Effects of the substrate temperature on the properties of CuIn5S8 thin films

Structural, optical and electrical properties of CuIn₅S₈ thin films grown by thermal evaporation have been studied relating the effects of substrate heating conditions of these properties. The CuIn₅S₈ thin films were carried out at substrate temperatures in the temperature range 100-300 °C. The effects of heated substrate on their physico-chemical properties were investigated using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), optical transmission and hot probe method. X-ray diffraction revealed that the films are strong preferred orientation along the (3 1 1) plane upon substrate temperature 200 °C and amorphous for the substrate temperatures below 200 °C. No secondary phases are observed for all the films. The composition is greatly affected by heated substrate. From the optical transmission and reflection, an important absorption coefficient exceeds 10⁵ cm⁻¹ at 800 nm was found. As increasing the substrate temperature, the optical energy band gap decreases from 1.70 eV for the unheated films to 1.25 eV for the deposited films at 300 °C. It was found that CuIn₅S₈ thin film is an n-type semiconductor at 250° C.     

Investigation of the optoelectronic properties of columbite ZnNb2O6 crystal

A high-quality ZnNb₂O₆ single-crystal grown by optical floating zone method has been used as a research prototype to analyze the optoelectronic parameters by measuring the absorption coefficient and transmittance spectra along the b-axis from 200 nm to 1000 nm at room temperature. The optical interband transitions of ZnNb₂O₆ have been determined as a direct transition with a band gap of 3.84 eV. The refractive index, extinction coefficient, and real and imaginary parts of the complex dielectric constants as functions of the wavelength for ZnNb₂O₆ crystal are obtained from the measured absorption coefficients and transmittance spectra. In the Urbach tail of 3.16–3.60 eV, the validity of the Cauchy–Sellmeier equation has also been evaluated. Using the single effective oscillator model, the oscillator energy E_o is found to be 4.77 eV. The dispersion energy E_d is 26.88 eV and ZnNb₂O₆ crystal takes an ionic value.     

Temperature variation of electrical conductivity and absorption edge in Cu7GeSe5I advanced superionic conductor

Single crystals of Cu₇GeSe₅I superionic conductor were grown by chemical transport. Their electrical conductivity in the frequency range 1.0×10⁶–1.2×10⁹ Hz and in the temperature range 196–295 K was measured. Cu₇GeSe₅I crystal is shown to exhibit a rather high electrical conductivity (σ₂₉₅=64.0 S/m at 295 K) and a low activation energy (ΔE_a=0.125 eV). Optical absorption edge of Cu₇GeSe₅I crystals in the temperature range 77–300 K was studied, the temperature dependences of the optical pseudogap and Urbach energy being obtained. The effect of different types of disordering on the Urbach absorption edge and electron–phonon interaction parameters was investigated.     

Optimization of annealing conditions of In2S3 thin films deposited by vacuum thermal evaporation

In₂S₃ thin films were grown on glass substrates by means of the vacuum thermal evaporation technique and subsequently thermally annealed in nitrogen and free air atmosphere from 250 to 350 °C for different durations. Experimental parameters have been adjusted in order to optimize the annealing conditions, and to obtain high band gap energy at low deposition temperature, as required for photovoltaic applications. In order to improve our understanding of the influence of the deposition and annealing parameters on device performance, we have investigated our indium sulfide material by X-ray diffraction, energy dispersive X-ray analysis (EDAX), atomic force microscopy (AFM) and spectrophotometry. The optical and structural properties of the films were studied as a function of the annealing temperature and durations. X-ray diffraction analysis shows the initial amorphous nature of deposited In-S thin films and the phase transition into crystalline In₂S₃ upon thermal annealing. Films show a good homogeneity and optical direct band gap energy about 2.2 eV. An annealing temperature of 350 °C during 60 min in air atmosphere were the optimal conditions.     

Investigations on co-evaporated Cu2SnSe3 and Cu2SnSe3-ZnSe thin films

Cu₂SnSe₃ is an important precursor material for the growth of Cu₂ZnSnSe₄, an emerging solar cell absorber layer via solid state reaction of Cu₂SnSe₃ and ZnSe. In this study, we have grown Cu₂SnSe₃ (CTSe) and Cu₂SnSe₃-ZnSe (20%) films onto soda-lime glass substrates held at 573 K by co-evaporation technique. The effect of annealing of these films at 723 K for an hour in selenium atmosphere is also investigated. XRD studies of as-deposited Cu₂SnSe₃ and Cu₂SnSe₃-ZnSe films indicated SnSe as secondary phase which disappeared on annealing. The direct optical band gap of annealed Cu₂SnSe₃ and Cu₂SnSe₃-ZnSe films were found to be 0.90 eV and 0.94 eV respectively. Raman spectroscopy studies were used to understand the effect of ZnSe on the properties of Cu₂SnSe₃.     

Preparation and luminescent characteristic of Li3NbO4 nanophosphor

Synthesis and luminescence properties of Li₃NbO₄ oxides by the sol-gel process were investigated. The products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and absorption spectra. The PL spectra excited at 247 nm have a broad and strong blue emission band maximum at 376 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectra of the samples sintered at temperatures of 600 and 700 °C exhibited the band-gap energies of 4.0 and 4.08 eV.     

Investigation on spectral features of tungsten ions in PbO-Bi2O3-As2O3 glass matrix

Lead bismuth arsenate glasses mixed with different concentrations of WO₃ (ranging from 0 to 6.0 mol%) were synthesized. Differential thermal analysis (DTA), optical absorption, ESR and IR spectral studies have been carried out. The results of DTA have indicated that there is a gradual decrease in the resistance of the glass against devitrification with increase in the concentration of WO₃ upto 4.0 mol%.The optical absorption spectra of these glasses exhibited a relatively broad band peaking at about 880 nm identified due to d_xy→d_x²_−y² transition of W⁵⁺ ions; this band is observed to be more intense in the spectrum of glass containing 4.0 mol% of WO₃. Further, two prominent kinks attributed to ³P₀→¹S₀, ¹D₂ transitions of Bi³⁺ ions have also been located in the absorption spectra. The ESR spectra of these glasses recorded at room temperature exhibited an asymmetric signal at g_⊥∼1.71 and g_ll∼1.61. The intensity of the signal is observed to be maximal for the spectrum of the glass W₄. The quantitative analysis of optical absorption and ESR spectral studies have indicated that there is a maximum reduction of tungsten ions from W⁶⁺ state to W⁵⁺ state in the glass containing 4.0 mol% of WO₃. The IR spectral studies have indicated that there is a increasing degree of disorder in the glass network with increase in the concentration of WO₃ upto 4.0 mol%.     

新型GeSe2-In2Se3-AgI玻璃性能研究

采用传统熔融-淬冷法制备了一系列新型(100-x) (4GeSe₂-In₂Se₃) -xAgI(x=20,30,40 mol%)硫系玻璃样品.利用X射线衍射分析、差热分析、可见-近红外吸收光谱、红外透过光谱、喇曼分析等技术手段研究了该玻璃系统的组成、结构、热稳定性和光学特性等.利用Tauc方程计算出了样品的间接带隙;测试了部分样品在不同升温速率下的差示扫描量热曲线,并采用Kissinger法计算了玻璃样品的析晶活化能.X射线衍射数据表明,该玻璃体系在较宽的组分范围内有良好的非晶特性,成玻范围较宽;差热分析和析晶动力学研究表明,玻璃样品70(4GeSe₂-In₂Se₃)-30AgI具有较好的热稳定性(ΔT=114℃)和较高的活化能(E_a=320.4 kJ/mol).随着AgI含量的增加,玻璃的短波吸收限蓝移,并且光学带隙有增大的趋势.此外,红外透过光谱分析表明该玻璃体系具有良好的红外透过性能,其红外截止波长不会随着AgI含量的增加而发生明显变化,皆为16μm左右.     

Characterization of chemically deposited ZnSe/SnO2/glass films: Influence of annealing in Ar atmosphere on physical properties

The Zinc Selenide (ZnSe) thin films have been deposited on SnO₂/glass substrates by a simple and inexpensive chemical bath deposition (CBD). The structural, optical and electrical properties of ZnSe films have been characterized by X-ray diffraction (XRD), Energy Dispersive X-ray Analysis (EDAX), optical absorption spectroscopy, and four point probe techniques, respectively. The films have been subjected to different annealing temperature in Argon (Ar) atmosphere. An increase in annealing temperature does not cause a complete phase transformation whereas it affects the crystallite size, dislocation density and strain. The optical band gap (E_g) of the as-deposited film is estimated to be 3.08 eV and decreases with increasing annealing temperature down to 2.43 eV at 773 K. The as-deposited and annealed films show typical semiconducting behaviour, dρ/dT > 0. Interestingly, the films annealed at 373 K, 473 K, and 573 K show two distinct temperature dependent regions of electrical resistivity; exponential region at high temperature, linear region at low temperature. The temperature at which the transition takes place from exponential to linear region strongly depends on the annealing temperature.     

Low-temperature absorption edge and photoluminescence in layered structured Tl2Ga2S3Se single crystals

The absorption edge of undoped Tl₂Ga₂S₃Se crystals have been studied through transmission and reflection measurements in the wavelength range 440–1100 nm and in the temperature range 10–300 K. The absorption edge was observed to shift toward lower energy values with increasing temperature. As a result, the rate of the indirect band gap variation with temperature γ=−2.6×10⁻⁴ eV/K and the absolute zero value of the band gap energy E_gi(0)=2.42 eV were obtained.     

Photoluminescence study of disordering in the cation sublattice of Cu2ZnSnS4

In this study we investigated the influence of the degree of disordering in the cation sublattice on low temperature photoluminescence (PL) properties of Cu₂ZnSnS₄ (CZTS) polycrystals. The degree of disordering was changed by using different cooling rates after post-annealing at elevated temperatures. The results suggest that in the case of higher degree of cation sublattice disorder radiative recombination involving defect clusters dominates at T = 10 K. These defect clusters induce local band gap energy decrease in CZTS. The concentration of defect clusters can be reduced by giving more time for establishing ordering in the crystal lattice. As a result, radiative recombination mechanism changes and band-to-impurity recombination involving deep acceptor defect with ionization energy of about 200 meV starts to dominate in the low temperature PL spectra of CZTS polycrystals.     

Blue luminescence in Tm-doped KGd(WO4)2 single crystals

Up-conversion blue emissions of trivalent thulium ions in monoclinic KGd(WO₄)₂ single crystals at 454 and 479 nm are reported for a single pump laser source at 688 nm. We grew thulium-doped KGd(WO₄)₂ single crystals at several concentrations from 0.1% to 10%. We recorded a polarized optical absorption spectrum for the ³F₂+³F₃ energy levels of thulium at room temperature and low temperature (6 K). From the low temperature emission spectra we determined the splitting of the ³H₆ ground state. The blue emissions are characterized as a function of the dopant concentration and temperature from 10 K to room temperature. To our knowledge, this is the first time that sequential two-photon excitation process (STEP) generated blue emissions in thulium-doped single crystals with a single excitation wavelength.     

Line shape of the far-wing beyond the band head of the CO2ν3 band

Carbon dioxide is one of the most important trace gases in the terrestrial atmosphere. The spectral data required in remote sensing are the spectral parameter of each absorption line and a line shape model. This paper describes the absorption properties of CO₂ near 2400 cm⁻¹; these properties are of interest to those in the atmospheric temperature sounding field. The shape of the far-wing of N₂- and O₂-broadened CO₂ lines was investigated in the 2200-2500 cm⁻¹ spectral region in a temperature range of atmospheric interest (230-318 K). We focused on the higher rotational quantum number of the R-branch in the ν₃ band, where the effect of the far-wing is enhanced. The effect of the far-wing has been studied extensively by others, since the CO₂ν₃ band is known to exhibit sub-Lorentzian behavior. Here, we show the observed spectra along with calculated spectra for five temperatures. We used first-order line-mixing and the χ-factor, which accounts for the effect of the far-wing, to create the calculated spectra. Our results provide new knowledge of quantum interference of the spectral line in the ν₃ band of CO₂.     

Structural and optical properties of SrCu2O2 films deposited on sapphire substrates by pulsed laser deposition

We deposited SrCu₂O₂ (SCO) films on sapphire (Al₂O₃) (0 0 0 1) substrates by pulsed laser deposition. The crystallographic orientation of the SCO thin film showed clear dependence on the growth temperature. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis showed that the film deposited at 400 °C was mainly oriented in the SCO [2 0 0] direction, whereas when the growth temperature was increased to 600 °C, the SCO film showed a dominant orientation of SCO [1 1 2]. The SCO film deposited at 500 °C was obvious polycrystalline, showing multi peaks from (2 0 0), (1 1 2), and (2 1 1) diffraction in the XRD spectrum. The SCO film deposited at 600 °C showed a band gap energy of 3.3 eV and transparency up to 80% around 500 nm. The photoluminescence (PL) spectra of the SCO films grown at 500 °C and 600 °C mainly showed blue-green emission, which was attributed to the intra-band transition of the isolated Cu⁺ and Cu⁺–Cu⁺ pairs according to the temperature dependent-PL analysis.     

Annealing effect on CdS/SnO2 films grown by chemical bath deposition

The extensive investigation of the annealing effect in nitrogen atmosphere on the structural optical and electrical properties of chemically deposited CdS films on SnO₂ has been performed. The as-deposited film shows 2.45 eV band gap (E_g) and decreases with increasing annealing temperature. The film annealed at 623 K having pure hexagonal phase (a = 4.14 Å, c = 6.71 Å for [1 0 0] plane) and E_g = 2.36 eV shows 10 times higher conductivity for all temperature range, and shows two different activation energies E_a = 0.114 eV and E_a = 0.033 eV for the temperature range 395 K ≤ T ≤ 515 K and 515 K ≤ T ≤ 585 K, respectively. The structural parameters such as dislocation density, strain and optical parameters such as absorption and extinction coefficient are calculated and compared for all the films.     

Comparative study of optical parameters of fullerene C60 film at different temperatures

Fullerene C₆₀ thin films on glass substrate (around 2000 ? thickness) were prepared by thermal evaporation technique. The structural, surface morphology and optical properties of the films were studied. The optical properties of fullerene C₆₀ were investigated in the spectral range 200 nm to 900 nm using a UV-Vis spectrophotometer at room temperature as well as at liquid nitrogen temperature (77 K). The optical band gap at room temperature is found to be 2.30 eV, which gradually decreases with lowering the temperature and reaches to 2.27 at 77 K. The thickness and refractive index of fullerene C₆₀ film were calculated by ellipsometry. From the X-ray analysis, we have calculated the grain size, dislocation density, number of crystallite per unit area, and strain of the film at room temperature. The surface morphology of film was analyzed by scanning electron microscope (SEM). The present result show that the fullerene C₆₀ film becomes more conducting at low temperature.     

Structural,optical, FTIR and photoluminescence properties of Zn0.96−xCo0.04CuxO (x=0.03, 0.04 and 0.05) nanopowders

Un-hydrogenated and hydrogenated Cu, Co co-doped ZnO (Zn_0.96−xCo_0.04Cu_xO, x=0.03, 0.04 and 0.05) nanopowders have been synthesized by co-precipitation method. The synthesized samples have been characterized by powder X-ray diffraction, energy dispersive X-ray spectra, UV–Visible spectrophotometer and Fourier transform infrared spectroscopy. The calculated average crystalline size increases from 37.3 to 50.6 nm for un-hydrogenated samples from x=0.03 to 0.05 and it changes from 29.4 to 34.9 nm for hydrogenated samples. The change in lattice parameters, micro-strain, a small shift of X-ray diffraction peaks towards lower angles and reduction in energy gap reveal the substitution of Cu²⁺ ions into Zn–Co–O lattice. The hydrogenation effect reduces the particle size and induces the more uniform distribution of particles than the un-hydrogenated samples which is confirmed by SEM micrographs. Photoluminescence spectra of Zn_0.96−xCo_0.04Cu_xO system shows that red shift in near band edge ultraviolet emission from 393 to 403 nm with suppressing intensity and a blue shift in green band emission from 537 to 529 nm with enhancing intensity confirms the substitution of Cu into the Zn–Co–O lattice.     

Photoluminescence characterization of polycrystalline n-type Cu2O films

Electrodeposition was used to deposit Cu₂O thin films on ITO substrates. Photoresponse of the film clearly indicated n-type behavior of Cu₂O in photoelectrochemical cells. The temperature dependence of photoluminescence (PL) revealed that the spectra consist of donor-acceptor pair emissions and the recombination between electrons bound to donors and free holes. We observed that the dominant intrinsic defect, oxygen vacancies, creates a donor energy level at 0.38 eV below the bottom of the conduction band. As a result, this donor level acts as a center for both PL emissions and to produce n-type conductivity in the electrodeposited Cu₂O films. In addition, an acceptor energy level at 0.16 eV from the top of the valence band was observed.     

A novel chemical synthesis and characterization of Mn3O4 thin films for supercapacitor application

Mn₃O₄ thin films have been prepared by novel chemical successive ionic layer adsorption and reaction (SILAR) method. Further these films were characterized for their structural, morphological and optical properties by means of X-ray diffraction (XRD), Fourier transform infrared spectrum (FTIR), field emission scanning electron microscopy (FESEM), wettability test and optical absorption studies. The XRD pattern showed that the Mn₃O₄ films exhibit tetragonal hausmannite structure. Formation of manganese oxide compound was confirmed from FTIR studies. The optical absorption showed existence of direct optical band gap of energy 2.30 eV. Mn₃O₄ film surface showed hydrophilic nature with water contact angle of 55°. The supercapacitive properties of Mn₃O₄ thin film investigated in 1 M Na₂SO₄ electrolyte showed maximum supercapacitance of 314 F g⁻¹ at scan rate 5 mV s⁻¹.     

KrF pulsed laser deposition of La5Ca9Cu24O41 thin films on various substrates

Recent studies on single crystals of cuprate oxides containing spin chains and ladders have reported large anisotropic magnon-mediated thermal conductivity. A potential use of thin films of such materials could be in the thermal management of electronic devices for the guiding of unwanted heat to a heat sink. In this article, the pulsed laser deposition and characterization of La₅Ca₉Cu₂₄O₄₁ thin films on SrLaAlO₄, SrTiO₃, MgO, and Si substrates are reported for the first time. The films were grown using a pulsed UV laser (KrF, 248 nm) and various substrate temperatures up to 650 °C. The XRD spectra revealed successful target-film stoichiometric transfer and high texturing of the thin films with (0 k 0) preferred orientation.