bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dependence of phonon widths on pressure and isotopic mass: ZnO
Authors: Serrano J. , Widulle F. , Romero A.H. , Rubio A. , Lauck R. , Cardona M. 
Published: February 2003

AbstractConsiderable attention has been devoted recently to the dependence of the widths of the Raman phonons of semiconductors on pressure and on isotopic mass. The dependence on pressure is usually small and monotonic unless the phonon happens to be close to a singularity of the two‐phonon density of states (DOS) which determines its width. In the latter case, strong nonmonotonic dependences of the phonon width on pressure and on isotopic mass can appear. We have investigated the E2high phonons of ZnO crystals with different isotopes and observed a wide range of FWHM depending on isotopic masses. Ab initio calculations of the two‐phonon DOS provide an explanation for this variation of the FWHM: the E2high frequency falls on a sharp ridge of the 2‐DOS corresponding to combinations of TA and LA phonons. Changes in isotopic mass result in a motion of the E2high frequency up and down that ridge which produces the changes in FWHM. These phenomena suggest a decrease of the FWHM with pressure which seems to be present in existing data obtained at 300 K. Similar phenomena are discussed for the E2low phonons. Applications of the isotope and pressure techniques to the elucidation of two‐phonon spectra will be presented.
Specific features of the electronic structure of III–VI layered semiconductors: recent results on structural and optical measurements under pressure and electronic structure calculations
Authors: Segura A. , Manjón F. J. , Errandonea D. , Pellicer‐Porres J. , Muñoz V. , Tobias G. , Ordejón P. , Canadell E. , San Miguel A. , Sánchez‐Portal D. 
Published: February 2003

AbstractIn this paper we review some recent results on the electronic structure of III–VI layered semiconductors and its dependence under pressure, stressing the specific features that differentiate their behaviour from that of tetrahedrally coordinated semiconductors. We will focus on several unexpected results that have led to changes in the image that was currently accepted a few years ago. Intralayer bond angles change under pressure and the layer “thickness” remains virtually constant or increases. As a consequence, models based in intra‐ and inter‐layer deformation potentials fail in explaining the low pressure nonlinearity of the band gap. Numerical‐atomic‐orbital/density‐functional‐theory electronic structure calculations allow for an interpretation of the evolution of the absorption edge under pressure. In particular, they show how the structure of the non‐degenerated valence band maximum in InSe becomes more complex under pressure leading to a non‐conventional direct‐to‐indirect crossover. The valence band maximum in InSe above 4 GPa exhibits a quite singular feature: a “ring‐shaped” constant energy surface and, consequently, a density of states depending on energy as in 2D electronic systems.
Photoluminescence studies of GaAs/partially ordered GaInP quantum wells grown by metalorganic vapor phase epitaxy
Authors: Kobayashi T. , Tomoda H. , Prins A. D. , Homma Y. , Uchida K. , Nakahara J. 
Published: February 2003

AbstractWe report the results of a study on GaAs/partially ordered Ga0.5In0.5P quantum wells using up‐converted photoluminescence (UPL), in which a sample emits photons with an energy (1.89 eV) higher than that of the excitation photon (1.58 eV), together with the normal photoluminescence (PL) excited at a photon energy higher than that of the GaInP band gap and at high pressures up to ∼5 GPa. Both the ∼1.46 eV emission and the UPL observed in this work provide new evidence of a type II band alignment.
Pressure dependence of the natural birefringence in the II–IV–V2 chalcopyrite CdGeP2
Authors: Choi In‐Hwan , Yu P. Y. 
Published: February 2003

AbstractChalcopyrite semiconductors are birefringent as a result of their tetragonal crystal lattice structure. The dispersion of this birefringence contains contributions from the near‐bandgap transitions and also from higher energy band‐to‐band transitions. We report the effect of pressure on the dispersion of the natural birefringence in CdGeP2. We found that pressure tends to decrease both contributions. The pressure effect on the near‐bandgap contribution results mostly from an increase of the bandgap with pressure.
High‐pressure phase in the chalcopyrites CuGaTe2 and CuInTe2
Authors: Mori Y. , Ikai T. , Takarabe K. 
Published: February 2003

AbstractA high‐pressure X‐ray diffraction study was carried out for CuGaTe2 and CuInTe2 chalcopyrite semiconductors up to 18.0 and 13.0 GPa, respectively. The high‐pressure phase was conclusively assigned to the d‐Cmcm phase (cation site disordered Cmcm). In the case of CuGaTe2, the chalcopyrite phase transformed to the d‐Cmcm phase at 12.7 GPa through the tentative d‐SC phase. The bulk moduli for the three phases were determined to be 64, 81, and 103 GPa, respectively. In the case of CuInTe2, the chalcopyrite phase transformed to the d‐Cmcm phase at 3.6 GPa. The d‐SC phase did not appear. The bulk moduli for the two phases were determined to be 59.8 and 77 GPa, respectively.
Raman scattering in CdGa2Se4 under pressure
Authors: Mitani T. , Naitou T. , Matsuishi K. , Onari S. , Allakhverdiev K. , Gashimzade F. , Kerimova T. 
Published: February 2003

AbstractThe Raman scattering spectra of CdGa2Se4 under pressure were investigated at 300 K up to 20.9 GPa. TO as well as LO modes were observed. Two stages were observed in the pressure dependences of Raman bands. Such a behaviour was attributed to the ordedisorder phase transition in the cation sublattice. A first‐order phase transition under pressure was observed at 20.2 GPa. Using the HarrisoKeating model of the lattice dynamics modified for crystals with the tetragonal structure, the bulk modulus B and the mode‐Grüneisen parameters Γi were determined for the first time. It is shown that a better agreement between the experimental and calculated values of Γi is observed if one takes into consideration the different behaviour with pressure for the bond‐bending and the bond‐stretching parameters, which determine the low‐ (lower than 140 cm–1) and high‐ (higher than 140 cm–1) frequency phonons, respectively.
Conductivity of graphite and fullerene under pressures up to 50 GPa
Authors: Tikhomirova G. V. , Babushkin A. N. 
Published: February 2003

AbstractThe DC resistance of polycrystalline fullerene C60 and graphite in the temperature range 77–450 K were studied at pressures up to 50 GPa. The AC measurements were performed at room temperature. The temperature and pressure dependences of resistance for both materials are of a similar character. However, the resistance of both materials is different by many orders of magnitude. It is shown that both fullerene and graphite keep some features of their original microscopic structure even at high pressures.
Pressure and k · p studies of band parameters in dilute‐N GaInNAs/GaAs multiple quantum wells
Authors: Choulis S. A. , Hosea T. J. C. , Tomić S. , Kamal‐Saadi M. , Weinstein B. A. , O'Reilly E. P. , Adams A. R. , Klar P. J. 
Published: February 2003

AbstractWe report pressure dependent photomodulated reflectance (PR) measurements on a series of dilute‐N InGaNAs/GaAs multiple quantum wells (MQWs). Our experimental results indicate the presence of important N‐related disorder effects due to different nearest‐neighbour N‐cation configurations The quantum well transition energies obtained from the PR spectra are modelled using a realistic 10‐band k · p Hamiltonian that includes tight‐binding‐based energies and coupling parameters for the N‐levels. By matching experiment with theory we are able to determine accurately the band structure and thus predict some important material parameters for dilute‐N InGaAsN alloys.
Absolute deformation potential with a compressed atom model
Authors: Kosaka K. , Takarabe K. 
Published: February 2003

AbstractA compressed atom model is developed to study the one‐electron energy level in the FLAPW (full‐potential linearized augmented plane wave) calculation. The reference energy level in the FLAPW calculations is shown to be dominated by the exchange‐correlation potential. Taking this into account it is possible to evaluate the absolute deformation potential.
Large excitation‐power dependence of pressure coefficients of InxGa1–xN/InyGa1–yN quantum wells
Authors: Li Q. , Fang Z.L. , Xu S.J. , Li G.H. , Xie M.H. , Tong S.Y. , Zhang X.H. , Liu W. , Chua S.J. 
Published: February 2003

AbstractExcitation‐power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1–xN/InyGa1–yN multiple quantum wells is reported. When the excitation power increases from 1.0 to 33 mW, dE/dP increases from 26.9 to 33.8 meV/GPa, which is an increase by 25%. A saturation behavior of dE/dP with the excitation power is observed. The increment of dE/dP with increasing carrier density is explained by an reduction of the internal piezoelectric field due to an efficient screening effect of the free carriers on the field.
Pressure and temperature dependence of the band‐gap in CdTe
Authors: Gilliland S. , González J. , Güder H. S. , Segura A. , Mora I. , Muñoz V. 
Published: February 2003

AbstractIn this paper we report on isothermal compression measurements (up to 5 GPa and 500 K) of the optical absorption edge of 1 μm epitaxial layers of CdTe growth by metalorganic chemical vapor deposition (MOCVD) on GaS substrates. The isothermal blue shift under pressure of the direct energy gap (Γv15 → Γc1) in the zinc‐blende phase is about 7.1 × 10–2 eV GPa–1 and is found to be independent of temperature within the experimental errors. The isobaric red shift in the stability range of the zinc‐blende phase is about –3.76 × 10–4 eV K–1. Regarding the phase transitions, no discontinuity in the energy gap has been found in the narrow pressure range where the cinnabar phase can be present. The transition pressure to the NaCl‐type structure in CdTe is found to decrease with increasing temperature (294–500 K) following the law Pt = 4.1 GPa – 6.6 × 10–3 (T – 273) (K).
Effect of pressure on structural properties and energy band gaps of γ‐InSe
Authors: Olguín D. , Cantarero A. , Ulrich C. , Syassen K. 
Published: February 2003

AbstractWe have investigated theoretically the effect of hydrostatic pressure on interatomic bond lengths and energy band gaps of γ‐InSe. Total energy calculations were performed using the linear augmented plane wave (LAPW) method, taking into account scalar relativistic corrections as well as spin‐orbit coupling. Internal structural parameters were optimized for different pressures by adopting as input the unit cell parameters known from experiment. Our theoretical results for the nearest‐neighbor In–Se bond length are in excellent agreement with a recent experimental determination from high‐pressure EXAFS measurements. The covalent In–In bond is found to be more compressible than the partially ionic In–Se bond. We also present the calculated pressure dependence of band gaps and compare to recent high‐pressure experimental studies of optical and transport properties. A large negative pressure coefficient is obtained for the indirect Z–A gap. This leads to a crossover from a direct to an indirect fundamental gap within the stability range of the γ‐polytype of InSe, in qualitative agreement with recent experiments.
Gain‐cavity alignment profiling of 1.3 μm emitting GaInNAs vertical cavity surface emitting lasers (VCSELs) using high pressure techniques
Authors: Knowles G. , Tomić S. , Jin S. , Fehse R. , Sweeney S. J. , Sale T. E. , Adams A. R. 
Published: February 2003

AbstractVertical‐cavity surface‐emitting lasers with a GaInNAs quantum well active region have been studied as a function of hydrostatic pressure and compared with similar edge‐emitting lasers. The variation of threshold currents and lasing energies is studied and compared with a gain model calculated from a 10 band k · p model which includes the N interaction in the conduction band. Good agreement is obtained between experiment and model and indicates that a large Lorentzian broadening parameter of 17.5 meV applies. The gain spectrum is therefore broad and the devices have a large degree of temperature stability and growth error tolerance.
Quantifying pressure‐dependent recombination currents in GaInNAs lasers using spontaneous emission measurements
Authors: Jin S. R. , Sweeney S. J. , Tomić S. , Adams A. R. , Riechert H. 
Published: February 2003

AbstractThe pressure dependence of the total threshold current and its respective recombination components in 1.3 μm GaInNAs single quantum‐well lasers has been determined by measuring for the first time the window‐spontaneous emission under hydrostatic pressures at room temperature. It is shown that, above 6 kbar, the rapid increase of the threshold current with increasing pressure in GaInNAs lasers is related to the unusual increase of the Auger recombination current, while the monomolecular non‐radiative current in the total threshold current is almost constant in the pressure range studied. Theoretical calculations show that the unusual increase of the Auger current is due to a large increase in the threshold carrier density with pressure, stronger than the reduction of the Auger coefficient leading to an overall increase in the Auger current.
Semiconductor–metal transitions in lead chalcogenides at high pressure
Authors: Ovsyannikov S. V. , Shchennikov V. V. , Popova S. Vict. , Derevskov A. Yu. 
Published: February 2003

AbstractThe results of thermoelectric power (S) measurements of the lead chalcogenides PbS, PbSe, and PbTe at the initial NaCl‐phase, as high‐pressure semiconductors (above 2–6 GPa), and at metal phases (above 10–15 GPa) are presented. Phase transitions are discussed in terms of the model of Peierls distortion of lattice.
Electronic structure of tellurium under high pressure
Authors: Nishikawa Atsushi , Shindo Koichi 
Published: February 2003

AbstractWe have performed band structure calculations of high‐pressure phases of tellurium within the local density‐functional formalism and the norm‐conserving pseudo‐potential method. We have calculated the band structure for the newly proposed model of Te‐III phase, and the result suggests that the monoclinic distortion lowers the band structure energy and contributes to the structural stability.
Elastic properties and pressure‐induced phase transitions of single‐walled carbon nanotubes
Authors: Reich S. , Thomsen C. , Ordejón P. 
Published: February 2003

AbstractWe studied the structure of single‐walled carbon nanotubes under hydrostatic pressure by first‐principles calculations. The circular tubes collapse at high pressure (7 GPa) to a phase with an elliptical cross‐section. The elliptical structure leads to the formation of diamond‐like bonds between the tubes at the point of strongest curvature. The bulk modulus of the circular, ambient‐pressure phase that we found from our calculations is very similar to graphite (37 GPa). The interlinked phase also shows graphite‐like behavior in the low‐ and high‐pressure range: between 3.5 and 6.5 GPa its compressibility is very large. We compare our theoretical predicitions to X‐ray scattering and piston–cylinder experiments.
3D QSAR of Serotonin Transporter Ligands: CoMFA and CoMSIA Studies
Authors: Wellsow Julia , Machulla Hans‐Jürgen , Kovar Karl‐Artur 
Published: February 2003

AbstractThe main purpose of this study was the investigation of quantitative structure‐activity relationships of serotonin transporter ligands with regard to the future development of potential new and selective PET radiotracers for the serotonin transporter. A heterogeneous data set of 19 selective and non‐selective serotonin reuptake inhibitors was used. Affinity data for both the serotonin transporter and the norepinephrine transporter was available. As a necessary prerequisite for our 3D QSAR studies a reasonable alignment of the compounds was developed using GASP. It was based on an existing pharmacophore model. In addition to the widely used CoMFA method, the somewhat newer CoMSIA method was applied. Statistically reliable CoMFA models for both the serotonin transporter (q2=0.538) and the norepinephrine transporter (q2=0.445) were developed, further improving the internal predictability by applying region focusing for the serotonin transporter (q2=0.674). These models were compared with the CoMSIA models for the serotonin and the norepinephrine transporter that yielded comparable cross‐validated correlation coefficients (q2=0.531 and q2=0.502, respectively). Certain structural features that are distinctive of each transporter and important for high binding affinity were identified. Highly comparable results were obtained for CoMFA and CoMSIA. Both methods were applied to elucidate structural requirements for serotonin transporter selectivity. The resulting CoMSIA map provides important information for lead optimization with respect to selectivity enhancement.
Scaffold Searching: Automated Identification of Similar Ring Systems for the Design of Combinatorial Libraries
Authors: Bohl Martin , Dunbar James , Gifford Eric M. , Heritage Trevor , Wild David J. , Willett Peter , Wilton David J. 
Published: February 2003

AbstractRigid ring systems can be used to position receptor‐binding functional groups in 3D space and they thus play an increasingly important role in the design of combinatorial libraries. This paper discusses the use of shape‐similarity methods to identify ring systems that are structurally similar to, and aligned with, a user‐defined target ring system. These systems can be used as alternative scaffolds for the construction of a combinatorial library.
Identification of Diverse Database Subsets using Property‐Based and Fragment‐Based Molecular Descriptions
Authors: Ashton Mark , Barnard John , Casset Florence , Charlton Michael , Downs Geoffrey , Gorse Dominique , Holliday John , Lahana Roger , Willett Peter 
Published: February 2003

AbstractThis paper reports a comparison of calculated molecular properties and of 2D fragment bit‐strings when used for the selection of structurally diverse subsets of a file of 44295 compounds. MaxMin dissimilarity‐based selection and k‐means cluster‐based selection are used to select subsets containing between 1% and 20% of the file. Investigation of the numbers of bioactive molecules in the selected subsets suggest: that the MaxMin subsets are noticeably superior to the k‐means subsets; that the property‐based descriptors are marginally superior to the fragment‐based descriptors; and that both approaches are noticeably superior to random selection.
Accurate measurement of the relative bond energies of CO and H2O ligands in Fe+ mono‐ and bis‐ligated complexes
Authors: le Caër Sophie , Heninger Michel , Maître Philippe , Mestdagh Hélène 
Published: February 2003

AbstractThe systems Fe(H2O)n+/COH2O and Fe(CO)n+/COH2O (n = 1 and 2) were investigated in a triple cell Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometer. Using mixtures of CO with a very small amount of water, the ligand exchange equilibrium was reached, allowing experimental determination of the relevant equilibrium constants and free energies of reaction. Quantum chemical calculations at the B3LYP level of theory on the reactant and product species allowed us to determine the entropic terms and to derive the relative bond energies of CO and H2O in the mono‐ and bis‐ligated complexes. For n = 1, H2O is more strongly bound to Fe+ than CO by 4.1 ± 1.6 kJ·mol−1 at 298 K. For n = 2, at the same temperature, H2O is more strongly bound than CO to (H2O)Fe+ by 7.6 ± 1.6 kJ·mol−1, and to (CO)Fe+ by more than 20.1 kJ·mol−1. Copyright © 2003 John Wiley & Sons, Ltd.
Tool command language automation of the modular ion cyclotron data acquisition system (MIDAS) for data‐dependent tandem Fourier transform ion cyclotron resonance mass spectrometry
Authors: Freitas Michael A. , King Eric , Shi Stone D.‐H. 
Published: February 2003

AbstractThis manuscript describes the addition of data‐dependent automation to the modular ion cyclotron resonance data acquisition system (MIDAS). The automation is made possible by developments and incorporation of a tool command language (Tcl) interpreter for automated acquisition. To accomplish the automation, real‐time generation of excitation waveforms and scriptable data post‐processing has been implemented into the MIDAS source code. In addition a new excitation event has also been added to allow for run‐time generation of a single notch stored waveform inverse Fourier transform (SWIFT) excitation event. Examples of these new features and discussion of their enhancement to the existing data station are presented. Copyright © 2003 John Wiley & Sons, Ltd.
A Stable Carbene Phosphenic Chloride Complex: First Structural Characterization of a PO2Cl Base Adduct [1]
Authors: Kuhn Norbert , Ströbele Markus , Walker Michael 
Published: February 2003

AbstractThe phosphenic chloride adduct Im—PO2Cl (4, Im = 2, 3‐dihydro‐1, 3‐diisopropyl‐4, 5‐dimethylimidazol‐2‐ylidene) was prepared by partial hydrolysis of [Im—POCl2]Cl (5) and characterized by X‐ray structure analysis.
Synthesis and Molecular Structure of a Hexaaminodistannane Comprising two Identical Triaminotin Subunits
Authors: Lutz Matthias , Haukka Matti , Pakkanen Tapani A. , Gade Lutz H. 
Published: February 2003

AbstractReaction of the previously characterized lithium stannate [HC{SiMe2N(4‐CH3C6H4)}3SnLi(thf)3] (1) with AgCl afforded the corresponding distannane [HC{SiMe2N(4‐CH3C6H4)}3Sn]2 (2) as the product of an oxidative coupling in good yield. Its [2, 2, 2]bicyclooctane‐related cage structure, comprising the trisilylmethane unit and the triamido‐tin fragment, as well as the Sn‐Sn bond (2.8204(4)Å) were established by single crystal structure analysis: Space group group P21/n, Z = 2, lattice dimensions at 120(2) K: a = 13.6515(3), b = 15.8391(3), c = 16.3522(3)Å, β = 102.7760(10)°, R1 = 0.0347.
Tellurium‐Halogen Secondary Bonding in the Crystal Structures of [Q]+[PhTeCl4]— (Q = C5NH6, 2‐Br‐C5NH5, {2‐Br‐C5NH5}{Co(NH3)4Cl2})
Authors: Schulz Lang Ernesto , Fernandes Jr Ramão Marceli , Peppe Clóvis , Burrow Robert Alan , Vázquez‐López Ezequiel M. 
Published: February 2003

AbstractThe reaction of diphenylditelluride with pyridine, 2‐bromopyridine or 2‐bromopyridine/tetraamminedichlorocobalt(III) chloride in 12 M hydrochloric acid afforded the tetrachlorophenyltellurate(IV) compounds [C5NH6][PhTeCl4] (1), [2‐Br‐C5NH5] [PhTeCl4] (2), and [{2‐Br‐C5NH5}{Co(NH3)4Cl2}] [PhTeCl4]2 (3). They were all characterized structurally by single crystal X‐ray diffraction. In all structures, the arrangement about the tellurium atoms is square pyramidal. The [PhTeCl4]— anions in 1 and 2 form trimeric and dimeric units, respectively, through Te···Cl secondary bonding. Compound 3 shows an unusual face‐to‐face packing of the [PhTeCl4]—anions with hydrogen bonding to the bromopyridium cation.
Synthesis and Structure of K[Cd(O2N‐C6H4‐NNN‐C6H4‐NO2)3], an Anionic 1, 3‐Bis(4‐nitrophenyl)triazenido Complex of Cadmium
Authors: Hörner Manfredo , Santana Carratu Vanessa , Herbst‐Irmer Regine , Maichle Mössmer Cäcilia , Strähle Joachim 
Published: February 2003

AbstractThe reaction of cadmium acetate in methanol with 1, 3‐bis(4‐nitrophenyl)triazene in THF in the presence of KOH yields K[Cd(O2NC6H4NNNC6H4NO2)3] in form of hexagonal prismatic, red crystals with the trigonal space group R3¯ and a = 12.229(2), c = 48.988(10) Å and Z = 6. In the anionic cadmium complexes, which are located along the threefold axis, the Cd atoms are coordinated in a trigonal prismatic arrangement by the atoms N(1) and N(3) of three triazenido ligands. The potassium cations are coordinated icosahedrally by oxygen atoms of each one nitro group of six neighbouring anionic complexes. The Cd‐N distances are 2.376(4) and 2.350(4) Å, and the K‐O distances are in the range of 2.833(6) to 3.365(6) Å.