A study of the physical properties of sprayed CdS thin films

CdS films have been prepared by spray pyrolysis and characterized by several methods. The spray solution is made of cadmium chloride or cadmium acetate and thiourea. Optical and compositional properties and structure of the CdS films have been investigated. An analysis of the film's structure, preferred cyrstallographic orientation and presence of impurity phases have been obtained using X-ray diffraction technique as well as infrared spectroscopy. The visible absorption measurements have been carried out for the study of the impurity phases. Quantitative Auger analysis shows the composition of the spray solution and a post-spray heat treatment have also been investigated.     

Controlled growth of Cu2O thin films by electrodeposition approach

Thin films of Cu₂O comprised of wavelike surface characteristic of compact nanoparticles were synthesized using a facile and cost-effective electrodeposition approach. The distinct surface morphologies with well-aligned crystal orientation were obtained through the controlled electrodeposition parameters. The high resolution AFM combined with the peak force AFM images mapped the nanomechanical and chemical properties of the Cu₂O nanostructured films. The structural, optical, and compositional analyses of the as-deposited thin films show bulk Cu₂O material. The electrodeposition approach could proceed non-intermittently under ambient conditions, and provides a facile and economic way of depositing thin films of Cu₂O with wavelike characteristics. The photoluminescence lifetime was found be very short in the range of 0.8–1.3 ns for Cu₂O films. The Mott-Schottky measurement exhibited p-type conductivity and carrier density was found to be ~2×10¹⁸. The observed photoluminescence lifetimes, and carrier densities could help implementing the Cu₂O films as an efficient hole-conducting, and photoelectrode materials in solar cells and water splitting devices.     

Analytical Expression of Relaxation Luminescence in ZnS：Er^3＋ Thin Films

The relaxation luminescence of ZnS:Er^3 thin films is studied with luminescence dynamics model.The excitation and emission processes of Er^3 in ZnS host are described through the resonant energy transfer method.Taking the energy storing effect of the traps into account,an expression is obtained by using the convolution formula,which may describe luminescence decay process containing the multiple relaxation luminescence peaks.The experimental results confirm that the relaxation characteristics of the electroluminescence are related to the carriers captured by the bulk traps.     

Synthesis and characterization of castor oil and ricinoleic acid capped CdS nanoparticles using single source precursors

We report the synthesis of castor oil and ricinoleic acid capped CdS nanoparticles by the thermolysis of piperidine (1) and tetrahydroquinoline (2) dithiocarbamate complexes of cadmium(II) at temperatures varying from 190 °C to 300 °C. Reaction parameters such as time and temperature were varied to study their effect on the properties and morphology. The optical properties of CdS were typical of particles that displayed quantum confinement effects. X-ray diffraction studies revealed the existence of both cubic and hexagonal phases depending on the reaction conditions. Ricinoleic acid capped CdS gave cubic phase particles whereas castor oil capped CdS gave both cubic and hexagonal phases dependent on the reaction temperature and the type of complex used. The morphology of the particles varied from oval-short rods to spherical shaped particles with sizes ranging from 10 to 22 nm. Rhodamine B (RhB) dye photodegradation studies of a representative CdS nanoparticles’ sample have been carried out in the presence of halogen light and studied using UV–visible spectroscopy.     

Improved barrier and mechanical properties of Al2O3/acrylic laminates using rugged fluorocarbon layers for flexible encapsulation

Thin film encapsulation (TFE) with high barrier performance and mechanical reliability is essential and challenging for flexible organic light-emitting diodes (OLEDs). In this work, SF₆ plasma treatments were introduced for surface modifications of acrylic in Al₂O₃/acrylic laminates fabricated by atomic layer deposition (ALD) and ink-jet printing (IJP). It was found that micro-/nano-structures and surface fluoridation appeared on the surface of acrylic, and could be modulated by the discharge power and irradiation of plasma treatment. The water vapor transmission rates (WVTR) of Al₂O₃/acrylic multi-layers decreased evidently because of reducing surface polarity and strong cross-link of acrylic after plasma treatments. Furthermore, the rugged surface and relieved residual stress resulted from etching and heating of acrylic could enhance the mechanical property remarkably. The plasma treated Al₂O₃/acrylic multi-layers with only 3 dyads exhibited a low WVTR value of 1.02 × 10⁻⁶ g/m²/day and more stable mechanical property under 200 iterations blending test by comparative measurements, proving that the introduction of SF₆ plasma surface modifications could improve simultaneously the barrier performance and mechanical reliability prominently of the inorganic/organic multi-layers with no need of extra neutral axis design.     

Effect of sputtering power on optical properties of prepared TiO2 thin films by thermal oxidation of sputtered Ti layers

In this research, TiO₂ thin films prepared via thermal oxidation of Ti layers were deposited by RF-magnetron sputtering method at three different sputtering powers. The effects of sputtering power on structure, surface and optical properties of TiO₂ thin films grown on glass substrate were studied by X-ray diffraction (XRD), atomic force microscopic (AFM) and UV–visible spectrophotometer. The results reveal that, the structure of layers is changed from amorphous to crystalline at anatase phase by thermal oxidation of deposited Ti layers and rutile phase is formed when sputtering power is increased. The optical parameters: absorption coefficient, dielectric constants, extinction coefficient, refractive index, optical conductivity and dissipation factor are decreased with increase in sputtering power, but increase in optical band gap is observed. The roughness of thin films surface is affected by changes in sputtering power which is obtained by AFM images.     

On the temperature dependent electrical resistivity of CNT layers in view of Variable Range Hopping models

Thin films of randomly dispersed carbon nanotubes make highly promising material for transparent electrode applications. Knowing and understanding the nature of the films conductivity is crucial for improvement of their electrical properties. In the paper we present our investigation of electrical conductivity of single wall and multiwalled carbon nanotube (SWCNT and MWCNT) thin films deposited on a polymeric substrate by Langmuir-Schaefer technique. The conductivity of the films is consistent with the Variable Range Hopping (VRH) model. Moreover, remarkable differences in SWCNT and MWCNT films conductivity are observed. A significant impact of the thin film annealing and its temperature history on the conductivity properties is shown. The study of the carbon nanotubes layers transferred on polymeric substrate was undertaken in view of the films possible applications in flexible transparent electrodes. The VRH conductivity in carbon nanotube Langmuir-Schaefer layer is reported for the first time.     

Studies in CuInS2 based solar cells,including ZnS and In2S3 buffer layers

The influence of the growth conditions on the surface chemistry and on the homogeneity of the chemical composition of CuInS₂ (CIS) thin films, prepared by sequential evaporation of metallic precursors in presence of elemental sulfur in a two-stage process, was studied by X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). It was found that the growth temperature affects the phase in which this compound grows. The samples deposited at temperatures around 500 °C (2nd stage) contain mainly the CuInS₂ phase; however, secondary phases like In₂S₃, Cu₂S were additionally identified at the surface and in the bulk of CuInS₂ samples deposited at temperatures greater than 550 °C. Also, the elemental composition of the layers constituting the Glass/Mo/CuInS₂/buffer/ZnO structure was studied through Auger electron spectroscopy (AES) depth profile measurements. AES measurements carried out across the Glass/Mo/CuInS₂/buffer/ZnO heterojunction gave evidence of Cu diffusion from the CuInS₂ layer towards the rest of the layers constituting the device, and of the formation of a MoS₂ layer in the Mo/CuInS₂ interface. The performance of CuInS₂-based solar cells fabricated using CBD (chemical bath deposition) deposited ZnS as buffer layer was compared to that of cells fabricated using CBD deposited In₂S₃ as buffer.     

Improved performance in ZnO/CdS/CuGaSe2 thin‐film solar cells

We report the growth and characterization of improved efficiency wide‐bandgap ZnO/CdS/CuGaSe₂ thin‐film solar cells. The CuGaSe₂ absorber thickness was intentionally decreased to better match depletion widths indicated by drive‐level capacitance profiling data. A total‐area efficiency of 9·5% was achieved with a fill factor of 70·8% and a V_oc of 910 mV. Published in 2003 by John Wiley & Sons, Ltd.     

Resistive switching behavior of Sb2S3 thin film prepared by chemical bath deposition

The chalcogenides are the excellent memristor materials. Here we report the resistive switching properties of an amorphous Sb₂S₃ thin film. Sb₂S₃ films were deposited on FTO glass using a low-temperature (10 °C) chemical bath deposition technique. SEM and XRD results indicate that the as-grown Sb₂S₃ film is dense and amorphous with uniform thickness and smooth surface. The Ag/Sb₂S₃/FTO memristor shows typical bipolar switching behavior with low operating voltage, high resistance ratio, long retention time, and good endurance. The electrical tests demonstrate that the switching behavior of the amorphous Sb₂S₃ film is based on electrochemical metallization mechanisms.     

ILGAR In2S3 buffer layers for Cd‐free Cu(In,Ga)(S,Se)2 solar cells with certified efficiencies above 16%

In₂S₃ buffer layers have been prepared using the spray ion layer gas reaction deposition technique for chalcopyrite‐based thin‐film solar cells. These buffers deposited on commercially available Cu(In,Ga)(S,Se)₂ absorbers have resulted in solar cells with certified record efficiencies of 16.1%, clearly higher than the corresponding CdS‐buffered references. The deposition process has been optimized, and the resulting cells have been studied using current–voltage and quantum efficiency analysis and compared with previous record cells, cells with a thermally evaporated In₂S₃ buffer layer and CdS references. Copyright © 2012 John Wiley & Sons, Ltd.     

Formation of Highly Crystallized β‐PbO Thin Films by Cathodic Electrodeposition of Pb and Its Rapid Oxidation in Air

The process of electrodeposition of β‐PbO thin films from aqueous solutions of Pb^II salts has been studied in detail. Contrary to the mechanism assumed in previous studies, thin films of crystalline β‐PbO are obtained after cathodic electrolysis in aqueous solutions of various soluble salts of Pb^II (Pb(NO₃)₂, Pb(ClO₄)₂, and Pb(CH₃COO)₂), and in both the presence and the absence of O₂, thus indicating no contribution of OH^– generation by electroreduction of NO₃^– and/or O₂ to the formation of β‐PbO. A gradual color change is noted: a freshly electrodeposited gray film turns yellow as it dries in air. Drying of the films under controlled atmosphere (Ar or O₂), combined with scanning electron microscopy (SEM) observation and X‐ray diffraction (XRD) measurement, has revealed that freshly deposited films are of metallic Pb, which are oxidized and converted into β‐PbO. Such a reaction is operative only when a freshly electrodeposited activated wet Pb film is in contact with gaseous O₂. Despite the rapid conversion of a solid material, the resultant β‐PbO thin films are highly crystallized and possess highly ordered internal nanostructure. Elongated nanoparticles (30 nm × 100 nm) are assembled in a regular alignment to compose a large platelet (greater than 10 μm in size) with single‐crystalline character, as revealed by transmission electron microscopy (TEM) observation and selected‐area electron diffraction (SAED) measurement.     

Composition and electrical characteristics of Al2O3-HfO2-HfTiO nanolaminates on Si

A dielectric constant of 27 was demonstrated in the as deposited state of a 5 nm thick, seven layer nanolaminate stack comprising Al₂O₃, HfO₂ and HfTiO. It reduces to an effective dielectric constant (k_eff) of ∼14 due to a ∼0.8 nm interfacial layer. This results in a quantum mechanical effective oxide thickness (EOT) of ∼1.15 nm. After annealing at 950 °C in an oxygen atmosphere k_eff reduces to ∼10 and EOT increases to 1.91 nm. A small leakage current density of about 8 × 10⁻⁷ and 1 × 10⁻⁴ A/cm², respectively at electric field 2 and 5 MV/cm and a breakdown electric field of about 11.5 MV/cm was achieved after annealing at 950 °C.     

Realizing High Thermoelectric Performance in Earth-Abundant Bi2S3 Bulk Materials via Halogen Acid Modulation

Bi₂S₃-based thermoelectric materials without toxic and expensive elements have a high Seebeck coefficient and intrinsic low thermal conductivity. However, Bi₂S₃ suffers from low electrical conductivity, which makes it a less-than-perfect thermoelectric material. In this work, halogen elements F, Cl, and Br from halogen acid are successfully introduced into the Bi₂S₃ lattice using a hydrothermal procedure to efficiently improve the carrier concentration. Compared with the pure sample, the electron concentration of the Bi₂S₃ sample treated with HCl is increased by two orders of magnitude. An optimal power factor of 470 µW m⁻¹ K⁻² for the Bi₂S_2.96Cl_0.04 sample at 673 K is obtained. Density functional theory calculations reveal that an effective delocalized electron conductive network forms after Cl doping, which raises the Fermi level into the conduction bands, thus generating more free electrons and improving the conductivity of the Bi₂S₃-based materials. Ultimately, an excellent ZT of ≈0.8 is achieved at 673 K for the Bi₂S_2.96Cl_0.04 sample, which is one of the highest values reported for a state-of-the-art Bi₂S₃ system. The energy conversion efficiency of the module reaches 2.3% at 673 K with a temperature difference of 373 K. This study offers a new method for enhancing the thermoelectric properties of Bi₂S₃ by adding halogen acid in the hydrothermal process for powder synthesis.     

Effects of annealing on nanocrystalline Bi2S3 thin films prepared by chemical bath deposition

Nanocrystalline Bi₂S₃ thin films are deposited on tin chloride treated glass substrate from the solution containing bismuth nitrate, triethanolamine (TEA) and thioacetamide (TAM) at a bath temperature 318 K. The prepared films are subsequently annealed at different temperatures for studying the effect of thermal treatment on the structural, surface morphology, optical and electrical properties of the films. The X-ray diffraction studies affirmed that the deposited films are orthorhombic structures with average crystallites size of 14 nm to 28 nm. The scanning electron microscopy (SEM) images revealed that the films comprise of grains of spherical shape of unequal size. It is also observed that the small particles aggregate together to form a larger cluster. The average grain sizes determined from the TEM images are smaller than the crystallites size obtained from the XRD studies. The optical band gap of the films has been estimated to be 2.24–2.05 eV for the as-prepared and annealed films, respectively. The electrical conductivity of the as prepared Bi₂S₃ films at room temperature is found to be in the order of 10⁻³ Ω⁻¹ m⁻¹.     

Role of ultrathin Al2O3 layer in organic/inorganic hybrid gate dielectrics for flexibility improvement of InGaZnO thin film transistors

We investigated flexible amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) on a polyimide (PI) substrate by using organic/inorganic hybrid gate dielectrics of poly-4vinyl phenol (PVP) and ultrathin Al₂O₃. IGZO TFTs were fabricated with hybrid PVP/Al₂O₃ gate dielectrics having Al₂O₃ layers of different nanoscale thicknesses, which were deposited by atomic layer deposition (ALD). The electrical characteristics of the TFTs with the organic/inorganic hybrid gate dielectrics were measured after cyclic bending up to 1,00,000 cycles at the bending radius of 10 mm. The ultrathin Al₂O₃ layer in the hybrid gate dielectrics improved the mechanical flexibility and protected the organic gate dielectric against damage during the sputter deposition of the IGZO layer. Finite elements method (FEM) simulations along with the structural characterization of the cyclically bent device showed the importance of optimizing the thickness of the Al₂O₃ layer in the hybrid gate dielectrics to obtain mechanically stable and flexible a-IGZO TFTs.     

Effect of aqueous electrolyte on pseudocapacitive behavior of chemically synthesized La2S3 electrode

Lanthanum sulfide electrode (La₂S₃) is prepared by a low cost, simple and room temperature chemical route for energy storage. The surface morphology of La₂S₃ film is revealed through field emission scanning electron microscopy. For the energy storage purpose, the pseudocapacitive behavior of La₂S₃ electrode is studied in 1 M aqueous Na₂SO₄ and 1 M KOH electrolytes. La₂S₃ electrode achieved maximum specific capacitance of 358 F g⁻¹ at 5 mV s⁻¹ scan rate with 78% electrochemical cyclic stability over 1000 cycles in 1 M Na₂SO₄ electrolyte. The galvanostatic charge–discharge study demonstrated the energy density of 35 Wh kg⁻¹ at power density of 1.26 kW kg⁻¹. The electrochemical impedance study showed field assisted charge transfer process with relaxation time of 32 ms in 1 M Na₂SO₄ electrolyte ensuring fast redox reaction.     

The preparation of (Al2O3)x(SiO2)y thin films using [al(OSiEt3)3]2 as a single-source precursor

Amorphous (Al₂O₃)_x(SiO₂)_y thin films have been grown by atmospheric pressure metal-organic chemical vapour deposition using the single-source precursor [Al(OSiEt₃)₃]₂. Characterisation by X-ray photoelectron spectroscopy indicated that the films consisted of a mixture of Al₂O₃, SiO₂ and an aluminosilicate. The relative amount of each species was dependent on the deposition temperature and the carrier gas composition. Use of NH₃ as the carrier gas resulted in the increased volatility of the precursor by the in situ formation of the low-melting Lewis acid–base adduct Al(OSiEt₃)₃(NH₃); however, no nitrogen incorporation was observed in these deposited films.     

Antimony sulfide (Sb2S3) thin films by pulse electrodeposition: Effect of thermal treatment on structural,optical and electrical properties

Antimony sulfide films have been deposited by pulse electrodeposition on Fluorine doped SnO₂ coated glass substrates from aqueous solutions containing SbCl₃ and Na₂S₂O₃. The crystalline structure of the films was characterized by X-ray diffraction, Raman spectroscopy and TEM analysis. The deposited films were amorphous and upon annealing in nitrogen/sulfur atmosphere at 250 °C for 30 min, the films started to become crystalline with X-ray diffraction pattern matching that of stibnite, Sb₂S₃, (JCPDS 6-0474). AFM images revealed that Sb₂S₃ films have uniformly distributed grains on the surface and the grain agglomeration occurs with annealing. The optical band gap calculated from the transmittance and the reflectance studies were 2.2 and 1.65 eV for as deposited and 300 °C annealed films, respectively. The annealed films were photosensitive and exhibited photo-to-dark current ratio of two orders of magnitude at 1 kW/m² tungsten halogen radiation.     

Synthesis and characterization of cerium oxide nano-particles in chloride bath: Effect of the H2O2 concentration and bath temperature on morphology

Cerium oxide has been used extensively for various applications over the past two decades. The use of cerium oxide nanoparticles is beneficial in present applications and can open new avenues for future uses. In this paper, some samples of cerium hydroxide/oxide have been synthesized by cathodic deposition on steel electrode in chloride bath in two electrode systems by the galvanostatic mode. The effects of bath temperature and H₂O₂ concentration on particle size and morphology were studied. The effect of calcination temperature on the crystallite growth of cerium oxide nano-powders was investigated by X-ray diffraction. The results were characterized by the differential scanning calorimetry (DSC), thermogramimetric analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The SEM results show that the samples synthesized at low bath temperature have an average size of 40 nm. In the presence of H₂O₂, the cerium oxide films are adherent and smooth. They present very thin cracks whereas with the increase of H₂O₂ concentration the size and number of cracks are reduced. The results show that the as-prepared nanoparticles are essentially amorphous and after heat treatment, the obtained oxide product is well crystallized.