Comparison of Si-O-C interfacial bonding of alcohols and aldehydes on Si(111) formed from dilute solution with ultraviolet irradiation

Aliphatic alcohols and aldehydes were reacted with the Si(111)-H surface to form Si-O-C interfacial bonds from dilute solution by using ultraviolet light. The resulting monolayers were characterized by using transmission infrared spectroscopy, spectroscopic ellipsometry, and contact angle measurements. The effect of different solvents on monolayer quality is presented. The best monolayers were formed from CH(2)Cl(2). The optimized monolayers were thoroughly characterized to determine the film structure and monolayer stability. The UV-promoted, alcohol-functionalized, and aldehyde-functionalized monolayers are of comparable quality to those previously prepared by other means. Although both molecules are tethered through a Si-O-C bond, the film reactivity is distinctly different with the aldehyde films being more chemically resistant. The differences in chemical reactivity, vibrational spectra, hydrophobicity, and ellipsometric thickness between the alcohol and aldehyde monolayers are attributed to a difference in molecular coverage and monolayer formation.     

Initial formation of contact layers on Ni/SiC samples studied by XPS

This study deals with the quantitative assessment of the coverage and thickness of Ni silicide films formed during annealing of SiC substrates with sputtered thin films of Ni. The analytical approach involves the use of XPS and depth profiling by means of successive ion etchings and XPS analyses. For either 3 or 6 nm initial Ni film thickness, a 10 nm Ni₂Si product is formed. On top of this product, the C released is accumulated in a very thin (1–2 nm) film. In neither case, the Ni₂Si covers the whole surface, although the coverage is almost complete (～90%) in the latter case. For the greater initial Ni‐film thickness of 17 nm, the thickness of the Ni₂Si product corresponds well to the value of 25 nm expected from the Ni/Ni₂Si stoichiometric relationship. This thickness is significantly greater than a critical level and the film covers the whole surface. Carbon is similarly accumulated in a very thin layer on the top surface, although the major part of C (～70%) is found inside the main reaction product layer. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation of an A-type zeolite film on the surface of an alumina ceramic filter

An A-type zeolite film was prepared on the outer surface of an alumina ceramic filter by repeated hydrothermal syntheses using the same sample (referred to as repeated batch synthesis). The thickness of the film was found to increase to 35 μm by precipitating the crushed zeolite crystal on the ceramic filter and to 50 μm by precipitating the crushed alumina before repeated batch synthesis. The structure and atomic composition of the zeolite film obtained were found to the same as those of the corresponding original zeolite using several spectrometric methods: X-ray diffraction (XRD), ²⁹Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and electron-probe microanalysis (EPMA). The morphology and thickness of the zeolite film were dependent on the reaction time and temperature, and especially on the types of silica and alumina sources. The preferred silica and alumina sources were Na₂SiO₃ and Al(OH)₃, respectively; these are different from the usual sources for the synthesis of powdery A-type zeolites.     

C(膜)/Si(SiO2 )(纳米微粒)/C(膜)热处理的形态及结构分析

用直流辉光溅射+真空镀膜法制备了一种新型结构的硅基纳米发光材料- C(膜)/Si(SiO2)(纳米微粒)/C(膜)夹层膜,并对其进行了退火处理.用TEM、 SEM、 XRD和XPS对其进行了形态结构分析.TEM观察表明: Si(SiO2)纳米微粒基本呈球形,粒径在30 nm左右.SEM观察表明: 夹层膜样品总厚度约为50 μm,膜表面比较平整、致密.400℃退火后,样品表面变得凹凸不平,出现孔状结构; 650℃退火后,样品表面最平整、致密且颗粒均匀.XRD分析表明:制备出的夹层膜主要由SiO2和Si组成,在C原子的还原作用和氧气的氧化作用的共同作用下, SiO2和Si的含量随加热温度的升高而呈现交替变化: 400℃时, C的还原作用占主导地位, SiO2几乎全部被还原成了Si,此时Si含量最高; 400～650℃时,氧化作用占主导地位, Si又被氧化成SiO2, Si含量降低, SiO2含量逐渐上升,在650℃达到最高.XPS分析表明: 在加热过程中, C原子逐渐扩散进入Si(SiO2)微粒层,在650℃与Si反应生成了新的SiC.     

Photochemistry on ultrathin metal films: strongly enhanced cross sections for NO2 on Ag/Si(100)

The surface photochemistry of NO(2) on ultrathin Ag(111) films (5-60 nm) on Si(100) substrates has been studied. NO(2), forming N(2)O(4) on the surface, dissociates to release NO and NO(2) into the gas phase with translational energies exceeding the equivalent of the sample temperature. An increase of the photodesorption cross section is observed for 266 nm light when the film thickness is decreased below 30 nm despite the fact that the optical absorptivity decreases. For 4.4 nm film thickness this increase is about threefold. The data are consistent with a similar effect for 355 nm light. The reduced film thickness has no significant influence on the average translation energy of the desorbing molecules or the branching into the different channels. The increased photodesorption cross section is interpreted to result from photon absorption in the Si substrate producing electrons with no or little momenta parallel to the surface at energies where this is not allowed in Ag. It is suggested that these electrons penetrate through the Ag film despite the gap in the surface projected band structure.     

Size‐Dependent Surface Migration of Au Alloys on Si Nanowires at Different Cooling Rates

Understanding metal alloy migration in metal‐catalyzed nanowires growth is a prerequisite for improving its potential applications in the field of nanodevices. Here, we explored the surface migration of Au alloys in vertically aligned Si nanowires with different cooling rates. We varied the diameter of Au alloys by controlling the thickness of Au film as a catalyst for SiNW growth, and found that the behavior of Au alloys migration is dependent on size of Au alloys. In addition, the size‐dependent migration mechanism of Au alloys was investigated at different cooling rates, which is related to different Au‐Si eutectics.     

Ultrathin cobalt silicide film formation on Si(100)

The interfacial reaction between ultrathin Co film and substrate Si(100) was studied by in situ XPS using monochromatized Al Kα. When the Co is deposited on Si(100) at room temperature, CoSi₂ is formed during the initial stage of Co deposition and then metallic Co starts to grow sequentially. For 8 ML Co deposition on Si(100) the interfacial reaction layer is relatively thin compared with the pure Co overlayer, which is not involved in the interfacial reaction in depth. The Co layers change rapidly to CoSi layers after annealing at 270°C, and then CoSi₂ layers form after annealing at 540°C for 2 min. The CoSi₂ layers are changed to CoSi₂ islands by post‐annealing at >650°C. Copyright © 2003 John Wiley & Sons, Ltd.     

基底界面效应对聚苯乙烯薄膜分子运动行为的影响

本文研究了Si／Si02、Si／Si—H基底与聚苯乙烯（Ps）之间的界面相互作用对Ps薄膜的玻璃化转变及相关力学性能的影响．结果显示,无论何种基底,Ps薄膜的玻璃化转变温度（L）都随其厚度降低而降低．但相同厚度（〈110nm）下,以Si／Si-H为基底时Ps薄膜的瓦比以Si／Si02为基底的PS薄膜高．Si／Si02表面Ps薄膜疋开始下降的临界厚度为110nm,远高于以Si／Si—H为基底时的40nm．对Ps薄膜的膨胀系数和弹性模量进行研究,也得到相似的临界厚度．另外,与Si／Si02基底相比,在Si／Si-H上的Ps薄膜具有更低的膨胀系数以及较高弹性模量．可能原因是Si／Si-H与Ps具有较强的相互作用,限制了该界面分子的运动能力,导致基底／PS界面效应对薄膜分子运动的影响力增强,造成该薄膜瓦的厚度依赖性下降,并呈现出相对较硬的力学特征．     

MoO3在Al2O3薄膜表面扩散的研究

氧化物和盐类在高比表面载体上的单层分散现象已被大量实验所证实［１］．ＭｏＯ_３在γ－Ａｌ_２Ｏ_３等高比表面载体上的分散已经研究很多,近来的研究证实ＭｏＯ３等在α－Ａｌ２Ｏ３等小比表面载体上也能自发单层分散［２］,但是分散的过程仍然缺乏直接的观察研究．本工作通过多种表面分析方法首次研究了ＭｏＯ３在平整无定形的Ａｌ２Ｏ３薄膜上的扩散过程以及影响因素．发现除温度升高外、水汽的存在对该扩散过程也有促进作用．１实验部分１．１样品的制备采用ＳＳ－３２００真空磁控溅射镀膜机,通入Ａｒ－Ｏ２作为反应气,直流磁控…     

Electrical and Optical Properties of MgO Thin Film Prepared by Sol-Gel Technique

MgO thin films with either (111) or (200) preferential orientation have been prepared on (100) Si substrates by sol-gel method after a heat-treatment at 800°C. The obtained (111) preferentially oriented MgO film has a dielectric constant of 7.0 with a loss factor of 5% and a dielectric strength higher than 8 × 10⁵ V/cm. The optical refractive index, which depends on the film thickness, is 1.71 when the film thickness is 260 nm. The surface structure of the Si substrate is believed to affect the preferential orientation of the sol-gel derived MgO film. Specifically, the microstructures at the interface indicate an interdiffusion of Mg, O, and Si between the film and the substrate.     

Water-barrier properties of mixed bis[trimethoxysilylpropyl]amine and vinyltriacetoxysilane films

X-ray and neutron reflectivity were employed to elucidate the morphologies of bis[trimethoxysilylpropyl]amine silane (A) and vinyltriacetoxysilane (V) mixed films on Si wafers at different A/V ratios, and the response of these films to saturated water vapor. Due to its insensitivity to chemical composition, X-ray reflectivity was used to assess the film density, whereas neutron reflectivity was used to probe water absorption and chemical change on exposure to water. NMR was employed to determine the reaction mechanism in neat AV mixtures and stoichiometry of the initial reaction. X-ray reflectivity reveals about 30% void volume in the films with the least void volume detected near stoichiometry. Grazing incidence small-angle scattering (GISAXS) shows that the void volume is at the molecular level, with no distinct pores. Neutron reflectivity on D2O-conditioned films shows that silane film is not an effective water barrier with about 30 vol % water being absorbed with only a slight thickness increase. Most water is physically absorbed in the void space with the least amount being absorbed near the stoichiometric A/V ratio. The scattering length density of the films almost returns to the virgin state after re-dry following D2O vapor exposure. The film thickness, however, remains at the water-vapor-conditioned state. The slight increase in scattering length density and irreversible thickness change after re-dry indicate some reaction with water during D2O conditioning. A D-rich layer is also observed at the air side surface in D2O-conditioned films regardless of A/V ratio.     

电沉积铁前对称交流电对阴极表面的影响

研究了低碳钢在镀铁溶液内经对称交流电处理后在表面形成活化膜的组成及厚度,观察了镀铁层与基体界面的形貌,结果发现,活化膜的厚度随活化电流密度而变化,当电流密度为７Ａｄｍ￣（－２）时,在表面形成了一个厚度为２０～２５ｎｍ的洁净活化膜,镀铁层与基体结合牢固。探讨了对称交流电对阴极表面的作用机理。     

Interfacial structure in thin water layers formed by forced dewetting on self-assembled monolayers of omega-terminated alkanethiols on Ag

A method for the spectroscopic characterization of interfacial fluid molecular structure near solid substrates is reported. The thickness and interfacial molecular structure of residual ultrathin D20 films remaining after forced dewetting on alkanethiolate self-assembled monolayers (SAMs) of 11 1-mercaptoundecanoic acid (11-MUA), 11-mercaptoundecanol (11-MUD), and undecanethiol (UDT) on Ag are investigated using ellipsometry and surface Raman spectroscopy. The residual film thickness left after withdrawal is greater on hydrophilic SAMs than on hydrophobic SAMs. This behavior is rationalized on the basis of differing degrees of fluid slip within the interfacial region due to different interfacial molecular structure. The v(O-D) regions of surface Raman spectra clearly indicate unique interfacial molecular properties within these films that differ from bulk D20. Although the residual films are created by shear forces and Marangoni flow at the three-phase line during the forced dewetting process, the nature of the films sampled optically must also be considered from the standpoint of thin film stability after dewetting. Thus, the resulting D20 films exist in vastly different morphologies depending on the nature of the water-SAM interactions. Residual D20 is proposed to exist as small nanodroplets on UDT surfaces due tospontaneous rupture of the film after dewetting. In contrast, on 11-MUD and 11-MUA surfaces, these films exist in a metastable state that retains their conformal nature on the underlying modified surface. Analysis of the peak intensity ratios of the so-called "ice-like" to "liquid-like" v(O-D) modes suggests more ice-like D20 character near 11-MUD surfaces, but more liquid-like character near 11-MUA and UDT surfaces. The creation of residual ultrathin films by forced dewetting is thus demonstrated to be a powerful method for characterizing interfacial molecular structure of fluids near a solid substrate under ambient conditions of temperature and pressure.     

钛金属有机物热解制备TiO2-SiO2复合膜及其光催化活性研究

混有一定量SiO_2溶胶的钛金属有机化合物膜液通过旋液成膜法制备前驱物膜 ，经热解得到TiO_2-SiO_2复合膜。于610 ℃焙烧15min所得复合膜(Ti:Si=9:1)经 SEM，XRD，UV-vis和XPS研究表明，膜面由30 nm * 200 nm大小的晶体粒子组成， 结构致密，膜厚约200 nm，其可见光透过率为玻璃基质的80%，膜表面Ti~(3+)OH~- 的比值为1.06。对不同SiO_2含量的膜液凝胶进行DSC分析显示，少量的SiO_2就能 显著提高TiO_2锐钛矿型晶相的形成温度。膜的光催化活性研究表明一定量的Fe~ (3+)有利于提高膜的光催化活性，但是如果以氯化物的形式加入则对光催化反应不 利，铬的氯化物同样如此。另外，在钛金属有机物热解制备TiO_2-SiO_2复合膜中 ，溶胶SiO_2不利于光催化反应，但是它可以改善膜的耐磨性。     

液相沉积法制备TiO2颗粒表面包覆SiO2纳米膜

研究了用液相沉积法在TiO2颗粒表面包覆SiO2纳米膜的过程.通过透射电镜(TEM)和酸溶实验分析,证实本实验在TiO2颗粒表面包覆了一层连续、致密的SiO2纳米膜.ζ-电位分析表明,颗粒表面只需少量包覆就可以显著改变颗粒表面的电动力学行为.采用 X射线荧光光谱分析仪（XRF）测定SiO2包覆量随包覆过程的变化.通过X射线光电子能谱（XPS）分析,获得Ti 2p、Si 2p及 O 1s电子结合能及其相对强度随包覆过程的变化规律,揭示硅酸分子在TiO2颗粒表面的包覆过程.分析表明,初期形成的活性硅酸分子与TiO2颗粒表面的羟基反应形成Ti－O－Si键,后期形成的硅酸分子与已键合在表面的硅酸发生缩合反应,形成连续致密的硅膜,膜层在陈化过程中继续缓慢生长.     

Facile interfacial electron transfer through n-alkyl monolayers formed on silicon (111) surfaces

Electron transfer (ET) kinetics through alkyl monolayers, formed on n-type Si(111) surface by the direct reaction of alkylmagnesium bromide (n-C_nH_2n+1MgBr, n=2, 6, 10, and 15) with hydrogen-terminated Si(111), was investigated in acetonitrile (MeCN) with anthraquinone (AQ) as the electrochemical probe. Cyclic voltammetric measurements indicate that the ability of the monolayer to block interfacial electron transfer increases with increasing alkyl chain length. In particular, the voltammetric behavior changes from non-rectifying (i.e., chemically reversible redox couple), to rectifying (i.e., diode-like when the reverse wave is pushed into the gap) with increasing chain length. The dependence of the logarithm of the electron transfer rate constant as a function on the number of carbons in the alkyl chain is not consistent with electron tunneling through the full thickness of the film. In fact, the measured constant, 0.05 ± 0.03 per methylene, is much smaller than the well-established tunneling constant, ∼1.0/CH₂ in the closely packed alkanethiol monolayers on gold suggesting permeation of the AQ into the film.     

Covalent molecular assembly of oligoimide ultrathin films in supercritical and liquid solvent media

An ultrathin film of oligoimide has been fabricated on amine-modified substrates of silicon and quartz through alternate layer-by-layer (LBL) assembly of pyromellitic dianhydride (PMDA) and diaminodiphenyl ether (DDE), with interlayer links established by covalent bonds. The assembly was formed in supercritical carbon dioxide (SCCO2) and in solution (dimethyl acetamide, DMAc), and the imidization reaction was performed by thermal and chemical methods, in benzene and in the supercritical medium. X-ray photoelectron and UV-visible absorption spectroscopies, atomic force microscopy (AFM), and ellipsometry were employed to study the interfacial chemistry, growth, morphology, and thickness of the assembled film. XPS analysis confirmed the sequential deposition of PMDA and DDE through formation of amic acids. At each deposition step, surface functionalities for the assembly of the next layer were generated. The interfacial chemical reaction was almost complete in the SCF (supercritical fluid) medium, as compared to the conversions observed in conventional assembly. Both the PMDA and DDE molecules were assembled in an organized manner, resulting in uniform surface morphology. Uniform film growth was revealed from the increase of UV absorption intensity and film thickness. The overall growth and quality of the films in SCF medium were greater than that for films formed in DMAc. The results of this novel study show that an environmentally friendly solvent can be used to obtain mechanically robust and thermally stable ultrathin films with little loss of material during the imidization step. In contrast to conventional deposition of the molecular layers that utilizes liquid solvents, use of SCCO(2) avoids solvent effects and posttreatment for solvent removal, while ensuring facile transport during contact.     

Effect of interfacial mobility on rupture of thin stagnant films on a solid surface due to random mechanical perturbations

Previous analysis of Narsimhan [G. Narsimhan, J. Colloid Interface Sci. 287 (2005) 624-633] for the evaluation of rupture of a nondraining thin film on a solid support due to imposed random mechanical perturbations modeled as a Gaussian white noise has been extended for partially mobile gas-liquid interfaces. The average rupture time of film is evaluated by first passage time analysis (as the mean time for the amplitude of perturbation to become equal to film thickness). The interfacial mobility is accounted for through surface viscosity as well as Marangoni effect. The mean rupture time for partially mobile gas-liquid interface, as characterized by two dimensionless groups, dimensionless surface viscosity and Marangoni number, lies between the two extreme limits for fully mobile and immobile films. The critical wavenumber for minimum rupture time is shown to be insensitive to interfacial mobility. However, the critical dimensionless surface viscosity and critical Marangoni number at which the behavior of thin film deviates from that of fully mobile film and the behavior approaches that of fully immobile film are smaller for higher Hamaker constants, smaller film thickness and smaller surface potentials.     

Solvent‐induced surface instability of thin metal films on a polymer substrate

The solvent‐provoked formation and evolution of thin film buckling‐delamination on a compliant substrate have been studied. The film surface is observed by an optical microscope showing a remarkable dynamic buckling‐delamination development and a subsequent stable branched‐straight state. It is revealed that the initiation, propagation, and the resulting patterns of film buckles are strongly dependent on the solvent type, film stress, interfacial adhesion, and film thickness. The buckling could be controlled further by a reasonable chemical solvent configuration and used to provide useful information for the pattern creation on polymer systems in diverse fields, such as micro/nanofabrication and optics.     

Thin Film Elastic Modulus of Degradable Tyrosine-Derived Polycarbonate Biomaterials and Their Blends

The integrity, function, and performance of biomedical devices having thin polymeric coatings are critically dependent on the mechanical properties of the film, including the elastic modulus. In this report, the elastic moduli of several tyrosine-derived polycarbonate thin films, specifically desaminotyrosyl ethyl tyrosine polycarbonates p(DTE carbonate), an iodinated derivative p(I(2)-DTE carbonate), and several discrete blends are measured using a method based on surface wrinkling. The data shows that the elastic modulus does not vary significantly with the blend composition as the weight percentage of p(I(2)-DTE carbonate) increases for films of uniform thickness in the range of 67 to 200 nm. As a function of film thickness, the observed elastic moduli of p(DTE carbonate), p(I(2)-DTE carbonate) and their 50:50 by mass blend show little variation over the range 30 to 200 nm.