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- 1. Appl. Phys. Lett. 90, 072502 (2007) , “Effect of oxygen vacancies on spin-dependent tunneling in Fe/MgO/Fe magnetic tunnel junctions”, J. P. Velev, K. D. Belashchenko, S. S. Jaswal, and E. Y. TsymbalFirst-principles calculations based on density functional theory are used to elucidate the effect of O vacancies, forming F centers, on spin-dependent tunneling in Fe/MgO/Fe(001) magnetic tunnel junctions. O vacancies produce occupied localized s states and unoccupied resonant p... (Read more)
- 2. Phys. Rev. B 75, 144404 (2007) , “Ferromagnetism in Fe-doped ZnO nanocrystals: Experiment and theory”, Debjani Karmakar, S. K. Mandal, R. M. Kadam, P. L. Paulose, A. K. Rajarajan, T. K. Nath, A. K. Das, I. Dasgupta, and G. P. DasFe-doped ZnO nanocrystals are successfully synthesized and structurally characterized by using x-ray diffraction and transmission electron microscopy. Magnetization measurements on the same system reveal a ferromagnetic to paramagnetic transition temperature above 450 K with a low-temperature... (Read more)
- 3. Phys. Rev. B 75, 144102 (2007) , “Theoretical investigation of nitrogen substitution in cubic zirconia”, Thomas BredowNitrogen substitution of oxygen ions in cubic zirconia was studied theoretically at density functional level. Nitrogen contents of 12.5 and 3.1% were studied with Zr8O16−mN2 and Zr32O64−mN2 supercells. For... (Read more)
- 4. Phys. Rev. Lett. 98, 216803 (2007) , “High Mobility in LaAlO3/SrTiO3 Heterostructures: Origin, Dimensionality, and Perspectives”, G. Herranz, M. Basletić, M. Bibes, C. Carrétéro, E. Tafra, E. Jacquet, K. Bouzehouane, C. Deranlot, A. Hamzić, J.-M. Broto, A. Barthélémy, and A. FertWe have investigated the dimensionality and origin of the magnetotransport properties of LaAlO3 films epitaxially grown on TiO2-terminated SrTiO3(001) substrates. High-mobility conduction is observed at low deposition oxygen pressures... (Read more)
- 5. 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)
- 6. 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)
- 7. 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)
- 8. 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)
- 9. Appl. Phys. Lett. 89, 262904 (2006) , “Oxygen vacancy in monoclinic HfO2: A consistent interpretation of trap assisted conduction, direct electron injection, and optical absorption experiments”, Peter Broqvist and Alfredo PasquarelloThe authors calculate energy levels associated with the oxygen vacancy in monoclinic HfO2 using a hybrid density functional which accurately reproduces the experimental band gap. The most stable charge states are obtained for varying Fermi level in the HfO2 band gap. To compare... (Read more)
- 10. Appl. Phys. Lett. 89, 262112 (2006) , “Identification of oxygen and zinc vacancy optical signals in ZnO”, T. Moe Børseth, B. G. Svensson, A. Yu. Kuznetsov, P. Klason, Q. X. Zhao, and M. WillanderPhotoluminescence spectroscopy has been used to study single crystalline ZnO samples systematically annealed in inert, Zn-rich and O-rich atmospheres. A striking correlation is observed between the choice of annealing ambient and the position of the deep band emission (DBE) often detected in ZnO. In... (Read more)
- 11. Appl. Phys. Lett. 89, 202904 (2006) , “Effects of O vacancies and C doping on dielectric properties of ZrO2: A first-principles study”, Gargi Dutta, K. P. S. S. Hembram, G. Mohan Rao, and Umesh V. WaghmareThe authors determine electronic properties, structural stability, and dielectric response of zirconia (ZrO2) with oxygen vacancies (O vacancies) and carbon doping (C doping) using first-principles density functional theory calculations based on pseudopotentials and a plane wave basis.... (Read more)
- 12. Appl. Phys. Lett. 89, 172906 (2006) , “Oxygen vacancy motion in Er-doped barium strontium titanate thin films”, Junling Wang and Susan Trolier-McKinstryAmphoteric dopants are widely used in BaTiO3-based dielectrics to improve capacitor reliability. In this work, an analogous approach was explored for barium strontium titanate thin films. Ba0.7Sr0.3TiO3 thin films were prepared by chemical solution... (Read more)
- 13. Appl. Phys. Lett. 89, 152904 (2006) , “First principles calculations of oxygen vacancy passivation by fluorine in hafnium oxide”, Wei Chen, Qing-Qing Sun, Shi-Jin Ding, David Wei Zhang, and Li-Kang WangThe fluorine incorporation into HfO2 with oxygen vacancies has been investigated using first principles calculations. The authors show that atomic fluorine can efficiently passivate the neutral oxygen vacancy with excess energies of 4.98 and 4.39 eV for threefold- and... (Read more)
- 14. Appl. Phys. Lett. 89, 142914 (2006) , “Defect passivation in HfO2 gate oxide by fluorine”, K. Tse and J. RobertsonThe authors have calculated that fluorine substituting for oxygen gives no gap states in HfO2. This accounts for the good passivation of oxygen vacancies by F seen experimentally. Bonding arguments are used to account for why F may be the most effective passivant in ionic oxides such as... (Read more)
- 15. Appl. Phys. Lett. 89, 082908 (2006) , “Negative oxygen vacancies in HfO2 as charge traps in high-k stacks”, J. L. Gavartin, D. Muñoz Ramo, A. L. Shluger, G. Bersuker, and B. H. LeeThe optical excitation and thermal ionization energies of oxygen vacancies in m-HfO2 are calculated using a non-local density functional theory with atomic basis sets and periodic supercell. The thermal ionization energies of negatively charged V and... (Read more)
- 16. Appl. Phys. Lett. 88, 182903 (2006) , “Effects of Al addition on the native defects in hafnia”, Q. Li, K. M. Koo, W. M. Lau, P. F. Lee, J. Y. Dai, Z. F. Hou, X. G. GongTwo occupied native defect bands are experimentally detected in pure HfO2. The density of states of band one in the middle of the band gap reduces drastically with the Al addition, while that of band two slightly above the valence-band maximum remains rather unaffected. We attribute the... (Read more)
- 17. Appl. Phys. Lett. 88, 162107 (2006) , “Physical origin of threshold voltage problems in polycrystalline silicon/HfO2 gate stacks”, Dae Yeon Kim, Joongoo Kang, and K. J. ChangBased on theoretical calculations, we find that at p+ polycrystalline silicon (poly-Si)/HfO2 gates, Si interstitials are easily migrated from the electrode, forming HfSi bonds with a charge transfer to the electrode, and the resulting interface dipole raises the Fermi level... (Read more)
- 18. J. Appl. Phys. 99, 044105 (2006) , “Passivation of oxygen vacancy states in HfO2 by nitrogen”, K. Xiong, J. Robertson, and S. J. ClarkNitrogen is known to reduce leakage currents and charge trapping in high-dielectric-constant gate oxides such as HfO2. We show that this occurs because nitrogen, substituting for oxygen atoms next to oxygen vacancy sites, repels the occupied gap states due to the neutral and positively... (Read more)
- 19. Phys. Rev. B 74, 235208 (2006) , “Theoretical study of the magnetism of Mn-doped ZnO with and without defects”, D. Iuan, B. Sanyal, and O. ErikssonWe calculate the exchange interaction parameters of a classical Heisenberg Hamiltonian for Mn-doped ZnO (Mn concentration between 5% and 20%) by an ab initio Korringa-Kohn-Rostoker coherent-potential-approximation method in the framework of density functional theory. A weak antiferromagnetic... (Read more)
- 20. Phys. Rev. B 74, 235207 (2006) , “Vacancy-enhanced ferromagnetism in Fe-doped rutile TiO2”, Jun Chen, Paul Rulis, Lizhi Ouyang, S. Satpathy, and W. Y. ChingBased on a series of supercell density functional calculations of Fe-doped TiO2 both with and without O vacancy (VO), we show that VO plays an important role in determining the magnetic properties of the dilute magnetic semiconductors (DMS). Without... (Read more)
- 21. Phys. Rev. B 74, 184117 (2006) , “Ab initio thermodynamic properties of point defects and O-vacancy diffusion in Mg spinels”, Zbigniew odziana and Jacek PiechotaWe report ab initio plane wave density functional theory studies of thermodynamic properties of isolated cation substitutions and oxygen vacancies in magnesium spinel, MgAl2O4. The formation enthalpy of Ca, Cu, and Zn substitutions of Mg cation indicate that transition... (Read more)
- 22. Phys. Rev. B 74, 174407 (2006) , “Superexchange in dilute magnetic dielectrics: Application to (Ti,Co)O2”, K. Kikoin and V. FleurovWe extend the model of ferromagnetic superexchange in dilute magnetic semiconductors to the ferromagnetically ordered highly insulating compounds (dilute magnetic dielectrics). The intrinsic ferromagnetism without free carriers is observed in oxygen-deficient films of anatase TiO2 doped... (Read more)
- 23. Phys. Rev. B 74, 144432 (2006) , “Role of defects in ferromagnetism in Zn1−xCoxO: A hybrid density-functional study”, C. H. PattersonExperimental studies of Zn1−xCoxO as thin films or nanocrystals have found ferromagnetism and Curie temperatures above room temperature and that p- or n-type doping of Zn1−xCoxO can change its magnetic... (Read more)
- 24. Appl. Phys. Lett. 87, 062105 (2005) , “Negative-U property of oxygen vacancy in cubic HfO2”, Y. P. Feng, A. T. L. Lim, M. F. LiOxygen vacancy in cubic HfO2 was investigated using first-principles calculation based on density functional theory and generalized gradient approximation. Five different charge states (V++, V+, V0, V, and... (Read more)
- 25. Appl. Phys. Lett. 87, 022903 (2005) , “Electron spin resonance investigation of oxygen-vacancy-related defects in BaTiO3 thin films”, V. V. Laguta, A. M. Slipenyuk, I. P. Bykov, M. D. Glinchuk, M. Maglione, D. Michau, J. Rosa, L. JastrabikThe Ti3+ center, based on a regular Ti site perturbed by an oxygen vacancy (VO), is identified by electron spin resonance (ESR) in textured BaTiO3 films. The center shows tetragonal symmetry along cubic 100 axes with g-factors: g=1.997,... (Read more)
- 26. Appl. Phys. Lett. 86, 143507 (2005) , “First-principles studies of the intrinsic effect of nitrogen atoms on reduction in gate leakage current through Hf-based high-k dielectrics”, N. Umezawa, K. Shiraishi, T. Ohno, H. Watanabe, T. Chikyow, K. Torii, K. Yamabe, K. Yamada, H. Kitajima, T. ArikadoThe atomistic effects of N atoms on the leakage current through HfO2 high-k gate dielectrics have been studied from first-principles calculations within the framework of a generalized gradient approximation (GGA). It has been found that the intrinsic effects of N atoms drastically... (Read more)
- 27. J. Appl. Phys. 97, 053704 (2005) , “The role of nitrogen-related defects in high-k dielectric oxides: Density-functional studies”, J. L. Gavartin, A. L. Shluger, A. S. Foster, G. I. BersukerUsing ab initio density-functional total energy and molecular-dynamics simulations, we study the effects of various forms of nitrogen postdeposition anneal (PDA) on the electric properties of hafnia in the context of its application as a gate dielectric in field-effect transistors. We... (Read more)
- 28. Appl. Phys. Lett. 81, 1818 (2002) , “Interface structures generated by negative-bias temperature instability in Si/SiO2 and Si/SiOxNy interfaces”, J. Ushio, T. Maruizumi, K. Kushida-AbdelghafarWe used a density functional method to investigate the mechanism of negative-bias temperature instability (NBTI) and resultant structural changes of Si/SiO2 and Si/SiOxNy interfaces. The reaction energies for the water- and hydrogen-originated... (Read more)
- 29. Phys. Rev. Lett. 83, 372 (1999) , “Hydrogen Electrochemistry and Stress-Induced Leakage Current in Silica”, Peter E. Bl?chl and James H. StathisHydrogen-related defects in oxygen-deficient silica, representing the material of a thermal gate oxide, are analyzed using first-principles calculations. Energetics and charge-state levels of oxygen vacancies, hydrogen, and their complexes in the silica framework are mapped out. The neutral hydrogen... (Read more)
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