Effect of high copper and oxygen concentrations on the optical and electrical properties of (CdTe)xCuyOz films

Thin films of (CdTe)_xCu_yO_z have been prepared by reactive RF cosputtering using high concentrations of copper and oxygen. The films were grown at 350 °C on glass and Si substrates. Under these conditions samples of amorphous nature were obtained with some clusters of Cu₂O for the larger concentrations of Cu and O used in this work. The largest band gap variation, from 3.5 to 1.4 eV, was obtained for the samples grown with an oxygen flow of 17 standard cubic centimeters per minute (sccm) in the growth chamber. The samples are highly resistive for most cases, but for high Cu concentrations resistivities of the order of 10³ Ω-cm were obtained in the case of films grown with a flow of 15 sccm of oxygen.     

Highly transparent and conductive Zn0.85Mg0.15O:Al thin films prepared by pulsed laser deposition

Zn_1−xMg_xO:Al thin films have been prepared on glass substrates by pulsed laser deposition (PLD). The effect of substrate temperature has been investigated from room temperature to 500 °C by analyzing the structural, optical and electrical properties. The best sample deposited at 250 °C shows the lowest room-temperature resistivity of 5.16×10⁻⁴ Ω cm, and optical transmittance higher than 80% in the visible region. It is observed that the optical band gap decreases from 3.92 to 3.68 eV when the substrate temperature increases from 100 to 500 °C. The probable mechanism is discussed.     

Heat treatment effects on the optical properties of Sol–gel Ta2O5 thin films

In this work optical properties of Ta₂O₅ thin films with respect to heat treatment temperature were investigated. Ta₂O₅ thin films were prepared by sol–gel process using dip-coated method with a constant speed of 107 mm/min. Optical properties have been calculated from optical transmission measurements as a function of heat treatment temperature. The refractive indices and absorption coefficients were affected by heat treatment. The refractive index at λ=550 nm increased from 1.84 to 2.04 and absorption coefficient increased from 241 to 5668 cm⁻¹ when heat treatment temperature increased from 100°C to 500°C. The thickness of the film decreased from 272 to 190 nm and their optical band gap decreased from 3.68±0.09 eV to 3.51±0.08 eV for the film heated from 100°C to 500°C.     

Optical and electrochemical characteristics of sol–gel deposited iron oxide films

Homogenous, crack free iron oxide films are prepared by the sol–gel spin coating technique from a solution of iron iso-propoxide and isopropanol. The films were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV-visible (UV–Vis) spectroscopy and cyclic voltammetry (CV). XRD of the films showed that they had an amorphous structure. The optical constants refractive index (n) and extinction coefficient (k) were measured by scanning spectrometer in the wavelength range of 390–990 nm. The n and k values were found n =2.3±0.01 and k =0.2±0.002 at 650 nm. The electrochemical behavior investigated in 0.5 M LiClO₄ propylene carbonate (PC) electrolyte-CV examinations showed good rechargeability of the Li⁺/e⁻ insertion extraction process beyond 300 cycles. Spectroelectrochemistry showed that these films exhibit weak cathodic coloration in the spectral range of 350–800 nm.     

Transformation of amorphous iron oxide thin films predeposited by spray pyrolysis into a single FeSe2-phase by selenisation

The present paper investigates a simple and non-toxic method to transform amorphous iron oxide pre-deposited by spray pyrolysis of FeCl₃·6H₂O (0.03 M)-based aqueous solution onto glass substrates heated at 350 °C into FeSe₂ thin films. The amorphous iron oxide films were heat treated under a selenium atmosphere (10⁻⁴ Pa) at different temperatures for 6 h. X-ray diffraction (XRD) was used to investigate the structure of the obtained films. Single FeSe₂-phase films having good crystallinity were obtained at a selenisation temperature of 550 °C. Optical analyses of the FeSe₂ films obtained at 550 °C enabled us to deduce a large absorption coefficient (, ). Surface scanning electron microscopy (SEM) observations show inhomogeneous films. Electrical conductivity of the as-prepared films was measured at high and low temperatures.     

Photoelectrochemical cells based on CdSe films brush plated on high-temperature substrates

CdSe thin films were brush plated on substrates maintained at temperatures in the range 30–90 °C from the precursors. The films exhibited hexagonal crystal structure. Optical band gap of 1.65 eV was obtained. XPS measurements indicated the formation of CdSe. Capacitance–voltage measurements indicated the films to exhibit n-type behaviour. A carrier density of 10¹⁷ cm⁻³ was obtained. Photoelectrochemical cells have exhibited higher efficiency compared to earlier reports on brush-plated films. Spectral response measurements indicated a peak quantum efficiency of 75% at 1.65 eV.     

Electrochromic properties of NiOxHy thin films

NiO_xH_y films were prepared by DC magnetron sputtering in H₂/O₂ atmosphere. NiO_xH_y coatings with transparency and high electrochromic efficiency were obtained by changing H₂ content. A 60 nm thick NiO_xH_y film with transmittance of 0.57 (as-deposited state), 0.78 (bleached state) and 0.24 (coloured state) at wavelength of 550 nm was deposited in an atmosphere of H₂(60%)+O₂(40%). Analysis of infrared spectra (60002400 cm⁻¹) showed that the absorption peaks for bleached and colored states are associated with free ‘OH’ and OH stretching vibrations, respectively. XPS Ni2p core level spectra of colored NiO_xH_y film exhibited a peak at 856.2±0.2 eV which is attributed to Ni³⁺. Ni2p core level spectra of the bleached and as-deposited films exhibited two peaks at 856.4±0.2 and 854.6±0.2 eV which are attributed to Ni³⁺ and Ni²⁺.     

Determination of optical properties of amorphous Ta2O5 films deposited by spin- and dip-coating methods

The optical properties of amorphous Ta₂O₅ films prepared by the sol-gel dip- and spin-coating deposition technique and dried at 60°C have been investigated. Refractive index, extinction coefficient and optical energy gap have been calculated from optical transmission measurements using the Swanepoel method. The films of similar thickness deposited by the two methods were compared. It is shown that the optical properties are dependent on the deposition methods. The energy band gap of the Ta₂O₅ films is 3.75 ± 0.12 eV and is independent of the coating methods.     

Preparation and characterization of thin films of electrodeposited CdTe semiconductors

Thin films of CdTe semiconductors were prepared by electrodeposition technique in aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry. The potential regions for the formation of the n-CdTe and p-CdTe films were determined. The structure, composition and morphology characteristics of as-deposited thin films of CdTe grown on SnO₂/glass and CdS/SnO₂/glass were investigated by XRD, EDAX and SEM techniques. The optical properties were measured to determine the absorption coefficient and band gap values. The as-deposited CdTe films grown on SnO₂/glass contained free Te while those grown on CdS/SnO₂/Glass did not contain this phase. The CdTe has the cubic structure with strong (111) orientation. The EDAX analysis showed a nearly stiochiometric Cd:Te ratio. The band gap has a value of 1.48 eV, which is in a good accordance with those reported in the literature. The effect of annealing at 350 and 400°C after CdCl₂ treatment on the structure and morphology was also examined.     

Optical and electrical properties of vanadium dioxide films prepared under optimized RF sputtering conditions

Vanadium dioxide films were prepared by DC and rf reactive magnetron sputtering of a 99.7% pure vanadium target in an Ar+O₂ plasma with a well-controlled oxygen partial pressure. The films were deposited onto normal glass substrates at 400°C. The films showed a metal–semiconductor transition at the temperature, τ_c=65–68°C. Optical and electrical properties of the films were investigated around the metal–semiconductor phase transition and found to be very sensitive to the oxygen flow rate. Sheet resistance of the films were recorded using a two-point probe over the temperature range 26τ100°C. It was observed that the sheet resistance can change by three orders of magnitude when heating the films from room temperature to temperatures above the transition. Transmittance of the films was obtained in the 300λ2500 nm wavelength range at two extreme temperatures (i.e. 26°C and 100°C). The luminous transmittance for the films was rather unaffected with heating, whereas near-infrared transmittance showed lower values. Optical constants, n and k were measured using ellipsometry. The semiconducting state optical constants were found to be 2.67 and 0.04 for n and k, respectively, while the metallic state values were 2.26 for refractive index and 0.3 for the extinction coefficient. The samples showed a slow deterioration when left in the laboratory for a period of one year.     

Chemically grown Bi2S3 nanorod films for hydrogen evolution

Bi₂S₃ nanorod films were grown on ITO-coated glass substrates through chemical bath deposition (CBD) and annealing in a sulfur atmosphere. The as-deposited films were amorphous/nanocrystalline, with a particle size of 20 nm and a direct optical band gap of 1.87 eV. Upon annealing at 350 °C, the films exhibited a nanorod morphology with a length of 300 nm. Further increasing the temperature from 400 to 450 °C resulted in an increased diameter of nanorods. The direct optical band gap decreased from 1.68 to 1.47 eV upon increasing the annealing temperature from 350 to 400 °C. Photoelectrochemical (PEC) measurements showed that the nanorod films grown on ITO-coated glass substrates exhibited significantly increased PEC activity owing to their nanorod structures. The Bi₂S₃ nanorod films formed at 400 °C exhibited a maximum photocurrent density of 6.1 mA/cm² at 1 V, which was 2.5 times higher than that of the as-deposited films. The enhancement in the photocurrent density could be due to the effective visible-light absorption of Bi₂S₃ nanorods as a result of the increased crystallinity and decreased band gap. This study demonstrates the synthesis route involving a simple and inexpensive CBD method of Bi₂S₃ nanorod films for the optimized PEC water-splitting applications.     

Electrochromic properties of Nb2O5 sol–gel coatings

Sol–gel niobium oxide coatings are promising electrochromic materials. The sols have been prepared by a sonocatalytic mixing of NbCl₅ powder, butanol and acetic acid. Thermal analysis (DTA/TG) coupled to mass spectrometry has been performed on Nb₂O₅ precipitates to quantitatively analyse the effluents. Transparent and defect-free single and multilayers coatings have been deposited on ITO-coated glass by a dip-coating process and then calcined between 400°C and 600°C. The coatings structure change from amorphous to crystalline (TT form) and the later ones are highly textured. The films present a reversible and fast insertion/extraction kinetics for Li⁺ ions. After insertion the amorphous coatings present a grey-brown color, while the crystalline ones are dark blue. The maximum charge density exchanged with a three-layer 200 nm thick coating sintered at 600°C was 16 mC/cm² with a corresponding spectral transmission change practically wavelength-independent varying from 80% to 20%. The coloring efficiency determined at λ=600 nm was 22 cm²/C.     

Photoluminescence studies of CdS thin films annealed in CdCl2 atmosphere

We have grown CdS films by the Close Spaced Vapor Transport technique under specific conditions: substrate temperature (T_s): 450 °C, source temperature (T_so): 725 °C, argon pressure in the chamber (P_Ar): 100, 200 and 500 mT, deposition time (t_d): 100 s. The films were studied by measuring the luminescence properties at different temperatures in the range 10–300 K. The room-temperature PL spectrum of the as-grown CdS films showed a very broad band centered at 2.26 eV and a shoulder in the low-energy side at 1.80 eV. After CdCl₂ thermal annealing at 300 K, the spectrum showed better PL characteristics: a strong band in the low-energy side at 1.67 eV and a band in the high-energy side at 2.47 eV. The analysis at lower temperatures showed that the high-energy band becomes most intense and shifts to higher energies reaching a value of 2.54 eV, very close to the energy band gap at 10 K. The low-energy band becomes broader and centered around 1.9 eV. Analysis of the PL intensity as a function of temperature in an Arrhenius representation, allows applying a theoretical model for the quenching of the PL intensity.     

Influence of pulse reversal on the PEC performance of pulse-plated CdSe films

This paper embodies the first report on the pulse reversal deposition of CdSe thin films. The as-deposited and heat-treated films were characterised by XRD, optical absorption spectroscopy and electrical properties. The polycrystalline deposits of CdSe obtained indicated a hexagonal structure after heat treatment at 550°C. From the optical absorption measurements the band gap was found to be 1.71 eV. At an illumination of 70 mW cm⁻² conversion efficiencies of 3.20% and 6.57% were obtained for the photoelectrodes without and with pulse reversal.     

Optical characterization of a-C:N thin films deposited by RF sputtering

In this work we present the main results of the optical properties study of amorphous carbon nitride (a-C:N) thin films prepared by reactive radio frequency (RF) sputtering. The a-C:N films were deposited, at room temperature, onto glass substrates, from a graphite target, in a pure nitrogen plasma. During the deposition, the pressure of nitrogen and the power density were maintained at 10⁻² mbar and 0.79 W cm⁻², respectively. Optical properties of these films were deduced from optical transmission spectra in the ultraviolet–visible–near infrared (UV–Vis–NIR) range. The refractive index follows well the Cauchy law with an extrapolated value of 1.68 in the far IR region. The optical band gap of the a-C:N films is about 1.2 eV. This value is relatively high in comparison with that of amorphous carbon films (0.8 eV) obtained in similar conditions. The incorporation of nitrogen in the amorphous carbon network leads to an increase of the optical band gap.     

Comparison of electrochromic amorphous and crystalline tungsten oxide films

A detailed systematic study of the tungsten oxide thin films has been carried out using WO₃ films after they were annealed at progressively increasing temperatures ranging from 350°C to 450°C in oxygen environments. The structural properties of the films were characterized using X-ray diffraction and Raman spectroscopy. The amorphous WO₃ films remain as an amorphous phase up to 385°C and begin to crystallize at 390°C and then are completely crystallized at 450°C. Absorption peaks of the films are found to shift to a higher energy side with increasing annealing temperature up to 385°C and then shift abruptly to a lower energy as the films begin to crystallize at 390°C. Deconvolution of the absorption spectra shows that there are two different polaron transitions in the amorphous WO₃ films.     

Development of CZTS thin films solar cells by pulsed laser deposition: Influence of pulse repetition rate

High-quality Cu₂ZnSnS₄ (CZTS) thin films were synthesized by pulsed laser deposition as a function of pulse repetition rate onto the SLG substrates. Influence of pulse repetition rate onto the structural, morphological, compositional and optical properties have been investigated for as-deposited and annealed thin films. X-ray diffraction study shows transformation of amorphous to crystalline phase after tuning pulse repetition rate and annealing of samples. FESEM images of thin films show increase in grain size upon annealing. Films are nearly stoichiometric deposited at 10 Hz repetition rate has been confirmed with the help of EDAX and XPS analysis. The direct band gap energy of the deposited CZTS thin films are in the solar energy range. The performance of solar cell based on CZTS absorber layer has been tested and the efficiency is about 2%.     

Optical properties of sol–gel deposited Al2O3 films

Highly transparent, uniform and corrosion resistant Al₂O₃ films were prepared on stainless-steel and quartz substrates by the sol–gel process from stable coating solutions using aluminum-sec-butoxide, Al(OBu^s)₃ as precursor, acetylacetone, AcAcH as chelating agent and nitric acid, HNO₃, as catalyzer. Films up to 1000 nm thick were prepared by multiple spin coating deposition, and were characterized by X-ray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), optical spectroscopy and micro Vickers hardness test. XRD of the film heat treated at 400°C showed that they had an amorphous structure. XPS confirmed that they were stoichiometric Al₂O₃. The refractive index (n) and extinction coefficient (k) were found to be n=1.56±0.01 and k=0.003±0.0002 at 600 nm, respectively. The surface microhardness and corrosion resistance investigations showed that Al₂O₃ films improved the surface properties of stainless-steel substrates.     

Structure–property relationships in electrochromic WO3 films deposited by reactive sputtering

WO_x electrochromic (EC) films deposited by DC magnetron sputtering technique were investigated by XRD and STM measurements. The reversible microstructure changes of the WO_x film between the bleached and colored EC states were revealed. The study indicates that the amorphous as-deposited WO_x film (a-WO_x) is of amorphous microstructure both in bleached and colored states; however, the crystalline WO_x (c-WO_x) is stoichiometric triclinic lattice WO₃ in bleached state (the lattice parameters: a=7.2944 Å, b=7.4855 Å, c=3.7958 Å, α=89.38°, β=90.42°, γ=90.80°), and changes into nonstoichiometric tetragonal lattice WO_2.9 in colored state (a=b=5.336 Å, c=3.788 Å, α=β=γ=90°). The surface morphologies of the colored WO_x films are very different from those of the bleached WO_x films.     

Effect of different annealing conditions on the properties of chemically deposited ZnS thin films on ITO coated glass substrates

The effects of different annealing conditions such as atmospheres, temperatures and times on the structural, morphological and optical properties of ZnS thin films prepared on ITO coated glass substrates by chemical bath deposition were studied. Aqueous solutions of zinc acetate and thiourea were used as precursors along with stable complexing agents, such as Na₂EDTA and Na₃-citrate, in an alkaline medium. X-ray diffraction patterns showed that the as-deposited and as-annealed ZnS films had an amorphous structure or poor crystallinity below the optimized annealing conditions of 500 °C and 60 min with the exception of the films annealed in N₂+H₂S annealing atmosphere. The ZnS thin films annealed in N₂+H₂S atmosphere for 1 h at 500 °C showed three sharp peaks for the (1 1 1), (2 2 0) and (1 1 3) planes of polycrystalline cubic ZnS without any unwanted secondary ZnO phases. X-ray photoelectron spectroscopy revealed Zn-OH and Zn-S bonding in the as-deposited ZnS thin film. However, the ZnS thin films annealed at 500 °C showed Zn-S bonding regardless of the annealing atmosphere. The sharp absorption edge and band gap energy of the as-deposited and as-annealed ZnS thin films varied from 295 to 310 nm and 3.5 to 3.89 eV, respectively.