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Germanium
Terms modified by Germanium Selected AbstractsSynthesis and Characterization of Novel Titanium, Germanium, and Tin Silazane Complexes Bearing a Cyclohexasilazanetriido LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2007Christian Lehnert Abstract Novel heterometallic silazane complexes were synthesized by the reaction of 1-lithio-2,2,4,4,6,6-hexamethylcyclotrisilazane Li(HMCTS)H2 with the tetrachloride salts of titanium and germanium as well as by the reaction of 1,1,3,3,5,5-hexamethylcyclotrisilazane H3(HMCTS) with tin tetrachloride and excess triethylamine. The products [H3(DMCHS)TiCl] (1), [H3(DMCHS)GeCl] (2), and [H3(DMCHS)SnCl] (3) {H3(DMCHS) = 2,2,4,4,6,6,8,8,10,10,12,12-dodecamethylcyclohexasilazane-1,5,9-triido} were characterized by 1H-, 13C-, 14N-, and 29Si NMR spectroscopy, elemental analyses and single-crystal X-ray structure analyses. The complexes have a surprising and interesting structure, that of a new dodecamethylcyclohexasilazane system with the Ti, Ge, or Sn atom in the center. These metal atoms are coordinated by one chlorine atom and three nitrogen atoms. The metal centers are part of three six-membered hetero-silazane rings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Molecular Structures and NMR Studies of Lithium and Germanium(II) Complexes of a New Chelating Amido,Imino Ligand Obtained by Addition of nBuLi to 1,2-Bis(arylimino)acenaphthene,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2006Igor L. Fedushkin Abstract The reaction of 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-bian, 1) with 1 equiv. of nBuLi in diethyl ether or with 2 equiv. of nBuLi in hexane produces [{dpp-bian(nBu)}Li(Et2O)] (3) and [{dpp-bian(nBu)Li}nBuLi]2 (4), respectively. Complexes 3 and 4 are formed by the transfer of an nBu anion to one of the imine carbon atoms of the dpp-bian ligand. Treatment of 3 and 4 with H2O affords the C -alkylated N -protonated amino-imino compound dpp-bian(H)(nBu) (5). The reaction of 3 with GeCl2(dioxane) affords the three-coordinate germylene complex [{dpp-bian(nBu)}GeCl] (6). The molecular structures of 3,6 were determined by single-crystal X-ray structure analysis. The lack of symmetry in the alkylated bian system in 3,6 causes the non-equivalence of all protons except those of the CH3 groups of the iPr substituents. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Direct Synthesis of (PhSe)4Ge and (PhTe)4Ge from Activated Hydrogenated Germanium , Crystal Structure and Twinning of (PhTe)4GeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2003Sabine Schlecht Abstract The germanium chalcogenolates (PhSe)4Ge and (PhTe)4Ge were synthesized from activated hydrogenated germanium (Ge*) and diphenyldiselenide or diphenylditelluride, respectively. (PhTe)4Ge is the first homoleptic organotellurolate of germanium. It was characterized spectroscopically and by X-ray crystal structure analysis. (PhTe)4Ge crystallizes in the monoclinic space group P21/c with a = 12.8018(14), b = 9.1842(9), c = 23.690(3) Å and , = 105.458(8)°. The molecules show a tetrahedral GeTe4 core. Weak Te-Te interactions connect neighbouring tetrahedra to infinite helices along [010]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Spin polarization and electronic structure of ferromagnetic Mn5Ge3 epilayersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 8 2005R. P. Panguluri Abstract Germanium-based alloys hold great promise for future spintronics applications, due to their potential for integration with conventional Si-based electronics. High-quality single phase Mn5Ge3(0001) films, grown by solid-phase epitaxy on Ge(111) and GaAs(111), exhibit strong ferromagnetism up to the Curie temperature TC , 296 K. Point Contact Andreev Reflection (PCAR) measurements on Mn5Ge3 epilayers reveal a spin-polarization P = 42 ± 5% for both substrates. We also calculate the spin polarization of bulk Mn5Ge3 in the diffusive and ballistic regimes using density-functional theory (DFT). The measured spin polarization exceeds the theoretical estimates of PDFT = 35 ± 5% and 10 ± 5% for the diffusive and ballistic limits, respectively. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Designing the Si(100) conversion into SiC(100) by GePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 2 2010Richard Nader Abstract The deposition of Germanium (Ge) prior to the conversion of Si(100) into 3C-SiC(100) results in changes of the structure and surface morphology of the formed silicon carbide layer. First of all it reduces the thickness of the 3C-SiC layer grown during the conversion process and therefore the probability of voids formation. Secondly, it increases the nucleation density of the formed 3C-SiC nuclei and therefore, decreases the grain size at Ge coverages below two monolayers. These affect the roughness of the SiC surface positively by modifying the width of the SiC-Si interface. If the Ge coverages exceed two monolayers the structural and morphological properties begin to degrade. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Theoretical Evaluation of the Interface Modification for Aluminium Nitride Growth on SiPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003P. Masri Abstract In this work, we propose a strategy for the optimization of the SiC/Si structure as a subsequent substrate to grow aluminium nitride (AlN) layers on Si. Several routes are investigated within the framework of a theoretical approach which we recently developed and which has proved itself to be very useful in many aspects of the physics of heteroepitaxy. In this paper, we investigate one useful task of using Si as substrate with SiC buffer layer which may be grown by carbonization (C) of the Si surface. Germanium (Ge) incorporation is also modelled. The AlN/SiC/Si structure is theoretically optimized by determining the composition out of C and Ge of the buffer layer. [source] Synthese und Charakterisierung von Digerma- closo -dodecaborat, einem höheren Homologen des ikosaedrischen ortho -Carborans,ANGEWANDTE CHEMIE, Issue 42 2009Claudia Nickl Lücke gefüllt: Aus Germanium(II)-bromid, Decaboran und Triethylamin wurde das dimere 2,2,-Bis(1,2-digerma- closo -dodecaborat) synthetisiert. Reduktive Spaltung ergab das monomere Dianion [Ge2B10H10]2,. Mit Alkylhalogeniden wurden neutrale, disubstituierte Spezies erhalten (siehe Beispiel), die NMR-spektroskopisch und röntgenographisch charakterisiert wurden. Die Lücke in der Serie der Dihetero- closo -dodecaborane der Gruppe XIV ist nun geschlossen. [source] Germanium carboxylates: the first X-ray diffraction study of germanium(II) dicarboxylate and germanium(IV) tetracarboxylateAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2005Victor N. Khrustalev Abstract Germanium(II) dipropionate (1) has been synthesized and its crystal structure, as well as that of germanium(IV) tetrapropionate (2), has been determined. By contrast to monomeric 2 with monodentate propionate ligands, compound 1 is associated, forming a cyclotetramer [Ge(O2CEt)2]4 (1a) via intermolecular dative CO , Ge interactions. Copyright © 2005 John Wiley & Sons, Ltd. [source] MOCVD of Hafnium Silicate Films Obtained from a Single-Source Precusor on Silicon and Germanium for Gate-Dielectric Applications,CHEMICAL VAPOR DEPOSITION, Issue 2-3 2007M. Lemberger Abstract In this work, hafnium silicate layers on Si and Ge wafers for gate dielectric application in metal,oxide,semiconductor devices are investigated. Films are deposited by metal,organic (MO)CVD using the single-source precursor Hf(acac)2(OSitBuMe2)2. This precursor exhibits good properties in terms of hydrolysis stability, volatility, and deposition. However, precursor decomposition is affected by surface conditions. Films deposited on Si wafers reveal high C contamination (up to 20,at,%) and low Si content (up to 20,at,%). In contrast, for film deposition on Ge wafers, no C contamination can be detected and Si incorporation is delayed until after about 15,nm HfO2 dielectric growth. Post-deposition rapid thermal annealing in an O2 atmosphere causes crystallization of deposited films, Si and Ge redistribution in the dielectric, respectively, and interfacial layer growth. However, oxygen annealing was also found to reduce effective oxide thickness (EOT) significantly compared to as-deposited films, which is attributed to crystallization effects. However, scaling of EOT is limited by that interfacial layer growth. Leakage currents are mainly caused by trap-related conduction mechanisms. Energy levels of involved traps decrease with increasing crystallization and/or Hf content, and values of 0.5,eV and 1,eV related to Hf and Si bonds, respectively, are obtained. [source] Germanium(II)-Mediated Reductive Cross-Aldol Reaction of Aldehydes: Synthesis of Aldols with Diastereocontrolled Quaternary Carbon Centers.CHEMINFORM, Issue 44 2007Shin-ya Tanaka Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Interaction of Triatomic Germanium with Lithium Atoms: Electronic Structure and Stability of Ge3Lin ClustersCHEMINFORM, Issue 32 2007G. Gopakumar Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Reductive Cross-Aldol Reaction Using Bromoaldehyde and an Aldehyde Mediated by Germanium(II): One-Pot, Large-Scale Protocol.CHEMINFORM, Issue 38 2005Makoto Yasuda Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Characterization of Novel Titanium, Germanium, and Tin Silazane Complexes Bearing a Cyclohexasilazanetriido LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2007Christian Lehnert Abstract Novel heterometallic silazane complexes were synthesized by the reaction of 1-lithio-2,2,4,4,6,6-hexamethylcyclotrisilazane Li(HMCTS)H2 with the tetrachloride salts of titanium and germanium as well as by the reaction of 1,1,3,3,5,5-hexamethylcyclotrisilazane H3(HMCTS) with tin tetrachloride and excess triethylamine. The products [H3(DMCHS)TiCl] (1), [H3(DMCHS)GeCl] (2), and [H3(DMCHS)SnCl] (3) {H3(DMCHS) = 2,2,4,4,6,6,8,8,10,10,12,12-dodecamethylcyclohexasilazane-1,5,9-triido} were characterized by 1H-, 13C-, 14N-, and 29Si NMR spectroscopy, elemental analyses and single-crystal X-ray structure analyses. The complexes have a surprising and interesting structure, that of a new dodecamethylcyclohexasilazane system with the Ti, Ge, or Sn atom in the center. These metal atoms are coordinated by one chlorine atom and three nitrogen atoms. The metal centers are part of three six-membered hetero-silazane rings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Crystal Structure, Solid-State NMR Spectroscopic and Photoluminescence Studies of Organic-Inorganic Hybrid Materials (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O, L = hqn or phen,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 23 2006Luís Mafra Abstract Two germanium,hedp4, solids with heteroaromatic amines 8-hydroxyquinoline (hqn) and 1,10-phenanthroline (phen), (HL)6[Ge6(OH)6(hedp)6]·2(L)·nH2O (L = hqn or phen), in I and II respectively, have been prepared and characterised by single-crystal XRD, thermogravimetry, FTIR and UV/Vis spectroscopy. The complex hydrogen-bond networks, particularly in compound I, have been studied by advanced high-resolution solid-state NMR spectroscopy that combines homonuclear recoupling techniques (two-dimensional 1H- 1H DQF and 1H- 1H RFDR MAS NMR) and combined rotation and multiple-pulse spectroscopy (two-dimensional 1H- 1H FS-LG, 1H- 31P FS-LG). The fine details of the crystal structure of I have been elucidated, mainly those involving the ,,, stacking of 8-hydroxyquinoline and the relative orientation of adjacent such molecules. Compound II exhibits an emission from the lowest triplet-state energy (,,,* 0-phonon transition) of the aromatic rings at 320 nm (31250 cm,1) from 14 K to room temperature. In contrast, the triplet emission of I at 530 nm (18868 cm,1) is only detected at low temperature, because of thermally activated non-radiative mechanisms. The emission spectra of I and II display a lower-energy component with a larger life time, which results from the formation of an excimer state that originated from the ,,, phenanthroline and hydroxyquinoline interactions, respectively. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Direct Synthesis of (PhSe)4Ge and (PhTe)4Ge from Activated Hydrogenated Germanium , Crystal Structure and Twinning of (PhTe)4GeEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2003Sabine Schlecht Abstract The germanium chalcogenolates (PhSe)4Ge and (PhTe)4Ge were synthesized from activated hydrogenated germanium (Ge*) and diphenyldiselenide or diphenylditelluride, respectively. (PhTe)4Ge is the first homoleptic organotellurolate of germanium. It was characterized spectroscopically and by X-ray crystal structure analysis. (PhTe)4Ge crystallizes in the monoclinic space group P21/c with a = 12.8018(14), b = 9.1842(9), c = 23.690(3) Å and , = 105.458(8)°. The molecules show a tetrahedral GeTe4 core. Weak Te-Te interactions connect neighbouring tetrahedra to infinite helices along [010]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Neutron Reflectometry: A Tool to Investigate Diffusion Processes in Solids on the Nanometer Scale,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Harald Schmidt Abstract The investigation of self-diffusion for the characterization of kinetic process in solids is one of the most fundamental tasks in materials science. We present the method of neutron reflectometry (NR), which allows the detection of extremely short diffusion lengths in the order of 1,nm and below at corresponding low self-diffusivities between 10,25 and 10,20,m2 s,1. Such a combination of values cannot be achieved by conventional methods of diffusivity determination, like the radiotracer method, secondary ion mass spectrometry, quasielastic neutron scattering, or nuclear magnetic resonance. Using our method, the extensive characterization of materials which are in a non-equilibrium state, like amorphous or nanocrystalline solids becomes possible. Due to the small experimentally accessible diffusion length microstructural changes (grain growth and crystallization) taking place simultaneously during the actual diffusion experiment can be avoided. For diffusion experiments with NR isotope multilayers are necessary, which are chemical homogeneous but isotope modulated films. We illustrate the basic aspects and potential of this technique using model systems of different classes of materials: single crystalline germanium, amorphous silicon nitride, and nanocrystalline iron. [source] New methods of synthesis of boron, germanium, and tin derivatives of pentavalent phosphorus thioacidsHETEROATOM CHEMISTRY, Issue 1 2002Il'yas S. Nizamov The reactions of S-trimethylsilyl esters of S-propyl-4-methoxyphenyltrithiophosphonic, bis(dialkylamido)dithiophosphoric, and S-ethyl-diethylamidotrithiophosphoric acids with trialkyl borates, triorganylbromogermanes, trimethyl(isobutylthio)germane, and trialkylchlorostannanes were studied. On the basis of these studies, new methods of synthesizing S-boron, S-germyl, and S-stannyl derivatives of pentavalent phosphorus thioacids were developed. S-Diethylaminomethyl O-isopropyl-4-ethoxyphenyldithiophosphonate was obtained by the reaction of the diisopropylboron derivative of the corresponding dithiophosphonic acid with the aminal 6. © 2002 John Wiley & Sons, Inc. Heteroatom Chem 13:27,35, 2002; DOI 10.1002/hc.1103 [source] Supercritical Fluid,Liquid,Solid (SFLS) Synthesis of Si and Ge Nanowires Seeded by Colloidal Metal Nanocrystals,ADVANCED MATERIALS, Issue 5 2003T. Hanrath Abstract Semiconductor nanowires, 5 to 20 nm in diameter and micrometers in length, appear to be promising candidates for a variety of new technologies, including computing, memory, and sensor applications. Suitable for these applications, silicon (Si) and germanium (Ge) nanowires ranging from 4 to 30 nm in diameter and micrometers in length can be produced in high temperature supercritical fluids by thermally degrading organosilane or organogermane precursors in the presence of organic-monolayer-protected gold nanocrystals. Although gas phase vapor,liquid,solid (VLS) methods can be used to produce a variety of different nanowire materials, high temperature supercritical fluids provide wire size control through nanocrystal size selection prior to synthesis, and high product yields due to the high precursor solubility. [source] Mixed-mode analysis of the sensitivity of a radiofrequency oscillator disturbed by parasitic signalsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2009Christian Gontrand Abstract The first step of this work is to study the susceptibility of a radiofrequency oscillator to deterministic disturbance sources. A Colpitts oscillator, working around a 4,GHz frequency, contains a heterojunction bipolar transistor with a silicon,germanium base as an active device. A mixed-mode analysis is involved, applying a microscopic drift diffusion model to the device, whereas the rest of the circuit used is governed by Kirchhoff's laws. We assume that this tool is very relevant to grasp the influence of intrinsic or extrinsic noisy sources of the oscillator. Our first simulation raw results motivate us to discuss, and perhaps extend, via some analytical models, the so-called impulse sensitivity function model. In this paper, we try to develop quantitative predictions about the phase noise of such oscillators, and to give some new tracks on this field. Copyright © 2008 John Wiley & Sons, Ltd. [source] Hot pressing of germanium monochromator crystalsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 2 2004S. F. Treviño The method and parameters for vacuum hot pressing of single-crystal germanium, suitable for a large-area double-focusing neutron monochromator, are presented. The square virgin crystals have a mosaic that is less than 0.01° and isotropic. After appropriate pressing at high temperature (1073,K at a pressure of 10.7,MPa) the mosaic becomes anisotropic, about 0.5° in one direction and 0.2° in the other. The distribution of the mosaic widths of the crystals in the two directions are given, together with their composite values. [source] Poly(urethanes) containing silarylene and/or germarylene unitsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008C. A. Terraza Abstract A series of 10 poly(urethanes) were synthesized by solution polymerization from bis(chloroformates) and aromatic diamines, containing both silicon or germanium as central atom. So, the polymers prepared contain two silicon atoms or two germanium atoms exclusively or combinations of both. Me, Et, and Ph groups were bonded to the central atoms according to the nature of the monomers employed. Poly(urethanes) were characterized by FTIR, 1H, 13C, and 29Si NMR spectroscopy and the results agreed with the proposed structures. Additionally, intrinsic viscosity values were established in DMSO solutions and thermal analyses were developed. In all cases, thermostable oligomers were obtained, which showed a degradation process beginning at ,240,260°C. Polymers showed a thermal dependence with the nature of the heteroatom employed. Thus, in general, when germanium was used as central atom, the thermal stability was higher than the polymers containing silicon which agrees with the lower polarity and higher energy of the CGe bond in comparison with the CSi one. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008. [source] Structural, electronic, and optical properties of 9-heterofluorenes: A quantum chemical studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 13 2007Run-Feng Chen Abstract Density-functional theory studies were applied to investigate the structural, electronic, and optical properties of 9-heterofluorenes achieved by substituting the carbon at 9 position of fluorene with silicon, germanium, nitrogen, phosphor, oxygen, sulfur, selenium, or boron. These heterofluorenes and their oligomers up to pentamers are highly aromatic and electrooptically active. The alkyl and aryl substituents of the heteroatom have limited influence, but the oxidation of the atom has significant influence on their molecular structures and properties. The highest occupied molecular orbital (HOMO)-lowest occupied molecular orbital (LUMO) interaction theory was successfully applied to analyze the energy levels and the frontier wave functions of these heterofluorenes. Most heterofluorenes belong to type B of interaction with low-lying LUMO and have the second kind of wave function. Carbazole and selenafluorene have type C of interaction with high-lying HOMO and the third kind of wave function. Types C and D of heterofluorenes, such as carbazole, oxygafluorene, sulfurafluorene, and selenafluorene also have high triplet state energies. The extrapolated HOMO and LUMO for polyheterofluorenes indicate that polyselenonafluorene has the lowest LUMO; polycarbazole has the highest HOMO; polyselenafluorene has the highest bandgap (Eg); and polyborafluorene has the lowest Eg. Heterofluorenes and their oligomers and polymers are of great experimental interests, especially those having extraordinary properties revealed in this study. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007 [source] Isotope and disorder effects in the Raman spectra of LiHxD1,x crystalsJOURNAL OF RAMAN SPECTROSCOPY, Issue 8 2001V. G. Plekhanov Most of the physical properties of a solid depend on its isotopic composition in some way or another. Scientific interest, technological promise and increased availability of highly enriched isotopes have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled crystals. A great number of stable isotopes and well-developed methods for their separation have made it possible to grow crystals of C, LiH, ZnO, ZnSe, CuCl, GaN, GaAs, CdS, Cu2O, Si, Ge and ,-Sn with a controllable isotopic composition. Among these compounds, LiH possesses the largest value of the isotope effect. The great number of theoretical and experimental data suggest that the isotopic composition of a crystal lattice exerts some influence on the vibrational properties of crystals. These effects are fairly large and can be readily measured by modern experimental techniques (ultrasound, Brillouin and Raman scattering and neutron scattering). In addition, crystals of different isotopic compositions possess different Debye temperatures. This difference between an LiH crystal and its deuterated analogue exceeds a 100 K. Very pronounced and general effects of isotopic substitution are observed in phonon spectra. The scattering lines in isotopically mixed crystals are not only shifted (the shift of LO lines exceeds 100 cm,1) but are also broadened. This broadening is related to the isotopic disorder of the crystal lattice. It is shown that the degree of a change in the scattering potential is different for different isotopic mixed crystals. In the case of germanium and diamond crystals, phonon scattering is weak, which allows one to apply successfully the coherent potential approximation (CPA) for describing the shift and broadening of scattering lines. In the case of lithium hydride, the change in the scattering potential is so strong that it results in phonon localization, which is directly observed in experiments. The common nature of the isotopic and disorder effects in a wide range of crystals is emphasized. Copyright © 2001 John Wiley & Sons, Ltd. [source] High-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium compoundsMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2004Yoshito Takeuchi Abstract High-resolution solid-state magic angle spinning 73Ge NMR spectra of hexavalent germanium compounds, i.e. diiodogermylene (1a) and bis(1-pyrrolyl)(meso -tetraphenylporphyrinato)germanium (3a), were determined. To the best of our knowledge, this is the first example of high-resolution solid-state 73Ge NMR spectra of hexacoordinated germanium nuclei. The symmetry requirement for observation of high-resolution solid-state 73Ge NMR spectra is discussed. Copyright © 2004 John Wiley & Sons, Ltd. [source] A hybrid functional scheme for defect levels and band alignments at semiconductor,oxide interfacesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 2 2010Peter Broqvist Abstract We introduce a theoretical scheme to study defect energy levels and band alignments at semiconductor,oxide interfaces. The scheme relies on hybrid functionals to overcome the band gap underestimation typically achieved with semilocal density functionals. For atomically localized defects, the more accurate description achieved with hybrid functionals does not lead to significant shifts of the charge transition levels, provided these levels are referred to a common reference potential. This result effectively decouples the shifts of the band edges with respect to the defect levels. We also show that relative shifts of conduction and valence band edges as determined by exact nonlocal exchange lead to band offsets in excellent agreement with experimental values for several semiconductor,oxide interfaces. The proposed scheme is illustrated through a series of applications, including the dangling bond defects in silicon and germanium, the charge state of the O2 molecule during silicon oxidation, and the oxygen vacancy in Si,SiO2,HfO2 stacks. [source] Observation of nanocrystals in porous stain-etched germaniumPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 1 2003V. A. Karavanskii Abstract Porous nanocrystalline films were prepared by stain etching and subsequent annealing in hydrogen at 600 °C. The structural properties of the as-etched and annealed films were investigated using Raman scattering and various X-ray techniques. It was shown that the as-etched film had a thickness of ,2 ,m and consisted of two sublayers of different porosity and amorphous-like microstructure The annealing did not change essentially the porosity and thickness but resulted in notable crystallinity transformation. The results of Raman spectroscopy and X-ray measurements and modelling revealed the presence of germanium nanocrystals with mean sizes of about 8,10 nm in the annealed films. [source] Crystallographically oriented high resolution lithography of graphene nanoribbons by STM lithographyPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2010G. Dobrik Abstract Due to its exciting physical properties and sheet-like geometry graphene is in the focus of attention both from the point of view of basic science and of potential applications. In order to fully exploit the advantage of the sheet-like geometry very high resolution, crystallographicaly controlled lithography has to be used. Graphene is a zero gap semiconductor, so that a field effect transistor (FET) will not have an "off" state unless a forbidden gap is created. Such a gap can be produced confining the electronic wave functions by etching narrow graphene nanoribbons (GNRs) typically of a few nanometers in width and with well defined crystallographic orientation. We developed the first lithographic method able to achieve GNRs that have both nanometer widths and well defined crystallographic orientation. The lithographic process is carried out by the local oxidation of the sample surface under the tip of a scanning tunneling microscopy (STM). Crystallographic orientation is defined by acquiring atomic resolution images of the surface to be patterned. The cutting of trenches with controlled depth and of a few nanometer in width, folding and manipulation of single graphene layers is demonstrated. The narrowest GNR cut by our method is of 2.5,nm width, scanning tunneling spectroscopy (STS) showed that it has a gap of 0.5,eV, comparable to that of germanium, which allows room temperature operation of graphene nanodevices. [source] Photoluminescence studies of isotopically enriched siliconPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2003D. Karaiskaj Abstract We report the first high resolution photoluminescence studies of isotopically pure silicon. New information is obtained on isotopic effects on the indirect band gap energy, phonon energies, and phonon broadenings, which is in good agreement with previous results obtained in germanium and diamond. Remarkably, the line widths of the no-phonon boron and phosphorus bound exciton transitions in the 28Si sample (99.896% 28Si) are much sharper than in natural Si, revealing new fine structure in the boron bound exciton luminescence. Most surprisingly, the small splittings of the neutral acceptor ground state in natural Si are absent in the photoluminescence spectra of acceptor bound excitons in isotopically purified 28Si, demonstrating conclusively that they result from the randomness of the Si isotopic composition. [source] Laser-induced self organization of silicon,germanium hillocks for field emission displaysPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 10 2008M. Weizman Abstract We report here on the formation of a self-organized hillock structure in polycrystalline silicon,germanium (SiGe) thin films with a Ge content of 30 to 70%, due to the irradiation of the films with a sequence of laser pulses. By varying the crystallization parameters it is possible to control the periodicity length of the structure from 0.4 to 2 µm. The self organization phenomenon can be switched on and off by using substrates with different thermal conductivities. In addition, we show that the self-organized hillock structure exhibits a low field emission threshold of 20 V/µm and therefore has an immense potential for field emission displays. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Peculiarities of dislocation photoluminescence in germanium with quasi-equilibrium dislocation structurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2007S. Shevchenko Abstract The dislocation photoluminescence (DPL) at 4.2 K was studied in germanium (Ge) single crystals of n- and p-type with quasi-equilibrium structure of 60° dislocations. The DPL spectra for different samples were decomposed on Gaussian lines (Gm -lines) over the range 0.47-0.58 eV characterized by practically the same peak energies Em and the widths under 15 meV. The G-lines with Em , 0.55 eV were ascribed to the radiation of regular segments of 60° dislocations with different stacking fault (SF) widths , between 30 and 90° partials. An increase of the dislocations density up to ND , 107 cm,2 was found to result in a considerable growth of the intensity of the G-lines with Em <0.513 eV. The factors, which promote the appearance of different , values for quasi-equilibrium 60° dislocation structure, are discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||||||||||||||||||||