Nano ZrO2 reinforced cellulose incorporated polyethylmethacrylate/polyvinyl alcohol composite films as semiconducting packaging materials

A simple in situ polymerization process is used to synthesize nanocomposite films with incorporation of cellulose and nano ZrO₂ (PEMA/PVA-C@ZrO₂). The change in structural, morphological, and functional properties are noticed due to combine effect of cellulose and zirconia which is studied by FTIR, XRD, XPS, FESEM, HRTEM, DLS, and AFM. The distribution of particle in the film is determined from dynamic light scattering (DLS). It is found that, dielectric permittivity is increased with percolation at 3 wt% of the nano ZrO₂. Further, the dielectric permittivity (ε') value is found to be 110 at 1 Hz with a low dielectric loss (Tan δ = 1.74) and an optimum dielectric permittivity is 172 at 1 Hz for 4 wt% loading of nano ZrO₂. Mechanical and thermal characteristics of the as-synthesized films are improved due to interfacial adhesion between zirconia and polymeric matrix. The chemical resistance, biodegradable characteristics, and refractive index of the nanocomposite films are also measured. It is noticed that, the barrier properties are increased by 20-folds due to the synergistic combination of nano ZrO₂ and cellulose with polymeric matrix. The enhancement in barrier properties with improved dielectric permittivity can enable the as-synthesized films for semiconducting packaging applications.     

Photoelectrochemical analysis of the effects of pH and sulfate ions on the structure and the composition of the passive film formed on Fe-20Cr-15Ni alloy

The effects of pH and sulfate ions on the structure and compositions of the passive film formed on Fe-20Cr- 15Ni were examined using a photoelectrochemical technique and Mott-Schottky analysis. The photocurrent spectra for the passive film formed on Fe-20Cr-15Ni in the buffer solutions are composed of two spectral components, one of which is generated from Cr-substituted γ-Fe₂O₃ and the other of which is generated from NiO. However, the passive film formed in sulfate solutions showed only the photocurrent spectrum of Cr-substituted γ-Fe₂O₃, suggesting that the formation of NiO in the passive film is suppressed because of a severe selective dissolution of Ni in the presence of sulfate ions. Mott-Schottky plots confirmed that the base structure of the passive film on Fe-20Cr-15Ni is n-type (Cr, Ni)-substituted γ-Fe₂O₃ regardless of solution pH and sulfate ions. The photocurrent intensity, flat band potential, and donor density for the passive film varied depending on the solution pH or the presence of sulfate ions in the solution, due primarily to the Cr enrichment in the film caused by the preferential dissolution of Fe and Ni that is more appreciable in highly acidic solutions containing sulfate ions.     

Polymer electronic materials: a review of charge transport

This article presents an overview of the charge transport phenomenon in semiconducting polymer materials. In these disordered systems both intrinsic and extrinsic parameters play significant roles. In general, π‐electron delocalization, interchain interaction, band gap, carrier density, extent of disorder, morphology and processing of materials determine the electrical and optical properties. The chemical structure, especially the role of side groups, is quite important in both physical and processing properties. The nature of charge carriers and their role in charge transport depend on the structure and morphology of the system. Hence in several semiconducting polymer devices, the correlations among structure, morphology and transport are rather strong. The dependence of carrier mobility on temperature and electric field needs to be understood in the framework of competing models based on carrier hopping, trapping/detrapping and tunneling. Exactly what determines the dispersive/nondispersive, polaronic and correlative transport regimes is yet to be quantified. An understanding of the carrier mobility in semiconducting polymers is necessary to optimize the performance of polymeric electronic devices. Copyright © 2006 Society of Chemical Industry     

Changes in Electrical Characteristics of ZnO Thin Films Due to Environmental Factors

The impact of light and controlled gas ambient on the electrical characteristics of ZnO:P grown by pulsed laser deposition (PLD) is investigated with temperature-dependent Hall-effect and photo-Hall-effect using above-bandgap light. Exposure to blue/ultraviolet (UV) light results in long-lived persistent photoconductivity (PPC) effects dominated by electron conduction. However, these persistent effects can be largely reversed by exposing the sample to a controlled ambient of dry O₂ gas. These O₂-induced changes in the electronic properties persist in vacuum up to at least 400 K. Exposure to dry N₂ gas following blue/UV light has no effect on the observed PPC characteristics. The implications of these effects on the preparation of p-type ZnO will be discussed.     

钇钡铜氧半导体薄膜的宽光谱响应特性

对以 Si为衬底的钇钡铜氧 (分子式 :Y1 Ba2 Cu3O7-δ　δ≥ 0 .5 ,简称 :YBCO)半导体薄膜的宽光谱响应特性进行了研究 .采用该薄膜作灵敏元的单元测辐射热计分别对红外波段 (1— 15μm)、亚毫米波段 (5个波长 )及毫米波 (3m m )进行光谱响应测试 ,结果表明这种半导体探测器不仅在红外波段 ,而且在亚毫米波甚至毫米波段都有良好的响应特性 .该薄膜是继 VO2 薄膜之后用于非制冷红外焦平面的一种新材料     

Growth and optical properties of gallium nitride nanowires produced via different routes

Several vapor phase processes for the preparation of GaN nanowires, such as chemical vapor deposition (CVD), direct reaction (DR), and hydride vapor phase epitaxial growth (HVPE), have been previously reported. To determine the most appropriate route for fabrication and engineering of GaN nanowires, we prepared nanowires via the three aforementioned routes and characterized their microstructures and photoluminescence (PL) properties. All prepared nanowires were single-crystalline, whowing well-defined crystal structure in X-ray diffraction and transmission electron microscopic analyses. However, high-quality nanowires could most readily be obtained by DR. Large-scale and selective area growth of nanowires could most readily be achieved by CVD and HVPE. PL spectra for the nanowires prepared by HVPE showed a red-shifted center wavelength and wider full width-half maximum (FWHM) value as compared to those prepared by DR or CVD. This indicates the presence of unknown impurities and/or defects in the nanowires prepared by HVPE. Our results indicate that high-quality nanowires can be prepared by DR and CVD, while large-scale selective growth can be achieved by CVD and HVPE.     

Recent Progress in Obtaining Semiconducting Single‐Walled Carbon Nanotubes for Transistor Applications

High purity semiconducting single‐walled carbon nanotubes (s‐SWCNTs) with a narrow diameter distribution are required for high‐performance transistors. Achieving this goal is extremely challenging because the as‐grown material contains mixtures of s‐SWCNTs and metallic‐ (m‐) SWCNTs with wide diameter distributions, typically inadequate for integrated circuits. Since 2000, numerous ex situ methods have been proposed to improve the purity of the s‐SWCNTs. The majority of these techniques fail to maintain the quality and integrity of the s‐SWCNTs with a few notable exceptions. Here, the progress in realizing high purity s‐SWCNTs in as‐grown and post‐processed materials is highlighted. A comparison of transistor parameters (such as on/off ratio and field‐effect mobility) obtained from test structures establishes the effectiveness of various methods and suggests opportunities for future improvements.     

Signatures of Quantized Energy States in Solution‐Processed Ultrathin Layers of Metal‐Oxide Semiconductors and Their Devices

Physical phenomena such as energy quantization have to‐date been overlooked in solution‐processed inorganic semiconducting layers, owing to heterogeneity in layer thickness uniformity unlike some of their vacuum‐deposited counterparts. Recent reports of the growth of uniform, ultrathin (<5 nm) metal‐oxide semiconductors from solution, however, have potentially opened the door to such phenomena manifesting themselves. Here, a theoretical framework is developed for energy quantization in inorganic semiconductor layers with appreciable surface roughness, as compared to the mean layer thickness, and present experimental evidence of the existence of quantized energy states in spin‐cast layers of zinc oxide (ZnO). As‐grown ZnO layers are found to be remarkably continuous and uniform with controllable thicknesses in the range 2–24 nm and exhibit a characteristic widening of the energy bandgap with reducing thickness in agreement with theoretical predictions. Using sequentially spin‐cast layers of ZnO as the bulk semiconductor and quantum well materials, and gallium oxide or organic self‐assembled monolayers as the barrier materials, two terminal electronic devices are demonstrated, the current–voltage characteristics of which resemble closely those of double‐barrier resonant‐tunneling diodes. As‐fabricated all‐oxide/hybrid devices exhibit a characteristic negative‐differential conductance region with peak‐to‐valley ratios in the range 2–7.