Structure dependence of second harmonic generation in asymmetricquantum-well structures

Second harmonic generation in stepped asymmetric quantum wells (AQW) is discussed and shown to depend strongly on several controllable AQW parameters. The influence of inter-subband absorption is also investigated. It is demonstrated that with appropriate choice of semiconductor materials and precise bandgap engineering, optimized devices may be developed for a given input laser frequency     

TiOx interlayer characterization for sol–gel derived Pb(Zr, Ti)O3 thin films on titanium foil

Pb(Zr, Ti)O₃ films were prepared on titanium foil using sol–gel processing. The films were of large area, crack-free, uniform, with perovskite structure and exhibiting strong adhesion to the titanium foil substrate. Films and the interface region between the film and the substrate were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and dielectric property measurements. The measurements revealed the formation of a TiO_x layer at the interface between the film and the foil. The thickness of the TiO_x interlayer increases with increasing annealing temperature, and was amorphous when annealed below 600 °C. The dielectric properties of films depend on the thickness of the TiO_x interlayer. Films on Ti foil with dielectric constant of 200–400, dielectric loss <5%, leakage current of <1×10^–7 A cm^–2 at 100 kV cm^–1 and breakdown field strength of 0.6–1.13 MV cm^–1 were demonstrated. The TiO_x interlayer resulted in asymmetric C–V hysterisis behavior attributed to trapped charge in the vicinity of the TiO_x interlayer and to elastic mismatch strain.     

Hydrogen absorption in Pd thin-films

Hydrogen absorption isotherms for Pd thin films were modeled at atomistic scale by Monte Carlo (MC) simulation in the TPμN ensamble and by Molecular Dynamics (MD) simulations at 300 K. The interaction among atoms was modeled by embedded atom method (EAM) potentials. Simulated samples consisted of monocrystalline nanofilms with different thickness (2–8 nm) and two crystallographic surface orientations, (001) and (111). The isotherms were compared to bulk Pd and a few available experimental results. Instead of the plateau corresponding to the α-β PdH equilibrium in the bulk, the isotherms at nano-films show a two-plateaux behavior: a small one corresponding to a surface–subsurface hydride formation, and a larger one for the subsequent bulk hydride formation. This is strongly correlated with the atomic stress distribution induced within the thin film. The equilibrium pressures at the isotherms depend on the thin-film thickness, with pressure being larger for thicker films. The isotherms of the (001) films display lower equilibrium pressures than those for (111) films.     

Modeling and prospects for a solid-state quantum computer

Traditional approaches to computing based on nanoelectronics will likely need to embrace quantum phenomena over the coming decade with the trend toward decreasing on-chip feature sizes. Concurrently, as resonant tunneling and single-electron-based quantum devices become more prevalent, one can expect quantum computing and quantum information based on appropriate isolated and coupled low-dimensional semiconducting systems to attract more attention. We report on work aimed at understanding the limitations on how to implement practical quantum information systems that counter the natural effects of decoherence and offer suitable approaches to control of such systems. The emphasis in this paper is on open systems. We close the paper with some remarks on possible practical schemes for fabricating such systems and identify some of the challenges that lie ahead in realizing these schemes.     

A study of replanted permanent teeth in different age groups

In the inpatient treatment of acute psychiatric episodes in children and adolescents, the psychiatrist must set up an initial treatment plan incorporating one or more psychotherapeutic modalities and adapt this plan to the patient's clinical course. This article summarises the clinical experience of a model unit at the University of Heidelberg, the result of a collaboration between the Department of General Psychiatry and the Department of Child and Adolescent Psychiatry at the Clinic of Psychiatry. A series of 116 adolescent admissions was reviewed for clinical diagnosis, the nature and frequency of psychotherapeutic modalities, and the role of family involvement in patient care. Differential and adaptative approaches to the selection of treatment modalities in the context of an acute care setting are emphasised.     

Applications for advanced solid-state lamps

Since lighting accounts for a large fraction of electrical usage in the industrial sector, the energy efficiency of lamp systems is of major interest. One promising technology which has the potential for use in specialised energy-efficieny lighting applications is solid-state lamp technology. There are many reasons solid-state lamps may be especially useful for new applications. They exhibit long lifetimes, in the order of 100000 hours. Coupled with the ruggedness inherent in solid-state devices, this indicates usefulness for low maintenance applications. Fast response times also make them ideal for some applications. This review surveys the state-of-the-art in solid-state semiconductor lamp technology, with a focus on the potential for such applications, and on energy efficiency and brightness considerations. The different types of solid state light source are described: LED, diode lasers, superluminescent diodes and electroluminescent diodes. Their operating characteristics are discussed and the following applications described: illuminated signs, exit-signs, traffic control lights, airport runway lighting, vision sensors illumination, spotlighting, interactive and fast adaptive lighting and fibre-optic channeled lighting     

Defect studies of ZnSe nanowires

During the synthesis of ZnSe nanowires various point and extended defects can form, leading to observed stacking faults and twinning defects, and strong defect related emission in photoluminescence spectra. In this paper, we report on the development of a simple thermodynamic model for estimating the defect concentration in ZnSe nanowires grown under varying Se vapour pressure and for explaining the results of our experimental findings. Positron annihilation spectroscopy was used successfully for the first time for nanowires and the results support predictions from the defect model as well as agreeing well with our structural and optical characterization results. Under very high Se vapour pressure, Se nodules were observed to form on the sidewalls of the nanowire, indicating that beyond a limit, excess Se will begin to precipitate out of the liquid alloy droplet in the vapour-liquid-solid growth of nanowires.     

Barium Titanate Inverted Opals—Synthesis,Characterization, and Optical Properties

Barium titanate inverted opals with powder and film morphologies were synthesized from barium ethoxide and titanium isopropoxide in the interstitial spaces of a polystyrene opal. This procedure involves infiltration of precursors into the interstices of the polystyrene opal template followed by hydrolytic polycondensation of the precursors to amorphous barium titanate and removal of the polystyrene opal by solvent extraction or calcination. In‐situ variable temperature powder X‐ray diffraction and micro‐Raman spectroscopy allow one to observe the thermally induced transformation of the as‐synthesized amorphous barium titanate inverted opal to the nanocrystalline form. In this way, a nanocrystalline barium titanate inverted opal can be engineered as either the cubic or tetragonal polymorph. Control of this process is key to the practical realization of a room‐temperature stable ferroelectric barium titanate inverted opal that can be thermally tuned through the ferroelectric–paraelectric transition around the Curie temperature. Optical characterization demonstrated photonic crystal behavior of the inverted barium titanate opals and results were in good agreement with photonic band structure calculations. The synthesis of optical quality ferroelectric barium titanate inverted opals provides an opportunity to electrically and optically engineer the photonic band structure and the possibility of developing tunable three‐dimensional photonic crystal devices.