Porous silicon layers prepared by electrochemical etching for application in silicon thin film solar cells

In this paper, multilayer structures of porous silicon were fabricated by using electrochemical etching and characterized for its optical properties and surface morphology. Samples of monolayer of porous silicon were grown to study the characteristics of porous layer formation with respect to applied current density, etching time and hydrofluoric acid concentrations. Photoluminescence peaks of red emission at wavelength 695 and 650 nm were observed from multilayer porous silicon structures. By atomic force microscopy measurement, hillocks like surface were clearly observed within the host material, which confirmed the formation of pores.     

Effect of solvent volume on the physical properties of undoped and fluorine doped tin oxide films deposited using a low-cost spray technique

Undoped and fluorine doped tin oxide films were deposited from starting solutions having different values of solvent volume (10-50 ml) by employing a low cost and simplified spray technique using perfume atomizer. X-ray diffraction studies showed that there was a change in the preferential orientation from (2 1 1) plane to (1 1 0) plane as the volume of the solvent was increased. The sheet resistance (R_sh) of undoped SnO₂ film was found to be minimum (13.58 KΩ/□) when the solvent volume was lesser (10 ml) and there was a sharp increase in R_sh for higher values of solvent volume. Interestingly, it was observed that while the R_sh increases sharply with the increase in solvent volume for undoped SnO₂ films, it decreases gradually in the case of fluorine doped SnO₂ films. The quantitative analysis of EDAX confirmed that the electrical resistivity of the sprayed tin oxide film was mainly governed by the number of oxygen vacancies and the interstitial incorporation of Sn atoms which in turn was governed by the impinging flux on the hot substrate. The films were found to have good optical characteristics suitable for opto-electronic devices.     

环保型制冷剂R600a制冷系统设计及其维修工艺

大气臭氧层的破坏和温室效应的加剧,是当前世界面临的主要环境问题。文中通过对R600a制冷剂物理化学特性的介绍以及与R12制冷剂的对比,得出在冰箱领域,R600a是一种可以永久替代CFCs的环保型制冷剂,分析了R600a替代R12的制冷系统设计的一些要点,最后基于提高工作效率以及保障操作安全的考虑,阐述了R600a冰箱的维修工艺。     

Diffusion barrier performance of TiVCr alloy film in Cu metallization

In this study, 15 nm-thick sputter-deposited TiVCr alloy thin films were developed as diffusion barrier layers for Cu interconnects. The TiVCr alloy film tends to form a solid solution and a simple crystal structure from the constituted elements. Under TEM, the 15 nm-thick as-deposited TiVCr alloy film was observed to have a dense semi-amorphous or nanocrystalline structure. In conjunction with X-ray diffraction, transmission electron microscopy, and energy-dispersive spectroscopy analyses, the Si/TiVCr/Cu film stack remained stable at a high temperature of 700 °C for 30 min. The electrical resistance of Si/TiVCr/Cu film stack remained as low as the as-deposited value. These indicated that the mixed TiVCr refractory elements’ alloy barrier layer is very beneficial to prevent Cu diffusion.     

Evolution of Zn based high purity phases under NH3 gas atmosphere and their PL properties

We report here the evolution of zinc based high purity phases with novel morphologies such as Zn₃N₂ hollow structures, ZnO nanowires and nanopowders, as well as metallic Zn layered hexagonal microparticles at progressively increased reaction temperature of 600 °C, 700 °C, 800 °C under NH₃ gas atmosphere using Zn powder precursor and keeping all other experimental parameters unchanged. Growth mechanism for Zn₃N₂ obtained by nitridation, ZnO by oxidation and Zn microparticles via thermal evaporation & condensation process are discussed briefly. The as-synthesized products were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM). Photoluminescence (PL) studies have revealed very interesting and infrequently observed emission bands at 378 and 661 nm for Zn₃N₂, 359 and 396 nm for ZnO as well as 389 nm for Zn polyhedral microparticles.     

Theoretical investigation of CO adsorption on TM-doped (MgO)12 (TM = Ni, Pd, Pt) nanotubes

CO adsorption on TM-doped magnesia nanotubes (TM = Ni, Pd and Pt) have been studied by using density functional theory. Our calculation results show that CO favors adsorption on TM-doped magnesia nanotubes in the form of C atom bonding with TM atom. Fukui indices analysis clearly exhibits that doping of impurity TM atom allows for a noticeably enhancement of nucleophilic reactivity ability of magnesia nanotube. The adsorption energies demonstrate that CO molecule is more strongly bound on the 3-fold TM atoms than the 4-fold TM atoms. This finding is well confirmed by TM-C bond length, charge transfer and C-O vibrational frequency. The high adsorption energy of 2.55 eV is found when CO adsorbs on 3-fold Pt in Pt-doped magnesia nanotubes, implying the kind of the doping TM atom has a significant influence on the chemical reactivity.     

Effect of substrate bias voltage on the structure, electric and dielectric properties of TiO2 thin films by DC magnetron sputtering

Titanium dioxide (TiO₂) films have been deposited on glass and p-silicon (1 0 0) substrates by DC magnetron sputtering technique to investigate their structural, electrical and optical properties. The surface composition of the TiO₂ films has been analyzed by X-ray photoelectron spectroscopy. The TiO₂ films formed on unbiased substrates were amorphous. Application of negative bias voltage to the substrate transformed the amorphous TiO₂ into polycrystalline as confirmed by Raman spectroscopic studies. Thin film capacitors with configuration of Al/TiO₂/p-Si have been fabricated. The leakage current density of unbiased films was 1 × 10⁻⁶ A/cm² at a gate bias voltage of 1.5 V and it was decreased to 1.41 × 10⁻⁷ A/cm² with the increase of substrate bias voltage to −150 V owing to the increase in thickness of interfacial layer of SiO₂. Dielectric properties and AC electrical conductivity of the films were studied at various frequencies for unbiased and biased at −150 V. The capacitance at 1 MHz for unbiased films was 2.42 × 10⁻¹⁰ F and it increased to 5.8 × 10⁻¹⁰ F in the films formed at substrate bias voltage of −150 V. Dielectric constant of TiO₂ films were calculated from capacitance–voltage measurements at 1 MHz frequency. The dielectric constant of unbiased films was 6.2 while those formed at −150 V it increased to 19. The optical band gap of the films decreased from 3.50 to 3.42 eV with the increase of substrate bias voltage from 0 to −150 V.     

Characterization of the hole transport and electrical properties in poly(9,9-dioctylfluorene)

A systematic study of the hole transport and electrical properties in blue-emitting polymers as poly(9,9-dioctylfluorene) (PFO) has been performed. We show that the temperature dependent and thickness dependent current density versus voltage characteristics of PFO hole-only devices can be accurately described using our recently introduced improved mobility model based on both the Arrhenius temperature dependence and non-Arrhenius temperature dependence. Within the improved model, the mobility depends on three important physical quantities: temperature, carrier density, and electric field. For the polymer studied, we find the width of the density of states σ=0.115 eV and the lattice constant a=1.2 nm. Furthermore, we show that the boundary carrier density has an important effect on the current density versus voltage characteristics. Too large or too small values of the boundary carrier density lead to incorrect current density versus voltage characteristics. The numerically calculated carrier density is a decreasing function of distance from the interface. The numerically calculated electric field is an increasing function of distance. Both the maximum of carrier density and minimum of electric field appear near the interface.     

Transport properties of boron-doped single-walled silicon carbide nanotubes

The doped boron (B) atom in silicon carbide nanotube (SiCNT) can substitute carbon or silicon atom, forming two different structures. The transport properties of both B-doped SiCNT structures are investigated by the method combined non-equilibrium Green’s function with density functional theory (DFT). As the bias ranging from 0.8 to 1.0 V, the negative differential resistance (NDR) effect occurs, which is derived from the great difficulty for electrons tunneling from one electrode to another with the increasing of localization of molecular orbital. The high similar transport properties of both B-doped SiCNT indicate that boron is a suitable impurity for fabricating nano-scale SiCNT electronic devices.     

Comparative study on BIS thiourea cadmium acetate crystals using HRXRD, etching, microhardness, UV-visible and dielectric characterizations

〈1 1 1〉 oriented bis thiourea cadmium acetate (BTCA) crystal of diameter 15 mm and length 45 mm was grown for the first time by the unidirectional Sankaranarayanan-Ramasamy (SR) method. The conventional and SR method grown BTCA crystals were characterized by using high-resolution X-ray diffraction (HRXRD), chemical etching, Vickers microhardness, UV-vis, dielectric studies and differential scanning calorimetry. The HRXRD analysis indicates that the crystalline perfection of SR method grown crystal is good without having any low angle internal structural grain boundaries. The transmittance of SR method grown BTCA is 14% higher than that of conventional grown crystal. The dielectric constant was higher and the dielectric loss was less in SR method grown crystal. The crystals grown by SR method possess less dislocation density and higher microhardness.