Formation of an amorphous powder during the polymerization of ethylene in a radio-frequency discharge

An investigation has been carried out to determine the influence of operating conditions on the character of the final product resulting from the polymerization of ethylene in a radio-frequency discharge. It has been found that low pressures and high ratios of discharge power to gas flow rate lead to the deposition of a powder as well as a film. From visual observations of powder deposition, it has been possible to divide the plane formed by the axis of pressure and flow rate into a region in which powder is deposited together with a film and a region in which only a film is deposited. Numerous physical measurements have been carried out in order to characterize the powder. From these measurements, it has been concluded that the powder is a relatively dense, amorphous, and highly crosslinked polymer composed of short-chain segments containing no more than two adjacent methylene groups. Many forms of unsaturation have been observed which, together with the high crosslink density, explain the measured hydrogen-to-carbon ratio of 2.7 to 2. Evidence of oxidation has been observed through the appearance of hydroxyl and carbonyl bands in the infrared spectrum of the polymer. A mechanism for the formation of the powder has been proposed which suggests that the polymerization of the powder takes place totally in the gas phase.     

A comparison between chemical and sputtering methods for preparing thin-film silver electrodes for in situ ATR-SEIRAS studies

Stable silver thin films were prepared either by chemical deposition or by argon sputtering on germanium and silicon substrates, respectively, and used as electrodes for in situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. The spectra obtained for acetate anions adsorbed from neutral solutions showed a noticeable intensity enhancement (SEIRA effect). This enhanced absorption has been related to the surface structure of the films that have been characterized by ex situ STM and in situ electrochemical measurements (lead underpotential deposition, UPD). STM images of the chemically deposited silver films show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, and the absence of flat domains. On the other hand, STM images of the films deposited by argon sputtering show mean grain sizes around 30 nm for a film growth rate of 0.05 nm s⁻¹ and 70 nm for a film growth rate of 0.005 nm s⁻¹. In this latter case, atomically flat domains up to 50 nm wide have been observed. This observation is consistent with a more defined voltammetric profile for lead UPD, that indicates a higher degree of surface order. Moreover, the roughness factor obtained from the charge density involved in lead UPD in the case of the sputtered silver film is lower than that measured for the chemically deposited silver film. All these structural data can be connected with the observations on the effect of deposition conditions of the silver film on the SEIRA effect for adsorbed acetate. Maximum enhancement is observed for chemically deposited films and sputtered films at high deposition rate for which the grain size is around 40-60 nm. The increase of the grain size for the sputtered silver films deposited at decreasing deposition rates can be related to the observed decrease in the SEIRA effect.     

Diamond-like carbon — present status

Hydrogen free diamond-like carbon (DLC) films have been the subject of investigation all over the world during the past 25 years due to the unique combination of their properties that can be found between those of diamond and those of graphite. Intensive work throughout the world in the past 10 years has led to a much better understanding of the complicated mechanisms involved in the deposition of these films. This led to a significant improvement in the deposition processes in the variety of systems employed, enabling fabrication of films with better properties. The present work gives the author's assessment of the current status of DLC film deposition. Topics addressed include: deposition systems; characterization methods; film properties; and possible applications.     

Film formation from cationic electropaint systems containing resins with different glass transition temperature

Some phenomena in the deposition process of electropainting have not been well elucidated till now. In this paper, to investigate an influence of glass transition temperature (T_g) on film formation, the deposited film was observed with an atomic force microscope and the electrochemistry was investigated, using two kinds of cationic acrylate resin with different T_g (methyl methacrylate system (MMAs): T_g=70°C, and methyl acrylate system (MAs): T_g=5°C). Electrodeposition was performed under constant voltage or current condition.

At constant voltage, the deposition behavior in the two resin systems differed extremely. The MMAs, the resin with high T_g, produced a high resistance film. The MAs, the resin with low T_g, was deposited forming a film at a voltage lower than 20 V. At constant current, the film formation did not result in a rise in voltage. It behaved like a conductive film. When the resin with high T_g was used, particulate deposits were observed by AFM even in the induction period. The resin with low T_g formed flat deposits. These results suggest that paint deposition is initiated once electrolysis of water starts. In addition, there are two types of film formation on the cationic electropainting: high resistance film formation for the resin with high T_g, and ion-permeable film formation for the resin with low T_g. In both cases, film growth occurs at the film/bulk solution interface.     

Microstructure,Surface Morphology and Photoluminescence Properties of Al-Doped ZnO Thin Films Prepared by Plasma Focus Method

Al-doped ZnO (AZO), as one of the most promising transparent conducting oxide (TCO) materials, has now been widely utilized in thin film solar cells. In this research the optimization process of AZO thin films deposited by plasma focus device was carried out by investigation of its physical properties under different deposition conditions for its utilize as a front contact for the Cadmium Telluride (CdTe) based thin film solar cell applications. The effects of number of focus shots and angular position of substrate on the microstructure, surface morphology and photoluminescence properties of the thin films have been systematically studied. X-ray diffraction (XRD) study confirmed the polycrystalline nature of the all deposited AZO thin films. XRD analysis also revealed that crystal structure characteristics of obtained samples strongly depend on deposition conditions (number of shots and angular position). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses revealed the structure growth and enhancement of surface roughness, with increasing of focus shots or decreasing of angular position. From Photoluminescence (PL) emission spectra, the variations of structural defects and band gap energy for all the AZO thin films prepared under different deposition conditions were also discussed.     

氮化硅薄膜生长随时间演化过程及其特性研究

氮化硅SiN_x薄膜凭借介电常数高和稳定性好的特点而被广泛应用于光电器件中,但薄膜的厚度对器件的性能有重要影响。针对此问题采用等离子体化学气相沉积技术,以高纯NH₃、N₂和SiH₄为反应气体,优化其他沉积参数,通过改变沉积时间来生长SiN_x薄膜。用X射线衍射谱(XRD),紫外-可见光光谱(UV-VIS)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对薄膜结构进行表征,详细研究了沉积时间与薄膜厚度的关系以及沉积时间对薄膜性能的影响。试验结果表明:所制备的样品为非晶SiN_x薄膜结构,薄膜厚度随沉积时间均匀增加;薄膜折射率随沉积时间的增加而增大,光学带隙基本不随时间变化。SEM测试结果表明,随着沉积时间增加,薄膜致密性与均匀性越来越好,氧含量也越来越少,说明薄膜致密性提高可以有效阻挡O原子进入薄膜,阻止后氧化现象的发生。     

甲烷浓度对金刚石薄膜(100)织构生长的影响

以H2和CH4的混合气体为气源,用微波等离子体辅助化学气相沉积法(MPECVD)在1 cm×1 cm S i(100)基体上沉积了金刚石薄膜。研究了不同的甲烷浓度对金刚石薄膜(100)织构生长趋势的影响。分别采用扫描电子显微镜(SEM),Ram an光谱对金刚石膜的表面形貌、质量进行了分析。结果表明,当基体温度为750℃,气压为4.8×103Pa,甲烷浓度为1.4%时,薄膜表面为(100)织构。     

Capacitance properties of electrochemically deposited polyazulene films

Polyazulene films formed by electrochemical oxidation of azulene have been studied as active components in electrochemical capacitors. The film shows reversible electrochemical behavior in the positive potential range and exhibits p-doping properties. The influence of film formation conditions on the films electrochemical properties has been investigated. A strong effect of solvent on the polyazulene deposition has been observed. The highest yield of film deposition was found for dichloromethane. Polyazulene films also exhibit stable voltammetric properties in aprotic solvents. The voltammetric response of the film is affected by the size of the anion of the supporting electrolyte. In solutions containing tetra(alkyl)ammonium perchlorates, tetrafluoroborates or hexafluorophosphates, reversible oxidation of polyazulene is obtained. In the presence of large tetra(phenyl)borate anions, polyazulene is irreversibly oxidized upon electrochemical oxidation. The capacitance properties of these materials have been investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The polyazulene film displays a relatively high specific capacitance close to 400 F g⁻¹. Such high value of C_s locates this material among very good polymeric redox pseudo-capacitors.     

砷化镓上生长金刚石薄膜的研究

以CH4和H2为气源,用微波辅助等离子体装置,在10.0 mm×7.0 mm的砷化镓基底上沉积了CVD金刚石薄膜,用扫描电子显微镜观察沉积效果,拉曼光谱表征沉积质量,分析薄膜附着力与砷化镓材料性能的关系。结果表明,当基体温度为600℃,气压为5 kPa,甲烷浓度为2.0%时,在砷化镓片表面上沉积出了CVD金刚石薄膜,晶粒尺寸均匀,晶形完整、规则,晶界非常清晰。     

影响金刚石膜刀具涂层形貌的因素分析

采用高分辨金相显微镜对硬质合金刀生上沉各的ＣＶＤ金刚石薄膜进行了表面形貌和膜／基横截面组织形貌的观察;并利用该显微镜配备的功能测量了金刚石颗粒大小,膜厚;利用显微镜正焦／过焦观察判断了金刚石薄膜的成膜状况。初步观察结果表明：甲烷浓度和基体钴含量对金刚石薄膜的表面形貌和膜／基横截面组织形貌有显著的影响。     

High-density DLC films prepared using a magnetron sputter type negative ion source

Diamond-like carbon (DLC) films have been deposited at room temperature using a magnetron sputter type negative ion source (MSNIS). The film characteristics such as density, surface roughness, film structure and thicknesses are obtained and analyzed using X-ray reflectivity (XRR), XPS and AFM methods. XRR results showed that the density of the film varies from 1.9 to 3.0 g/cm³ with respect to the different deposition parameters. At average negative carbon ion energy 700 eV and Cs injector temperature 150 °C, the densest film (3.0 g/cm³) was observed at 1 nm/s deposition rate. The surface roughness of the film was less than 1.0 nm in most cases for the 10-nm thickness film. XPS peak showed no Cs content on the film. The films prepared at different negative ion production yields and negative ion energies were compared. The result suggests that the density is the strong function of negative ion energy and the negative ion production yield.Higher cathode voltage induced denser film, while Cs flow rate had optimum temperature condition around 150 °C.     

Diluted chemical bath deposition of CdZnS as prospective buffer layer in CIGS solar cell

In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn²⁺ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn²⁺ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn²⁺. Optical characterization has shown that the transparency of the film is influenced by Zn²⁺ concentration and when the Zn²⁺ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn²⁺ concentration would be a promising candidate in CIGS solar cell.     

Self-assembled folding of a biaxially compressed film on a compliant substrate

Amorphous carbon films grown by ion beam deposition from hydrocarbon precursors on compliant polymer substrates are shown here to undergo spontaneous self-assembled folding during growth. When deposited up to 30 min, the deposition-induced stretch strain of an amorphous carbon film on poly(dimethylsiloxane) (PDMS) with a Young’s modulus of 1–2 MPa reached more than 50%, which is much higher than usually observed compressive mismatch strains of approximately 1–2% on silicon. During deposition of the carbon film, compliant PDMS substrates allowed large amplitude film buckling to let in lateral growth of the film with the significant compressive mismatch strain. The film wrinkled at a low strain of approximately 1% at an early stage of deposition. Then, the wrinkled film was observed to transform its configuration through two different nonlinear modes; formations of ridges and asymmetric localized folds. Due to the biaxial nature of the deposited thin film, the wrinkled film showed herringbone or labyrinth patterns for strains less than 10%, while the folds were made in random orientations to create asymmetric disordered tessellation for strains more than 30%.     

Periodic vapor-phase fluctuation influence on growth of diamond films

A computer control system was designed to work with diamond film deposition apparatus to control methane flow automatically. In experiments, the methane flow can fluctuate with a fixed period and fixed amplitude cosine curve. Diamond films were deposited by direct current arc plasma jet and their morphologies were examined by scanning electron microscopy. This proved that the reaction vapor-phase periodic fluctuation had an obvious influence upon the growth and nucleation of diamond. The phenomena of alternate growth and nucleation were observed; especially interesting are the two-dimensional fractal carbon clusters that have been observed for the first time.     

Preparation of nanocrystalline titanium carbonitride coatings using Ti(N(Et)<Subscript>2</Subscript>)<Subscript>4</Subscript>

Titanium carbonitride films with a thickness of 80–150 nm have been synthesized by low pressure chemical vapor deposition from a gas mixture of tetrakis(diethylamino)titanium and ammonia at temperatures of 773–973 K. The film properties have been studied by spectroscopy (IR, XPS, and EDS), scanning electron and atomic force microscopy, and ellipsometry. The studies have shown that the films consist of polycrystals with a size of 15–80 nm; their structure contains chemical bonds of titanium with atoms of carbon, nitrogen, and oxygen. The film composition is consistent with the data of the previously performed thermodynamic modeling of the deposition of different condensed phases in the Ti-C-N-H-O system. As the deposition temperature increases in the range under study, the refractive index of the films increases from 2.1 to 2.7.     

Magnesium(II) polyporphine: The first electron-conducting polymer with directly linked unsubstituted porphyrin units obtained by electrooxidation at a very low potential

Electrooxidation of magnesium(II) porphine, a totally unsubstituted porphyrin, in acetonitrile solution under potentiostatic or potentiodynamic regime leads to a polymer film at the electrode surface. Polymer deposition takes place at extremely low potential, several hundred mV less positive even compared to the deposition potential for pyrrole or EDOT (at identical monomer concentrations) in the same solvent. Film thickness can be controlled by the passed deposition charge. This material and its THF-soluble fraction have been characterized by various electrochemical methods as well as by UV-visible and IR spectroscopies, XPS, XRD and MALDI-TOF techniques. This analysis has allowed us to conclude that the polymer film is composed by chains of Mg porphine building blocks, with single bonds between the neighboring units. In the course of the potential sweep, this polymer film demonstrates a redox response resembling that of polythiophene-coated electrodes. Namely, the film is electroactive and electronically conducting in two potential ranges (p- and n-doping), which are separated by a broad interval where the film possesses a much higher resistance. The polymer may be switched between all these redox states repeatedly by the change of the potential. The film capacitance in the electroactive potential intervals is proportional to the deposition charge.     

Thermoelectric properties of thin films of bismuth telluride electrochemically deposited on stainless steel substrates

Bismuth telluride thin films have been synthesized by electrochemical deposition onto stainless steel substrates from acidic solutions. The influence of deposition variables on film composition, morphology and crystal orientation associated with the growth of the film was investigated by means of constant potential deposition and pulsed potential deposition. In-plane thermoelectric and transport properties of the electrodeposited films were measured. The carrier concentration of the electrodeposited films was found to be one order of magnitude larger than typically reported for optimized bulk bismuth telluride, which explains the unusually low Hall mobility and Seebeck coefficient values found for the electrodeposited films. Pulse deposited films showed slightly lower electrical resistivity and higher Seebeck coefficient due to the lower porosity and less preferred crystal orientation of the films compared to the continuously deposited films. Improvements of the film properties are necessary to make them viable for applications.     

REMOTE PLASMA COPPER CVD WITH HYDROGEN AND OXYGEN ATOMS

Thin copper films have been deposited by the room temperature reaction of gaseous copper (II) hexa-fluoroacetylacetonate [Cu(hfa)₂] with hydrogen atoms produced in a remote discharge tube. The resulting films are conductive and adherent on a wide variety of substrates. Copper atoms have been observed and measured in the gas phase and were found by atomic absorption spectroscopy to have a maximum concentration of approximately 10¹¹ atoms/cc in the mixing/reaction zone. The reaction of Cu(hfa)₂ with oxygen atoms was also studied. The reaction again resulted in the deposition of a film and in addition a green chemiluminescent glow was observed which was identified as due to the gaseous diatomic CuF molecule. Copper atoms were also observed by absorption spectroscopy within this chemiluminescent reaction with oxygen atoms. The copper atom concentration was found to be approximately the same as that found with the H-atom reaction. The copper atom concentrations and the relative emission intensities of CuF were studied as a function of time and position to gain insight into the deposition process.     

Modeling and measurement of aerosol deposition on a heated substrate

Formation of an inorganic film by chemical aerosol deposition has been investigated experimentally and theoretically. Carrier gas flow rate, nozzle-to-substrate distance and substrate temperature were chosen as major process variables. The experimental work has been carried out to find their effect on the deposition efficiency, film thickness and its distribution. Both the deposition efficiency and film thickness increased with the carrier gas flow rate and substrate temperature but decreased with the nozzle-to-substrate distance. Especially at higher deposition rates, the central part of the film has a concave surface like a bowl. Flow and temperature fields of the fluid phase in the region between the nozzle and substrate were calculated numerically. Particle trajectories and particle evaporation were simulated numerically. As a result, the evaporation of the aerosol particles occurred so abruptly that the aerosol-existing region has a clear boundary. The extent of the region was found to be a determining factor in the film deposition, which characterizes the process of the chemical aerosol deposition.     

Boron carbide thin film deposition using supersonic plasma jet with substrate biasing

Hard, microcrystalline boron carbide thin films have been deposited from the thermal dissociation of hydrogen, methane and boron trichloride in a supersonic plasma jet. The influence of negative and positive substrate bias on the film properties and morphology has been investigated. A continuous ion bombardment has been found to increase the film crystallinity, however, it has led to poor adhesion to the substrate. Pulsed d.c. positive biasing has been developed as a means to elevate the electron temperature and control the gas phase chemistry, while limiting the total current flowing in the secondary discharge. In this case, it has been found that the deposition rates increase with bias voltage as a function of the third power, without affecting the film hardness and morphology. Also, the boron-to-carbon atomic ratio of the films increases with increasing positive bias voltage, from carbon-rich to stoichiometric boron carbide. Correlations between deposition rates and gas species line emission indicate that atomic boron is the primary growth species. The pulsed d.c. biasing enhancement presented in this paper constitutes a novel approach to controlling the film composition and deposition rate.