Low temperature and self catalytic growth of ultrafine ITO nanowires by electron beam evaporation method and their optical and electrical properties

We report the self catalytic growth of Sn-doped indium oxide (ITO) nanowires (NWs) over a large area glass and silicon substrates by electron beam evaporation method at low substrate temperatures of 250-400 degrees C. The ITO NWs growth was carried out without using an additional reactive oxygen gas and a metal catalyst particle. Ultrafine diameter (similar to 10-15 nm) and micron long ITO NWs growth was observed in a temperature window of 300-400 degrees C. Transmission electron microscope studies confirmed single crystalline nature of the NWs and energy dispersive spectroscopy studies on the NWs confirmed that the NWs growth proceeds via self catalytic vapor-liquid-solid (VLS) growth mechanism. ITO nanowire films grown on glass substrates at a substrate temperature of 300-400 degrees C have shown similar to 2-6% reflection and similar to 70-85% transmission in the visible region. Effect of deposition parameters was systematically investigated. The large area growth of ITO nanowire films would find potential applications in the optoelectronic devices. (C) 2014 Elsevier Ltd. All rights reserved.

Design and analysis of integrated optic quadrature phase shift keying modulator

Quadrature phase shift keying (QPSK) is one of the most popular modulation schemes in coherent optical communication systems for data rates in excess of 40 Gbps because of its high spectral efficiency. This paper proposes a simple method of implementing a QPSK modulator in integrated optic (IO) domain. The QPSK modulator is realized using standard IO components, such as Y-branches and electro-optic modulators (EOMs). Design optimization of EOM is carried out considering the fabrication constraints, miniaturization aspects, and simplicity. Also, the interdependency between electrode length, operating voltage, and electrode gap of an EOM has been captured in the form of a family of curves. These plots enable designing of EOMs for custom requirements. An innovative approach has been adopted in demonstrating the operation of IO QPSK modulator in terms of phase data extracted from beam propagation model. The results obtained by this approach have been verified using the conventional interferometric approach. The operation of the proposed IO QPSK modulator is experimentally demonstrated. The design of IO QPSK modulator is taken up as a part of a broader scheme that aims at generation of QPSK modulated microwave signal based on optical heterodyning. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)

Nanostructure Patterning on Flexible Substrates Using Electron Beam Lithography

Patterning nanostructures on flexible substrates plays a key role in the emerging flexible electronics technology. The flexible electronic devices are inexpensive and can be conformed to any shape. The potential applications for such devices are sensors, displays, solar cells, RFID, high-density biochips, optoelectronics etc. E-beam lithography is established as a powerful tool for nanoscale fabrication, but its applicability on insulating flexible substrates is often limited because of surface charging effects. This paper presents the fabrication of nanostructures on insulating flexible substrates using low energy E-beam lithography along with metallic layers for charge dissipation. Nano Structures are patterned on different substrates of materials such as acetate and PET foils. The fabrication process parameters such as the proximity gap of exposure, the exposure dosage and developing conditions have been optimized for each substrate.

Zoledronic acid in combination with alfacalcidol has additive effects on trabecular microarchitecture and mechanical properties in osteopenic ovariectomized rats

We conducted the present study to investigate the therapeutic effects of the antiresorptive agent zoledronic acid (ZOL), alone and in combination with alfacalcidol (ALF), in a rat model of postmenopausal osteoporosis. Female Wistar rats were ovariectomized (OVX) or sham-operated at 3 months of age. Twelve weeks post surgery, rats were randomized into six groups: (1) sham + vehicle, (2) OVX + vehicle, (3) OVX + ZOL (100 mu g/kg, i.v. single dose), (4) OVX + ZOL (50 mu g/kg, i.v. single dose), (5) OVX + ALF (0.5 mu g/kg, oral gauge daily) and (6) OVX + ZOL (50 mu g/kg, i.v. single dose) + ALF (0.5 mu g/kg, oral gauge daily) for 12 weeks. After treatment, we evaluated the mechanical properties of the lumbar vertebra and femoral mid-shaft. Femurs were also tested for bone density, porosity and trabecular micro-architecture. Biochemical markers in serum and urine were also determined. With respect to improvement in the mechanical strength of the lumbar spine and the femoral mid-shaft, the combination treatment of ZOL and ALF was more effective than each administered as a monotherapy. Moreover, combination therapy using ZOL and ALF preserved the trabecular micro-architecture and cortical bone porosity. Furthermore, the combination treatment of ZOL and ALF corrected the decrease in serum calcium and increase in serum alkaline phosphatase and the tartarate-resistant acid phosphatase level better than single-drug therapy using ZOL or ALF in OVX rats. In addition, the combination treatment of ZOL and ALF corrected the increase in urine calcium, phosphorous and creatinine levels better than single-drug therapy using ZOL or ALF in OVX rats. These data suggest that the combination treatment of ZOL and ALF has a therapeutic advantage over each monotherapy for the treatment of osteoporosis.

Atom Lithography

We review the two kinds of forces that near-resonant light exerts on atoms the spontaneous force that is used for laser cooling, and the stimulated force that is used for coherent manipulation of atoms. We will discuss an experiment where laser cooling is used to collimate an atomic beam of sodium atoms, and the stimulated force within one period of a one-dimensional standing wave is used as a lens to focus the atoms to a narrow line about 20 nm wide. This kind of atom lithography is an example of the general field of atom optics in which light is used to manipulate atoms.

Crack stability in edge-notched clamped beam specimens: modeling and experiments

Stability of a fracture toughness testing geometry is important to determine the crack trajectory and R-curve behavior of the specimen. Few configurations provide for inherent geometric stability, especially when the specimen being tested is brittle. We propose a new geometrical construction called the single edge notched clamped bend specimen (SENCB), a modified form of three point bending, yielding stable cracking under load control. It is shown to be particularly suitable for small-scale structures which cannot be made free-standing, (e.g., thin films, coatings). The SENCB is elastically clamped at the two ends to its parent material. A notch is inserted at the bottom center and loaded in bending, to fracture. Numerical simulations are carried out through extended finite element method to derive the geometrical factor f(a/W) and for different beam dimensions. Experimental corroborations of the FEM results are carried out on both micro-scale and macro-scale brittle specimens. A plot of vs a/W, is shown to rise initially and fall off, beyond a critical a/W ratio. The difference between conventional SENB and SENCB is highlighted in terms of and FEM simulated stress contours across the beam cross-section. The `s of bulk NiAl and Si determined experimentally are shown to match closely with literature values. Crack stability and R-curve effect is demonstrated in a PtNiAl bond coat sample and compared with predicted crack trajectories from the simulations. The stability of SENCB is shown for a critical range of a/W ratios, proving that it can be used to get controlled crack growth even in brittle samples under load control.

Application of lateral photovoltage towards contactless light beam induced current measurements and its dependence on the finite beam size

The nature of the signal due to light beam induced current (LBIC) at the remote contacts is verified as a lateral photovoltage for non-uniformly illuminated planar p-n junction devices; simulation and experimental results are presented. The limitations imposed by the ohmic contacts are successfully overcome by the introduction of capacitively coupled remote contacts, which yield similar results without any significant loss in the estimated material and device parameters. It is observed that the LBIC measurements introduce artefacts such as shift in peak position with increasing laser power. Simulation of LBIC signal as a function of characteristic length L-c of photo-generated carriers and for different beam diameters has resulted in the observed peak shifts, thus attributed to the finite size of the beam. Further, the idea of capacitively coupled contacts has been extended to contactless measurements using pressure contacts with an oxidized aluminium electrodes. This technique avoids the contagious sample processing steps, which may introduce unintentional defects and contaminants into the material and devices under observation. Thus, we present here, the remote contact LBIC as a practically non-destructive tool in the evaluation of device parameters and welcome its use during fabrication steps. (C) 2014 AIP Publishing LLC.

Cold beam of isotopically pure Yb atoms by deflection using 1D-optical molasses

We demonstrate the generation of an isotopically pure beam of laser-cooled Yb atoms by deflection using 1D-optical molasses. Atoms in a collimated thermal beam are first slowed using a Zeeman slower. They are then subjected to a pair of molasses beams inclined at 45(a similar to) with respect to the slowed atomic beam. The slowed atoms are deflected and probed at a distance of 160 mm. We demonstrate the selective deflection of the bosonic isotope Yb-174 and the fermionic isotope Yb-171. Using a transient measurement after the molasses beams are turned on, we find a longitudinal temperature of 41 mK.

A feasibility study of a post-buckled beam for actuating helicopter trailing edge flap

Active trailing edge flaps (TEFs) are one of the most promising devices for helicopter vibration reduction. Smart actuators such as the piezoelectric stack actuators (PEAs) are used for TEF actuation. PEAs possess high energy density and have large force in dynamic condition but are limited to small displacements. In this investigation, we study a linear to rotary motion amplification mechanism (AM-2) based on a pinned-pinned post-buckled beam to actuate trailing edge flaps. A linear motion amplification mechanism is developed and coupled with AM-2 to amplify angular flap deflections. Experiments are conducted on bench top-test setup, and maximum flap angle deflections of the order of 12A degrees are achieved in the static case. An aeroelastic analysis is performed and 91 % reduction in helicopter vibration is obtained with multiharmonic control inputs.

Microstructure-hardness-fretting wear resistance correlation in ultrafine grained Cu-TiB2-Pb composites

The retention of the desired combination of mechanical/tribological properties in ultrafine grained materials presents important challenges in the field of bulk metallic composites. In order to address this aspect, the present work demonstrates how one can achieve a good combination of hardness and wear resistance in Cu-Pb-TiB2 composites, consolidated by spark plasma sintering at low temperatures ( < 500 degrees C). Transmission electron microscope (TEM) studies reveal ultrafine grains of Cu (100-400 nm) with coarser TiB2 particles (1-2 mu m) along with fine scale Pb dispersoid at triple junctions or at the grain boundaries of Cu. Importantly, a high hardness of around 2.2 GPa and relative density of close to 90% relative density (rho(theo)) have been achieved for Cu-15 wt% TiB2-10 wt% Pb composite. Such property theo, combination has never been reported for any Cu-based nanocomposite, by conventional processing route. In reference to the tribological performance, fretting wear tests were conducted on the sintered nanocomposites and a good combination of steady state COF (0.6-0.7) and wear rate (10-4 mm(3)/N m) were measured. An inverse relationship between wear rate and hardness was recorded and this commensurates well with Archard's relationship of abrasive wear. The formation of a wear-resistant delaminated tribolayer consisting of TiB2 particles and ultrafine oxide debris, (Cu, Fe, Ti)(x)O-y as confirmed from subsurface imaging using focused ion beam microscopy has been identified as the key factors for the low wear rate of these composites. (C) 2014 Elsevier B.V. All rights reserved.

Biocompatible and Antibacterial SnO2 Nanowire Films Synthesized by E-Beam Evaporation Method

In this work, the biocompatibility and antibacterial activities of novel SnO2 nanowire coatings prepared by electron-beam (E-Beam) evaporation process at low temperatures were studied. The nanowire coatings were characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction (XRD) methods. The results of in vitro cytotoxicity and cell proliferation assays suggested that the SnO2 nanowire coatings were nontoxic and promoted the proliferation of C2C12 and L929 cells (> 90% viability). Cellular activities, cell adhesion, and lactate dehydrogenase activities were consistent with the superior biocompatibility of the nanowire materials. Notably, the nanowire coating showed potent antibacterial activity against six different bacterial strains. The antibacterial activity of the SnO2 material was attributed to the photocatalytic nature of SnO2. The antibacterial activity and biocompatibility of the newly developed SnO2 nanowire coatings may enable their use as coating materials for biomedical implants.

Semipolar and nonpolar GaN epi-films grown on m-sapphire by plasma assisted molecular beam epitaxy

We hereby report the development of non-polar epi-GaN films of usable quality, on an m-plane sapphire. Generally, it is difficult to obtain high-quality nonpolar material due to the planar anisotropic nature of the growth mode. However, we could achieve good quality epi-GaN films by involving controlled steps of nitridation. GaN epilayers were grown on m-plane (10-10) sapphire substrates using plasma assisted molecular beam epitaxy. The films grown on the nitridated surface resulted in a nonpolar (10-10) orientation while without nitridation caused a semipolar (11-22) orientation. Room temperature photoluminescence study showed that nonpolar GaN films have higher value of compressive strain as compared to semipolar GaN films, which was further confirmed by room temperature Raman spectroscopy. The room temperature UV photodetection of both films was investigated by measuring the I-V characteristics under UV light illumination. UV photodetectors fabricated on nonpolar GaN showed better characteristics, including higher external quantum efficiency, compared to photodetectors fabricated on semipolar GaN. X-ray rocking curves confirmed better crystallinity of semipolar as compared to nonpolar GaN which resulted in faster transit response of the device. (C) 2014 AIP Publishing LLC.

Effects of growth temperature on nonpolar a-plane InN grown by molecular beam epitaxy

Nonpolar a-plane InN films were grown on r-plane sapphire substrate by plasma assisted molecular beam epitaxy with GaN underlayer. Effect of growth temperature on structural, morphological, and optical properties has been studied. The growth of nonpolar a-plane (1 1 -2 0) orientation was confirmed by high resolution X-ray diffraction study. The film grown at 500 degrees C shows better crystallinity with the rocking curve FWHM 0.67 degrees and 0.85 degrees along 0 0 0 1] and 1 - 1 0 0] directions, respectively. Scanning electron micrograph shows formation of Indium droplets at higher growth temperature. Room temperature absorption spectra show growth temperature dependent band gap variation from 0.74-0.81 eV, consistent with the expected Burstein-Moss effect. The rectifying behaviour of the I-V curve indicates the existence of Schottky barrier at the InN and GaN interface. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Synthesis of a new tungsten-free gamma-gamma ` cobalt-based superalloy by tuning alloying additions

The paper presents the synthesis of a new class of gamma-gamma' cobalt-based superalloy that is free of tungsten as an alloying addition. It has much lower density and higher specific strength than the existing cobalt-based superalloys. The current superalloys have a base composition of Co-10Al and are further tuned by the addition of a binary combination of molybdenum and niobium, with the optimum composition of Co-10Al-5Mo-2Nb. The solvus temperature of the alloy (866 degrees C) can be further enhanced above 950 C by the addition of Ni to give the form Co-xNi-10Al-5Mo-2Nb, where x can be from 0 to 30 at.%. After heat treatment, these alloys exhibit a duplex microstructure with coherent cuboidal L1(2)-ordered precipitates (gamma') throughout the face-centred cubic matrix (gamma), yielding a microstructure that is very similar to nickel-based superalloys as well as recently developed Co-Al-W-based alloys. We show that the stability of the gamma' phase improves significantly with the nickel addition, which can be attributed to the increase in solvus temperature. A very high specific 0.2% proof stress of 94.3 MPa g(-1) cm(-3) at room temperature and 63.8 MPa g(-1) cm(-3) at 870 degrees C were obtained for alloy Co-30Ni-10Al-5Mo-2Nb. The remarkably high specific strength of these alloys makes this class of alloy a promising material for use at high temperature, including gas turbine applications. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Fabrication and Experimentation of a Cantilever Beam Based Piezoelectric Actuator and Sensor for Vibration Energy Harvesting

In the immediate surroundings of our daily life, we can find a lot of places where the energy in the form of vibration is being wasted. Therefore, we have enormous opportunities to utilize the same. Piezoelectric character of matter enables us to convert this mechanical vibration energy into electrical energy which can be stored and used to power other device, instead of being wasted. This work is done to realize both actuator and sensor in a cantilever beam based on piezoelectricity. The sensor part is called vibration energy harvester. The numerical analyses were performed for the cantilever beam using the commercial package ANSYS and MATLAB. The cantilever beam is realized by taking a plate and fixing its one end between two massive plates. Two PZT patches were glued to the beam on its two faces. Experiments were performed using data acquisition system (DAQ) and LABVIEW software for actuating and sensing the vibration of the cantilever beam.