Optical properties of CdxZn(1−x)O films deposited by ultrasonic spray pyrolysis method

Cd_xZn_(1−x)O (x = 0, 0.59, 0.78 and 1) films have been produced by ultrasonic spray pyrolysis technique using aqueous solutions of CdCl₂ H₂O and ZnCl₂ on the microscope glass substrate between 325 and 400 °C. The Cd_xZn_(1−x)O samples have been crystallized both cubic and hexagonal structures. The optical properties of the samples were characterized by transmittance and absorption spectroscopy measurements. Transmissions of the samples have decreased with increasing x values. The optical band gap energies of the Cd_xZn_(1−x)O samples from the absorption spectra have been calculated between 2.48 and 3.23 eV by different Zn contents. The samples were annealed at 350 and 450 °C. The optical band gap energy has decreased at 350 °C whereas it increased at 450 °C.     

Comparison of ordered structure in buried oxide layers in high-dose, low-dose, and internal-thermal-oxidation separation-by-implanted-oxygen wafers

The ordered SiO₂ in the buried oxide (BOX) layer of high-dose, low-dose, and internal-thermal-oxidation (ITOX) separation-by-implanted-oxygen (SIMOX) wafers was investigated by X-ray diffraction. From the results, it was found that the SiO₂ molecules in the low-dose and ITOX SIMOX wafers are better ordered than those in the high-dose SIMOX wafer and that the ordered structure of the ITOX layer is different from that of the originally formed BOX layer, suggesting that the ITOX layer has a structure similar to that of the ordered SiO₂ in the thermal oxide layer.     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

Structural, electrical and optical properties of Bi2Se3 and Bi2Se(3−x)Tex thin films

Thin films of Bi₂Se₃, Bi₂Se_2.9Te_0.1, Bi₂Se_2.7Te_0.3 and Bi₂Se_2.6Te_0.4 are prepared by compound evaporation. Micro structural, optical and electrical measurements are carried out on these films. X-ray diffraction pattern indicates that the as-prepared films are polycrystalline in nature with exact matching of standard pattern. The composition and morphology are determined using energy dispersive X-ray analysis and scanning electron microscopy (SEM). The optical band gap, which is direct allowed, is 0.67 eV for Bi₂Se₃ thin films and the activation energy is 53 meV. Tellurium doped thin films also show strong optical absorption corresponding to a band gap of 0.70-0.78 eV. Absolute value of electrical conductivity in the case of tellurium doped thin film shows a decreasing trend with respect to parent structure.     

In-situ X-ray investigations of quench-condensed thin gold films

Thin gold films were deposited on float glass substrates held at cryogenic temperatures down to 77 K and investigated in-situ using X-ray reflectometry and surface sensitive reflection mode X-ray absorption spectroscopy (XAFS). The combination of these in-situ X-ray methods with simultaneous electrical resistivity measurements yields information about the surface and volume microstructure of the deposited films as a function of the deposition temperature and their changes induced by a subsequent annealing treatment. The surface sensitive XAFS experiments clearly proved that the films exhibit a polycrystalline structure throughout the temperature range studied here. The data were fitted using a correlated Debye-model. The results show that for film deposition at low substrate temperatures < 130 K, a significantly decreasing Debye-temperature was found, reaching values of about 100 K in comparison to 165 K for the polycrystalline bulk material. This decrease was interpreted to be predominantly related to defective film regions with an increased static disorder.     

Thickness dependence of structural, electrical and optical properties of sprayed ZnO:Cu films

ZnO:Cu thin films have been deposited by spray pyrolysis techniques within two different (450 °C and 500 °C) substrate temperatures. The structural properties of ZnO:Cu thin films have been investigated by X-ray diffraction techniques. The X-ray diffraction spectra showed that ZnO:Cu thin films are polycrystalline with the hexagonal structure and show a good c-axis orientation perpendicular to the substrate. The most preferential orientation is along the (002) direction for all spray deposited ZnO:Cu films together with orientations in the (100) and (101) planes also being abundant. Some parameters of the films were calculated and correlated with the film thickness for two different substrate temperatures. The optical properties of ZnO:Cu thin films have been investigated by UV/VIS spectrometer and the band gap values were found to be ranging from 3.29 eV to 3.46 eV.     

Growth and electrical properties of ZnO thin films deposited by novel ion plating method

The URT(Uramoto-gun with Tanaka magnetic field)-IP(ion plating) method is a technique for depositing a thin film on a substrate. This method offers the advantage of low-ion damage, low deposition temperatures, large area deposition and high growth rates. Ga-doped ZnO thin films were grown using the URT-IP method, and the material properties were evaluated. The quality of ZnO thin films grown by the URT-IP method was found to be sensitive to oxygen supply during growth. It was observed that the saturation point of the growth rate corresponding to the optimum oxygen supply leads to the best electrical properties. The profiles of the dependence of film properties on oxygen supply revealed a part of growth mechanism of the URT-IP method.     

Influence of Fe ions on the photocatalytic activity of TiO2 films prepared by micro-plasma oxidation method

Microporous titanium dioxide thin films have been fabricated on titanium plates by the micro-plasma oxidation method with the electrolyte of H₂SO₄. The influence of Fe³⁺ ions addition in the electrolyte on the photocatalytic activities was investigated. The results reveal that titanium dioxide thin films produced with Fe³⁺ addition electrolyte exhibit higher photoactivity than pure electrolyte for the oxidation of rhodamine B. The removal of rhodamine B reaches 90% for 30 min when Fe³⁺ addition concentrate is 0.2 g/L. Experimental results of X-ray diffraction and atom force microscopy show that the increase in activity is related to change in the lattice parameters and cell volume.     

Annealing effect on structural and electrical properties of thermally evaporated Cd1−xMnxS nanocrystalline films

Thin films of Cd_1−xMn_xS (0 ≤ x ≤ 0.5) were deposited on glass substrates by thermal evaporation. All the films were deposited at 300 K and annealed at 573 K. The as-deposited and the annealed films were characterized for composition, structure and microstructure by using energy-dispersive analysis for X-rays, X-ray diffraction, scanning electron microscopy and atomic force microscopy. Electrical conductivity was studied in the temperature range 190-450 K. All the films exhibited wurtzite structure of the host material with the grain size varying in the range between 36 and 82 nm. Resistivity of all the films is strongly dependent on Mn content and annealing temperature and lies in the range 13-160 Ω cm.     

Oxidation kinetics of Ni metallic films: Formation of NiO-based resistive switching structures

Resistive switching controlled by external voltage has been reported in many Metal/Resistive oxide/Metal (MRM) structures in which the resistive oxide was simple transition metal oxide thin films such as NiO or TiO₂ deposited by reactive sputtering. In this paper, we have explored the possibility to form NiO-based MRM structures from the partial oxidation of a blanket Ni metallic film using a Rapid Thermal Annealing route, the remaining Ni layer being used as bottom electrode. X-ray diffraction was used to apprehend the Ni oxidation kinetics while transmission electron microscopy enabled investigating local microstructure and film interfaces. These analyses have especially emphasized the predominant role of the as-deposited Ni metallic film microstructure (size and orientation of crystallites) on (i) oxidation kinetics, (ii) NiO film microstructural characteristics (crystallite size, texture and interface roughness) and (iii) subsequent electrical behavior. On this latter point, the as-grown NiO films were initially in the low resistance ON state without the electro-forming step usually required for sputtered films. Above the threshold voltage varying from 2 to 5 V depending on oxidation conditions, the Pt/NiO/Ni MRM structures irreversibly switched into the high resistance OFF state. This irreversibility is thought to originate in the microstructure of the NiO films that would cause the difficulty to re-form conductive paths.     

Growth of rod-like crystal BiSI films by ultrasonic spray pyrolysis

Rod-like crystals BiSI films were synthesized by asynchronous ultrasonic spray pyrolysis method on glass substrates at 320 °C. The results show that an appropriate ratio of pulse time to interval time between pulses plays an important role in crystal growth direction of the rods, and a possible growth mechanism was proposed.     

超声喷雾热解法制备ZnO薄膜及性能研究

以醋酸锌水溶液为前驱体溶液,使用自制的超声喷雾热解系统在玻璃基板上制备得到了ZnO薄膜.经X射线衍射(XRD),扫描电镜(SEM)分析得到ZnO薄膜的晶体结构和微观形貌.测试结果表明,ZnO薄膜为六角纤锌矿结构,在450～500℃下制备的薄膜显示出良好的结晶性能,并且沿(002)晶面择优取向生长,薄膜具有优良的均匀性和致密性.同时,制备得到的薄膜在可见光区也表现出80%以上的高透过率.     

Local strain in a 3D nano-crystal revealed by 2D coherent X-ray diffraction imaging

The coherent X-ray diffraction from an isolated strained nano-crystal is given by the Fourier transform of a complex-valued electron density where the modulus and phase are linked to the physical electron density and the displacement field, respectively. The possibility to reconstruct a complex-valued object from a coherent diffraction pattern is demonstrated using iterative algorithms. In the case of a 2D intensity slice, the reconstructed 2D object is strongly dependent on the distribution function of the displacement field values along the direction perpendicular to the observation plane. It is shown that valuable 3D information can, however, still be extracted. This work is of particular interest as soon as the complete 3D measurement is not accessible.     

Temperature dependence of Fluorine-doped tin oxide films produced by ultrasonic spray pyrolysis

Fluorine-doped tin oxide (FTO) films were prepared at different substrate temperatures by ultrasonic spray pyrolysis technique on glass substrates. Among F-doped tin oxide films, the lowest resistivitiy was found to be 6.2 × 10^− 4 Ω-cm for a doping percentage of 50 mol% of fluorine in 0.5 M solution, deposited at 400 °C. Hall coefficient analyses and secondary ion mass spectrometry (SIMS) measured the electron carrier concentration that varies from 3.52 × 10²⁰ cm^− 3 to 6.21 × 10²⁰ cm^− 3 with increasing fluorine content from 4.6 × 10²⁰ cm^− 3 to 7.2 × 10²⁰ cm^− 3 in FTO films deposited on various temperatures. Deposition temperature on FTO films has been optimized for achieving a minimum resistivity and maximum optical transmittance.     

Effects of growth ambient on electrical properties of Al-N co-doped p-type ZnO films

p-Type zinc oxide thin films with c-axis orientation were prepared in N₂O-O₂ atmosphere by an Al-N co-doping method using reactive magnetron sputtering. Secondary ion mass spectroscopy (SIMS) measurements indicate that as-grown ZnO films were co-doped with Al and N. Hall effect measurements show a dependence of types of conduction, carrier concentration and mobility of as-grown ZnO films on N₂O partial pressure ratios. p-Type ZnO thin films deposited in a N₂O partial ratio of 10% show the highest hole concentration of 1.1×10¹⁷ cm⁻³, the lowest resistivity of about 100 Ω cm, and a low mobility of 0.3 cm² V⁻¹ s⁻¹.     

Transmission electron microscopy study of the initial growth stage of GaSb grown on Si (001) substrate by molecular beam epitaxy method

The microstructural properties at the initial growth stage of the GaSb heteroepitaxial growth on a silicon (Si) substrate were investigated using transmission electron microscopy. Well-separated and tall GaSb islands were observed when GaSb was directly grown on a Si substrate (sample A). On the other hand, GaSb was grown to the coalesced and flat islands when a low-temperature AlSb buffer (sample B) was introduced. The different morphologies of the GaSb islands were related to the microstructural properties of the interface between the GaSb and the Si substrate. The GaSb/Si interface was rough, and disordered atomic arrangements were observed at the interface in sample A. On the other hand, the GaSb/Si interface was flat, and well-ordered atomic arrangements appeared at the interface in sample B. Entirely different mechanisms for the relaxation of a misfit strain were demonstrated from a microstructural viewpoint.     

Temperature dependent grain-size and microstrain of CdO thin films prepared by spray pyrolysis method

CdO thin films on glass substrate were prepared by home built spray pyrolysis unit from aqueous solution of Cd(CH₃COO)₂·2H₂O at different substrate temperatures. X-ray diffraction (XRD) studies indicate the formation of polycrystalline cubic CdO phase with preferential orientation along (111) plane. X-ray line broadening technique is adopted to study the effect of substrate temperature on microstructural parameters such as grain size and microstrain. Scanning electron microscopy (SEM) shows that the film prepared at 250°C consists of spherical shape grains with size in nanometer range and is comparable with the XRD studies.     

Anatase-rutile transformation through high-temperature annealing of titania films produced by ultrasonic spray pyrolysis

Titanium dioxide films were prepared by ultrasonic spray pyrolysis on (0001) α-quartz substrates at 400 °C and/or annealed in air at 600°, 800°, or 1000 °C. The as-deposited films at 400 °C (50 nm grains) and annealed at 600 °C (100 nm grains) showed single-phase anatase of high transparency in the visible region. Films annealed at 800 °C and 1000 °C showed mixed-phase anatase (100 nm grains) plus rutile (700 nm agglomerates) and pure rutile, (700 nm grains), respectively. Raman and X-ray data indicate the presence of residual stress in the films, which may arise from contamination, silicon diffusion into the films, and/or oxygen deficiency.     

Electrical properties of ZnO/Au/ZnS/Au films deposited by ultrasonic spray pyrolysis

Polycrystalline ZnS semiconducting films have been prepared by ultrasonic spray pyrolysis technique in the form of planar and sandwich configurations using amorphous and ZnO coated glass substrates. Deposition of ZnS films by the spray pyrolysis has been studied extensively by several investigators and the process parameters have been optimized to obtain films with good characteristics. However we report for the first time the preparation of ZnS films sandwiched between top and bottom electrodes on the transparent conducting ZnO films that have been produced by the spray pyrolysis technique. The produced ZnS films have been crystallized in a wurtzite structure. The electrical properties of the samples having planar and sandwich structures have been measured in dark at room temperature by applying the voltage values between 0.01 and 100 V.