A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

In the past ten years we have witnessed a revival of, and subsequent rapid expansion in, the research on zinc oxide (ZnO) as a semiconductor. Being initially considered as a substrate for GaN and related alloys, the availability of high-quality large bulk single crystals, the strong luminescence demonstrated in optically pumped lasers and the prospects of gaining control over its electrical conductivity have led a large number of groups to turn their research for electronic and photonic devices to ZnO in its own right. The high electron mobility, high thermal conductivity, wide and direct band gap and large exciton binding energy make ZnO suitable for a wide range of devices, including transparent thin-film transistors, photodetectors, light-emitting diodes and laser diodes that operate in the blue and ultraviolet region of the spectrum. In spite of the recent rapid developments, controlling the electrical conductivity of ZnO has remained a major challenge. While a number of research groups have reported achieving p-type ZnO, there are still problems concerning the reproducibility of the results and the stability of the p-type conductivity. Even the cause of the commonly observed unintentional n-type conductivity in as-grown ZnO is still under debate. One approach to address these issues consists of growing high-quality single crystalline bulk and thin films in which the concentrations of impurities and intrinsic defects are controlled. In this review we discuss the status of ZnO as a semiconductor. We first discuss the growth of bulk and epitaxial films, growth conditions and their influence on the incorporation of native defects and impurities. We then present the theory of doping and native defects in ZnO based on density-functional calculations, discussing the stability and electronic structure of native point defects and impurities and their influence on the electrical conductivity and optical properties of ZnO. We pay special attention to the possible causes of the unintentional n-type conductivity, emphasize the role of impurities, critically review the current status of p-type doping and address possible routes to controlling the electrical conductivity in ZnO. Finally, we discuss band-gap engineering using MgZnO and CdZnO alloys.

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Fundamentals of zinc oxide as a semiconductor

BHJ solar cells are typically fabricated with a transparent conductive anode (e.g. indium tin oxide, ITO), a low-work-function metal cathode (e.g., Al, Ca), and an active layer (a mixture of conjugated polymer and fullerene derivative) sandwiched between the anode and cathode. The BHJ layer and cathode dramatically affect the stability. In particular, the cathode is susceptible to degradation by oxygen and water vapor. Poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is often used as an anode buffer layer. Long-term stability is a problem because PEDOT:PSS is hygroscopic and acidic. [ 17–21 ]

Inverted Polymer Solar Cells Integrated with a Low‐Temperature‐Annealed Sol‐Gel‐Derived ZnO Film as an Electron Transport Layer

Chemical vapour deposition of coatings

The present invention provides a heterocyclic compound and an organic light-emitting device including the heterocyclic compound. The organic light-emitting devices using the heterocyclic compounds have high-efficiency, low driving voltage, high luminance and long lifespan.

Organic light-emitting device

Sol-gel synthesis of ZnO thin films

White organic light emitting devices (WOLEDs) are being considered as substitutes for conventional white light sources. They are efficient solid-state lighting sources and their power efficiencies have surpassed those of the incandescent light sources, especially due to recent improvement in device architectures, molecular engineering in synthesis of new materials and the incorporation of electrophosphorescent emitters. This paper reviews the various approaches to achieve white light emission from organic light emitting diodes (OLEDs), their advantages, disadvantages and recent progress. The device architecture and problems related to various device designs have been discussed.

https://iopscience.iop.org/article/10.1088/0268-1242/21/7/R01/pdf

White organic LEDs and their recent advancements

BaTiO3 thin films having a perovskite structure were deposited onto stainless steel and fused quartz substrates by sol‐gel processing. Crystalline, transparent, and crack‐free films of 5000 A thickness were fabricated by spinning and post‐deposition annealing at a temperature of 600 °C. Ferroelectric properties were confirmed by P‐E hysteresis loops. The dielectric constant and optical transmission were also measured.

Structural and optical properties of sol-gel-processed BaTiO3 ferroelectric thin films

Transparent smooth and crack‐free BaTiO3 thin films were deposited on stainless steel, fused silica, platinum plates, and platinized silicon wafers (100) using the sol‐gel process. Barium 2‐ethyl hexanoate and titanium isopropoxide were used as precursors. Annealing of the films at 750 °C for 2 h was necessary to get polycrystalline films. The electrical properties of the films prepared on stainless‐steel substrates showed an electrode barrier effect whereas those prepared on platinum substrates were susceptible to ambient atmospheric humidity. However, films grown on platinum substrates and measured under dry conditions showed very good electrical properties. Ferroelectric hysteresis and C‐V characteristics were also studied on these films.

Dielectric and ferroelectric properties of BaTiO3 thin films grown by the sol‐gel process

Transparent and crackfree SrTiO3 thin films were deposited on silicon wafers, fused silica, and stainless‐steel substrates by sol‐gel technique. Strontium ethyl hexanoate and titanium isopropoxide were used as starting materials. The surface topology of the films were studied by electron micrography and the structural properties by x‐ray diffraction. The refractive index and band gap were measured by optical transmission and absorption spectroscopy. The films show very low leakage current and nearly temperature independent dielectric constant at high frequencies. The dielectric constant and loss factor at 1 kHz at room temperature were 131 and 0.022, respectively. The frequency dependent ac conductivity has been explained on the basis of potential barriers formed by the charge carriers trapped at intercrystalline regions.

Modeeparampil N. Kamalasanan

Papers

Sol-gel synthesis of ZnO thin films

White organic LEDs and their recent advancements

Structural and optical properties of sol-gel-processed BaTiO3 ferroelectric thin films

Dielectric and ferroelectric properties of BaTiO3 thin films grown by the sol‐gel process

Structural, optical, and dielectric properties of sol-gel derived SrTiO3 thin films