Formation of silicon nanodots from dysprosium-doped amorphous SiCxOy films grown by hot-filament assisted chemical vapor deposition of CH3SiH3 and Dy(DPM)3 gas jets

We report on Si nanodot formation by chemical vapor deposition (CVD) of ultrathin films and following oxidation. The film growth was carried out by hot-filament assisted CVD of CH₃SiH₃ and Dy(DPM)₃ gas jets at the substrate temperature of 600 °C. The transmission electron microscopy observation and X-ray photoelectron spectroscopy analysis indicated that ∼35 nm Dy-doped amorphous silicon oxycarbide (SiC_xO_y) films were grown on Si(1 0 0). The Dy concentration was 10-20% throughout the film. By further oxidation at 860 °C, the smooth amorphous film was changed to a rough structure composed of crystalline Si nanodots surrounded by heavily Dy-doped SiO₂.     

Selective MOCVD of titanium oxide and zirconium oxide thin films using single molecular precursors on Si(1 0 0) substrates

Titanium oxide (TiO₂) and zirconium oxide (ZrO₂) thin films have been deposited on modified Si(1 0 0) substrates selectively by metal-organic chemical vapor deposition (MOCVD) method using new single molecular precursor of [M(OⁱPr)₂(tbaoac)₂] (M=Ti, Zr; tbaoac=tertiarybutyl-acetoacetate). For changing the characteristic of the Si(1 0 0) surface, micro-contact printing (μCP) method was adapted to make self-assembled monolayers (SAMs) using an octadecyltrichlorosilane (OTS) organic molecule which has -CH₃ terminal group. The single molecular precursors were prepared using metal (Ti, Zr) isopropoxide and tert-butylacetoacetate (tbaoacH) by modifying standard synthetic procedures. Selective depositions of TiO₂ and ZrO₂ were achieved in a home-built horizontal MOCVD reactor in the temperature range of 300-500 °C and deposition pressure of 1×10⁻³-3×10⁻² Torr. N₂ gas (5 sccm) was used as a carrier gas during film depositions. TiO₂ and ZrO₂ thin films were able to deposit on the hydrophilic area selectively. The difference in surface characteristics (hydrophobic/hydrophilic) between the OTS SAMs area and the SiO₂ or Si-OH layer on the Si(1 0 0) substrate led to the site-selectivity of oxide thin film growth.     

The photocatalytic application and regeneration of anatase thin films with embedded commercial TiO2 particles deposited on glass microrods

Anatase thin films (<200 nm in thickness) embedding Degussa P25 TiO₂ were prepared by sol-gel method. TiO₂-anatase thin films were deposited on a fiberglass substrate and then ground to obtain glass microrods containing the composite films. The film structure was characterized using Raman spectroscopy, atomic absorption and UV-vis spectrophotometry, and atomic force microscopy. The photocatalytic activity of the composite films, calcined at 450 °C, and the regeneration of the activity under the same experimental conditions, were assessed using gas chromatography to study the photodegradation of phenol, an industrial pollutant, in water under 365 nm irradiation. The film with 15.0 wt.% of P25 TiO₂ was found to be more photoactive (54 ppm of degraded phenol at 6 h of illumination) than the other ones.     

Improved dielectric properties of (Pb,Ca)TiO3 thin films prepared by metal-organic decomposition method

(Pb,Ca)TiO₃ (PCT) thin films have been deposited on Pt/Ti/SiO₂/Si substrate by metal-organic decomposition (MOD) technique. The film processing parameters such as drying and annealing temperatures have been optimized to obtain good-quality PCT films. Compositional analysis of the film has been studied by X-ray photoelectron spectroscopy (XPS). The effect of the annealing temperature on the crystalline structure, microstructure and electrical properties have been investigated by X-ray diffraction, atomic force microscopy (AFM) and impedance analyzer, respectively. Amorphous PCT films form at 350 °C and crystallize in the perovskite phase following the isothermal annealing at ?650 °C for 3 h in oxygen ambient. Typical tetragonal structure of the PCT film is evidenced from X-ray diffraction pattern. The grain size in the PCT films increases with an increase in annealing temperature. Significant improvement in the dielectric constant value is observed as compared to other reported work on PCT films. The observed dielectric constant and dissipation factor at 100 kHz for 650 °C annealed PCT films are 308 and 0.015, respectively. The correlation of the film microstructural features and electrical behaviors is described.     

Sputter deposition of high transparent TiO2−xNx/TiO2/ZnO layers on glass for development of photocatalytic self-cleaning application

In this study, TiO_2−xN_x/TiO₂ double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO₂ film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO₂ film thickness, the optical transmittance of TiO_2−xN_x/TiO₂ film was compared with TiO₂ thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.     

Solid phase epitaxy of Ge films on CaF2/Si(1 1 1)

At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF₂/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 °C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 °C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.     

Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

Laser-induced voltage characteristics of Bi2Sr2Co2Oy thin films on LaAlO3 substrates

We report the laser-induced voltage (LIV) effects in c-axis oriented Bi₂Sr₂Co₂O_y thin films grown on (0 0 1) LaAlO₃ substrates with the title angle α of 0°, 3°, 5° and 10° by a simple chemical solution deposition method. A large open-circuit voltage with the sensitivity of 300 mV/mJ is observed for the film on 10° tilting LaAlO₃ under a 308 nm irradiation with the pulse duration of 25 ns. When the film surface is irradiated by a 355 nm pulsed laser of 25 ps duration, a fast response with the rise time of 700 ps and the full width at half maximum of 1.5 ns is achieved. In addition, the experimental results reveal that the amplitude of the voltage signal is approximately proportional to sin 2α and the signal polarity is reversed when the film is irradiated from the substrate side rather than the film side, which suggests the LIV effects in Bi₂Sr₂Co₂O_y thin films originate from the anisotropic Seebeck coefficient of this material.     

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.     

Photocatalytic abilities of gel-derived P-doped TiO2

P-doped TiO₂ nanoparticles were synthesized through hydrolysis and condensation of Ti(OC₂H₅)₄ with H₃PO₄ additions. Effects of [H₃PO₄]/[Ti(OC₂H₅)₄] molar ratios on the anatase-to-rutile phase transformation, crystallite sizes, surface areas, and photocatalytic abilities of the gel-derived P-doped TiO₂ were investigated. The P-doped TiO₂ nanoparticles prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 were composed of anatase monophase even at 900 ^oC and possessed very strong photocatalytic ability. Kinetic studies on the P-doped TiO₂ to photocatalytically decompose methylene blue under irradiation of 365 nm UV light found that the P-doped TiO₂ prepared by [H₃PO₄]/[Ti(OC₂H₅)₄]=0.03 and calcined at 800 ^oC had the specific reaction rates, at 25 °C, k_A,m=0.76 m³/(kg min) (based on the mass of P-doped TiO₂) and k_A,BET=46.2×10⁻⁶ m/min (based on the BET surface area of P-doped TiO₂), which is superior to the performance of a commercial product, P25 (k_A,m=0.22 m³/(kg min) and k_A,BET=4.8×10⁻⁶ m/min).     

Role of growth temperature and oxygen partial pressure on the structural and electrical properties of pulsed laser deposited La1−xSrxnO3−δ thin films

The paper presents the fabrication and characterization of La_0.65Sr_0.35MnO_3−δ (LSMO) polycrystalline thin films deposited directly on Si (1 0 0) substrates using pulsed laser deposition technique. Various deposition parameters like substrate temperature and oxygen partial pressure have been varied systematically to obtain stoichiometric, crack-free films with smooth surface morphology having nearly monodisperse grain size distribution. The substrate temperature variation from 600 to 800 °C had profound effects on the microstructure and topography of the deposited film, with optimum result being obtained at 700 °C. The variation of partial pressure of oxygen controls the deposition kinetics as well as the stoichiometry of the film in terms of oxygen vacancy, which influences the magnetic and electrical transport properties of the manganate films. The microstructure and crystallinity of the deposited films have been studied using X-ray diffraction, scanning electron microscopy and atomic force microscopy. A correlation between the oxygen stoichiometry and micro-structural and transport properties of the deposited films has been obtained.     

Preparation and properties of spray-deposited ZnIn2Se4 nanocrystalline thin films

Zinc indium selenide (ZnIn₂Se₄) thin films have been deposited onto amorphous and fluorine doped tin oxide (FTO)-coated glass substrates using a spray pyrolysis technique. Aqueous solution containing precursors of Zn, In, and Se has been used to obtain good quality deposits at different substrate temperatures. The preparative parameters such as substrate temperature and concentration of precursors solution have been optimized by photoelectrochemical technique and are found to be 325 °C and 0.025 M, respectively. The X-ray diffraction patterns show that the films are nanocrystalline with rhombohedral crystal structure having lattice parameter a=4.05 Å. The scanning electron microscopy (SEM) studies reveal the compact morphology with large number of single crystals on the surface. From optical absorption data the indirect band gap energy of ZnIn₂Se₄ thin film is found to be 1.41 eV.     

Effects of substrate temperature on properties of NbNx films grown on Nb by pulsed laser deposition

NbN_x films were deposited on Nb substrate using pulsed laser deposition. The effects of substrate deposition temperature, from room temperature to 950 °C, on the preferred orientation, phase, and surface properties of NbN_x films were studied by X-ray diffraction, atomic force microscopy, and electron probe micro analyzer. We find that the substrate temperature is a critical factor in determining the phase of the NbN_x films. For a substrate temperature up to 450 °C the film showed poor crystalline quality. With temperature increase the film became textured and for a substrate temperature of 650−850 °C, mix of cubic δ-NbN and hexagonal phases (β-Nb₂N + δ′-NbN) were formed. Films with a mainly β-Nb₂N hexagonal phase were obtained at deposition temperature above 850 °C. The c/a ratio of β-Nb₂N hexagonal shows an increase with increased nitrogen content. The surface roughness of the NbN_x films increased as the temperature was raised from 450 to 850 °C.     

Effect of surface fluorination on the photocatalytic and photo-induced hydrophilic properties of porous TiO2 films

Porous surface-fluorinated TiO₂ (F-TiO₂) films were prepared through PEG modified sol-gel method and surface fluorination. The as-prepared films were characterized with XRD, FTIR, AFM, XPS and UV-vis DRS. The effects of surface fluorination on the photocatalytic activity and hydrophilicity of porous TiO₂ film were studied by photocatalytic degradation of rhodamine B (RhB) as well as water contact angle (CA) on porous TiO₂ film. The results showed that the surface fluorination increased the adsorption of RhB on the porous TiO₂ film and enhanced the photocatalytic degradation of RhB. The concentration and pH of NaF solutions affected much the photocatalytic activity of porous TiO₂ film. Porous F-TiO₂ film prepared in 40 mM NaF solution at pH 4.0 showed the highest photocatalytic activity. Because of its porous structure, the porous F-TiO₂ film had original water CA of 22.7°, which is much smaller than that of normal F-TiO₂ film. Under UV light irradiation, the water CA of porous F-TiO₂ film decreased to 5.1° in 90 min.     

Dielectric properties of continuous composition spreaded MgO-Ta2O5 thin films

The dielectric properties of MgO-Ta₂O₅ continuous composition spread (CCS) thin films were investigated. The MgO-Ta₂O₅ CCS thin films were deposited on Pt/Ti/SiO₂/Si substrates by off-Axis RF magnetron sputtering system, and then the films were annealed at 350 °C with rapid thermal annealing system in vacuum. The dielectric constant and loss of MgO-Ta₂O₅ CCS thin films were plotted via 1500 micron-step measuring. The specific point of Ta₂O₅-MgO CCS thin film (post annealed at 350 °C) showing superior dielectric properties of high dielectric constant (k ∼ 28) and low dielectric loss (tan δ < 0⋅004) at 1 MHz were found in the area of 3-5 mm apart from Ta₂O₅ side on the substrate. The cation's composition of thin film was Mg:Ta = 0.4:2 at%.     

Nanocrystalline Sr2FeMoO6 prepared by citrate-gel method

Double perovskite Sr₂FeMoO₆ powders with small crystallite size have been synthesised with citrate-gel method. The starting solution pH was varied between 1.5 and 9.0 resulting in large differences in the phase composition and ordering of B^′/B^″ sites. The samples prepared at 975 °C had crystallite sizes under 40 nm whereas crystallite sizes of the samples prepared at 1050 °C were between 78 and 239 nm. The XRD patterns were refined with spacegroup I 4/m, which gave good results for both batches, although clearly better results were obtained with monoclinic P 2₁/n spacegroup for the 975 °C batch. The ordering and the saturation magnetization agreed well with each other after treatment at 1050 °C, but the samples prepared at 975 °C had a strongly reduced saturation magnetization from that given by the ordering.     

Adsorption and photocatalytic degradation of methylene blue on Zn1−xCuxS nanoparticles prepared by a simple green method

Nanoparticles of Zn_1−xCu_xS with various dopant contents (0 ≤ x ≤ 0.15) were prepared in water by refluxing for 90 min at about 95 °C. Powder X-ray diffraction (XRD) patterns of the nanoparticles demonstrate that loading of Cu²⁺ ions does not change the crystal structure of ZnS. Scanning electron microscopy (SEM) images demonstrate that size of the nanoparticles decreases with increasing Cu²⁺ ions. UV-Vis diffuse reflectance spectra (DRS) of the nanoparticles show significant absorption in visible light region. Adsorption capacity of the nanoparticles for methylene blue (MB) increases with mole fraction of copper ions. Photocatalytic activity of the nanoparticles toward photodegradation of MB was evaluated under visible light irradiation. The results indicate that Zn_0.85Cu_0.15S nanoparticles exhibit highest photocatalytic activity among the prepared samples. Moreover, effects of refluxing time applied for preparation of the nanoparticles and calcination temperature were investigated.     

Photoluminescence in amorphous (PbLa)TiO3 thin films deposited on different substrates

Pb_1−XLa_XTiO₃ thin films, (X=0.0; 13 and 0.27 mol%) were prepared by the polymeric precursor method. Thin films were deposited on Pt/Ti/SiO₂/Si (1 1 1), Si (1 0 0) and glass substrates by spin coating, and annealed in the 200-300°C range in an O₂ atmosphere. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used for the microstructural characterization of the thin films. Photoluminescence (PL) at room temperature has been observed in thin films of (PbLa)TiO₃. The films deposited on Pt/Ti/SiO₂/Si substrates present PL intensity greater than those deposited on glass and silicon substrates. The intensity of PL in these thin films was found to be dependent on the thermal treatment and lanthanum molar concentration.     

Annealing temperature influence on electrical properties of ion beam sputtered Bi2Te3 thin films

Ion beam sputtering process was used to deposit n-type fine-grained Bi₂Te₃ thin films on BK7 glass substrates at room temperature. In order to enhance the thermoelectric properties, thin films are annealed at the temperatures ranging from 100 to 400 °C. X-ray diffraction (XRD) shows that the films have preferred orientations in the c-axis direction. It is confirmed that grain growth and crystallization along the c-axis are enhanced as the annealing temperature increased. However, broad impurity peaks related to some oxygen traces increase when the annealing temperature reached 400 °C. Thermoelectric properties of Bi₂Te₃ thin films were investigated at room temperature. The Bi₂Te₃ thin films, including as-deposited, exhibit the Seebeck coefficients of −90 to −168 μV K⁻¹ and the electrical conductivities of 3.92×10²-7.20×10² S cm⁻¹ after annealing. The Bi₂Te₃ film with a maximum power factor of 1.10×10⁻³ Wm⁻¹ K⁻² is achieved when annealed at 300 °C. As a result, both structural and transport properties have been found to be strongly affected by annealing treatment. It was considered that the annealing conditions reduce the number of potential scattering sites at grain boundaries and defects, thus improving the thermoelectric properties.     

Preparation of five-layered Si/SixGe1−x nano-films by RF helicon magnetron sputtering

Five-layered Si/Si_xGe_1−x films on Si(1 0 0) substrate with single-layer thickness of 30 nm, 10 nm and 5 nm, respectively were prepared by RF helicon magnetron sputtering with dual targets of Si and Ge to investigate the feasibility of an industrial fabrication method on multi-stacked superlattice structure for thin-film thermoelectric applications. The fine periodic structure is confirmed in the samples except for the case of 5 nm in single-layer thickness. Fine crystalline Si_xGe_1−x layer is obtained from 700 °C in substrate temperature, while higher than 700 °C is required for Si good layer. The composition ratio (x) in Si_xGe_1−x is varied depending on the applied power to Si and Ge targets. Typical power ratio to obtain x = 0.83 was 7:3, Hall coefficient, p-type carrier concentration, sheet carrier concentration and mobility measured for the sample composed of five layers of Si (10 nm)/Si_0.82Ge_0.18 (10 nm) are 2.55 × 10⁶ /°C, 2.56 × 10¹² cm⁻³, 1.28 × 10⁷ cm⁻², and 15.8 cm⁻²/(V s), respectively.