Pulsed laser deposition of cobalt ferrite in a reactive O2:N2 atmosphere: effect of the deposition pressure and temperature

Thin films of CoFe₂O₄ have been fabricated by pulsed laser ablation of a metallic CoFe₂ target at two different temperatures (200 and 400 °C) and in various O₂:N₂, 20:80 pressures [from 0.7 Pa (5×10^-3 Torr) up to 26.7 Pa (2×10^-1 Torr)]. Too low pressures resulted in an insufficient oxidation of the deposited material and an antiferromagnetic (Fe,Co)O phase is observed together with CoFe₂O₄. A minimum pressure of 6.7 Pa was found necessary to obtain pure CoFe₂O₄ films with magnetic properties close to the bulk. The higher the pressure and the temperature, the larger was the roughness of the films. The optimum deposition temperature and pressure to obtain flat (3 nm rms roughness) CoFe₂O₄ films were, respectively, 200 °C and 6.7 Pa.     

Cu<Subscript>2</Subscript>O and CuO Films Produced by Chemical and Anodic Oxidation on the Surface of Copper Foil

The processes underlying the chemical and anodic oxidation of the surface of copper foil have been studied by X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. It has been shown that, in the case of anodic oxidation, at a given process duration (τ) the composition and density of initially forming Cu(OH)₂ films depend not only on the current density (j_a) but also on whether or not the electrolyte is stirred. A Cu₂O film with an optimal, coral-like structure has been produced by the anodic oxidation of copper foil for τ = 10 min at j_a = 5 mA/cm² without stirring, followed by the thermal reduction of the Cu(OH)₂ in a nitrogen atmosphere for 1 h at 500°C. In the case of the chemical oxidation of the copper foil surface, similar Cu₂O films with a coral-like structure can also be produced by the thermal reduction of initially forming Cu(OH)₂ at 500°C for 1 h.     

Exciting Dilute Magnetic Semiconductor: Copper-Doped ZnO

The present study is focused on the copper-doped ZnO system. Bulk copper-doped ZnO pellets were synthesized by a solid-state reaction technique and used as target material in pulsed laser deposition. Thin films were grown for different Cu doped pellets on sapphire substrates in vacuum (5×10^?5 mbar). Thin films having (002) plane of ZnO showed different oxidation states of dopants. M–H curves exhibited weak ferromagnetic signal for 1–3 % Cu doping but for 5 % Cu doped thin film sample showed the diamagnetic behavior. For deeper information, thin films were grown for 5 % Cu doped ZnO bulk pellet in different oxygen ambient pressures and analyzed. PL measurement at low temperature showed the emission peak in thin films samples due to acceptor-related transitions. XPS results show that copper exists in Cu²⁺ and Cu⁺¹ valence states in thin films and with increasing O₂ ambient pressure the valence-band maximum in films shifts towards higher binding energy. Furthermore, in lower oxygen ambient pressure (1×10^?2 mbar) thin films showed magnetic behavior but this vanished for the film grown at higher ambient pressures of oxygen (6×10^?2 mbar), which hints towards the decrease in donor defects.     

Structural and optical studies on dc reactive magnetron sputtered Cu2O films

Cuprous oxide (Cu₂O) thin films were deposited by dc reactive magnetron sputtering technique onto glass substrates by sputtering of pure copper target in a mixture of argon and oxygen gases under various oxygen partial pressures in the range 8 × 10^− 3–1 × 10^− 1 Pa at a constant substrate temperature of 473 K and a sputtering pressure of 4 Pa. The dependence of cathode potential on the oxygen partial pressure was explained in terms of cathode poisoning effect. The influence of oxygen partial pressure on the structural and optical properties of Cu₂O films was systematically studied. Single phase films of Cu₂O were obtained at an oxygen partial pressure of 2 × 10^− 2 Pa. The films formed at an oxygen partial pressure of 2 × 10^− 2 Pa were polycrystalline with cubic structure and exhibited an optical band gap of 2.04 eV.     

Structure and composition of Cu<Subscript>2</Subscript>O films produced by anodizing copper foil on fiberglass laminate

The effect of process conditions on the composition and structure of anodic Cu₂O films grown in sulfate-chloride electrolytes has been studied using Auger electron spectroscopy, x-ray diffraction, and atomic force microscopy. The results demonstrate that the copper and oxygen depth profiles in the anodic copper(I) oxide films (ACOFs) are similar in shape. The copper content near the surface is only slightly lower than the bulk copper content. Starting at a depth of 9 nm, the Cu content is constant at an average of 62.7 at %. The Cu₂O films grown at a current density j = 3 mA/cm² have the most perfect stoichiometry, with deviations only in the surface layer. Anodic oxidation produces unoriented polycrystalline films of complex composition. In addition to Cu₂O, the films contain CuCl and trace levels of copper. Raising the anode current density influences, for the most part, the formation of (111)-oriented crystallites, changing their orientation from (111) to (220). We assume that nonmetal (oxygen or chlorine) atoms are incorporated into the cubic structure of copper without changing its symmetry but increasing its unit-cell parameter: from 0.3607 (Cu) to 0.426 (Cu₂O) and to 0.541 nm (CuCl).     

The structure and ferromagnetic properties of (Fe0.12CuxZn0.88−x)O thin films deposited on Si substrates by R.F. sputtering

Fe–Cu co-doped ZnO thin films deposited on silicon substrates were prepared by R.F. magnetron sputtering. The effects of various amounts of copper on the microstructure, surface morphology, composition, and magnetic properties of ZnO thin films were examined. The results of the experiments show that the structures of the ZnO thin films grown on the silicon substrate have a preferred orientation of (002). By increasing the copper concentration, the Fe ions exist as Fe²⁺ in the Fe_0.12Cu_xZn_0.88−xO system, but Cu²⁺ and Cu¹⁺ ions coexist when the Cu replaces the Zn. In addition, the ZnO thin films show ferromagnetic behaviour at room temperature and the largest saturation magnetization (Ms) is 5.64 × 10⁴ A/m for the as-grown Fe_0.12Cu_0.02Zn_0.86O thin film.     

Properties of TiNxfilms reactively sputtered in an argon-nitrogen atmosphere

The dependence of the resistivity and temperature coefficient of resistivity (TCR) of TiN_x films on nitrogen pressure is described. The partial nitrogen pressure was varied from 10^?5 Torr to 2×10^?4 Torr. The maximum value of the resistivity (216 μΩ cm) and the lowest negative value of TCR (?33ppmK^?1) were obtained in the nitrogen pressure range (2?4)×10^?5 Torr. The minimum value of the resistivity (44 μΩ cm) and the highest positive value of the TCR (1160 ppm K^-1 were obtained in the nitrogen pressure range (4?10)×10^?5 Torr. The influence of aging temperature up to 573 K on the resistance changes are shown. X-ray diffraction analysis indicated the presence of oriented or non-oriented TiN in these films.     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

The microstructure and orientation of silver on NaCl: The influence of surface conditions

Silver films up to 1000 Å thick (coalescence stage and continuous films) were evaporated onto vacuum-cleaved NaCl at constant temperature and constant deposition rate but under various vacuum conditions (ultrahigh vacuum (UHV), high vacuum (oil pumped and ion pumped), a partial pressure of contaminant (10^-10–10^-6 Torr) etc.). The films were characterized by low energy electron diffraction, Auger electron spectroscopy, transmission electron microscopy and transmission electron diffraction to determine their orientation, microstructure and cleanliness. The UHV-grown films were always polycrystalline. In contrast with previous observations, however, an increase in the partial pressure of H₂O alone did not improve the epitaxy. Hence the influence of other materials such as O₂, H₂O + O₂, hydrocarbons etc. was investigated. In addition, films were grown in UHV after pre-irradiation of the substrate with electrons and prenucleation at room temperature. If the prenucleated silver clusters were small and if their orientation was improved by annealing, continuous films were perfectly epitaxial even when the deposition of silver was carried out at room temperature after prenucleation. This indicates a post-nucleation mechanism of epitaxy.     

Copper(I) oxide micro-cubical structures formation by metal organic chemical vapor deposition from copper(II) acetylacetonate

The copper oxide films were deposited by decomposition of copper(II) acetylacetonate precursor in a hot wall horizontal flow tubular furnace by chemical vapor deposition method. The obtained data revealed change in phase of the deposits from crystalline copper(I) oxide (Cu₂O) to copper(II) oxide (CuO) structures on increasing the substrate temperature from 195 to 430 °C. The scanning electron microscope images showed the formation of mono-dispersed micron-sized Cu₂O cubical structures. The Cu₂O micro-cubes were observed to have a comparatively higher optical transmittance than CuO film in the visible spectral region. The Cu₂O micro-cubical films are expected to underlie the potential use as cost effective transparent conducting oxide electrode in solar cell applications.     

Growth and characterisation of CaCu2Ox thin films by pulsed injection MOCVD

Oxides with the structure MCu₂O₂ (M = Ca, Ba, Mg and Sr) are promising materials for the development of new p-type transparent conducting oxide thin films. This paper reports preliminary results on the growth and characterisation of CaCu₂O_x thin films by pulsed injection MOCVD. By using as precursors calcium and copper tetramethylheptanedionate dissolved in meta-xylene, mixed calcium-copper films have been grown in the temperature range from 450 °C to 550 °C. At these temperatures, deposited films exhibited a high mirror reflection effect, good adherence and were reasonably uniform with the cationic composition of the films being easily controlled by adjusting the copper-calcium ratio in the precursor solution. In CaCu₂O₂, copper is in the Cu¹⁺ oxidation state and depending on the oxygen partial pressure used, the films either contained CaCu₂O₃ or a mixture of CaO, CuO and Cu₂O. Optimisation of annealing conditions increased the presence of Cu¹⁺ in the film. Films had a maximum transmittance of 50% in the visible range and were highly resistive. Appropriate annealing conditions reduced the resistivity of the films.     

Photoelectrochemical solar cell studies on electroplated cuprous oxide thin films

Cuprous oxide (Cu₂O) is an interesting p-type semiconductor with a band gap of 2 eV suitable for solar cell applications. Deposition of Cu₂O thin films by electrodeposition from aqueous solutions is a low temperature and inexpensive technique. in the present work, Cu₂O thin films were cathodically deposited on Cu and tin oxide coated glass substrates by the cathodic reduction of copper (II) lactate solution. The optimized deposition conditions to synthesize cuprous oxide thin films were experimentally identified as; Deposition potential: −0.555 V versus SCE, pH: 9.0 ± 0.1, Bath temperature: 70^∘C. X-ray diffraction studies revealed the formation of single phase cubic Cu₂O films. The effect of annealing on the structure and morphology of Cu₂O thin films are studied. The dielectric susceptibility, optical conductivity and packing density are evaluated. Photoelectrochemical solar cells based on p-Cu₂O films are constructed. Spectral response studies indicate a peak in photo current density around 600 nm corresponding to the band gap of Cu₂O thin films. The effects of annealing, chemical etching and photo etching on the solar cell parameters are studied.     

Controlled growth and characteristics of single-phase Cu2O and CuO films by pulsed laser deposition

Copper oxide, Cu₂O and CuO, thin films have been synthesized on Si (100) substrates using pulsed laser deposition method. The influences of substrate temperature and oxygen pressure on the structural properties of copper oxide films were discussed. The X-ray diffraction results show that the structure of the films changes from Cu₂O to CuO phase with the increasing of the oxygen pressure. It is also found that the (200) and (111) preferred Cu₂O films can be modified by changing substrate temperature. The formation of Cu₂O and CuO films are further identified by Fourier transform infrared spectroscopy. For the Cu₂O films, X-ray photoelectron spectroscopic studies indicate the presence of CuO on the surface. In addition, the optical gaps of Cu₂O and CuO films have been determined by measuring the transmittance and reflectance spectra.     

The annealing of misfit dislocations in the (111) Cu/(111) Cu2O system

Recent work on the early stages of the epitaxial oxidation of (111) Cu at 350 °C and in oxygen pressures between 10^-7 and 10^-4 Torr has resulted in the determination of the growth modes that occur and the accompanying elastic strains. Initially a hexagonal 3 × 3 oxide superlattice is formed which continues to grow by a layer growth mechanism up to a theoretically estimated thickness of approximately five monomolecular layers. Subsequent oxidation occurs by the formation of lamellar islands containing misfit dislocations which reduce the coincidence lattice misfit strain. In the present work these (111) Cu/(111) Cu₂O bilayers were annealed and examined in situ in the transmission electron microscope in the temperature range 25–350 °C. The misfit dislocation density decreased as the temperature was increased. The annealing effects are complex and interdiffusion phenomena can be observed even at 60 °C.     

Cu2O thin films deposited by reactive direct current magnetron sputtering

The Cu₂O thin films were prepared on quartz substrate by reactive direct current magnetron sputtering. The influences of oxygen partial pressure and gas flow rate on the structures and properties of deposited films were investigated. Varying oxygen partial pressure leads to the synthesis of Cu₂O, Cu₄O₃ and CuO with different microstructures. At a constant oxygen partial pressure of 6.6 × 10^− 2 Pa, the single Cu₂O films can be obtained when the gas flow rate is below 80 sccm. The as-deposited Cu₂O thin films have a very high absorption in the visible region resulting in the visible-light induced photocatalytic activity.     

Influence of oxygen partial pressure on structural, electrical, and optical properties of Al-doped ZnO film prepared by the ion beam co-sputtering method

Aluminum doped zinc oxide (AZO) films were prepared at room temperature by ion beam co-sputtering system under various oxygen partial pressures. The structural, electrical, and optical properties of the films were studied by XRD, XPS, Hall measurement, and spectrometer. The AZO film with low resistivity, 7.8 × 10^?4 Ω cm, and high transparency, ~80 %, was obtained at the optimum oxygen partial pressure of 1.3 × 10^?4 Torr and the intense (002) diffraction peak was observed simultaneously. Different optical band gaps observed in the films prepared under various oxygen partial pressures are closely related to the carrier concentrations in the films. Three O_1s components were applied to fit the XPS O_1s spectra. They consist of adsorbed oxygen species, oxygen in O-Zn bonds surrounded by oxygen vacancies, and oxygen in the O-Zn bonds. Two components, Zn in Zn–O bonds and Zn with higher than +2 oxidation states, were used to fit Zn_2p3/2 spectra. It was found that the increase of film’s resistivity which may result from the drops in the oxygen vacancy, Zn interstitial, carrier concentration, and grain size. No apparent transmission change of the film in the visible light region as a function of oxygen partial pressure was detected.     

Characterization of copper oxide nanolayers deposited by direct current magnetron sputtering

Direct current reactive magnetron sputtering was used to deposit the thin layers of copper oxide (Cu₂O) on glass substrates. A solid disc of pure copper as the target was sputtered in an argon gas under sputtering pressures varying from 0.133 to 4 Pa. The effects of the sputtering power and pressure on the structural and optical properties of Cu₂O thin films were systematically studied. The deposited layers were characterized using X-ray diffraction, atomic force microscopy, profilometry and spectrophotometry. The optical transmission of the films was measured in the visible region. The increase in pressure resulted in a higher growth rate than increasing sputtering power. The increase in power produced Cu₂O thin films that were detrimental to the optical transmission of the films.     

Properties of Cu-doped ZnO films by RF sputtering method: Thickness dependence

We present results concerning the thickness dependence of structural, morphological and optical properties of the Zn_0.98Cu_0.02O films deposited on glass substrates using radio frequency (RF) sputtering method. The microstructure and the chemical state of oxygen, copper and zinc in ZnO and Zn_0.98Cu_0.02O films were investigated by X-ray diffraction spectroscopy (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The results indicate that Zn_0.98Cu_0.02O films are the wurtzite structure with strong c-axis orientation. Crystallinity of the films is closely related to the film thickness. With increasing film thickness, there are more surface (mainly nanopores) defects existing in the Zn_0.98Cu_0.02O films and surface roughness increases. XRD and XPS data show that the valence state of copper in the Zn_0.98Cu_0.02O films is Cu²⁺. The transparency of all films is more than 85% in the visible region.     

Room temperature oxidation rate constants of ultra- thin (discontinuous) molybdenum films

Following the method developed by Fehlner, an attempt is made to determine the room temperature oxidation rate constants of ultra-thin (discontinuous) molybdenum films. Thin films of molybdenum of thickness less than 100 Å, corresponding to resistance of 0.55–12.0 Mω, were deposited onto glass substrates at pressures of less than 10^?8 Torr and were exposed to oxygen pressures of 10^?7?10^?5 Torr at room temperature. The oxidation rate constants were calculated from the slope of log R_dcversus log t plots using the electron tunneling conduction model of Neugebauer and Webb. Values of the logarithmic oxidation rate constants obtained ((0.05?0.18) × 10^?9 cm) are compared with those for various refractory metal films and agree fairly well with those published in the literature for discontinuous metal films.     

Preparation of nanocrystalline Cu<Subscript>2</Subscript>O thin film by pulsed laser deposition

In this paper, the synthesis of nanocrystalline copper oxides Cu₂O and CuO thin films on glass substrates using a pulsed 532 nm Nd:YAG laser is presented. Deposition of films is achieved at two different substrate temperatures. The influence of substrate temperature on the structural and optical properties of copper oxide films are discussed and analyzed. The X-ray diffraction (XRD) results show that the deposited films are crystalline in nature. Films prepared at 300 °C substrate temperature were Cu₂O and has (111) and (200) diffracted peaks, while films grown at 500 °C were CuO and has (111) and (020) planes. The morphology of deposited films were characterized by scanning electron microscope (SEM) and atomic force microscope (AFM). The optical energy gap of Cu₂O and CuO films have been determined and found to be 2.04 and 1.35 eV respectively.