Synthesis and characterization of Sn1Mg1−xO2 thin films fabricated by aero-sole assisted chemical vapor deposition

In order to achieve high conductivity and transmittance of transparent conducting oxide, Mg doped SnO₂ (Mg_xSn_1?xO₂) thin films have been fabricated and characterized to investigate their structural and optical properties. The Mg_xSn_1?xO₂ thin films have been deposited on glass substrate using aero-sole assisted chemical vapor deposition. The molar concentration of Mg contents was changed from 0 to 8 %. The confirmation of tetragonal structure and particle size (32–87 nm) of thin films was analyzed by X-ray diffraction. The surface roughness has been found to decrease with the increase of the dopant concentration as investigated by atomic force microscopy. The optical transmission increased from 54 to 78 % and the band gap of pure SnO₂ has been found to be 3.75 eV while it rises up to 3.88 eV with increasing Mg doping. The sheet resistance (R_s) of undoped SnO₂ is maximum which become lowest at 4 % Mg doped SnO₂.     

Blue shift in optical band gap of sol–gel derived Sn1−xZnxO2 polycrystalline thin films

Undoped and Zn doped SnO₂ thin films are deposited by sol–gel spin coating on glass substrate. XRD spectra with prominent peaks along (110) and (101) planes shows the polycrystalline nature of thin films. The particle size lies between 9.30 and 42.09 nm as estimated by Debye–Scherer method. SEM micrographs of the films contain pebble like structures spread throughout whose diameter decreases with increase in dopant concentration. Surface topology of the films is studied by atomic force microscopy. Transmission spectra show that all the films are highly transparent in the visible and IR spectral region (80–90 %) and a sharp absorption occurs near 300 nm. Approximately a change of 4 % is observed in the optical band gap by Zn doping. The optical band gap is tunable between 3.55 and 3.68 eV for 0 ≤ x ≤ 0.15 in nanocrystalline Sn_1?xZn_xO₂. Broad UV emission at 395 nm is observed in photoluminescence spectra of the films along with a blue emission. Emission intensity decreases as amount of Zn incorporated into SnO₂ increases.     

Influence of Zn doping on electrical and optical properties of multilayered tin oxide thin films

In this study, the electrical and optical properties of Zn doped tin oxide films prepared using sol-gel spin coating process have been investigated. The SnO² : Zn multi-coating films were deposited at optimum deposition conditions using a hydroalcoholic solution consisting of stannous chloride and zinc chloride. Films with Zn doping levels from 0–10 wt% in solution are developed. The results of electrical measurements indicate that the sheet resistance of the deposited films increases with increasing Zn doping concentration and several superimposed coatings are necessary to reach expected low sheet resistance. Films with three coatings show minimum sheet resistance of 1–479 kΩ/ in the case of undoped SnO₂ and 77 kΩ/ for 5 wt% Zn doped SnO₂ when coated on glass substrate. In the case of single layer SnO₂ film, absorption edge is 3.57 eV and when doped with Zn absorption edge shifts towards lower energies (longer wavelengths). The absorption edge lies in the range of 3.489-3.557 eV depending upon the Zn doping concentration. The direct and indirect transitions and their dependence on dopant concentration and number of coatings are presented.     

Structural,optical and electrical properties of Zn-doped SnO2 nanoparticles synthesized by the co-precipitation technique

Nanometric size Zn-doped SnO₂ particles with Zn concentration varying from 1 to 6 % were prepared using the co-precipitation method. X-ray diffraction patterns show for all samples a typical rutile-type tetragonal structure of SnO₂ without any additional peaks from spurious phases. These results together with transmission electron microscopy analyses have shown that the size of the nanoparticles decreases with Zn doping down to 4 nm. According to UV–visible absorption measurements this decrease of particle size is accompanied by a decrease of the band gap value from 3.34 eV for SnO₂ down to 3.28 eV for 6 % Zn doping. The electrical conductivity of the system has been investigated between 473 and 718 K, in the 200 Hz–5 MHz frequency range, by means of impedance spectroscopy. The temperature dependence of the bulk conductivity was found to obey the Arrhenius law with activation energies of 0.74 eV for SnO₂ and 0.69 eV for 6 % Zn doping.     

Spectroscopic,microscopic, and electrical characterization of nanostructured SnO2:Co thin films prepared by sol–gel spin coating technique

Cobalt doped SnO₂ thin films were prepared by sol–gel spin coating technique and influence of dopant concentration on structural, morphological and optical properties of thin films were investigated by XRD, XPS, FTIR, SEM, AFM, PL, UV–vis, and Hall effect measurement. All samples have a tetragonal rutile structure and the grain size decreases with increasing the doping concentration. XPS results clearly showed the presence of Co²⁺ ions into the SnO₂. The SEM and AFM images reveal that the morphology of samples was affected by dopant. Conductivity type of the films changes from n-type to p-type with increasing Co-dopant above 3 mol% and electrical resistivity increases with increasing Co content. The optical band gap gradually decreases with improved cobalt concentration from 3.91 eV to 3.70 eV. The PL measurements revealed the decrease in intensity of blue emission lines and increase in green emission when content of Co is enhanced in the thin films.     

Electrical properties and extension mechanism of Ohmic region of sol–gel derived Ba0.7Sr0.3TiO3 thin films by Zn doping

Undoped and 3 mol% Zn-doped barium strontium titanate thin films were deposited on Pt/Ti/SiO₂/Si substrates using a sol–gel method. The microstructure and morphology of the films were characterized by X-ray diffraction and atomic force microscopy. It showed that both films are polycrystalline with a perovskite structure and smaller grains were observed for the Zn-doped thin films. Dielectric measurements showed that the dielectric loss at 500 kHz was reduced from 0.042 to 0.019 by Zn doping, which was accompanied by a slight decrease of the dielectric constant from 303 to 273. At an applied electric field of 60 kV/cm, the leakage current density of the Zn-doped Ba_0.7Sr_0.3TiO₃ thin films was 2.5 × 10⁻⁸ A/cm², which was by two orders of magnitude lower than that of the undoped films. The leakage current characteristics also indicated that the Ohmic conduction region of barium strontium titanate thin films was extended by Zn dopant. The microstructure, electrical properties and extension mechanism of Ohmic conduction region of the Zn-doped barium strontium titanate thin films were discussed in relation to the effect of Zn doping.     

Hydrothermal synthesis of Zn-doped Ni–Mn–Al–O thin films toward high-performance negative temperature coefficient thermistor

In this study, Zn-doped Ni–Mn–Al–O negative temperature coefficient thermistor (NTC) film with high electrical performance has been demonstrated. XRD, XPS, SEM and electrical measurements were carried out to explore the impact of Zn-doping. The XRD analysis of NiMn_1.8?xAl_0.2Zn_xO₄ films confirmed the cubic spinel crystal phase regardless of x. The SEM image illustrated that the morphology of NiMn_1.8?xAl_0.2Zn_xO₄ is closely related to the Zn doping amount. The XPS showed that the relative molar content of Mn³⁺ and Mn⁴⁺ increased with the increase of Zn doping concentration. Remarkably, the Zn-doped Ni–Mn–Al–O film presented the typical NTC characteristics, and the room temperature resistance (R₂₅) increased with the improvement in Zn doping concentration. Moreover, the thermistor constant B_25/50 remained reasonably high from 4088 to 4272 K. Meanwhile, the aging test showed that the Zn-doped films were more stable, even aging at 150 °C for 500 h.     

The variation of the features of SnO2 and SnO2:F thin films as a function of V dopant

V doped SnO₂ and SnO₂:F thin films were successfully deposited on glass substrates at 500 °C with spray pyrolysis. It was observed that all films had SnO₂ tetragonal rutile structure and the preferential orientation depended on spray solution chemistry (doping element and solvent type) by X-ray diffraction measurements. The lowest sheet resistance and the highest optical band gap, figure of merit, infrared (IR) reflectivity values of V doped SnO₂ for ethanol and propane-2-ol solvents and V doped SnO₂:F films were found to be 88.62 Ω–3.947 eV–1.02 × 10^?4 Ω^?1–65.49 %, 65.35 Ω–3.955 eV–8.54 × 10^?4 Ω^?1–72.58 %, 5.15 Ω–4.076 eV–6.15 × 10^?2 Ω^?1–97.32 %, respectively, with the electrical and optical measurements. Morphological properties of the films were investigated by atomic force microscope and scanning electron microscope measurements. From these analysis, the films consisted of nanoparticles and the film morphology depended on doping ratio/type and solvent type. It was observed pyramidal, polyhedron, needle-shaped and spherical grains on the films’ surfaces. The films obtained in present study with these properties can be used as front contact for solar cells and it can be also one of appealing materials for other optoelectronic and IR coating applications.     

Influence of (Zn + F) double doping on the structural,morphological, photoluminescence,optoelectrical properties and antibacterial activity of CdS thin films

The effects of (Zn + F) double doping on the structural, morphological, optical and electrical properties of CdS thin films is reported in this paper. Polycrystalline nature is observed for all the films. Zn-doped and (Zn + F) doubly doped CdS films exhibit a strong (0 0 2) preferential orientation similar to that of the undoped film. The (0 0 2) plane of the Zn-doped and (Zn + F) doubly doped films shift towards higher Bragg angles favoring a contraction in their lattice parameter values. Increased transparency and blue shift in optical band gap is observed for the doubly doped films. The electrical resistivity values of the undoped, Zn-doped, (Zn + F) doubly doped CdS thin films are found to be in the order of 10^?1 Ω-cm. From the obtained results it is found that the physical properties of Zn-doped CdS films got enhanced when co-doped with fluorine, and the (Zn + F) doubly doped CdS thin films seem to be a potential candidate for future optoelectronic device applications. Antibacterial activity of the as deposited films were carried against E. coli gram negative bacteria and from the zone of inhibition it is confirmed that the (Zn + F) doubly doped CdS thin films can be used as a good antimicrobial agent against pathogenic microorganisms.     

Effect of Zn doping on optical properties and photoconductivity of SnS2 nanocrystalline thin films

Zn-doped SnS₂ thin films have been deposited simply by spray pyrolysis technique. The doping level was changed from [Zn/Sn] = 0 to 7·5 at%. The films were characterized by means of X-ray diffraction, scanning tunneling microscopy (STM), energy dispersive X-ray analysis (EDX), photoluminescence and UV-Vis spectroscopy. XRD patterns of the films with different zinc contents show that all samples have polycrystalline structure with Berndtite dominant phase and preferred orientation of (001) growth plane. Zn insertion causes a significant decrease in grain size. Optical bandgap of the films have been calculated for different dopant concentrations and they lie in the region of 2·3–2·7 eV. Surprisingly, regardless of doping level, the luminescent properties of films are related to the fundamental bandgap energy and deep levels inside the bandgap. Photoconductivity of the films have been measured under visible light. Sensitivity to the light increases by zinc incorporation, which was a large amount for SnS₂:Zn of 7·5%.     

Vanadium doped SnO<Subscript>2</Subscript> nanoparticles for photocatalytic degradation of methylene blue

Nanometric V-doped particles with vanadium concentration varying from 0 to 10% were prepared using the polyol method. The influence of the doping on the textural, structural and optical properties was studied by various methods of characterization. X-ray diffraction (XRD) patterns disclose that nanocrystallites of cassiterite, i.e. rutile-like tetragonal structure SnO₂ and the absence of a new vanadium phase in the XRD pattern in the different concentration of doping were formed after annealing, the ordinary crystallite size decreased from 20.6 to 12.3 when the doping concentration increased from 0 to 10%, respectively. Moreover, the N₂ sorption porosimetry and transmission electron microscopic show that all samples synthesized were constituted of an aggregated network of almost spherical nanoparticles, which sizes changed with the altitude in the doping concentration to 10%. In accordance with UV–visible absorption measurements, this diminution of nanoparticles sizes was followed by a decrease in the band gap value from 3.25 eV, for undoped SnO₂, to 2.75 eV, for SnO₂ doped at 10%. On the other part, the photocatalytic activity of undoped and V-doped SnO₂ nanoparticles was studied using methylene blue (MB) as model organic pollutants. The SnO₂ nanoparticles doped at 10% of vanadium disclosed that the discoloration of MB reached 97.4% after irradiation of 120 min, with an apparent constant rate of the degradation reaching 0.035 min^?1 for MB degradation that was about 2.5 times more than that of pure SnO₂ (0.014 min^?1).     

Variation of structural,optical, dielectric and magnetic properties of SnO<Subscript>2</Subscript> nanoparticles

We report effect of oxygen vacancies on band gap narrowing, enhancement in electrical conductivity and room temperature ferromagnetism of SnO₂ nanoparticles synthesized by simple chemical precipitation approach. As the calcination temperature is elevated from 400 to 800 °C, the average particle size increases from 12.26 to 34.43 nm, with enhanced grain growth and crystalline quality. At low temperatures, these nanoparticles are in a rather oxygen-poor state revealing the presence of many O vacancies and Sn interstitials in SnO₂ nanoparticles as in this case Sn⁺² is not oxidized completely to Sn⁺⁴ and small sized nano particles have more specific surface area, hence defects are more prominent. The oxygen content increases steadily with increasing temperature, with the Sn:O atomic ratio very near to the stoichiometric value of 1:2 at high temperatures suggesting the low density of defects. The optical band gap energies of all SnO₂ nanoparticles are in the visible light region, decreasing from 2.89 to 1.35 eV, while room temperature ferromagnetism and electrical conductivity are enhanced with reduced temperatures. The dielectric constant (ε_r) exhibited dispersion behaviour and the Debye’s relaxation peaks were observed in tanδ. The variation of dielectric properties and ac conductivity revealed that the dispersion is due to Maxwell–Wagner interfacial polarization and hopping of charge carriers between Sn⁺²/Sn⁺⁴. The narrowed band gap energies and enhanced ferromagnetism are mainly attributed to the increase of defects density (e.g., oxygen vacancies). The presence of oxygen vacancies is confirmed by EDX, Raman, PL, XPS, and UV–Vis spectra. The band gap of 1.35 eV is the smallest value for SnO₂ reported so far. This rather small band gap, enhanced conductivity and room temperature ferromagnetism demonstrate that SnO₂ nanoparticles are very promising in the visible light photo catalysis and optoelectronic devices.     

Chemical bath deposition of CdS thin films doped with Zn and Cu

Zn- and Cu-doped CdS thin films were deposited onto glass substrates by the chemical bath technique. ZnCl₂ and CuCl₂ were incorporated as dopant agents into the conventional CdS chemical bath in order to promote the CdS doping process. The effect of the deposition time and the doping concentration on the physical properties of CdS films were investigated. The morphology, thickness, bandgap energy, crystalline structure and elemental composition of Zn- and Cu-doped CdS films were investigated and compared to the undoped CdS films properties. Both Zn- and Cu-doped CdS films presented a cubic crystalline structure with (1 1 1) as the preferential orientation. Lower values of the bandgap energy were observed for the doped CdS films as compared to those of the undoped CdS films. Zn-doped CdS films presented higher thickness and roughness values than those of Cu-doped CdS films. From the photoluminescence results, it is suggested that the inclusion of Zn and Cu into CdS crystalline structure promotes the formation of acceptor levels above CdS valence band, resulting in lower bandgap energy values for the doped CdS films.     

Structural and optoelectronic properties of indium doped SnO2 thin films deposited by sol gel technique

Indium doped tin oxide (SnO₂:In) thin films were deposited on glass substrates by sol–gel dip coating technique. X-ray diffraction pattern of SnO₂:In thin films annealed at 500 °C showed tetragonal phase with preferred orientation in T (110) plane. The grain size of tin oxide (SnO₂) in SnO₂:In thin films are found to be 6 nm which makes them suitable for gas sensing applications. AFM studies showed an inhibition of grain growth with increase in indium concentration. The rms roughness value of SnO₂:In thin films are found to 1 % of film thickness which makes them suitable for optoelectronic applications. The film surface revealed a kurtosis values below 3 indicating relatively flat surface which make them favorable for the production of high-quality transparent conducting electrodes for organic light-emitting diodes and flexible displays. X-ray photoelectron spectroscopy gives Sn 3d, In 3d and O 1s spectra on SnO₂:In thin film which revealed the presence of oxygen vacancies in the SnO₂:In thin film. These SnO₂:In films acquire n-type conductivity for 0–3 mol% indium doping concentration and p type for 5 and 7 mol% indium doping concentration in SnO₂ films. An average transmittance of >80 % (in ultra-violet–Vis region) was observed for all the SnO₂:In films he In doped SnO₂ thin films demonstrated the tailoring of band gap values. Photoluminescence spectra of the films exhibited an increase in the emission intensity with increase in indium doping concentration which may be due structural defects or luminescent centers, such as nanocrystals and defects in the SnO₂.     

Enhanced visible light photocatalytic activity of Zn2SnO4 via sulfur anion-doping

Sulfur anion doped Zn₂SnO₄ was prepared by calcining the mixture of thiourea and spinel Zn₂SnO₄ at 300 °C under argon atmosphere and characterized by XRD, XPS and DRS. It was found that S^2? was incorporated interstitially into the bulk phase of Zn₂SnO₄. After the doping of S^2?, the band gap of Zn₂SnO₄ was sharply decreased to 2.7 eV compared with that of undoped Zn₂SnO₄ (~ 3.6 eV). The photocatalytic activity of S-doped Zn₂SnO₄ was enhanced for photodegradation of Rhodamine B (RhB) in aqueous solution under visible light irradiation.     

Effect of the substrate temperature on the properties of spray-deposited SnO2:F thin films

The effect of the substrate temperature on the properties of spray-deposited SnO₂:F thin films is investigated. X-ray diffraction patterns show that the crystallinity of the films is enhanced with the increasing of substrate temperature. Comparing the SEM images, both the particle size and density are increased at a higher deposition temperature. The lowest sheet resistance of 8.43 Ω/□ is obtained at the substrate temperature of 350 °C. In addition, the average optical transmittance of the three films reaches up to 85 % in the visible range. The absorption coefficient is the lowest at 350 °C. The band gap increases from 3.36 to 3.61 eV while the electrical resistivity of SnO₂:F thin films decreases from 8.51 × 10^?3 to 9.86 × 10^?4 Ω cm as elevating the substrate temperature from 250 to 350 °C.     

Growth and characterization of tin oxide thin films and fabrication of transparent p-SnO/n-ZnO p–n hetero junction

p-Type and n-type tin oxide thin films were deposited by rf-magnetron sputtering of metal tin target by varying the oxygen pressure. Chemical composition of SnO thin film according to the intensity of the XPS peak is about 48.85% and 51.15% for tin and oxygen respectively. Nearest neighbor distance of the atoms calculated from SAED patterns is 2.9 Åand 2.7 Åfor SnO and SnO₂ respectively. The Raman scattering spectrum obtained from SnO thin films showed two peaks, one at 113 cm⁻¹ and the other at 211 cm⁻¹. Band gap of as-deposited SnO_x thin films vary from 1.6 eV to 3.2 eV on varying the oxygen partial pressure from 3% to 30% which indicates the oxidization of metallic phase Sn to SnO and SnO₂. p-Type conductivity of SnO thin films and n-type conductivity of SnO₂ thin films were confirmed through Hall coefficient measurement. Transparent p–n hetero junction fabricated in the structure glass/ITO/n-ZnO/p-SnO shows rectification with forward to reverse current ratio as 12 at 4.5 V.     

Ti doped hematite thin film photoanode with enhanced photoelectrochemical properties

Ti-doped Fe₂O₃ thin films were prepared on fluorine-doped SnO₂ substrate as visible light active photoelectrochemical anodes. The fabricated films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM), X-ray energy dispersive spectroscopy and X-ray photoelectron spectroscopy (XPS). XRD data showed all films exhibited rhombohedral hematite phase, and the cell parameters showed that Titanium atoms substituted Fe atoms in the hematite lattice. AFM demonstrated that Ti doping could decrease the particle size on the surface compared with pure hematite. XPS results presented that Ti atom concentration was about 2.23 % in the doped film surface. The incident photon to electron conversion efficiency of Ti doped α-Fe₂O₃ film reached 23 % at 400 nm under 0.30 V bias versus AgCl in 1 M NaOH, which was nearly four times than that of undoped film. Titanium atoms in α-Fe₂O₃ lattice could increase the conductivity of hematite film. And excited electrons and holes in the bulk film could be separated more efficiently, rather than recombining with each other rapidly as that in pure hematite, which ultimately prolonged the life of electrons and holes and obtained the high efficiency Fe₂O₃ photo anode.     

Structural,morphological and optical properties of undoped and Co-doped ZnO thin films prepared by sol–gel process

Undoped and Co-doped ZnO thin films with different amounts of Co have been deposited onto glass substrates by sol–gel spin coating method. Zinc acetate dihydrate, cobalt acetate tetrahydrate, isopropanol and monoethanolamine (MEA) were used as a precursor, doping source, solvent and stabilizer, respectively. The molar ratio of MEA to metal ions was maintained at 1.0 and a concentration of metal ions is 0.6 mol L^?1. The Co dopant level was defined by the Co/(Co + Zn) ratio it varied from 0 to 7 % mol. The structure, morphology and optical properties of the thin films thus obtained were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis), photoluminescence (PL) and Raman. The XRD results showed that all films crystallized under hexagonal wurtzite structure and presented a preferential orientation along the c-axis with the maximum crystallite size was found is 23.5 nm for undoped film. The results of SEM indicate that the undoped ZnO thin film has smooth and uniform surface with small ZnO grains, and the doped ZnO films shows irregular fiber-like stripes and wrinkle network structure. The average transmittance of all films is about 72–97 % in the visible range and the band gap energy decreased from 3.28 to 3.02 eV with increase of Co concentration. DRX, EDX and optical transmission confirm the substitution of Co²⁺ for Zn²⁺ at the tetrahedral sites of ZnO. In addition to the vibrational modes from ZnO, the Raman spectra show prominent mode representative of Zn_yCo_3?yO₄ secondary phase at larger values of Co concentration. PL of the films showed a UV and defect related visible emissions like violet, blue and green, and indicated that cobalt doping resulted in red shifting of UV emission and the reduction in the UV and visible emissions intensity.     

Fast response time alcohol gas sensor using nanocrystalline F-doped SnO2 films derived via sol–gel method

Pure and fluorine-modified tin oxide (SnO₂) thin films (250–300 nm) were uniformly deposited on corning glass substrate using sol–gel technique to fabricate SnO₂-based resistive sensors for ethanol detection. The characteristic properties of the multicoatings have been investigated, including their electrical conductivity and optical transparency in visible IR range. Pure SnO₂ films exhibited a visible transmission of 90% compared with F-doped films (80% for low doping and 60% for high doping). F-doped SnO₂ films exhibited lower resistivity (0· 12 × 10^???4 Ω  cm) compared with the pure (14·16 × 10^???4 Ω  cm) one. X-ray diffraction and scanning electron microscopy techniques were used to analyse the structure and surface morphology of the prepared films. Resistance change was studied at different temperatures (523–623 K) with metallic contacts of silver in air and in presence of different ethanol vapour concentrations. Comparative gas-sensing results revealed that the prepared F-doped SnO₂ sensor exhibited the lowest response and recovery times of 10 and 13 s, respectively whereas that of pure SnO₂ gas sensor, 32 and 65 s, respectively. The maximum sensitivities of both gas sensors were obtained at 623 K.