The Experts below are selected from a list of 276 Experts worldwide ranked by ideXlab platform
J. Mašek - One of the best experts on this subject based on the ideXlab platform.
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Electronic states in Ga 1 − x Mn x As : Substitutional versus Interstitial Position of Mn
Physical Review B, 2002Co-Authors: František Máca, J. MašekAbstract:By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, Interstitial, and both Positions. It is shown that the Interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional Positions. This explains why the number of holes in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and Interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and Interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two Positions of Mn.
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electronic states in ga 1 x mn x as substitutional versus Interstitial Position of mn
Physical Review B, 2002Co-Authors: František Máca, J. MašekAbstract:By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, Interstitial, and both Positions. It is shown that the Interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional Positions. This explains why the number of holes in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and Interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and Interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two Positions of Mn.
František Máca - One of the best experts on this subject based on the ideXlab platform.
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Electronic states in Ga 1 − x Mn x As : Substitutional versus Interstitial Position of Mn
Physical Review B, 2002Co-Authors: František Máca, J. MašekAbstract:By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, Interstitial, and both Positions. It is shown that the Interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional Positions. This explains why the number of holes in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and Interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and Interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two Positions of Mn.
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electronic states in ga 1 x mn x as substitutional versus Interstitial Position of mn
Physical Review B, 2002Co-Authors: František Máca, J. MašekAbstract:By using spin-polarized full potential linearized augmented plane wave method we obtained the electronic structure of (Ga,Mn)As crystals with Mn in substitutional, Interstitial, and both Positions. It is shown that the Interstitial Mn acts as a double donor and compensates the holes created by two Mn atoms in substitutional Positions. This explains why the number of holes in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ is usually much smaller than x. The effective Mn doping efficiency is simply related to the proportion of substitutional and Interstitial Mn and does not depend on x provided that the proportion is fixed. The calculated local electronic structure of the substitutional and Interstitial Mn differ appreciably, so that the x-ray L emission spectra can be used to distinguish the two Positions of Mn.
Seetha Rama Rao Kamaraju - One of the best experts on this subject based on the ideXlab platform.
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Synthesis and Industrial Catalytic Applications of Binary and Ternary Molybdenum Nitrides: A Review
Catalysis Surveys from Asia, 2018Co-Authors: Venkata Ramesh Babu Gurram, Siva Sankar Enumula, Raji Reddy Chada, Kumara Swamy Koppadi, David Raju Burri, Seetha Rama Rao KamarajuAbstract:Despite the enormous interest raised in a few industrially important reactions (ammonia synthesis and decomPosition, hydrodenitrogenation, hydrodesulphurization, hydrogenation, dehydrogenation and reforming reactions) molybdenum nitrides are the less studied class of compounds and fascinated keen attention to replace the noble metals as the catalytic activities of these materials resembles or exceed to that of noble metals. Out of the above said reactions nitride catalysts have been extensively studied for ammonia synthesis and decomPosition reactions due to the presence of active molybdenum–nitrogen sites. Nitride materials can be produced by incorporation of nitrogen into the Interstitial Position of the early transition metals by dissimilar methods at higher temperatures. The present review focus mainly on the synthesis of binary and ternary molybdenum nitrides via different routes and application of these materials to the industrial catalytic reactions. Graphical Abstract
Horst P. Strunk - One of the best experts on this subject based on the ideXlab platform.
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Cluster Model Study of the Incorporation Process of Excess Arsenic into Interstitial Positions of the GaAs Lattice
MRS Proceedings, 2011Co-Authors: T. Marek, Sándor Kunsági-máté, Horst P. StrunkAbstract:AbstractWe study an As2 molecule approaching a planar, non-reconstructed, As terminated GaAs(001) surface by using a suitable cluster and quantum mechanical ab-initio calculation methods. During our calculations the As2 molecule is always oriented perpendicularly to the surface and its bonding length may vary. We find a metastable Position below the growing surface which facilitates the incorporation of the leading As atom into an Interstitial Position of the crystal during growth. We give a first model for this incorporation process.
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Molecular-dynamics-based model for the formation of arsenic Interstitials during low-temperature growth of GaAs
Physical Review B, 2005Co-Authors: Sándor Kunsági-máté, T. Marek, Carsten Schür, Eszter Végh, Horst P. StrunkAbstract:The formation of Interstitial arsenic defects in low-temperature grown (LT) GaAs layers is examined by temperature dependent, direct trajectory molecular dynamics calculations at semiempirical level. In agreement with earlier ab initio calculations, a metastable Interstitial Position of an As{sub 2} molecule just below the As-rich c(4x4){beta} reconstructed GaAs(001) surface (characterized by As-As dimers) is obtained. We model this conformation as a precursor state for excess Interstitial As in the LT-GaAs layers. Furthermore, a migration layer was found above the surface, where As{sub 2} molecules can move practically freely. We identify the hopping of As{sub 2} molecules from the Interstitial Position into this migration layer as the process that controls the experimentally observed dependencies of the excess arsenic content on substrate temperature and arsenic overpressure during growth of LT-GaAs layers.
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Theoretical and experimental energy barriers associated with the incorporation of excess As into GaAs(0 0 1)
Surface Science, 2002Co-Authors: Sándor Kunsági-máté, T. Marek, Carsten Schür, Horst P. StrunkAbstract:We present the results of calculations on the incorporation process of an As atom into a tetrahedral Interstitial Position of the GaAs lattice. To model this particular step of the As-incorporation process, the interactions between an As2 molecule and an As-terminated, partially relaxed GaAs(0 0 1) surface represented by a Ga24As25H44 cluster are studied. We use quantum chemical ab initio methods for these simulations. From the interaction characteristics we obtain an energy barrier that governs the thermally activated escape of an As2 molecule from an Interstitial surface site. On this basis a Langmuir-adsorption-like model can be formulated which describes the experimentally determined excess As concentration in a GaAs crystal grown at low temperatures rather well. 2002 Elsevier Science B.V. All rights reserved.
T. Marek - One of the best experts on this subject based on the ideXlab platform.
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Cluster Model Study of the Incorporation Process of Excess Arsenic into Interstitial Positions of the GaAs Lattice
MRS Proceedings, 2011Co-Authors: T. Marek, Sándor Kunsági-máté, Horst P. StrunkAbstract:AbstractWe study an As2 molecule approaching a planar, non-reconstructed, As terminated GaAs(001) surface by using a suitable cluster and quantum mechanical ab-initio calculation methods. During our calculations the As2 molecule is always oriented perpendicularly to the surface and its bonding length may vary. We find a metastable Position below the growing surface which facilitates the incorporation of the leading As atom into an Interstitial Position of the crystal during growth. We give a first model for this incorporation process.
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Interstitial to antisite defect conversion during the molecular beam epitaxial dePosition on c 4 3 4 gaas 001 surfaces
Physica Status Solidi (a), 2005Co-Authors: Sandor Kunsagimate, Carsten Schür, T. MarekAbstract:In the model describing the origin of excess arsenic content in low-temperature grown GaAs layers developed by the research group of professor Strunk during the last ten years, formation of an Interstitial As atom was identified as precursor to excess arsenic formation. After an As2 molecule interacts with the GaAs surface, a metastable conformation can form, where one of the As atoms of the As2 molecule is located in an Interstitial Position. Starting from this geometry, during growth stable conformations can easily arise by the assistance of one or two arriving Ga atoms which stabilize the Interstitial As atom in its Position by forming a half or full cage-like structure. Another model describes how the antisite excess As atoms form in GaAs layers by an incomplete exchange of As atoms in the surface reconstruction layer with arriving Ga atoms. The present article connects these two aspects of the excess As formation by analyzing the stability of the Interstitial excess As atom, calculated in four different atomic arrangements according to experimentally observed surface structures. Energies of initial, final and transition states of Interstitial to antisite reaction path were calculated by DFT/B3LYP/6-31++G method. Results show that Interstitial to antisite conversion happens preferably after a half-cage formation, while after a full cage has been formed, the Interstitial As atom remains fixed in its Position. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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Molecular-dynamics-based model for the formation of arsenic Interstitials during low-temperature growth of GaAs
Physical Review B, 2005Co-Authors: Sándor Kunsági-máté, T. Marek, Carsten Schür, Eszter Végh, Horst P. StrunkAbstract:The formation of Interstitial arsenic defects in low-temperature grown (LT) GaAs layers is examined by temperature dependent, direct trajectory molecular dynamics calculations at semiempirical level. In agreement with earlier ab initio calculations, a metastable Interstitial Position of an As{sub 2} molecule just below the As-rich c(4x4){beta} reconstructed GaAs(001) surface (characterized by As-As dimers) is obtained. We model this conformation as a precursor state for excess Interstitial As in the LT-GaAs layers. Furthermore, a migration layer was found above the surface, where As{sub 2} molecules can move practically freely. We identify the hopping of As{sub 2} molecules from the Interstitial Position into this migration layer as the process that controls the experimentally observed dependencies of the excess arsenic content on substrate temperature and arsenic overpressure during growth of LT-GaAs layers.
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Theoretical and experimental energy barriers associated with the incorporation of excess As into GaAs(0 0 1)
Surface Science, 2002Co-Authors: Sándor Kunsági-máté, T. Marek, Carsten Schür, Horst P. StrunkAbstract:We present the results of calculations on the incorporation process of an As atom into a tetrahedral Interstitial Position of the GaAs lattice. To model this particular step of the As-incorporation process, the interactions between an As2 molecule and an As-terminated, partially relaxed GaAs(0 0 1) surface represented by a Ga24As25H44 cluster are studied. We use quantum chemical ab initio methods for these simulations. From the interaction characteristics we obtain an energy barrier that governs the thermally activated escape of an As2 molecule from an Interstitial surface site. On this basis a Langmuir-adsorption-like model can be formulated which describes the experimentally determined excess As concentration in a GaAs crystal grown at low temperatures rather well. 2002 Elsevier Science B.V. All rights reserved.
