bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scanning capacitance microscopy as a tool for the assessment of unintentional doping in GaN
Authors: Oliver Rachel A. , Bakshi Subhankar Das , Sumner Joy , Kappers Menno J. 
Published: March 2009

AbstractScanning capacitance microscopy (SCM) is a technique based on atomic force microscopy which provides information about the concentration and distribution of charge carriers in a semiconducting sample. As an imaging technique it provides an advantage over more conventional approaches such as secondary ion mass spectrometry and depth‐profiling Hall voltage measurement since it provides a two‐dimensional dataset rather than a one dimensional line profile. Here, we demonstrate the utility of SCM for GaN‐based materials by assessing the unintentionally doped layer at the GaN/sapphire interface in a series of samples in which the growth conditions initially favoured the formation of three‐dimensional islands, which later coalesced to form a two‐dimensional film. Using SCM we observe that the width of the resulting conductive layer at the GaN/sapphire interface depends on the time taken to achieve coalescence but that the carrier density does not. We also assess and attempt to explain the roughness of the top surface of the conductive interface layer, which can only be addressed using an imaging technique. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Influence of thermal anneal steps on the current collapse of fluorine treated enhancement mode SiN/AlGaN/GaN HEMTs
Authors: Lorenz Anne , Derluyn Joff , Das Jo , Cheng Kai , Degroote Stefan , Medjdoub Farid , Germain Marianne , Borghs Gustaaf 
Published: March 2009

AbstractGallium nitride based high electron mobility transistors offer high carrier density combined with high electron mobility and enable operation at high frequencies, voltages and temperatures. However, they are generally working in depletion mode, requiring a negative bias to switch them off. As this is disadvantageous for circuit design, power consumption and safety of operation, enhancement mode devices would be favourable. This operation mode can be reached by shifting the threshold voltage towards more positive values by implantation of negatively charged fluorine ions. As these ions were reported to form deep level trap states in the material, we investigated the influence of the implantation and subsequent anneal steps on current collapse and threshold voltage. We found that anneal steps of over 550 °C are effective in reducing the current collapse up to factor 4, but also shift the threshold voltage again to negative values, thus eliminating enhancement mode operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Volmer‐Weber growth mode of InN quantum dots on GaN by MOVPE
Authors: Meissner Christian , Ploch Simon , Pristovsek Markus , Kneissl Michael 
Published: March 2009

AbstractThe growth of indium nitride quantum dots on c‐plane GaN/sapphire was investigated by metal‐organic vapour phase epitaxy using in situ spectroscopic ellipsometry and ex situ atomic force microscopy. Using an ammonia stabilisation for temperatures above 500 °C desorption of InN structures could be prevented during cool down. At a growth temperature of 520 °C and a trimethylindium partial pressure of 0.5 Pa (V/III ratio of 5000) we observe growth without a wetting layer in the Volmer‐Weber mode, indicated by the presence of InN quantum dots for sub‐monolayer coverages and a constant ratio of quantum dot volume to total InN amount. At this transport limited growth regime the typical quantum dot density of 7 × 1010 cm–2 is independent from coverage. Coalescence occurs after 20 s growth time at an average structure diameter of 51 nm as expected for such a density. Smallest uncapped hexagonal structures are realised with an average diameter of 28 nm and a height of 3.1 nm (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Energetics of oxygen adsorption and incorporation at InN polar surface: A first‐principles study
Authors: Belabbes A. , Kioseoglou J. , Komninou Ph. , Karakostas Th. 
Published: March 2009

AbstractFirst principles calculations are performed to study the adsorption and incorporation of oxygen at InN polar surfaces as a function of oxygen coverage. We find that the adsorption of oxygen at InN surfaces is higher on the N‐polar than on In‐polar. The calculations show that for the low coverage regime (x ≤ 0.5 ML) both orientations are active towards the adsorption of oxygen; this implies that the reaction between the O atoms and the surface is strongly exothermic. As the coverage of O exceeds 0.5 ML a large difference in adsorption energies, of almost 2.5 eV, is observed between (0001) and (000$ \bar 1 $) surfaces indicating that the (000$ \bar 1 $) surface is more active towards oxygen adsorption than the (0001) surface. The high coverage of oxygen changes the surface structure of InN due to the difference in binding energy (O‐In bonds are stronger than In‐N ones). This result shows explicitly that the formation of In adlayer is disturbed by the O adsorption. Concerning the energetics of O incorporation our results show that it is more favourable for O to substitute a N atom in one of the top layers near the surface than in bulk, indicating that there is a strong tendency for O to reside at the surface rather than in subsurface layers. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Fabrication of a low threading dislocation density ELO‐AlN template for application to deep‐UV LEDs
Authors: Hirayama Hideki , Fujikawa Sachie , Norimatsu Jun , Takano Takayoshi , Tsubaki Kenji , Kamata Norihiko 
Published: March 2009

AbstractWe have fabricated low threading dislocation density (TDD) AlN templates on sapphire substrates for application to deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) by employing an epitaxial lateral overgrowth (ELO) process. An AlN stripe structure with a width of 5 μm and a spacing of 3 μm was formed by using inductive coupled plasma (ICP) etching. The AlN stripes were completely coalesced and embedded to create a flat surface after the growth of an approximately 15 μm‐thick ELO‐AlN layer, grown by low‐pressure metal‐organic chemical vapor deposition (LP‐MOCVD). We systematically investigated the appropriate V/III ratio and growth temperature for the ELO‐AlN. The edge‐type TDD of the AlN was reduced from 2×109 cm–2 (AlN stripe region) to 3×108 cm–2 (in the wing region of the ELO‐AlN), as estimated by cross‐sectional transmission electron microscope (TEM) imaging. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Milliwatt power 270 nm‐band AlGaN deep‐UV LEDs fabricated on ELO‐AlN templates
Authors: Hirayama Hideki , Norimatsu Jun , Noguchi Norimichi , Fujikawa Sachie , Takano Takayoshi , Tsubaki Kenji , Kamata Norihiko 
Published: March 2009

AbstractWe demonstrated CW milliwatt power operations of 270 nm‐band AlGaN multi‐quantum well (MQW) deep‐ultraviolet (DUV) light‐emitting diodes (LEDs) fabricated on epitaxial lateral overgrowth (ELO) AlN templates on sapphire. An initial AlN stripe layer was grown directly on sapphire by using ammonia (NH3) pulse‐flow multilayer (ML) growth method. An AlN stripe structure with a width of 5 μm and a spacing of 3 μm was completely coalesced after the growth of an approximately 15 μm‐thick ELO‐AlN layer grown by low‐pressure metal‐organic chemical vapor deposition (LP‐MOCVD). The edge‐type threading dislocation density (TDD) of the wing region of the ELO‐AlN layer was 3×108 cm‐2, as observed by cross‐sectional transmission electron microscope (TEM) image. The maximum output power of 2.7 mW was obtained from an AlGaN MQW LED with emission wavelength at 273 nm fabricated on ELO‐AlN template under room temperature (RT) CW operation. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Inhomogeneity of a highly efficient InGaN based blue LED studied by three‐dimensional atom probe tomography
Authors: Gu G. H. , Park C. G. , Nam K. B. 
Published: March 2009

AbstractThe InGaN based multiple quantum well (MQW) structure in a commercially available white light emitting diode (LED) was studied by transmission electron microscopy (TEM) and three‐dimensional atom probe tomography (APT). The average In mole fraction by three‐dimensional (3D) APT was found to be about 18% in the InGaN well which is consistent with the secondary ion mass spectrometry (SIMS) analysis. The In distribution in the InGaN well layer was analyzed by the iso curve mapping of 3D APT and found to be non‐uniform in the InGaN active layer. In clustering or In rich regions in the range of 2–3 nm size were found, in contrast to recent reports. Our results thus indicate that In clustering is essential for high‐brightness InGaN based LEDs. We have also observed a discontinuity in the range of 50–100. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Predicting the Androgenicity of Structurally Diverse Compounds from Molecular Structure Using Different Classifiers
Authors: Ji Li , Wang Xiaodong , Qin Liang , Luo Si , Wang Liansheng 
Published: March 2009

AbstractMany environmental and industrial chemicals are reported to have androgenic or antiandrogenic activities. These androgenic chemicals may act as hormones and have the potential to disrupt the endocrine systems of wildlife and humans. In this study, the probabilistic neural network (PNN), support vector machine (SVM), and learning vector quantization (LVQ), three types of machine learning, were used to develop binary classification models to predict androgenicity directly from the organic compounds' molecular structures which were represented by only eleven numerical descriptors. The PNN model acquired the best overall classification rate of 86.67% for prediction data set, with Matthews Correlation Coefficient of 0.64, and the LVQ model gave the lowest false negative rate of 0.00%, which will tend to give relatively high priority during toxicology evaluation. In addition, a consensus model was produced that integrated all three of the basic model types. Compared with the individual models, this consensus model correctly predicted the androgenicity of 86.67% of the prediction set compounds, with false negative rate of 0.00% and the highest Matthews Correlation Coefficient of 0.65. The obtained results indicate that the proposed classification models could provide a feasible and practical tool for the rapid screening of potential androgens.
Effective collision strengths for electron‐impact excitation of transitions within the ground 1s2 2s2 2p4 manifold of O‐like Fe18+
Authors: Santana Juan A. , Ishikawa Yasuyuki 
Published: March 2009

AbstractCollision strengths have been computed for the electron impact excitations of parity and spin forbidden transitions within the ground 1s22s22p4 manifold of Fe XIX (Fe18+). The calculations were carried out using a relativistic R‐matrix close‐coupling method based on the effective many‐body Hamiltonian. Twenty‐six target states were included in the close‐coupling expansion. Effective collision strengths, assuming a Maxwellian electron velocity distribution, were evaluated for all transitions within the ground configuration. Good agreement is found with previous Breit‐Pauli R‐matrix calculations at low electron temperatures, 5.0 ≤ log Te ≤ 6.0 K, for all the transitions, whereas significant differences are found for electron temperatures in the range 6.0 ≤ log Te ≤ 7.0 K. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
First‐principles study of the structure and the electronic structure of yttrium aluminum garnet Y3Al5O12
Authors: Muñoz‐García Ana Belén , Anglada Eduardo , Seijo Luis 
Published: March 2009

AbstractDensity functional theory calculations have been performed on the electronic structure and the atomistic structure of yttrium aluminum garnet Y3Al5O12, YAG, and related crystals (yttrium aluminum perovskite YAlO3, yttria Y2O3, and corundum α‐Al2O3). The quality of the computed data provides reliability to further structural studies with the same methods on local and extended bulk and surface defects in YAG. The structure of the computed conduction band is coherent with available electron‐loss near‐edge spectroscopy (ELNES) data. Previous Y‐Al covalent interactions are not observed here. Reaction energies involving YAG and its related materials are given. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Role of electronic curve crossing of benzene S1 state in the photodissociation of aryl halides, effect of fluorination: RASSI‐SO MS‐CASPT2 study
Authors: Devarajan Ajitha , Gaenko Alexander , Lindh Roland , Malmqvist Per‐Åke 
Published: March 2009

AbstractAn ab initio study of the role of electronic curve crossing of benzene S1 state in the photo dissociation dynamics of the iodobenzene and effect of fluorination is presented. Two dissociative life times observed in iodobenzene is attributed to the coupled repulsive potential energy curves of the low‐lying n−σ*, π−σ*, π−π* states. The direct channel is attributed to the alkyl like transition and the indirect channel is attributed to the mixing of the alkyl like transitions with the low lying benzene π−π* transitions. Fluorination of iodobenzene results in a substantial increase in the direct channel product. To analyze the possible role of electronic curve crossing of these transitions, potential energy curves of low‐lying n−σ*, π−σ*, π−π* states were studied including spin‐orbit and relativistic effects using the Restricted Active Space state interaction multistate complete active space perturbation theory (RASSI‐MS‐CASPT2) method. Crossing behavior of spin‐free and spin‐orbit potential energy curves was analyzed for the role of the benzene S1 state. Our results indicate the curve crossing region to be around 2.00–2.35 Å for both C6H5I and C6F5I. Analysis of effect of fluorination on the energies of states corresponding to benzene π−π* and n−σ* transitions suggests an increase in the energy of benzene π−π* states and a decrease in the energy of the states corresponding to n−σ* transitions. Increased spin‐orbit gap, increased separation of the benzene S1(π−π*) state and n−σ* states in the region of curve crossing, lesser mixing of the π−π* and n−σ* states, an order of magnitude decrease in the transition strength to the benzene singlet transition all contributed to the observed substantial increase in the quantum yield of the direct channel product on fluorination of aryl halides. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
A theorem for complex symmetric matrices revisited
Authors: Brändas Erkki J. 
Published: March 2009

AbstractIn this contribution we will revisit the celebrated theorem that every square matrix is similar to a (complex) symmetric matrix and that every symmetric matrix is orthogonally similar to a given normal canonical form. Specifically we will re‐examine the proof as well as the derivation of an explicit n‐dimensional complex symmetric form. We will extend the formula to incorporate the various powers of the original normal form, a derivation not previously provided. Some examples of these complex symmetric forms in chemical and physical applications are indicated. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009
Matrix‐assisted laser desorption/ionization by using femtosecond laser pulses in the near‐infrared wavelength regime
Authors: Wichmann J. M. , Lupulescu C. , Wöste L. , Lindinger A. 
Published: March 2009

AbstractWe observe a substantial matrix‐assisted laser desorption/ionization (MALDI) signal when irradiating femtosecond laser pulses in the near‐infrared spectral range centered around 800 nm and using standard MALDI matrices with absorption bands in the ultraviolet (UV) regime. The laser pulse energy dependence of this novel phenomenon is investigated in comparison with MALDI with near‐UV laser pulses. Our observations show that multiphoton absorption/ionization could be a major issue among the MALDI processes when the sample is irradiated with ultra‐short laser pulses. Copyright © 2009 John Wiley & Sons, Ltd.
Mass spectrometry of nanodiamonds
Authors: Houška Jan , Panyala Nagender Reddy , Peña‐Méndez Eladia Maria , Havel Josef 
Published: March 2009

AbstractDetonation nanodiamonds (NDs) were studied by time‐of‐flight mass spectrometry (TOF MS). The formation of singly charged carbon clusters, C, with groups of clusters at n = 1–35, n ∼160–400 and clusters with n ∼8000 was observed. On applying either high laser energy or ultrasound, the position and intensity of the maxima change and a new group of clusters at n ∼70–80 is formed. High carbon clusters consist of an even number of carbons while the percentage of odd‐numbered clusters is quite low (≤5–10%). On increasing the laser energy, the maximum of ionization (at n ∼200 carbons) is shifted towards the lower m/z values. It is suggested that this is mainly due to the disaggregation of the original NDs. However, the partial destruction of NDs is also possible. The carbon clusters (n ∼2–35) are partially hydrogenated and the average value of the hydrogenation was 10–30%. Trace impurities in NDs like Li, B, Fe, and others were detected at high laser energy. Several matrices for ionizing NDs were examined and NDs themselves can also be used as a matrix for the ionization of various organic compounds. When NDs were used as a matrix for gold nanoparticles, the formation of various gold carbides AumCn was detected and their stoichiometry was determined. It was demonstrated that TOF MS can be used advantageously to analyze NDs, characterize their size distribution, aggregation, presence of trace impurities and surface chemistry. Copyright © 2009 John Wiley & Sons, Ltd.
A mass spectrometry based imaging method developed for the intracellular detection of HIV protease inhibitors
Authors: Dekker Lennard J. M. , van Kampen Jeroen J. A. , Reedijk Mariska L. , Burgers Peter C. , Gruters Rob A. , Osterhaus Albert D. M. E. , Luider Theo M. 
Published: March 2009

AbstractMass spectrometry imaging is a promising technique for measuring drugs and drug metabolites in cells and tissues. In this manuscript we describe a method for the imaging of HIV protease inhibitors. As a model system we used Mono Mac 6 cells cultured with the HIV protease inhibitors saquinavir and nelfinavir deposited on glass slides using a cytocentrifuge. A sublimation/deposition device for homogeneous matrix deposition was constructed which allows imaging of these HIV protease inhibitors at clinically relevant concentrations. Using this matrix sublimation/deposition method, glass slides containing the cytocentrifuged cells can be measured and analyzed by two types of mass spectrometry techniques, viz. matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) and MALDI Fourier transform ion cyclotron resonance (FTICR), and this makes it possible to perform imaging rapidly (MALDI‐TOF) and with a very high selectivity (MALDI‐FTICR). Copyright © 2009 John Wiley & Sons, Ltd.
Systematic characterization of the covalent interactions between (−)‐epigallocatechin gallate and peptides under physiological conditions by mass spectrometry
Authors: Cao Dong , Zhang Yangjun , Zhang Huihui , Zhong Liangwei , Qian Xiaohong 
Published: March 2009

Abstract(−)‐Epigallocatechin gallate (EGCG) is a major bioactive component in leaves of green tea, and has been widely investigated for its anti‐tumor activity. The interaction between EGCG and the key peptides or proteins (e.g. glutathione, enzymes) in vivo is thought to be involved in the toxicity and anti‐cancer mechanism of EGCG. However, the true anti‐tumor mechanism of EGCG is not clear, and few studies have focused on the reactivity of EGCG toward peptides or proteins under physiological conditions (pH 7.4, 37°C). In this work, the covalent interactions between EGCG and model peptides containing one or more nucleophilic residues (i.e. Arg, Cys, Met, and α‐NH2 of the N‐terminus of peptides) under physiological condition were fully characterized using mass spectrometry. It was found that EGCG can react with the thiol groups of peptides to form adducts under physiological conditions (pH 7.4, 37°C), even in the absence of the peroxidase/hydrogen peroxide system. Besides the thiol groups of peptides, it is firstly reported that EGCG also reacts with α‐NH2 of the N‐terminus or arginine residues of model peptides to form Schiff base adducts, and the methionine residues of model peptides can be easily oxidized by hydrogen peroxide (H2O2) generated during the process of EGCG auto‐oxidation to form methionine sulfoxide products. The preference for the reaction of nucleophlic residues of peptides with EGCG was determined to have the following order: Cys > α‐NH2 of the N‐terminus > Arg. The neutral loss ions of [M+H–170]+ and [M+H‐138]+ were detected in all tandem mass spectra of the EGCG adducts of peptides, which indicates that these two neutral loss ions can be considered as the characteristic neutral loss ions of peptides modified by EGCG. Results of the present research provide insights into the toxicology and anti‐tumor mechanism of EGCG in vivo. Copyright © 2009 John Wiley & Sons, Ltd.
Identification of hydroxyl radical oxidation products of N‐hexanoyl‐homoserine lactone by reversed‐phase high‐performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry
Authors: Cui Yiling , Frey Rebecca L. , Ferry John L. , Ferguson P. Lee 
Published: March 2009

AbstractA reversed‐phase high‐performance liquid chromatography/electrospray tandem mass spectrometry method was developed for the characterization of hydroxyl radical oxidation products of N‐hexanoyl‐homoserine lactone (C6‐HSL), a member of the N‐acylhomoserine lactone (AHL) class of microbial quorum‐sensing signaling molecules identified in many Gram‐negative strains of bacteria. Six products were identified: four with molecular weight (MW) of 213 and two with MW of 260. The characteristic product ions formed through collision‐induced dissociation (CID) provided diagnostic structural information. One of the photolysis products was determined to be N‐(3‐oxohexanoyl)homoserine lactone (3OC6‐HSL), a highly active quorum‐sensing signal, by comparison with a reference standard. Three structural isomers with the same mass as 3OC6‐HSL were identified as acyl side chain oxidized C6‐HSL (keto/enol functionalized) by accurate mass measurement and the structures of these products were proposed from CID spectral interpretation. Two structural isomers formed from concurrent oxidation and nitration of C6‐HSL were also observed and their structures were postulated based on CID spectra. In addition to the six hydroxyl radical oxidation products formed from the C6‐HSL precursor, five additional compounds generated from combined oxidation and lactonolysis of C6‐HSL were identified and structures were postulated. Copyright © 2009 John Wiley & Sons, Ltd.