Narrow Results

Single layer (SLAR: TiO₂ and ZnO), and DLAR: TiO₂/ZnO bi-layer were deposited on glass substrates by sol–gel dip and spray pyrolysis for TiO₂ and ZnO thin films respectively. The structural and optical properties have been studied by different characterization techniques: Raman spectroscopy, UV–Visible spectrophotometer and m-lines spectroscopy. The SLAR of TiO₂ and ZnO thin films crystallizes in the Anatase and the wurtzite phase, respectively. The fabrication of the DLAR bi-layer increased the optical gap energies. Also, the DLAR film experienced a decrease in the visible transmittance. However, the present work is principally focused on the influence of the DLAR on the performance of the waveguide characterized by the m-lines measurements. The SLAR samples exhibit a single mode in the TE and TM polarizations. The DLAR sample had two modes in each polarization, one mode in the TE polarization was due to light traveling in the TiO₂ film and the rest three were assigned to ZnO. The results shed light on the effect of the deposition method and the role of refractive index difference in bi-layer waveguide design.

Vertically aligned arrays of multi-walled carbon nanotubes (VACNTs) were grown by spray pyrolysis of turpentine oil and ferrocene mixture at temperatures higher than 700°C. Using this simple method, we report the successful growth of vertically aligned nanotubes of ~300μm length and diameter in the range of ?20–80nm on Si(100) substrate. The ferrocene acts as an in situFe catalyst precursor, forming the nano-sized metallic iron particles for formation of VACNTs on the Si substrate. The morphological characteristics of VACNTs are confirmed by SEM, TEM and Raman spectroscopy and growth mechanism is discussed in short.

The MgB₂ films have been prepared on the c-cut sapphire substrates by ultrasonic spray pyrolysis (USP) technique using Boric acid and Magnesium acetate tetrahydrate dissolved into distillated water and ethanol as starting materials. The overall concentrations were fixed at 0.1mol/L. During the deposition, 96% Ar - 4% H₂ was used as carrier gas. The reaction temperatures were 850 °C, 900 °C and 950 °C . The deposited MgB₂ films showed strongly (1 0 1) plane orientation. In the sample deposited at 950 °C for 5min, MgB₂ film showed a homogeneous surface, with good grain connectivity. The critical temperature (T_c) was observed to be 31.5 K. The crystal structural and microstructural properties of the MgB₂ films prepared by USP were observed to be strongly dependent on the reacting temperature.

In present paper, we report the preparation of CdTe films on thoroughly cleaned glass substrates by using the novel spray pyrolysis technique with CdCl_2.H₂O and TeO₂ as precursor materials. The films were deposited on glass substrates by using the parameters: (a) spray nozzle - substrate distance = 30 cm, (b) sparing solution conc. = 0.02 M, (c) carrier N₂ gas flow rate = 15 lpm, (d) substrate temperature = 350°C, (e) deposition time = 15 min. (f) N₂ gas purging time for deposition chamber = 45 min. and (g) amount of spray solution = 50 ml solution. The resultant films were characterized by using physical techniques: XRD, FTIR, EDAX and SEM. The characterization results showed that the resultant films are having material purity and cubic CdTe phase purity with zinc blend symmetry. The SEM study revealed the nano-rod morphological feature of CdTe films with rod diameter in range of 100 - 250 nm and average rod length ~ 5μm. The values of absorptance (α) and band gap energy (E_g) for these films are found to be 0.91 and ~ 1.42 eV respectively. These results indicated the high potential of CdTe films prepared in the present work for solar cell applications.

Undoped and manganese (Mn)-doped zinc oxide (ZnO) thin films have been deposited onto glass substrates at 300${}^{\circ }$C using a low cost spray pyrolysis technique. Structural, optical and electrical properties of the as-deposited films have been investigated. Scanning electron microscopy images show the existence of clusters with well-defined nucleation centers consisting of highly dense ganglia-like fibers over a large area around the nucleation center. Chemical compositions of the ZnO and Mn-doped ZnO thin films are studied by using energy dispersive X-ray (EDX) analysis. X-ray diffraction spectra depict that the films have polycrystalline wurtzite structure. The average crystallite sizes are calculated in the range of 8–16 nm by Williamson–Hall method and found in good agreement with Scherer method. Optical transmittance of the films is about 80% in the visible region. Bandgap energy is tuned to 2.83 eV from 3.10 eV with increasing Mn doping. Electrical resistivity at room-temperature decreases significantly with increasing Mn doping as well as increasing temperature from 300–440 K. The activation energies in the temperature ranges 300–350 K and 350–440 K are found to be in the range of 0.25–0.16 eV and 0.35–0.59 eV, respectively. Hall Effect measurements show that the thin films have negative Hall co-efficient indicating $n$-type conductivity at room-temperature. Carrier concentration is found to be of the order of 10${}^{18}$ cm${}^{-3}$.

Near-ideal p-CdS/n-Si heterojunction (HJ) band edge lineup has been investigated for the first time with the aid of I–V and C–V measurements. The heterojunction was obtained by the deposition of CdS films prepared by chemical spray pyrolysis technique (CSP), on the monocrystalline n-type silicon. The experimental data of the conduction band offset, ΔE_c and the valence band offset, ΔE_c were compared with theoretical values. The band offsets ΔE_c=530 meV and ΔE_v=770 meV were obtained at 300 K. The energy band diagram of p-CdS/n-Si HJ was constructed. The C–V measurements depicted that the junction was an abrupt type and the built-in voltage was determined from the C^-2–V plot.

We have investigated the effect of fluorine dopant concentration (0–15 F/Sn wt.%) on structural, optical and electrical properties of SnO₂ thin films grown by spray pyrolysis technique. According to the experimental evidences and data analysis, we found in these samples: (1) the polycrystalline layers, while in undoped conditions it mainly grow along (211) direction in doped ones (200) is the preferred direction with a direct band gap energy of about 3.7–3.9 eV; (2) The main cause for the relatively high absorption coefficients below E_g could be due to the presence of wide (~ 1–2 eV) band tails in the forbidden gap; (3) the highest (5.4 × 10^-3 Ω^-1) figure of merit belongs to the sample with 5 wt.% F/Sn concentration; (4) the grain boundary scattering is the main limiting mechanism in the electrical transport properties of the layers.

By using spray pyrolysis method, 0.65Ba(Mg_1/3, Nb_2/3)O₃-0.35BaTiO₃ thin films were deposited on glass/aluminum substrates. The effect of annealing temperature on perovskite phase and crystalline structure analysis of the BMN-BT films performed on an X-ray diffraction (XRD). The optical properties of the resultant materials have been characterized as a function of substrate's temperature. The absorption coefficient (α) and extinction coefficient (k) of the films are obtained by using UV-vis spectroscopy. The band gap energy values of the films using analysis of the absorption coefficient and Tauc's formula have also been determined. For films deposited at different substrate temperatures, direct transitions occur with energies varying from 4.57 eV to 4.21 eV.

In this paper, we have investigated the effect of Mn doping on the electrical properties of ZnO thin films. ZnO thin films with different amounts of Mn concentrations (0, 5, 10 and 15 mol.%) were prepared by spray pyrolysis technique. The crystal structure was examined by X-ray diffraction (XRD) analysis. XRD patterns showed that all the samples were crystallized in wurtzite structure while a decrease in crystallinity and switch in preferential orientations were observed in Mn-doped thin films comparing to undoped ZnO. The element composition of all thin films was detected by energy dispersive X-ray (EDX). The surface morphology of the films was investigated using field emission scanning electron microscope (FESEM) and optical properties were studied using UV-vis spectroscopy. UV-vis study revealed that the band gap blueshifts with the increase in Mn content and $E_g$ increases with the increase in Mn concentration. The resistivity and activation energy were measured at room temperature and ranging from 373 K to 573 K. Comparing to undoped ZnO thin film, the resistivity of Mn-doped ZnO films increased because of different parameters such as increasing barrier height energy and reducing the oxygen deficiency.

In this study, undoped and cobalt (Co)-doped zinc oxide (ZnO) films were successfully produced by ultrasonic spray pyrolysis (USP) technique at low temperature (350${}^{\circ }$C). The optical and surface properties were investigated as a function of Co content. The optical parameters (thickness, refractive index and extinction coefficient) were determined using spectroscopic ellipsometry (SE) and it was seen that the refractive index and extinction coefficient values of Co-doped ZnO films decreased slightly depending on the increasing of Co doping. For investigation, the transmittance and photoluminescence (PL) spectra of the films, UV–Vis spectrophotometer and PL spectroscopy were used at room temperature. The transmittance spectra show that transmittance values decreased and Co${}^{+2}$ ions substitute Zn${}^{+2}$ ions of ZnO lattice. The optical band gap values decreased from 3.26 eV to 2.85 eV with the changing of Co content. The results of PL spectra exhibit the position of the different emission peaks unchanged but the intensity of peaks increased with increasing Co doping. Also, the surface properties of the films were obtained by atomic force microscopy (AFM) and these results indicated that the surface morphology and roughness values were prominently changed with Co doping.

Single-crystal precursor of hybrid oxides NiO–MnCo₂O₄–Ni₆MnO₈ (SCNCM) is synthesized via an improved continuous two-step spray pyrolysis system (CTSP). This kind of mixed oxide is to be regarded as an ideal precursor for the single-crystal Ni-rich Li[Ni${}_{0.6}$Co${}_{0.2}$Mn${}_{0.2}$]O₂ cathode materials (SCLNCM). The new pilot plant (30 t/a), method, and chlorate in this work could extremely improve the lengthy process, reducing segregation of metal element, excessive sintering temperature, high water consumption, non-polluting, and production efficiency of the SCLNCM. The resulting SCLNCM powders have a type of fine particle size and porous structure with a typical $\alpha$-NaFeO₂ lamellar structure. It also has a type of better cyclic stability, safety, rate capability, crystallinity, and surface area than polycrystalline cathode materials. It delivers an initial discharge capacity of 184 mAh/g at 0.1 C (18 mA/g) with a capacity retention of 91% after 100 cycles in the voltage window of 2.8–4.3 V.

Undoped, antimony doped and fluorine doped tin oxide films have been prepared by spray pyrolysis technique. The films were deposited on glass substrates at temperatures ranging between 300°C and 370°C by spraying an alcoholic solution of tin tetra chloride (SnCl₄). Dopants used were antimony tri chloride (SbCl₃) for antimony doped tin oxide (ATO) films, and ammonium fluoride (NH₄F) for fluorine doped tin oxide (FTO) films. Among undoped tin oxide films, the least resistivity was found to be 3.1 × 10^-3 Ω-cm for a molar concentration of 0.75 M. In case of antimony doped films minimum resistivity value was found to be 7.7 × 10^-4 Ω-cm for a film with (Sb/Sn) = 0.065, deposited at 370°C and in case of fluorine doped films it was found to be 1.67 × 10^-3 Ω-cm for a doping percentage of 3 at% of fluorine in 0.1 M solution. The corresponding values of the carrier concentrations were found to be 1.8 × 10²⁰/cm³ and 9.98 × 10²⁰/cm³, respectively. The electrical and optical properties of these films were studied as a function of both doping concentration and substrate temperature. Doping percentage of antimony and fluorine in the spray solution has been optimized for achieving a minimum electrical resistivity. The dependence of electrical properties such as resistivity, carrier concentration and mobility of doped films were analyzed. Influence of antimony dopant on the optical band gap of the films has been reported on the basis of electron conduction mechanism. Air and argon annealing effects on the electrical properties of antimony doped tin oxide films were also studied.

The NiO and Fe-doped NiO thin films have been prepared by using spray pyrolysis technique. The effects of change in the volumetric concentration and substrate temperature on the film characteristics have been investigated. With the increase in volumetric concentration, the grain size and the roughness of the film increase; while the number of voids has been reduced. In case of NiO thin films the activation energy was found to increase from 0.33 eV to 0.40 eV with the increase in the film thickness. The analysis of the data suggests that the density of states at the Fermi level increase with the thickness of the film. In Fe-doped NiO film the density of states was found to increase with the increase in the substrate temperature. The optical measurements show that the maximum transmittance (≈77.13%) occurs for the film corresponding to the lowest volumetric concentration. On increasing the substrate temperature the transmittance also increases, thus displaying the decrease in the film thickness.

This paper reports morphological and structural details, optical and electrical properties of fluorine doped SnO₂ thin films prepared via spray pyrolysis route using SnCl₂·2H₂O as precursor and methanol as a solvent. The effect of fluorine concentration on the properties of the films is presented and discussed. X-ray diffraction pattern reveals the presence of SnO₂ films in the rutile structure with a preferential growth along the (200) direction. FTIR spectrum confirms the films to be made of SnO₂. EDS was used to estimate the fluorine concentration. SEM reveals the surface of FTO to be made of nanocrystalline particles. The grain size calculated using Debye–Scherrer formula is in the range of 8–34 nm. Film thickness measured using optical transmission method is in the range of 425–538 nm. The sheet resistance was found to decrease with increase in fluorine concentration, to a minimum of 6.35 Ω/□ for 7.5 mol% of NH₄F, and it showed an increase beyond this concentration. The 2.5 mol% of F doped films gave 95.20% transmission at 704 nm. The calculated reflectivity in the IR region is 93.57% for 7.5 mol% of F doping, and figure of merit for the same film is 0.025(Ω/□)^-1 at 550 nm. The total work was optimized by fixing the temperature at 550°C for the usage of Electrochromic Device preparations on FTO coated glass substrates.

Highly (002)-oriented nanocrystalline ZnO thin films were deposited on glass substrates at a substrate temperature of 500°C in air atmosphere by low-cost spray pyrolysis method. Room temperature photoluminescence spectral studies show the presence of near band edge emission and defect level emission (DLE) from the samples. The DLE wavelength is blueshifted about 22 nm and further emission intensity enhancement is observed in (002)-oriented sample as compared to that of wurtzite ZnO phase. The modifications in local defect levels and change in crystalline symmetry are attributed to the blue shift in the DLE region of c-axis oriented sample. The increased emission intensity of (002)-oriented samples is due to improvement in crystalline quality, preferential oriented growth and spherical morphology of nanocrystalline grains.

The 0.65Ba(Mg_1/3,Nb_2/3)O₃-0.35BaTiO₃ thin films was deposited on glass/aluminum substrates by using spray pyrolysis method. The effect of annealing temperature on perovskite phase and crystalline structure analysis of the BMN-BT films was performed on an X-ray diffraction (XRD). Surface morphology, roughness and particle size of the BMN-BT thin films was characterized with atomic force microscopy (AFM) and scanning electronic microscopy (SEM). Polarization hysteresis measurements was performed at different temperatures. From the P–E hysteresis loops one can observe the best temperature that led to improved properties of dielectric constant, polarization and piezoelectric coefficients were 600°C.

Nitrogen doped ZnO films with different N/Zn atomic ratio have been prepared by spray pyrolysis technique on glass substrate at 500°C. N/Zn atomic ratio has been selected 0, 0.5, 1, 2 and 3. The effect of N/Zn ratio on structural, optical and electrical properties has been investigated. Hall effect measurement studies show that the conductivity type of the films is affected by N/Zn ratio. The conductivity type of films changes from n for N/Zn = 0 and 0.5 to p for N/Zn = 1 and 2. Further increasing in N/Zn to 3 again led to n-type conductivity. p-type ZnO:N microrods film prepared with N/Zn = 1 has highest carrier concentration (1.36 × 10¹⁶ cm^-3) and lowest resistivity (628 Ω.cm). All films are polycrystalline with hexagonal wurtzite structure. (002) plane is preferential orientation for all films. Surface morphology changes from rods to grains by increasing in N/Zn ratio. Optical transmission of the films increases with increasing in N/Zn ratio. Photoluminescence spectra at room temperature show the ultraviolet emission and two visible emissions at 440 nm and 520 nm. X-ray photoelectron spectroscopy analysis confirms the incorporation of nitrogen in ZnO:N film with N/Zn = 1.

Indium sulfide (In₂S₃) thin films were deposited onto the glass substrates by a low cost simple spray pyrolysis technique at 300°C temperature. Aqueous solution of indium chloride and thiourea were used to deposit the binary In-S film. The deposited thin films were annealed at 400° and 500°C temperatures and characterized structurally, optically and electrically using EDX, X-ray diffraction, UV-visible spectroscopy and four probe van der Pauw methods. The optical constants such as refractive index and extinction coefficient are calculated from absorbance and transmittance data from 300 to 1100 nm wavelength. The optical transmittance increased after annealing at 400° and 500°C. The band gap energy was reduced from 2.90 to 2.50 eV after annealing the as deposited films. The electrical conductivity as well as the activation energy was increased after annealing the samples.

CuO thin films on porous silicon (PSi) substrates were prepared via spray pyrolysis method. The structural, optical and electrical properties of the films and the heterojunctions were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscope (AFM) and UV-Vis spectrophotometer. XRD results show that the film is polycrystalline and have a monoclinic crystal structure. Optical measurement indicates that the films had a low transmittance at the visible range and an optical bandgap of 2.2eV. High rectification was achieved with a maximum photoresponsivity of about 0.59A/W at 400nm, so that the CuO/PSi heterojunction may act as a good candidate for the fabrication of an efficient photodiode.

This paper deals with the investigation of annealing effects on the structural, morphological and optical properties of V₂O₅ nanorods (NRs) grown on the glass substrates by using chemical spray pyrolysis technique. The as-prepared samples were annealed at $500^{\circ }$ for 40, 60 and 120 min in a quartz tube furnace. The high resolution X-ray diffraction (XRD) analysis revealed V₂O₅ NRs with preferred orientation along (001) plane. The crystallite size of the V₂O₅ NRs was increased by increasing the annealing duration. The morphological observations using field emission scanning electron microscope (FESEM) displayed NRs structures whose diameter and length were found to increase with increase of the annealing duration. The transmission electron microscopy (TEM) analysis confirmed the orthorhombic structures of the NRs. The AFM measurements indicated an increase of the average surface roughness by increasing the annealing time. The Raman spectroscopy revealed V–O–V phonon mode in the NRs annealed for 120 min. The optical bandgap was found in the range 2.6–2.58eV and observed to decrease with various duration annealed.