Fabrication of SmBa2Cu3O7 Films on CeO2 Buffered Sapphire

SmBa₂Cu₃O_7−δ (SmBCO) thin films and CeO₂ buffer layers were deposited on γ-cut sapphire by pulsed laser deposition (PLD) and characterized with X-ray diffraction (XRD) and atomic force microscope (AFM). The θ–2θ XRD scans of the SmBCO/CeO₂/sapphire structures revealed that the CeO₂ and SmBCO films were grown with c-axis perpendicular to the substrate. In Φ-scan XRD patterns, four (103) peaks of the SmBCO film were observed and the peak positions were shifted by 45° from (202) peaks of the CeO₂ films. From the peak shifts we could conclude that the [110]_SmBCO crystal axis is parallel to the [100]_CeO2 crystal axis. Moreover, pole figure also confirmed that SmBCO films were grown on the substrates epitaxially along in-plane direction. The SmBCO films show very flat surfaces with root mean square (RMS) about 5 nm. In agreement with this crystalline perfection, SmBCO thin films present excellent superconducting properties: T _c0 > 90 K, transition width 0.4 K, and J _c(77 K) > 2 MA/cm².     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Optical properties of tin diselenide films

SnSe₂ films were deposited on substrates at 300 K by a conventional thermal evaporation technique. The as-deposited films were amorphous and transformed to the crystalline phase on post-deposition annealing above 573 K in an inert atmosphere. The optical properties of the films were investigated, using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the wavelength range 400–2000 nm. The refractive index data fit a single oscillator model with a dispersion parameter 5.149×10^–14 and 5.773×10^–14 eVm² for the amorphous and crystalline films, respectively. The high-frequency dielectric constant of the amorphous films decreased from 9.871 to 7.475 for the crystalline films. The analysis of the spectral behaviour of the absorption coefficient in the intrinsic absorption region revealed an indirect forbidden and a direct allowed transition with energy gaps 0.99 and 2.05 eV for the amorphous films and 0.96 and 2.02 eV for the crystalline films, respectively.     

Studies on tin oxide films prepared by electron beam evaporation and spray pyrolysis methods

Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2.65 × 10⁻² ω-cm to 3.57 × 10⁻³ ω-cm in the temperature range 150–200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1.2 × 10⁻¹ to 1.69 × 10⁻² ω-cm in the temperature range 250–370° C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7.74 × 10⁻⁴ ω-cm, which was deposited at 350°C with 0.26 g of SbCl₃ and 4 g of SnCl₄ (SbCl₃/SnCl₄ = 0.065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300– 370°C were poly crystalline. The morphology of tin oxide films was studied using SEM.     

Growth and optical properties of ZnIn2Se4 films

Thin films of ZnIn₂Se₄ were deposited on quartz substrates at 297 K by the conventional thermal evaporation technique. The as-deposited films were amorphous. On annealing at 623 K under vacuum for 3 h, the films crystallized with a preferred (1 1 2) orientation corresponding to the chalcopyrite-type structure. Films deposited on a quartz substrate heated to 573 K were also crystalline. The optical constants were computed from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. The analysis of the data gave a direct gap of 2.2 and 2.06 eV for the amorphous and crystallized films, respectively. The dispersion curve exhibited a peak above the absorption edge. An indirect gap of 1.8 eV for the crystallized films and a direct forbidden gap of 1.75 eV for the amorphous films were also deduced. A direct allowed transition with a gap of 2.065 eV and an indirect transition with a gap of 1.69 eV were deduced for the crystalline films deposited on the heated substrate.     

Preparation and thermoelectric properties of BP films on SOI and sapphire substrates

The chemical vapor deposited (CVD) BP films on Si(100) (190 nm)/SiO _x (370 nm)/Si(100) (625 μm) (SOI) and sapphire (R-plane) (600 μm) substrates were prepared by the thermal decomposition of the B₂H₆–PH₃–H₂ system in the temperature range of 800–1050 °C for the deposition time of 1.5 h. The BP films were epitaxially grown on the SOI substrate, but a two-step growth method, i.e., a buffer layer at lower temperature and sequent CVD process at 1000 °C for 1.5 h was effective for obtaining a smooth film on the sapphire substrate. The electrical conduction types and electrical properties of these films depended on the growth temperature, gases flow rates and substrates. The thermal conductivity of the film could be replaced by the substrate, so that the calculated thermoelectric figure-of-merit (Z) for the BP films on the SOI substrate was 10⁻⁴–10⁻³/K at 700–1000 K. Those on the sapphire substrate were 10⁻⁶–10⁻⁵/K for the direct growth and 10⁻⁵–10⁻⁴/K for the two-step growth at 700–900 K, indicating that the film on a sapphire by two-step growth would reduce the defect concentrations and promote the electrical conductivity.     

Eu doped silica xerogel luminescent layer having antireflection and spectrum modifying properties suitable for solar cell applications

A spectrum modifying glassy luminescent layer with antireflection properties has been prepared with Eu³⁺ ions embedded in silica gel for solar cell applications. Preparation of such matrix by sol-gel process and change in luminescence properties in transforming from amorphous to crystalline phase are described. Luminescent Eu³⁺ species in amorphous silica matrix show intense red emission at 614 nm by absorbing UV/blue light. Amorphous environment with reduced symmetry for Eu³⁺ ions results in an unprecedented short decay time of 145 μs for ⁵D₀-⁷F₂ electric dipole transition. In the crystalline monoclinic phase of Eu₂O₃ nanoparticles, concentration quenching of Eu³⁺ species reduces luminescence output.     

Optical and structural characteristics of Y<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films synthesized from yttrium acetylacetonate

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)₃). The decomposition of Y(acac)₃ was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)₃. The rest of the complex is then dissociated or degraded partially until Y₂O₃ is obtained in the final step with the presence of carbon related residues. Then the Y(acac)₃ was used to synthesize Y₂O₃ thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase.     

Nanoindentation of LaCrO3 thin films

Nanoindentation of LaCrO₃ thin films deposited by radio-frequency magnetron sputtering onto stainless steel substrates was performed using an XP Nanoindenter. The “as-deposited” film was amorphous but transformed to an orthorhombic LaCrO₃ perovskite structure after annealing at 1073 K for 1 h. The film thickness in the “as-deposited” state was 800 nm. Single loading/unloadings were performed in the displacement control mode on the crystalline film using different maximum displacements (50, 200, 400, and 800 nm). Therefore, the integral response of the film−substrate system was probed at different distances from the substrate. Nanoindentation experiments on LaCrO₃ perovskite films revealed sharp “pop-in” events at certain loads. Such “pop-ins”, are most likely caused by the orthorhombic-to-rhombohedral phase transition which is known to occur in a LaCrO₃ perovskite structure under pressure. However, such discontinuities have never been observed upon indentation of the amorphous “as-deposited” La-Cr-O thin films, and the pressure found to be typical of this transition in the LaCrO₃ thin films is higher than previous bulk LaCrO₃ sample studies. Mechanical characteristics of the films, such as hardness and Young’s modulus, were also measured.     

Long afterglow phosphorescent characteristics of BaAl2O4:Eu,Dy films

BaAl₂O₄:Eu,Dy (BAO) films have been fabricated on Si substrate by laser ablation, and their fundamental optical property and afterglow characteristics are discussed in comparison with the SrAl₂O₄:Eu,Dy (SAO) films. The intense green emission near 500 nm that originates from 5d to 4f transition in Eu²⁺ ions was clearly observed from the BAO films. This photoluminescence peak was at a shorter wavelength than that of the SAO films (λ = 520 nm). The afterglow intensity from the BAO films disappeared within a few minutes whereas that of the SAO films lasts over 20 min. The hole-trap depth (E_t) created by Dy as the auxiliary activators, which strongly affects the afterglow characteristics, was estimated on the basis of the thermally stimulated luminescence (TSL) result. The TSL glow curve for BAO films showed two broad peaks at 320 K and 450 K. The calculated E_t for each peak was 0.2 eV (for the 320 K peak) and 1.2 eV (for the 450 K peak). On the other hand, E_t = 0.5 eV was obtained from the SAO films. The hole-trap depths of the BAO film are either too shallow or too deep to affect the afterglow characteristics at room temperature.     

Photoluminescence and magnetic properties of β-Ni(OH)2 nanoplates and NiO nanostructures

Single-crystalline β-nickel hydroxide (β-Ni(OH)₂) nanoplates of hexagonal structure have been synthesized through hydrothermal process. The β-Ni(OH)₂ nanoplates possess well-defined hexagonal shapes with landscape dimension of 45–140 nm and thickness of 20–50 nm. Post-thermal decomposition of the β-Ni(OH)₂ nanoplates led to the formation of single-crystalline NiO nanostructures with landscape dimension of 25–120 nm including nanorolls, nanotroughs and nanoplates. The sizes of the central hole in NiO nanorolls and the low-lying ground in NiO nanotroughs are in the range of 10–24 nm. Two photoluminescence emission peaks appear at 390.5 nm and 467 nm in the photoluminescence spectrum of NiO nanostructures and were assigned to the ¹T_{1 g} (G) → ³A_{2 g} and ¹T_{2 g} (D) → ³A_{2 g} transitions of Ni²⁺ in oxygen octahedral sites, respectively. Temperature-dependent magnetic measurement results show that an antiferromagnetic-paramagnetic transition occur at 26.3 K in β-Ni(OH)₂ nanoplates.     

Properties of GaAs films deposited by pulse periodic technique

GaAs is a III-V compound possessing high mobility and a direct band gap of 1.43 eV , making it a very suitable candidate for photovoltaic applications. Thin GaAs films were prepared at room temperature by plating an aqueous solution containing GaCl₃ and As₂O₃ at a pH of 2. The current density was kept as 50 mA cm⁻² and the duty cycle was varied in the range 10–50%. The films were deposited on titanium and tin oxide coated glass substrates. Films exhibited polycrystalline nature with peaks corresponding to single phase GaAs. Optical absorption measurements indicated a direct band gap of 1.40 eV. The surface roughness of the films varied from 3 nm to 6 nm as the duty cycle increased. Raman spectra indicated both the LO and TO phonons for the films deposited at duty cycles above 25%. Photoelectrochemical studies indicated that the current and voltage output are higher than earlier reports on thin film electrodes.     

Structural and optical properties of amorphous and crystalline antimony sulfide thin-films

Smooth and compact thin films of amorphous and crystalline antimony sulfide (Sb₂S₃) were prepared by radio frequency sputtering of an Sb₂S₃ target. As-deposited films are amorphous. Polycrystalline antimony sulfide films composed of ∼ 500 nm grains are obtained by annealing the as-deposited films at 400 °C in sulfur vapors. Both amorphous and crystalline antimony sulfide have strong absorption coefficients of 1.8 × 10⁵ cm^− 1 at 450 nm and 7.5 × 10⁴ cm^− 1 at 550 nm, and have direct bandgaps with band energies of 2.24 eV and 1.73 eV, respectively. These results suggest the potential use of both amorphous and crystalline antimony sulfide films in various solid state devices.     

Influence of deposition parameters on preferred orientation of RF magnetron sputtered BST thin films

Ba_0.65Sr_0.35TiO₃ (BST) thin films have been deposited by radio frequency magnetron sputtering. The effects of the deposition parameters on the crystallization and microstructure of BST thin films were investigated by X-ray diffraction and field emission scanning electron microscopy, respectively. The crystallization behavior of these films was apparently affected by the substrate temperature, annealing temperature and sputtering pressure. The as-deposited thin films at room temperature were amorphous. However, the improved crystallization is observed for BST thin films deposited at higher temperature. As the annealing temperature increased, the dominant X-ray diffraction peaks became sharper and more intense. The dominant diffraction peaks increased with the sputtering pressures increasing as the films deposited at 0.37–1.2 Pa. With increasing the sputtering pressure up to 3.9 Pa, BST thin films had the (110) + (200) preferred orientation. Possible correlations of the crystallization with changes in the sputtering pressure were discussed. The SEM morphologies indicated the film was small grains, smooth, and the interface between the film and the substrate was sharp and clear.     

Luminescence characterization of ultrathin MgO films of high crystallinity prepared by pulsed laser deposition

Thin MgO films with thicknesses ranging from 127 to 35 nm were prepared by pulsed laser deposition on Si substrates. The crystalline films were smooth (rms roughness 0.6–1.2 nm) with an average density of 3.5 g/cm³. Cathodoluminescence study revealed emissions peaked at 7.65 eV and ascribed to the edge emission of large radius exciton states as well as luminescence due to the F and F⁺ colour centres in the range of 2–4 eV. This luminescence is efficiently excited in the absorption band peaked at 6.2 eV and in the intrinsic absorption with the onset at 7.4 eV via energy transfer processes.     

Evidence of hexagonal diamond in plasma-deposited carbon films

Hexagonal diamond grains of 30 nm diameter together with graphite and SiC are seen in predominantly amorphous carbon films deposited at low temperature on Si substrates from a CH₄ plasma vapour source. The different crystalline phases are identified by grazing-angle X-ray diffraction which allows for substrate rotation and tilting to enable the 2 peaks to be correlated with the angular displacements of specific planes. Electron energy-loss spectroscopy shows the chemical composition of the films to be predominantly carbon with traces of oxygen. Raman spectroscopy shows the peaks to be associated with amorphous carbon and graphite, together with a peak at 1170 cm^–1 which is attributed to microcrystalline hexagonal diamond.     

Composite phosphor films based on spherical Lu2O3:Eu3+ nanoparticles

A nanopowder of Lu₂O₃:Eu³⁺ (C _Eu = 5 at.%) was obtained by coprecipitation with urea (NH₂)₂CO from aqueous solutions. Using this nanopowder, compact Lu₂O₃:Eu³⁺ films with thicknesses within 20–200 μm and a relative density up to 65% of the theoretical limit were deposited using the spin-coating and painting techniques. The films were characterized by scanning electron microscopy, X-ray diffraction, and X-ray luminescence (XRL) measurements. It is established that the XRL intensity depends on the phosphor/organic binder ratio and thickness of the film. The most intense XRL and most homogeneous structure are observed for 20-μm-thick Lu₂O₃:Eu³⁺ films.     

Synthesis and luminescence properties of Eu<Superscript>2+</Superscript>-doped Li<Subscript>2</Subscript>SrSiO<Subscript>4</Subscript>

We have studied the luminescence spectra of Li₂Sr_{1 − x} Eu _x SiO₄ (x = 0.0001–0.01) solid solutions prepared by solid-state reactions and a sol-gel process in a reducing atmosphere. The spectra show a broad band in the range 500–700 nm, centered at 578 nm, which is due to the 4f ⁶5d → 4f ⁷ transition. The luminescence excitation spectrum shows, in addition to bands due to Eu²⁺ 4f ⁷ → 4f ⁶5d transitions, a strong band centered at 174 nm, attributable to absorption in the SiO₄⁴⁻ group.     

Electrical, optical and structural characterization of high-k dielectric ZrO2 thin films deposited by the pyrosol technique

High-k dielectric zirconium oxide (ZrO₂) thin films have been deposited on silicon substrates at temperatures from 400 to 600 °C using the spray pyrolysis technique. The films were deposited from two spraying solution concentrations (0.033 and 0.066 M) of zirconium acetylacetonate dissolved in N,N-dimethylformamide. These films were stoichiometric, transparent and with a very low surface roughness (5–40 ). The refractive index of these films was of the order of that obtained for a bulk material (2.12). Films deposited with high molar concentration presented the best electrical characteristic, have a dielectric constant in the range 12.5–17.5, depending on the deposition temperature, and can stand electric fields up to 3 MV cm^–1 without observing destructive dielectric breakdown. Transmission electron microscopy measurements, indicate that the films consist of nano-crystallites of the tetragonal ZrO₂ crystalline phase embedded into an amorphous matrix. Infrared spectroscopy measurements of the films show peaks associated with ZrO₂ and a peak related to silicon dioxide (SiO₂). The analysis of spectroscopic ellipsometry measurements on these films indicates the existence of a layer at the ZrO₂/Si interface composed of SiO₂ as well as ZrO₂ and crystalline silicon.     

Upconversion emissions in Yb<Superscript>3+</Superscript>–Tm<Superscript>3+</Superscript>-doped tellurite glasses excited at 976 nm

Intense Tm³⁺ blue upconversion emission has been observed in Tm³⁺–Yb³⁺ codoped oxyfluoride tellurite glass under excitation with a diode laser at 976 nm. Three emission bands centered at 475, 650 and 796 nm corresponding to the transitions ¹G₄→ ³H₆, ¹G₄→ ³H₄ and ³F₄→ ³H₆, respectively, simultaneously occur. The dependence of upconversion intensities on Tm³⁺ ions concentration and excitation power are investigated. For fixed Yb₂O₃ concentrations of 5.0 mol%, the maximum upconversion intensity was obtained with Tm₂O₃ concentration of about 0.1 mol%. The blue upconversion luminescence lifetimes of the Tm³⁺ transitions ¹G₄→ ³H₆ are measured. The results are evaluated by the possible upconversion mechanisms.