Change in the interfacial reaction of Hf-silicate film as a function of thickness and stoichiometry

Medium energy ion scattering and high-resolution transmission electron microscopy are used to investigate the depth of the interfacial reaction of Hf-silicate film. The interfacial reaction is critically affected by the film thickness and the mole fraction of HfO(2) in silicate film. The interfacial compressive strain generated at the surface of the Si substrate is dependent on the film thickness during the postannealing process in film with a thickness of approximately 4 nm. Finally, the phase separation phenomenon demonstrates critically different behaviors at different film thicknesses and stoichiometries because the diffusion of Si from interface to surface is dependent on these factors. Moreover, the oxidation by oxygen impurity in the inert ambient causes SiO(2) top formation.     

Study of the growth process of in situ polyaniline deposited films

Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to approximately 25 nm. The film growth process was monitored by measuring the UV-vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponent n=3, thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition.     

Preparation and characterization of thin films of monomeric and polymeric octacyanophthalocyanines

Thin films were prepared on substrates, cleavage surface of KCl single crystal, and metallic copper, by reaction of 1,2,4,5-tetracyanobenzene with the substrate at various temperatures. The films were characterized by elemental analysis, IR, and UV/VIS spectroscopies. The films were observed by scanning electron microscopy. The films produced on copper at temperatures between 300 and 400°C consisted of copper octacyanophthalocyanine and its polymer with ladder structure. The ratio of polymer to monomer increased with elevating the reaction temperature. The films were composed of ribbon-like crystals. The film produced on copper above 450°C was composed of an amorphous and continuous layer of polymeric copper phthalocyanine. The film produced on KCl at temperatures between 250 and 350°C consisted of potassium octacyanophthalocyanine and its polymer with ladder structure. The film produced on KCl above 450°C was polymeric potassium phthalocyanine. Those films contained more metal content than that required stoichiometrical.     

Zur Analytik der photochemischen Oxidation schwimmender Ölfilme

The photochemical oxidation of oil films from about 1–100 μm thickness is indicated by an increase in carbonyl band extinction and a decrease in the concentration of the aromatic fraction. The aromatics are determined by way of fluorescence measurement (313/360 nm) on a thin-layer plate. The formation of polar reaction products (365/445 nm) is observed at the same time. The corresponding CH₂/CH₃ groups can be determined quantitatively by way of infrared spectroscopy at 2930 cm^?1. The photochemical changes taking place in the oil film as a function of its age develop in the sense of an exponential function.     

Role of capillary stresses in film formation

Stresses generated during film formation were deduced from the deflection of a copper cantilever coated with a drying latex. Experiments with particles of varying radii and glass transition temperatures (Tg) focused on conditions for which capillary stresses normal to the film deform the particles to close the voids. Soft particles (low Tg) formed continuous films, but hard ones (high Tg) produced fascinating arrays of cracks. For both soft and rigid particles, the lateral stresses were tensile and scaled on the surface tension divided by the particle radius. Clearly, tensile stresses in the plane of the film responsible for cracking arise from the same capillary pressure that drives compression in the normal direction. Solving the model (Routh & Russel 1996, 1999) for lateral flow of the fluid dispersion prior to close packing and deformation of the solid beyond close packing yields volume fraction, film thickness, and stress profiles for comparison with observations for both film-forming and film-cracking cases.     

Atom probe tomography characterization of thin copper layers on aluminum deposited by galvanic displacement

″Ultrathin″ metallization layers on the order of nanometers in thickness are increasingly used in semiconductor interconnects and other nanostructures. Aqueous deposition methods are attractive methods to produce such layers due to their low cost, but formation of ultrathin layers has proven challenging, particularly on oxide-coated substrates. This work focused on the formation of thin copper layers on aluminum, by galvanic displacement from alkaline aqueous solutions. Analysis by atom probe tomography (APT) showed that continuous copper films of approximately 1 nm thickness were formed, apparently the first demonstration of deposition of ultrathin metal layers on oxidized substrates from aqueous solutions. The APT reconstructions indicate that deposited copper replaced a portion of the surface oxide film on aluminum. The results are consistent with mechanisms in which surface hydride species on aluminum mediate deposition, either by directly reducing cupric ions or by inducing electronic conduction in the oxide, thus enabling cupric ion reduction by Al metal.     

Adsorption, desorption, and diffusion of nitrogen in a model nanoporous material. II. Diffusion limited kinetics in amorphous solid water

The adsorption, desorption, and diffusion kinetics of N2 on thick (up to approximately 9 microm) porous films of amorphous solid water (ASW) films were studied using molecular beam techniques and temperature programmed desorption. Porous ASW films were grown on Pt(111) at low temperature (<30 K) from a collimated H2O beam at glancing incident angles. In thin films (<1 microm), the desorption kinetics are well described by a model that assumes rapid and uniform N2 distribution throughout the film. In thicker films (>1 microm), N2 adsorption at 27 K results in a nonuniform distribution, where most of N2 is trapped in the outer region of the film. Redistribution of N2 can be induced by thermal annealing. The apparent activation energy for this process is approximately 7 kJ/mol, which is approximately half of the desorption activation energy at the corresponding coverage. Preadsorption of Kr preferentially adsorbs onto the highest energy binding sites, thereby preventing N2 from trapping in the outer region of the film which facilitates N2 transport deeper into the porous film. Despite the onset of limited diffusion, the adsorption kinetics are efficient, precursor mediated, and independent of film thickness. An adsorption mechanism is proposed, in which a high-coverage N2 front propagates into a pore by the rapid transport of physisorbed second layer N2 species on top of the first surface bound layer.     

Why is copper locally etched by scanning electrochemical microscopy?

The etching of thin copper films by scanning electrochemical microscopy (SECM) was investigated. It is not trivial that locally injected charge by an oxidized mediator will lead to dissolution of copper as the charge can easily be dissipated by lateral charge propagation. We studied the effect of different parameters, such as thickness of the Cu film and concentration of the mediator, on the efficiency of etching. The feedback current is the sum of three charge transfer contributions: diffusion of mediator species, chemical reaction on the surface and lateral charge propagation across the copper film. We have introduced an approach for isolating the lateral contribution and studied the parameters affecting the fate of the locally injected charge. We found that etching becomes effective once the lateral contribution cannot dissipate the locally injected charge. This occurs as the concentration of the etchant increases or the film thickness decreases. Measuring the steady-state current above Cu films with different thickness, allowed estimating the potential difference across the Cu area underneath the tip. We conclude that driving local processes, such as etching, depends on creating a mechanism which maintains the injected charge focused.     

固相配位化学反应研究LXVII．金属铜表面M－S（M＝Mo，W）簇合物膜的组成

采用ＦＴＩＲ、ＸＰＳ和ＡＥＳ研究了金属铜表面Ｍ－Ｓ（Ｍ＝Ｍｏ，Ｗ）簇合物膜。结果表明，Ｍｏ（Ｗ）与铜表面的Ｃｕ＿２Ｏ反应，形成了Ｍｏ（Ｗ）－Ｓ－Ｃｕ键；簇合物膜由Ｍｏ（Ｗ）、Ｓ、Ｃｕ、Ｏ元素组成，分别呈＋６、－２、＋１、－２价，膜为多分子层结构并保持ＭｏＳ＿４，或ＷＳ＿２单元，膜表面只有Ｃｕ、Ｏ而不存在Ｍｏ（Ｗ）、Ｓ．膜层厚度与反应时间有关，时间越长，膜越厚。膜为多组分的复杂体系，其颜色是各组分统计分布的结果。     

Aggregation of photolytic gold nanoparticles at the surface of chitosan films

Formation and aggregation of photolytic gold nanoparticles at the surface of chitosan (CTO) films have been investigated. When thin films of chloroauric acid salt of CTO were irradiated with UV light in wet air at room temperature for 10 min, gold nanoparticles of approximately 10 nm size are formed at the film surface. Detailed X-ray photoelectron spectroscopy (XPS) study and field emission type scanning electron microscopy (FE-SEM) observation have been carried out to characterize gold nanoparticles at the film surface. The shift of Au(4f) peak to the higher energy side and broadening of full width at half-maximum in the XPS spectrum are the direct evidence of the existence of gold atoms and small clusters in the early stage of photolysis. According to FE-SEM observation, growth in the particle diameter and aggregation of nanoparticles were observed after prolonged irradiation, and, finally, the film surface was densely covered with gold particles of 20-100-nm size. Gold atoms and clusters could move in the film and precipitate to the irradiated surface. Chemical composition analysis further suggests that gold particles at the surface are covered with an ultrathin CTO layer, which is partly oxidized by oxygen and chlorinated by chlorine during photochemical reactions.     

Photo-crosslinking and negative-type micropattern formation of a polymeric photobase generator containing phthalimido carbamate groups

The photo-crosslinking reaction of a polymeric photobase generator containing phthalimido carbamate (PC) groups was studied and applied to the formation of a negative type micropattern. The copolymer containing PC groups was prepared through the polymerization of methyl methacrylate and phthalimido methacryloxyethylcarbamate (PMC). The photochemical and cross-linking reaction of the copolymer film were studied using the UV and IR absorption spectral changes along with the normalized thickness measurements upon irradiation. The copolymer film was effectively cross-linked upon irradiation with 254 nm UV light, and the cross-linking reaction progressed further with increasing irradiation dose and the amount of PMC units in the copolymer. The photochemical formation of the isocyanato groups was evidenced by comparing the IR absorption spectral changes of the exposed and masked copolymer film. The photo-crosslinking reaction of the copolymer was further studied by using a model compound. The results indicated that the cross-linking reaction occurred because of the formation of urea-type chemical bonds, which were produced through the reaction of the photochemically produced isocyanato and amino groups in the copolymer. A negative micropattern was obtained by using the photo-crosslinking reaction.     

Vibrational and surface-enhanced vibrational spectra of 6-nitrochrysene

The infrared and Raman spectra of solids and thin solid films of 6-nitrochrysene, its electronic spectra, and resonance Raman scattering (RRS) obtained with UV-laser excitation at 325 nm are reported. The vibrational assignment is supported by ab initio computations at the B3LYP/6-311G(d, p) level of theory. The molecular organization in nanometric films evaporated onto smooth metal surfaces of silver and copper was probed using reflection-absorption infrared spectroscopy (RAIRS). The results of the surface-enhanced Raman scattering (SERS) and surface-enhanced infrared absorption (SEIRA) obtained from nanometric films evaporated onto silver island films are also discussed. It was found that the molecule efficiently interacts with silver island film surfaces, and that the interaction leads to extensive photochemical reaction at the metal surface under laser illumination.     

Uptake and UV-photooxidation of gas-phase polyaromatic hydrocarbons on the surface of atmospheric water films. 2. Effects of dissolved surfactants on naphthalene photooxidation

The adsorption and photochemical transformations of gas-phase naphthalene were studied in a flow-tube reactor with a view to understanding the photochemical reactions occurring in thin water films such as those of aerosols and fogs. Suwannee River fulvic acid (SRFA) was chosen as a surrogate for the surface active humic-like substances present in atmospheric water films. Experiments were performed on both 450 and 22 mum water films over a wide concentration range of SRFA (0-1000 mg.L-1). The effect of singlet oxygen on the reaction rate in the presence and absence of SRFA was ascertained. Naphthalene molecules can be bound to SRFA through hydrophobic interactions and be distributed in both the water and the SRFA regions. The rate constants for the photochemical reactions of naphthalene were fitted to a model that described the effect of SRFA in these two regions. The kinetic study on the 22 mum film revealed a greater surface reaction enhancement than for the 450 mum film at low SRFA concentrations. However, there was no surface reaction enhancement at high SRFA concentrations. To compare with SRFA, the effect of a conventional surfactant, sodium dodecyl sulfate, on the uptake and photochemical transformations of naphthalene was also studied.     

Kinetics of film formation by interfacial polycondensation

An approximate analytical model of film formation by interfacial polycondensation is presented. The analysis requires knowledge of a minimal set of certain kinetic parameters (monomer diffusivities and reaction rate constants) and reaction conditions (monomer concentrations and thickness of the unstirred layer). The process proceeds as a succession of two or three markedly different kinetic regimes. Each regime (insipient film formation, slowdown, and diffusion-limited growth) sets a different pattern of local polymer accumulation, with important implications for the structure of the emerging film. At the incipient stage, a loose polymer film begins to emerge in a fixed narrow region inside the boundary layer, followed by gradual densification of the middle part of the film. A condition for film formation is thus formulated on the basis of our analysis. The model predicts that two different scenarios are possible, which depend on the permeability of the polymer: films with a low permeability to both monomers pass through an abrupt slowdown of film growth, whereas permeable films undergo a smooth transition between the incipient film formation and diffusion-limited regimes. The model incorporates the highly important effects of the accumulation of reactive end groups and the decrease of monomer diffusion with the polymer concentration on the kinetics of the process and film characteristics. In addition, the validity of the utilized mean-field approach is analyzed, and the analysis suggests a direct correlation between the roughness and the thickness of the film. The results are in good agreement with an earlier numerical study and the direct structural studies of polyamide membrane films.     

Nitridation of Niobium Pentoxide Films in Ammonia by Rapid Thermal Processing

The feasibility of niobium oxynitride formation through nitridation of niobium pentoxide films in ammonia by rapid thermal processing (RTP) was investigated. Niobium films 200 and 500 nm thick were deposited by sputtering on Si(100) wafers covered by a 100 nm thick thermally grown SiO₂ layer. These as‐deposited films exhibited distinct texture effects. They were processed in three steps using an RTP system. The as‐deposited niobium films were first nitridated in an ammonia atmosphere at 1000 °C for 1 min and then oxidised in molecular oxygen at temperatures ranging from 400 to 600 °C. Those samples in which a single Nb₂O₅ phase was determined after oxidation were additionally nitridated in ammonia at 1000 °C for 1 min. Investigations show that surface roughness of the samples after oxidation of niobium films first nitridated in ammonia is lower than after direct oxidation of as‐deposited films in oxygen, although the niobium pentoxide phase formed after annealing was the same in both cases. We explain this result as being due to the large expansion of the niobium lattice during the direct oxidation of the niobium film in molecular oxygen and also to the high oxidation rate of the as‐deposited niobium film in oxygen. By incorporation of oxygen in the crystal lattice of niobium and rapid formation of niobium pentoxide, substantial intrinsic stress was built up in the film, frequently resulting in delamination of the film from the substrate. Nitrogen hinders the diffusion of oxygen in nitridated films, which leads to a decrease of the oxidation rate and thus slower formation of Nb₂O₅. Nitridation of the completely oxidised niobium films in ammonia leads to the formation of niobium oxynitride and niobium nitride phases.     

Characterization of silver selenide thin films grown on Cr‐covered Si substrates

Thermal stability of silver selenide thin films formed from the solid‐state reaction of Ag‐Se diffusion couples on Si substrates covered with a thin Cr film, is investigated. Glancing angle X‐ray diffraction (GXRD), XPS, atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) are used to characterize the as‐deposited films and those annealed at 100, 200, 300, and 400 °C. The results reveal the formation of polycrystalline orthorhombic silver selenide films that remain stable without compositional change upon thermal annealing, in marked contrast to the agglomeration exhibited by silver selenide films deposited on Si without Cr film. The improvement in the thermal stability is attributed to compressive stress relief by a grainy morphology with large surface area, the formation of which is promoted by partially oxidized Cr adhesion film. Copyright © 2008 John Wiley & Sons, Ltd.     

Uptake and UV-photooxidation of gas-phase PAHs on the surface of atmospheric water films. 1. Naphthalene

The adsorption and photochemical reaction of naphthalene vapor at the air-water interface of water films (22 microm and 450 microm) were studied in a horizontal flow reactor. Experiments were conducted in the regime where gas-phase mass transfer resistance did not limit the uptake. The equilibrium uptake was dependent on water film thickness only below 1 microm. Bulk water-air and air-to-interface partition constants were estimated from the experiments. The equilibrium partition constant between the water film and air decreased with increasing temperature. Photochemical reaction products were isolated in the water film after exposure to UV light. Four main oxygenated products were identified (1,3-indandione, 1(3H)-isobenzofuranone (phthalide), 2H-1-benzopyran-2-one (coumarin), and 1-naphthol). The initial rates of product formation were 46 to 154% larger for the thin film (22 microm) compared to both a thick film (450 microm) and bulk aqueous phase photooxidation. The atmospheric implications of reactions in water films are discussed.     

非对称双嵌段共聚物薄膜在平板受限和溶剂蒸发下自组装行为的分子模拟研究

采用模拟退火和Monte Carlo方法研究体相形成柱状相的双嵌段共聚物薄膜在平板受限和溶剂蒸发条件下的自组装,特别关注柱状相形貌的取向.对于平板受限下的薄膜,研究了表面选择性、溶剂选择性和膨胀程度对柱状相取向的影响.对于溶剂蒸发的薄膜,研究了表面选择性和薄膜厚度对柱状相取向的影响,并讨论了柱状相取向的机理.结果表明,薄膜内存在中性溶剂时形成垂直柱形貌的表面选择性范围较小;存在亲长嵌段的溶剂时形成垂直柱形貌的表面选择性范围较大.溶剂蒸发后薄膜生成垂直柱形貌的参数范围较热退火下增大;柱状相取向取决于蒸发过程中体系由球状相演化为柱状相时的薄膜厚度与体相周期的匹配性.     

Niobium nitride films formed by rapid thermal processing (RTP): a study of depth profiles and interface reactions by complementary analytical techniques

The nitridation of niobium films approximately 250 and 650 nm thick by rapid thermal processing (RTP) at 800 °C in molecular nitrogen or ammonia was investigated. The niobium films were deposited by electron beam evaporation on silicon substrates covered by a 100 or 300 nm thick thermally grown SiO₂ layer. In these investigations the reactivity of ammonia and molecular nitrogen was compared with regard to nitride formation and reaction with the SiO₂ substrate layer. The phases formed were characterized by X-ray diffraction (XRD). Depth profiles of the elements in the films were recorded by use of secondary neutral mass spectrometry (SNMS). Microstructure and spatial distribution of the elements were imaged by transmission electron microscopy (TEM) and energy-filtered TEM (EFTEM). Electron energy loss spectra (EELS) were taken at selected positions to discriminate between different nitride, oxynitride, and oxide phases. The results provide clear evidence of the expected higher reactivity of ammonia in nitride formation and reaction with the SiO₂ substrate layer. Outdiffusion of oxygen into the niobium film and indiffusion of nitrogen from the surface of the film result in the formation of oxynitride in a zone adjacent to the Nb/SiO₂ interface. SNMS profiles of nitrogen reveal a distinct tail which is attributed to enhanced diffusion of nitrogen along grain boundaries.