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Highly crystalline copper nitride (Cu3N) thin films have been deposited on glass substrates at room temperature by a novel and commercially viable growth technique, known as modified activated reactive evaporation (MARE). The effects of change in radio frequency (RF) power and deposition pressure on the structural and optical properties of the films have been investigated. RF power plays a significant role for the preferential growth of these films along a particular plane whereas the deposition pressure has comparatively lesser impact on the same. However, the lattice parameter, film thickness and optical band gap are found to be strongly dependent on the deposition pressure. The MARE grown Cu3N films undergo complete decomposition into metallic Cu upon vacuum annealing at 400 �C which makes them promising candidates to be used in write once optical recording media. � 2014 Elsevier B.V. All rights reserved.

In this report, we have studied the compositional dependence of structural, optical and electrical properties of polycrystalline In x Ga1−x N thin films grown by modified activated reactive evaporation. The growth was monitored by optical emission spectroscopy. The thickness of the films was in the range ~600–800 nm. The phase, crystallinity and composition of the films were determined by X-ray diffraction, Raman spectroscopy and energy dispersive X-ray analysis. The surface morphology was studied by atomic force microscopy. The band gaps of these films obtained from transmittance and photoluminescence measurements were found to vary from 1.88 to 3.22 eV. All the films show n-type conductivity. The carrier concentration was found to be decreasing with increase in gallium incorporation which is in good agreement with the free carrier absorption observed in transmittance spectra.

We report on the charge carrier transport mechanisms of undoped and Ga doped (2 wt. % and 4 wt. %) ZnO thin films grown by pulsed dc magnetron sputtering technique. Temperature dependent resistivity measurements showed typical semiconducting behaviour for undoped ZnO thin films where as Ga doped ZnO thin films showed metallic nature at higher temperatures and insulating nature with a metal to insulator transition at lower temperatures. The observed transition temperatures are 91 K and 140 K for 2 wt. % and 4 wt. % Ga doped ZnO films respectively. The observed metal insulator transition is attributed to the electron-electron interactions at low temperatures. The variations in the transition temperatures are explained based on the disorderness induced in the system due to the doping effect. ZnO doped with 4 wt. % Ga showed the lowest resistivity of 5. 7 � 10 -4 ? cm with a carrier concentration of 1. 2 � 10 21/cm 3. Undoped and doped ZnO thin films are about 90% transparent in the visible region. Blue shift is observed in the absorption edge with the effect of doping and it is explained based on B-M shift. The Fermi level measured from valance band spectroscopy showed a shift of +0. 6 eV for 2 wt. % Ga doped ZnO thin film and +0. 7 eV for 4 wt. % Ga doped ZnO thin film compared to the Fermi edge of undoped ZnO thin films. This ascertains the movement of Fermi level in to the conduction band with the effect of doping. � 2012 The Korean Institute of Metals and Materials and Springer Netherlands.

In the present work, InxGa1 - xN films with different indium compositions (x = 0.88, 0.63, 0.36 and 0.18) were prepared on glass substrates using a commercially viable technique known as modified activated reactive evaporation. Electrochemical impedance was used to investigate the anion sensing properties of these films for KCl, KI and KNO3 salt solutions of different molar concentrations. The anion sensing behaviour of InGaN films is attributed to the presence of high n-type background carrier concentration and positively charged surface donor states. The InGaN based anion sensors were found to have good sensitivity with faster response and recovery time. The film with x = 0.63 was found to have the highest sensitivity for all the anions due to the presence of more active surface area together with large number of surface donor states. � 2011 Elsevier B.V. All rights reserved.

Polycrystalline AgIn3Te5 synthesized by melt-quench technique has been analyzed using proton induced X-ray emission (PIXE), X-ray diffraction (XRD), and selected area electron diffraction. PIXE analysis yielded the content of Ag, In, and Te, respectively, to be 9.76%, 31.18%, and 59.05% by weight. Structure refinement was carried out considering those space groups from I- and P-type tetragonal systems which possess 4 symmetry and preserve the anion sublattice arrangement of the chalcopyrite structure (space group: I42d) as well. The results showed that AgIn3Te5 synthesized by melt-quench method crystallizes with P-type tetragonal structure (space group: P42c; unit-cell parameters a = 6.2443(8) and c = 12.5058(4) Å), the presence of which was corroborated by selected area electron diffraction studies.

Nano-crystalline c-axis oriented InxGa1−xN (x = 0.93, 0.63, 0.5, 0.36 and 0.18) thin films were prepared by modified activated reactive evaporation technique. Phase segregation was clearly observed for x = 0.5 composition. Scanning electron microscopy images reveal the average grain size for all the films to be varying from 40 to 85 nm. From, the absorption spectra the band gaps for the InGaN films were found to be varying from 1.89 to 2.92 eV. Micro-Raman scattering at two different excitation energies (1.96 and 2.54 eV) were used to study the phase separation and compositional fluctuations of InGaN layers across their thickness. All the spectra exhibit the characteristic A1(LO) and E2 (high) modes corresponding to hexagonal wurtzite structure for both the excitations. No appreciable change in the peak positions for the two excitations confirms the absence of any significant phase separation across the thickness of InGaN films with x = 0.36 and 0.18 composition. However, for x = 0.93 and 0.63 films, gallium rich minority phase could be detected with 1.96 eV excitation. The changes in the area and FWHM of the two characteristic Raman peaks for different excitations are attributed to the increased structural defects across the sample depth and also to the near resonance effects.

Indium-rich In x Ga 1-x N thin films were prepared on glass substrates by a mixed source modified activated reactive evaporation technique. All the films exhibit hexagonal wurtzite structure preferentially oriented along the c-axis. The band gap values obtained through Urbach fitting of the absorption edge were found to be in good agreement with the values obtained from photoluminescence spectra. The decrease in band gap below 1.9 eV (i.e., for pure InN ) for indium-rich films is mainly due to the compensation of Burstein–Moss shift due to gallium incorporation into the lattice which is further confirmed from the carrier concentration measurements.

In the present work, we describe the effect of crystallization on humidity sensing properties of nanocrystalline TiO2 thin films prepared by sol-gel techniques. Here, we report an enhancement in the relative humidity (RH) sensitivity just after the crystallization at 375��C, which is attributed to increased surface activity near crystallization and lower crystallite size. After crystallization, the RH sensitivity was found to decrease with increasing grain size. The complex impedance of the sensor, measured using impedance spectroscopy, fits well with an equivalent circuit consisting of inter-granular resistance and capacitance in parallel. It was found that with the change in RH, only resistance changes significantly, when compared with the capacitance. � 2007 Elsevier B.V. All rights reserved.

Zn1-xCdxO thin films have been prepared by sol-gel spin coating method. Structural analysis shows that the Cd substitution into the wutrzite ZnO lattice is achieved up to about 20 mol %. The optical band gap is found to decrease with the increase in Cd content. Increase in the annealing temperature up to a certain critical temperature leads to band gap narrowing because of the proper substitution of Zn by Cd and thereafter the band gap increases due to Cd re-evaporation from the lattice sites. This critical temperature lowers down with the increase in Cd doping concentration. The resistivity decreases with the increase in Cd content and increases with the increase in annealing temperature.

Monolithic microwave integrated circuits (MMICs) play an important part in today's wireless communication electronics. GaAs-based pseudomorphic High Electron Mobility Transistor (pHEMT) is used in MMIC-based low noise amplifier (LNA) and power amplifier (PA) stages. The latter requires high device current (Ids) and high reverse breakdown voltage (BVgd). In addition, the ON-state breakdown voltage should be high enough to operate the device at higher source-drain voltage (Vds). Double gate recessing is a well-established technique used to increase the ON and OFF-state breakdown voltages of a pHEMT device for power applications, which requires two levels of masking and recessing. In this paper, we present a single mask processing technique for realizing double recess structure with the help of silicon nitride layer. The new process involves deposition of silicon nitride after mesa isolation step of device fabrication. After gate lithography, two etching steps of silicon nitride and GaAs, followed one after the other, generates the double recess structure, wherein the various etch times decide the width and shape of double recess structure. The electric field distribution at the Schottky interface as well as along the channel has been simulated using ATLAS for the double recess structure used in this work. The fabricated recess structure showed improvement in breakdown voltage of the device which has been correlated to the effective redistribution of electric field in the device, as shown by simulation. � 2014 Elsevier B.V. All rights reserved.

We report on a novel acoustic method for measurement of liquid temperature, viscosity and density using magneto-acoustic sensors. The sensors are comprised of free-standing magnetoelastic thick films that oscillate in response to an externally applied time-varying magnetic field; depending upon the physical geometry and surface roughness of the film these mechanical deformations launch an acoustic wave that can be detected remotely from the test area. These oscillations are strongest at the characteristic resonant frequency of the sensor, which shifts linearly in response to temperature and, when immersed in a liquid, the damping forces associated with liquid viscosity and density.

In response to a magnetic field impulse, magnetostrictive magnetoelastic sensors mechanically vibrate. These vibrations can be detected in several ways: optically from the amplitude modulation of a reflected laser beam, acoustically using a microphone or hydrophone, and by using a pickup coil to detect the magnetic flux emitted from the sensor. Earlier work has shown that the resonant frequency of a magnetoelastic sensor shifts in response to different environmental parameters, including temperature, pressure, fluid flow velocity and mass loading, with each parameter determined in an otherwise constant environment. To extend the utility of the sensor technology in this work we report on the fabrication and application of a miniaturized array of four magnetoelastic sensors that enable the simultaneous remote query measurement of pH, temperature, and pressure from a passive, wireless platform.

In response to an externally applied time-varying magnetic field, freestanding sensors made of magnetoelastic thick or thin films mechanically oscillate. These oscillations are strongest at the characteristic resonant frequency of the sensor. Depending upon the physical geometry and the surface roughness of the magnetoelastic sensor, these mechanical deformations launch an acoustic wave that can be detected remotely from the test area by a microphone. By monitoring changes in the characteristic resonant frequency of a magnetoacoustic sensor, multiple environmental parameters can be measured. In this work we report on the application of magnetoacoustic sensors for the remote query measurement of temperature, the monitoring of phase transitions and, in combination with a humidity-responsive mass-changing Al2O3 ceramic thin film, the in situ measurement of humidity levels.

Humidity sensors are widely used in domestic and industrial environments. The authors have investigated 0.5ZrO2–0.5TiO2 ceramic for its humidity sensing electrical properties at room temperature. The bulk humidity sensors were prepared by the conventional ceramic method. Salt doping with Li+ ions is found to increase the sensitivity by an order of two, and also improves the linearity. X-ray and scanning electron microscopy (SEM) investigations have established that ZrTiO4 phase grows at a sintering temperature of 1200°C. The abnormal behaviour in humidity sensing characteristics for samples sintered at 1150°C may be due to micropores in between the grains.

Copper nitride thin films have been prepared by pulsed direct current reactive magnetron sputtering. Structural, morphological and optical properties of the as-deposited films have been studied. X-ray diffraction analysis shows that the films are polycrystalline single phase of Cu3N. Prominent growth along (100) plane is observed for higher nitrogen flow rate whereas growth along (111) plane is observed for relatively lower nitrogen flow rate. The band gap of this material changes from 1.02 to 1.40 eV by varying the nitrogen flow rate and deposition time.

Nitrogen doped ZnO (NZO) thin films, at different +{\hbox{N}} 2 flow rates have been deposited on glass substrates by pulsed DC reactive magnetron sputtering technique. The effect of +{\hbox{N}} 2 flow rate (1.0 sccm - 3.0 sccm) on the structural, optical, electrical and chemical state of N has been studied. With the effect of +{\hbox{N}} 2 flow rate: the crystallinity of the films decreased, tensile stress is developed, optical transmittance decreased (80% to 60%), conductivity decreased till 1.5 sccm and films were n-type conducting. At 2.0 sccm and 2.5 sccm of +{\hbox{N}} 2 flow rates, NZO thin films showed p-type conductivity. The changes in the magnitude and type of conductivity have a direct relation with the changes observed in N-chemical state in ZnO lattice. p- NZO thin films are electrically unstable; this instability has been explained based on the changes occurred in the N chemical states, resulting from the stress release in NZO lattice. � 2005-2012 IEEE.

Phase homogeneity and crystal structure of melt-quenched AgInSbTe system have been analyzed using X-ray diffraction (XRD) and Raman spectroscopy. Rietveld refinement of crystal structure of Ag4In12Sb56Te28 has revealed the formation of AgIn3Te5, Sb8Te3 and Sb phases respectively with P-type tetragonal (P42c), 11R (R3m) and A7 (R3m) structures. Addition of suitable amount of Te to Ag4In12Sb56Te28 yielded Ag3.54In10.62Sb49.56Te36.28, alloy with AgIn3Te5 and Sb8Te3 phases. Optical micrographs of surface of the samples have shown the existence of three kinds of regions (AgIn3Te5 rich, Sb8Te3 rich and Sb rich regions) with different reflectivity. Presence of multiphase and effect of laser-sample interaction at these regions have been investigated using Raman spectroscopy. Analysis of Raman spectra has revealed that the regions with more content of AgIn3Te5 exhibit amorphous phase during laser-sample interaction.

Using ab initio density functional calculations, we have investigated the stability and electronic structure of pure and oxygen doped semiconducting Cu3N. The oxygen can be accommodated in the system without structural instability as the formation energy either decreases when oxygen substitutes nitrogen, or remains nearly same when oxygen occupies the interstitial position. The interstitial oxygen (OI) prefers to stabilize in the unusual charge neutral state and acts as an acceptor to make the system a p-type degenerate semiconductor. In this case the hole pockets are formed by the partially occupied OI-p states. On the other hand, oxygen substituting nitrogen (OS) stabilizes in its usual −2 charge state and acts as a donor to make the system an n-type degenerate semiconductor. The electron pockets are formed by the conducting Cu-p states. In the case of mixed doping, holes are gradually compensated by the donor electrons and an intrinsic gap is obtained for stoichiometry. Our calculations predict the nature of doping as well as optical band gap variation in experimentally synthesized copper oxynitride. While interstitial doping contracts the lattice and increases the substitutional doping increases both lattice size and Mixed doping reduces Additionally we show that a rare intra-atomic d–p optical absorption can be realized in the pristine Cu3N as the Fermi level lies in the gap between the Cu-d dominated anti-bonding valence state and Cu-p conducting state.

In the present investigation, the effects of annealing in oxygen atmosphere on the electrical and optical properties of pulsed direct-current (DC) magnetron-sputtered ZnO thin films have been studied. With annealing, the electrical conductivity was found to increase from 2.3 S cm to 123 S cm. The optical transparency was also found to improve from 83% to 90%. The improvement in the electrical properties with annealing is attributed to the reduction of the grain boundary potential from 34 meV to 8 meV. X-ray photoelectron spectroscopy (XPS) measurements revealed oxygen deficiency in as-deposited films, whereas adequate incorporation of oxygen was observed in the annealed films. Ultraviolet photoelectron spectroscopy (UPS) measurements showed a shift of +0.8 eV in the Fermi level with annealing. This shift indicates significant changes in the electrical conductivity with annealing, which is due to an increase in the carrier concentration. � 2012 TMS.

Polycrystalline InxGa1-xN thin films were prepared by mixed source modified activated reactive evaporation (MARE) technique. The films were deposited at room temperature on glass substrates without any buffer layer. All the films crystallize in the hexagonal wurtzite structure. The indium concentration calculated from XRD peak shift using Vegard's law was found to be varying from 2% to 92%. The band gap varies from 1.72 eV to 3.2 eV for different indium compositions. The indium rich films have higher refractive indices as compared to the gallium rich films. The near infra-red absorption decreases with gallium incorporation into InN lattice which is mainly due to decrease in the free carrier concentration in the alloy system. This fact is further supported from Hall effect measurements. MARE turns out to be a promising technique to grow InxGa1-xN films over the entire composition range at room temperature. � 2011 Elsevier B.V. All rights reserved.

We report the role of charged species N2 + on the growth of GaN films by modified activated reactive evaporation MARE . In MARE technique, substrate is subjected to low energy nitrogen ion bombardment by keeping it in conjunction with the radio frequency cathode. The low energy ion irradiation contributes to the effective formation of GaN as well as in the drastic reduction of the oxygen impurity content by resputtering of the weakly bonded oxygen adatoms. Significant reduction in oxygen impurity can be achieved in the MARE by increasing the concentration of the charged species in the plasma. © 2010 The Electrochemical Society. DOI: 10.1149/1.3512991 All rights reserved.

In the present work, we report the temperature dependent carrier transport properties of InxGa1-xN thin films in the entire composition range grown by modified activated reactive evaporation. The carrier transport in these degenerate semiconductors is controlled by impurity band conduction. A transition from metallic to semiconducting type resistivity was observed for indium rich films. The semiconducting behavior originates from electron-electron interaction and weak localization, whereas higher temperature scattering contributes to the metallic type resistivity. A transition of resistivity behavior from the quantum phenomena to the classical Arrhenius approach was observed for x 0.12 film. � 2011 American Institute of Physics.

Melt quenched CuIn(SexTe1−x)2, where x = 0.1 and 0.9, have been analyzed using X‐ray diffraction (XRD) and Raman spectroscopy. Rietveld refinements of XRD data revealed that CuIn(Se0.1Te0.9)2 has formed as a single phase whereas CuIn(Se0.9Te0.1)2 has exhibited two phases, CuIn(Se0.87Te0.13)2 and CuIn(Se0.95Te0.05)2, with phase fraction of 67 and 33% respectively. Raman spectra of CuIn(Se0.1Te0.9)2 showed a well defined high intensity peak at 130 cm−1 while CuIn(Se0.9Te0.1)2 exhibited a high intensity peak at 165.6 cm−1 and an adjacent peak at 174.2 cm−1. The peaks observed at 130, 165.5 and 174.2 cm−1 were attributed to the characteristic A1 mode of the phases with Se percentage 10, 87 and 95 respectively. The XRD and Raman results showed that substitution of 10% of selenium in CuInTe2 yields single phase while 10% substitution of Te in CuInSe2 yields two phases.

Visible photoluminescence at 515 nm of ruthenium-doped multiwall carbon nanotubes, fabricated on quartz substrates using a chemical vapor deposition technique, is reported. The well-aligned nanotubes serve as templates for the luminescent, residual ruthenium–iron catalyst particles contained within the nanotubes, restricting the particle size to about 10 nm. The synthesis technique can be readily extended to other luminescent dopants; moreover, since nanotube arrays can be readily grown from patterned substrates, nanotube-based optoelectronic devices may be achieved.

Magnetoelastic thick film sensors mechanically deform when subjected to a magnetic field impulse, launching elastic waves within the sensor the magnitude of which is greatest at the mechanical resonant frequency. As the sensors are magnetostrictive, the mechanical deformations launch magnetic flux that can be detected remotely. The characteristic resonant frequency of a magnetoelastic sensor, which is a function of the length, density, elasticity and Poisson's ratio of the sensor material, changes in response to temperature, pressure, ambient flow rate and, in combination with a mass changing, chemically responsive layer different analyte concentrations. By using an array of such sensors different environmental parameters can be simultaneously determined in a complex environment; we have designed and fabricated such an array for the simultaneous measurement of temperature and pressure.

Remote query magneto-acoustic and magneto-optical sensors are used to measure liquid temperature, viscosity and density. Sensors comprising magnetoelastic Metglas(R) 2826MB thick-films, alloy composition Fe/sub 40/Ni/sub 38/Mo/sub 4/B/sub 18/, oscillate in response to an externally applied, time-varying magnetic field. The sensor oscillations are strongest at the characteristic mechanical resonant frequency of the sensor. Depending upon the physical geometry and surface roughness of the magnetoelastic films, the mechanical sensor-vibrations launch an acoustic wave that can be detected remotely using a hydrophone or microphone. Furthermore, the sensor oscillations act to modulate the intensity of a laser beam reflected from the sensor surface. The sensor vibrations were optically monitored using a photo detector placed in the path of a laser beam back-scattered off the sensor ribbon. Using a Fast Fourier Transform, the signal obtained in the time-domain from acoustical or optical detectors is converted into the frequency-domain from which the resonant frequency of the sensor is determined. The resonant frequency shifts linearly with temperature and, when immersed in a liquid, with the frictional damping forces associated with liquid viscosity and density, thus allowing a remote measurement of temperature and liquid viscosity.

A 2 kHz–100 MHz constant-output dynamic amplifier design is presented. Application of the amplifier is shown for tracking wireless magnetoelastic and magnetoacoustic environmental sensors [C. A. Grimes et al., Rev. Sci. Instrum. 70, 4711 (1999); K. Loiselle and C. A. Grimes, Rev. Sci. Instrum. 71, 1141 (2000)], the detected amplitude which varies significantly with spatial location from the detector. The amplification of the dynamic amplifier, 80 dB, is controlled by inverted feedback voltage; the design is suitable for an input voltage range of −150 to −10 dB. The dynamic amplifier enhances the detection range of magnetoacoustic sensors by an approximate factor of three, and that of magnetoelastic sensors by a factor of 1.25, with the magnetoelastic sensors having comparatively less detection range increase due to higher background noise levels.

In this paper we report for the first time, a method of generating wide gate recess structure in single recess step by the help of a bi-layer lithography technique, which can be used to generate varying gate recess width by varying developmental time. It is established that the gate recess structure decides the schottky breakdown voltages in these devices. The distance from gate edge-to-n+ in the recess structure becomes very critical for high Vb. Commonly, double recessing is used to achieve this, which is more complicated. We have achieved Vb as high as 20Volts using single recess.

We describe the effect of annealing in air and in vacuum on structural, electrical and optical properties of indium nitride (InN) thin films. The films were grown by modified activated reactive evaporation. Films annealed in air were transformed to In 2O 3 at 450 �C whereas films annealed in vacuum started decomposing at 500 �C. The c-lattice constant was found decreasing for increasing annealing temperature due to reduction of excess nitrogen in the films. The major changes in structural, electrical and optical properties appear around 400 �C. Both air and vacuum-annealed films show a reduction in the carrier concentration with annealing, explaining the observed reduction in bandgap (Moss-Burstein shift) for vacuum-annealed films. For air-annealed films, the bandgap increases when annealed, which may be due to oxynitride formation overcoming the effect of reduced carrier concentration. A decrease in the photoluminescence intensity was observed at 400 �C for air-annealed and 500 �C for vacuum-annealed films which can be attributed, respectively, to the presence of indium oxide and indium in the films. Optimal annealing temperature was observed between 400 and 450 �C in vacuum. � 2009 Elsevier B.V. All rights reserved.

Nano‐crystalline c‐axis orientated indium nitride (InN) thin films were prepared on amorphous polycarbonate, polyimide and glass substrates by modified activated reactive evaporation (MARE) method without any intentional heating of the substrate. The films show strong visible photoluminescence (PL) peak at ∼1.95 eV indicating the band edge transition which is in good agreement with the optical absorption. The shift in the band gap from reported value is mainly due to Burstein‐Moss shift and presence of residual oxygen. InN film grown on inexpensive flexible substrates at room temperature opens opportunity for large scale device applications like solar cells and displays.

In the present work, we describe humidity sensing properties of nano-structured multilayered TiO2:ZrO2 ceramic thin films prepared by sol-gel processing. An enhancement in the sensitivity is observed for both TiO2/ZrO2 (TZ) and ZrO2/TiO2 (ZT) thin film samples that are annealed at 400 �C, due to simultaneous crystallization of ZrO2 and TiO2. The multilayered ZrO2:TiO2 thin film shows less drift and low hysteresis compared to pure TiO2. The experimental data are fitted to an equivalent circuit containing a resistance and a non-Debye capacitance in parallel. Typical response and recovery time of the sensor are 56 and 124 s, respectively. We demonstrate the possibility of a practical device without heating the humidity sensitive element for regeneration. � 2007 Elsevier B.V. All rights reserved.

We report the effect of rf power on the structural, optical and electrical properties of InN films grown by modified activated reactive evaporation. In this technique, the substrates were kept on the cathode instead of ground electrode. The films grown at higher rf power shows preferential c-axis orientations for both silicon and glass substrates. The films prepared at 100 W show best structural, electrical and optical properties. The c-axis lattice constant was found to decrease with increase in rf power which can be attributed to reduction in excess nitrogen in the films. The band gap decreases with increase in rf power due to Moss-Burstein shift. The decrease in carrier concentration and optical band gap with increase in rf power can also be related to excess nitrogen in the film. The Raman spectra shows a red shift in the A 1(LO) and E 2 (high) mode from the reported value. The possible origin of the present large band gap is due to Moss-Burstein shift. The new film growth method opens opportunities for integrating novel substrate materials with group III nitride technologies. � 2008 Elsevier B.V. All rights reserved.

The MgO-doped ZrO2–TiO2 ceramic pellets were studied for its humidity-sensitive electrical conduction. An equivalent circuit model has been proposed to define the humidity-sensitive electrical properties. This model is in agreement with the experimental findings. The electrical conduction is largely controlled by the intergranular impedance except at very high humidities. The impedance of the pellets showed inductive behavior in high-humidity region. This behavior can be attributed to the spherical paths adopted by charge carrier because conduction is mainly through the spherical grain surface.

We have investigated the temperature dependent carrier transport properties of nano-crystalline copper nitride thin films synthesized by modified activated reactive evaporation. The films, prepared in a Cu-rich growth condition are found to be highly disordered and the carrier transport in these films is mainly attributed to the impurity band conduction. We have observed that no single conduction mechanism is appropriate to elucidate the carrier transport in the entire temperature range of 20 - 300 K. Therefore, we have employed different conduction mechanisms in different temperature regimes. The carrier transport of the films in the low temperature regime (20 - 150 K) has been interpreted by implementing quantum correction to the conductivity. In the high temperature regime (200 - 300 K), the conduction mechanism has been successfully analyzed on the basis of Mott's variable range hopping mechanism. Furthermore, it can be predicted that copper ions present at the surface of the crystallites are responsible for the hopping conduction mechanism. � 2015 Author(s).

Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5�10-6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films. � 2015 Author(s).

The resonant frequency and quality factor Q of a liquid immersed magnetoelastic sensor are shown to shift linearly with the liquid viscosity and density product. Measurements using different grade oils, organic chemicals, and glycerol-water mixtures show that the surface roughness of the sensor in combination with the molecular size of the liquid play important roles in determining measurement sensitivity, which can be controlled through adjusting the surface roughness of the sensor surface. A theoretical model describing the sensor resonant frequency and quality factor Q as a function of liquid properties is developed using a novel equivalent circuit approach. Experimental results are in agreement with theory when the liquid molecule size is larger than the average surface roughness. However, when the molecular size of the liquid is small relative to the surface roughness features molecules are trapped, and the trapped molecules act both as a mass load and viscous load; the result is higher viscous damping of the sensor than expected. c2002 Elsevier Science B.V. All rights reserved.

This paper presents a wireless, remote query ammonia sensor comprised of a free-standing magnetoelastic thick-film coated with a polymer, poly(acrylic acid-co-isooctylacrylate), that changes mass in response to atmospheric ammonia concentration. The mass of the polymer layer modulates the resonant frequency the ferromagnetic magnetoelastic substrate, hence by monitoring the frequency response of the sensor, atmospheric NH3 concentration can be determined remotely, without the need for physical connections to the sensor or specific alignment requirements. The effect of copolymer composition, polymer film thickness, and relative humidity level (RH) on the sensitivity of the sensor were investigated. The sensor linearly tracks ammonia concentration below 0.8 vol.%, and tracks higher concentrations logarithmically; within the linear calibration range, a 0.02 vol.% change in NH3 concentration can be detected.

Magnetoelastic sensors, made of amorphous metallic glass ribbons or wires, have been used to measure various environmental parameters such as temperature, humidity, viscosity, and chemical concentration including pH, carbon dioxide, and ammonia. The parameter of interest is determined by remote detection of the shift in the resonant frequency of the magnetoelastic sensors, which is dependent upon several factors including stress, pressure, temperature, and magnetic field. This paper describes the operating principles of the magnetoelastic sensors and presents several proven applications, as well as methods for optimizing the sensor performance.

Two wireless, passive remote query magnetism-based glucose sensors, which operate in combination with a mass and volume changing glucose responsive polymer, are presented. One sensor design is based upon the magnetostatic coupling of magnetically soft thin-film elements, as the polymer volume changes in response to glucose concentration so does the magnetostatic coupling between elements. In response to a time varying magnetic field, upon reversal of the magnetization vector of the elements the magnetostatic coupling determines the time rate of change of magnetic flux, and hence the amplitude of the voltage spike generated in a pick-up coil. The other sensor consists of a free-standing magnetoelastic thick-film, coated with a thin layer of the glucose responsive polymer. In response to a time varying magnetic field the sensor mechanically vibrates at a characteristic resonant frequency, the characteristic resonant frequency of the sensor linearly tracks the change in mass of the glucose responsive polymer.

This paper begins with an overview of nanostructured magnetoelastic materials, namely the amorphous ferromagnetic alloys, detailing how the material structure gives rise to unique magnetic and physical properties suitable for sensor applications, such as a high magnetostriction coefficient, high magnetoelastic coupling, as well as low coercive force and anisotropy field. With the correlation between the material structure and the magnetic and physical properties established, we then show how these unique properties are utilized for measuring multiple physical parameters such as stress/strain, liquid density and viscosity, fluid flow velocity, coating elasticity, ambient temperature, and chemical analyte concentrations including glucose, pH, carbon dioxide, and ammonia.

We report the fabrication of pseudomorphic high electron mobility transistors (pHEMTs) with engineered recess structure of any width of choice, by a single lithography and etching step with the help of silicon-nitride-assisted process. In this process, a silicon nitride layer is deposited prior to gate lithography. First, the silicon nitride is etched by buffered hydrofluoric acid (BHF) in the gate opening and then selective recessing is performed. The recess base width can be engineered by varying etch time of silicon nitride in BHF. The base width increases linearly with etch time as shown by SEM. We demonstrate that the top photoresist gate opening that decides the gate length is unaffected by any duration of silicon nitride etch time. Thereby, we have engineered the distance from gate edge to n +-GaAs (L gn+) which decides the gate-to-drain breakdown voltage (BV gd). With this method, BV gdincreased from 12 to 20V as a function of L gn+. The electric field distribution across the recess structure has been simulated to interpret this result. Since the high BV gdof pHEMT is essential for power applications as well as switch applications, this method can be easily adopted even though the corresponding reduction in transconductance and unit current gain cut-off frequency (f t) is only marginal from 375 to 350 mS mm 1and from 39 to 31GHz, respectively. � 2012 IOP Publishing Ltd.

Indium nitride films have been grown using modified activated reactive evaporation (MARE). The films were grown on glass and silicon substrates at room temperatures, i.e. without any intentional substrate heating. In this technique, the substrates were kept on the cathode instead of the grounded electrode and hence subjected to low energy nitrogen ion bombardment leading to highly c-axis oriented films. The photoluminescence (PL) and Raman spectrum shows significant improvement in the quality of the films compared with conventional activated reactive evaporation. The band gap measured from the room temperature PL was found to be 1.9 eV. Very high growth rates can be achieved in the MARE growth technique. The modification in the activated reactive evaporation technique may have a large impact on the growth of various compounds such as metal oxides. � 2008 IOP Publishing Ltd.

The MgO doped ZrO2–TiO2 composite is studied for its humidity sensing characteristics. Though dc electrical properties show very high sensitivity to humidity, it is not useful for practical applications because of the charging effect. The ac conductivity vs relative humidity characteristics of the pellet becomes linear with an increase in sintering temperature. The post treatment at high temperature and high humidity is found to accelerate initial ageing of the pellet and therefore, stabilizes the characteristics more quickly. A physical model has been proposed to correlate initial ageing, effect of sintering temperature and response time with pore size distribution. Pores below 300 Å radii are present in abundance near the ZrTiO4 phase formation temperature. These pores are responsible for higher sensitivity in low humidity region and linear characteristics.