Spray deposition and characterization of undoped and In‐doped tin disulphide thin films

Undoped and Indium doped tin disulphide (SnS₂) thin films had been deposited onto glass substrates at T_s = 300 °C using spray pyrolysis technique under atmospheric pressure with stannous chloride, indium chloride and thiourea as precursors. The structural, optical and electrical properties of the deposited films were characterized. The XRD pattern revealed that the undoped and doped films had preferred orientation along (002) plane with hexagonal structure. FESEM micrographs had shown that morphologies of the films changed with indium doping. Optical constant such as refractive index (n), extinction coefficient (k), real and imaginary parts of dielectric constants were evaluated from transmittance and reflectance spectra in UV‐Visible spectroscopy. The optical absorption data were used to determine the band gap energy and it was found to be 2.75 eV for undoped and 2.50 eV for indium doped films respectively. The room temperature dark resistivity was found to be 4.545 × 10³ Ω‐cm and 5.406 × 10³ Ω‐cm for undoped and In‐doped films respectively.     

Nanocrystalline transparent SnO2‐ZnO films fabricated at lower substrate temperature using a low‐cost and simplified spray technique

Nanocrystalline and transparent conducting SnO₂‐ ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (360±5 °C) compared with conventional spray method. The structural studies reveal that the SnO₂‐ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.48×10¹⁵lines/m²), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26–34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 kΩ/□ to 32.4 kΩ/□ as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.63×10^–2 (Ω/□)^–1), low temperature coefficient of resistance (–1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO₂ ‐ ZnO films for solar cells, sensors and opto‐electronic applications. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigations on the Optical Properties of Undoped,Fluorine Doped and Antimony Doped Tin Oxide Films

Undoped, fluorine doped and antimony doped tin oxide films are prepared on quartz plates by Spray pyrolysis technique. The films grown at the optimum substrate temperature with different doping levels have been chosen for this study. Optical properties of these films are investigated in the entire UV-Visible -IR region (0.2 - 10 mikrom). The observed absorption edge lies at 3.65 eV for undoped tin oxide and on doping it shifts towards higher energies, which is due to the Moss - Burstein effect. For fluorine doping depending upon the fluorine concentration, the absorption edge lies in the range 3.9 - 4.14 eV and for antimony doping it lies in the range 3.82 - 4.1 eV. In the undoped tin oxide films the direct allowed transition occurs at 4.02 eV and indirect allowed transition occurs at 2.43 eV, whereas for fluorine doped tin oxide and antimony doped tin oxide films, the direct allowed transitions occur in the range 4.18 - 4.28 and 4.13 - 4.22 eV respectively and the indirect allowed transitions occur in the range 2.63 - 2.73 and 2.54 - 2.65 eV respectively. Optical properties near the plasma edge have been analyzed using Drude's theory. The dependence of effective mass on carrier concentration has been explained on the basis of nonparabolicity of the conduction band. The shift in the fermi energy, calculated on the basis of energy dependent effective mass, is consistent with the measured shift in the absorption edge.     

X-ray diffraction studies of sprayed SnO2: Sb films

Antimony-doped tin oxide films were deposited by spray pyrolysis on Corning 7059 substrates. The structural and electrical properties of the films deposited with different doping levels were studied. Relative variations in the structural properties were explained on the basis of structure factor calculations. The results show that the incorporation of antimony atoms takes place only at substitutional sites. As expected, the substitutional replacement of tin by antimony atoms increased appreciably the free carrier density of the film.     

Spray pyrolysis deposition and characterization of highly (100) oriented magnesium oxide thin films

Transparent dielectric thin films of MgO has been deposited on quartz substrates at different temperatures between 400 and 600°C by a pneumatic spray pyrolysis technique using Mg(CH₃COO)₂·4H₂O as a single molecular precursor. The thermal behavior of the precursor magnesium acetate is described in the results of thermogravimetry analysis (TGA) and differential thermal analysis (DTA). The prepared films are reproducible, adherent to the substrate, pinhole free and uniform. Amongst the different spray process parameters, the substrate temperature effect has been optimized for obtaining single crystalline and transparent MgO thin films. The films crystallize in a cubic structure and X‐ray diffraction measurements have shown that the polycrystalline MgO films prepared at 500°C with (100) and (110) orientations are changed to (100) preferred orientation at 600°C. The MgO phase formation was also confirmed with the recorded Fourier Transform Infrared (FTIR) results. The films deposited at 600°C exhibited highest optical transmittivity (>80%) and the direct band gap energy was found to vary from 4.50 to 5.25 eV with a rise in substrate temperature from 500 to 600°C. The measured sheet resistance and the resistivity of the film prepared at 600°C were respectively 10¹³Ω/□ and 2.06x10⁷Ω cm. The surface morphology of the prepared MgO thin films was examined by atomic force microscopy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation of indium tin oxide thin films without external heating for application in solar cells

Indium tin oxide (ITO) films were grown without external heating in an ambient of pure argon by RF-magnetron sputtering method. The influence of argon ambient pressure on the electro-optical properties of as-deposited ITO films was investigated. The morphology, structural and optical properties of ITO films were examined and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV–VIS transmission spectroscopy. The deposited ITO films with a thickness of 300 nm show a high transparency between 80% and 90% in the visible spectrum and 14–120 Ω/□ sheet resistance under different conditions. The ITO films deposited in the optimum argon ambient pressure were used as transparent electrical contacts for thin film Cu(In,Ga)Se₂ (CIGS) solar cells. CIGS solar cells with efficiencies of the order of 7.0% were produced without antireflective films. The results have demonstrated that the developed ITO deposition technology has potential applications in thin film solar cells.     

Changes of Auger parameter in doped SnO2 powders

Doped SnO₂ powders were studied using X‐ray photoelectron spectroscopy (XPS). The Auger parameters (AP) for Sn and different doping elements were determined. A dependence of the Auger parameter on the doping element and doping concentration was observed. The detected shift could be correlated with the electrical properties of the studied samples as well as with the formation of a second phase and a segregation layer at the surface. Bulk doping with elements having a valency greater than 4 (Sb), leads to an increase of the electron density connected with a decrease of resistivity. In this case we can observe the shift of the AP to higher values. This means that the relaxation of the electron holes is energetically more favourable for Sb doped than for pure tin oxide. On the other side, doping with elements the valency of which is less than 4 (In) on tin sites leads to a decrease in electron density and causes an increase of resistivity of the material. We observe in this case a shift of the AP to lower values due to lower relaxation energy. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and optical properties of Mg‐doped ZnO thin films prepared by a modified Pechini method

ZnO thin films with different Mg doping contents (0%, 3%, 5%, 8%, 10%, respectively) were prepared on quartz glass substrates by a modified Pechini method. XRD patterns reveal that all the thin films possess a polycrystalline hexagonal wurtzite structure. The peak position of (002) plane for Mg‐doped ZnO thin films shifts toward higher angle due to the Mg doping. The crystallite size calculated by Debey‐Scherrer formula is in the range of 32.95–48.92 nm. The SEM images show that Mg‐doped ZnO thin films are composed of dense nanoparticles, and the thickness of Mg‐doped ZnO thin films with Mg doped at 8% is around 140 nm. The transmittance spectra indicate that Mg doping can increase the optical bandgap of ZnO thin films. The band gap is tailored from 3.36 eV to 3.66 eV by changing Mg doping concentration between 3% and 10%. The photoluminescence spectra show that the ultraviolet emission peak of Mg‐doped ZnO thin films shifts toward lower wavelength as Mg doping content increases from 3% to 8%. The green emission peak of Mg‐doped ZnO thin films with Mg doping contents were 3%, 8%, and 10% is attributed to the oxygen vacancies or donor‐acceptor pair. These results prove that Mg‐doped ZnO thin films based on a modified Pechini method have the potential applications in the optoelectronic devices.     

Structural and optoelectrical properties of Ga‐doped ZnO semiconductor thin films grown by magnetron sputtering

Transparent conductive gallium‐doped zinc oxide (Ga‐doped ZnO) films were prepared on glass substrate by magnetron sputtering. The influence of substrate temperature on structural, optoelectrical and surface properties of the films were investigated by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), spectrophotometer, four‐point probe and goniometry, respectively. Experimental results show that all the films are found to be oriented along the c‐axis. The grain size and optical transmittance of the films increase with increasing substrate temperature. The average transmittance in the visible wavelength range is above 83% for all the samples. It is observed that the optoelectrical property is correlated with the film structure. The Ga‐doped ZnO film grown at the substrate temperature of 400 °C has the highest figure of merit of 1.25 × 10⁻² Ω⁻¹, the lowest resistivity of 1.56 × 10⁻³ Ω·cm and the highest surface energy of 32.3 mJ/m².     

Effect of annealing and composition on crystal structure,surface morphology and optical absorption of chemically deposited Cd1‐xSnxS films

Cd_1‐xSn_xS thin films were successfully deposited on suitably cleaned glass substrate by chemical bath deposition method at 74 °C. Hydrated Stannous Chloride (SnCl₂.2H₂O) in aqueous solution was added to the CdS growing solution in different proportions. The experimental results indicate, a successful doping for lower concentration of Sn, saturation for intermediate doping levels, and a degradation of the doping process for higher concentration of Sn. Indirect (X‐ray diffraction) and Direct (Scanning electron microscopy) measurements were performed to characterize the growth and the nature of crystallinity of the different Cd_1‐xSn_xS films. The effect of annealing on the crystal structure and morphology of the deposited films has also been discussed. The X‐ray diffraction spectra show that the thin films are polycrystalline and have both cubic and hexagonal structure. The Interplanar spacing, lattice constant, grain size, strain, and dislocation density were calculated for as‐deposited and annealed films. The grain size was found to decrease from 5 nm to 0.89 nm with doping concentration of Sn. The grain size further decreased due to annealing at 400 °C. SEM studies show layered growth and long needle like structures along with some voids. After annealing the densification and smaller size of the particles was also observed. The optical absorption spectra show shifting of absorption peaks towards lower wavelength side (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the effect of aluminum doped zinc oxide (ZnO:Al) thin films by spray pyrolysis

ABSTRACT

In this study, aluminum doped zinc oxide thin films were deposited on ordinary glass substrates at the temperature of 425°C by spray pyrolysis technique for various doping concentrations of aluminum ranging from 1 to 5 at.%. The effect of dopant concentration on structural, morphological and optical properties of ZnO:Al thin films was studied. Optical band gap of the films increased with doping percentage and started to decrease from 2 at.% of dopant. The average transmittance for 2at.% ZnO:Al film is significantly increased over 90% in the visible region at 450 nm which is crucial for optoelectronic applications.     

Influence of substrate temperature on the structure of ZnO:Al thin films

ZnO: Al films were prepared using low cost spray pyrolysis technique. The dependence of the physical properties on the substrate temperature was studied. The best films obtained at 500°C substrate temperature with preferred [002] orientation. The sheet resistance decreases with increased substrate temperature, and values as low as R_sh = 207 Ω/cm² are reached for substrate temperature of 500°C. The optical transmittance of films increased by increasing the substrate temperature and received to 75% at 500°C. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of Al‐doped ZnO thin films deposited by two different sputtering methods

Aluminum‐doped zinc oxide (AZO) thin films were deposited on sapphire (002) and glass substrates by two different sputtering techniques radio frequency magnetron cosputtering of AZO and ZnO targets and sputtering of an AZO target. The dependence of the photoluminescence (PL) and transmittance properties of the AZO films deposited by cosputtering and sputtering on the AZO/ZnO target power ratio, R and the O₂/Ar flow ratio, r were investigated, respectively. Only a deep level emission peak appears in the PL spectra of cosputtered AZO films whereas both UV emission and deep level emission peaks are observed in the PL spectra of sputtered AZO films. The absorption edges in the transmittance spectra of the AZO films shift to the lower wavelength region as R and r increase. Also effects of crystallinity, surface roughness, PL on the transmittance of the AZO films were explained using the X‐ray diffraction (XRD), atomic force microscopy (AFM), and PL analysis results. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sol–gel derived highly transparent and conducting yttrium doped ZnO films

This paper reports the structural, electrical and optical properties of Yttrium doped zinc oxide (YZO) thin films deposited on Corning (7059) glass substrates by spin coating technique. A precursor solution of ZnO, 0.2 M in concentration was prepared from zinc acetate dissolved in anhydrous ethanol with diethanolamine as a sol gel stabilizer. Yttrium nitrate hexahydrate (Y₂NO₃ · 6H₂O) was used as the dopant (3 wt%) in the present study. The films of different thickness in the range (200–500 nm) were prepared. The films were annealed in air at 450 °C for 1 h. It was observed that the c-axis orientation improves and the grain size increases as is indicated by an increase in intensity of the (0 0 2) peak and the decrease in the FWHM with the increase of film thickness. The resistivity decreased sharply from 2.8 × 10⁻² to 5.8 × 10⁻³ Ω-cm as the thickness increased from 200 to 500 nm. However, the average transmittance decreased from 87% to 82.6% as the film thickness increased to 500 nm. The lowest sheet resistance of ∼120 Ω/□ was obtained for the 500 nm thick film.     

Substrate effect on microstructure and optical performance of sputter‐deposited TiO2 thin films

This study deals with the role of the different substrates on the microstructural, optical and electronical properties of TiO₂ thin films produced by conventional direct current (DC) magnetron sputtering in a mixture of pure argon and oxygen using a Ti metal target with the aid of X–ray diffractometer (XRD), ultra violet spectrometer (UV–vis) and atomic force microscopy (AFM) measurements. Transparent TiO₂ thin films are deposited on Soda lime glass, MgO(100), quartz and sitall substrates. Phase purity, surface morphology, optical and photocatalytic properties of the films are compared with each other. It is found that the amplitude of interference oscillation of the films is in a range of 77‐89%. The transmittance of the film deposited on Soda lime glass is the smallest while the film produced on MgO(100) substrate obtains the maximum transmittance value. The refractive index and optical band gap of the TiO₂ thin films are also inferred from the transmittance spectra. The results show that the film deposited on Soda lime glass has the better optical property while the film produced on MgO(100) substrate exhibits much better photoactivity than the other films because of the large optical energy band gap. As for the XRD results, the film prepared on MgO(100) substrate contains the anatase phase only; on the other hand, the other films contain both anatase and rutile phases. Furthermore, AFM images show that the regular structures are observed on the surface of all the films studied. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Morphology of polycrystalline cassiterite films

Polycrystalline cassiterite films have been grown by the hydropyrolytic method from a 10(H₂O) + 5(SnCl₂ · 2H₂O) solution (in weight fractions) on corundum substrates. The crystallization regularities are considered and a comparative analysis of the properties of natural and artificial cassiterite crystals is performed. The surface morphology is investigated and the size of crystalline grains is determined by scanning electron microscopy. X-ray microprobe analysis showed that all films contain tin and oxygen atoms in a ratio corresponding (within the experimental error) to the chemical formula of tin dioxide. It is established that the surface morphology of cassiterite films is characterized by both single crystallites and aggregates of two or more crystals typical of twins. It is suggest that doping can efficiently be used to control the concentration of twins and the stability of their formation.     

Structural change of laser-irradiated Ge2Sb2Te5 films studied by electrical property measurement

Sheet resistance of laser-irradiated Ge₂Sb₂Te₅ thin films prepared by magnetron sputtering was measured by the four-point probe method. With increasing laser power the sheet resistance undergoes an abrupt drop from 10⁷ to 10³ Ω/□ at about 580 mW. The abrupt drop in resistance is due to the structural change from amorphous to crystalline state as revealed by X-ray diffraction (XRD) study of the samples around the abrupt change point. Crystallized dots were also formed in the amorphous Ge₂Sb₂Te₅ films by focused short pulse laser-irradiated, the resistivities at the crystallized dots and the non-crystallized area are 3.375 × 10^?3 and 2.725 Ω m, sheet resistance is 3.37 × 10⁴ and 2.725 × 10⁷ Ω/□ respectively, deduced from the I–V curves that is obtained by conductive atomic force microscope (C-AFM).     

溅射温度对ITO/Ag/ITO多层复合薄膜的结构和光电性能的影响

本文采用直流磁控溅射分层溅射制备了氧化铟锡(ITO)/银(Ag)/ITO多层复合薄膜。系统研究了溅射温度对ITO/Ag/ITO多层复合薄膜的结构和光电性能影响。采用ITO(m(In₂O₃)∶m(SnO₂)=9∶1;直径60 mm)靶材和Ag(纯度99.999%;直径60 mm)靶材分层溅射,使ITO薄膜和Ag薄膜依次沉积在钠-钙玻璃基片上。结果表明,溅射温度对该薄膜的形貌和结构具有显著的影响。在中间Ag薄膜和顶层ITO薄膜的溅射温度均为120 ℃时,薄膜表面晶粒形貌由类球形转变为菱形,此时薄膜方阻为3.68 Ω/Sq,在488 nm处透射率为88.98%,且品质因数为0.03 Ω^-1,实现了低方阻高可见光透射率ITO/Ag/ITO多层复合薄膜的制备。     

Microstructural and optoelectrical properties of transparent conducting ZnO:Al thin films for organic solar cells

The Al‐doped zinc oxide (ZnO:Al) thin films were grown on glass substrates by the magnetron sputtering technique. The films were characterized with X‐ray diffractometer, four‐point probe and optical transmission spectroscopy, respectively. The dependence of microstructural, electrical and optical properties on deposition temperature was investigated. The results show that all the films have hexagonal wurtzite structure with highly c‐axis orientation. And the microstrural and optoelectrical properties of the films are observed to be subjected to the deposition temperature. The ZnO:Al film prepared at the deposition temperature of 650 K possesses the best optoelectrical properties, with the lowest electrical resistivity (6.1×10⁻⁴ Ω·cm), the highest average visible transmittance (85.3%) and the maximum figure of merit (0.41 Ω⁻¹). The optical energy gap of the films was estimated from Tauc's law and observed to be an increasing tendency with the increment of the deposition temperature. Furthermore, the refractive index of the films was determined by the optical characterization methods and the dispersion behavior was studied by the single electronic oscillator model.     

Synthesis and tribological properties of Mo‐doped WSe2 Nanolamellars

The Mo‐doped WSe₂ nanolamellars have been successfully prepared via solid‐state thermal (750 °C) reaction between micro‐sized W, Mo with Se powders under inert atmosphere in a closed reactor and characterized by X‐ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that the morphologies of the as‐prepared products changed from microplates to nanolamellars to aggregations composed of nanoparticles with the doping of Mo powders. And the sizes of crystallites evidently reduced while the contents of dopant increased within a certain limit (1 wt.%–7 wt.%). The tribological properties of the as‐prepared products as additives in HVI750 base oil were investigated by UMT‐2 multispecimen tribotester. The friction coefficient of the base oil containing Mo‐doped WSe₂ nanolamellars was lower and more stable than that of WSe₂ nanolamellars. A combination of rolling friction, sliding friction, and stable tribofilm on the rubbing surface could further explain the good friction and wear properties of Mo‐WSe₂ nanoparticles as additives than that of WSe₂.