Electrical and sensory properties of zinc oxide – porous silicon nanosystems

Abstract

Zinc oxide nanostructures have been grown by electrochemical deposition on porous silicon–silicon substrate. The photoelectric and sensory properties of the obtained ZnO–porous silicon nanosystems were investigated in both DC and AC regimes. The obtained structures were characterized by photosensitivity in the 400–1100?nm wavelength range and by high sensitivity to moisture. Increase of relative humidity resulted in significant decrease of the electrical resistance and increase of the capacitance of the hybrid structures. To estimate the sensory properties of the ZnO–porous silicon nanostructures their adsorption sensitivity and dynamic characteristics were analyzed. Discovered features of the charge transport processes broaden the prospects of the semiconductor nanosystems application in gas sensors and photodetectors.     

Design and application of dielectric distributed Bragg back reflector in thin-film silicon solar cells

A dielectric distributed Bragg reflector (DBR) formed by four pairs of hydrogenated amorphous silicon/silicon nitride layers is used as the back reflector in thin-film silicon solar cells. The DBR was designed to perform in a broad wavelength range with the peak reflectance at 600 nm. The DBR was fabricated at low substrate temperature (172 °C) and applied at the rear side of flat and textured amorphous silicon single-junction solar cells in both superstrate (pin) and substrate (nip) configurations. The spectral response and electrical I–V characteristics were measured. Solar cells with optimized DBR exhibit an enhanced external quantum efficiency in the long wavelength range and the electrical performance is comparable to solar cells having conventional Ag back reflector.     

Photosensitive Structures of Conjugated Polymer - Porous Silicon

The photosensitive hybrid structures poly-3,4-ethylenedioxythiophene (PEDOT)– porous silicon (PS)–n-Si are fabricated. Current-voltage characteristics of the obtained structures are investigated. It is shown that PS surface modification by PEDOT conjugated polymer gives rise to the appearance of a pronounced rectifying effect on the current-voltage characteristics. Spectral characteristics of photoresponse in the 450–1100 nm wavelength range, its temperature dependence in the 125–325 K range, and energy characteristics of the hybrid photovoltaic structures are studied. We propose possible mechanisms of the photoelectric processes in the hybrid structures PEDOT–PS–n-Si.     

Preparation of New Fibrous Organic-Inorganic Layered Compounds Derived from Zinc Hydroxyde

Abstract

A new preparation method of the fibrous organic-inorganic nanohybrids was established by the reaction of Zn(OH)₂ with various organic carboxylic acids. Interlayer spacings of the reaction products of Zn(OH)₂ with benzoic acid and p-phenyl azobenzoic acid were 1.46 and 2.04 nm, and these reaction products have layered structure. In IR spectra, new peaks of RCOO-Zn band appeared at around 1400 cm^?1 and 1550 cm^?1 indicating that hydroxyl groups reacted with organic carboxylic acids. SEM images of these reaction products showed fibrous morphology. The TEM image showed that the layer structure was constructed along the fiber direction.     

Spectral and barrier properties of heterocomposites based on poly (para-phenylene) disposed between the silicon films

ABSTRACT

Within the framework of the methods of the electron density functional and the ab initio pseudopotential, we have obtained the spatial distributions of the valence electrons density, the electron energy spectra and the Coulomb potential for heterocomposites based on poly (para-phenylene) and carbon nanotube disposed between the silicon films.

?It was revealed that the maximal value of the potential barrier was noticed in a composite material from polyparaphenylene filaments placed between silicon films and completed with carbon nanotubes perpendicularly to the surface of the silicon films and along them.     

Structural and optical properties of thin films prepared from surface modified ZrO2

This paper describes the preparation and characterization of ZrO₂ thin films deposited on silicon wafer by spin coating method. Nanocrystalline ZrO₂ was synthesized by hydrothermal method using zirconium (IV)-n-propoxide as a precursor material. Surface of the ZrO₂ particles was then modified with 2-acetoacetoxyethyl methacrylate used as a copolymer for coatings. The optical properties, nanostructure and surface morphology of the thin films prepared from surface modified ZrO₂ nanoparticles were examined by optical spectroscopy, X-ray diffraction and scanning electron microscopy, respectively. It was found that the films deposited on silicon wafer have crystalline structure of monoclinic (111) at temperature of 150 °C. It was observed that films depict very dense material that does not present any granular or columnar structure. It was found that optical transparency of thin ZrO₂ films distributed in the range of 30-40 percent in the spectral range 400-800 nm. Refractive index of ZrO₂ films were determined as functions of ZrO₂ content and it was found that the refractive index increases from 1.547 to 1.643 with increased ZrO₂ content.     

Synthesis and crystal structure elucidation of 1-(4-fluorobenzyl)-2-(4-cyanophenyl)-1H- benzimidazole-5-carbonitrile

The synthesis and spectral identification of 1-(4-fluorobenzyl)-2-(4-cyanophenyl)-1H-benzimidazole-5-carbonitrile (1) have been reported. IR, ¹H NMR, and EI mass spectral analysis were used for its spectral identification. The structure of 1 was confirmed by X-ray crystallographic studies. Intramolecular hydrogen bond occurs between the imidazole nitrogen and one of hydrogen of the florobenzene. The crystal packing is governed by C–HN intermolecular hydrogen bonds. The molecular structure observed in crystal and the optimised geometries at the HF level by doing semi-empirical and ab initio calculations were compared.     

Synthesis and characterization of a polyacetylene derivative: Poly(N-methylpropargylamine)

ABSTRACT

The polymerization of N-methylpropargylamine was carried out by var-ious transition metal catalysts. The polymerizations of N-methylpropar-gylamine using the Pd, Pt, and Ru chlorides proceeded well in mild homogeneous manner to give the corresponding polymers in moderate yields. The chemical structure of poly(N-methylpropargylamine) was characterized by such instrumental methods as NMR (¹H-, ¹³C-), IR, UV-visible spectroscopies, and elemental analysis to have the designed conjugated polymer structure. The photoluminescence peak of poly(N-methylpropargylamine) was observed at 444 nm, which is corresponded to the photon energy of 2.79 eV. The electrochemical properties were also measured and discussed.     

MBE growth and transport properties of silicon δ-doped GaAs/AlAs quantum well structures for terahertz frequency detection

We present the electrical characterization of n-type GaAs/AlAs multiple quantum well (MQW) structures designed for terahertz (THz) radiation sensing at cryogenic temperatures. The samples were grown by solid source molecular beam epitaxy (MBE) and were δ-doped with silicon atoms at each potential well center. Temperature dependent Hall effect data show that (i) the conduction in these planar doped structures is thermally activated below 180 K, (ii) the free carriers sheet densities are near the metal–insulator transition, and (iii) the low temperature mobility is controlled by ionized impurities scattering. The study of the magneto-transport properties at 1.3 K further indicates that only the fundamental electronic sub-band of the two-dimensional electronic gas is populated. The MQW samples were then processed into lateral mesa-shaped photodetectors to investigate their spectral response in the THz frequency range. The preliminary experimental results for the proposed detection scheme, which involves transitions in the confined shallow donor impurity states, are described.     

Morphology,composition, structure and optical properties of thermally annealed Cu2O thin films prepared by reactive DC sputtering method

Abstract

Thin films copper oxides are perspective materials for many optoelectronic applications, including photovoltaics. The samples were deposited on glass and silicon substrates by magnetron sputtering method using Modular Platform PREVAC. After deposition the samples were thermally treated by annealing in oxygen atmosphere for 60?min at 450?°C. Morphology confirms that all the films have crystalline structure. Optical measurements show that the films have wide band gap within the range 2.20÷2.48?eV before and 2.03÷2.40?eV after annealing. The article presents the discussion about the influence of annealing on Cu₂O thin film parameters.     

Ultraviolet Photoelectron Spectra of Potassium Dosed Higher Fullerenes

Abstract

Ultraviolet photoelectron spectra of potassium dosed higher fullerenes are measured with a synchrotron radiation light source. Potassium dosing to higher fullerenes brings a new structure between the spectral onset of pristine fullerenes and the Fermi level. As the spectral edge of the new structure does not cross the Fermi level, potassium dosed higher fullerenes are not metallic but semiconductive. When the potassium is excessively dosed to the fullerenes, the lower binding energy structures above 5 eV become faint. In contrast to this phenomenon, four distinct structures appear between 5 and 14 eV.     

Effect of plasma carrier gas on the moisture barrier properties of plasma-enhanced chemical vapor deposited (PECVD) polyorganosiloxane thin film

Abstract

A polyorganosiloxane thin film was deposited on an optically transparent poly(ethylene 2,6-naphthalate) (PEN) film using plasma-enhanced chemical vapor deposition (PECVD) at room temperature to improve the moisture barrier property of the PEN film. In the PECVD process, hexamethyldisiloxane (HMDSO) was used as the monomer. Argon or oxygen and their mixture gases were used as the plasma carrier gas. Poly(HMDSO) thin film was successfully deposited through plasma-induced radical polymerization reaction on the surface of PEN film. It was observed that the mixture ratio of argon-oxygen carrier gas significantly affected the surface and the moisture barrier properties of the resulting poly(HMDSO) film. Chemical structures of the poly(HMDSO) were confirmed using FT-IR analysis. Surface properties of the poly(HMDSO) thin film were investigated by water contact angle measurement and atomic force microscopy (AFM). Water vapor transmission rate (WVTR) value was obtained by an electrical calcium test (Ca test) at 85?°C and 85% relative humidity condition. It was confirmed that the poly(HMDSO) thin film exhibited excellent water vapor barrier capability. WVTR value of the PEN film coated with poly(HMDSO) deposited with a mixture of argon and oxygen (Ar: O₂ = 2: 8) was 5.09?g/m²-day, which is much lower than 18.4?g/m²-day of a bare PEN film.     

Liquid crystal material with gold nanoparticles as optical sensors active medium for the amino acids detection

Abstract

In the article, the possibility of using the cholesteric liquid crystal mixture doped by the gold nanoparticles as an active medium of optical amino acid sensors is shown. The BLO-62 and the 5CB were used as a cholesteric liquid crystal and a nematic liquid crystal correspondingly. This mixture was doped by the gold nanoparticles. The method of gold nanoparticles synthesis is considered and their parameters are determined. Studies on the spectral characteristics of the investigated materials have shown that the addition of gold nanoparticles to the system leads to a significant decreasing in the spectral characteristic steepness and give the possibility of expanding the measurement range of amino acid concentration.     

Development of porous silicon matrix and characteristics of porous silicon/tin oxide structures

Porous silicon (PSi) was formed at different current densities in the range of 5-60 mA/cm² by electrochemical anodized etching in HF for different durations in the range of 10-30 min. Above this PSi structure, SnO₂ films were deposited by the spin coating technique. The PSi has been characterized by X-ray diffraction studies. Peaks pertaining to PSi along with those corresponding to SnO₂ are observed. Atomic force microscopic studies indicate that very fine needle like silicon nanostructures are observed which is the result of the best PSi structure formed at 30 mA/cm². For the SnO₂ covered PSi structures, larger grains are observed with uniform coverage. The PSi samples prepared at current densities above and below 30 mA/cm² show PL spectra with asymmetric and overlapped peaks. The PL profile of thin SnO₂ film coated on PSi shows a peak at 633 nm and a small hump at about 660 nm.     

Local structure around phosphorus and silicon in the CaO–SiO2–PO2.5 system

The local structure of phosphorus and silicon in the molten CaO–SiO₂–PO_2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The ³¹P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO₄^3?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the ²⁹Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO₂ ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qⁿ (Qⁿ means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].     

New Simple Model of a Liquid Crystal Light Valve

Abstract

A liquid crystal light valve, using a heterojunction indium oxide/silicon of high resistivity (10,000 Ω.cm) and based on the cholesteric-nematic transition is described. The characteristics of this device are determined: optimum voltage to be applied to the cell in order to produce the cholestericnematic phase change, incident light power sensitivity, spectral response, rise and decay times. It has been shown that this light valve has an incident power sensitivity of less than 10 μW.cm^?2 which passes through a maximum for an incident wavelength of 0.8 μm. This valve can be used in the near infrared; rise times of a few tens of ms are obtained.     

Vegetal nanoclusters in hybrid silica films prepared by sol-gel spin coating technique

Hybrid sol-gel films containing Rosemary extract nanoclusters embedded into hybrid silica network have been successfully synthesized using the sol-gel procedure by exploiting the template route, in association with an adequate spin-coating method. Formation of film precursor sols and effect of selected amounts of octyl trimethoxysilane and ethyl oleate succinic anhydride into the starting acid sols on the sol-gel product size have been evaluated by dynamic light scattering technique. The spectral characteristics of hybrid organic-inorganic films have shown that the multiple functional groups from Rosemary extract associated with residual Si-OH groups can cause the increase in the degree of physical interaction. The effect of hybrid sols meaning the silica precursors molar ratio and template concentration on the fluorescence of hybrid films has been also investigated. The fluorescence properties of synthesized films were found to be dependent on template and natural extract concentration. A higher amount of template resulted in doubling the fluorescence intensity in the 400-480 nm domain. The microstructural characteristics of the hybrid films revealed by atomic force microscopy have shown a homogeneous surface morphology with cluster-like structure. Hybrid silica films exhibit a periodic structure with cluster size less than 150 nm.     

Electronic structures of silicon nitride revealed by tight binding calculations

A new tight binding (TB) potential model was proposed for determining the electronic structures of ionic-covalent materials. In the TB model, the matrix elements were determined from the atomic characteristics of the crystal. The atomic parameters of the solid were determined based on the general quantum principles and no adjustable parameter was needed. Electronic structures of amorphous silicon nitride (Si₃N₄) were calculated using this method. A good agreement between the calculated and experimental values in terms of fundamental properties such as the position of the valence-band edge, the conduction-band edge, and the energy bandgap were obtained. Charge transfer between the silicon and nitrogen atoms was also precisely calculated in this work.     

Stereochemistry of silicon in oxygen-containing compounds

Specific stereochemical features of silicon in oxygen-containing compounds, including hybrid silicates with all oxygen atoms of SiO_n groups (_n = 4, 5, or 6) entering into the composition of organic anions or molecules, are described by characteristics of Voronoi—Dirichlet polyhedra. It is found that in rutile-like stishovite and post-stishovite phases with the structures similar to those of СаСl₂, α-PbO₂, or pyrite FeS₂, the volume of Voronoi—Dirichlet polyhedra of silicon and oxygen atoms decreases linearly with pressure increasing to 268 GPa. Based on these results, the possibility of formation of new post-stishovite phases is shown, namely, the fluorite-like structure (transition predicted at ~400 GPa) and a body-centered cubic lattice with statistical arrangement of silicon and oxygen atoms (~900 GPa).     

Investigation of the structure and mechanisms of thermal motion in nanostructured undecylenic acid

Abstract

We have compared the structure, phase transitions and the thermal motion mechanisms of the undecylenic acid in bulk and inside a porous matrix using powder X-ray diffraction, calorimetry and IR-spectroscopy methods. The matrix used was a porous silicon with cylindrical pores (D?=?20?nm). The interaction between the walls of the porous silicon and the nanocrystals of the undecylenic acid results in a crystalline structure, which is significantly different from the structure of bulk undecylenic acid. A phase transition in the wall-adjacent layer of the undecylenic acid nanocrystals was shown to take place. The solid-state phase transition temperatures, as well as the melting point, were shown to be lower for nanocrystals. Topological soliton motion mechanism was suggested to explain the thermal motion of the undecylenic acid molecules in the rotator phase.