Exchange coupling in CoO–Co bilayer

In this work, exchange bias and coercivity enhancement in ferromagnet (FM)–antiferromagnet (AFM) bilayer have been investigated. CoO film (50 nm) was deposited by sputtering with a relatively high oxygen partial pressure. The deposited films were subsequently annealed at varied temperature up to 973 K in the air atmosphere. The CoO film shows a disordered structure in the as-deposited state and an increase of crystallinity after annealing characterized by XRD and Raman spectra. A 40-nm Co film was deposited on the as-deposited CoO and annealed films. The Co–CoO bilayer shows a large exchange bias up to 1600 Oe and relatively high coercivity up to 3200 Oe (H_C−) at 5 K, which is much larger than that of crystalline Co–CoO bilayer films without any treatment. The spin glass behavior combined with increasing crystallinity, surface roughness of CoO after annealing may be attributed to the large exchange bias and high coercivity.     

Influence of N2 flow ratio on the properties of hafnium nitride thin films prepared by DC magnetron sputtering

Hafnium nitride (Hf-N) thin films were deposited on fused silica at different N₂ flow ratio (N₂/N₂ + Ar) using a reactive DC magnetron sputtering system. A gradual evolution in the composition of the films from Hf₃N₂, HfN, to higher nitrides was found through X-ray diffraction (XRD). Films of Hf₃N₂ and HfN show positive temperature coefficients of resistivity, while higher nitride has a negative one. Highly oriented growth of (0 0 1) Hf₃N₂ and NaCl-structure (1 0 0) HfN films were fabricated on fused silica substrate at relatively lower temperature of 300 °C. The electrical resistivity values of both as-deposited and post-deposition annealed films were measured by a four-point probe method. The obtained minimum resistivity of as-deposited film is 20 μΩ cm, and this result shows potential application of HfN films as electrode materials in electronic devices.     

Effect of post-annealing on the properties of copper oxide thin films obtained from the oxidation of evaporated metallic copper

Thin films of copper oxide were obtained through thermal oxidation (100-450 °C) of evaporated metallic copper (Cu) films on glass substrates. The X-ray diffraction (XRD) studies confirmed the cubic Cu phase of the as-deposited films. The films annealed at 100 °C showed mixed Cu-Cu₂O phase, whereas those annealed between 200 and 300 °C showed a single cubic Cu₂O phase. A single monoclinic CuO phase was obtained from the films annealed between 350 and 450 °C. The positive sign of the Hall coefficient confirmed the p-type conductivity in the films with Cu₂O phase. However, a relatively poor crystallinity of these films limited the p-type characteristics. The films with Cu and CuO phases show n-type conductivity. The surface of the as-deposited is smooth (RMS roughness of 1.47 nm) and comprised of uniformly distributed grains (AFM and SEM analysis). The post-annealing is found to be effective on the distribution of grains and their sizes. The poor transmittance of the as-deposited films (<1%) is increased to a maximum of ∼80% (800 nm) on annealing at 200 °C. The direct allowed band gap is varied between 2.03 and 3.02 eV.     

Influence of annealing temperature on the properties of ZnO thin films deposited by thermal evaporation

ZnO thin films were deposited by thermal evaporation of a ZnO powder. The as-deposited films are dark brown, rich zinc and present a low transmittance. Then, these films were annealed in air atmosphere at different temperatures between 100 and 400 °C. Their microstructure and composition were studied using XRD and RBS measurements respectively. By increasing the temperature, it was found that film oxidation starts at 250 °C. XRD peaks related to ZnO appear and peaks related to Zn decrease. At 300 °C, zinc was totally oxidised and the films became totally transparent. The electrical conductivity measurement that were carried out in function of the annealing temperature showed the transition from highly conductive Zn thin film to a lower conductive ZnO thin film. The optical gap (E_g) was deduced from the UV-vis transmittance, and its variation was linked to the formation of ZnO.     

Growth and characterization of Y2O3 thin films

Y₂O₃ thin films were grown on silicon (1 0 0) substrates by pulsed-laser deposition at different substrate temperatures and O₂ pressures. The structure and composition of films are studied by using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The Y₂O₃ thin films deposited in vacuum strongly oriented their [1 1 1] axis of the cubic structure and the film quality depended on the substrate temperature. The magnitude of O₂ pressure obviously influences the film structure and quality. Due to the silicon diffusion and interface reaction during the deposition, yttrium silicate and SiO₂ were formed. The strong relationship between composition and growth condition was discussed.     

The thermoluminescence properties of CdS films under nitrogen atmosphere

Chemically deposited cadmium sulphide (CdS) films have been grown on glass at 60 °C and annealed at nitrogen atmosphere at different temperatures. The as-deposited film shows a mix phase of cubic and hexagonal. Once the film subjected to annealing the hexagonal phase becomes dominant and the crystal size increases due to these changes optical band gap energy decreases from 2.44 to 2.28 eV. The electrical conductivity increases depending on temperature and the film annealed at 423 K shows the highest conductivity. Thermoluminescence (TL) intensity of the films was measured after irradiating the films with ⁹⁰Sr/⁹⁰Y β-source and the trap depths were calculated after the TL curves deconvoluted by using the computer glow curve deconvolution (CGCD) method. It is observed that the as-deposited film has three different trap depths, at around 0.257, 0.372, and 0.752 eV corresponding to 383, 473, and 608 K, respectively.     

Effect of annealing on properties of electrochemically deposited CdTe thin films

Thin films of CdTe have been deposited onto stainless steel and fluorine-doped tin oxide (FTO)-coated glass substrates from aqueous acidic bath using electrodeposition technique. The different preparative parameters, such as deposition time, bath temperature and pH of the bath have been optimized by photoelectrochemical (PEC) technique to get good quality photosensitive material. The deposited films are annealed at different temperature in presence of air. Annealing temperature is also optimized by PEC technique. The film annealed at 200 °C showed maximum photosensitivity. Different techniques have been used to characterize as deposited and also as annealed (at 200 °C) CdTe thin film. The X-ray diffraction (XRD) analysis showed the polycrystalline nature, and a significant increase in the XRD peak intensities is observed for the CdTe films after annealing. Optical absorption shows the presence of direct transition with band gap energy 1.64 eV and after annealing it decreases to 1.50 eV. Energy dispersive analysis by X-ray (EDAX) study for the as-deposited and annealed films showed nearly stoichiometric compound formation. Scanning electron microscopy (SEM) reveals that spherically shaped grains are more uniformly distributed over the surface of the substrate for the CdTe film.     

Influence of air annealing on the structural, morphological, optical and electrical properties of chemically deposited ZnSe thin films

Zinc selenide nanocrystalline thin films are grown onto amorphous glass substrate from an aqueous alkaline medium, using chemical bath deposition (CBD) method. The ZnSe thin films are annealed in air for 4 h at various temperatures and characterized by structural, morphological, optical and electrical properties. The as-deposited ZnSe film grew with nanocrystalline cubic phase alongwith some amorphous phase present in it. After annealing metastable nanocrystalline cubic phase was transformed into stable polycrystalline hexagonal phase with partial conversion of ZnSe into ZnO. The optical band gap, E_g, of as-deposited film is 2.85 eV and electrical resistivity of the order of 10⁶-10⁷ Ω cm. Depending upon annealing temperature, decrease up to 0.15 eV and 10² Ω cm were observed in the optical band gap, E_g, and electrical resistivity, respectively.     

Optical and electrical properties of plasma-oxidation derived HfO2 gate dielectric films

High-k gate dielectric HfO₂ thin films have been deposited on Si(1 0 0) by using plasma oxidation of sputtered metallic Hf thin films. The optical and electrical properties in relation to postdeposition annealing temperatures are investigated by spectroscopic ellipsometry (SE) and capacitance-voltage (C-V) characteristics in detail. X-ray diffraction (XRD) measurement shows that the as-deposited HfO₂ films are basically amorphous. Based on a parameterized Tauc-Lorentz dispersion mode, excellent agreement has been found between the experimental and the simulated spectra, and the optical constants of the as-deposited and annealed films related to the annealing temperature are systematically extracted. Increases in the refractive index n and extinction coefficient k, with increasing annealing temperature are observed due to the formation of more closely packed thin films and the enhancement of scattering effect in the targeted HfO₂ film. Change of the complex dielectric function and reduction of optical band gap with an increase in annealing temperature are discussed. The extracted direct band gap related to the structure varies from 5.77, 5.65, and 5.56 eV for the as-deposited and annealed thin films at 700 and 800 °C, respectively. It has been found from the C-V measurement the decrease of accumulation capacitance values upon annealing, which can be contributed to the growth of the interfacial layer with lower dielectric constant upon postannealing. The flat-band voltage shifts negatively due to positive charge generated during postannealing.     

Investigation of thermal annealing effects on microstructural and optical properties of HfO2 thin films

In the present paper, we investigate the effect of thermal annealing on optical and microstructural properties of HfO₂ thin films (from 20 to 190 nm) obtained by plasma ion assisted deposition (PIAD). After deposition, the HfO₂ films were annealed in N₂ ambient for 3 h at 300, 350, 450, 500 and 750 °C. Several characterisation techniques including X-ray reflectometry (XRR), X-ray diffraction (XRD), spectroscopic ellipsometry (SE), UV Raman and FTIR were used for the physical characterisation of the as-deposited and annealed HfO₂ thin films. The results indicate that as-deposited PIAD HfO₂ films are mainly amorphous and a transition to a crystalline phase occurs at a temperature higher than 450 °C depending on the layer thickness. The crystalline grains consist of cubic and monoclinic phases already classified in literature but this work provides the first evidence of amorphous-cubic phase transition at a temperature as low as 500 °C. According to SE, XRR and FTIR results, an increase in the interfacial layer thickness can be observed only for high temperature annealing. The SE results show that the amorphous phase of HfO₂ (in 20 nm thick samples) has an optical bandgap of 5.51 eV. Following its transition to a crystalline phase upon annealing at 750 °C, the optical bandgap increases to 5.85 eV.     

Effect of complexing agent on the properties of electrochemically deposited Cu2ZnSnS4 (CZTS) thin films

The Cu₂ZnSnS₄ (CZTS) thin films have been electrochemically deposited on Mo-coated glass substrate from weak acidic medium (pH 4.5-5) at room temperature. The effect of complexing agent (tri-sodium citrate) on the structural, morphological and compositional properties of CZTS thin films has been investigated. The as-deposited and annealed thin films were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM),EDAX and X-ray photoelectron spectroscopy (XPS) techniques for their structural, morphological, compositional and chemical properties, respectively. XRD studies reveal that the amorphous nature of as-deposited thin film changes into polycrystalline with kesterite crystal structure after annealing in Ar atmosphere. The film prepared without complexing agent showed well-covered surface morphology on the substrate with some cracks on the surface of the film whereas those prepared using complexing agent, exhibited uneven and slightly porous and some overgrown particles on the surface of the films. After annealing, morphology changes into the flat grains, uniformly distributed over the entire surface of the substrate. The EDAX and XPS study reveals that the films deposited using 0.2 M tri-sodium citrate are nearly stoichiometric.     

Optical and electrical properties of thermally evaporated In49Se48Sn3 films

Nearly stoichiometric thin films of In₄₉Se₄₈Sn₃ were deposited at room temperature, by conventional thermal evaporation of the presynthesized materials, onto precleaned glass substrates. The microstructural studies on the as-deposited and annealed films, using transmission electron microscopy and diffraction (TEMD), revealed that the as-deposited films are amorphous in nature, while those annealed at 498 K are crystalline. The optical properties of the investigated films were determined from the transmittance and reflectance data, in the spectral range 650-2500 nm. An analysis of the optical absorption spectra revealed a non-direct energy gap characterizing the amorphous films, while both allowed and forbidden direct energy gaps characterized the crystalline films. The electrical resistance of the deposited films was carried out during heating and cooling cycles in the temperature range 300-600 K. The results show an irreproducible behavior, while after crystallization the results become reproducible. The analysis of the temperature dependence of the resistance (ln(R) vs. 1000/T) for crystalline films shows two straight lines corresponding to both extrinsic and intrinsic conduction. The room temperature I-V characteristics of the as-deposited films sandwiched between similar Ag metal electrodes shows an ohmic behavior, while non-ohmic behavior attributed to space charge limited conduction has been observed when the films are sandwiched between dissimilar Ag/Al metal electrodes.     

Effect of annealing temperature on the microstructure and optical–electrical properties of Cu–Al–O thin films

We have successfully prepared Cu–Al–O thin films on silicon (100) and quartz substrates by radio frequency (RF) magnetron sputtering method. The as-deposited Cu–Al–O film is amorphous in nature and post-annealing treatment in argon ambience results in crystallization of the films and the formation of CuAlO₂. The annealing temperature plays an important role in the surface morphology, phase constitution and preferred growth orientation of CuAlO₂ phase, thus affecting the properties of the film. The film annealed at 900 °C is mainly composed of CuAlO₂ phase and shows smooth surface morphology with well-defined grain boundaries, thus exhibiting the optimum optical–electrical properties with electrical resistivity being 79.7 Ω·cm at room temperature and optical transmittance being 80% in visible region. The direct optical band gaps of the films are found in the range of 3.3–3.8 eV depending on the annealing temperature.     

Effects of annealing in nitrogen atmosphere and HCl-etching on the photoluminescence spectra of spray-deposited CdS:In thin films

The aim of this work is to find the effect of processing on the photoluminescence (PL) of spray-deposited CdS:In thin films. So the PL spectra of the as-deposited, annealed and HCl-etched CdS:In thin films prepared by the spray pyrolysis (SP) technique were recorded at T = 23 K. The yellow and red bands were observed in the spectrum of the as-deposited film beside bands with weaker intensity in the infrared region. The PL signal was weakened by annealing in nitrogen atmosphere at T = 400 °C and HCl-etching. A deconvolution peak fit was established to find the effects of these treatments on the different bands. The spectrum of the as-deposited film was deconvoluted to 12 peaks, which were reduced to 6 peaks after both treatments. It was found that both treatments have approximately the same effects on the PL spectra; that is they removed most of the peaks and shoulders in the red and infrared regions and attenuated most of the peaks in the yellow region. Some peaks were blue-shifted after annealing which was explained by the growth of nanocrystallites due to the thermal stress that results from the different expansion coefficients of the film and the substrate. These changes were accompanied by a phase change from the mixed (cubic and hexagonal) phase to the hexagonal phase as shown in the X-ray diffractograms.     

Studies on the effect of nozzle-to-substrate distance on the structural, electrical and optical properties of spray deposited CdIn2O4 thin films

The physical, chemical, electrical and optical properties of as-deposited and annealed CdIn₂O₄ thin films deposited using spray pyrolysis technique at different nozzle-to-substrate distances are reported. These films are characterized by X-ray diffraction, XPS, SEM, PL, Hall effect measurement techniques and optical absorption studies. The average film thickness lies within 600-800 nm range. The X-ray diffraction study shows that films exhibit cubic structure with orientation along (3 1 1) plane. The XPS study reveals that CdIn₂O₄ films are oxygen deficient. Room temperature PL indicates the presence of green shift with oxygen vacancies. The typical films show very smooth morphology. The best films deposited with optimum nozzle-to-substrate distance (NSD) of 30 cm, has minimum resistivity of 1.3 × 10⁻³ Ω cm and 2.6 × 10⁻⁴ Ω⁻¹ figure of merit. The band gap energy varies from 3.04 to 3.2 eV with change in NSD for annealed films. The effect of NSD as well as the annealing treatment resulted into the improvement of the structural, electrical and optical properties of the studied CdIn₂O₄ thin films.     

Transmission electron microscopy studies of HfO2 thin films grown by chloride-based atomic layer deposition

Detailed transmission electron microscopy characterization of HfO₂ films deposited on Si(1 0 0) using atomic layer deposition has been carried out. The influence of deposition temperature has been investigated. At 226 °C, a predominantly quasi-amorphous film containing large grains of cubic HfO₂ (a₀ = 5.08 Å) was formed. Grain morphology enabled the nucleation sites to be determined. Hot stage microscopy showed that both the cubic phase and the quasi-amorphous phase were very resistant to thermal modification up to 500 °C. These observations suggest that nucleation sites for the growth of the crystalline cubic phase form at the growing surface of the film, rather homogeneously within the film. The films grown at higher temperatures (300-750 °C) are crystalline and monoclinic. The principal effects of deposition temperature were on: grain size, which coarsens at the highest temperature; roughness with increases at the higher temperatures due to the prismatic faceting, and texture, with texturing being strongest at intermediate temperatures. Detailed interfacial characterization shows that interfacial layers of SiO₂ form at low and high temperatures. However, at intermediate temperatures, interfaces devoid of SiO₂ were formed.     

Effect of complexing agent on the photoelectrochemical properties of bath deposited CdS thin films

In the present paper photoelectrochemical (PEC) performance of bath deposited CdS thin films based on complexing agents i.e. ammonia and triethanolamine (TEA) has been discussed. Effect of annealing has also been analyzed. The as-deposited and annealed (at 523 K for 1 h in air) films were characterized by X-ray diffraction (XRD), ultraviolet-visible (UV-vis) absorption spectroscopy, SEM, electrochemical impedance spectroscopy (EIS), and PEC properties. XRD studies revealed that the films were nanocrystalline in nature with mixed hexagonal and cubic phases. TEA complex resulted in better crystallinity. Further improvement in the crystallinity of the films was observed after air annealing. The marigold flower-like structure, in addition to flakes morphology, was observed with TEA complex, whereas for ammonia complex only flakes morphology was observed. The UV-vis absorption studies revealed that the optical absorption edge for the films with ammonia and TEA complex was around 475 nm and 500 nm, respectively. Annealing of the films resulted in red shift in the UV-vis absorption. The PEC cell performance of CdS films was found to be strongly affected by crystallinity and morphology of the films resulted due to complexing agent and annealing. The air annealed film deposited using TEA complex showed maximum short circuit current density (J_sc) and open circuit voltage (V_oc) i.e. 99 μA/cm² and 376 mV respectively, under 10 mW/cm² of illumination. The films deposited using TEA complex showed good stability under PEC cell conditions.     

Growth, structural and optical transport properties of nanocrystal Zn1−xCdS thin films deposited by solution growth technique (SGT) for photosensor applications

Solution Growth Technique (SGT) has been used for deposition of Zn_1−xCdS nanocrystalline thin films. Various parameters such as solution pH (10.4), deposition time, concentration of ions, composition and deposition and annealing temperatures have been optimized for the development of device grade thin film. In order to achieve uniformity and adhesiveness of thin film on glass substrate, 5 ml triethanolamine (TEA) have been added in deposition solution. The as-deposited films have been annealed in Rapid Thermal Annealing (RTA) system at various temperature ranges from 100 to 500 °C in air. The changes in structural formation and optical transport phenomena have been studied with annealing temperatures and composition value (x). As-deposited films have two phases of ZnS and CdS, which were confirmed by X-ray diffraction studies; further the X-ray analysis of annealed (380 °C) films indicates that the films have nanocrystalline size (150 nm) and crystal structure depends on the films stoichiometry and annealing temperatures. The Zn_0.4CdS films annealed at 380 °C in air for 5 min have hexagonal structure where as films annealed at 500 °C have represented the oxide phase with hexagonal structure. Optical properties of the films were studied in the wavelength range 350-1000 nm. The optical band gap (E_g=2.94-2.30 eV) decreases with the composition (x) value. The effect of air rapid annealing on the photoresponse has also been observed on Zn_1−xCdS nanocrystal thin films. The Zn_1−xCdS thin film has higher photosensitivity at higher annealing temperatures (380-500 °C), and films also have mixed Zn_1−xCdS/Zn_1−xCdSO phase with larger grain size than the as-deposited and films annealed up to 380 °C. The present results are well agreed with the results of other studies.     

Magnetic,structural and electrical properties of ordered and disordered Co50Fe50 films

Co₅₀Fe₅₀ films with thickness varying from 100 to 500 Å were deposited on a glass substrate by sputtering process, respectively. Two kinds of CoFe films were studied: one was the as-deposited film, and the other the annealed film. The annealing procedure was to keep the films at 400 °C for 5 h in a vacuum of 5×10⁻⁶ mbar. From the X-ray study, we find that the as-deposited film prefers the CoFe(1 1 0) orientation. Moreover, the body-centered cubic (bcc) CoFe(1 1 0) line is split into two peaks: one corresponding to the ordered body-centered tetragonal (bct) phase, and the other, the disordered bcc phase. After annealing, the peak intensity of the ordered bct phase becomes much stronger, while that of the disordered bcc phase disappears. The annealing has also caused the ordered CoFe(2 0 0) line to appear. When the amount of the ordered bct phase in Co₅₀Fe₅₀ is increased, the saturation magnetization (M_s) and coercivity (H_c) become larger, but the electrical resistivity (ρ) decreases. From the temperature coefficient of resistance (TCR) measurement, we learn that the bct grains in the CoFe film start to grow at temperature 82 °C.     

W doped SnO2 growth via sol–gel routes and characterization: Nanocubes

The effects of W doping on the characteristical properties of SnO₂ thin films prepared by sol–gel spin coating method were investigated. The SnO₂ thin films were deposited at various W doping ratios and characterized by various measurements. XRD studies indicated that the undoped and W doped SnO₂ films had cubic and tetragonal phases. The SEM images of WTO thin films showed cubic shaped nanocubes corresponding to cubic phase and the smaller particles corresponding to tetragonal phase were formed on the film surfaces, and their distributions and sizes were dependent on the W doping ratio. EDX spectroscopy analyses showed that the calculated and participated atomic ratios of W/(W + Sn) (at.%) in the starting solution and in the WTO thin films were almost close. It was found that the sheet resistance depended on W doping ratio and 2.0 at.% W doped SnO₂ (WTO) exhibited lowest value of sheet resistance (7.11 × 10³ Ω/cm²).