X-ray photoelectron spectroscopic studies on pyrolysis of thin films of plasma-polymerized acrylonitrile

X-ray photoelectron spectroscopy is used to elucidate the chemical environments of the atoms in as-deposited plasma-polymerized acrylonitrile (PPAN) thin film and PPAN films pyrolysed at the temperatures 573 and 773 K. The photoelectron spectra are collected at the electron take-off angles of 20° and 70°. The C 1s, N 1s, and O 1s spectra of all the samples demonstrate clearly that the structural modifications take place owing to pyrolysis in the PPAN structure. Apart from the structural modifications, a decrease of nitrogen and an uptake of oxygen are evidenced. A few chemical species other than the usual ones are also detected.     

X-ray photoelectron spectroscopic studies of sprayed CdS films

The chemical composition of sprayed CdS films has been evaluated using X-ray photoelectron spectroscopy. The general impurity content in the film is discussed, throwing light on the pyrolysis reaction involved in CdS deposition. Further, the stoichiometry of these films is studied as a function of process parameters such as pyrolysis temperature, Cd/S ratio in the solution, deposition rate and film thickness. A definite correlation is observed between composition and process parameters. The compositional variation appears to be related to the structure of CdS films as well as the growth mechanism. The effects induced by annealing in nitrogen, hydrogen and ambient air are also discussed. Hydrogen and nitrogen annealing is responsible for oxygen desorption from CdS. On the other hand air annealing induces stoichiometric variations along with oxygen intake in the films.     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Interfacial energy induced microstructure of thin magnetic iron/gold multilayer films

Magnetron sputtered iron/gold multilayers are investigated by cross-sectional transmission electron microscopy. Thermodynamic considerations can explain the different observed microstructures near the substrate and near the top of the multilayers.     

Nanogravimetric studies of tungsten oxide thin films obtained by the polymeric precursor method

In this work, the intercalation/de-intercalation process of Li⁺ ions in the tungsten oxide matrix was investigated. The reaction mechanism involved was also investigated. The WO₃ films, prepared by the polymeric precursor method, were deposited on a Pt covered quartz crystal using the dip-coating technique. The electrolyte was 0.1 mol L^− 1 LiClO₄ in acetonitrile. The morphology and structure of the deposit was accomplished by scanning electron microscopy and X-ray diffraction, respectively. In the electrochemical quartz crystal nanobalance results, it was observed that the mass transport as well as the kinetic processes involved are facilitated in the films cycled at lower potential sweep-rates. The mass variation data as a function of the charge variations in the anodic and cathodic regions indicate the participation of solvent molecules (acetonitrile) during the Li⁺ ion intercalation/de-intercalation process. This was confirmed by the development of a model of the species flux as a function of the potential.     

Optical properties of bismuth niobate thin films studied by spectroscopic ellipsometry

We performed optical analysis of bismuth niobate thin films using spectroscopic ellipsometry (SE). The films were grown on Pt/Ti/SiO₂/Si substrates with pulsed laser deposition. Six films were prepared using various deposition temperatures and thermal-annealing times. The room-temperature SE spectra of these films were measured by a rotating-analyzer ellipsometer from 1.12 to 6.52 eV at incidence angles of 50, 55, 60, 65, and 70°. The resulting refractive indices and extinction coefficients show significant changes with deposition temperature and thermal annealing.     

Photoemission study of the tin doped cerium oxide thin films prepared by RF magnetron sputtering

Ce-Sn-O mixed oxide films prepared by simultaneous Sn metal and cerium oxide magnetron sputtering were studied by high resolution photoemission. The analysis showed that the degree of reduction of the cerium oxide depends on the tin concentration in the film. Ce⁴⁺ → Ce³⁺ conversion is explained by a charge transfer from Sn atoms to unoccupied orbital Ce 4f⁰ of cerium oxide by forming Ce 4f¹ state. The X-ray Photoelectron Spectroscopy data were compared with study of the single-crystalline CeO₂ thin films and Sn/CeO₂(111) model system prepared and studied in situ excluding air exposure effects.     

Microstructural characterization of thin gold films on a polyimide substrate

The study of thin metal films on flexible substrates is of interest for manufacture of many devices, such as implantable electrode arrays consisting of gold film on polyimide substrates. Adhesion of the film to the substrate is of utmost importance for device durability. Gold adhesion to a polyimide has previously been shown to increase when a variety of substrate treatments are performed prior to gold sputter deposition, but little microstructural analysis has been made to complete the process-structure-properties relationship. Here, the grain size is shown to increase slightly but statistically significantly if an oxygen plasma etch and adhesion layer treatment of the film is performed prior to deposition of the gold. A log-normal grain size distribution is found for gold on each sample, and the grains are shown to be columnar. Gold deposited on non-treated polyimide shows a strong {111} texture, but a random texture is seen in both pretreated systems, indicating that the pretreatment affects the surface energy of the polyimide and alters the gold film growth.     

Interactions of thin films of Pd and Pd/Si on GaAs: an X-ray photoelectron spectroscopic study combined with a thermodynamic analysis

Interfacial reactions of Pd and Pd/Si films on [0 0 1]-oriented GaAs substrates have been studied by X-ray photoelectron spectroscopy. In the as-deposited Pd/GaAs system, Pd interacts with Ga and the As is isolated. A Pd–Ga–As compound is observed to form under the Pd–Ga and As layers. Annealing the Pd/GaAs system at 450°C leads to the formation of islands composed of Pd–Ga and Pd–As, amongst which a Pd–Ga–As compound forms. In the Pd/Si/GaAs system, Pd diffuses in to the GaAs substrate, the Pd–Ga and Pd–Ga–As compounds are formed. In the 450°C-annealed Pd/Si/GaAs system, little interfacial reaction at the GaAs substrate occurs. Possible interfacial reactions in the Pd/GaAs and Pd/Si/GaAs systems, including the previously investigated Pt/GaAs, Pt/Si/GaAs, Ni/GaAs and Ni/Si/GaAs systems are considered by calculation of the change in enthalpy of the reactions. The thermodynamic analyses agree with the experimental results.     

New ultrasonic method for studies of superfluidity in thin helium films

Thin helium films have been deposited on a LiNbO₃ SAW plate composed of three identical collinear transducers. The center one was used as a generator at 720 MHz and the two others, asymetrically positioned, permit a differential measurement of the SAW attenuation as a function of the film thickness. An anomalous attenuation peak is observed which we analyzed as the onset of superfluidity. The results are compared with previous work and discussed in the framework of the two-dimensional model of Kosterlitz and Thouless.This work was supported by the Natural Sciences and Engineering Research Council of Canada, the GRSD (Groupe de Recherches sur les Semiconducteurs et les Diélectriques), the FCAC (Formation de chercheurs et Action concertée), and the Social Sciences and Humanities Research Council of Canada.     

Elasticity and adhesion of thin films by a mechanical resonance method

We describe a simple experimental apparatus capable of simultaneous measurements of elastic and anelastic properties of film/substrate composites in controlled atmospheres (10^-6-10⁴ Pa) from 25 to 1000°C. The apparatus employs the technique of dynamic resonance in which the mechanical response of a material can be determined over a wide range of frequency (0.1–100 kHz) with a resolution of ±1 μHz. We present experimental results for thin films (approximately 100 nm) of nickel and gold on sapphire substrates. These results demonstrate the sensitivity of the apparatus to both the adhesion and the elasticity of the supported film.     

Microstructure evolution of gold thin films under spherical indentation for micro switch contact applications

RF MEMS (Radio Frequency Micro Electro Mechanical System) switches are promising devices but their gold-on-gold contacts, assimilated for this study to a sphere/plane contact, represent a major reliability issue. A first step toward understanding failure mechanisms is to investigate the contact metal microstructure evolution under static and cyclic loading. After static and cyclic loading of sputtered gold thin films under spherical indentation, high-resolution Electron Back Scatter Diffraction (EBSD) is used to investigate the contact area. Grain rotation against {111} fiber texture of 1-μm-thick sputtered gold thin film is a signature of plastic deformation. Grain rotation is observed above 1.6 mN under static loading using a spherical diamond indenter with 50-μm tip radius. The heterogeneity in grain rotation observed corresponds to a greater plastic deformation in the middle of the indent than at the edge. A 30° grain rotation due to cyclic work hardening is observed for a half-million mechanical cycles under 300 μN load using a spherical gold tip (20 μm radius). The same test in hot switching mode induces a grain growth in the contact area. Therefore, thermal effects occurring during hot switching are underlined.     

Unambiguous determination of thickness and dielectric function of thin films by spectroscopic ellipsometry

We present a spectroscopic method of determining both thickness and dielectric functions of thin films on previously characterized substrates. The method requires that spectroscopic ellipsometric data be taken over an energy range where the substrate has a sharp optical structure, e.g. a critical point. These data are used to determine a “pseudodielectric” function for the film, which necessarily depends on the assumed film thickness. We develop a general first-order theory which shows that the correct thickness and dielectric function of the film are those for which the substrate feature vanishes in the calculated pseudodielectric function. The theory is also used to investigate sensitivity and applicability. We show that sensitivity can be enhanced by differentiating the pseudodielectric function with respect to energy. The method is demonstrated with several numerical and experimental examples, which illustrate that monolayer thickness accuracy can be achieved.     

Controllable low energy ion assistance as a tool for tailoring properties of gold oxide and gold-silver oxide thin films

In the present study, gold oxide (AuO_x) and gold-silver oxide (AuAgO_x) thin films are deposited by reactive sputtering in a magnetron with unbalanced ratio continuously controlled by the current I_s trough an external solenoid. Two film characteristics: the specific electric resistivity ρ_o of as deposited films and their life-times τ are systematically investigated in dependence of the oxygen gas pressure p_O2, magnetron discharge power P_m and solenoid current I_s.It is demonstrated that employing optimal regime of ion assistance and gradient sublayers, AuO_x and AuAgO_x films with a high electric resistivity and long life-times (up to 3 years) can be deposited.Incorporation of the more reactive silver atoms into the film structure significantly changes the behavior of AuAgO_x films as compared to that of AuO_x films. While the initial electric resistivity and the life-time of AuAgO_x films monotonously increase with the combined parameter I_sp_O2/P_m, tending to saturation at higher values of this parameter, films of thermodynamically unstable gold oxide with long life-times can be produced within a narrow range of deposition parameters, only.     

Fine structure of gold particles in thin films prepared by metal-insulator co-sputtering

Thin films containing a homogeneous dispersion of small gold particles were formed by co-sputtering composite targets of gold with Al₂O₃ and polyester in separate experiments. The nanostructure of these films was studied using transmission electron microscopy (TEM) and high resolution scanning-transmission electron microscopy (STEM). Diffraction data obtained from STEM show the gold islands to be simple and multiply twinned crystallites even in particles as small as 15 Å across. The existence of such fine structure in sputtered gold particles is consistent with the earlier TEM work reported by other workers for gold particles grown from colloidal solutions and by evaporation onto single-crystal substrates.     

Optical properties of post-annealed ZnO:Al thin films studied by spectroscopic ellipsometry

In this paper, effects of the thermal annealing on the structural, electrical, and optical properties of Al-doped ZnO (ZnO:Al) thin films prepared by reactive radio-frequency sputtering were investigated. From the X-ray diffraction observations, the orientation of ZnO:Al films was found to be a c-axis in the hexagonal structure. The optical properties of the films were investigated by optical transmittance and spectroscopic ellipsometry characterization. Based on Tauc–Lorentz model, the optical constants of ZnO:Al films were extracted in the photon energy ranging from 1.0 to 4.5 eV. Our result showed that the refractive index and extinction coefficient of the films changed consistently with annealing temperature.     

A simple method of forming small gold particles on a thin gold film

We have produced gold particles whose sizes range from several tenth nanometers up to about 1 μm. The small gold particles are distributed on a gold thin film of thickness 50–80 Å. The method for the formation is simple. We first evaporated the gold thin film, and then applied DC field along the film. When the field increases from 0 to 30 V, and the measured current increases from 0 to 650 mA, the particles were formed. The sizes and the distribution distances could be controlled by the applied DC field.