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61.
Injection of tunneling electrons and holes from the probe tips of a scanning tunneling microscope was found to enhance the hopping motion of Cl atoms between neighboring dangling-bond sites of Si dimers on Si(1 0 0)-(2 × 1) surfaces, featured by the rate of hopping linearly dependent on the injection current. The hopping rate formed peaks at sample biases of VS∼+1.25 and −0.85 V, which agree with the peaks in the local density of states spectrum measured by scanning tunneling spectroscopy. The Cl hopping was enhanced at Cl-adsorbed sites even remote from the injection point. The Cl hopping by hole injection was more efficiently enhanced by sweeping the tip along the Si dimer row than by tip-sweeping along the perpendicular direction. Such anisotropy, on the other hand, was insignificant in the electron injection case. All of these findings can be interpreted by the model that the holes injected primarily into a surface band originated from the dangling bonds of Si dimers propagate quite anisotropically along the surface, and become localized at Cl sites somehow to destabilize the Si-Cl bonds causing hopping of the Cl atoms. The electrons injected into a bulk band propagate in an isotropic manner and then get resonantly trapped at Si-Cl antibonding orbitals, resulting in bond destabilization and hopping of the Cl atoms. 相似文献
62.
First the analytical tools, preparation methods and surface crystallography of clean GaAs surfaces are briefly reviewed. Besides the usual methods of cleaving, ion bombardment and annealing, molecular beam epitaxy is mainly used as a growth method under UHV conditions, and has brought a manifold of differently reconstructed structures on the same crystallographic surface, depending on the exact experimental conditions during growth. Quantitative analysis of the surface composition by AES gives the result that these structures differ only in the amount of As in the topmost layer. From the combination of theoretical LEED analysis, UPS results and arguments considering the different physicochemical nature of Ga and As atoms, rehybridisation of the surface atomic bonds emerges as the driving force for reconstruction: the surface Ga atoms try to assume a trivalent planarsp2 and the As atoms a trivalentp3 configuration with three mutually perpendicularp-bonds. The better this rehybridised configuration can be achieved, the better is the chemical stability of the respective structure. The sticking coefficient for oxygen, although generally low, thus varies between ~10-4 and <10-9, depending on the crystallographic surface and, on the same surface, on the degree of surface bond saturation given by the respective structure. However, it emerges that, at least on As-depleted polar surfaces, adsorption proceeds via a mechanism of removal of Ga atoms during exposure and adsorption on the defect sites created in this way. The existence of such a complicated mechanism is consistent with the difficulties arising with the preparation of thick stoichiometric oxide layers, the preparation methods and properties of which are reviewed briefly in the last section. 相似文献
63.
64.
The desorption kinetics of sodium dodecyl sulfate (SDS) from nylon particles was investigated by applying the stopped-flow technique. A stopped-flow spectrophotometer commercially available was modified in order to study the desorption kinetics of ionic surfactants from solid surfaces in aqueous solutions. The modification provided a mixing cell with platinum electrodes for electric conductivity detection. Nylon particle suspensions containing various concentrations of SDS were rapidly diluted with distilled water by using the modified mixing apparatus. The changes in specific electric conductivity with time were monitored by a memory-recorder system. It was found that the rate constant in the early stage of desorption could be accurately determined by the modified stopped-flow method. 相似文献
65.
多晶的六角密排的c轴平行于衬底的ZnO膜已用射频溅射的方法制备出来,一电场感应的氧吸附在这些膜上被观察到由紫外光照射或与Ar离子反应所产生的氧的脱附可使膜的电导率增加6-7个数量级,并且一个积累层在膜的表面显现出来。 相似文献
66.
采用解析电子轰击质谱对电弧法合成的稀土富勒烯衍生物的提取液进行了质谱分析,有效地检测到富勒烯,稀土富勒烯单电荷、双电荷的分子离子峰。利用同位素贡献确证了某些稀土富勒烯的生成。采用高电流瞬间解析样品,使得谱图中的谱峰强度更加真实地反应出提取液中各组分的相对含量。 相似文献
67.
The practical importance of alloy surfaces in catalysis, corrosion andother aspects of materials performance is widely recognized. What is needed now is sufficient knowledge of the relationship between externally controllable factors — alloy composition, temperature, environment — and surface properties — composition, structure, chemical activity — to control materials performance in these applications. Our purpose here is to review progress in determining and predicting the relationship between one surface property, composition, and certain externally controllable variables: overall composition, temperature, environment and physical form.We find that theoretical treatments of metal alloy surface composition now include essentially all significant physical effects and can predict values for most parameters of interest. Though improvements are still possible, the accuracy of predictions is more often limited by uncertainties or absence of the basic data for the calculations (e.g., thermochemical values) than by the models themselves.Alloy surface composition can now be measured well. The first monolayercomposition of large alloy slabs can be determined quantitatively over a wide temperature range in ultra-high vacuum. Difficulties with specimens of practical interest still challenge experimentalists. Among these are supported catalysts, surfaces under chemisorbed layers and composition of layers below the first. Significant progress is being made and we expect the next few years will see success. 相似文献
68.
《Analytical letters》2012,45(3):303-311
Abstract Field desorption mass spectra of Technetium and Rhenium anionic coordinate complexes have been obtained. lonization was principally by electron extraction from the anion, cation or neutral anion-cation pair, or by cation attachment to the intact molecule. The spectra were generally simple and allowed confirmation of known of proposed coordinate complex structures. 相似文献
69.
Effective equations of motion of a surface atom placed in an anharmonic surface potential are derived for three kinds of substrates (i) continuous dispersionless, (ii) discrete with nearest neighbours harmonic interactions, and (iii) a substrate showing a strong spatial dispersion. The resulting equations of motion are differential equations in the case (i) and Volterra Integro-Differential Equations (VIDE) in the cases (ii) and (iii). Examples of non-linear surface response to phonons coming from the bulk are given for the dispersionless substrate. 相似文献
70.
Xueyang Wang Xiuqiang Li Guoliang Liu Jinlei Li Xiaozhen Hu Ning Xu Wei Zhao Bin Zhu Jia Zhu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(35):12182-12186
Harvesting water from air is a promising strategy for fresh‐water production, and it is particularly desirable for areas that lack direct access to clean water. While high‐concentration liquid sorbent is well‐known for high sorption, it has not been widely used for atmospheric water collection, being primarily limited by the difficulty in desorption. Interfacial solar heating based on a salt‐resistant GO‐based aerogel is now shown to enable a high‐concentration liquid sorbent (CaCl2 50 wt % solution) based atmospheric water generator. Fresh water (2.89 kg m?2 day?1) can be produced at about 70 % relative humidity, with only solar energy input and energy efficiency of desorption as high as 66.9 %. This low‐cost and effective approach provides an attractive pathway to extract water from air, to relieve the thirst of arid, land‐locked, and other areas where fresh water is scarce. 相似文献