Enhanced surface evolution induced by the molecular desorption in dodecanethiol self-assembled monolayer on Au(1 1 1)

The evolution of the surface structure in dodecanethiol self-assembled monolayer on Au(1 1 1) substrate has been studied with ultra high vacuum scanning tunneling microscopy at several temperatures. The structure of substrate Au(1 1 1) surface changed suddenly at a temperature of 110 °C. The enhanced mobility of the substrate gold atoms at this temperature is attributed to the desorption of the dodecanethiol molecules.     

Thermal reactions of 2-iodoethanol on Cu(1 0 0)

Temperature-programmed reaction/desorption, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy have been employed to investigate the reactions of ICH₂CH₂OH on Cu(1 0 0) under ultrahigh-vacuum conditions. ICH₂CH₂OH can dissociate on Cu(1 0 0) at 100 K, forming a -CH₂CH₂OH surface intermediate. Density functional theory calculations predict that the -CH₂CH₂OH is most probably adsorbed on atop site. -CH₂CH₂OH on Cu(1 0 0) further decomposes to yield C₂H₄ below 270 K. No evidence shows the formation of -CH₂CH₂O- intermediate in the reactions of ICH₂CH₂OH on Cu(1 0 0) in contrast to the decomposition of BrCH₂CH₂OH on Cu(1 0 0) and ICH₂CH₂OH on Ag(1 1 1) and Ag(1 1 0), exhibiting the effects of carbon-halogen bonds and metal surfaces.     

Desorption of H ions from water chemisorbed on Si(100) by O 1s excitation - an Auger electron-photoion coincidence spectroscopy study

Auger electron-photoion coincidence (AEPICO) spectroscopy, which has been recently developed and proved to be a very powerful technique for investigating the dynamics of desorption induced by the core-level excitation, is applied to the investigation of Auger-stimulated ion desorption from the chemisorbed-water-Si(100) surface induced by O 1s excitation. It is shown that the fast relaxation of the excited state with a core hole and an excited electron takes place before the core hole decay, and that the desorption yield is enhanced by the shake-up (and/or shake-off) excitation. The relative cross-section for Auger-stimulated ion desorption is estimated, and is shown to increase as holes are created at deeper levels of the valence bands as the final state of the Auger decay. A comparison is also made with condensed H₂O.     

Absolute desorption yields of metastable atoms from the surface of solid rare gases induced by exciton creation

Absolute yields of the metastable excited atoms desorbed from the surfaces of solid Ne and Ar by the creation of surface and bulk excitons have been measured using monochromated synchrotron radiation as a selective excitation source. We have obtained the absolute yields of (2.3 ± 0.7) × 10⁻³, (1.4 ± 0.4) × 10⁻³, and (7.8 ± 2.3) × 10⁻⁴ atoms/photon at the excitation of S1, B1 and S′ exciton for Ne, respectively, and 1 × 10⁻⁵ atoms/photon at S1 excitation for Ar. The probability for metastable atom desorption is found to be about 2 to 10% at the excitation of S1 exciton on the surface of solid Ne.     

Desorption of metastable species induced by electronic excitation at the surface of solid krypton with physisorbed hydrogen

The effect of the physisorbed hydrogen molecules on the electron stimulated desorption of metastables from the surface of solid Kr was investigated. At the clean surface of solid Kr, the desorption of Kr metastables occurs only through an excimer dissociation mechanism. Physisorption of hydrogen molecules causes the following effects: (1) the total desorption yield of the metastable species increased by an order of magnitude or more; (2) metastable Kr, which is probably desorbed through the cavity ejection mechanism, emerges; (3) metastable Kr by excimer dissociation is also enhanced; and (4) a new metastable species, which seems to be composed of metastable hydrogen molecule, appears.     

Hopping motion of chlorine atoms on Si(1 0 0)-(2 × 1) surfaces induced by carrier injection from scanning tunneling microscope tips

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 V_S∼+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.     

Structure and reactivity of GaAs surfaces

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.     

吸附树脂对紫背天葵的水溶性色素精制研究

研究吸附树脂吸附精制紫背天葵红色素的方法和工艺。以吸附量、解吸量为指标,在pH=7时吸附,确定出S-8极性树脂和盐酸-乙醇溶液为最佳吸附剂和解吸剂。正交动态吸附和解吸实验结果表明,当原花液浓度3g/L,吸附流速3ml/min,树脂床层径高比1:1时,树脂对色素的吸附量最大;以盐酸-乙醇为解吸剂,解吸液用量30ml/g,解吸流速是1/5BV。经树脂吸附精制后的色素色价是未精制色素的3.74倍。     

Measurements of the desorption rate of sodium dodecyl sulfate from nylon particles by the stopped-flow method

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.     

射频溅射制备的多晶ZnO膜表面氧的吸附和脱附

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。