Preparation and characterization of CuIn1 − xGaxSe2 − ySy thin film solar cells by rapid thermal processing

This paper describes the synthesis and characterization of CuIn_1 − xGa_xSe_2 − yS_y (CIGSeS) thin-film solar cells prepared by rapid thermal processing (RTP). An efficiency of 12.78% has been achieved on ~ 2 µm thick absorber. Materials characterization of these films was done by SEM, EDS, XRD, and AES. J-V curves were obtained at different temperatures. It was found that the open circuit voltage increases as temperature decreases while the short circuit current stays constant. Dependence of the open circuit voltage and fill factor on temperature has been estimated. Bandgap value calculated from the intercept of the linear extrapolation was 1.1-1.2 eV. Capacitance-voltage analysis gave a carrier density of 4.0 × 10¹⁵ cm^− 3.     

Optical and electrical properties of vapour phase grown Zn1 − xCrxTe crystals

The optical and electrical properties of vapour phase grown crystals of diluted magnetic semiconductor Zn_1 − xCr_xTe were investigated for 0 ≤ x ≤ 0.005. The diffuse reflectance spectra exhibited an increase in the fundamental absorption edge (E₀) with composition x and were also dominated by a broad absorption band around 5200 cm^− 1 arising from ⁵T₂ → ⁵E transition. The ⁵T₂ and ⁵E levels originate from the crystal field splitting of the ⁵D free ion in the ground state. The electrical resistivity measurements revealed semiconducting behaviour of the samples with p-type conductivity in the temperature range of 200-450 K.     

Structural, electrical and optical properties of transparent Zn1 − xMgxO nanocomposite thin films

Zn_1 − xMg_xO thin films of various Mg compositions were deposited on quartz substrates using inexpensive ultrasonic spray pyrolysis technique. The influence of varying Mg composition and substrate temperature on structural, electrical and optical properties of Zn_1 − xMg_xO films were systematically investigated. The structural transition from hexagonal to cubic phase has been observed for Mg content greater than 70 mol%. AFM images of the Zn_1 − xMg_xO films (x = 0.3) deposited at optimized substrate temperature clearly reveals the formation of nanorods of hexagonal Zn_1 − xMg_xO. The variation of the cation-anion bond length to Mg content shows that the lattice constant of the hexagonal Zn_1 − xMg_xO decreases with corresponding increase in Mg content, which result in structure gradually deviating from wurtzite structure. The tuning of the band gap was obtained from 3.58 to 6.16 eV with corresponding increase in Mg content. The photoluminescence results also revealed the shift in ultraviolet peak position towards the higher energy side.     

A comparative study of the properties of thermally evaporated CuIn2n + 1S3n + 2 (n = 0, 1, 2 and 3) thin films

CuInS₂, CuIn₃S₅, CuIn₅S₈ and CuIn₇S₁₁ compounds were synthesized by the horizontal Bridgman method using high-purity copper, indium and sulphur elements. Crushed powders of these ingots were used as raw materials for the vacuum thermal evaporation. So, CuIn_2n + 1S_3n + 2 (n = 0, 1, 2, and 3) thin films were deposited by single source vacuum thermal evaporation onto glass substrates heated at 150 °C. The structural, compositional, morphological, electrical and optical properties of the deposited films were studied using X-ray diffraction (XRD), energy dispersive X-ray, atomic force microscopy and optical measurement techniques. XRD results revealed that all the films are polycrystalline. However, CuInS₂ and CuIn₃S₅ films had a chalcopyrite structure with preferred orientation along 112 while CuIn₅S₈ and CuIn₇S₁₁ films exhibit a spinel structure with preferred orientation along 311. The absorption coefficients of the all CuIn_2n + 1S_3n + 2 films are in the range of 10⁻⁴ and 10⁻⁵ cm⁻¹. The direct optical band gaps of CuIn_2n + 1S_3n + 2 layers are found to be 1.56, 1.78, 1.75 and 1.30 eV for n = 0, 1, 2, and 3, respectively. CuIn₃S₅ and CuIn₅S₈ films are p type with electrical resistivities of 4 and 12 Ω cm whereas CuInS₂ and CuIn₇S₁₁ are highly compensated with resistivities of 1470 and 1176 Ω cm, respectively.     

Band alignment of Cd(1 − x)ZnxS produced by spray pyrolysis method

Cd_(1 − x)Zn_xS thin films have been grown on glass substrates by the spray pyrolysis method using CdCl₂ (0.05 M), ZnCl₂ (0.05 M) and H₂NCSNH₂ (0.05 M) solutions and a substrate temperature of 260 °C. The energy band gap, which depends on the mole fraction × in the spray solution used for preparing the Cd_(1 − x)Zn_xS thin films, was determined. The energy band gaps of CdS and ZnS were determined from absorbance measurements in the visible range as 2.445 eV and 3.75 eV, respectively, using Tauc theory. On the other hand, the values calculated using Elliott-Toyozawa theory were 2.486 eV and 3.87 eV, respectively. The exciton binding energies of Cd_0.8Zn_0.2S and ZnS determined using Elliott-Toyozawa theory were 38 meV and 40 meV, respectively. X-ray diffraction results showed that the Cd_(1 − x)Zn_xS thin films formed were polycrystalline with hexagonal grain structure. Atomic force microscopy studies showed that the surface roughness of the Cd_(1 − x)Zn_xS thin films was about 50 nm. Grain sizes of the Cd_(1 − x)Zn_xS thin films varied between 100 and 760 nm.     

Electrical properties of lead-free thick film NTC thermistors based on perovskite-type BaCoxCo2xBi1 − 3xO3

Lead-free thick film negative temperature coefficient (NTC) thermistors based on perovskite-type BaCo^II_xCo^III_2xBi_1 − 3xO₃ (x ≤ 0.1) were prepared by mature screen-printing technology. The microstructures of the thick films sintered at 720 °C were examined by X-ray diffraction and scanning electron microscopy. The electrical properties were analyzed by measuring the resistance-temperature characteristics. For the BaBiO₃ thick films, the room-temperature resistivity is 0.22 MΩ cm, while the room-temperature resistivity is sharply decreased to about 3 Ω cm by replacing of Bi with a small amount of Co. For compositions 0.02 ≤ x ≤ 0.1, the values of room-temperature resistivity (ρ₂₃), thermistor constant (B_25/85) and activation energy are in the range of 1.995-2.975 Ω cm, 1140-1234 K and 0.102-0.111 eV, respectively.     

Photocatalytical water decomposition on visible light-driven solid-solution compounds K4Ce2Ta10−xNbxO30 (x = 0-10)

A series of single phase solid-solution K₄Ce₂Ta_10−xNb_xO₃₀ (x = 0-10) photocatalysts were synthesized by conventional high temperature solid state reaction. Their UV-vis diffuse reflectance spectra showed their absorbance edges shifted to long wavelength zone consistently with the increase of the amount of Nb for substituting Ta in these compounds, and the onsets of absorbance edges ranging from about 540 nm to 690 nm, corresponding to bandgap energy of 1.8-2.3 eV. These series of photocatalysts possess appropriate band gap (ca. 1.8-2.3 eV) and chemical level to use solar energy to decompose water into H₂, and the photocatalytical activities under visible light (λ > 420 nm) demonstrated that the activities decreased correspondingly with the increase of the amount of Nb in these compounds, which is regarded as the result of the differences of their band structures. Furthermore, the photocatalytical activities and the photophysical properties of these visible light-driven photocatalysts K₄Ce₂Ta_10−xNb_xO₃₀ (x = 0-10) were bridged by the first principle calculation based on Density Functional Theory with General Gradient Approximation and Plane-wave Pseudopotential methods.     

Structure and thermal conductivity of Gd2(TixZr1 − x)2O7 ceramics

The Gd₂(Ti_xZr_1 − x)₂O₇ (x = 0, 0.25, 0.50, 0.75, 1.00) ceramics were synthesized by solid state reaction at 1650 °C for 10 h in air. The relative density and structure of Gd₂(Ti_xZr_1 − x)₂O₇ were analyzed by the Archimedes method and X-ray diffraction. The thermal diffusivity of Gd₂(Ti_xZr_1 − x)₂O₇ from room temperature to 1400 °C was measured by a laser-flash method. The Gd₂Zr₂O₇ has a defect fluorite-type structure; however, Gd₂(Ti_xZr_1 − x)₂O₇ (0.25 ≤ x ≤ 1.00) compositions exhibit an ordered pyrochlore-type structure. Gd₂Zr₂O₇ and Gd₂Ti₂O₇ are infinitely soluable. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ increases with increasing Ti content under identical temperature conditions. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ first decreases gradually with the increase of temperature below 1000 °C and then increases slightly above 1000 °C. The thermal conductivity of Gd₂(Ti_xZr_1 − x)₂O₇ is within the range of 1.33 to 2.86 W m^− 1 K^− 1 from room temperature to 1400 °C.     

The adsorption properties of PdZnx alloy on Pd(1 0 0): Preparation and characterization

The formation of PdZn_x alloy on Pd(1 0 0) and its characteristics were investigated by various methods, such as photoelectron, auger-electron, electron energy loss, thermal desorption spectroscopic methods and work-function measurement. The alloy was produced by the decomposition of diethyl zinc on Pd(1 0 0). The alloy surface reacts with O₂ and ZnO_x is formed. The reactivity of alloy to hydrogen is similar to that of K/Pd. The stability of adsorbed CO is lower than on clean Pd(1 0 0).     

Site dependent metal adsorption on (3 × 3) h-BN monolayer: Stability, magnetic and optical properties

Cu, Pd and Au metal adatom adsorption on different adsorption sites of graphene analog h-BN monolayer is presented. The results demonstrate that the atop N (A_N) being the most favorable site for Cu while atop B (A_B) for Pd/Au; as well as occurrence of chemisorption is also found in these sites. A general model has been proposed which essentially indicate electronegativity (χ) to be the governing reason regarding the choice of adsorption sites on h-BN sheet in a way such that the adatoms with χ < 2.04 are the most stable on A_N site while adatoms with χ lying in the range 2.04-3.04 are the most stable on A_B site. A detail study regarding magnetic properties reveal 100% spin polarization at Fermi level i.e. half metallic characteristics and 1μ_B/supercell magnetic moment in case of Cu and Au adatom adsorption at the most favorable sites. For Cu adsorbed h-BN system, the half metallic characteristics and strong chemical bonds arise from good hybridization at 0 eV between the outermost 2p orbital of nitrogen and the outermost 4s orbital of copper and at −1.49 eV between Cu 3d and 4s orbital with N 2p orbital. A thorough optical study on the above mentioned systems exhibits evolution/disappearance of different hump/shoulder peaks in the calculated absorption coefficient vs. energy plot which may be useful for experimental identification of the adsorbed systems.     

Simulations of Si and SiO2 etching in SF6 + O2 plasma

Chemical etching of Si and SiO₂ in SF₆ + O₂ plasma is considered. The concentrations of plasma components are calculated using values extrapolated from experimental data. Resulting calculations of plasma components are used for the calculation of Si and SiO₂ etching rates. It is found that the reaction constants for reactions of F atoms with Si atoms and SiO₂ molecules are equal to (3.5 ± 0.1) × 10⁻² and (3.0 ± 0.1) × 10⁻⁴, respectively. The influence of O₂ addition to SF₆ plasma on the etching rate of Si is quantified.     

The microwave-assisted synthesis and characterization of Zn1 − xCoxO nanopowders

In this paper, we present a simple microwave-assisted synthesis of Zn_1 − xCo_xO nanopowders. With the advantages of the microwave-assisted method, we have successfully synthesized good crystalline quality and good surface morphology Zn_1 − xCo_xO nanopowders. The nanopowders are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-VIS absorption, and micro-Raman spectroscopy. We found, in the synthesis process, the surfactant Triethanolamine (TEA) plays an important role on the morphology of Zn_1 − xCo_xO nanoparticles. The XRD study shows that for Co doping up to 5%, Co²⁺ ions are successfully incorporated into the ZnO host matrix. The absorption spectra of Zn_1 − xCo_xO (x = 1-5%) nanopowders show several peaks at 660, 611 and 565 nm, indicating the presence of Co²⁺ ions in the tetrahedral sites. The Raman study shows that the linewidth of E₂^low mode increases with Co concentration, which further indicates the incorporation of Co²⁺ ions into the ZnO host matrix.     

Growth process of CuO(1 1 1) and Cu2O(0 0 1) thin films on MgO(0 0 1) substrate under metal-mode condition by reactive dc-magnetron sputtering

The growth process of CuO and Cu₂O thin films on MgO(0 0 1) substrates by reactive dc-magnetron sputtering was studied by reflection high-energy electron diffraction (RHEED) and atomic-force microscopy (AFM). The RHEED pattern and AFM image showed that (1) three-dimensional Cu(0 0 1) islands grew on MgO under the nonreactive sputtering condition, (2) CuO(1 1 1) was deposited layer by layer on MgO at 400 °C under the reactive sputtering condition, and (3) the film deposited at 600 °C in the initial growth stage was composed of three-dimensional Cu islands because O₂ gas could not be incorporated into them due to the low sticking coefficient of O₂ on MgO under the reactive sputtering condition. The layer-by-layer CuO(1 1 1) thin-film growth process is discussed from the viewpoint that Cu and oxygen species are supplied in stoichiometry onto the MgO substrate to form CuO thin-film crystals while maintaining minimum interfacial energy between CuO and MgO.     

TOF-SARS study of hydrogen adsorption and desorption kinetics on Si(1 0 0)

The kinetics of atomic hydrogen isothermal adsorption and desorption on a Si(1 0 0) surface was studied using the time-of-flight scattering and recoiling spectrometry technique at temperatures below and above the thermal desorption threshold. A continuous decrease in saturation coverage with temperature under constant atomic hydrogen exposure has been observed in both regions for temperatures in the range 325-820 K. For T_S=500-650 K, the decrease is described by a kinetic model where Eley-Rideal (ER) abstraction is responsible for hydrogen removal from the surface and hydrogen coverage depends on the temperature due to the changing rate of migration from precursor to primary monohydride sites. For T_S=650 K and higher, in addition to the ER abstraction, the thermal desorption from primary monohydride sites leads to a further decrease of the saturation coverage. The first-order desorption rates after source shut-off have been measured and an activation barrier of 1.89 eV has been obtained.     

Tuning the optical properties of alloyed CdSexS1 − x nanoparticles by changing the constituent stoichiometry

The spherical particles CdSe_xS_1 − x with 30-80 nm in radius have been successfully prepared by the hydrothermal reaction at 200 °C. The structure characterization which has been carried out using X-ray diffraction (XRD) shows hexagonal crystal structure. Novel properties have been observed via UV-visual absorption spectra and photoluminescence (PL) spectra. The absorption shoulder and the luminescence emission peaks have been tuned by changing the mole ratio of Se in the CdSe_xS_1 − x samples.     

Fabrication of (K, Na)NbO3 glass-ceramics and crystal line patterning on glass surface

Crystallization behavior of (30−x)K₂O-xNa₂O-25Nb₂O₅-45SiO₂ (KNNS; x = 0, 5, 10, 20 and 30) (mol%) glasses was clarified and perovskite-type nonlinear optical (K, Na)NbO₃ (KNN) crystals were synthesized by using a conventional glass-ceramics method. It was found that Na₂O amounts over around x = 10 mol% were necessary to form perovskite-type KNN crystals showing second-harmonic generations. The substitution of K⁺ and Na⁺ ions was confirmed from X-ray diffraction (XRD) analysis. A continues-wave of Yb:YVO₄ fiber laser (wavelength: 1080 nm) was irradiated onto CuO doped KNNS; x = 10 (Cu-KNNS) surface. The absorption coefficient of this Cu-KNNS glass was determined to be α = 5.0 cm⁻¹. Perovskite-type KNN crystals were patterned in the condition of the laser power of >1.20 W and the laser scanning speed of S = 7 μm/s, and their structure was determined by Raman scattering spectra and XRD analysis.     

Preferentially oriented thin-film growth of CuO(1 1 1) and Cu2O(0 0 1) on MgO(0 0 1) substrate by reactive dc-magnetron sputtering

Copper oxide films deposited on MgO(0 0 1) substrates by reactive magnetron sputtering under the metal-mode condition were studied by X-ray diffraction (XRD) and reflection high-energy electron diffraction (RHEED) analyses for structural analysis, and X-ray-excited Auger electron spectroscopy (XAES) for chemical bonding analysis. CuO(1 1 1) thin films grew from their initial growth stage maintaining the same crystallinity on MgO(0 0 1) substrates at 400°C. When the substrate temperature was increased to 600 °C, the as-sputtered films comprise Cu(0 0 1), amorphous Cu₂O phase, and Cu₂O(0 0 1) phase. The Cu(0 0 1) phase was observed at initial growth stage. This is probably because O₂ gas molecules could not sufficiently stick to the MgO substrate at 600 °C. Single phase of Cu₂O(0 0 1) was obtained by the cooling of the as-sputtered films in O₂ atmosphere. The growth of single phase Cu₂O(0 0 1) is considered as a solid-phase heteroepitaxial growth on MgO(0 0 1) surface, which was caused by incorporating O₂ gas into the as-sputtered films.     

Microstructure tuning of epitaxial BaTiO3 − x thin films grown using laser molecular-beam epitaxy by varying the oxygen pressure

Microstructural properties are found to be variant in the BaTiO_3 − x films grown on SrTiO₃(001) substrate under various oxygen pressures from 2 × 10^− 2 Pa to 2 × 10^− 5 Pa by laser molecular-beam epitaxy. Transmission electron microscopic studies reveal that the predominant defects in the films change from threading dislocations into (111) planar defects (i.e. stacking faults and nanotwins) by lowering the oxygen pressure. High density of these defects was observed in the BaTiO_3 − x film prepared at the oxygen pressure of 2 × 10^− 5 Pa, which shows metallic behavior. The relationships between oxygen pressure, microstructure, and electrical properties are established on the basis of oxygen deficiency. The formation of nanotwins in highly oxygen-deficient BaTiO_3 − x epitaxial thin films results from accommodating excess oxygen vacancies induced by lowering oxygen pressure.     

Ionization energies of the non-stoichiometric LinFn−1 (n = 3, 4, 6) clusters

Ionization energies of non-stoichiometric Li_nF_n−1 (n = 3, 4, 6) clusters determined by a thermal ionization mass spectrometry (TIMS) were 4.2 ± 0.2 eV for Li₃F₂, 4.3 ± 0.2 eV for Li₄F₃ and 4.1 ± 0.2 eV for Li₆F₅. The ionization energy of Li₆F₅ cluster was obtained experimentally for the first time. The ionization energies of Li₃F₂ and Li₄F₃ are in correlation with the results obtained by photoionization time-of-flight mass spectrometry. The determined ionization energies are comparable with theoretical ionization energies calculated by ab initio method. The theoretical predictions supported that the most stable isomers of a non-stoichiometric cluster Li_nF_n−1 (n = 3 and n = 4) in which the excess electron localizes on a specific site have a “segregated” electronic structure composed of the metallic part and ionic part.     

Enhancing epitaxial SixC1 − x deposition by adding Ge

In this work, a possible way to enhance the epitaxial growth of metastable, tensile strained Si_xC_1 − x layers by the addition of germanium is demonstrated. During ultra-high vacuum chemical vapor deposition growth, the co-mixing of germane to the Si_xC_1 − x precursors was found to enhance the growth rate by a factor of ~ 3 compared to the growth of pure Si_xC_1 − x. Furthermore, an increase of the amount of substitutional incorporated carbon has been observed. Selective Si_xGe_yC_{1 − x − y} deposition processes utilizing a cyclic deposition were developed to integrate epitaxial tensile strained layers into source and drain areas of n-channel transistors.