TOF-SIMS study of alkanethiol adsorption and ordering on gold

A systematic study of alkanethiol self-assembly on gold was undertaken with the time-of-flight-secondary ion mass spectrometry (TOF-SIMS) technique. Following adsorption, the TOF-SIMS spectra exhibit sulfur-containing peaks (specially AuxSx clusters) and a rise of all hydrocarbon peaks (CxHy). But the most specific peaks are those directly related to the adsorbed molecules (M) such as deprotonated monomers (M-H)(-), thiolate (MAu-). dimers (M2Au-), trimers (M3Au2-) and even tetramers (M4Au3-) By examining the ion yield of the most relevant fragments as a function of adsorption time, it is possible to follow the self-assembly kinetics for all the alkanethiols chosen. The hydrocarbon and Au,S, peak intensities quickly rise and reach a saturation level after typically an adsorption period of a few minutes. However, the oligomer fragments exhibit a much slower rise and reach saturation only after a few hours. This observation corroborates the widely accepted theory of alkanethiol adsorption on gold, starting with a fast adsorption of a disordered layer followed by a slower phase of monolayer self-assembly leading to a high packing of the alkane chains. The oligomer ions clearly reflect, to some extent, the degree of organization of the monolayer, whereas hydrocarbon and AuxSy, clusters just indicate the chemical changes at the surface. (C) 2001 Elsevier Science B.V. All rights reserved

ToF-SIMS study of organosilane self-assembly on aluminum surfaces

In order to understand the adsorption and self-assembly of organosilanes, we have studied the adsorption of octyltrichlorosilane (OS) and ocradecyltrichlorosilane (OTS) on an aluminum surface, naturally oxidized. The self-assembled monolayer (SAM) formation was followed with the time-of-flight-secondary ion mass spectrometry (ToF-SIMS) technique. The adsorption is readily detected by means of the Si-containing ions, such as SiH+, SiH-, SIOH ' or SiO2-. Heavier ions that carry information on the surface structure were also identified, such as C8H17SiO2- for an OS adsorption or C18H37SiO2- for an OTS adsorption, The adsorption kinetics can be easily followed by monitoring several characteristic fragments as a function of the adsorption time. The OS adsorption on aluminum appears to have an oscillatory behavior, with a fast adsorption during the first minute followed by a desorption, then a slow adsorption again. All the Si-containing peaks reflect this trend. A possible model that explains the oscillation is given. The aluminum oxide fragments of the type AlxOyHz- exhibit a dramatic decrease with increased coverage, due to the reaction of the active surface sites with the: silanols. Interestingly. the OTS adsorption appears to he monotonic, with a coverage slowly increasing with time. The final achieved coverage is more complete with OTS than with OS. The ToF-SIMS technique appears to be well suited to study the chemical changes and the degree of surface coverage during the adsorption. (C) 2001 Elsevier Science S.V. All rights reserved

Corrosion Behavior of Reinforcing Steel in Concrete Subjected to Chloride Contamination By EIS

　应用电化学阻抗谱(EIS)研究环境介质中氯离子对混凝土中钢筋腐蚀行为的影响.结果表明,在测量的频率范围内,钢筋混凝土体系的阻抗谱图包含两个时间常数,分别对应于界面的双电层和钢筋表面的混凝土保护层.其低频段的半圆有些压扁,表明界面双电层的充放电行为偏离理想电容器,可归因于钢筋表面的不均一性.在浸泡后期,低频段出现拖尾,同时电荷转移电阻Rct减小了近两个数量级,这是由于钢筋表面的钝化膜已经破裂,发生活性腐蚀,况且氯离子浓度的增大加速了腐蚀发展过程.讨论了混凝土中在钢筋腐蚀发生,发展的过程中,其腐蚀电位Ecorr以及等效电路中的Rct和Warburg阻抗等元件的变化特征.Electrochemical impedance spectroscopy(EIS) was employed to study the influence of chloride on the corrosion behavior of reinforcing steel in concrete.In Nyquist plot,the spectrum consists of two semicircles,indicating that the reinforced concrete system contained two time constants,one derived from electrical double layer of reinforcing steel and the other from the deposition film of concrete layer.The depressed semicircle in lower frequency featured the non_faradic behavior of the electrical double layer (EDL) deviated from idea capacitor due to diffusive effect which was attributed to the surface roughness of rebar and the inhomogenity of concrete layer.Then the EDL was denoted by a constant phase element (CPE) other than a capacitor in the equivalent circuit.At the late stage of immersion,a new element,Warburg resistance W evolved along with dramatic decrease in the value of polarization resistance,Rp,convincing the break down of the passive film and the initiation of active corrosion.The increase of [Cl-] in external solution prominently accelerated this trend.作者联系地址：厦门大学化学系固体表面物理化学国家重点实验室,厦门大学化学系固体表面物理化学国家重点实验室,厦门大学化学系固体表面物理化学国家重点实验室 福建厦门361005 ,福建厦门361005 ,福建厦门36100

CCDC 857213: Experimental Crystal Structure Determination

Related Article: Bin Mao, Yining Ji, M.Fananas-Mastral, G.Caroli, A.Meetsma, B.L.Feringa|2012|Angew.Chem.,Int.Ed.|51|3168|doi:10.1002/anie.201109075,An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Probing the organization of adsorbed protein layers: Complementarity of atomic force microscopy, X-ray photoelectron spectroscopy and radiolabeling

Atomic force microscopy (AFM) has been used to investigate the organization of the collagen layer present on polymer substrata after adsorption and drying, while the adsorbed amount was monitored using X-ray photoelectron spectroscopy (XPS) and radiochemical measurements. Differences in the organization of the adsorbed collagen layer (surface coverage, layer thickness) observed by AFM fitted well with those found by models obtained from XPS and radiolabeling data. (C) 1999 Elsevier Science B.V. All rights reserved

Synergetic effect of Te2MoO7 and MoO3 (WO3) oxides in the partial oxidation of propylene

This paper presents the synergetic effect of Te2MoO7 and MoO3 (WO3) in the partial oxidation of propylene to acrolein. The study found that the addition of MoO3 (or WO3) to Te2MoO7 greatly promoted the propylene conversion and acrolein yield. As the results of the investigation revealed, the higher catalytic performance could be attributed to the increased acidity, which is beneficial for the adsorption of propylene.Zhejiang Normal University [ZC304008169