bluuebunny/crossref_metadata_2025_split huggingface dataset:
AlGaN based MEMS structures
Authors: Hähnlein Bernd , Tonisch Katja , Ecke Gernot , Grieseler Rolf , Michael Steffen , Schaaf Peter , Pezoldt Jörg 
Published: January 2014

AbstractAlxGa1‐xN solid solutions were heteroepitaxially grown on 3C‐SiC(111)/Si(111) pseudo substrates fabricated by low pressure chemical vapour deposition. Free standing doubly‐clamped resonator bars and cantilevers were fabricated from these AlxGa1–xN layers. The resonance frequencies of the microelectromechanical structures were measured using electrostatic excitation and vibrometry at ambient conditions. The obtained resonance frequencies allowed a self consistent determination of the Young's modulus of the AlxGa1‐xN layers and the residual strain in the free standing structures. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The (0001)A surface phase diagram
Authors: Elyukhin Vyacheslav A. 
Published: January 2014

AbstractThe (0001)A surface phase diagram of InxGa1‐xN is investigated by using different approximations of the cluster variation method with the one‐, two‐ and three‐point basic clusters. The surface layer is considered in the total composition range as a binary regular solution on the triangular lattice. The miscibility gap temperature and concentration of the nearest neighbor surface atoms at this temperature are estimated as functions of the composition. The miscibility gap temperatures of In0.5Ga0.5N obtained by one‐, two‐ and three‐point cluster approximations are 710 °C, 535 °C and 370 °C, respectively. The strong InIn and GaGa pair clustering in comparison with InGa pair formation at temperatures higher than the miscibility gap one is demonstrated in the three‐point approximation. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Crosstalk suppression of CMOS compatible AlN based SAW devices on low resistive Si(100)
Authors: Kaletta Udo Ch. , Wolansky D. , Wipf M. Fraschke Ch. , Wenger Ch. 
Published: January 2014

AbstractAluminum nitride (AlN) based high frequency surface acoustic wave (SAW) devices are produced by using a new CMOS compatible concept. Textured c‐axis oriented AlN films have been deposited on tungsten based embedded interdigital transducers (IDTs) by the reactive pulse DC‐sputter technique within the thermal budget of back end of line (BEOL) processes. Two SAW Rayleigh modes with different acoustic velocities were measured and identified by finite element method (FEM) simulation (Kaletta and Wenger, FEM Simulation of Rayleigh waves for CMOS compatible SAW devices based on AlN/SiO2/Si(100) (Elsevier Ultrasonics, available online 18 April 2013, ISSN 0041‐624X, 10.1016/j.ultras.2013.04.009) [1]). Electromagnetic crosstalk between in‐ and output IDTs via low resistive Silicon substrates is one of the most troublesome sources of integrated SAW devices. The impact of several device parameters like the acoustic aperture, the number of fingers and the delay line length on the electromagnetic crosstalk was studied and routes for optimizing SAW filter designs on low resistive Si(100) will be presented. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Sequential multiple‐step europium ion implantation and annealing of GaN
Authors: Miranda S. M. C. , Edwards P. R. , O'Donnell K. P. , Boćkowski M. , Alves E. , Roqan I. S. , Vantomme A. , Lorenz K. 
Published: January 2014

AbstractSequential multiple Eu ion implantations at low fluence (1×1013 cm‐2 at 300 keV) and subsequent rapid thermal annealing (RTA) steps (30 s at 1000 °C or 1100 °C) were performed on high quality nominally undoped GaN films grown by metal organic chemical vapour deposition (MOCVD) and medium quality GaN:Mg grown by hydride vapour phase epitaxy (HVPE). Compared to samples implanted in a single step, multiple implantation/annealing shows only marginal structural improvement for the MOCVD samples, but a significant improvement of crystal quality and optical activation of Eu was achieved in the HVPE films. This improvement is attributed to the lower crystalline quality of the starting material, which probably enhances the diffusion of defects and acts to facilitate the annealing of implantation damage and the effective incorporation of the Eu ions in the crystal structure. Optical activation of Eu3+ ions in the HVPE samples was further improved by high temperature and high pressure annealing (HTHP) up to 1400 °C. After HTHP annealing the main room temperature cathodo‐ and photoluminescence line in Mg‐doped samples lies at ∼ 619 nm, characteristic of a known Mg‐related Eu3+ centre, while after RTA treatment the dominant line lies at ∼ 622 nm, typical for undoped GaN:Eu. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optically pumped AlGaN quantum‐well lasers at sub‐250 nm grown by MOCVD on AlN substrates
Authors: Liu Yuh‐Shiuan , Lochner Zachary , Kao Tsung‐Ting , Satter Md. Mahbub , Li Xiao‐Hang , Ryou Jae‐Hyun , Shen Shyh‐Chiang , Yoder P. Douglas , Detchprohm Theeradetch , Dupuis Russell D. , Wei Yong , Xie Hongen , Fischer Alec , Ponce Fernando 
Published: January 2014

AbstractIn this study, we employed bulk (0001) AlN substrates for the metalorganic chemical vapor deposition growth of AlGaN multi‐quantum‐well heterostructures in an Aixtron 6 × 2″ close‐coupled showerhead reactor. The wafers were fabricated into cleaved bars with a cavity length of ∼1 mm. Two different layer structure designs are presented in this work. Both laser bars were optically pumped by a pulsed 193 nm ArF excimer laser at room temperature. The lasing wavelengths are 243.5 nm and 245.3 nm with threshold power density 427 kW/cm2 and 297 kW/cm2, respectively. Both laser bars showed transverse electric‐polarization‐dominated optical emission when operating above threshold. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Properties of AlN based lateral polarity structures
Authors: Kirste Ronny , Mita Seiji , Hoffmann Marc P. , Hussey Lindsay , Guo Wei , Bryan Isaac , Bryan Zachary , Tweedie James , Gerhold Michael , Hoffmann Axel , Collazo Ramón , Sitar Zlatko 
Published: January 2014

AbstractGrowth and characterization of AlN based lateral polarity structures (LPS) are presented. The LPS were grown by MOCVD using patterned low temperature AlN/sapphire substrates: the Al‐polar and N‐polar AlN grew on AlN buffer layer and nitrided sapphire, respectively. AFM images showed a height difference between the two adjacent domains of different polarity on the order of 30 nm, which was equivalent to the low temperature AlN buffer layer thickness. SEM images provided an insight in the growth mode of the two polarities. It was shown that Al‐polar AlN grew two‐dimensionally, leading to a smooth well coalesced layer, while N‐polar AlN grew primarily three‐dimensionally, leading to a columnar structure. This difference in the growth mode led to different properties of domains with opposite polarity, including strain and defect incorporation, as observed by X‐ray diffraction, photoluminescence, and Raman spectroscopy measurements. Finally, an outlook on the applicability and future development of AlN‐based LPS is given. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Cubic GaN/AlN multi‐quantum wells grown on pre‐patterned 3C‐SiC/Si (001)
Authors: Kemper R. M. , Mietze C. , Hiller L. , Stauden T. , Pezoldt J. , Meertens D. , Luysberg M. , As D. J. , Lindner J. K. N. 
Published: January 2014

AbstractWe report for the first time on the growth of cubic AlN/GaN multi‐quantum wells (MQWs) on pre‐patterned 3C‐SiC/Si (001) substrates. The sample structure consists of 10 periods of 2 nm c‐AlN barriers with a 4 nm c‐GaN layer in between, which were grown on 3C‐SiC post shaped structures by means of molecular beam epitaxy. Substrate patterning has been realized by electron beam lithography and a reactive ion etching process. The 3C‐SiC posts have a length of about 550 nm and a height of about 700 nm. (Scanning) transmission electron microscopy studies show that the morphology of the MQWs is clearly influenced by {111} stacking faults, modulating the local growth rate. Further, the growth at the edges of the surface pattern is investigated. The MQW layers cover the 90° edges by developing low‐index facets rather than by forming a conformal system of 90° angled layers. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Biological detection by high electron mobility transistor (HEMT) based AlGaN/GaN
Authors: Zeggai Oussama , Ould‐Abbas Amaria , Bouchaour Mama , Zeggai Hichem , Sahouane Nordine , Madani Malika , Trari Djamel , Boukais Meriem , Chabane‐Sari N.‐E. 
Published: January 2014

AbstractMaterials based on gallium nitride are characterized by a wide bandgap. The excellent chemical, physical and electronic properties give them a place in various fields: electronics, optoelectronics, photovoltaics, military, biological and medical. The use of biosensors based III‐N has been confirmed for the detection of biological substances in cells, blood or in solutions. This effect of detection results in various chemical and electric changes in a medium that is contacted with the devices without gate metallization of a high electron mobility transistor (HEMT). HEMT sensors can thus be used to detect gases, ions, pH values, proteins and DNA. In this work, we are interested in HEMT‐based heterostructure AlGaN/GaN used in the construction of biosensors. The principle of operation of the HEMT is based on the properties of a high‐mobility two‐dimensional gas (2DEG) and high‐speed saturation channel of a 2DEG AlGaN HEMT is very close to the surface that is very sensitive to absorption of analytes. We use this microsystem for detection of substances found in biological solutions. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Void formation during GaN MOVPE on Si (111) employing low temperature AlN interlayers
Authors: Liu Cai , Wang Hongbo , Sodabanlu Hassanet , Sugiyama Masakazu , Nakano Yoshiaki 
Published: January 2014

AbstractDuring the growth of GaN on Si (111), voids were found in GaN layers in between AlN interlayers. Void formation mechanism is the decomposition of GaN in H2. Void formation process is carefully studied. It is clarified that voids are formed during the period between the growth of two neighbouring GaN layers, after the growth of AlN interlayer between them. There are some openings in AlN interlayers and they act as the pass for H2 to react with GaN. NH3 partial pressure, temperature, etching time, and conditions such as thickness of AlN interlayers can be utilized to tune the volume, size and shape of the voids. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitons and exciton‐phonon coupling in the optical response of GaN
Authors: Shokhovets S. , Bärwolf F. , Gobsch G. , Runge E. , Köhler K. , Ambacher O. 
Published: January 2014

AbstractWe carried out reflectance and spectroscopic ellipsometry measurements of high‐purity c ‐plane epitaxial films of wurtzite GaN in a temperature range 5‐840 K. Analysis of the data reveals three main contributions to the dielectric function related to optical transitions involving discrete exciton states, excitonic continuum and exciton‐phonon complexes, respectively. The observed contributing mechanisms show different temperature dependence. This behavior is related to specific interactions between optical excitations and thermal LO phonons. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Normally‐off GaN MOSFETs with high‐k dielectric CeO2 films deposited by RF sputtering
Authors: Ogawa Hiroki , Okazaki Takuya , Kasai Hayao , Hara Kenta , Notani Yuki , Yamamoto Yasuhiro , Nakamura Tohru 
Published: January 2014

AbstractThis paper describes normally‐off GaN MOSFETs with high‐k dielectric CeO2 films made by ion implantation. Ion implantation process reduces sheet and contact resistances of source and drain regions of this device. To obtain high Idss and gmmax, high‐k dielectric CeO2 was used as gate oxide films for GaN MOSFETs for the first time. Nitrogen ion implantation isolation processes were also adopted to fabricate isolation region. Normally‐off GaN MOSFETs with Idss of 350 mA/mm, gmmax of 40 mS/mm and threshold voltage of +0.5 V were obtained. The high Idss and normally‐off mode show the potential and advantages of GaN MOSFETs for high voltage operations. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
A hybrid current controller for dual three‐phase permanent magnet synchronous motors
Authors: Yuan Feixiong , Huang Shenghua 
Published: January 2014

AbstractControl of the current harmonics is a critical issue for dual three‐phase (DTP) permanent magnet synchronous motors (PMSMs). Considering the limitations of conventional synchronous frame proportional‐integral (PI) current regulator, this paper presents a hybrid current controller that combines the PI current regulator with a multiresonant controller. With the proposed hybrid current controller, precise current control can be achieved with only a slight increase in the computational effort. Theoretical analysis and experimental results confirm the effectiveness of proposed current controller. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.
Effects of nonuniform incident velocity on a dynamic wind turbine airfoil
Authors: Gharali Kobra , Johnson David A. 
Published: January 2014

AbstractFor further insight into the performance of a horizontal axis wind turbine blade section under yaw loads, a 2D numerical simulation of a pitching S809 airfoil under dynamic stall with an unsteady incident velocity is presented. The streamwise incident velocity and pitch angle of incidence oscillated with the same frequency but with a range of phase differences, − π ≤ Φ ≤ π. Changing Φ caused variation of the results, which can be highlighted as significantly augmented and dramatically damped dynamic stall loads, both increasing and decreasing trends for vortex growth time during Φ increase, a shifted location of the maximum loads and a change in the order of the vortex pair circulation in each cycle. The results showed strong dependency on the velocity and acceleration of the freestream during dynamic stall, which categorized the results in four individual subdomains with different behaviors. Copyright © 2014 John Wiley & Sons, Ltd.
Parametric investigation of the soil–structure interaction effects on the dynamic behaviour of a shallow foundation supported wind turbine considering a layered soil
Authors: Taddei F. , Butenweg C. , Klinkel S. 
Published: January 2014

AbstractThe proposed investigation is concerned with influential factors of soil–structure interaction issues for onshore wind turbines. Indeed, the awareness of these aspects encounters hardly a straightforward application in practical regulations and therefore is often neglected. However, with the rapid recent growth, the wind energy installations are expanding into regions where the soil conditions may be unfavorable. A consciousness raising of the significance of interaction between the wind turbine, its foundation and the underlying soil is lacking. This paper aims to fill this research gap. It involves a three‐blade wind turbine grounded on a layered half space. The layered soil is simplified as a horizontal layer over an homogeneous half space. However, the method can consider multilayered soil and different bottom conditions, such as rigid bedrock or flexible half space. The soil–structure system is modeled by means of a coupling between finite element and boundary element method. The analysis is carried out in frequency domain. At the first stage, the only foundation–soil system is investigated, and subsequently, the focus shifts to the whole turbine‐soil assembly. The effects of different parameters are systematically evaluated, in order to provide a range of values for which the soil–structure interaction has to be accounted for. The investigation highlighted the importance of the relative stiffness of structure and soil. Also, the ratio of the layer stiffness to the half space stiffness plays an important role. Copyright © 2014 John Wiley & Sons, Ltd.
Entropy of controlled invariant subspaces
Authors: Colonius F. , Helmke U. 
Published: January 2014

AbstractFor continuous‐time linear control systems invariance entropy of controlled invariant subspaces is introduced. It is shown that it coincides with a variant of topological entropy for linear flows which we call subspace entropy. Using this characterization, upper bounds in terms of eigenvalues of an induced flow are derived. Under additional assumptions (diagonalizability, single inputs) these bounds are improved.
The Shelf Life of a Safety Climate Assessment: How Long Until the Relationship with Safety–Critical Incidents Expires?
Authors: Bergman Mindy E. , Payne Stephanie C. , Taylor Aaron B. , Beus Jeremy M. 
Published: January 2014

Abstract

Purpose

This study investigates safety climate as both a leading (climate → incident) and a lagging (incident → climate) indicator of safety–critical incidents. This study examines the “shelf life” of a safety climate assessment and its relationships with incidents, both past and future, by examining series of incident rates in order to determine when these predictive relationships expire.

Design/Methodology/Approach
A survey was conducted at a large, multinational chemical manufacturing company, with 7,467 responses at 42 worksites in 12 countries linked to over 14,000 incident records during the 2 years prior and 2 years following the survey period. Regressions revealed that safety climate predicts incidents of varying levels of severity, but it predicts the most severe incidents over the shortest period of time. The same is true for incidents predicting safety climate, with more severe incidents having a shorter predictive window. For the most critical relationship (climate predicting more severe incidents), the ability of a safety climate assessment to predict incidents expires after 3 months.

Implications
The choice of aggregation period in constructing incident rates is essential in understanding the safety climate–incident relationship. The common yearly count of incidents would make it seem that more severe incidents cannot be predicted by safety climate and also fails to show the strongest predictive effects of less severe incidents.

Originality/Value
This research is the first to examine assumptions regarding aggregation periods when constructing safety-related incident rates. Our work guides organizations in planning their survey program, recommending more frequent measurement of safety climate.
Determination of pKa Values of Oxocholanoic Acids by Potentiometric Titration
Authors: Farkaš Zita , Poša Mihalj , Tepavčević Vesna 
Published: January 2014

AbstractThe pKa and the maximum solubility values of cholic, deoxycholic salts and their oxo‐derivatives have been measured by the method of potentiometric titration. In the monomer phase (under the critical micellar concentration, CMC), the bile salts have different pKa values, as a result of their structural differences (the number of hydroxyl and oxo groups in the steroid skeleton) and different hydration properties of the acid anions. In the micellar phase (above the CMC), the bile salts have higher pKa values than in the monomer phase (under the CMC). This increase in the pKa values is greater in more hydrophobic bile salts (cholate and deoxycholate), than in less hydrophobic oxo derivatives, which can be explained by the different aggregation numbers of these bile salts. The oxo‐derivatives are more likely to form dimeric micelles, where the carboxylic groups are situated on the two sides of the micelle, not causing any electrostatic repulsion. In the more hydrophobic bile salts, aggregation numbers are higher, which causes electrostatic repulsion of the nearby situated carboxylic anions and consequential protonation of these anions (which leads to the stabilization of the micelle). The maximum solubility values are higher for the oxo‐derivatives. If the steroid skeleton of the bile salt is more hydrophobic, the capacity to solubilize the unionized bile acid is higher, i.e. a smaller amount of the bile acid anion is needed for the solubilization of the bile acid monomer. The oxo‐derivatives are less hydrophobic, but alongside their hydrophobicity, the structure of the micelle determines the solubilization capacities.
Genetics and Epigenetics of Recurrent Hydatidiform Moles: Basic Science and Genetic Counselling
Authors: Nguyen Ngoc Minh Phuong , Slim Rima 
Published: January 2014

Abstract
Gestational trophoblastic disease (GTD) is a group of conditions that originate from the abnormal hyperproliferation of trophoblastic cells, which derive from the trophectoderm, the outer layer of the blastocyst that would normally develop into the placenta during pregnancy. GTDs encompass hydatidiform mole (HM) (complete and partial), invasive mole, gestational choriocarcinoma, placental-site trophoblastic tumor, and epithelioid trophoblastic tumor. Of these, the most common is HM, and it is the only one that has been reported to recur in the same patients from independent pregnancies, which indicates the patients’ genetic predisposition. In addition, HM is the only GTD that segregates in families according to Mendel’s laws of heredity, which made it possible to use rare familial cases of recurrent HMs (RHMs) to identify two maternal-effect genes, NLRP7 and KHDC3L, responsible for this condition. Here, we recapitulate current knowledge about RHMs and conclude with the role and benefits of testing patients for mutations in the known genes.
Assessment of human hippocampal developmental neuroanatomy by means of ex‐vivo 7 T magnetic resonance imaging
Authors: Milesi Gloria , Garbelli Rita , Zucca Ileana , Aronica Eleonora , Spreafico Roberto , Frassoni Carolina 
Published: January 2014

AbstractDuring development, the hippocampus undergoes numerous changes in its cell morphology and cyto‐ and myelo‐architecture that begin during the fetal period and continue after birth. We investigated the developmental changes occurring in healthy fetal (20–32 gestational weeks) and post‐natal human hippocampi (from 1 day to adulthood) by combining high‐resolution 7 T magnetic resonance imaging (MRI) and histological and immunohistochemical analyses in order to compare variations in signal intensity with cyto‐ and myeloarchitectural organization. During fetal period the intensity of the T2‐weighted images was related to the cell density and the subregions of Ammon's horn and dentate gyrus, characterized by densely packed neurons, were recognizable as hypointense areas. The inverse correlation between MRI signal intensity and cell density was visualized by line profile results. At the age of two post‐natal weeks, the low MRI signal was still related to cell density, although thin myelinated fibers were observed in hypointense regions such as the alveus and stratum lacunosum‐moleculare. The myelin content subsequently increases until the complete hippocampal myeloarchitecture is reached in adulthood. Comparison of the MRI findings and corresponding histological sections indicated that the differences in the T2‐weighted images between the age of seven years and adulthood reflect the increasing density of myelinated fibers.These results provide useful information concerning the interpretation of MRI signals and the developmental changes visualized by in vivo MRI at lower field strengths, and may be used as a reference for the future use of high spatial resolution MRI in clinical practice.