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- 226. Phys. Rev. Lett. 98, 216103 (2007) , “Influence of Cumulenic Chains on the Vibrational and Electronic Properties of sp-sp2 Amorphous Carbon”, L. Ravagnan, P. Piseri, M. Bruzzi, S. Miglio, G. Bongiorno, A. Baserga, C. S. Casari, A. Li Bassi, C. Lenardi, Y. Yamaguchi, T. Wakabayashi, C. E. Bottani, and P. MilaniWe report the production and characterization of a form of amorphous carbon with sp-sp2 hybridization (atomic fraction of sp hybridized species 20%) where the predominant sp bonding appears to be (=C=C=)n cumulene.... (Read more)
- 227. Phys. Rev. Lett. 98, 215503 (2007) , “Nature of the Bound States of Molecular Hydrogen in Carbon Nanohorns”, F. Fernandez-Alonso, F. J. Bermejo, C. Cabrillo, R. O. Loutfy, V. Leon, and M. L. SaboungiThe effects of confining molecular hydrogen within carbon nanohorns are studied via high-resolution quasielastic and inelastic neutron spectroscopies. Both sets of data are remarkably different from those obtained in bulk samples in the liquid and crystalline states. At temperatures where bulk... (Read more)
- 228. Phys. Rev. Lett. 98, 206406 (2007) , “Role of Intermolecular Coupling in the Photophysics of Disordered Organic Semiconductors: Aggregate Emission in Regioregular Polythiophene”, Jenny Clark, Carlos Silva, Richard H. Friend, and Frank C. SpanoWe address the role of excitonic coupling on the nature of photoexcitations in the conjugated polymer regioregular poly(3-hexylthiophene). By means of temperature-dependent absorption and photoluminescence spectroscopy, we show that optical emission is overwhelmingly dominated by weakly coupled H... (Read more)
- 229. Phys. Rev. Lett. 98, 206403 (2007) , “H-Induced Dangling Bonds in H–Isoelectronic-Impurity Complexes Formed in GaAs1-yNy Alloys”, A. Amore Bonapasta, F. Filippone, and G. MattioliComplexes formed by H and the isoelectronic impurity N in GaAs1-yNy alloys have been widely investigated because the significant effects of N on the GaAs properties and their passivation by H represent a unique tool for a defect engineering of semiconductors.... (Read more)
- 230. Phys. Rev. Lett. 98, 196802 (2007) , “Origin of Charge Density at LaAlO3 on SrTiO3 Heterointerfaces: Possibility of Intrinsic Doping”, Wolter Siemons, Gertjan Koster, Hideki Yamamoto, Walter A. Harrison, Gerald Lucovsky, Theodore H. Geballe, Dave H. A. Blank, and Malcolm R. BeasleyAs discovered by Ohtomo and Hwang, a large sheet charge density with high mobility exists at the interface between SrTiO3 and LaAlO3. Based on transport, spectroscopic, and oxygen-annealing experiments, we conclude that extrinsic defects in the form of oxygen vacancies... (Read more)
- 231. Phys. Rev. Lett. 98, 196101 (2007) , “Oxygen Vacancies in High Dielectric Constant Oxide-Semiconductor Films”, Supratik Guha and Vijay NarayananWe provide evidence that the oxygen vacancy is a dominant intrinsic electronic defect in nanometer scaled hafnium oxide dielectric films on silicon, relevant to microelectronics technology. We demonstrate this by developing a general model for the kinetics of oxygen vacancy formation in... (Read more)
- 232. Phys. Rev. Lett. 98, 186804 (2007) , “Room-Temperature Electron Spin Dynamics in Free-Standing ZnO Quantum Dots”, William K. Liu, Kelly M. Whitaker, Alyssa L. Smith, Kevin R. Kittilstved, Bruce H. Robinson, and Daniel R. GamelinConduction band electrons in colloidal ZnO quantum dots have been prepared photochemically and examined by electron paramagnetic resonance spectroscopy. Nanocrystals of 4.6 nm diameter containing single S-shell conduction band electrons have g*=1.962 and a room-temperature... (Read more)
- 233. Phys. Rev. Lett. 98, 185501 (2007) , “Enhanced Ductile Behavior of Tensile-Elongated Individual Double-Walled and Triple-Walled Carbon Nanotubes at High Temperatures”, J. Y. Huang, S. Chen, Z. F. Ren, Z. Wang, K. Kempa, M. J. Naughton, G. Chen, and M. S. DresselhausWe report exceptional ductile behavior in individual double-walled and triple-walled carbon nanotubes at temperatures above 2000 °C, with tensile elongation of 190% and diameter reduction of 90%, during in situ tensile-loading experiments conducted inside a high-resolution transmission... (Read more)
- 234. Phys. Rev. Lett. 98, 146403 (2007) , “Evidence for an Oxygen Diffusion Model for the Electric Pulse Induced Resistance Change Effect in Transition-Metal Oxides”, Y. B. Nian, J. Strozier, N. J. Wu, X. Chen, and A. IgnatievElectric-pulse induced resistance hysteresis switching loops for Pr0.7Ca0.3MnO3 perovskite oxide films were found to exhibit an additional sharp “shuttle tail” peak around the negative pulse maximum for films deposited in an oxygen-deficient ambient. The... (Read more)
- 235. Phys. Rev. Lett. 98, 137202 (2007) , “Magnetizing Oxides by Substituting Nitrogen for Oxygen”, I. S. Elfimov, A. Rusydi, S. I. Csiszar, Z. Hu, H. H. Hsieh, H.-J. Lin, C. T. Chen, R. Liang, and G. A. SawatzkyWe describe a possible pathway to new magnetic materials with no conventional magnetic elements present. The substitution of nitrogen for oxygen in simple nonmagnetic oxides leads to holes in N 2p states which form local magnetic moments. Because of the very large Hund's rule coupling of... (Read more)
- 236. Phys. Rev. Lett. 98, 135506 (2007) , “Possible Approach to Overcome the Doping Asymmetry in Wideband Gap Semiconductors”, Yanfa Yan, Jingbo Li, Su-Huai Wei, and M. M. Al-JassimThe asymmetry doping problem has severely hindered the potential applications of many wideband gap (WBG) materials. Here, we propose a possible approach to overcome this long-standing doping asymmetry problem for WBG semiconductors. Our approach is based on the reduction of the ionization energies... (Read more)
- 237. Phys. Rev. Lett. 98, 117202 (2007) , “Density-Functional Theory Study of Half-Metallic Heterostructures: Interstitial Mn in Si”, Hua Wu, Peter Kratzer, and Matthias SchefflerUsing density-functional theory within the generalized gradient approximation, we show that Si-based heterostructures with 1/4 layer δ doping of interstitial Mn (Mnint) are half-metallic. For Mnint concentrations of 1/2 or 1 layer, the states induced in the band... (Read more)
- 238. Phys. Rev. Lett. 98, 115503 (2007) , “Oxygen Vacancy Clustering and Electron Localization in Oxygen-Deficient SrTiO3: LDA+U Study”, Do Duc Cuong, Bora Lee, Kyeong Mi Choi, Hyo-Shin Ahn, Seungwu Han, and Jaichan LeeWe find, using a local density approximation +Hubbard U method, that oxygen vacancies tend to cluster in a linear way in SrTiO3, a prototypical perovskite oxide, accompanied by strong electron localization at the 3d state of the nearby Ti transition metal ion. The vacancy... (Read more)
- 239. Phys. Rev. Lett. 98, 096805 (2007) , “Observation of the Linear Stark Effect in a Single Acceptor in Si”, L. E. Calvet, R. G. Wheeler, and M. A. ReedThe Stark splitting of a single fourfold degenerate impurity located within the built-in potential of a metal-semiconductor contact is investigated using low temperature transport measurements. A model is developed and used to analyze transport as a function of temperature, bias voltage, and... (Read more)
- 240. Phys. Rev. Lett. 98, 095901 (2007) , “Experimental Evidence of the Vacancy-Mediated Silicon Self-Diffusion in Single-Crystalline Silicon”, Yasuo Shimizu, Masashi Uematsu, and Kohei M. ItohWe have determined silicon self-diffusivity at temperatures 735–875 °C based on the Raman shift of longitudinal optical phonon frequencies of diffusion annealed 28Si/30Si isotope superlattices. The activation enthalpy of 3.6 eV is obtained in such low temperature... (Read more)
- 241. Phys. Rev. Lett. 98, 077601 (2007) , “Multiple-Pulse Coherence Enhancement of Solid State Spin Qubits”, W. M. Witzel and S. Das SarmaWe describe how the spin coherence time of a localized electron spin in solids, i.e., a solid state spin qubit, can be prolonged by applying designed electron spin resonance pulse sequences. In particular, the spin echo decay due to the spectral diffusion of the electron spin resonance frequency... (Read more)
- 242. Phys. Rev. Lett. 98, 075503 (2007) , “Pseudoclimb and Dislocation Dynamics in Superplastic Nanotubes”, Feng Ding, Kun Jiao, Mingqi Wu, and Boris I. YakobsonPlastic relaxation of carbon nanotubes under tension and at high temperature is described in terms of dislocation theory and with atomistic computer simulations. It is shown how the glide of pentagon-heptagon defects and a particular type of their pseudoclimb, with the atoms directly breaking out of... (Read more)
- 243. Phys. Rev. Lett. 98, 055504 (2007) , “Ortho-Para Conversion of Interstitial H2 in Si”, M. Hiller, E. V. Lavrov, and J. WeberOrtho-para conversion of isolated interstitial H2 in single-crystalline Si is studied by Raman scattering. This process is suggested to be caused by the interaction of H2 with the nuclear magnetic moment of 29Si. At 77 K the ortho-to-para conversion rate is... (Read more)
- 244. Phys. Rev. Lett. 98, 045501 (2007) , “Dopability, Intrinsic Conductivity, and Nonstoichiometry of Transparent Conducting Oxides”, Stephan Lany and Alex ZungerExisting defect models for In2O3 and ZnO are inconclusive about the origin of conductivity, nonstoichiometry, and coloration. We apply systematic corrections to first-principles calculated formation energies ΔH, and validate our theoretical defect model against... (Read more)
- 245. Phys. Rev. Lett. 98, 026802 (2007) , “Microscopic Basis for the Mechanism of Carrier Dynamics in an Operating p-n Junction Examined by Using Light-Modulated Scanning Tunneling Spectroscopy”, Shoji Yoshida, Yuya Kanitani, Ryuji Oshima, Yoshitaka Okada, Osamu Takeuchi, and Hidemi ShigekawaThe doping characteristics and carrier transport in a GaAs p-n junction were visualized with a ~10 nm spatial resolution, using light-modulated scanning tunneling spectroscopy. The dynamics of minority carriers under operating conditions, such as recombination, diffusion, and electric... (Read more)
- 246. Phys. Rev. Lett. 98, 026801 (2007) , “Surface Dangling-Bond States and Band Lineups in Hydrogen-Terminated Si, Ge, and Ge/Si Nanowires”, R. Kagimura, R. W. Nunes, and H. ChachamWe report an ab initio study of the electronic properties of surface dangling-bond (SDB) states in hydrogen-terminated Si and Ge nanowires with diameters between 1 and 2 nm, Ge/Si nanowire heterostructures, and Si and Ge (111) surfaces. We find that the charge transition levels ε(+/-)... (Read more)
- 247. Phys. Rev. Lett. 98, 026101 (2007) , “Bonding at the SiC-SiO2 Interface and the Effects of Nitrogen and Hydrogen”, Sanwu Wang, S. Dhar, Shu-rui Wang, A. C. Ahyi, A. Franceschetti, J. R. Williams, L. C. Feldman,, and Sokrates T. PantelidesUnlike the Si-SiO2 interface, the SiC-SiO2 interface has large defect densities. Though nitridation has been shown to reduce the defect density, the effect of H remains an open issue. Here we combine experimental data and the results of first-principles calculations to... (Read more)
- 248. Phys. Rev. Lett. 98, 015501 (2007) , “First-Principles Simulations of Boron Diffusion in Graphite”, I. Suarez-Martinez, A. A. El-Barbary, G. Savini, and M. I. HeggieBoron strongly modifies electronic and diffusion properties of graphite. We report the first ab initio study of boron interaction with the point defects in graphite, which includes structures, thermodynamics, and diffusion. A number of possible diffusion mechanisms of boron in graphite are... (Read more)
- 249. phys. stat. sol. (b) 244, 437 (2007) , Wiley InterScience , “Thermoelectric properties and phase transitions of II-VI semiconductors at ultrahigh pressure”, V.V. Shchennikov, S.V. OvsyannikovThe high-pressure phase transitions in II-VI semiconductors (HgTe, HgSe, HgS, HgO, CdTe, CdSe, CdS, ZnTe, ZnSe, ZnS, ZnO) are analyzed in light of recent findings. A contribution is emphasized of the thermoelectric power (Seebeck effect) technique to registration of new electronic phases and to... (Read more)
- 250. phys. stat. sol. (b) 244, 279 (2007) , Wiley InterScience , “High-pressure X-ray diffraction study of ternary and non-stoichiometric PbTe and PbSe crystals”, S.V. Ovsyannikov, V.V. Shchennikov, A.Y. Manakov, A.Y. Likhacheva, I.F. Berger, A.I. Ancharov, M.A. SheromovThe paper reports the pressure-induced phase transitions observed in ternary PbTe and PbSe compounds (Pb1-x Snx Te, Pb1-x Mnx Te, Pb1-x Snx Se) and non-stoichiometric PbTe ones... (Read more)
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