bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrostatically Directed Assembly of Silver Nanoparticles for Application to Metal Enhanced Fluorescence Biosensing
Authors: Tsai De-Hao , Guo Shy-Hauh , Phaneuf Ray J , Zachariah Michael R. 
Published: April 2011

ABSTRACTIn this paper we demonstrate a gas-phase process to fabricate Ag nanoparticles-based bio-sensing devices. Ag nanoparticles, prepared from the gas phase through spray pyrolysis, are size-selected via electrostatic classification. These size-selected nanoparticles are then successfully attracted and aligned onto an electrostatic-patterned biased P-N junction substrate to form high- resolution nanoparticle patterns. Particles in the size range of 30-100 nm were evaluated. Our approach provides a promising tool for precise assembly of nanoparticles for future device applications.
A Novel Gas-phase Hydrogen Peroxide Sensor Basing on a Combined Physical/chemical Transduction Mechanism
Authors: Naether Niko , Emmerich Ruediger , Berger Joerg , Friedrich Peter , Henkel Hartmut , Schneider Andreas , Schoening Michael J. 
Published: April 2011

ABSTRACTIn this work, different set-ups as well as different transducer materials have been investigated in order to develop a hydrogen peroxide (H2O2) sensor for the gas phase. The sensor is based on a combined physical/chemical transduction mechanism and should be able to detect high H2O2 concentrations up to 10 Vol.%. Different sensor arrangements are presented that are based on a “three sensor” cell and a diffusion cell. As transducer materials manganese oxide and copper alloys have been investigated. For the reference part of the sensor set-up, Teflon and enamel have been tested as passivating material.
Simulations of Sub-wavelength Metallo-dielectric Photonic Crystals for Gas Sensing
Authors: Biswas Rana , Puscasu Irina , Pralle Martin , McNeal Martin , Greenwald Anton , Daly James , Johnson Edward , Neginhal Srinivas , Ding Changgeng 
Published: April 2011

ABSTRACTWe have simulated metallo-dielectric photonic crystals that are sharp thermal emitters at infrared wavelengths, and are being employed in gas sensors. The simulations were performed with a rigorous scattering matrix approach where Maxwell's equations are solved in Fourier space. These metallo-dielectric photonic crystals consist of a sub-wavelength hole array in a metal layer coupled to a two-dimensional photonic crystal of the same periodicity. The sub-wavelength hole array has an enhanced transmission mode that couples to a guided mode of the photonic crystal. The transmissive mode of the hole array is absorbed by the photonic crystal to create a sharp absorption and reflective minimum feature found for a range of lattice spacing. The structure thermally emits in a narrow band of wavelengths controlled by the lattice spacing that can be tuned over the infrared region. The underlying physics of this emissive device is modeled with rigorous scattering matrix simulations.
Multispectral Photonic Crystal Photo Sensor
Authors: Sun Xiaochen , Hu Juejun , Hong Ching-yin , Viens Jeff , Das Rupa , Agarwal Anuradha M. M. , Kimerling Lionel C. 
Published: April 2011

ABSTRACTA novel photo sensor pixel using a one-dimensional (1D) photonic crystal structure incorporating photoconductive layers has been realized. The fabricated device exploits mode discrimination to provide simultaneous multispectral photo sensing capability. Resonant cavity enhancement (RCE) design allows the use of very thin photoconductive layer to achieve dramatically suppressed shot noise, as well as high quantum efficiency. Low cost amorphous silicon is used to be photoconductive material and the simply fabrication process is completely CMOS-compatible. Detectivities as high as 2.6×1010 cmHz1/2W−1 and 2.0×1010 cmHz1/2W−1 at the two pre-selected wavelengths, 632nm and 728nm, were achieved, respectively.
Effect of Aggregation on the Rheological Properties of Carbon Nanotube Dispersions
Authors: Rahatekar Sameer Sharad , Gilman Jeffrey W , Koziol K K , Butler Simon , Elliott James A , Shaffer Milo , Mackley Malcolm , Windle Alan H 
Published: April 2011

ABSTRACTIn this pape effect of nanotube aggrates on the rheological properties of multiwall carbonanntube abd epoxy suspension in epoxy resin.The base epoxy resin was found to be essentially Newtonian, and the progressive incorporation of nanotubes enhanced the low shear rate viscosity of the suspension by nearly two decades. At higher shear rates, the suspension viscosity asymptotically thinned to the viscosity of the matrix alone. The low shear rate viscosity enhancement was correlated with the optical observations of interconnected aggregates of carbon nanotubes, which themselves were induced by the low shear conditions. Intermediate shear rates resulted in a reduction in the size of the aggregates. High shear rates appeared to cause near complete dispersal of the aggregates. From these results it is conjectured that for this suspension, shear thinning is connected with the breaking of the interconnected network between aggregates of nanotubes, and not by nanotube alignment.
Synthesis and control of micro to noanscale porous structures of diamond like carbon films
Authors: Feng Peter , Yang Ben , Zhang H. X. , Wang X. P. , Upia Noel , Morella G. , Weinerd B.R. 
Published: April 2011

ABSTRACTDiamond like carbon (DLC) films are synthesized on various substrates using a pulsed KrF excimer laser ablation deposition technique. Variations of laser power density, substrate temperature, angle and distance between the substrate and target yield different sizes of porous surfaces of DLC films. Microscope is used to examine the surfaces. Raman scattering is used to characterize the samples, and the typical G and D bands have been identified. Intensities and profiles of the G and D bands closely depend on laser power density. The relationship between the deposition rate and the power density is also studied.
Electrical Characterization of GaN Based Ultraviolet and Blue Light Emitting Diodes
Authors: Tegueu Alphonse-Marie Kamto , Akpa Okechukwu , Guha Arindra , Das Kalyankumar 
Published: April 2011

ABSTRACTGallium nitride based ultraviolet (UV) and blue AlGaN/GaN/AlGaN double heterojunction structure light emitting diodes (LEDs) were electrically characterized using current-voltage (I-V) and capacitance-voltage (C-V) measurements as a function of frequency. An analysis of logarithmic plots of the forward I-V characteristics indicated that current in these diodes was proportional to Vx, as opposed to eqV/nkT, where x was observed to be either 1 or 2 at low biases increasing to as high as 40 at higher biases. The dependence of diode forward current on Vx is likely to be due to space charge limited current in the presence of a high concentration of deep level states in the bandgap. The concentration of deep states and their position in the band gap were extracted from these logarithmic plots. For both the blue and the UV LEDs, several closely spaced levels were obtained, located most likely in the range between EV and EV + 0.5 eV with concentrations of the order of 1016/cm3 to 1017/cm3. Capacitance-voltage measurements as a function of frequency (200 Hz - 1 MHz) at room temperature yielded a density of approximately 1 × 1015 cm−3 located at 0.46 eV above the valence band-edge for both the UV and blue LED. Even though the location of these deep states from the I-V and C-V measurements are within the same range, the two orders magnitude difference in the concentration of deep states is not well understood at this point.
Selective Area Growth of GaN Nano Islands by Metal Organic Chemical Vapor Deposition: Experiments and Computer Simulations
Authors: Chandolu Anilkumar , Kipshidze Gela D , Nikishin Sergey A , Tian Lu , Daoying Song , Holtz Mark , Lobanova Anya 
Published: April 2011

ABSTRACTWe report the properties of GaN islands selectively grown by MOCVD on (0001) GaN/sapphire templates and on bare (0001) sapphire substrates. The approach allows us to grow GaN crystals with control over size and density through optical (micro-scale) and e-beam (nano-scale) lithography, and control over shape through MOCVD growth parameters. We have obtained complete pyramidal and prismatic hexagonal GaN islands. The growth characteristics are found to be very different from what we obtain for epitaxial layers, an effect which is attributed to micro/nanoloading and surface diffusion of source materials on the hard mask. From the dependence of growth rate of the pyramids with pitch we evaluate Ga surface diffusion length of ∼ 10 μm over SiO2 mask. We present a growth model based on diffusion and discuss the results of modeling with experimental data. Using micro-Raman spectroscopy the stress in pyramidal and prismatic islands was evaluated to be 20 MPa and 85 MPa, respectively. This implies that the selectively grown islands are relatively more relaxed compared to similar thickness of uniform layers. Micro catholdoluminescence (CL) shows a narrow line width and a better quality of GaN nano islands grown on e-beam lithography patterned templates. The GaN islands, of varying shapes, were overgrown with InGaN multiple quantum wells, which showed a few times stronger micro-CL emission than from GaN.
Position-Controlled InN Nano-dot Growth on Patterned Substrates by ECR-MBE
Authors: Yamaguchi Taihei , Araki Tsutomu , Naoi Hiroyuki , Nanishi Yasushi 
Published: April 2011

ABSTRACTWe report on the growth of self-aligned InN nano-dots on nano-patterned GaN templates by electron cyclotron resonance plasma-excited molecular beam epitaxy (ECR-MBE). In the fabrication of the nano-dots, InN was grown on GaN templates with reticular patterns of holes, which were prepared by the focused ion beam (FIB) technique. The InN nano-dots were formed selectively at the holes, resulting in the reticular array of InN nano-dos. The size of InN dots was controlled by varying the hole-pitch and the growth temperature. Furthermore, the shape of InN dots improved by thermal annealing after the growth. We have succeeded in controlling the position and size of InN nano-dots on nano-patterned substrates. Typically, InN nano-dots with a diameter of 50 nm and a height of 10 nm were fabricated in 410°C growth.
Electroluminescence from Single 3D GaN Nanowire Grown by Self-Catalytic Molecular Beam Epitaxy
Authors: Kendrick Chito E. , Tilley R. , Kobayashi M. , Reeves R. J. , Durbin S. M. 
Published: April 2011

ABSTRACT3-D branching GaN nanowires have been grown using the intermediate and Ga-rich growth regimes of plasma assisted molecular beam epitaxy. Evidence that the growth is due to an auto-catalytic VLS process is obtained through SEM images showing droplet termination heads, the composition of which is essentially pure Ga. TEM analysis revealed a defect free crystal structure, even in the trunk to branch junction. Cathodoluminescence from the trunk of the branching nanowires produced a strong luminescence feature at 3.44 eV, while a slight decrease in energy to 3.1 eV was observed at the interface between the nanowire and epilayer or kink site. No yellow luminescence was detected, further suggesting a defect free growth. Preliminary I-V measurements give mixed results, suggesting intrinsic n-type nanowires.
Properties of InN layers grown by High Pressure CVD
Authors: Alevli Mustafa , Durkaya Goksel , Kirste Ronny , Weesekara Aruna , Perera Unil , Fenwick William , Woods Vincent , Ferguson Ian T. , Hoffmann Axel , Dietz Nikolaus 
Published: April 2011

ABSTRACTIndium nitride (InN) and indium-rich group III-nitride alloys are promising materials for advanced optoelectronic device applications. Indium-rich alloys, e.g. (Ga1-y-xAlyInx)N will enable the fabrication of high-efficient light emitting diodes tunable in the whole visible spectral region, as well as advanced high speed optoelectronics for optical communication operating. The present limitation in this area is the growth of high quality InN and indium-rich group III-nitride alloys as documented in many controversial reports on the true physical properties of InN. The difficulties arise from the low dissociation temperature of InN that requires an extraordinarily high nitrogen overpressure to stabilize the material up to optimum growth temperatures. We developed a novel “high-pressure chemical vapor deposition” (HPCVD) system, capable to control and analyze the vast different partial pressures of the constituents. Our results show that the chosen HPCVD pathway leads to high-quality single crystalline InN, demonstrating that HPCVD is a viable tool for the growth of indium rich group III nitride alloys. The structural analysis of InN deposited on GaN-sapphire substrate by XRD show single phase InN(0002) peaks with full width half maximum (FWHM) around 400 arcsec. Infrared reflectance spectroscopy is used to analyze the plasmon frequencies, high frequency dielectric constants, the free carrier concentrations and carrier mobilities in these layers. For nominal undoped InN layers, free carrier concentrations in the mid 1019 cm−3 and mobilities around 600 cm−2-V-1-s-1 are observed. Further improvements are expected as the growth parameters are optimized. The explored growth parameters are close to of those employed for GaN growth conditions, which is a major step towards the fabrication of indium rich (Ga1−y−xAlyInx)N alloys and heterostructures.
Photoluminescence, Capacitance-Voltage, and Variable Field Hall Effect Measurements of Mg-Doped InN
Authors: Swartz Craig Hartley , Durbin Steven M. , Reeves Roger J. , Prince Katherine , Kennedy John V. , Chandril Sandeep , Myers Thomas H. , Carder Damian 
Published: April 2011

ABSTRACTVariable magnetic field Hall effect, photoluminescence (PL) and capacitance-voltage (CV) analysis have been used to study InN layers grown by plasma assisted molecular beam epitaxy. All three techniques reveal evidence of a buried p-type layer beneath a surface electron accumulation layer in heavily Mg-doped samples. The use of lattice-matched Yttria-stablized Zirconia substrates also provides evidence of a p-type layer.
Photoluminescence from Gd-implanted AlN and GaN Epilayers
Authors: Zavada John M , Nepal Neeraj , Lin J. , Kim K. H. , Jiang H. X. , Hite J. , Thaler G. T. , Frazier R. M. , Abernathy C. R. , Pearton S. J. 
Published: April 2011

ABSTRACTGaN and AlN thin films were implanted with gadolinium (Gd)atoms and characterized using deep ultra-violet (UV) photoluminescence(PL). The Gd-implanted samples were annealed at temperatures up to 1178K in a flowing N2 gas to facilitate recovery of implantation-related damage. Using the output at 195 nm from a quadrupled Ti:sapphire laser, narrow PL emission was observed at 318 nm from the Gd- implanted AlN thin films. This emission is characteristic of the lowest energy 4f transition of the trivalent Gd ion. A boarder emission band, also centered at 318 nm, was observed under excitation at 266 nm. No PL emission was observed from the Gd-implanted GaN thin films at either the bandedge or due to a 4f transition. The dependence of the UV emission on AlN sample temperature was systematically studied. The peak PL emission intensity decreased by less that a factor of 3 over the temperature range of 10 K to 300 K. Decay transients of the UV emission were measured indicating that the lifetime of this emission is very fast.
Structural Defects in Laterally Overgrown GaN Layers Grown on Non-polar Substrates
Authors: Liliental-Weber Zuzanna , Ni X. , Morkoc H. 
Published: April 2011

ABSTRACTTransmission electron microscopy was used to study defects in lateral epitaxial layers of GaN which were overgrown on a template of a-plane (1120) GaN grown on (1102) r-plane Al2O3. A high density of basal stacking faults is formed in these layers because the c-planes of wurtzite structure are arranged along the growth direction. Density of these faults is decreasing at least by two orders of magnitude lower in the wings compared to the seed areas. Prismatic stacking faults and threading dislocations are also observed, but their densities drastically decrease in the wings. The wings grow with opposite polarities and the Ga-wing width is at least 6 times larger than N-wing and coalescence is rather difficult. Some tilt and twist was detected using Large Angle Convergent Beam Electron Diffraction.
AlGaN/GaN-sensors for Monitoring of Enzyme Activity by pH-Measurements
Authors: Kittler Gabriel , Spitznas Armin , Luebbers Benedikt , Lebedev Vadim , Wegener Dennis , Gebinoga Michael , Weise Frank , Schober Andreas , Ambacher Oliver 
Published: April 2011

ABSTRACTGaN based pH-sensors were used to measure the reaction and the kinetics of a lipase assay producing caprylic acid. Sensor structures consist of an AlGaN/GaN-heterostructure grown by plasma-induced molecular beam epitaxy with a thin GaN cap layer. The carrier concentration of the two-dimensional electron gas is manipulated by changing the surface potential due to changes in pH value.
Magnetic and Optical Properties of Eu-doped GaN
Authors: Hite Jennifer , Thaler G T , Park J H , Steckl A J , Abernathy C R , Zavada J M , Pearton Stephen 
Published: April 2011

ABSTRACTGaN films were doped with Eu to a concentration of ∼0.12 at. % during growth at 800°C by molecular beam epitaxy, with the Eu cell temperature held constant at 470°C. All samples were post-annealed at 675°C. The films exhibited strong photoluminescence (PL) in the red (622 nm) whose absolute intensity was a function of the Ga flux during growth, which ranged from 3-5.4×10−7 Torr. The maximum PL intensity was obtained at a Ga flux of 3.6×10−7 Torr. The samples showed room temperature ferromagnetism with saturation magnetization of ∼0.1-0.45 emu/cm3, consistent with past reports where the Eu was found to be predominantly occupying substitutional Ga sites. There was an inverse correlation between the PL intensity and the saturation magnetization in the films. X-ray diffraction showed the presence of EuGa phases under all of our growth conditions but these cannot account for the observed magnetic properties.
Resonant Energy Transfer due to Exciton Coupling in Hybrid Persovskites Conjugated to GaN Semiconductors
Authors: Li Jianyou , Neogi Arup , Ishihara Teruya 
Published: April 2011

ABSTRACTExciton-Exciton coupling in hybrid persovskites conjugated to GaN Semiconductors system has been studied. Excitons are strongly coupled in (C6H5C2H4NH3)2PbI4[bis(phenethyl-ammonium)tetraiodoplumbatel] (PEPI) is a hybrid inorganic-organic layered, with a perovskite structure quantum well (QW). The inorganic PbI4 monolayer is sandwiched between organic layers. The interaction between electron and hole forming the bound exciton is significantly stronger due to dielectric confinement. The lowest exciton binding energy is 220 meV, which is 20 times in comparison to GaAs. Gallium nitride (GaN) semiconductor has defect bound excitons with absorption band, which overlaps with the emission spectra of the PEPI system. This facilitates resonant energy transfer (RET) from the GaN defect bound exciton states to the excitons confined in the PEPI layer. We investigated the interaction by photoluminescence (PL) and found that 1s exciton in the PEPI layer strongly couples with the GaN defect level exciton, which is pronounced at lower temperature (< ∼ 100 K).
Electrical Properties, Deep Levels Spectra and Luminescence of Undoped GaN/InGaN Multi-quantum-well Structures as Affected by Electron Irradiation
Authors: Polyakov Alexander Y , Smirnov Nikolai B , Govorkov Anatoliy V , Markov Alexander V , Lee Cheul-Ro , Lee In-Hwan , Kolin Nikolai G , Merkurisov Denis I , Boiko Vladimir M , Wright James S 
Published: April 2011

ABSTRACTEffects of 10 MeV electron and fast reactor neutron irradiations on carrier removal rate and deep traps spectra were compared for undoped n-GaN samples. It is shown that for electron irradiation the carrier removal rate is well accounted for by the difference in introduction rates of nitrogen-vacancy-related donors with activation energy 0.2 eV and of nitrogen-interstitial-related acceptors at Ec-1.2 eV. In the case of neutron irradiation the introduction rate of all deep traps was much lower than the carrier removal rate indicating that the main contribution to electron removal was due to disordered regions. These regions give rise to a marked persistent photocapacitance signal and a hole-trap-like feature in deep traps spectra. The Fermi level position in the core of disordered regions is located near Ec-(0.85-1) eV.
Loss of Quantum Efficiency in Green Light Emitting Diode Dies at Low Temperature
Authors: Li Yufeng , Zhao Wei , Xia Yong , Zhu Mingwei , Senawiratne Jayantha , Detchprohm Theeradetch , Schubert E. Fred , Wetzel Christian M 
Published: April 2011

ABSTRACTThe electroluminescence, photoluminescence and cathodoluminescence of GaInN/GaN multiple quantum well light emitting diode dies are analyzed at variable low temperature. Three dies of nominally identical structure but strongly different RT performance from 510 nm to 525 nm have been studied. The electroluminescence peak energy exhibits a blue shift from RT to 158 K followed by a red shift for lower temperature. In the same low-temperature range, a secondary emission peak appears near 390 nm (3.18 eV) that resembles a donor-acceptor pair transition from GaN. Depth profiling spectroscopy of this transition at 77 K reveals its location either in the unintentionally doped quantum barriers or within the n-GaN layer, rather than the commonly believed Mg doped p-type GaN layers. The external quantum efficiency of each die increases as the temperature is lowered. A maximum is reached for all near 158 K while for lower temperature as low as 7.7 K, the efficiency continuously drops. The pronounced efficiency maximum is tentatively assigned to a combination of temperature dependent mobility and shift of the actual pn-junction location.
Low-voltage Avalanche Breakdown in AlGaN Multi-quantum Wells
Authors: Zhang Shengkun , Zhou X. , Wang Wubao , Alfano R. R. , Dabiran A. M. , Osinky A. , Wowchak A. M. , Hertog B. , Plaut C. , Chow P. P. 
Published: April 2011

ABSTRACTIn this work, electro-luminescence (EL) of a AlGaN p-i-n diode have been investigated in both avalanche and injection modes. The active i-region of the diode consists of Al0.1Ga0.9N/Al0.15Ga0.85N MQWs. Strong interband luminescence from the Al0.1Ga0.9N active layers was observed when operating the device in both avalanche and injection modes. The threshold voltage for avalanche breakdown is as low as 9 V. This indicates that the impact ionization coefficient of electrons is greatly enhanced in these Al0.1Ga0.9N/Al0.15Ga0.85N MQWs comparing to AlGaN bulk materials. Polarization-induced electric fields in the Al0.1Ga0.9N well layers are believed to be responsible for the enhancement of the ionization coefficient. In a control sample that has higher defect density, the electroluminescence was dominated by long-wavelength emissions, which results from impact ionizations of the defect levels.
Persistent Photoconductivity in High-mobility AlxGa1−xN/AlN/GaN Heterostructures Grown by Metal-organic Vapor-phase Epitaxy
Authors: Biyikli Necmi , Ozgur Umit , Ni Xianfeng , Fu Yi , Morkoc Hadis , Kurdak Cagliyan 
Published: April 2011

ABSTRACTWe report on the persistent photoconductivity (PPC) effect in AlxGa1−xN/AlN/GaN heterostructures with two different Al compositions (x=0.15 and 0.25). The two-dimensional electron gas (2DEG) was characterized by Shubnikov-de Haas and Hall measurements. At cryogenic temperatures under optical illumination, the 2DEG carrier density and mobility was enhanced. The persistent photocurrent in both samples exhibited a strong dependence on illumination wavelength.