Study of some physical properties of ultrasonically spray deposited silver doped lead sulphide thin films

In this study, undoped and Ag doped PbS thin films at different concentrations were deposited onto glass substrates at 225 °C by using ultrasonic spray pyrolysis technique, in order to investigate the effect of Ag doping on the physical properties of PbS thin films. Structural investigations revealed that all doped PbS:Ag thin films have cubic structure and Ag doping enhances crystalline level of PbS thin films. It was determined that average crystallite size of PbS:Ag thin films increased from 24 nm to 49 nm by increasing Ag doping concentration. Morphological studies showed that surfaces of the films become denser after Ag doping. Optical transmittance and absorption spectra revealed that all deposited thin films have low transmission and high absorbance within the visible region and band gap energy of the PbS:Ag thin films were determined to be in the range of 1.37 eV and 1.28 eV by means of optical method. Electrical conductivity type of PbS:Ag films was determined to be p-type and calculated electrical resistivity was found to be lowest for Ag-doped PbS thin films at 2%.     

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO₂ thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO₂ thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.     

Characterization and optical properties of bismuth chalcogenide films prepared by pulsed laser deposition technique

Thin films of Bi-based chalcogenides were prepared by pulsed laser deposition (PLD) technique according to the stoichiometric formula: Bi₂(Se_1−xTe_x)₃. Their optical properties were studied aiming to find the suitable area of application and the optimum composition amongst the samples under study. X-ray diffraction analysis proved the crystallinity of the deposited samples; in addition, surface roughness and films homogeneity were studied by atomic force microscopy (AFM) confirming the suitability of PLD technique to prepare homogenous and smooth films of the concerned alloys. Absorption coefficient calculations showed higher absorption values of 5×10⁵ and 6×10⁵ cm⁻¹ for Te contents of 90% and 100% in the Bi₂(Se_1−xTe_x)₃ system respectively. Optical band gap of the concerned films were calculated and found to be in the range of 0.76–1.11 eV, exhibiting comparable values with the previously reported by other authors. Optical studies conformed direct and allowed transitions in all films. Refractive index (n) and dielectric constants (Ɛ_r) and (Ɛ_i) were calculated and studied as a function of the wavelength. Values and behavior of (n), (Ɛ_r) and (Ɛ_i) indicated strong dependence on the composition and the wavelength range.     

Dependence of surface morphology of CVD diamond films on deposition conditions

The diamond films have been deposited by the hot filament CVD method on molybdenum substrates from the mixture reactant gas of acetone and hy-drogen.The surface morphologies of the obtained diamond films under various de-position conditions have been observed by scanning electron microscope (SEM).The experimental results strongly indicate that the surface morphologies of the re-sulting films have closely related to the deposition conditions,i.e.,reaction pres-sure.For molybdenum substrates,under the lower reaction pressure the surface morphologies of the grains comprising the resulting films mainly display the small single crystal cubo-octahedron and double small crystal cubo-octahedron;under the higher reaction pressure ,the surface morphologies mainly display the large cauliflower-like .These results show that there are various crystal habits for CVD diamond under various deposition conditions .     

Dependence of surface morphology of CVD diamond films on deposition conditions

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Properties of fluorine-doped tin oxide films prepared by an improved sol-gel process

Fluorine-doped tin oxide (FTO) films were prepared by an improved sol-gel process, in which FTO films were deposited on glass substrates using evaporation method, with the precursors prepared by the conventional sol-gel method. The coating and sintering processes were combined in the evaporation method, with the advantage of reduced probability of films cracking and simplified preparation process. The effects of F-doping contents and structure of films on properties of films were analyzed. The results showed the performance index (Φ_TC=3.535×10⁻³ Ω⁻¹ cm) of the film was maximum with surface resistance (R_sh) of 14.7 Ω cm⁻¹, average transmittance (T) of 74.4% when F/Sn=14 mol%, the reaction temperature of the sol was 50 °C, and the evaporation temperature was 600 °C in muffle furnace, and the film has densification pyramid morphology and SnO_2−xF_x polycrystalline structure with tetragonal rutile phase. Compared with the commercial FTO films (Φ_TC=3.9×10⁻³ Ω⁻¹ cm, R_sh=27.4 Ω cm⁻¹, T=80%) produced by chemical vapor deposition (CVD) method, the Φ_TC value of FTO films prepared by an improved sol-gel process is close to them, the electrical properties are higher, and the optical properties are lower.     

Electrical characterization and morphological properties of AlN films prepared by dc reactive magnetron sputtering

Aluminum nitride (AlN) films were deposited by dc reactive magnetron sputtering on p-Si-(1 0 0) substrate in Ar-N₂ gas mixtures. The effects of nitrogen concentration and sputtering power on AlN films deposition rate, crystallographic orientation, refractive index, and surface morphology are investigated by means of several characterization techniques. The results show that AlN films reasonably textured in (0 0 2) orientation with low surface roughness can be obtained with the deposition rate as high as 70 nm/min by the control of either target power or N₂ concentration in the gas mixture. Increasing the dc discharge power, Al atoms are not completely nitridized and the Al phases appear, as well as the AlN phases. MIS (Metal-Insulator-Semiconductor) structures were fabricated and electrically evaluated by I-V (current-voltage) and C-V (capacitance-voltage) measurements at high frequency (1 MHz). The results obtained from C-V curves indicate that charges at the dielectric/semiconductor interface occur, and the dielectric constant values (extracted under strong accumulation region) are compatible with those found in literature.     

Morphologies and optical properties of mixed tin oxysulfide produced by evaporation condensation of SnS

The goal of the present study was to use the evaporation-condensation method of SnS to synthesize mixed novel tin oxysulfide nanostructures. Structural, morphological and optical properties of these nanomaterials were investigated. Synthesis was carried out in horizontal tube furnace using Au coated quartz and Si(100) substrates. The substrates were set along 1–25 cm from the centered alumina boat. The deposition was observed mainly in two regions. Region A was close to the boat and extended approximately 6 cm from it and region B started approximately 15 cm from the center of the boat and extended over 10 cm towards the end of the tube. EDAX and XRD analysis revealed formation of mixed tetragonal SnO₂ and tetragonal tin oxide sulfate, SnO₂SO₄, in region A whereas mixed orthorhombic SnS and tetragonal tin oxide sulfate in region B. SEM investigations showed randomly oriented nanowires and cotton candy morphologies for samples prepared in regions A and B, respectively. Moderate transmittance, high refractive index (2.218 at 550 nm) and two optical band gaps of 1.87 eV and 3.35 eV were obtained for samples prepared in region A whereas high transmittance, moderate refractive index and optical band gap of 1.82 eV were obtained for the samples prepared in region B. The obtained results, especially the new oxysulfide samples, may have find applications in various fields.     

Temperature effect on the physical properties of CuIn11S17 thin films for photovoltaic applications

CuIn₁₁S₁₇ compound was synthesized by horizontal Bridgman method using high-purity copper, indium and sulfur elements. CuIn₁₁S₁₇ thin films were prepared by high vacuum evaporation on glass substrates. The glass substrates were heated at 30, 100 and 200 °C. The structural properties of the powder and the films were investigated using X-ray diffraction (XRD). XRD analysis of thin films revealed that the sample deposited at a room temperature was amorphous in nature while those deposited on heated substrates were polycrystalline with a preferred orientation along the (311) plane of the spinel phase. Ultraviolet–visible (UV–vis) spectroscopy was used to study the optical properties of thin films. The results showed that CuIn₁₁S₁₇ thin films have high absorption coefficient α in the visible range (10⁵–10⁶ cm⁻¹). The band gap E_g of the films decrease from 2.30 to 1.98 eV with increasing the substrate temperature (T_s) from 30 to 200 °C. We exploited the models of Swanepoel, Wemple–DiDomenico and Spitzer–Fan for the analysis of the dispersion of the refractive index n and the determination of the optical constants of the films. Hot probe method showed that CuIn₁₁S₁₇ films deposited at T_s=30 °C and T_s=100 °C are p-type conductivity whereas the sample deposited at T_s=200 °C is highly compensated.     

A study on phase transformation of SnOx thin films prepared by reactive magnetron sputtering

In the paper, SnO_x thin films were deposited by reactive magnetron sputtering from a tin target in O₂ containing working gas. The evolution from Sn-containing SnO to tetravalent SnO₂ films was investigated. The films could be classified into three groups according to their optical band gaps, which are E_g<2.5 eV, E_g=3.0–3.3 eV and E_g>3.7 eV. The electric measurements show that high conductivity can be obtained much easier in SnO₂ than in SnO films. A high electron mobility of 15.7 cm² V⁻¹ s⁻¹, a carrier concentration of 1.43×10²⁰ cm⁻³ and a resistivity of 2.8×10⁻³ Ω cm have been achieved in amorphous SnO₂ films. Films with the optical band gap of 3.0–3.3 eV remain amorphous though the substrate temperature is as high as 300 °C, which implies that °btaining high mobility in p-type SnO is more challenging in contrast to n-type SnO₂ films.     

Optical properties of ZnO thin films prepared by sol-gel process

The present study focused on ZnO thin films fabricated by sol-gel process and spin coated onto Si (1 0 0) and quartz substrates. ZnO thin films have a hexagonal würtzite structure with a grain diameter about 50 nm. Optical properties were determined by photoluminescence (PL) and absorption spectroscopy. The absorption spectrum is dominated by a sharp excitonic peak at room and low temperatures. At room temperature, two transitions were observed by PL. One near to the prohibited energy band in ultraviolet (UV) region and the other centered at 640 nm, characteristic of the electronic defects in the band-gap. The spectrum at 6 K is dominated by donor-bound exciton lines and donor-acceptor pair transition. LO-phonon replica and two-electron satellite transitions are also observed. These optical characteristics are a signature of high-quality thin films.     

Photoconductive properties of lead iodide films prepared by electron beam evaporation

Lead iodide(PbI_2) films have been prepared by the electron beam evaporation technique,and their photoconductive response to visible light was investigated under different deposition and illumination conditions.It is found that the films' photoconductive response speed increases and the relative sensitivity decreases with the increase of substrate temperature due to the opposite requests for photo-carrier lifetime.Further,appropriately increasing the film's thickness and rising substrate temperature simu...     

Photoconductive properties of lead iodide films prepared by electron beam evaporation

Lead iodide (PbI2) films have been prepared by electron beam evaporation technique, and their photoconductive response to visible light was investigated under different deposition and illumination conditions. It is found that the films’ photoconductive response speed increases and the relative sensitivity decreases with the increase of substrate temperature due to the opposite requests for photo-carrier lifetime. Further, appropriately increasing the film’s thickness and rising substrate temperature simultaneously can effectively balance the opposite demands. Under the optimized conditions of substrate temperature of 200℃, source-substrate distance of 30cm and deposition time of 10min, the prepared films exhibit best response properties. In addition, the response to illumination with different wavelengths was also measured, revealing that the decline of response performance with increasing wavelength is due to lower photon energy of incident light.     

Optical and structural properties of CuCrO2 thin films on c-face sapphire substrate deposited by reactive RF magnetron sputtering

Reactive sputtering with Ar/N₂ mixture gas was introduced to improve stoichiometry of p-type transparent CuCrO₂ films, and effects of N₂ partial pressure ratio (α_N) on optical and structural properties were investigated. Film composition was changed from Cu rich (i.e. Cr poor) to Cr rich (i.e. Cu poor) by N₂ addition, and the stoichiometric film was grown at α_N of about 20%. Although N atoms were not incorporated into the films from analyses of crystal structure and chemical bonding state, both transmittance from visible to near-infrared wavelength and crystallinity were improved at α_N up to 10%. These improvements were attributed to suppression of the CuO formation and promotion of the O-Cu-O dumbbell bonds formation. This was confirmed by the decrease of diffraction intensity from CuO and the increase of vibrational intensity corresponding A_1g mode. From these results, it can be considered that N atoms decreased not only Cu but also excess O in the film. At α_N of 20% or above, transmittance at wavelength of 450 nm and crystallinity deteriorated. This is supposed that excessive N₂ addition probably generated both O and Cu deficiencies. As a result, it was found that slightly Cu-rich composition is suitable to obtain high-transparency CuCrO₂ thin films for practical use.     

Properties of conducting zinc oxide films prepared by R.F. Sputtering

An effective method of dopant incorporation in rf sputtered ZnO film is reported. The electrical, optical and structural properties of zinc doped ZnO films are investigated. Electron mobility of∼10 cm² /V-sec and electron concentration of∼10¹⁹ cm⁻³ have been measured at room temperature. X-ray diffraction data obtained on films prepared on Corning 7059 glass show (002) peak, dominating. The high electrical conductivity and transmission makes ZnO films very attractive as a component for heterojunction solar cells.     

Structural and electrical properties of stable ni/cr thin films

The electrical and structural properties of nickel-chrome (NiCr) thin film resistors were studied for the effect of post-deposition annealing on stability. The temperature coefficient of resistance (TCR) of sheet resistivities in the range of 100 to 200 Ω/□ could be improved by both air and vacuum annealing to achieve 5 ± 5 ppm/°C over the temperature range of -180° C to +100° C. With stability tests, air annealing proved to be more favorable for stable TCR. Studies via SIMS and ESCA identified surface segregation of Cr whereas TEM micrographs revealed correlating structural transformation of the films upon annealing. An intentional impurity, Si, played an important role in achieving a low TCR.     

基片温度对电子束蒸发的ZnS薄膜性能的影响

采用电子束蒸发在不同基片温度下沉积ZnS薄膜,研究了基片温度对薄膜性能的影响.结果表明:不同基片温度下沉积的ZnS薄膜均呈多晶状态,为体心立方(闪锌矿)结构的β-znS,并具有明显的(111)面择优取向,导电类型为n型.随着成膜时基片温度的提高,薄膜结晶度越来越好,透过率增大,载流子浓度增大,而电阻率减小.     

Enhancement of photoluminescence in Sr doped ZnO thin films prepared by spray pyrolysis

Photoluminescence characteristics of strontium doped zinc oxide (ZnO:Sr) thin films grown by spray pyrolysis method were investigated. The ZnO:Sr films were highly transparent having polycrystalline hexagonal wurtzite structure. A redshift of 130 meV in the optical band gap was observed owing to atomic size mismatch induced defect states and increase in the crystallite size in ZnO:Sr films. The enhancement of intensity of violet emission in room temperature photoluminescence by 250% is in correlation with the improved surface morphology at higher concentration of Sr in ZnO:Sr thin film. The observed increment in visible emissions is attributed to Sr induced oxygen vacancy related recombination in ZnO.     

Deep reactive ion etching of thermally co-evaporated Te-Ge films for IR integrated optics components

Due to their remarkable transparency in the infrared region, telluride glasses are very promising materials for the realization of IR integrated optics components for specific applications, such as the detection of pollutant gases in the atmosphere or the detection of exoplanetary systems. In order to prove the feasibility of channel waveguiding structures based on this kind of materials, deep etching of thermally co-evaporated Te-Ge films, one of the most important and critical steps, was investigated. Reactive ion etching was carried out using different mixtures of three gases CHF₃, O₂ and Ar, and for different chamber pressures and RF powers. The influence of each parameter on the quality of etched Te-Ge films, in term of rib dimensions and surface roughness for example, was studied. Finally optimized parameters i.e. a CHF₃/O₂/Ar ratio of 59.5/10.5/30, a chamber pressure of 30 mTorr and a RF power of 50 W were used to fabricate a pattern showing the achievement in term of etching resolution.     

Octahydroacridine thin films grown by matrix-assisted pulsed laser evaporation for non linear optical applications

We report on the thin film growth of 1,2,3,4,5,6,7,8-octahydroacridine (OHA) by matrix-assisted pulsed laser evaporation (MAPLE), starting from a frozen solution of 1% OHA dissolved in methanol and using a Nd:YAG laser emitting at 266 nm wavelength with fluences in the range 0.1–1 J/cm². The optical properties were studied by spectroscopic-ellipsometry (SE), while Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and scanning electron microscopy (SEM) were performed for structure and surface morphology investigation. Second harmonic generation (SHG) capabilities of the thin films were investigated by using a tunable Ti:sapphire laser with maximum emission centred in near infra-red. The peak of emitted photons is located at 388 nm, therefore half the wavelength of the initial photons (776 nm). The semi logarithmic dependence of SHG intensity on incident power is almost linear, except the value obtained at highest power of incident photons. This value indicates a local changing of sample due to the heating produced by the high-power incident beam.