Studies of aluminum oxide thin films deposited by laser ablation technique

This paper presents the structural and optical investigations of the aluminum oxide nanocrystalline thin films. Investigated films were fabricated by laser ablation technique in high vacuum onto quartz substrates. The films were deposited at two different temperatures of the substrates equal to room temperature and 900 K. X-ray Diffraction spectra proved nanocrystalline character and the corundum phase of the film regardless on the substrate temperature during the deposition process. Values of the refractive indices, extinction and absorption coefficients were calculated by using Transmission and Reflection Spectroscopy in the UV–VIS–NIR range of the wavelength. Coupling Prism Method was used for films thickness estimations. Experimental measurements and theoretical calculations of the Third Harmonic Generation were also reported. Obtained results show that the lattice strain may affect obtained values of the third order nonlinear optical susceptibility.     

Selective atomic layer deposition of metal oxide thin films on patterned self-assembled monolayers formed by microcontact printing

We demonstrate a selective atomic layer deposition of TiO2, ZrO2, and ZnO thin films on patterned alkylsiloxane self-assembled monolayers. Microcontact printing was done to prepare patterned monolayers of the alkylsiloxane on Si substrates. The patterned monolayers define and direct the selective deposition of the metal oxide thin films using atomic layer deposition. The selective atomic layer deposition is based on the fact that the metal oxide thin films are selectively deposited only on the regions exposing the silanol groups of the Si substrates because the regions covered with the alkylsiloxane monolayers do not have any functional group to react with precursors.     

Influence of the growth conditions on the stoichiometry and on the optical properties of titanium oxide thin films prepared by reactive sputtering

Titanium oxide thin films are deposited at room temperature by reactive DC sputtering onto glass and Si (100) substrates. Different conditions of deposition were varied such as sputtering power, deposition time and oxygen partial pressure to study their influence on the titanium oxide thin films growth. The absolute amount of oxygen and the relative O/Ti composition of films have been determined by Nuclear Reaction Analysis and Rutherford Backscattering Spectroscopy, respectively. Additionally, the band-gap was determined by measuring the optical absorption and its behavior correlated with the oxygen film content. From the present study, it is possible to establish that the optical band-gap energy depends mainly on the sputtering oxygen partial pressure used at the preparation and that films prepared with a partial oxygen pressure of 4 × 10^− 2 Pa allows titanium oxide with near stoichiometric composition. Additionally, from the optical point of view, band-gap energies of 3.4 eV are obtained for near stoichiometric films and a decrease is observed for samples prepared with higher oxygen concentrations.     

Inorganic Thin Film Deposition and Application on Organic Polymer Substrates

This review details the emerging area of inorganic thin film coatings on polymer substrates, from examples of applications through to the fabrication processes and the underlying growth mechanism(s). Of particular focus is the use of physical vapor deposition to deposit thin metal and/or metal oxide films onto polymeric materials. This primary focus highlights an area of research, that is, gaining in popularity, as researchers attempt to provide insight into the adaption of a well‐established manufacturing process to be compatible with the ever expanding range of polymer substrates. The motivation for doing so comes from the evolution of existing industry (i.e., the semi‐conductor sector) to fabricate new devices (i.e., flexible electronics). In addition, the research challenges faced in achieving evaporated and sputtered thin film coatings on polymeric substrates, such as mechanical and thermal considerations will be discussed.

     

Carbon incorporation in chemical vapor deposited aluminum oxide films

We report results from an investigation into the nature and extent of carbon incorporation into aluminum oxide thin films deposited from the pyrolysis of dimethylaluminum isopropoxide via high-vacuum chemical vapor deposition. The chemical nature and distribution of carbon in films deposited in the 417-659 °C temperature range were investigated through X-ray photoelectron spectroscopy and Auger electron spectroscopy. Carbon composition increased with increasing deposition temperature, up to approximately 8 at.% at 659 °C. Carbon in films deposited at 477 °C was bonded only to oxygen or carbon, but films deposited above 538 °C also contained metal carbide-like bonding. Carbon content in films deposited on hydrogen-terminated Si (100) substrates increased toward the film-substrate interface, but no silicon-carbon bonding was observed.     

Growth and stability of Ga2O3 nanospheres

Gallium oxide thin films were prepared by thermal evaporation and deposition of Ga₂O₃ on NaCl(001) cleavage planes at varying substrate temperatures, oxygen pressures and deposition rates. The structure of the so-prepared thin films was checked by Transmission Electron Microscopy and Selected Area Diffraction and also characterized by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy, both in the as-deposited state and after different oxidative and reductive treatments. The substrate temperature proved to be most crucial for the structure of the gallium oxide films, ranging from low-contrast amorphous structures at low substrate temperatures (298 K) to nanosphere structures at higher temperatures (580 K). The stability of the films was found to be mainly determined by the interaction of substrate temperature and deposition rate. Crystalline β-Ga₂O₃ structures were obtained after oxidative, reductive and annealing treatments at and beyond 773 K suggesting that the crystallization is mainly a thermal annealing effect.     

Stability increase of fuel clad with zirconium oxynitride thin film by metalorganic chemical vapor deposition

A zirconium oxynitride (ZON) thin film was deposited onto HT9 steel as a cladding material by a metalorganic chemical vapor deposition (MOCVD) in order to prevent a fuel-clad chemical interaction (FCCI) between a U-10 wt% Zr metal fuel and a clad material. X-ray diffraction spectrums indicated that the mixture of structures of zirconium nitride, oxide and carbide in the MOCVD grown ZON thin films. Also, typical equiaxial grain structures were found in plane and cross sectional images of the as-deposited ZON thin films with a thickness range of 250-500 nm. A depth profile using auger electron microscopy revealed that carbon and oxygen atoms were decreased in the ZON thin film deposited with hydrogen gas flow. Diffusion couple tests at 800 °C for 25 hours showed that the as-deposited ZON thin films had low carbon and oxygen content, confirmed by the Energy Dispersive X-ray Spectroscopy, which showed a barrier behavior for FCCI between the metal fuel and the clad. This result suggested that ZON thin film cladding by MOCVD, even with the thickness below the micro-meter level, has a high possibility as an effective FCCI barrier.     

Gas-tight alumina films on nanoporous substrates through oxidation of sputtered metal films

The fabrication of ultrathin oxide films without gas leakage was investigated for the application to low-temperature solid oxide fuel cells (SOFCs). Aluminum thin films were deposited onto two types of anodic nanoporous alumina substrates with pore diameter of 20 and 200 nm, respectively, using dc-magnetron sputter at room temperature. By subsequent oxidation at temperatures over 500 °C, the metal films were successfully transformed into oxide films with thickness of about 35 and 410 nm. Volume expansion induced from oxidation of metal resulted in dense thin films that are free from hydrogen permeation.     

Effects of different needles and substrates on CuInS2 deposited by electrostatic spray deposition

Copper indium disulphide (CuInS₂) thin films were deposited using the electrostatic spray deposition method. The effects of applied voltage and solution flow rate on the aerosol cone shape, film composition, surface morphology and current conversion were investigated. The effect of aluminium substrates and transparent fluorine doped tin oxide (SnO₂:F) coated glass substrates on the properties of as-deposited CuInS₂ films were analysed. An oxidation process occurs during the deposition onto the metallic substrates which forms an insulating layer between the photoactive film and substrate. The effects of two different spray needles on the properties of the as-deposited films were also studied. The results reveal that the use of a stainless steel needle results in contamination of the film due to the transfer of metal impurities through the spray whilst this is not seen for the glass needle. The films were characterised using a number of different analytical techniques such as X-ray diffraction, scanning electron microscopy, Rutherford back-scattering and secondary ion mass spectroscopy and opto-electronic measurements.     

The effect of interfacial bonding on the adhesion of brittle film-polymer multilayered structures

A previously derived model and method to determine the adhesion of thin brittle films coated on flexible substrates are used to study the effect of changing the interfacial bonding on adhesion. Nickel films with oxidized and unoxidized surfaces are prepared by vacuum deposition onto Mylar. Various thickness of selenium are then deposited onto the nickel. By measuring the tensile force required to cause cohesive and adhesive failure, the approximate crack spacing and energy required to separate the interface are calculated. The calculated and measured crack spacings are compared and the chemical structure and fracture surface defined by electron spectroscopy for chemical analysis (ESCA).     

Structural and electrical properties of RuO2 thin films prepared by rf-magnetron sputtering and annealing at different temperatures

Conductive ruthenium oxide (RuO₂) thin films have been deposited at different substrate temperatures on various substrates by radio-frequency (rf) magnetron sputtering and were later annealed at different temperatures. The thickness of the films ranges from 50 to 700 nm. Films deposited at higher temperatures show larger grain size (about 140 nm) with (200) preferred orientation. Films deposited at lower substrate temperature have smaller grains (about 55 nm) with (110) preferred orientation. The electrical resistivity decreases slightly with increasing film thickness but is more influenced by the deposition and annealing temperature. Maximum resistivity is 861 μΩ cm, observed for films deposited at room temperature on glass substrates. Minimum resistivity is 40 μΩ cm observed for a thin film (50 nm) deposited at 540°C on a quartz substrate. Micro-Raman investigations indicate that strain-free well-crystallized thin films are deposited on oxidized Si substrates.     

Electrochemical synthesis and characterization of zinc selenide thin films

In this work, electrochemical deposition and characterization of zinc selenide (ZnSe) thin films is reported. ZnSe thin films were deposited onto tin oxide (SnO₂) coated conducting glass substrates from an aqueous solution bath containing ZnSO₄ and SeO₂. The effect of deposition parameters such as bath temperature, deposition time and electrolyte composition on the properties of the ZnSe films has been studied. Cyclic Voltammetric studies were carried out to optimize the deposition potential for the co-deposition of Zn and Se. Deposited ZnSe films have been characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM) and optical techniques for their structural, compositional and optical properties and the results are discussed.     

Yttrium oxide film deposition by a Langmuir-Blodgett processing technique and its incorpiration into oxide scales by substrate oxidation

Thin films (about 10 nm) of Y₂O₃ have been deposited by a Langmuir-Blodgett processing technique onto a variety of substrates: type 304 stainless steel, low carbon steel, titanium, zirconium and silicon. The substrates were afterwards oxidized in air at 800, 1000 (304 steel), 400 (low C steel), 500 (Ti), 450 (Zr) and 1000 (Si) °C. The effects of the film on the oxide scale thickness and the interaction between Y₂O₃ and the oxide of the substrate have been studied by ion backscattering. In stainless steel, the Y₂O₃ film reduces the oxidation rate by orders of magnitude and Y is distributed throughout the oxide scalw (1–10 at.% level). In other substrates, the effect on oxidation rate was less pronounced, but changes in the visual appearance often took place. The Y₂O₃ incorporation varied for the different substrates, and Y₂O₃ remained as a surface film in the cases of Ti and Si. Such films exhibited good adherence and could not be removed by wiping. The potential use of metal oxide thin films for surface analysis standards and diffusion marker studies is discussed.     

Thermodesorption of samarium from oxidized tungsten surface

Thermodesorption of samarium (Sm) atoms and samarium oxide (SmO) molecules from samarium films deposited in vacuum onto tungsten substrates covered with thin (<1 nm thick) layers of tungsten oxides has been studied. It is established that samarium reduces tungsten from its oxides. The parameters of Sm and SmO desorption from an oxidized tungsten surface are determined.     

Effect of substrate on the nucleation and growth of aluminum films deposited from methylpyrrolidine alane

Methylpyrrolidine alane complex was used to deposit aluminum films on various types of substrates in a low pressure chemical vapor deposition reactor. The films grow easily on metallic and transition metal oxide surfaces, but not on any other tested semiconductor and dielectric substrates below 200 °C, showing strong substrate dependency. The free energies of precursor adsorption, surface dissociation reaction and product desorption, as well as the film wettability to substrate are among the key factors which affect the energy barrier for nucleation or deposition selectivity. In general, a metal substrate can enhance nucleation because it catalyzes the surface reactions and bonds strongly with aluminum. The oxidation-reduction reaction may occur between the precursor and substrate on a metal oxide surface. The reduced metal sites can be the seed nuclei and are possibly responsible for Al growth on the surfaces of transition metal oxides.     

Influence of anode roughness and buffer layer nature on organic solar cells performance

Fluorine doped transparent conductive tin oxide thin films (FTO) of different surface roughness have been deposited by chemical vapor deposition (FTO_SOL), classical chemical spray pyrolysis (FTO_CSP), and spray pyrolysis onto heated substrates using infra red irradiation (FTO_IRSP); the three deposition methods inducing different surface roughness. It was found that the different FTOs presented similar electrical properties while their structural, morphological and optical properties were related to surface properties. These FTO films have been used as anode in multilayer organic solar cells, based on coupled donor/acceptor-copper phthalocyanine/fullerene. To improve solar cell performance, buffer layers of different natures have been tried at the anode/organic material interface. Deposition of a thin molybdenum oxide film onto FTO smooth films afforded reproducible devices with performance similar to those obtained with indium tin oxide anodes. However, cell efficiency decreased as FTO surface roughness increased. The degree of degradation depended on the nature of the buffer layer. We show that it is necessary to use buffer layer material that allows consistency and completeness of the electrode coverage.     

Growth of Arrayed Nanorods and Nanowires of ZnO from Aqueous Solutions

A novel approach to the rational fabrication of smart and functional metal oxide particulate thin films and coatings is demonstrated on the growth of ZnO nanowires and oriented nanorod arrays. The synthesis involves a template‐less and surfactant‐free aqueous method, which enables the generation of, at large‐scale, low‐cost, and moderate temperatures, advanced metal oxide thin films with controlled complexity. The strategy consists of monitoring of the nucleation, growth, and aging processes by means of chemical and electrostatic control of the interfacial free energy. It enables the control of the size of nano‐, meso‐, and microcrystallites, their surface morphology, orientations onto various substrates, and crystal structure.     

射频磁控反应溅射制备Al2O3薄膜的工艺研究

采用射频磁控反应溅射法,以高纯Al为靶材,高纯O2为反应气体,在不锈钢和单晶Si基片上成功地制备了氧化铝(Al2O3)薄膜,并对氧化铝薄膜的沉积速率、结构和表面形貌进行了研究.结果表明,沉积速率随着射频功率的增大先几乎呈线性增大而后缓慢增大;随着溅射气压的增加,沉积速率先增大,在一定气压时达到峰值后继续随气压增大而减小,同时随着靶基距的增大而减小;随着氧气流量的不断增加,靶面溅射的物质从金属态过渡到氧化物态,沉积速率也随之不断降低.X射线衍射图谱表明薄膜结构为非晶态;用原子力显微镜对薄膜表面形貌观察,薄膜微结构为柱状.     

On the structural, morphological, optical and electrical properties of sol-gel deposited ZnO:In films

Indium-doped zinc oxide thin films deposition was performed by the sol-gel technique using homogeneous and stable solutions of zinc acetate 2-hydrate and indium chloride in ethanol. Films were spin coated onto glass substrates. After drying and after a heat treatment at 450 °C, highly transparent (80%-90%) films were obtained. The effect on the structural, morphological, optical and electrical thin films properties of the dopant concentration was investigated. The temperature dependencies of the electrical conductivity under vacuum and in open atmosphere were analysed and discussed.     

Preparation and characterisation of silver particulate films on softened polystyrene substrates

The preparation of silver particulate films on softened polystyrene (PS) substrates and their characterisation using Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and optical absorption spectroscopy is reported in this paper. Silver films of 150 nm thickness were vacuum deposited onto PS coated glass substrates held at temperatures in the range 415–475 K at different deposition rates of 4 to 12 Å/s. SEM studies indicate that films deposited at 415 K are close to a semicontinuous structure and the structure is discontinuous at higher temperatures. The film morphology is strongly dependent on the deposition rate at any given substrate temperature. The film agglomeration increases with increasing rate of deposition. In the XPS studies, considerable attenuation of the signal corresponding to silver is observed at lower electron take of angles (ETOAs). This indicates that Ag is formed beneath the PS surface. Optical absorption studies showed an interesting red shift of the plasmon resonance wavelength for lower deposition rates again indicating that a sub-surface particulate structure is formed at lower deposition rates. These results are consistent with reported observations.