bluuebunny/crossref_metadata_2025 huggingface dataset:
High‐pressure phase in the chalcopyrites CuGaTe2 and CuInTe2
Authors: Mori Y. , Ikai T. , Takarabe K.
Published: February 2003

A 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

The 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

The 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

We 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

A 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

Excitation‐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

In 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

We 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

Vertical‐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

The 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

The 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

We 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

We 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

The 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

Rigid 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

This 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

The 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

This 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

The 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

Reaction 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

The 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

The 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.
Hydrolyse und Kondensation von Si(OEt)4: Trennung und massenspektrometrische Charakterisierung der Zwischenprodukte
Authors: Söger N. , Binnewies M.
Published: February 2003

Reaktionsgemische, die bei der Hydrolyse von Si(OEt)4 entstehen, wurden mittels Kapillargaschromatographie getrennt. Durch GC‐MS‐Kopplung konnten so die Massenspektren der reinen Ethoxysiloxane und ‐siloxanole erhalten werden. Zur Identifizierung dieser Verbindungen wurde deren Retentions‐ und Fragmentierungsverhalten untersucht. Es zeigte sich, daß Moleküle mit derselben Anzahl an Silicium‐Atomen nahezu identische Fragmentierungsmuster aufweisen. Eine massenspektrometrische Identifizierung der Siloxane und Siloxanole mit gleicher Anzahl an Silicium‐Atomen, aber unterschiedlicher Anzahl an Sauerstoff‐Atomen ist nur nach vorheriger Isolierung und nur für niedermolekulare Spezies möglich.
Unexpected Formation of the Mixed Ligand Complexes [Cu(OAc)(bipy)2]Cl·4H2O·1/2MeOH and [Co(OH2)2(phen)2](OAc)2·6H2O, and their Crystal Structures
Authors: Carballo R. , Covelo B. , Vázquez‐López E. M. , García‐Martínez E.
Published: February 2003

The mononuclear compounds [Cu(OAc)(bipy)2]Cl·4H2O·1/2MeOH(1) and [Co(OH2)2(phen)2](OAc)2·6H2O(2) were unexpectedly obtained as single crystals from mother liquors left following isolation of the expected products of the reactions, in ethanol of Cu(OAc)2, benzylic acid and 2, 2'‐bipyridine (for 1) and Co(OAc)2, D, L‐mandelic acid and 1, 10‐phenanthroline (for 2). The complexes were characterized by elemental analysis, IR and electronic spectroscopy and magnetic measurements at room temperature and their structures were determined by single‐crystal X‐ray analysis. In 1, the pentacoordinated copper atom has a basically square pyramidal coordination polyhedron, while in 2 the cobalt atom has a distorted octahedral environment. In both cases, the complexes are linked by hydrogen bonds and aromatic‐aromatic interactions.
Synthetic, Spectroscopic and Structural Studies of the Rhenium(I) Dicarbonyl Complexes of Phosphite, Phosphonite, and Phosphinite Ligands: cis, mer‐[ReBr(CO)2{PPh3‐n(OR)n}3] (R = Me, Et; n = 1—3)
Authors: Carballo Rosa , Losada‐González Pilar , Vázquez‐López Ezequiel M.
Published: February 2003

The reaction of [ReBr(CO)5] with phosphite and phosphonite ligands in toluene yielded cis, mer‐[ReBr(CO)2L3] (2: L = P(OMe)3 2a: P(OEt)3 2b: PPh(OMe)2 2c: PPh(OEt)2 2d). Compounds 2c and 2d were also obtained, as were the phosphinite complexes 2e [L = PPh2(OMe)] and 2f [L = PPh2(OEt)], by reaction of the corresponding phosphorus ligand with trans, mer‐[ReBr(CO)3L2]. Compounds 2 were all characterized by elemental analysis, mass spectrometry and NMR spectroscopy, and the structures of 2b, 2c and 2d were determined by X‐ray diffractometry. Compounds 2a‐d are stable in chloroform and dichloromethane, but 2e and 2f are transformed into the corresponding trans, mer‐[ReBr(CO)3L2] complexes by a reaction for which a partial mechanism is put forward.
Synthesis, Spectroscopic and Structural Aspects of Mono‐ and Diorganothallium(III) Complexes of 2, 6‐Diacetylpyridine Bis(thiosemicarbazone) (H2DAPTSC) — A New Coordination Mode of the HDAPTSC— Anion
Authors: Casas José. S. , Castellano Eduardo E. , Ellena Javier , García‐Tasende María S. , Sánchez Agustín , Sordo José , Vázquez‐López Ezequiel M. , Vidarte María J.
Published: February 2003

The reaction of 2, 6‐diacetylpyridine bis(thiosemicarbazone) (H2DAPTSC) with dimethylthallium hydroxide yielded the complexes [(TlMe2)2(DAPTSC)] and [TlMe2(HDAPTSC)]. The structure of [TlMe2(HDAPTSC)], determined by X‐ray diffractometry, exhibits a hitherto unknown coordination mode of the HDAPTSC— anion in which its deprotonated thiosemicarbazone chain coordinates one metal atom through its sulphur and hydrazinic N atoms while a second metal atom is weakly coordinated through the S atom of the undeprotonated thiosemicarbazone chain. Each thallium atom is coordinated in both ways, with the result that the [TlMe2(HDAPTSC)] units are linked in infinite helical chains in the direction of the b axis.

When reacting with diphenylthallium(III) hydroxide, H2DAPTSC induced a dephenylation process which led to the monophenylthallium(III) complex [TlPh(DAPTSC)]. Recrystallization from acetone yielded crystals of [TlPh(DAPTSC)]·C3H6O in which X‐ray diffractometry showed DAPTSC2— to be pentadentate, coordinating through its sulphur, azomethine N and pyridine N atoms.

The 1H, 13C and 205Tl NMR data of [TlPh(DAPTSC)] indicate that its solid state molecular structure persists in DMSO solution, while those of [TlMe2(HDAPTSC)] indicate rapid alternation between coordination of the metal atom to one of the HDAPTSC— thiosemicarbazone chains and its coordination to the other.
Tricarbonyl Complexes of Rhenium(I) with Acetylpyridine Benzoylhydrazone and Related Ligands
Authors: Grewe Jacqueline , Hagenbach Adelheid , Stromburg Brigitte , Alberto Roger , Vazquez‐Lopez Ezequiel , Abram Ulrich
Published: February 2003

Novel rhenium(I) tricarbonyl complexes have been prepared by reactions of (Et4N)2[Re(CO)3Br3] with acetylpyridine benzoylhydrazone, Hapbhyd, di(2‐pyridyl)ketone benzoylhydrazone, Hpy2bhyd, bis(2‐pyridine)ketone, py2CO, and pyridinealdehyde terephtalaldehydebishydrazone, pytehyd. The ligands remain protonated when no supporting base is added and the following complexes have been isolated: [Re(CO)3Br(Hapbhyd)], [Re(CO)3Br(Hpy2bhyd‐py, hyd)], [Re(CO)3Br(Hpy2bhyd‐py1, py2)], [Re(CO)3Br(py2CO‐N, N)] and [Re(CO)3Br(pytehyd)]. Addition of triethyl amine results in deprotonation of Hapbhyd and the formation of [Re(CO)3(OH2)(apbhyd)], whereas Hpy2bhyd is hydrolysed and a rhenium complex with the monoanionic bis(2‐pyridyl)hydroxymethanolato ligand, {py2C(OH)O}‐, is formed. The same compound, [Re(CO)3{py2C(OH)O}], is obtained when triethyl amine and water are added to a mixture of (Et4N)2[Re(CO)3Br3] and py2CO.

The air‐stable products have been studied by spectroscopic methods and X‐ray crystallography.
Die Kristallstrukturen von KNdTe4, RbPrTe4 und RbNdTe4 — Untersuchungen zur thermischen Stabilität von KNdTe4 sowie Bemerkungen zu einigen anderen Vertretern der Zusammensetzung ALnTe4 (A = K, Rb, Cs und Ln = Seltenerd‐Metall)
Authors: Stöwe Klaus , Napoli Christian , Appel Stephan
Published: February 2003

Von den Verbindungen der Zusammensetzung ALnQ4 (A = Na, K, Rb, Cs, mit Ln = Seltenerd‐Metall und mit Q = S, Se und Te) konnten die Strukturen der drei neuen Telluride KNdTe4, RbPrTe4 und RbNdTe4 durch Einkristallstrukturanalyse und des weiteren die der drei neuen Telluride KCeTe4, KPrTe4 und CsNdTe4 durch röntgenographische Untersuchungen an Pulvern bestimmt werden. Alle sechs neuen Verbindungen kristallisieren isotyp zu KCeSe4. Kennzeichnend für die Kristallstruktur der genannten Verbindungen sind Schichten mit (Q2)2—‐Hanteln in Form von 4.32.4.3‐Netzen, zwischen die die Kationen A+ und Ln3+ eingelagert sind und dort achtfach in Form von quadratischen Antiprismen von Q koordiniert sind. Der Te‐Te‐Abstand innerhalb der Hanteln liegt für alle untersuchten Telluride im Bereich von 277.8(2)pm. Röntgenographische und differenzthermoanalytische Untersuchungen zeigen, dass die Verbindung KNdTe4 bei Raumtemperatur metastabil ist und einen begrenzten Existenzbereich zwischen 260 und 498 °C hat.
Synthesis and Structure of Ln2(H4IO6)(I2O10)·H3O·5 H2O (Ln=Pr, Nd, Sm), a Lanthanide Periodate Diperiodate
Authors: Fischer Andreas
Published: February 2003

By slow evaporation of solutions containing Ln(ClO4)3 (Ln=Pr, Nd, Sm), H5IO6 and an excess of HClO4, crystals of the title compounds could be obtained. Their structures were determined by single‐crystal X‐ray diffraction. The compounds crystallize in the monoclinic crystal system, space group I2/a. They contain two types of periodate ions: octahedral H4IO6 groups and two crystallographically different I2O10 groups, which consist of two edge‐sharing octahedra. These anions coordinate to the cations as bridging groups yielding a three‐dimensional network. Together with some water of crystallization, a coordination number of 9 is achieved around the lanthanide ions with a tri‐capped trigonal prismatic geometry.
Synthesis and Structure of a One‐Dimensional Aluminum Phosphate, [NH3(CH2)2NH2(CH2)3NH3]3+[Al(PO4)2]3—
Authors: Natarajan Srinivasan , Klein Wilhelm , Nuss Jürgen , van Wüllen Leo , Jansen Martin
Published: February 2003

A one‐dimensional aluminum phosphate, [NH3(CH2)2NH2(CH2)3NH3]3+ [Al(PO4)2]3—, has been synthesized hydrothermally in the presence of N‐(2‐Aminoethyl‐)1, 3‐diaminopropane (AEDAP) and its structure determined by single crystal X‐ray diffraction. Crystal data: space group = Pbca (no. 61), a = 16.850(2), b = 8.832(1), c = 17.688(4)Å, V = 2632.4(2)Å3, Z = 8, R1 = 0.0389 [5663 observed reflections with I > 2σ(I)]. The structure consists of anionic [Al(PO4)2]3— chains built up from AlO4 and PO4 tetrahedra, in which all the AlO4 vertices are shared and each PO4 tetrahedron possesses two terminal P=O linkages. The cations, which balances the negative charge of the chains, are located in between the chains and interact with the oxygen atoms through strong N—H···O hydrogen bonds. Additional characterization of the compound by powder XRD and MAS‐NMR has also been performed and described.
Crystal Structure and Properties of Strontium Phosphate Apatite with Oxocuprate Ions in Hexagonal Channels
Authors: Kazin Pavel E. , Karpov Andrey S. , Jansen Martin , Nuss Jürgen , Tretyakov Yury D.
Published: February 2003

Strontium phosphate apatites containing different amounts of copper were prepared by a solid state reaction at 1100 °C or by arc melting above 1600 °C in air. The samples were characterized by X‐ray diffraction, ICP analysis, scanning electron microscopy, IR spectroscopy, MAS—1H—NMR, diffuse reflectance spectroscopy, and SQUID magnetometry. X‐ray crystal structure determination was carried out for a single crystal obtained from the melt. The compound is formulated as Sr5(PO4)3(CuO2)1/3 and has an apatite structure (space group P63/m, a = 9.7815(4)Å, c = 7.3018(4)Å, Z = 2) with linear CuO23— ions occupying hexagonal channels. For solid state synthesized samples, Rietveld refinement of powder XRD patterns was performed. The samples obtained at 1100 °C acquire the composition Sr5(PO4)3CuxOHy, with x changing from 0.01 to 0.62 and y < 1—x. The copper content can be increased to x = 0.85 by annealing in argon at 950 °C. The compounds represent a hydroxyapatite in which part of the protons is substituted by Cu+ and Cu2+ ions. The ions form linear O—Cu—O units which are progressively condensed creating the Cu—O—Cu bridges on increasing copper content. IR and NMR data testify existence of OH groups, non‐disturbed and disturbed by neighboring Cu atoms. In the electron spectra, the samples exhibit absorption bands at 7800‐7900, 14200‐14500 and 17500‐17550 cm—1, which were assigned to Cu2+ d‐electron transitions. By annealing the sample with x = 0.1 in oxygen at 800 °C copper is fully oxidized while retaining in channels in unusual for Cu2+ linear coordination.
Fabrication and time-resolved studies of visible microdisk lasers
Authors: Zwiller V. , Fälth S. , Persson J. , Seifert W. , Samuelson L. , Björk G.
Published: February 2003

We report on the fabrication and characterization of microdisk lasers emitting at around 650 nm. The structures were grown by metalorganic vapor phase epitaxy and processed using electron beam lithography and wet etching. Time-resolved photoluminescence measurements done at low temperature show a lasing threshold of 60 μW average power. A redshift in the whispering modes energy is observed.
Strong enhancement of the photoluminescence efficiency from InAs quantum dots
Authors: Zhao Q. X. , Willander M. , Wang S. M. , Wei Y. Q. , Sadeghi M. , Yang J. H.
Published: February 2003

InAs quantum dots (QDs) have been investigated using optical spectroscopy, in order to understand the experimental observation of strong enhancement of their photoluminescence efficiency. When a tunneling barrier is introduced between the InAs layer and the GaAs cap layer, the intensity of the InAs QD emission increases by more than an order of magnitude at the excitation density of 60 W/cm2. The enhancement of the optical recombination efficiency is due to the suppression of the nonradiative transitions in the wetting layer. The strong enhancement of the InAs emission can lead to an increase in the optical gain of the InAs laser structure.
Effect of Tl content on the growth of TlGaAs films by low-temperature molecular-beam epitaxy
Authors: Kajikawa Y. , Kametani M. , Kobayashi N. , Nishimoto N. , Yodo Y. , Kitano Y. , Ohtani Y.
Published: February 2003

TlGaAs layers with various Tl contents have been grown on GaAs(001) substrates by solid-source molecular-beam epitaxy at a substrate temperature of 210 °C and an As/Ga beam equivalent pressure ratio of 100. The Tl content was characterized by Rutherford backscattering spectrometry, secondary-ion mass spectrometry, and electron microprobe analysis. Nomarski microscope observation revealed that the surfaces of the TlxGa1−xAs layers were mirror like until a Tl content of x=7.0% while Tl droplets appeared on the surfaces of samples with a Tl content of x=7.7%. X-ray diffraction (XRD) curves showed clearly resolved epi-layer peaks until a Tl content of x=6.4%. We estimated the epitaxial thickness hepi, at which single-crystalline growth is replaced by polycrystalline growth, by two different methods using the XRD data. In one method we measured the change in diffracted intensity of the epi-layer peak after progressive gradual etching of the TlGaAs layers grown. The other was on the basis of a simulation of the diffraction curves of the as-grown samples within dynamical diffraction theory. The values of hepi estimated by the two methods agreed well and showed a remarkable decrease with an increase in Tl content. Cross-sectional transmission electron microscopy confirmed the reliability of the estimated value of hepi. In addition, the lattice mismatch was analyzed utilizing both symmetric and asymmertic XRD data. The analysis indicated that the lattice constant of an imaginary zinc-blende type crystal of stoichiometric TlAs (aTlAs) is slightly smaller than that of InAs (aInAs).
Tensile failure by grain thinning in micromachined aluminum thin films
Authors: Lee Hoo-Jeong , Zhang Ping , Bravman John C.
Published: February 2003

This article reports the results of microtensile tests and transmission electron microscopy (TEM) analyses of micron-scale free-standing aluminum thin films. We fabricated the free-standing aluminum beams using micromachining procedures and tested them in a piezo-actuator-driven test apparatus. Microtensile tests revealed that the mechanical characteristics of the free-standing beams are quite different from those of the bulk material. Some unique features of our free-standing Al beams are high yield strength, low ductility, and strain softening. While the high yield strength is attributed to the typically small grain size, the strain softening and the small ductility are explained by locally thinned grains found in TEM analyses. Further TEM analyses suggested that dislocations pass through the free surfaces in the interiors of some large grains and lead to strain softening, which, in turn, results in deformation concentration in such areas and hence localized thinning.
Emission of neutral Mg from single crystal MgO during abrasion with diamond
Authors: Kim Myoung-Won , Langford S. C. , Dickinson J. T.
Published: February 2003

We report observations of atomic, neutral Mg emitted from single crystal MgO during abrasion with a diamond stylus. These emissions take the form of bursts, where the onset of each burst coincides with a slip event often associated with the passage of the stylus over a cleavage step. After the onset, the emission intensity grows gradually to a peak, then drops sharply. Similar bursts of neutral Mg are observed when indented single crystal MgO is heated to temperatures above 1300 °C. We attribute these bursts to the emission of neutral Mg during the relaxation of dislocation-related structures produced by mechanical deformation. Strain energy released as these structures annihilate at the surface drive Mg emission and heat the surrounding material. This heating accelerates subsequent relaxation, increasing the emission intensity until relaxation is complete and the emission rate drops sharply.
Role of structural anisotropy in electrodynamics of single domain textured crystals
Authors: Aleksandrov V. V. , Fisher L. M. , Kalinov A. V. , Voloshin I. F. , Fuchs G. , Krabbes G. , Yampol’skii V. A.
Published: February 2003

The anomalies in the ac response of the melt textured Y-123 superconductors to the electromagnetic excitation are observed, studied, and interpreted. Significant deviations in the behavior of the dynamic magnetic susceptibility from the predictions of the critical state model are detected. In particular, good melt textured samples demonstrate a significant deviation from the ideal diamagnetism even at negligible amplitudes of the ac field. The anomalies are pronounced if the exciting ac magnetic-field h is oriented perpendicularly to the crystallographic axis c. The observed results are attributed to peculiarities of the defect structure that is characteristic of the melt textured superconductors.
Constitutive modeling of fracture waves
Authors: Resnyansky A. D. , Romensky E. I. , Bourne N. K.
Published: February 2003

A fracture wave (FW) in a brittle material is a narrow transition region (border) of a continuous fracture zone, which may be associated with the damage accumulation process initiated by propagation of shock waves. In multidimensional structures the fracture wave may behave in an unusual way. The high-speed photography of penetration of a borosilicate (Pyrex) glass block [N. K. Bourne, L. Forde, and J. E. Field, Proc. SPIE 2869, 626 (1997)] shows a visible fracture zone with an apparent flat front although the projectile is a hemispherically nosed rod. A strain-rate-sensitive model is being developed and employed for analysis of the role of the complex stress state and kinetic description of the damage accumulation to describe the process of the impact. Numerical analysis is conducted with a one-dimensional wave propagation code employing the model and with the LS-DYNA2D hydrocode in which the model has been implemented. The analysis demonstrates that (i) the second (plastic) shock wave is superseded by quicker FW relaxing stress behind the elastic precursor, and (ii) the FW front flattening is apparently caused by the change in the acoustic directional properties. This change is associated with the phase-like transition due to the damage accumulation within the FW. In particular, the FW transition separates a highly anisotropic zone of material characterized acoustically by longitudinal and shear waves in front of the FW from a nearly isotropic region of the material characterized only by bulk waves behind the FW.
Wave-packet oscillations in a strongly driven InAs quantum well
Authors: Cruz H.
Published: February 2003

In this work, we have numerically integrated in space and time the effective-mass nonlinear Schrödinger equation for an electron wave packet in a strongly driven InAs quantum well. Considering a time-dependent Hartree potential, we have calculated the tunneling dynamics between the two quantum well barriers when an external ac bias is applied. At certain ac oscillation periods, we have obtained a time-varying wave-function penetration in the barriers with an amplitude which is also oscillating with time. In this way, the possible time-dependent effects of electronic spins in a strongly driven InAs quantum well could be also investigated.
Growth and microstructural characterizations of GaN films grown by laser induced reactive epitaxy
Authors: Zhou H. , Rupp T. , Phillipp F. , Henn G. , Gross M. , Rühm A. , Schröder H.
Published: February 2003

Hexagonal GaN thin films have been grown by laser induced reactive epitaxy (LIRE) and characterized by various techniques. The films were deposited on sapphire (0001) and SiC (0001) without and with a buffer layer. Dislocations with predominant edge type and inversion domains were observed in the films. Dislocation density measured by x-ray diffraction is in fair agreement with that measured by transmission electron microscopy. Studies on the polarity of films indicate that Ga polarity was obtained for the films grown on SiC, while the films grown directly on sapphire were of N polarity. The atomic structure with a displacement of c/8 across the inversion domain boundary was deduced from the fringe contrast analyses and high resolution transmission electron microscopy studies. For the films grown on sapphire, the Ga polarity was achieved by using an AlGaN prelayer coupled with the introduction of low-temperature GaN buffer layer, which led to a clear improvement of the film quality. The typical cathodoluminescence spectra of such GaN films are comparable to those reported in the literature. The present work provides insight into the crystal growth and microstructure of GaN films and indicates that LIRE is a promising method to grow high quality GaN films.
Investigation of the folding profiles of evolutionarily selected model proteins
Authors: Nelson Erik , Grishin Nick
Published: February 2003

Minimalist models of proteins, in which amino acid chains are represented by a necklace of beads that reconfigure the native fold on the sites of a cubic lattice, have been an important tool to infer early events in folding and to typify the energy landscapes of small globular proteins. In this paper, we try to determine in what sense these models are viable to describe protein evolution. An important first step toward this goal is to establish whether there are any limitations on the lattice model, such as on heterogeneity of the interactions and the size and topology of the native folds, that are necessary before cooperative (2-statelike) folding behavior typical of small proteins evolves robustly from the sequence selection process. The model we construct to test this feature selects sequences that fold reliably to a fixed topology on relevant timescales near their folding transition temperatures. The cross-chain (nonbonded) interactions are defined by empirical amino acid contact potentials, and the sequences evolve by random drift subject to the selection criteria. We investigate the folding profiles of these evolutionarily selected sequences in terms of the free energy, F(Q), and the participation of native contacts, Qj(Q), along a folding reaction coordinate Q (the percentage of native contacts formed). Both size and topology effects are evident in the results, and weakly heterogeneous, 2-statelike folding behavior emerges most consistently from larger folds that are specially selected to suppress the effect of heterogeneity in native interactions.
Multisubband transport of the two-dimensional electron gas in AlxGa1−xN/GaN heterostructures
Authors: Zheng Z. W. , Shen B. , Jiang C. P. , Gui Y. S. , Someya T. , Zhang R. , Shi Y. , Zheng Y. D. , Guo S. L. , Chu J. H. , Arakawa Y.
Published: February 2003

Multisubband transport of the two-dimensional electron gas (2DEG) in modulation-doped Al0.22Ga0.78N/GaN heterostructures has been investigated by means of magnetotransport measurements at low temperatures and high magnetic fields. It is found that the mobility of the 2DEG in the first subband in a triangular quantum well at the heterointerface decreases significantly, while the mobility of the 2DEG in the second subband increases, when the Al0.22Ga0.78N barrier is partially relaxed. Such behavior of the 2DEG mobility is explained by the nonuniformity of the piezoelectric polarization field at the heterointerface induced by the Al0.22Ga0.78N relaxation and strong interface scattering. Meanwhile, it is concluded that the scattering from the remote ionized donors is the main mechanism contributing to the quantum scattering time and responsible for the intersubband scattering in the quantum well at the heterointerface.
Improved Fourier method of thickness determination by x-ray reflectivity
Authors: de Peralta L. Grave , Temkin H.
Published: February 2003

Layer thickness can be reliably determined from x-ray reflectivity data using an improved Fourier method presented here. Before performing the Fourier transform the logarithm of the intensity corresponding to the incoherent superposition of x rays reflected from sample’s interfaces is subtracted from the experimental reflectivity curve. The subtracted curve is found by simple local average of the data. The connection between the Fourier methods and the dynamic and kinematic approaches is discussed.
Diluted magnetic semiconductor of p-type GaN epilayers implanted with Mn+ ions
Authors: Shon Yoon , Kwon Young Hae , Yuldashev Sh. U. , Park Y. S. , Fu D. J. , Kim D. Y. , Kim H. S. , Kang T. W.
Published: February 2003

The study of diluted magnetic semiconductor based on GaN was performed employing a variety of various measurement techniques. p-type GaN epilayers were prepared by metalorganic chemical vapor deposition and were subsequently implanted with Mn+ ions. The properties of Mn+ ion-implanted GaN epilayers were investigated with optical and magnetic measurements. The results of photoluminescence (PL) measurement show that optical transitions related to Mn apparently appear at 2.5 and around 3.0 eV. It is confirmed that the PL peak at 2.5 eV is a donor-Mn acceptor transition and the PL peak around 3.0 eV is a conduction band-Mn acceptor transition. Ferromagnetic hysteresis loop was observed, and the temperature dependent-magnetization displayed a ferromagnetic behavior persisting up to ∼270 K.
Light amplification and lasing in a (meta-phenylene vinylene) copolymer
Authors: Manaa Hacene , Henari Fryad Z. , Al-Saie Ahmed , Drury Anna , Kobayashi Takeyuki , Blau Werner J.
Published: February 2003

We report on single pass optical gain and lasing measurements on a blue-emitting copolymer, poly(m-phenylene vinylene-co-2,5-dioctyloxy-p-phenylene vinylene) under 0.5 ns pulsed photoexcitation. This soluble copolymer is designed and synthesized for light amplification and lasing applications. Blue photoluminescence is achieved by introduction of the meta linkage of the phenylene rings in the polymer backbone, which reduces the extent of delocalization of π electrons. The large Stokes shift of about 70 nm implies a low reabsorption rate, and leads to easier creation of population inversion and hence to efficient light amplification. A solution of the polymer exhibits amplified spontaneous emission evidenced by spectral narrowing and a superlinear increase of output intensity when it is photoexcited at 337 nm. By means of the variable excitation stripe length method, net gains of 18 and 24 cm−1 are deduced for different pump energies of 71 and 113 μJ, respectively. Moreover, laser emission from the polymer solution is obtained in a simple cavity formed by Fresnel reflections at the cuvette–solution interfaces. A conversion efficiency as high as 27% and a wide tuning range between 470 and 492 nm in solutions are demonstrated.
Two-channel vibrational relaxation of H2 by He: A bridge between the Landau–Teller and Bethe–Wigner limits
Authors: Dashevskaya E. I. , Kunc J. A. , Nikitin E. E. , Oref I.
Published: February 2003

We present a two-channel model of the vibrational relaxation (VR) of H2 molecule, ν=1, j=0→ν=0, j=0, in collisions with a He atom over a broad energy range, bridging the gap between the Landau–Teller and Bethe–Wigner limits. The model is based on the generalized Landau approach for calculating the VR transition matrix element. The analytical expression for the VR cross section qualitatively reproduces the energy dependence of the numerically calculated cross section and identify the key parameters that determine this energy dependence: the steepness of the repulsive part of the potential, the depth of the potential well, and the s-wave elastic scattering length. On the basis of our findings and available data from the literature, we discuss the manifestation of the attractive interaction on the qualitative features of the VR cross sections and rate constants over a wide range of energies and temperatures.
Out-of-plane exchange coupling between epitaxial Ni (50 Å) and NiO (600 Å) bilayers
Authors: Liu Z. Y. , Adenwalla S.
Published: February 2003

We have investigated the exchange coupling between an epitaxial Ni (50 Å) film with an out-of-plane magnetic easy axis and a NiO (600 Å) film by polar magneto-optic Kerr-effect measurements. The temperature dependences of exchange field HE for both as-deposited and field-cooled states exhibit the same blocking temperature TB∼130 °C. The exchange field HE for the field-cooled state is lower than that for the as-deposited state. The hard-axis in-plane loop shows a much smaller value of HE. No coercivity enhancement is observed. The data are suggestive of linear coupling across the ferromagnet/antiferromagnet interface.