Thin film growth of epitaxial, polycrystalline and amorphous SrRuO3

The SrRuO₃ thin films were grown on amorphous fused silica and (100) single crystal LaAlO₃ substrates by pulsed laser deposition method. On fused silica substrates, polycrystalline SrRuO₃ thin film was obtained and below the crystallization temperature, SrRuO₃ thin films show an amorphous phase. For the case of epitaxial growth on (100) single crystal LaAlO₃ substrate, the crystallization temperature of SrRuO₃ thin film was increased by ∼ 100 °C indicating that additional energy is necessary in order to obtain the epitaxial thin film. By using the eclipse method and the control of substrate temperature, the variations of surface morphologies and grain size were observed by atomic force microscope. Below the crystallization temperature, amorphous SrRuO₃ thin film shows hopping transport property of an insulator.     

Synthesis, characterization and effect of low energy Ar ion irradiation on gadolinium oxide nanoparticles

In this work, we report on the surfactant assisted synthesis of gadolinium oxide (Gd₂O₃) nanoparticles and their characterization through various microscopic and spectroscopic tools. Exhibiting a monoclinic phase, the nanoscale Gd₂O₃ particles are believed to be comprising of crystallites with an average size of ∼3.2 nm, as revealed from the X-ray diffraction analysis. The transmission electron microscopy has predicted a particle size of ∼9 nm and an interplanar spacing of ∼0.28 nm. Fourier transform infrared spectroscopy studies show that Gd-O inplane vibrations at 536.8 and 413.3 cm⁻¹ were more prominent for 80-keV Ar-ion irradiated Gd₂O₃ nanosystem than unirradiated system. The photoluminescence (PL) spectra of irradiated specimen have revealed an improvement in the symmetry factor owing to significant enhancement of surface-trap emission, compared to the band-edge counterpart. Irradiation induced creation of point defects (oxygen vacancies) were predicted both from PL and electron paramagnetic resonance (EPR) studies. Further, the Raman spectra of the irradiated sample have exhibited notable vibrational features along with the evolution of a new peak at ∼202 cm⁻¹. This can be ascribed to an additional Raman active vibrational response owing to considerable modification of the nanostructure surface as a result of ion bombardment. Probing nanoscale defects through prime spectroscopy tools would find a new avenue for precise tuning of physical properties with generation and annihilation of defects.     

Studies on micro-structural and electrical properties of spray-deposited fluorine-doped tin oxide thin films from low-cost precursor

Thin films of fluorine-doped tin oxide (SnO₂:F) on glass were prepared by spray pyrolysis technique using stannous chloride (SnCl₂) and ammonium fluoride (NH₄F) as precursors. The as-prepared films were characterized for their structural and electrical properties and are discussed in detail in this article. The surface morphology studies revealed that the films are grainy and the roughness of undoped films has been reduced on fluorine doping. X-ray diffraction (XRD) studies revealed that the films are polycrystalline. It further revealed that the undoped films grow along the preferred orientation of (211), whereas all the doped films grow along (200). The minimum sheet resistance 1.75 Ω/□ achieved in the present study for the films doped with 15 wt.% F is the lowest among the reported values for these materials prepared using SnCl₂ precursor. The electrical transport phenomenon has been analyzed in order to find out the possible scattering mechanism that limiting the mobility of charge carriers.     

An investigation on electrochromic properties of (WO3)1−x-(Fe2O3)x thin films

In this research, the effect of Fe₂O₃ content on the electrochromic properties of WO₃ in thermally evaporated (WO₃)_1−x-(Fe₂O₃)_x thin films (0 ≤ x ≤ 0.4) has been studied. The atomic composition of the deposited metal oxides was determined by X-ray photoelectron spectroscopy analysis. The surface morphology of the thin films has been examined by atomic force microscopy. The surface roughness of all the films was measured about 1.3 nm with an average lateral grain size of 30 nm showing a smooth and nanostructured surface. The electrochromic properties of (WO₃)_1−x-(Fe₂O₃)_x thin films deposited on ITO/glass substrate were studied in a LiClO₄ + PC electrolyte by using ultraviolet-visible spectrophotometry. It was shown that increasing the Fe₂O₃ content leads to reduction of the optical density (ΔOD) of the colored films and also leads to increasing the optimum coloring voltage from 4 to 6 V in which ΔOD shows its maximum values, in our experimental conditions. Furthermore, by using this procedure, it is possible to make an electrochromical filter which behaves similar to the colored WO₃ film in the visible region, while it can be nearly transparent for near-infrared wavelengths, in contrast of the pure colored WO₃ film.     

Growth of cubic and hexagonal CdTe thin films by pulsed laser deposition

The paper reports the growth of cadmium telluride (CdTe) thin films by pulsed laser deposition (PLD) using excimer laser (KrF, λ=248 nm, 10 Hz) on corning 7059 glass and SnO₂-coated glass (SnO₂/glass) substrates at different substrate temperatures (T_s) and at different laser energy pulses. Single crystal target CdTe was used for deposition of thin films. With 30 min deposition time, 1.8- to ∼3-μm-thick films were obtained up to 200 °C substrate temperature. However, the film re-evaporates from the substrate surface at temperatures >275 °C. Atomic force microscopy (AFM) shows an average grain size ∼0.3 μm. X-ray diffraction analysis confirms the formation of CdTe cubic phase at all pulse energies except at 200 mJ. At 200 mJ laser energy, the films show hexagonal phase. Optical properties of CdTe were also investigated and the band gap of CdTe films were found as 1.54 eV for hexagonal phase and ∼1.6 eV for cubic phase.     

Chemical, optical, vibrational and luminescent properties of hydrogenated silicon-rich oxynitride films

X-ray photoelectron spectroscopy, spectroscopic ellipsometry, Fourier transform infrared and room temperature photoluminescence spectroscopy has been used to investigate the chemical, optical, vibrational and luminescent properties of Plasma Enhanced Chemical Vapor Deposited SiO_xN_y/H (0.17≤x≤0.96; 0.07≤y≤0.27), hydrogenated silicon-rich oxynitride (SRON). The linear dependence of the refractive index of the SRON films on the O/Si ratio was established. The photoluminescence from the SRON films were attributed to the embedded amorphous silicon clusters in the films. The dependence of luminescence maximum values on the O/Si and O/N ratios has been explored. We postulate that at O/Si ratio of 0.18 and an O/N ratio of 2.0 (SiO_0.18N_0.09) the film underwent a transformation from silicon-rich oxynitride to a-Si/H film with oxygen and nitrogen impurities.     

Dielectric properties of (Ba,Ca)(Zr,Ti)O3/CaRuO3 heterostructure thin films prepared by pulsed laser deposition

(Ba_0.90Ca_0.10)(Zr_0.25Ti_0.75)O₃ (BCZT) thin films were grown on Pt/Ti/SiO₂/Si substrates without and with a CaRuO₃ (CRO) buffer layer using pulsed laser deposition (PLD). The structure and surface morphology of the films have been characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). At room temperature and 1 MHz, the dependence of dielectric constant and tunability of the films with electric field were investigated; the dielectric constant and tunability are 725 and 47.0%, 877 and 50.4%, respectively, for the BCZT film on Pt/Ti/SiO₂/Si substrates without and with the CRO buffer layer at 400 kV/cm. The tunability of the BCZT/CRO heterostructure thin films on Pt/Ti/SiO₂/Si substrates was higher than that of the BCZT thin films on Pt/Ti/SiO₂/Si substrates. The high constant likely results from the oxide electrode (CRO).     

Evolution of the oxidation states at the WO3 thin film surface during annealing in gases

The main objective of the present study was identification of the electronic states associated with W ions and defects (oxygen vacancies), which determine the surface stoichiometry of WO₃ thin films and consequently their reactivity. The electronic surface structure of WO₃ thin films was deduced from electron energy loss spectroscopy (EELS) analyses. We have investigated the changes of the electronic structure associated with thermal treatments under reducing and oxidizing atmospheres. We analyzed 200 spectra obtained on 50 samples and we present here the main tendencies of surface evolution. We identified three kinds of surface electronic structure, which correspond to decrease in oxidation level of the surface. They were attributed to clean, slightly reduced reconstructed and WO₂ terminated surfaces, respectively.     

The effect of heating time on growth of NaxWO3 nanowhiskers

A simple method for synthesis of Na_xWO₃ nanowhiskers on tungsten thin films with 40 nm thickness sputtered on soda lime substrate as a source of sodium atoms has been reported for the first time. After heat treatment of the W thin films at 650 °C in N₂ ambient for different times (15, 80 and 180 min), crystalline Na_xWO₃ nanowhiskers with [0 0 1] direction were obtained. scanning electron microscopy (SEM), X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and optical transmission/reflection measurements were employed to determine various properties of the grown nanowhiskers. Experimental results revealed that size and density of nanowhiskers were dependent on the annealing time and found that the 80-min heat treatment was a proper time for the growth of sodium-doped tungsten oxide nanowhiskers, in our experimental conditions. According to SEM observations, the synthesized nanowhiskers have 70-300 nm in width and 1-10 μm in length. It was also observed that by increasing the heating time to 180 min resulted in diffusion of the nanowhiskers into the substrate.     

Microstructure and electrical conductivity of Au-MgF2 nanoparticle cermet films

Au-MgF₂ nanoparticle cermet films with Au volume fraction of 6-50% were prepared by radio-frequency magnetron co-sputtering and analyzed by X-ray diffraction, X-ray photoelectron spectroscopy and temperature-varying four-wire technique. Microstructure analysis shows that the films are composed of mainly amorphous MgF₂ matrix with embedded fcc Au nanoparticles with a mean size of 9.8-21.4 nm. The electrical properties of the films from 54 to 300 K were measured. The results show that the electrical percolation threshold occurs between Au 40 vol.% and 50%, and around the percolation threshold the electrical conductivity of the films changes by four orders.     

Annealing and oxidation mechanism of evaporated zinc thin films from zinc oxide powder

Zinc oxide (ZnO) thin films were deposited by thermal evaporation of a high quality ZnO powder; the obtained films were then oxidized in the air. We have systematically investigated the influence of annealing temperature ranged from 100 to 400 °C on the films composition and structural and optical properties by using Rutherford Back Scattering (RBS) analysis, X-ray Diffraction (XRD) and UV-Visible transmission respectively. The as grown films exhibit a hexagonal single phase of Zn with no preferential orientation and contain 28% oxygen. With an increase in the annealing temperature the oxygen content is enhanced to the detriment of Zn; samples were totally oxidized at 300 °C and the films are converted to stoichiometric ZnO material. However, in situ XRD pattern analysis shows that the oxidation starts at 250 °C. From the XRD results of annealed Zn samples under an electrical field we inferred that the oxidation mechanism is achieved by the ionization of oxygen atom at the film surface and subsequently followed by the diffusion of the produced ions in the film network.     

Spectroellipsometric assessment of HfO2 thin films

Present paper looks into the possibilities and limitations of near ultraviolet-visible range spectroscopic ellipsometry in investigating HfO₂ thin films (thickness < 7 nm). The “high k” dielectric films were produced by Atomic Layer Deposition—ALD, sputtering, and Metalo-Organic Chemical Vapour Deposition—MOCVD, on silicon and on silicon/silicon dioxide structures. Using a simple optical model (Cauchy dispersion, with an Urbach absorption tail), suitable for the optical range investigated, we extract the thickness of the layers and their optical constants. Results related to the optical properties show the important impact made by the initial surface and the growth/deposition procedure. It is also shown that for the case of ALD HfO₂ films grown on RTO oxides a significant increase in the absorption coefficient is recorded in the 4.7-5.15 eV range; this can be linked with the formation of defects related to oxygen vacancies. Subsequent anneal cycles performed in oxygen reveal that changes do occur both at the transition layer level, and in the structure of the HfO₂ film, for which an increase in the absorption is recorded.     

Electrochromic investigation of sol-gel-derived thin films of TiO2-V2O5

Thin films of TiO₂ and TiO₂-V₂O₅ were obtained by dip-coating sol-gel technique. Sols were prepared from titanium ethoxide and inorganic V₂O₅ sol received by dissolution of vanadium pentoxide in hydrogen peroxide. Sol-gel TiO₂ and TiO₂-V₂O₅ films are deposited on conductive glass substrates. TiO₂ and TiO₂-V₂O₅ systems were characterized by FTIR and Raman spectroscopy. Optical transmittance measurements were carried out. Electrochromic characterization was recorded by cyclic voltammetry using three-electrode arrangement. All samples demonstrated electrochromic effect.     

Structural properties of films grown by magnetron sputtering of a BiFeO3 target

Thin films have been prepared on silicon substrates by pulsed DC magnetron sputtering of a BiFeO₃ target under an Ar/O₂ mixture with various oxygen flow (0-50 sccm) at room temperature. Due to the low deposition-temperature, the as-grown films are amorphous. As a consequence, we have investigated the effect of the annealing temperature (400-900 °C) and atmosphere (100% N₂ or 90% N₂/10% O₂) on the crystallisation. Microstructural investigations (XRD, HREM, Raman and FTIR spectroscopy) have been performed in order to determine the structural properties of the films and to establish the experimental parameters leading to BiFeO₃ films. A temperature-dependent Raman study points to a spin-phonon coupling around the Néel temperature.     

Effect of solution concentration on surface morphology,chemical composition and photoresponse of CuO/Cu2O composite thin films grown by hydrothermal synthesis

Crystal structure, surface morphology, surface chemical composition and photocurrent response curves of the thin films were investigated by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and electrochemical workstation. The results show that the composite thin films are composed of CuO and Cu₂O phase. The relative content of copper (I) oxide on the composite thin films increases with the increase of solution concentration. Leaf-like CuO particles have been observed on the thin film grown in the 0.5 mol/L solution. Some regular octahedral and truncated octahedral Cu₂O particles have been observed on the surface of thin films grown in the 0.6 and 0.8 mol/L solution, respectively. The best photocurrent response and the fastest growth and decay have been observed in the thin film grown in 0.6 mol/L solution.     

Adsorption characteristics of 4,4′-bipyridine molecules on gold nanosphere films studied by surface-enhanced Raman scattering

We have measured and compared the surface-enhanced Raman scattering (SERS) spectra of 4,4′-bipyridine (bpy) molecules deposited (adsorbed) on the films of gold nanospheres (NSs, mean diameter 35 ± 5 nm), as prepared by the salting-out method using NaClO₄ and NaOH. The bpy-deposited (adsorbed) films were prepared by casting an aliquot of the bpy-ethanol solutions in different concentrations (less and above the monolayer converge on the gold surface), or on immersion of the NS films into the concentrated bpy solution. The enhancement of the SERS spectra of bpy was larger for the NS film prepared from NaClO₄ than that from NaOH. But, the SERS intensity was independent of the concentration of the bpy solution. The changes in the intensities and the shapes of the SERS spectra were distinctly observed on immersion of the bpy-deposited (adsorbed) NS films into pure ethanol, and these spectral changes were prominent for the NS film prepared from NaClO₄. This must be attributed to considerably coalesced structures of the NS film prepared from NaClO₄. From the comparison of the intensity changes before and after immersion into ethanol, it is suggested that the vertical orientation of the bpy molecules adsorbed on the NS films changes into the flat orientation with respect to the surface of the gold nanoparticles at the solid-liquid interface, on immersion of the film into pure ethanol.     

Basal plane-oriented gallium nitride films on fused silica via acetate dip coating

c-axis-oriented gallium nitride (wurtzite GaN) thin films were fabricated by nitridation of acetate derived precursor films deposited on fused silica substrates without any buffer layer on the top of the substrate. The acetate derived precursors were obtained by (i) preparing a gallium-acetate sol by reacting Ga metal with acetic acid, (ii) coating cleared fused silica substrate with the sol and (iii) after drying the coated films at 100 °C, annealing them in air at 300°, 500° and 900 °C. Only films showing crystallization of α-GaO(OH) (300 °C) and (α + β)-Ga₂O₃ (500 °C) were selected for nitridation. In spite of the amorphous nature of the substrate, the GaN films showed a strong preferred orientation for the basal plane (002) under selected conditions of precursor annealing (300°, 500 °C) and subsequent nitridation (under flowing NH₃) temperature and time. In other cases formation of an additional plane, i.e. (101) was indicated as a weaker peak in X-ray diffraction (XRD) patterns. The precursors and nitride films were characterized by Fourier transform infrared spectroscopy, UV-Visible spectroscopy, XRD, high resolution transmission electron microscopy and atomic force microscopy analyses.     

Gamma-irradiation-induced Ag/SiO2 composite films and their optical absorption properties

Small Ag particles or clusters dispersed mesoporous SiO₂ composite films were prepared by a new method: First the matrix SiO₂ films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO₃ solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO₂ films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements.     

Mechanical properties and density of BC<Emphasis Type="Italic">x</Emphasis>N<Emphasis Type="Italic">y</Emphasis> films grown by low-pressure chemical vapor deposition from triethylamine borane

Boron carbonitride (BC _x N _y ) films of different compositions have been grown by low-pressure chemical vapor deposition using triethylamine borane as a single-source precursor and ammonia as an additional nitrogen source. Experiments were performed at various initial vapor compositions. The resultant films have been characterized by ellipsometry, IR spectroscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, nanoindentation, and surface acoustic wave spectroscopy. The mechanical properties of the films are shown to correlate with their density and chemical composition. With increasing initial ammonia partial pressure in the vapor phase, the elemental composition of the films moves away from boron carbide, approaching boron nitride, which is accompanied by a reduction in the Young’s modulus, hardness, and density of the films.     

The ac conductivity and dielectric properties of Europium-Indium oxide films prepared on silicon (100) substrate

Thin Eu-In oxide films were prepared on glass and Si (P) substrates to form metal-oxide-semiconductor (MOS) devices. These films were annealed at different conditions and characterised by UV-absorption spectroscopy, X-ray fluorescence (XRF), and X-ray diffraction (XRD). The ac-conductance and capacitance of the devices were studied as a function of frequency in the range of (500 Hz-100 kHz), temperature in the range of (293-363 K), and gate voltage. It was observed that the frequency dependence of the ac-conductivity and capacitance of the insulator is controlled by the “corrected barrier hopping” model, which based on the relaxation processes of hopping of current carriers between equilibrium sites. The temperature dependence of ac-conductance showing small activation energy characterises the hopping process. The method of capacitance-gate voltage (C-V_g) and conductance-gate voltage (G-V_g) were used to investigate the effect of annealing in air or in vacuum on the trapped-charge density in the oxide and the surface density of states (N_ss) at the insulator/semiconductor interface. It was observed that the prepared solid solution (SS) of Eu₂O₃-In₂O₃ has a sufficiently high dielectric constant (ε), around 30, which suggests that it is a promising candidate for high-ε dielectric applications.