| 1. |
- Buyanova, Irina, 1960-, et al.
(författare)
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Effects of N incorporation on the electronic structure of GaNP : Origin of the 2.87 eV optical transition
- 2005
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Konferensbidrag (refereegranskat)abstract
- Temperature dependent photoluminescence excitation (PLE) spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered (I. A. Buyanova et al, PRB 69, 201303 (2004)) in the GaNxP1-x alloys. Whereas appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with N content. This questions a possible association of this feature with a N-related localized state. Based on the results of temperature dependent measurements, the involved state is concluded to have a non-$\Gamma $ character. Excitation of the known N-related localized states via this state is found to be non-selective, opposed to that between the N-related centers. The observed properties are shown to be hardly consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the ``2.87 eV'' state as being due to either a t2 component of the X3c (or L1c CBM or a level arising from a complex of N and H (in some form) are also discussed.
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| 2. |
- Buyanova, Irina, 1960-, et al.
(författare)
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On a possible origin of the 2.87 eV optical transition in GaNP
- 2006
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 18:2, s. 449-457
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Tidskriftsartikel (refereegranskat)abstract
- Temperature dependent photoluminescence excitation spectroscopy is employed to evaluate basic physical properties of the 2.87 eV absorption peak, recently discovered for the GaNxP1-x alloys. Whereas the appearance of this transition is found to be facilitated by incorporation of N and also H atoms, its intensity does not scale with the N content in the alloys. This questions the possible association of this feature with an N-related localized state. On the basis of the results of temperature dependent measurements, it is concluded that the state involved has a non-Γ character. Excitation of the known N-related localized states via this state is found to be non-selective, unlike that between the N-related centres. The observed properties are shown to be barely consistent with those predicted for the higher lying localized state of the isolated N atom derived from the Γ conduction band minimum (CBM). Alternative explanations for the '2.87 eV' state as being due to either a t 2 component of the X3c (or L1c) CBM or a level arising from a complex of N and H (in some form) are also discussed. © 2006 IOP Publishing Ltd.
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| 3. |
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| 4. |
- Felici, M, et al.
(författare)
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High Energy Optical Transitions in Ga(PN) : Contribution from Perturbed Valence Band
- 2005
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Ingår i: AIP Conference Proceedings / Volume 772. - : American Institute of Physics (AIP). - 0735402574 ; , s. 265-
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Konferensbidrag (refereegranskat)abstract
- The GaP1–xNx conduction band is investigated experimentally (by excitation photoluminescence) andtheoretically (by pseudopotential supercells) for N concentrations up to x=3.5%and photon energies ranging from the optical absorption edge to3.2 eV. With increasing x: (i) a direct-like absorption edgedevelops smoothly and red-shifts rapidly overtaking energy-pinned cluster states; (ii)a broad absorption plateau appears between the X1c and the1c critical points of GaP; (iii) the 1c absorption edgebroadens and gradually disappears. Empirical pseudopotential calculations for GaP1-xNx randomalloy supercells account well for all the PLE results byconsidering N induced changes in the valence band overlooked sofar. ©2005 American Institute of Physics
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| 5. |
- Li, Xin, et al.
(författare)
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Nuclear magnetic shielding of the Cd-113(II) ion in aqua solution : A combined molecular dynamics/density functional theory study
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112:36, s. 11347-11352
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined molecular dynamics simulation and density functional theory investigation of the nuclear magnetic shielding constant of the Cd-113(II) ion solvated in aqueous solution. Molecular dynamics simulations are carried out for the cadmium-water system in order to produce instantaneous geometries for subsequent determination of the nuclear magnetic shielding constant at the density functional theory level. The nuclear magnetic shielding constant is computed using a perturbation theory formalism, which includes nonrelativistic and leading order relativistic contributions to the nuclear magnetic Shielding tensor. Although the NMR shielding constant varies significantly with respect to simulation time, the value averaged over increasing number of snapshots remains almost constant. The paramagnetic nonrelativistic contribution is found to be most sensitive to dynamical changes in the system and is mainly responsible for the thermal and solvent effects in solution. The relativistic correction features very little sensitivity to the chemical environment, and can be disregarded in theoretical calculations when a Cd complex is used as reference compound in Cd-113 NMR experiments, due to the mutual cancelation between individual relativistic corrections.
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| 6. |
- Li, Xin, et al.
(författare)
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Paramagnetic Perturbation of the F-19 NMR Chemical Shift in Fluorinated Cysteine by O-2 : A Theoretical Study
- 2009
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Ingår i: Journal of Physical Chemistry B. - Washington, D. C. : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:31, s. 10916-10922
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Tidskriftsartikel (refereegranskat)abstract
- We present a combined molecular dynamics and density functional theory study of dioxygen-induced perturbation of the F-19 NMR chemical shifts in an aqueous solution of fluorinated cysteine under 100 atm of O-2 partial pressure. Molecular dynamics Simulations are carried out to determine the dominant structures of O-2 and the fluorinated cysteine complexes in water, and the collected structural information is exploited in computation of F-19 chemical shifts using density functional theory. The obtained results indicate that the density redistribution of the O-2 unpaired electrons between the dioxygen and fluorinated cysteine is responsible for the experimentally observed perturbation of the F-19 NMR chemical shifts, where the Fermi contact interaction plays the key role. The O-2-induced paramagnetic F-19 chemical shift, averaged over the simulation trajectory, is comparable with the reported experimental values, proving the availability of the developed strategy for modeling F-19 NMR chemical shifts in the presence of paramagnetic agents in ail aqueous solution. The applicability of the combined molecular dynamics/density functional theory approach for dioxygen NMR perturbation to all resonating nuclei including H-1, C-13, N-15, and F-19 is emphasized, and the ramification of this for investigations of membrane protein structures is discussed.
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| 7. |
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| 8. |
- Thinh, N.Q., et al.
(författare)
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Properties of Ga-interstitial defects in AlxGa 1-xNyP1-y
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:12
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Tidskriftsartikel (refereegranskat)abstract
- A detailed account of the experimental results from optically detected magnetic resonance (ODMR) studies of grown-in defects in (Al)GaNP alloys, prepared by molecular beam epitaxy, is presented. The experimental procedure and an in-depth analysis by a spin Hamiltonian lead to the identification of two Gai defects (Gai-A and Gai-B). New information on the electronic properties of these defects and the recombination processes leading to the observation of the ODMR signals will be provided. These defects are deep-level defects. In conditions when the defect is directly involved in radiative recombination of the near-infrared photoluminescence band, the energy level of the Gai-B defect was estimated to be deeper than ~1.2 eV from either the conduction or valence band edge. In most cases, however, these defects act as nonradiative recombination centers, reducing the efficiency of light emission from the alloys. They can thus undermine the performance of potential photonic devices. High thermal stability is observed for these defects. ©2005 The American Physical Society.
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| 9. |
- Vorona, Igor, et al.
(författare)
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Magnetic resonance signatures of grown-in defects in GaInNP alloys grown on a GaAs substrate
- 2005
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 86:22, s. 222110-
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Tidskriftsartikel (refereegranskat)abstract
- Dilute-nitride Ga0.44In0.56NyP1-y alloys with y=0-0.02, grown on a GaAs substrate using gas-source molecular beam epitaxy, are studied by the optically detected magnetic resonance (ODMR) technique. Grown-in paramagnetic defects were found to act as centers of nonradiative recombination. Resolved hyperfine structure for one of the detected ODMR signals suggests involvement of a Ga-interstitial or an As-antisite in the structure of the related defect. © 2005 American Institute of Physics.
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