Synthesis and properties of epitaxial SnO2 films deposited on MgO (100) by MOCVD

Epitaxial tin oxide (SnO₂) thin films have been prepared on MgO (100) substrates at 500-600 °C by metalorganic chemical vapor deposition method. Structural and optical properties of the films have been investigated in detail. The obtained films were pure SnO₂ with the tetragonal rutile structure. An in-plane orientation relationship of SnO₂ (110) [010]//MgO (200) [110] between the film and substrate was determined. Two variant structure of SnO₂ were analyzed. The structure of the film deposited at 600 °C was investigated by high-resolution transmission electron microscopy, and an epitaxial structure was observed. The absolute average transmittance of the SnO₂ film at 600 °C in the visible range exceeded 90%. The optical band gap of the film was about 3.93 eV.     

Microstructure and physical properties of nanofaceted antimony doped tin oxide thin films deposited by chemical vapor deposition on different substrates

Antimony doped tin oxide SnO₂: Sb thin films have been fabricated by atmospheric pressure chemical vapour deposition at substrate temperature varying between 350 °C and 420 °C in a horizontal reactor, from a mixture of hydrated SnCl₂, SbCl₃ and O₂ gas. The films were grown on glass substrates and onto polished and porous n-type silicon. Doped films fabricated with various Sb (Sb/Sn %) contents ranging from undoped 0% to 4% were characterised employing different optical characterisation techniques, like X-ray diffraction, transmittance and reflectance in the wavelength range of 300 to 2500 nm and ellipsometry. The films exhibit the usual cassiterite diffraction pattern with high crystalline structure. Examination of the surface by scanning electron microscopy (SEM) showed that the films are textured made up of many pyramidal crystallites with nanofaceted surfaces, indicating highly stabilised material. The presence of inverted pyramids indicates that the crystallites grown by coalescence. The surface morphology was found to be independent on the kind of the substrate. From X-Ray spectra and SEM observations we get the texture the lattice constant and the grain size. The optical results provide information on film thickness, optical parameters and transmittance upon antimony concentration. The microstructure of the films, the grain growth topics (nucleation, coalescence…) depend strongly on deposition conditions and doping concentration. The observed variations of both the resistivity ρ and transmittance T are correlated to antimony atoms concentration which induced variation in the microstructure and in the size of SnO₂ nanograins (typically 20-40 nm). In this work, we have determined the feasibility of incorporating the correct amount of Sb atoms in tin oxide film by means of resistivity and transmission. SEM observations showed that the substrate do not affect the morphology.     

Effect of N<Subscript>2</Subscript> gas annealing and SiO<Subscript>2</Subscript> barrier on the optical transmittance and electrical resistivity of a transparent Sb-doped SnO<Subscript>2</Subscript> conducting film

During the fabrication process of transparent conducting thin films of ATO (antimony-doped tin oxide) on a soda lime glass substrate by a sol-gel dip coating method, the effects of the SiO₂ buffer layer formed on the substrate and N₂ annealing treatment were investigated quantitatively. The deposited ATO thin film was identified as a crystalline SnO₂ phase and the film thickness was about 100 nm/layer at a withdrawal speed of 50 mm/min. Optical transmittance and electrical resistivity of the 400 nm-thick ATO thin film that was deposited on SiO₂ buffer layer/soda lime glass and then annealed under nitrogen atmosphere were 84% and 5.0 × 10^–3cm, respectively. The XPS analysis confirmed that a SiO₂ buffer layer inhibited Na ion diffusion from the substrate, preventing the formation of a secondary phase such as Na₂SnO₃ and SnO and increasing Sb ion concentration and ratio of Sb⁵⁺/Sb³⁺ in the film. It was found that N₂ annealing treatment leads to the reduction of Sn⁴⁺ as well as Sb⁵⁺, however the reduction of Sn⁴⁺ is more effective, and consequently results in a decrease in the electrical resistivity to produce excellent electrical properties in the film. © Springer Science + Business Media, Inc.     

Structural,optical and electrical studies on nanocrystalline tin oxide (SnO<Subscript>2</Subscript>) thin films by electron beam evaporation technique

Nanocrystalline tin oxide (SnO₂) thin films were coated using electron beam evaporation technique on glass substrates. To study the gleaming out look of the structure and surface morphological changes, the films were annealed in the temperature 350–550 °C for 1 h. The annealed films were subjected to X-ray diffraction (XRD) and atomic force microscopy (AFM) studies. The XRD patterns of SnO₂ thin films as-deposited and annealed at 350 °C illustrate that the films were amorphous, and beyond 350 °C and thereafter they became polycrystalline with tetragonal structure. The crystallite size of the annealed films, obtained through the XRD analysis, increased with the increasing annealing temperature, and it was found to be from 3.6 to 12 nm. The photoluminescence (PL) studies on these films were also carried out. The origin of luminescence was assigned to the defects of the nanocrystalline SnO₂ films. The Optical studies (UV-VIS) were performed and the optical band gab energy (Eg) calculations, the dependence of absorption coefficient on the photon energy at short wavelengths, were found to be increasing from 3.65 to 3.91 eV is also investigated.     

Influence of ZnO addition on the sintering properties of SnO<Subscript>2</Subscript> electrodes

The effect of ZnO doping in SnO₂ was investigated for electrodes. Zinc oxide in different concentration, 0.5–5 wt%, was added to tin dioxide powder prepared by a coprecipitation method. The products were characterized by powder X-ray diffraction, transmission electron microscopy, and by section scanning electron microscopy. The resistivity of those electrodes was measured with KEITHLEY236 high-resistance instrument. It was found that ZnO was expected to increase the electrical conductivity of SnO₂ ceramic. However, the range of solid solution of ZnO into SnO₂ lattice was found to be limited as it rapidly segregated to form secondary phases. Concentrations as high as 5 wt% of ZnO lead to the formation of a ZnSnO₃ phase whose presence yielded a non-linear electrical response that hinders the donor effect of zinc oxide.     

Nanocrystalline SnO2 and Au:SnO2 thin films prepared by direct current magnetron reactive sputtering

Nanocrystalline pure and gold doped SnO₂(Au:SnO₂) films were prepared on unheated glass substrates by dc magnetron reactive sputtering and, subsequently, the as deposited films were annealed in air. The films structure, surface morphology, photoluminescence, electrical and optical properties were investigated. After annealing the as deposited SnO₂ films, crystallinity increased and the surface roughness decreased. The intensity of PL peaks increases sharply with the annealing temperature. The optical transmittance of the films was around 89% after annealing the as deposited SnO₂ films at 450 °C. The as deposited Au:SnO₂ films show better crystallinity than the as deposited SnO₂ films, the average grain size was around 4.4 nm. The emission peaks of Au:SnO₂ films are slightly blue shifted as compare to undoped SnO₂ films. The Au:SnO₂ films show the lowest electrical resistivity of 0.001 Ωcm with optical transmittance of 76%, after annealing at 450 °C.     

Ethanol and LPG sensing characteristics of SnO<Subscript>2</Subscript> activated Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> thick film sensor

The sensing response of pure and SnO₂ activated Cr₂O₃ to ethanol vapours and liquefied petroleum gas (LPG) has been investigated. Fine particles of commercial chromium oxide powder were selected and deposited as thick film to act as a gas sensor. The sensor surface has been activated by tin dioxide, on surface oxidation of tin chloride. The concentration of tin chloride solution, used as activator, was varied from 0 to 5% and its effect on gas response, selectivity and operating temperature has been studied. It was found that response to ethanol vapours significantly improved, whereas response to LPG remained unaffected. Moreover, operating temperature remains unchanged both for LPG and ethanol vapours.     

Synthesis,characterization and gas sensing performance of SnO<Subscript>2</Subscript> thin films prepared by spray pyrolysis

In this work, SnO₂ thin films were deposited onto alumina substrates at 350°C by spray pyrolysis technique. The films were studied after annealing in air at temperatures 550°C, 750°C and 950°C for 30 min. The films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical absorption spectroscopy technique. The grain size was observed to increase with the increase in annealing temperature. Absorbance spectra were taken to examine the optical properties and bandgap energy was observed to decrease with the increase in annealing temperature. These films were tested in various gases at different operating temperatures ranging from 50–450°C. The film showed maximum sensitivity to H ₂S gas. The H₂S sensing properties of the SnO₂ films were investigated with different annealing temperatures and H ₂S gas concentrations. It was found that the annealing temperature significantly affects the sensitivity of the SnO₂ to the H ₂S. The sensitivity was found to be maximum for the film annealed at temperature 950°C at an operating temperature of 100°C. The quick response and fast recovery are the main features of this film. The effect of annealing temperature on the optical, structural, morphological and gas sensing properties of the films were studied and discussed.     

Electrical and optical properties of InSbSe<Subscript>3</Subscript> amorphous thin films

Electrical conductivity, I–V characteristics and optical properties are investigated for InSbSe₃ amorphous thin films of different thicknesses prepared by thermal evaporation at room temperature. The composition of both the synthesized material and thin films were checked by energy dispersive X-ray spectroscopy (EDX). X-ray analysis indicated that all samples under investigation have amorphous structure. The dc electrical conductivity was measured in the temperature range (303–393 K) and thickness range (149–691 nm). The activation energy ΔE _σ was found to be independent of film thickness in the investigated range. The obtained I–V characteristic curves for the investigated samples are typical for memory switches. The switching voltage increases linearly with film thickness in the range (113–750 nm), while it decreases exponentially with temperature in the range (303–393 K). The switching process can be explained according to an electrothermal process initiated by Joule-heating of the current channel. Measurements of transmittance and reflectance in the spectral range (400–2,500 nm) are used to calculate optical constants (refractive index n and absorption index k). Both n and k are practically independent of film thickness in the investigated range (149–691 nm). By analysis of the refractive index n the high frequency dielectric constant ε_∞ was determined via two procedures and was found to have the values of 9.3 and 9.15. Beyond the absorption edge, the absorption is due to allowed indirect transitions with energy gap of 1.46 eV independent on film thickness in the investigated range.     

The effect of post-annealing under CdCl<Subscript>2</Subscript> atmosphere on the properties of ITO thin films deposited by DC magnetron sputtering

Indium tin oxide (ITO) films deposited by DC magnetron sputtering were annealed under CdCl₂ atmosphere at different temperatures. The effects of CdCl₂ heat-treatment on the structural, electrical and optical properties of the films were investigated. The X-ray diffraction measurement proves the annealing results in a change of preferred orientation from (400) to (222). It is found the resistivity increases from 1.49 × 10⁻⁴ Ω cm of the as-deposited film to 6.82 × 10⁻⁴ Ω cm of the film annealed at 420 °C. The optical energy gap for the film varies from 3.97 to 3.89 eV. It is also found that the CdCl₂ heat-treatment results in narrowing the energy gap of ITO film.     

Preparation of Sb:SnO2 thin films and its effect on opto-electrical properties

The present study focuses on pure and antimony (Sb)-doped tin oxide thin film and its influence on their structural, optical, and electrical properties. Both undoped and Sb-doped SnO₂ thin films have been grown by using simple, inexpensive pyrolysis spray technique. The deposition temperature was optimized to 450 °C. X-ray diffractions pattern have revealed that the films are polycrystalline and have tetragonal rutile-type crystal structure. Undoped SnO₂ films grow along (110) preferred orientation, while the Sb-doped SnO₂ films grow along (200) direction. The size of Sb-doped tin oxide crystals changes from 26.3 to 58.0 nm when dopant concentration is changed from 5 to 25 wt%. The transmission spectra revealed that all the samples are transparent in the visible region, and the optical bandgap varies between 3.92 and 3.98 eV. SEM analysis shows that the surface morphology and grain size are affected by the doping rate. All the films exhibit a high transmittance in the visible region and show a sharp fundamental absorption edge at about 0.38–0.40 nm. The maximum electrical conductivity of 362.5 S/cm was obtained for the film doped with 5 wt% Sb. However, the carrier concentration is increased from 0.708?×?10¹⁸ to 4.058?×?10²⁰ cm³. The electrical study reveals that the films have n-type electrical conductivity and depend on Sb concentration. We observed a decrease in sheet resistance and resistivity with the increase in Sb dopant concentration. For the dopant concentration of 5 wt% of Sb in SnO₂, the Rs and ρ were found minimum with the values of 88.55 (Ω cm^?2) and 2.75 (Ω cm), respectively. We observed an increase in carrier concentration and a decrease in mobility with the addition of Sb up to 25 wt%. The highest figure of merit values 2.5?×?10^–3 Ω^?1 is obtained for the 5wt% Sb, which may be considered potential materials for solar cells' transparent windows.

     

Synthesis and optical properties of CeO<Subscript>2</Subscript> nanocrystalline films grown by pulsed electron beam deposition

The nanocrystalline cerium dioxide (CeO₂) thin films were deposited on soda lime (SLG) and Corning glass by pulsed e-beam deposition (PED) method at room temperature. The structure of the produced CeO₂ thin films was investigated by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), and micro Raman spectroscopy. The surface topography of the films was examined by atomic force microscopy (AFM). Film thickness and growth morphologies were determined with FEG-SEM from the fracture cross sections. XPS studies gave a film composition composed of +4 and +3 valent cerium typical to nanocrystalline ceria structures deficient in oxygen. The ceria films were polycrystalline in nature with a lattice parameter (a) of 0.542 nm. The Raman characteristics of the source material and the films deposited were very similar in character. Raman lines for thin film and bulk CeO₂ was observed at 465 cm⁻¹. The optical properties of the CeO₂ films were deduced from reflectance and transmittance measurements at room temperature. From the optical model, the refractive index was determined as 1.8–2.7 in the photon energy interval from 3.5 to 1.25 eV. The optical indirect band gap (E _g) of CeO₂ nanocrystalline films was calculated as 2.58 eV.     

Effects of oxygen concentration on the properties of sputtered SnO2:Sb films deposited at low temperature

Antimony doped tin oxide (SnO₂:Sb) films have been prepared by d.c. magnetron sputtering and the properties of the films depend on deposition conditions, such as O₂ gas ratio, were investigated. The gas composition was found to affect the properties of the films. With the incorporation additional oxygen, the electrical and optical properties of films significantly improved. The minimum value of resistivity of the films was 4.9 × 10^− 3 Ω cm at the oxygen concentration of 30% and the optical transmittance was over 80%.     

Effects of Al content on the properties of ZnO:Al films prepared by Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and ZnO co-sputtering

Aluminum doped zinc oxide (AZO) films were deposited on quartz substrates by radio-frequency magnetron co-sputtering method with ZnO and Al₂O₃ ceramic targets. The structural, optical and electrical properties of these films as a function of the Al content were investigated. XRD results reveal that the AZO films are wurtzite structure with (002) preferred orientation. The average transmittance of all the films is higher than 80% in a wide wavelength range from 400 to 1,500 nm. The band gap energy, calculated from their optical absorption spectra, is in the range of 3.50–3.66 eV depending on the Al content. Doping of Al³⁺ in the ZnO makes the film surface roughness decrease. The dopant Al³⁺ acts as electron donor by which the electrical conductivity and carrier concentration of the films are obviously increased until the Al³⁺ reaches its saturation content of about 4.50 at.%.     

Synthesis of orthorhombic structure epitaxial tin oxide film

Tin oxide (SnO₂) epitaxial film has been deposited on Y-stabilized ZrO₂ (YSZ) (100) substrate by metalorganic chemical vapor deposition (MOCVD). Structural and optical properties of the film as well as the epitaxial mechanism have been investigated in detail. The results of structure analyses show that the obtained film is epitaxial SnO₂ with orthorhombic columbite structure. A novel epitaxial relationship of orthorhombic SnO₂(100)||YSZ(100) with SnO₂ [001]||YSZ<001> was clearly observed from the interface area between the film and the substrate. The absolute average transmittance of the orthorhombic SnO₂ film in the visible range exceeds 90%, and the optical band gap of the film is about 3.79 eV.     

Effect of oxidation and annealing temperature on optical and structural properties of SnO2

Tin oxide thin films were deposited on glass substrate with 100 nm thickness of Sn, which was coated by magnetron sputtering followed by thermal oxidation at different temperatures. The effect of oxidation temperature on the optical and structural properties of SnO₂ films were investigated. Higher transmittance, lower absorption and lesser structural defects were obtained at higher temperatures. Optical bandgap increases with temperature, while the Urbach energy showed reduction. The X-ray diffraction studies showed that at lower temperatures (300, 350 °C), a combined phase of SnO and SnO₂ was obtained, while at higher temperatures (400, 450 °C), a nearly polycrystalline SnO₂ film with preferred orientation of (101) was produced. Annealing of the samples at 500–650 °C caused the transmittance and optical bandgap increased, while the absorption decreased. Reduction of the Urbach energy after annealing could be attributed to the reduction of the degree of thermal disorder. AFM studies showed that although the thin films were annealed under similar condition, their roughness was not similar because of different oxidation temperatures, which means that initial oxidation temperature played an important role on surface uniformity of SnO₂ thin films.     

Gas sensing properties of nano SnO<Subscript>2</Subscript> based thick films prepared by dip coating method with effect of molarity of PtCl<Subscript>2</Subscript> solution

Synthesized nanophase SnO₂ powder was used as a functional material along with optimized 15 wt% of glass, fired at 550 °C for better adhesion, to fabricate thick films using screen printing on alumina substrate. Their surface was modified by dip coating in platinum chloride solution (PtCl₂) of different molarities (0.05–0.2 M). A subsequent thermal treatment to these thick films was carried out at an optimized temperature of 750 °C in air atmosphere. The films were tested for 400 ppm concentration of H₂, CO and LPG. Sensors dip coated with 0.15 M solution of PtCl₂ show the highest sensitivity towards the test gases which is ten times higher than undoped SnO₂ sensors.XRD, EDX and SEM measurements showed that the behavior could be associated with the spatial distribution of the platinum within the tin oxide film. The sensors have fast response time of 10 s to all the three gases with a minimum detection limit of 10 ppm.     

Thermally evaporated thin films of SnS for application in solar cell devices

SnS (tin sulphide) is of interest for use as an absorber layer and the wider energy bandgap phases e.g. SnS₂, Sn₂S₃ and Sn/S/O alloys of interest as Cd-free buffer layers for use in thin film solar cells. In this work thin films of tin sulphide have been thermally evaporated onto glass and SnO₂:coated glass substrates with the aim of optimising the properties of the material for use in photovoltaic solar cell device structures. In particular the effects of source temperature, substrate temperature, deposition rate and film thickness on the chemical and physical properties of the layers were investigated. Energy dispersive X-ray analysis was used to determine the film composition, X-ray diffraction to determine the phases present and structure of each phase, transmittance and reflectance versus wavelength measurements to determine the energy bandgap and scanning electron microscopy to observe the surface topology and topography and the properties correlated to the deposition parameters. Using the optimised conditions it is possible to produce thin films of tin sulphide that are pinhole free, conformal to the substrate and that consist of densely packed columnar grains. The composition, phases present and the optical properties of the layers deposited were found to be highly sensitive to the deposition conditions. Energy bandgaps in the range 1.55 eV-1.7 eV were obtained for a film thickness of 0.8 μm, and increasing the film thickness to > 1 μm resulted in a reduction of the energy bandgap to less than 1.55 eV. The applicability of using these films in photovoltaic solar cell device structures is also discussed.     

Structural,morphological and optical properties of SnS<Subscript>2</Subscript> thin films by nebulized spray pyrolysis technique

The thin films of Nano crystalline tin disulfide (SnS₂) have been prepared by nebulized spray pyrolysis technique (NSP) with different molar concentrations (0.3, 0.4 and 0.5 M). Cleaned glass substrates were used and the substrate temperature was maintained at 300?°C. The films were deposited using tin tetrachloride monohydrate (SnCl₄·H₂O) and thiourea in de-ionized water and Isopropyl alcohol (1:3 ratio). The prepared films structural, morphological and optical properties were studied using X-ray diffraction (XRD), scanning electron microscope (SEM), UV–Vis spectrophotometer. The structure of the films were found to be face centered cubic with preferential orientation along (002) plane. X-ray line profile analysis was used to evaluate the micro structural parameters such as crystallite size, micro strain, dislocation density and texture coefficient. The average crystallite size values are 60 nm. Morphological results of the SnS₂ thin films are small needle shaped particles and the average grain size was 400 nm. The optical studies revealed that the band gap between 2.65 and 2.72 eV and high optical transmittance 98%. EDAX spectrum of tin disulfide result showed some amount of excess tin was present in the sample. This is the method with very low cost of producing tin disulfide (SnS₂) thin films, which is very important for many applications in industry.     

Fabrication of high-performance fluorine doped-tin oxide film using flame-assisted spray deposition

A high-performance fluorine-doped tin oxide (FTO) film was fabricated by flame-assisted spray deposition method. By varying the NH₄F doping concentration, the optimal concentration was established as 8 at.%. X-ray diffractograms confirmed that the as-grown FTO film was tetragonal SnO₂. In addition, the FTO film was comprised of nano-sized grains ranging from 40 to 50 nm. The heat-treated FTO film exhibited a sheet resistance of 21.8 Ω/? with an average transmittance of 81.9% in the visible region (λ = 400-800 nm). The figures of merit shows that the prepared FTO film can be used for highly efficient dye-sensitized solar cells electrodes.