation indicates that the decomposition of Mo(CO)₆ is also accompanied by oxidation of the deposited Mo species.     

Interaction of oxygen with nanocomposites made of n-type conducting polymers and carbon nanotubes: role of charge transfer complex formation between nanotubes and poly(3-octylthiophene)

Photo-induced conductivity changes in n-doped poly(3-octylthiophene) (P3OT)/single-walled carbon nanotube (SWNT) composites have been examined. When exposed simultaneously to ultraviolet (UV) light and oxygen, carbon nanotubes exhibit photo-induced oxidation. An analysis of n-doped P3OT/SWNT composite exposed to oxygen/UV shows that conductivity increases and that charge carrier mobility is governed by the formation of a charge transfer complex. Possible sites of oxygen photoadsorption and its implications on the observed electrical properties of nanocomposite are considered.     

Use of fluorescence to probe the surface dynamics during disorder-to-order transition and cluster formation in dihalonaphthalene-water thin films on Al2O3(0001)

Amorphous dihalonaphthalenes that are prepared by vacuum deposition onto a cold Al₂O₃ surface form electronically excited dimers when optically pumped, and their emission is characteristically red-shifted, broad and featureless compared to the monomeric fluorescence. If the surface is heated, the adlayer undergoes a disorder-to-order transition at a temperature characteristic of the molecule. Since pure crystalline dihalonaphthalenes typically fluoresce and do not exhibit excimeric features, the transition was studied by taking advantage of the changes in the spectral characteristics of the adlayer. These included transmittance, and emission from fluorescence and excimer. The combination of these methods allowed a close look at the surface dynamics of molecules on the surface of Al₂O₃ as the adlayer was heated from the deposition temperature to desorption.If a bilayer is formed by depositing water onto the surface with the organic adlayer on top, water, with its lower desorption energy, can be made to percolate into the organic layer. The optical probes indicate that the water clearly associates with the organic molecules while the excess water desorbs. By varying the coverage of either the water or the dihalonaphthalene, the stoichiometric composition of the cluster can be determined and are reported here.     

CO sensing with SnO2 thick film sensors: role of oxygen and water vapour

The paper investigates the gas response of nanocrystalline SnO₂ based thick film sensors upon exposure to carbon monoxide (CO) in changing water vapour (H₂O) and oxygen (O₂) backgrounds. The sensing materials were undoped, Pt- and Pd-doped SnO₂. We found that in the absence of oxygen, the sensor signal (defined as the ratio between the resistance in the background gas, R₀ and the resistance in the presence of the target gases, R, namely R₀/R) have the highest values. These values are higher for doped materials than for the undoped ones. The presence of humidity increases dramatically the sensor signal of the doped materials. In the presence of oxygen, the sensor signal decreases significantly for all sensor materials. The results indicate that there is a competitive adsorption between O₂ and H₂O related surface species and, as a result, different sensing mechanisms can be observed for CO.     

The adsorption of O on (001) and (111) CdTe surfaces: A first-principles study

Density-functional theory and a pseudopotential plane-wave approach are employed to study the structural and electronic properties of oxygen on CdTe (001) and (111) surfaces. The energetically favored configuration for oxygen adsorption on CdTe (001) is that where the O adatoms are located at the Cd-terminated B site, while O adatoms are at the Cd-terminated H₃ site of CdTe (111) surface among the structures examined. Some possible surface defects are also examined on CdTe (001) and (111) surfaces. Oxygen can easily diffuse into the CdTe substrate at the (111) surface compared with the (001) surface.     

继续发挥0328型高压氧气压缩机的作用

032 8型氧压机是杭氧 2 0世纪 5 0年代的产品 ,现在已经落后 ,建议两台 0 32 8氧压机串接使用 ,稍加改造 ,可继续发挥作用。     

Transmission electron microscope observation of Si deposited on W(110) surface

The (110) surface of a thin W crystal deposited with Si has been investigated by using a transmission electron microscope (TEM). It was found that an ordered Si–W alloy layer with a regular periodic arrangement of antiphase boundaries (APBs) is formed, as a result of intermixing of deposited Si with the W substrate at room temperature (RT). A crystal structure model of this W–Si superstructure is proposed in this study. After 800°C annealing of Si deposited at RT, grains of tetragonal WSi₂ are formed on the W–Si ordered alloy layer. Grains of WSi₂ are also formed when Si is deposited on a W substrate maintained at 900°C. These WSi₂ grains have epitaxial orientation relationships with the W(110) substrate as follows: (110)W//(01 ) WSi₂ and [001]W//[100]WSi₂.     

Kinetics and equilibrium isotherms of adsorption of Pb(II) and Cu(II) onto raw and arginine-modified montmorillonite

Arg-Mt, was fabricated by modifying sodium montmorillonite (Na-Mt) with Arginine monohydrochloride (Arg salt), to adsorb Pb(II) and Cu(II) in aqueous solution. The X-ray powder diffraction (XRD), Fourier transform infrared (FTIR) spectrum, thermal analysis (TG/DTG), Brunauer-Emmett-Teller (BET) and Scanning electron microscope (SEM) were employed to investigate the properties of Na-Mt and Arg-Mt. The effects of the amount of modifier, pH value, the initial concentration of M(II), temperature and contact time were tested in a single adsorption system. The isotherm model was well matched with the Langmuir curve and the kinetic adsorption fitted well with the pseudo-second-order rate equation. The saturated adsorption of Pb(II) and Cu(II) by Arg-Mt were 124.69 and 29.15?mg/g, respectively, which were higher than that of Na-Mt (89.08 and 23.93?mg/g). The thermodynamic equation indicated that the adsorption process was spontaneous, endothermic, and the randomness of the samples changed a little after adsorption. The adsorption capacity of heavy metal ions in the binary co-adsorption system was poor than single adsorption system. Furthermore, the adsorbed M(II) onto Arg-Mt can hardly be dissolved under weak acidic condition (pH?>?4) according to the desorption experiments. High-efficiency and low-cost make Arg-Mt to be used in the removal of heavy ions in aqueous solution.     

Ab initio simulation of Si-doped GaAs(110) cross-sectional surfaces

We study different configurations of the (110) cross-sectional surface of Si-doped GaAs, from the isolated Si donor up to an entire donor–acceptor Si bilayer embedded along the (001) growth direction. Electronic potentials, density of electronic states, cross-sectional scanning tunneling microscopy (XSTM) images are calculated using first-principles numerical simulations. Doping configurations with compensating Si impurities in cationic and anionic sites, such as the donor–acceptor bilayer, are characterized by XSTM images with bright signal at negative bias, strongly attenuated when the bias is reversed. These features are characteristic of real samples above the onset of self-compensation. The comparison of the experimental images with the numerical simulations allows to shed light on the microscopic picture of self compensation hitherto associated to a variety of mechanisms – including the formation of complexes of Si with native defects – and to uniquely attribute the observed experimental features to Si donor–acceptor configurations.     

Barrier height and surface states at cleaned InSb(110) surfaces

The electronic properties of p-InSb(110) surfaces which were cleaned by the ion bombardment annealing technique are investigated by measurements of the integral and differential field effects. The field-induced changes in surface conductivity imply inversion layers with electron conduction in the space charge layer. The analysis of the experimental results yields the barrier height at the surface and the term spectrum of surface states. The general shape of the surface state density per energy interval shows a disorder-dependent continuous distribution with a minimum about midgap and increasing tails towards the bulk band edges. Near the conduction band minimum a peaking distribution of donor-type surface states is superimposed on the continuous distribution depending on the ion bombardment annealing conditions. The nature of the spectrum of surface states is discussed on the basis of intrinsic and extrinsic states.     

Cu(Ⅰ)/AC(HZSM)吸附剂的制备及变压吸附CO的性能研究

选择活性炭(AC)或分子筛(HZSM-5)为吸附剂载体,采用等体积浸渍法制备Cu(I)/AC(HZSM)吸附剂.利用比表面积(BET)及H2程序升温还原(H2-TPR)表征手段.结合固定床评价了装置,研究了载体类型、预处理方法以及还原温度对吸附剂性能的影响.结果表明,以活性炭为载体时吸附性能优于分子筛为载体时的吸附性能;水洗处理降低了吸附剂的吸附能力;吸附剂原位活化还原温度过低不利于Cu2+→Cu+的还原,350℃时吸附剂的吸附性能最好.     

FTIR spectroscopy of hydrogen, carbon monoxide, and methane adsorbed and co-adsorbed on zinc oxide

Adsorption of dihydrogen, carbon monoxide and methane, and co-adsorption of H₂/CO, H₂/CH₄ and CO/CH₄ on zinc oxide was studied by means of Fourier transform infrared spectroscopy. Besides the already known dissociation of dihydrogen and molecular adsorption of CO, methane was found to be adsorbed molecularly on coordinatively unsaturated Zn²⁺ ions. Adsorption lowers the CH₄ symmetry from T_d to C_3v, which is reflected in activation of the v₁ (symmetric stretching) mode and discrete frequency shifts of the v₃ (antisymmetric stretching) and ν₄ (bending) modes. Co-adsorption of the above gases on ZnO having pre-adsorbed hydrogen results, in all cases, in a bathochromic shift of the v(Zn–H) band and a hypsochromic shift of the v(O–H) band, which originally appear at 1710 and 3492 cm⁻¹, respectively. The magnitude of these shifts depends upon the nature of the co-adsorbed gas.