bluuebunny/crossref_metadata_2025_split huggingface dataset:
III‐nitride grown on freestanding GaN nanostructures
Authors: Wang Yongjin , Hu Fangren , Zhu Hongbo , Hane Kazuhiro 
Published: February 2012

AbstractWe report here the epitaxial growth of III‐nitride on the freestanding GaN nanostructures by molecular beam epitaxy growth. Various GaN nanostructures are defined by electron beam lithography and realized on GaN‐on‐silicon substrate by fast atom beam etching. Silicon substrate beneath GaN nanostructures is removed from the backside to form the freestanding GaN slab, and the epitaxial growth of III‐nitride by MBE is performed on the prepared GaN template. The selective growth takes place with the assistance of GaN nanostructures and generates hexagonal III‐nitride pyramids. Thin epitaxial structures, depending on the shape and the size of GaN nanostructure, can produce the promising optical performance. This work opens the way to combine silicon micromachining with the epitaxial growth of III‐nitride by MBE on GaN‐on‐silicon substrate for further integrated optics (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Characterization of Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs by quasi‐static C‐V measurement
Authors: Huang Sen , Yang Shu , Roberts John , Chen Kevin J. 
Published: February 2012

AbstractThe threshold‐voltage (Vth) instability in AlGaN/GaN MIS‐HEMTs with ALD‐Al2O3 (15 nm) as gate dielectrics is systematically investigated by dc current‐voltage (I‐V), high‐frequency capacitance‐voltage (C‐V) (HFCV), and quasi‐static C‐V (QSCV) characterizations. For Al2O3/GaN/AlGaN/GaN MIS diodes, tiny Vth hysteresis (ΔVth) appears in double‐mode (up and down sweep) HFCV measurements if the maximum forward bias (VF,max) is only set to 0 V, while an apparent clockwise ΔVth (as large as 0.9 V) emerges as VF,max is increased to +5 V. The stability of Vth in the corresponding MIS‐HEMTs is thus studied by increasing the maximum VGS (VGS,max) in the measurement of double‐mode transfer characteristics. Significant clockwise ΔVth also occurred once the VGS,max exceeds +1.1 V, and it increased to ∼1 V at VGS,max= +3 V. Such Vth‐instability is absent in AlGaN/GaN HEMTs. It is suggested that the acceptor‐like deep states at Al2O3/GaN interface account for the Vth‐instability in Al2O3/GaN/AlGaN/GaN MIS‐HEMTs, and their filling and emission processes are successfully captured by QSCV measurements. The interface state density detected is about 4.6×1012 cm‐2 using 1 Hz QSCV. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Photoluminescence changes in n‐type GaN samples after photoelectrochemical treatment
Authors: Fujii Katsushi , Koike Kayo , Atsumi Mika , Goto Takenari , Itoh Takashi , Yao Takafumi 
Published: February 2012

AbstractPhotoelectrochemical water splitting using semiconductors to produce hydrogen is a promising technique for converting sunlight to chemical energy. However, anodic photocorrosion occurs during the reaction even when n‐type GaN, a chemically stable material, is used for the photo‐illuminated working electrode. We previously demonstrated that the stability is related to the amount of Si doping used to make the GaN to be n‐type. This means that, the surface damage after photoelectrochemical reaction depends on the amount of Si. We have now investigated the relationship between this surface change and the optical properties especially for the near band edge peaks. With the peak shift by the strain relaxation due to the surface change from smooth to rough, new peaks around 3.4 eV were observed after photoelectrochemical treatment. These new peaks are defect‐related emission, which has been reported as Yi lines. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
RF‐MBE growth of semipolar InN(10‐13) and InGaN(10‐13) on GaAs(110)
Authors: Orihara Misao , Yagi Shuhei , Hijikata Yasuto , Yaguchi Hiroyuki 
Published: February 2012

AbstractWe have studied InN and InGaN films grown on GaAs(110) substrates by RF‐assisted molecular beam epitaxy. Reflection high‐energy diffraction observation and X‐ray diffraction (XRD) measurements revealed that the InN films were epitaxially grown with InN(10‐13)// GaAs(110). From XRD pole figure measurements, only one InN(0002) peak was found at an angle of 31.8° from the pole, indicating that the semipolar InN films were free from twin crystals. This can be explained by the similarity in the anisotropic structure between InN(10‐13) and GaAs(110) surfaces. By using low‐temperature InN buffer layers, we could obtain semipolar InN films with a smooth surface. Polarization anisotropy in the photoluminescence peak observed at 0.67 eV from semipolar InN(10‐13) was weaker than that from a ‐plane InN, which is reasonable considering the smaller angle between the c‐axis and the perpendicular direction to the semipolar InN surface. We have also successfully grown In‐rich InGaN(10‐13) on GaAs(110) substrates with an InN(10‐13) intermediate layer, and observed strong photoluminescence from the semipolar InGaN films (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth of flat p‐GaN contact layer by pulse flow method for high light‐extraction AlGaN deep‐UV LEDs with Al‐based electrode
Authors: Akiba Masahiro , Hirayama Hideki , Tomita Yuji , Tsukada Yusuke , Maeda Noritoshi , Kamata Norihiko 
Published: February 2012

AbstractImprovement of light extraction efficiency (LEE) is strongly demanded in an AlGaN‐based deep ultraviolet (DUV) light‐emitting diode (LED), because the LEE of AlGaN DUV LED is low (usually below 10%) due to the light absorption at around p‐GaN contact layer and p‐type electrode. We have demonstrated improvement of LEE of AlGaN DUV LEDs by using thin p‐GaN contact layer and using Al‐based high‐reflectivity p‐electrode. It was difficult to grow thin and flat p‐type GaN layers with heavy Mg‐doping on high‐Al‐content AlGaN layers. We demonstrated the growth of flat and thin p‐GaN contact layer by using ‘an NH3 pulse‐flow growth method’. We investigated the growth conditions for thin p‐GaN contact layer with high‐hole‐concentration using the NH3 pulse‐flow growth method. The surface roughness of the p‐GaN layer on high‐Al‐content p‐AlGaN was markedly improved by using an NH3 pulse‐flow growth method. We fabricated 250 nm‐band AlGaN quantum well (QW) DUV LEDs with thin p‐GaN contact layers grown by an NH3 pulse‐flow growth method. We observed single‐peaked operation spectrum for the 251 nm AlGaN MQW LED. The maximum output power and external quantum efficiencies (EQE) were 17.7 mW and 1.32%, respectively, measured under room temperature cw operation. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Atomically controlled chemical polishing of GaN using platinum and hydrofluoric acid
Authors: Sadakuni Shun , Murata Junji , Sano Yasuhisa , Yagi Keita , Okamoto Takeshi , Tachibana Kazuma , Asano Hiroya , Yamauchi Kazuto 
Published: February 2012

AbstractWe have developed a novel planarization method called catalyst‐referred etching (CARE), which utilizes platinum as a catalyst that is immersed in hydrofluoric (HF) acid solution. In this process, chemical etching occurs only near the surface of a platinum plate that has a flat surface. The protrusions on a GaN substrate that is in contact with the surface of the catalyst plate are the only parts that are removed by the platinum and HF solution. The surface is therefore flattened without damaging the crystal. Morphological characterization showed that CARE produced smooth surfaces with single bilayer atomic terracing throughout the substrate. Cross‐sectional transmission electron microscope observations revealed that the surface was atomically flat with no subsurface damage (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Peculiarities of galvanomagnetic effects in GaN epilayers and GaN/InGaN quantum wells
Authors: Malinovskis P. , Mekys A. , Kadys A. , Malinauskas T. , Grinys T. , Bikbajevas V. , Tomašiūnas R. , Storasta J. 
Published: February 2012

AbstractTemperature dependent Hall effect, magnetoresistivity and time resolved photoconductivity studies have been performed on GaN epilayers and GaN/InGaN multiple quantum wells (MQWs) grown on sapphire films by Metal Organic Chemical Vapor Deposition (MOCVD) method. The MQW structures consisted of different width or different amount of quantum wells. We related the electrical parameters with the quantum structure parameters and found that the geometrical variation of the quantum wells may be substituted by the variation of the amount of the quantum wells. The Hall and the magnetoresistivity measurements showed the complex behavior, which was attributed to the inhomogeneities of the samples, similarly to the case of the crystals with great size defects (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Plasma affected 2DEG properties on GaN/AlGaN/GaN HEMTs
Authors: Linkohr Stefanie , Pletschen Wilfried , Kirste Lutz , Himmerlich Marcel , Lorenz Pierre , Krischok Stefan , Polyakov Vladimir , Müller Stefan , Ambacher Oliver , Cimalla Volker 
Published: February 2012

AbstractWe investigated the impact of SF6 plasma treatments on the electronic transport properties of GaN/AlGaN/GaN heterostructures by employing different plasma conditions as well as annealing in nitrogen atmosphere at 425 °C. The electrical properties are characterized by Hall‐effect measurements while electron spectroscopy and X‐ray measurements are used to investigate changes in the surface chemical composition and in the layer structure, respectively. It is demonstrated that plasma treatments strongly affect the 2DEG properties of the heterostructure due to altering of the surface potential accompanied by the formation of a thin fluorinated amorphous film. Increasing the DC bias voltage for the plasma treatment leads to an additional degradation of the mobility caused by incorporation of fluorine into the heterostructure interface. Furthermore, the thin GaN cap layer is etched by plasma treatments with higher bias potential, which increases the carrier density at the interface (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Ab initio study of the properties of GaN(0001) surface at MOVPE and HVPE growth conditions
Authors: Kempisty Pawel , Strak Pawel , Krukowski Stanislaw 
Published: February 2012

AbstractDensity functional theory (DFT) is used to simulate the properties of GaN(0001) surface employing a finite slab with additional modifications of the non‐real side by termination with variously charged pseudo‐hydrogen atoms. Different terminations change the electric field inside the slab and causes a relative shift of the energy of the surface and band states, which is known as Surface States Stark Effect (SSSE). It is shown that single hydrogen atom is barrierlessly adsorbed on GaN(0001) surface in the on‐top position. Its adsorption energy strongly depends on the surface coverage by other hydrogen atoms, being above 3 eV and below 1.5 eV for the coverage lower and higher than 0.75 ML, respectively. This large difference is due to the difference of electronic occupation of the surface states. The adsorption energies indicate that hydrogen can be stably attached to the surface up to 0.75 ML coverage. It is shown that the adsorption energy of molecular hydrogen depends to some degree on the electric field at the surface, i.e. doping in the bulk. The dependence of hydrogen coverage on the pressure in the vapor shows that complete removal of hydrogen from GaN(0001) surface is difficult. Also chemical potential of hydrogen at the surface as a function of its coverage is determined. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of crack‐free thick AlN film on a‐plane sapphire by low‐pressure HVPE
Authors: Takagi Yuta , Miyagawa Reina , Miyake Hideto , Hiramatsu Kazumasa 
Published: February 2012

AbstractThe periodic trench patterning of sapphire substrates is useful for the growth of crack‐free AlN thick films. However, the in‐plane epitaxial relationship between AlN and a‐plane sapphire depends on the initial growth temperature. Therefore, two trench directions, the <0001>a‐plane sapphire and <1‐100>a‐plane sapphire directions are investigated in this study. We investigated the control of in‐plane epitaxial relationship between AlN and a‐plane sapphire by low‐pressure HVPE and the effect of the trench direction of AlN, which results in two different in‐plane epitaxial relationships on a‐plane sapphire (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Growth and structural, optical and electrical properties study of bulk GaN
Authors: Gogova D. , Rudko G. , Siche D. 
Published: February 2012

AbstractHigh‐quality GaN substrates with a thickness of 0.5 to 1.2 mm were prepared by halide vapor‐phase epitaxy (HVPE) on c‐plane sapphire and by means of a post‐growth laser‐induced lift‐off or natural stress‐induced (self‐) separation process. Structural, optical and electrical properties of the grown material were studied in detail. Resistivity and doping concentrations dependence on temperature were investigated and the results revealed a low donor concentration (2 × 1015 cm‐3 at 273 K) and a moderate resistivity (10‐48 Ωcm) of the samples. Several deep levels observed in the DLTS spectra were identified. The study shows that the GaN material is self‐compensated and a strong influence of point defects related to dislocations on electronic transport is observed. The HVPE growth on InGaN/GaN multi‐quantum wells buffer layers and subsequent self‐separation method was seen as advantageous, in comparison to the laser‐induced lift‐off one, in respect to a lower cost and better crystalline quality of the GaN material obtained (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The number of graphs and a random graph with a given degree sequence
Authors: Barvinok Alexander , Hartigan J.A. 
Published: February 2012

AbstractWe consider the set of all graphs on n labeled vertices with prescribed degrees D = (d1,…,dn). For a wide class of tame degree sequences D we obtain a computationally efficient asymptotic formula approximating the number of graphs within a relative error which approaches 0 as n grows. As a corollary, we prove that the structure of a random graph with a given tame degree sequence D is well described by a certain maximum entropy matrix computed from D. We also establish an asymptotic formula for the number of bipartite graphs with prescribed degrees of vertices, or, equivalently, for the number of 0‐1 matrices with prescribed row and column sums. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2013
Percolation and limit theory for the poisson lilypond model
Authors: Last Günter , Penrose Mathew D. 
Published: February 2012

AbstractThe lilypond model on a point process in d ‐space is a growth‐maximal system of non‐overlapping balls centred at the points. We establish central limit theorems for the total volume and the number of components of the lilypond model on a sequence of Poisson or binomial point processes on expanding windows. For the lilypond model over a homogeneous Poisson process, we give subexponentially decaying tail bounds for the size of the cluster at the origin. Finally, we consider the enhanced Poisson lilypond model where all the balls are enlarged by a fixed amount (the enhancement parameter), and show that for d > 1 the critical value of this parameter, above which the enhanced model percolates, is strictly positive. © 2012 Wiley Periodicals, Inc. Random Struct. Alg., 2012
Cryptanalysis of a secure and efficient authentication protocol for anonymous channel in wireless communications
Authors: Lee Cheng‐Chi , Lin Tsung‐Hung , Tsai Chwei‐Shyong 
Published: February 2012

ABSTRACTTo enhance the efficiency and the security in an anonymous channel of wireless systems, Yang et al. proposed a secure and efficient authentication protocol for an anonymous channel in wireless communications. The protocol did not use asymmetric cryptosystems to protect the identity of the mobile user because the cryptosystems have high complex and high computation cost. Not only can the protocol resist some security attacks but also the computation cost is low. However, the authors shall point out that their protocol is vulnerable to key compromise attack. Through this attack, any adversary can obtain the secret key Kh, i shared between the home network (HN) and the mobile station (MS). Then, the adversary can wiretap any messages that he/she wants using the secret key between the HN and the MS. Copyright © 2012 John Wiley & Sons, Ltd.
Growth, Characterization, and Properties of Nanographene
Authors: Yang Wei , He Congli , Zhang Lianchang , Wang Yi , Shi Zhiwen , Cheng Meng , Xie Guibai , Wang Duoming , Yang Rong , Shi Dongxia , Zhang Guangyu 
Published: February 2012

AbstractA systematic study on nanographene grown directly on silicon dioxide substrates is reported. The growth is carried out in a remote plasma‐enhanced chemical vapor deposition system at a low temperature of around 550 °C with methane gas as the carbon source. Atomic force microscopy is used to characterize the nanographene morphology, and Raman spectroscopy, X‐ray photoelectron spectroscopy, and scanning tunneling microscopy are exploited to identify the in‐plane sp2 bonding structures of nanographene samples. Electrical transport properties are measured at various temperatures down to 4 K. Tunneling effects, minimal conductance at the charge‐neutral point, sheet resistances, and Dirac point position at different channel lengths are investigated. In addition, nanographene film possesses high transmittance properties, as indicated by transmittance spectra. Nanographene devices are fabricated from rippled structures, and show great promise for strain‐gauge sensor applications.
Graphoepitaxy of Block‐Copolymer Self‐Assembly Integrated with Single‐Step ZnO Nanoimprinting
Authors: Kim Sarah , Shin Dong Ok , Choi Dae‐Geun , Jeong Jong‐Ryul , Mun Jeong Ho , Yang Yong‐Biao , Kim Jaeup U. , Kim Sang Ouk , Jeong Jun‐Ho 
Published: February 2012

AbstractA highly efficient, ultralarge‐area nanaolithography that integrates block‐copolymer lithography with single‐step ZnO nanoimprinting is introduced. The UV‐assisted imprinting of a photosensitive sol–gel precursor creates large‐area ZnO topographic patterns with various pattern shapes in a single‐step process. This straightforward approach provides a smooth line edge and high thermal stability of the imprinted ZnO pattern; these properties are greatly advantageous for further graphoepitaxial block‐copolymer assembly. According to the ZnO pattern shape and depth, the orientation and lateral ordering of self‐assembled cylindrical nanodomains in block‐copolymer thin films could be directed in a variety of ways. Significantly, the subtle tunability of ZnO trench depth enabled by nanoimprinting, generated complex hierarchical nanopatterns, where surface‐parallel and surface‐perpendicular nanocylinder arrays are alternately arranged. The stability of this complex morphology is confirmed by self‐consistent field theory (SCFT) calculations. The highly ordered graphoepitaxial nanoscale assembly achieved on transparent semiconducting ZnO substrates offers enormous potential for photonics and optoelectronics.
Reversible Single‐Molecule Switching in an Ordered Monolayer Molecular Dipole Array
Authors: Li Huang Yu , Lu Yunhao , Niu Tian Chao , Huang Han , Kera Satoshi , Ueno Nobuo , Wee Andrew Thye Shen , Chen Wei 
Published: February 2012

AbstractMaking electronic devices using a single molecule has been the ultimate goal of molecular electronics. For binary data storage in particular, the challenge has been the ability to switch a single molecule in between bistable states in a simple and repeatable manner. The reversible switching of single molecules of chloroaluminum phthalocyanine (ClAlPc) dipolar molecules within a close‐packed monolayer is demonstrated. By pulsing an scanning tunneling microscopy tip, read–write operations of single‐molecular binary bits at ∼40 Tb/cm2 (∼250 Tb/in2) are demonstrated.
Synthesis and characterization of graft copolymers of Sago starch and acrylic acid
Authors: Kaur Inderjeet , Sharma Meenakshi 
Published: February 2012

AbstractSago starch has been graft copolymerized with acrylic acid (AAc) by mutual gamma radiation method. Reaction conditions such as total dose, monomer concentration and amount of methanol were optimized to obtain maximum grafting percentage. Maximum percentage of grafting, Pg (158.00%) was obtained at an optimum total dose of 62.64 kGy using 4.37 moles/L of AAc in 1 mL of methanol. Using optimum conditions, the effect of cross‐linker, glyoxal, on percent grafting was also studied and maximum grafting was obtained at [Glyoxal] = 54.70 moles/L. Characterization of the graft copolymer was carried out by FTIR, TGA, SEM, XRD analytical methods. The grafted Sago starch was found to have increased crystalline and improved thermal behavior. Swelling and solubility kinetics were measured for each of the samples and correlation between the effects of the reaction parameter on swelling‐solubility kinetics was evaluated. Maximum swelling (4192.3%) at 37°C in 8 h was observed for the sample with 59.9% graft level. Higher swelling percentage is indicative of the graft copolymer to have the properties of a hydro gels that can be utilized for use as drug delivery vehicle and purification of industrial effluents.
Amylopectin structure of heat–moisture treated starches
Authors: Jiranuntakul Wittawat , Puttanlek Chureerat , Rungsardthong Vilai , Puncha‐arnon Santhanee , Uttapap Dudsadee 
Published: February 2012

AbstractThe effects of heat–moisture treatment (HMT; moisture content of 25%, at 100°C for 24 h) on starch chain distribution and unit chain distribution of amylopectin in normal rice, waxy rice, normal corn, waxy corn, normal potato, and waxy potato starches were investigated. After HMT, starch chain distribution (amylose and amylopectin responses) of waxy corn and potato starches were identical to those of untreated starches, whereas the chromatographic response of waxy rice starch showed a slight decrease, but with a slight increase in peak tailing. This result indicated that HMT had no (or very limited) effect on the degradation of amylopectins. Analysis of unit chain distribution of amylopectins revealed that waxy characteristics affected the molecular structure of amylopectin in untreated starches, i.e., the CL of normal‐type starches was greater than that of waxy‐type starches. After HMT, the CL and unit chain distribution of all starches were no different than those of untreated starches. The results implied that changes in the physico‐chemical properties of HMT starches would be due to other phenomena rather than the degradation of amylopectin molecular structure. However, the thermal degradation of amylopectin molecules of waxy starches could occur by HMT at higher treatment temperatures (120 and 140°C).
Transient response of an annular interfacial crack between dissimilar piezoelectric layers under mechanical and electrical impacts
Authors: Ren J.H. , Wang W. , Li Y.S. , Cai Z.Y. 
Published: February 2012

AbstractThe dynamic response of an annular interfacial crack between dissimilar piezoelectric layers subjected to mechanical and electrical impact loadings is investigated. Laplace and Hankel transforms are employed to reduce the mixed boundary value problem to Cauchy singular integral equations. The integral equations are further reduced to a system of algebraic equations with the aid of Jacobi polynomials. The dynamic field intensity factors and dynamic energy release rates are determined. Numerical results reveal the effects of crack configuration, electrical impact loading on crack propagation, and growth.
Boundary layer separation of hydromagnetic flows
Authors: Núñez M. 
Published: February 2012

AbstractThe influence of the magnetic field on the boundary layer separation of a two‐dimensional incompressible flow of a conducting fluid subject to a non‐slip boundary condition is studied. It is found that the key factor differentiating this phenomenon from the hydrodynamic case is the angular velocity of the magnetic field at the boundary wall. The general equation governing the start of separation is illustrated by a class of flows generalizing the classical Hartmann one, where the physical meaning of the different terms is very clear.