bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermally stable ohmic contacts to n-type GaAs. I. MoGeW contact metal
Authors: Murakami Masanori , Price W. H. , Shih Yih-Cheng , Childs K. D. , Furman B. K. , Tiwari S. 
Published: July 2002

Thermally stable, low-resistance ohmic contacts on n-type GaAs are required to fabricate high-speed GaAs integrated circuits. MoGeW contacts prepared by annealing at high temperature around 800 °C in an InAs overpressure are attractive, because the contact is expected to be thermally stable during subsequent annealing at 400 °C, which is required by several process steps following ohmic contact formation. In the present experiment, the contact resistance measurements and microstructural analysis of MoGeW contacts were carried out to establish a fabrication process which forms ohmic contacts with low contact resistance. The contact metals were prepared by sequentially
depositing Ge, Mo, Ge, and W, with various Mo/Ge layer thickness ratios, onto (100)-oriented GaAs wafers. The conducting channels were formed by doping GaAs with about 1×1018 cm−3 Si. Contact resistances were determined by the transmission line method, and microstructural analysis was carried out by x-ray diffraction, Auger electron spectroscopy, secondary ion mass spectroscopy (SIMS), and transmission electron microscopy. Contact resistance (Rc) was found to be strongly influenced by the Mo/Ge layer thickness ratio and annealing temperature. Rc values lower than 0.5 Ω mm were obtained for samples with a Mo/Ge thickness ratio in the range 0.6–1.3 and annealed at around 800 °C. The lowest mean Rc value obtained in the present experiment was 0.3 Ω mm. The major compound formed in this contact was identified to be Mo5As4, which has a high melting point. No changes in the microstructure and the Rc values were observed after annealing the contacts at 400 °C for more than 100 h. Finally, an attempt to understand the carrier transport mechanism was carried out by correlating the electrical behavior with the film microstructure. For this purpose the samples were annealed in an InAs overpressure with or without a Si3N4 cap, by flash annealing, and in an arsine atmosphere. The ohmic behavior was observed only in the samples annealed in an InAs overpressure. The SIMS analysis indicated that a small amount of In, less than 1 at. %, was segregated at the metal/GaAs interfaces in this sample. The In could form compounds with GaAs and reduce the barrier height, resulting in reduction of the contact resistances.
Composition, microstructure, and properties of crystalline molybdenum silicide thin films produced by annealing of amorphous Mo/Si multilayers
Authors: Loopstra O. B. , Sloof W. G. , de Keijser Th. H. , Mittemeijer E. J. , Radelaar S. , Kuiper A. E. T. , Wolters R. A. M. 
Published: July 2002

Amorphous Mo/Si multilayers were prepared by alternately sputtering Mo and Si onto silicon single-crystal substrates covered with SiO2 and onto substrates covered with polycrystalline Si. The multilayer thickness was about 200 nm and the composition modulation period was about 0.8 nm. The Mo/Si atomic ratio averaged over the multilayer was about 0.6. These specimens were isochronally annealed for 1 h at temperatures up to 1000 °C. In order to analyze annealing-induced variations in composition, microstructure, resistivity, and internal stresses, the specimens were investigated by x-ray diffractometry, Rutherford backscattering spectroscopy, and resistometry. Although the multilayer remained amorphous during annealing at temperatures below 350 °C, interdiffusion of Mo and Si occurred. Above 350 °C the layered structure disappeared and crystalline phases, viz., hexagonal MoSi2, Mo5Si3, and tetragonal MoSi2, appeared successively for increasing temperatures. According to the (equilibrium) phase diagram both hexagonal MoSi2 and crystalline Mo5Si3 were expected to occur simultaneously. It
appeared, however, that hexagonal MoSi2 formed first, probably because of difficult nucleation of crystalline Mo5Si3. The hexagonal MoSi2 nucleated homogeneously, whereas Mo5Si3 nucleated heterogeneously. In MoSix layers on SiO2 the Mo5Si3 grew at the outer surface and at the MoSix/substrate interface. In MoSix layers on polycrystalline Si the Mo5Si3 reacted with Si to form hexagonal MoSi2 at temperatures above 700 °C. Finally, the hexagonal MoSi2 phase transformed into tetragonal MoSi2. The resistivity of the MoSix layer decreased distinctly as soon as hexagonal MoSi2 was formed and an even larger decrease occurred when hexagonal MoSi2 transformed into tetragonal MoSi2. The latter resistivity decrease was accompanied by a considerable improvement of overall crystalline perfection of the MoSix layer. The lowest resistivity (58 μΩ cm) was obtained after annealing at 1000 °C. The internal stress in the MoSix layer can be explained by the difference in thermal contraction between the MoSix layer and the Si substrate. After annealing at 1000 °C the internal stress equaled about 2.0 GPa.
Spin-wave properties in multilayered structures including interface anisotropies and exchange (abstract)
Authors: Hillebrands Burkard 
Published: July 2002

Results are presented of new theoretical investigations in which spin waves in multilayered structures are calculated, properly including both magnetic interface anisotropies and exchange.1 The work is an extension of a recently introduced theory for the calculation of single-layer spin-wave frequencies by Rado and Hicken, including interface anisotropies and exchange.2 The calculations were carried out for two different types of multilayered structures, i.e., for multilayers consisting of alternating magnetic and nonmagnetic multilayers, and for all-magnetic multilayers. In both cases all layers were of the same thickness. The solutions were obtained by solving for
the Maxwell equations and the Landau–Lifshitz torque equation. The boundary conditions consist of the Maxwell boundary conditions, and the Rado–Weertman boundary condition3 in the case of magnetic/nonmagnetic multilayers. In the case of all-magnetic multilayers, modified Rado–Weertman boundary conditions were used.4,5 In the case of magnetic/nonmagnetic multilayers, both dipolar-type (Damon–Eshbach-type) modes and exchange-dominated modes are obtained. The dipolar modes are frequency split as a result of the dipolar coupling of single-layer spin waves across the nonmagnetic spacer layers. The
exchange modes show no frequency splitting apart from the crossing regimes with the dipolar modes. In the regime of small layer thicknesses, where the dipolar modes are well frequency separated from the exchange modes, the calculations reproduce results obtained by neglecting exchange contributions.6 In the limit of very small layer thicknesses (&lt;40 Å), the influence of interface anisotropies manifests itself for the dipolar modes in a frequency increase, as well as in a reduced coupling across the nonmagnetic layers. In the crossing regimes of dipolar modes and exchange modes, the modes exchange their mode characteristics, leading to a pronounced frequency gap. The width of the gap is
mostly determined by the amount of interface anisotropy. The calculation of an all-magnetic multilayered structure, consisting of three Fe layers with interleaving Ni layers, was carried in the limit of maximum exchange coupling across the interfaces.1 The results show frequency splittings both for dipolar modes and for exchange modes. In the limit of an infinite number of layers, the exchange modes will eventually form a band of exchange-dominated collective spin waves reminiscent of the band of collective dipolar spin waves in magnetic/nonmagnetic multilayers. The crossing regimes of dipolar modes with the
exchange modes show frequency gaps close to those observed for magnetic/nonmagnetic multilayers.
Nonadiabatic coupling between the E
F+G
K+H 1Σ+g, I 1Πg, and J 1Δg states of the hydrogen molecule. Calculation of rovibronic structures in H2, HD, and D2
Authors: Quadrelli P. , Dressler K. , Wolniewicz L. 
Published: July 2002

The Born–Oppenheimer potential curves of the first two excited 1Σ+g states of H2, EF and GK, exhibit double minima which arise from avoided crossings between the electronic energy curves of the doubly excited 1σ2u configuration and of the 1Σ+g Rydberg states of the 1σg2sσg and 1σg3dσg configurations. The vibrational structures of the adiabatic electronic states are mutually coupled via strongly R-dependent off-diagonal electronic matrix elements of the d/dR and d2/dR2 operators. Furthermore the rotational structures are characterized by strong angular coupling within the complex of 3d-singlet-gerade states G 1Σ+g, I 1Πg, and J 1Δg.
We have evaluated the nonadiabatic coupling functions involving the first three excited 1Σ+g states EF, GK, and H, and the I 1Πg and J 1Δg states, and have calculated their nonadiabatic rovibronic structures for the J=0–5 levels of H2, HD, and D2 up to the H(1s)+H(2s,2p) dissociation limit. The simultaneous radial and angular couplings within these five electronic states have been treated using ab initio potential curves, adiabatic corrections, and nonadiabatic coupling functions. The coupled equations have been transformed into a diabatic electronic basis and solved numerically, and the resulting eigenfunctions have been transformed back into the adiabatic basis. Energy eigenvalues, nonadiabatic energy shifts, B values, Landé g factors, band transition moments, Einstein coefficients, and radiative lifetimes have been evaluated and compared with spectroscopic results where possible. The discrepancies between observed and calculated rovibronic term values depend systematically on electronic state, vibrational energy, and isotopic mass, and their magnitudes indicate that the absolute energy errors of the ab initio potential curves amount to less than 1 cm−1 near the minima of the EF 1Σ+g and I 1Πg states, approximately 2 cm−1 in the J 1Δg state, and 5 cm−1 in the H 1Σ+g state. The nonadiabatic ab initio results have already aided spectroscopic identifications of new energy levels and they indicate that several old assignments must be discarded.
Semiclassical surface-hopping approximations for the calculation of solvent-induced vibrational-relaxation rate constants
Authors: Arce Julio C. , Herman Michael F. 
Published: July 2002

Approximate schemes for the calculation of the rates of transitions between vibrational states of a molecule due to the interactions with a solvent are devised based on a rigorous, general semiclassical surface-hopping formalism developed earlier. The formal framework is based on an adiabatic separation of time scales between the fast molecular vibrations and the relatively slow bath motions. (The bath is composed of the solvent degrees of freedom plus all the molecular degrees of freedom other than vibrations.) As a result, the dynamics of the system are described in terms of bath motions occurring on adiabatic vibrational-energy surfaces, which are coupled by a nonadiabatic interaction. The time-dependent vibrational transition probability is evaluated by propagating the canonical density of the system, with the molecule in the initial adiabatic vibrational state, forward in time, and then projecting it onto the final adiabatic vibrational state of interest. The temporal evolution of the density is carried out with a semiclassical surface-hopping propagator, in which the motion of the bath on an adiabatic vibrational surface is described in terms of the familiar (adiabatic) semiclassical propagator, while transitions are accounted for in terms of instantaneous hops of the bath paths between the adiabatic vibrational surfaces involved, with an integration over all possible hopping points.
Energy is conserved in the hops, and the only component of momentum that changes is the one along the nonadiabatic coupling vector. When the nonadiabatic interaction is taken into account to first order, the transition probability is predicted to become linear in the long-time limit. Various methods for extracting the relaxation rate constant in this limit are presented, and a simple model system with a one-dimensional bath is employed to compare their practical efficiency for finite time. In addition, this system is used to numerically demonstrate that local approximations for the adiabatic vibrational surfaces and the nonadiabatic coupling yield accurate results, with great reduction of the amount of computation time. Since a local approximation for the vibrational surfaces makes an N-dimensional problem separable into N effectively one-dimensional ones, this treatment is seen to be more generally applicable to realistic systems.
Prescribing drug of choice to opiate dependent drug users: a comparison of clients receiving heroin with those receiving injectable methadone at a West London drug clinic
Authors: METREBIAN NICKY , SHANAHAN WILLIAM , STIMSON GERRY V. , SMALL COLIN , LEE MARK , MTUTU VICTOR , WELLS BRIAN 
Published: July 2002

AbstractFifty‐eight long‐term treatment resistant opiate‐dependent drug users were offered the choice of receiving injectable heroin or injectable methadone at a West London drug clinic. Drugs were dispensed on‐site at the clinic with weekend take‐home. There was no routine ongoing supervised injecting. A ceiling dose of 200mg/day of heroin or methadone was set. One‐third chose injectable methadone. Compared to those choosing heroin, these drug users were less likely to have used heroin or crack/cocaine before entering treatment, and were more likely to have previously received treatment with injectable methadone. Drug users reported choosing methadone because it was their primary drug of addiction, and compared with heroin has a longer duration of action and increased strength. Problems with each drug were reported: those choosing heroin complained that the upper dose limit was too low to maintain them adequately, and some receiving methadone complained of discomfort while injecting intravenously. While those choosing each drug had different baseline characteristics, both groups were well retained in treatment and at 3 months made significant reductions in drug use and crime, which were sustained over the 12‐month follow‐up period. There was no significant difference between treatment outcome between each group. There is an urgent need to conduct randomized controlled trials to establish the effectiveness of prescribing injectable methadone and heroin to inform policy and practice.
Factors related to self‐reported violent and accidental injuries
Authors: MACDONALD SCOTT , WELLS SAMANTHA 
Published: July 2002

AbstractThe main objective of this study is to gain a better understanding of factors that distinguish violent and accidental injuries. A secondary analysis was conducted on data from a randomized telephone survey of 10 385 Canadian residents. Three groups were compared using chi‐square tests and logistic regression analyses: respondents who reported no injuries in the previous year, those with at least one accidental injury and those with at least one violent injury. In the bivariate analyses, the violent injury group was significantly more likely than the accidental injury and non‐injury groups to be single, widowed, separated or divorced, have more than five drinks on a usual drinking occasion, experience harmful effects of alcohol and to have used illicit drugs, such as cocaine and marijuana, and licit drugs, such as antidepressants and sleeping pills. Finally, the violent injury group was significantly more likely than those with non‐violent injuries to report that the incident was related to either their own or someone else's alcohol or drug use. In the final multiple logistic regression analysis, variables significantly associated with injuries due to criminal victimizations compared with accidental injuries were being female, single, cocaine use of the injured and substance use of someone else during the injury.
Involvement of the corticostriatal glutamatergic pathway in ethanol‐induced ascorbic acid release in rat striatum
Authors: LIU JING , WU CHUN‐FU , LIU WEN , ZHANG HONG‐LING , LI CHUN‐LI 
Published: July 2002

AbstractThe mechanism of ethanol‐induced ascorbic acid (AA) release in striatum is not well understood. In the present work, the possible involvement of NMDA receptors in the corticostriatal pathway was studied by microdialysis coupled to high performance liquid chromatography with electrochemical detection. Ethanol (3.0 g/kg i.p.) stimulated significant striatal AA release to more than 200% above the baseline. This effect of ethanol could be partially antagonized by amantadine, a non‐selective NMDA receptor antagonist and dopamine releaser, at a dose of 200 mg/kg i.p. and significantly antagonized by MK‐801, a non‐competitive NMDA receptor antagonist, at the doses of 0.5 and 1.0 mg/kg i.p. Furthermore, deafferentation of the glutamatergic projection from cortex to striatum by undercutting the prefrontal cortex completely eliminated ethanol‐induced AA release in rat striatum. The basal level of AA in striatum could only be reduced by high doses of MK‐801, but not by low doses of MK‐801, amantadine or decortication. The results further confirm that NMDA receptors are involved in ethanol‐induced AA release and provide the first evidence for the necessity of the activation of corticostriatal glutamatergic pathway in ethanol‐induced AA release in rat striatum.
GeneGenerator--a flexible algorithm for gene prediction and its application to maize sequences.
Authors: Kleffe J , Hermann K , Vahrson W , Wittig B , Brendel V 
Published: July 2002

Abstract
MOTIVATION: We developed GeneGenerator because of the need for a tool to predict gene structure without knowing in advance how to score potential exons and introns in order to obtain the best results, pertinent in particular to less well-studied organisms for which suitable training sets are small. GeneGenerator is a very flexible algorithm which for a given genomic sequence generates a number of feasible gene structures satisfying user-defined constraints. The specific implementation described in detail requires minimum scoring for translation start and donor and acceptor splice sites according to previously trained logitlinear models. In addition, potential exons and introns are required to exceed specified minimal lengths and threshold scores for coding or non-coding potential derived as log-likelihood ratios of appropriate Markov sequence models. RESULTS: A database of 46 non-redundant genomic sequences from maize is used for illustration. It is shown that the correct gene structures do not always maximize the considered target function. However, in most cases, the correct or nearly correct structures are found in a small set of high-scoring structures. A critical review of the generated structures sometimes allows the choices to be narrowed by considering additional variables such as predicted splice site strength or local optimality of splice site scores. Summary statistics for prediction accuracy over all 46 maize genes are derived under cross-validation and non-cross-validation training conditions for the Markov sequence models. The algorithm achieved exon sensitivity of 0.81 and specificity of 0.75 on an independent set of 14 novel maize genomic segments. AVAILABILITY: GeneGenerator runs under Borland-Pascal 7.0 using MS-DOS and C on UNIX work stations. The source code is available upon request. CONTACT: jkleffe@euler.grumed.fu-berlin-de
Electrostatics in protein–protein docking
Authors: Heifetz Alexander , Katchalski‐Katzir Ephraim , Eisenstein Miriam 
Published: July 2002

AbstractA novel geometric‐electrostatic docking algorithm is presented, which tests and quantifies the electrostatic complementarity of the molecular surfaces together with the shape complementarity. We represent each molecule to be docked as a grid of complex numbers, storing information regarding the shape of the molecule in the real part and information regarding the electrostatic character of the molecule in the imaginary part. The electrostatic descriptors are derived from the electrostatic potential of the molecule. Thus, the electrostatic character of the molecule is represented as patches of positive, neutral, or negative values. The potential for each molecule is calculated only once and stored as potential spheres adequate for exhaustive rotation/translation scans. The geometric‐electrostatic docking algorithm is applied to 17 systems, starting form the structures of the unbound molecules. The results—in terms of the complementarity scores of the nearly correct solutions, their ranking in the lists of sorted solutions, and their statistical uniqueness—are compared with those of geometric docking, showing that the inclusion of electrostatic complementarity in docking is very important, in particular in docking of unbound structures. Based on our results, we formulate several “good electrostatic docking rules”: The geometric‐electrostatic docking procedure is more successful than geometric docking when the potential patches are large and when the potential extends away from the molecular surface and protrudes into the solvent. In contrast, geometric docking is recommended when the electrostatic potential around the molecules to be docked appears homogenous, that is, with a similar sign all around the molecule.
Optoelectronic Properties of MoS2 in Proximity to Carrier Selective Metal Oxides
Authors: Lattyak Colleen , Vehse Martin , Gonzalez Marco A. , Pareek Devendra , Gütay Levent , Schäfer Sascha , Agert Carsten 
Published: March 2022

AbstractTransition metal dichalcogenides are an exciting class of new absorber materials for photovoltaic applications due to their unique optoelectronic properties in the single to few‐layer regime. In recent years, these materials have been intensively studied, often utilizing conventional substrates such as sapphire and silicon dioxide on silicon. This study investigates the optical properties of molybdenum disulfide (MoS2) mono‐, bi‐, and multilayer films prepared by flake exfoliation and atomic layer deposition (ALD). These films are transferred to different photovoltaic relevant carrier‐selective contacts, such as titanium oxide, titanium–titanium oxide, molybdenum oxide, and silicon–silicon dioxide reference substrates. Raman and photoluminescence (PL) spectra of single‐crystalline exfoliated MoS2 flakes and ALD‐grown MoS2 films on different substrates are compared in order to investigate the influence of the different contact materials on the corresponding optical transitions in MoS2. It is demonstrated that the different substrates influence the Raman and PL spectra of MoS2 layers due to doping and charge transfer effects, and similar effects are observed in both the exfoliated single‐crystalline flakes and ALD‐grown MoS2 layers.
Wide‐Bandgap Organic–Inorganic Lead Halide Perovskite Solar Cells
Authors: Tong Yao , Najar Adel , Wang Le , Liu Lu , Du Minyong , Yang Jing , Li Jianxun , Wang Kai , Liu Shengzhong (Frank) 
Published: March 2022

AbstractUnder the groundswell of calls for the industrialization of perovskite solar cells (PSCs), wide‐bandgap (>1.7 eV) mixed halide perovskites are equally or more appealing in comparison with typical bandgap perovskites when the former's various potential applications are taken into account. In this review, the progress of wide‐bandgap organic–inorganic hybrid PSCs—concentrating on the compositional space, optimization strategies, and device performance—are summarized and the issues of phase segregation and voltage loss are assessed. Then, the diverse applications of wide‐bandgap PSCs in semitransparent devices, indoor photovoltaics, and various multijunction tandem devices are discussed and their challenges and perspectives are evaluated. Finally, the authors conclude with an outlook for the future development of wide‐bandgap PSCs.