Sol-gel silica thin films with copper selenide

The silica sol-gel films with copper selenide produced by the selenization of metallic copper nanoparticles were fabricated. The composition of the films was studied with X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and optical absorption spectroscopy. Several copper selenide phases were detected with XRD and contribute into the complicated behavior of core levels (Cu2p, Se3d, and Si2p) and Auger levels (Cu) in the XPS analysis. The optical absorption features of the films in the visible and near-infra red range are presented. The consistent interpretation of experimental data is proposed based on assumption of copper multivalence in the system “particles-silica matrix”.     

Nanocrystalline copper sulfide and copper selenide thin films with p-type metallic behavior

Copper chalcogenide materials are interesting for multiple applications due to the feasibility of suiting their optical absorption and electrical conduction by the creation of copper vacancies. Here, Cu _x S and Cu _x Se nanocrystalline films with p-type conductivity have been obtained by heating evaporated copper layers of various thicknesses with elemental sulfur or selenium, at temperatures ranging from 250 to 400 °C. These preparation parameters determine the composition and the crystalline structure of the samples, which in turn control their morphology, optical and electrical properties. Thus, the surface roughness increases with the mean crystallite size, whereas the hole concentration increases as the copper atomic proportion (or x value) decreases. Owing to the high carrier densities achieved, around 10²² cm^?3, the samples show a metallic behavior with plasmonic absorption in the near infrared and electrical transport dominated by phonon scattering. Apart from such common behavior, some differences have been established between the sulfide and selenide films. One is the superior thermal stability of hexagonal CuS, present in all the temperature range, with respect to hexagonal CuSe, which evolves to cubic Cu_1.8Se above 300 °C. Other is about the bandgap, wider for the sulfide than selenide samples.     

Photoelectrochemical studies on spray deposited copper selenide thin films

Thin films of copper selenide have been deposited by spraying a mixture of aqueous solutions (0.50 M) of copper chloride hydrate (CuCl₂·2H₂O) and selenourea [H₂NC(Se)NH₂] on preheated fluorine doped tin oxide coated glass substrates at various substrate temperatures. The cell configurations copper selenide/0.5 M K₂SO₄/C are used for studying the capacitance–voltage (C–V) characteristics in the dark, current–voltage (I–V) characteristics in dark and under illumination, photovoltaic power output and spectral response characteristics of the as deposited films. Photoelectrochemical study records that as deposited copper selenide thin films are of p-type. The spectral response characteristics of the films at room temperature show a prominent, sharp peak at 550 nm. The measured values of efficiency (η) and fill factor (FF) are found to be 0.99 % and 0.51 respectively for film deposited at 350 °C.     

Ellipsometry of thin films of copper phthalocyanine

Ellipsometric measurements have provided qualitative information on the optical properties of CuPC films deposited on a thin gold layer substrate. Detailed interpretation was complicated by variations in the density of the deposited layers and the surface roughness of the substrate. Films less than 100 nm thick can be satisfactory represented by a single homogeneous isotropic layer. Thicker films appear to be equivalent to an isotropic inner layer and an anisotropic outer layer, where the latter results from bulk deposition of CuPC with the molecules in a predominant orientation to the surface. Reasonable agreement has been obtained between film thicknesses measured by weighing and by ellipsometry, assuming a single homogeneous anisotropic film for thickness in excess of 150 nm.     

Diffusion of copper in thin TiN films

The diffusivity of copper in thin TiN layers was determined in specimens prepared by r.f. sputtering a copper (80 nm) layer onto a TiN (200 nm) layer on sapphire and silicon substrates. Specimens were isothermally heat treated at 608, 635 and 700 °C at pressures lower than 2 × 10^?6 Pa; they were compositionally analyzed by Rutherford backscattering spectroscopy and Auger sputter profiling; and they were microstructurally characterized by transmission electron microscopy and electron diffraction. The diffusivity D = 9 × 10⁷cm²s^?1exp(?427 kJmol^?1/RT) from 608 to 700 °C. The mechanisms of copper diffusion were not bulk processes, but they were probably processes involving primarily grain boundaries in the TiN. This very low diffusivity at these temperatures makes TiN/Cu an excellent candidate for a high temperature metallization for silicon solar concentrator cells.     

Substrate considerations for graphene synthesis on thin copper films

Chemical vapor deposition on copper substrates is a primary technique for synthesis of high quality graphene films over large areas. While well-developed processes are in place for catalytic growth of graphene on bulk copper substrates, chemical vapor deposition of graphene on thin films could provide a means for simplified device processing through the elimination of the layer transfer process. Recently, it was demonstrated that transfer-free growth and processing is possible on SiO(2). However, the Cu/SiO(2)/Si material system must be stable at high temperatures for high quality transfer-free graphene. This study identifies the presence of interdiffusion at the Cu/SiO(2) interface and investigates the influence of metal (Ni, Cr, W) and insulating (Si(3)N(4), Al(2)O(3), HfO(2)) diffusion barrier layers on Cu-SiO(2) interdiffusion, as well as graphene structural quality. Regardless of barrier choice, we find the presence of Cu diffusion into the silicon substrate as well as the presence of Cu-Si-O domains on the surface of the copper film. As a result, we investigate the choice of a sapphire substrate and present evidence that it is a robust substrate for synthesis and processing of high quality, transfer-free graphene.     

Effect of substrate on electroplated copper sulphide thin films

Copper Sulphide thin films have been prepared on different substrates using electrodeposition technique. X-ray diffraction analysis showed that the prepared films possess polycrystalline in nature with cubic structure. Microstructural parameters such as crystallite size, strain and dislocation density are determined using X-ray diffraction data. Film composition and surface morphology have been analyzed using Scanning electron microscopy and Energy dispersive analysis by X-rays. Optical absorption analysis showed that the prepared films possess band gap value in the range between 2.2 and 2.4 eV for films obtained on different substrates.     

Ductility of thin copper films on rough polymer substrates

Electronic components in modern flexible electronics are connected by interconnects, which typically have the form of metal films resting on polymer substrates. This paper firstly studies experimentally the ductility of Cu films deposited on polyimide substrate with roughened surface (due to sandblasting) and finds that, upon tensile loading along the direction of film surface, the density of surface cracks in the film decreases with increasing surface roughness. The method of finite elements is subsequently employed to study the distribution of tensile stresses in the film and their influence on film cracking (initiation and propagation). It is demonstrated that a rough (curved) interface can reduce the tensile stresses along the film surface so as to restrain channel cracking of the film. Finally, the cohesive zone model is used to study the initiation and spreading of damage in the film and interfacial debonding of the curved interface. Both the interfacial damage and interface crack length are reduced as a result of interface roughening.     

Effect of heat-treatment on the hydrogen sensitivity of ZnO thin films loaded with palladium salts

Porous ZnO thin films were impregnated with palladium salts from their aqueous solutions, and the effects of heat-treatments on the appearence of the hydrogen sensitivity were investigated. In the course of the impregnation of PdCl₂, a ZnCl₂·4Zn(OH)₂ phase is formed in a surface region which retards the appearence of the hydrogen sensitivities. By heating the sample at 140–200 °C, this phase is decomposed but the impregnated PdCl₂ is not decomposed, and a remarkable hydrogen sensitivity appears even at room temperature. Similar situations hold in the loading of other kind of palladium salts, although the magnitude of the sensitivity is different between different kinds of loaded salts. The mechanisms of the appearence of the hydrogen sensitivity and of the loss of the sensitivity caused by the heat-treatment at higher temperatures are discussed.     

Crystallization of amorphous silicon thin films: comparison between experimental and computer simulation results

Polycrystalline silicon obtained by the crystallization of thin amorphous silicon films has been an important material for microelectronics technology during the last decades. Many properties are improved in crystallized amorphous silicon compared to the as-deposited polysilicon such as larger grain size, smoother surface, and higher-carrier mobility. In this work, the crystallization of amorphous silicon is investigated by combining transmission electron microscopy (TEM) observations and molecular dynamics calculations. TEM observations on a series of specimens have shown that the majority of the silicon grains are oriented with a zone axis normal to the surface. In order to understand the crystallization mechanism molecular dynamic simulations were performed. It is found that the c/amorphous interface exhibits the lowest reduced interfacial energy density while the c/amorphous has the lowest reduced energy differences per unit interfacial area. The most energetically unfavorable interface is c/amorphous.     

Amplitude-dependent internal friction in copper thin films on silicon substrates

Internal friction in copper thin films 0.2–1.5 μm thick on silicon substrates has been measured between 180 and 340 K as a function of strain amplitude. Analysis of the amplitude-dependent internal friction in the copper films shows the relation between the plastic strain of the order of 10⁻⁹ and the effective stress on dislocation motion. The stress–strain curves thus obtained for the copper films tend to shift to a higher stress with decreasing film thickness and also with decreasing temperature, both indicating a suppression of microplastic flow. It is concluded that the microflow stress at a constant level of the plastic strain varies inversely with the film thickness at all temperatures examined. The film thickness effect in the microplastic range can be explained on the basis of a dislocation-bowing model.     

Thermoelectric textile devices with thin films of nanocellulose and copper iodide

Owing to the rapid development of wearable electronics and smart textiles, demands for flexible and wearable thermoelectric (TE) devices, which can generate electricity in a ubiquitous, unintermittent and noiseless way for on-body applications are growing rapidly. Due to the inherent flexibility and wearability features, textile-based thermoelectric generators (TEGs) possess significant potential for biomedical and consumer health and safety applications. In this study, using commercial cotton fabric, we created efficient thermoelectric (TE) textile that, unlike analogs, is based on thin-film composite of biocompatible semiconductor copper iodide (CuI) and biodegradable polymer nanocellulose (NC_p) obtained by processing a widespread plant common reed. The CuI films with average thickness 10 µm were deposited via low-temperature aqueous cheap, facile, and scalable fabrication technique Successive Ionic Layer Adsorption and Reaction (SILAR). The NC_p sublayer made it possible to fabricate thin-film ohmic contacts through vacuum deposition of chromium on the nanostructured CuI film in the TE textile. The topping of CuI film with NC_p layer improved durability and wear resistance of the wearable thermoelectric module fabricated with this TE textile. The developed TE module has shown output power density 44 µW/cm² at temperature gradient 50 K that is among the best currently known results for solid miniature flexible and fabric-based TEGs.

     

Electric conduction in copper gallium telluride thin films

P type copper gallium telluride (CuGaTe₂) synthesized from the elements was used as a source for the preparation of films by flash evaporation. Films of different thicknesses were prepared and their electrical conductivity was measured in the temperature range 100–300 K. While in the case of thin films the low temperature conduction could be explained by a variable range hopping process, for thicker films the conduction process could be attributed to thermally assisted tunnelling through the grain boundary barrier. The high temperature conductivity data fits well to the process of transport by thermionic emission over the grain boundaries.