| 51. |
- Bulgakov, EN, et al.
(author)
-
Multiple bound states in scissor-shaped waveguides
- 2002
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:15
-
Journal article (peer-reviewed)abstract
- We study bound states of the two-dimensional Helmholtz equations with Dirichlet boundary conditions in an open geometry given by two straight leads of the same width which cross at an angle theta. Such a four-terminal junction with a tunable theta can realized experimentally if a right-angle structure is filled by a ferrite. It is known that for theta=90degrees there is one proper bound state and one eigenvalue embedded in the continuum. We show that the number of eigenvalues becomes larger with increasing asymmetry and the bound-state energies are increasing as functions of theta in the interval (0,90degrees). Moreover, states which are sufficiently strongly bound exist in pairs with a small energy difference and opposite parities. Finally, we discuss how the bound states transform with increasing theta into quasibound states with a complex wave vector.
|
|
| 52. |
- Bulgakov, EN, et al.
(author)
-
Spin rotation for ballistic electron transmission induced by spin-orbit interaction
- 2002
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:7
-
Journal article (peer-reviewed)abstract
- We study spin-dependent electron transmission through one- and two-dimensional curved waveguides and quantum dots with account of spin-orbit interaction. We prove that for a transmission through an arbitrary structure there is no spin polarization provided the electron transmits in an isolated energy subband and only two leads are attached to the structure. In particular there is no spin polarization in the one-dimensional wire, for which a spin-dependent solution is found analytically. The solution demonstrates the spin evolution as dependent on a length of wire. The numerical solution for transmission of electrons through the two-dimensional curved waveguides coincides with the solution for the one-dimensional wire if the energy of electron is within the first energy subband. In the vicinity of edges of the energy subbands there are sharp anomalies of spin flipping.
|
|
| 53. |
- Bulgakova, Nadya, 1956, et al.
(author)
-
Electronic transport and consequences for material removal in ultrafst pulsed laser ablation of materials
- 2004
-
In: Physical Review B. - 1098-0121. ; 69
-
Journal article (peer-reviewed)abstract
- Fast electronic transport is investigated theoretically based on a drift-diffusion approach for different classes of materials (metals, semiconductors, and dielectrics) under ultrafast, pulsed laser irradiation. The simulations are performed at intensities above the material removal threshold, characteristic for the ablation regime. The laser-induced charging of dielectric surfaces causes a subpicosecond electrostatic rupture of the superficial layers, an effect which, in comparison, is strongly inhibited for metals and semiconductors as a consequence of superior carrier transport properties.
|
|
| 54. |
|
|
| 55. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Analysis of band anticrossing in GaNxP1-x alloys
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70, s. 085209-
-
Journal article (peer-reviewed)abstract
- Temperature-dependent absorption, photoluminescence excitation, and spectroscopic ellipsometry measurements are employed to accurately determine compositional and temperature dependences of the conduction band (CB) states in GaNP alloys. The CB edge and the higher lying Γc CB minimum (CBM) are shown to exhibit an apparently anticrossing behavior, i.e., the N-induced redshift of the bandgap energy is accompanied by a matching blueshift of the Γc CBM. The obtained data can be phenomenologically described by the band anticrossing model. By considering strong temperature dependence of the energy of the interacting N level, which has largely been overlooked in earlier studies of GaNP, the interacting N level can be attributed to the isolated substitutional NP and the coupling parameter is accurately determined.
|
|
| 56. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Experimental evidence for N-induced strong coupling of host conduction band states in GaNP : insight into the dominant mechanism for giant band-gap bowing
- 2004
-
In: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 69, s. 201303-
-
Journal article (peer-reviewed)abstract
- Direct evidence for N-induced strong coupling of host conduction band (CB) states in GaNxP1-x is provided by photoluminescence excitation. It is manifested as: (1) a drastic change in the ratio of oscillator strengths between the optical transitions involving the CB minimum (CBM) and the high-lying Γ CB state; (2) a strong blueshift of the Γ CB state with increasing x accompanying a redshift of the CBM, (3) pinning of the localized N states and a newly emerging t2 (L or X3) CB state. These findings shed new light on the issue of the dominant mechanism responsible for the giant band-gap bowing of dilute nitrides.
|
|
| 57. |
- Buyanova, Irina, 1960-, et al.
(author)
-
Type I band alignment in the GaNxAs1-x/GaAs quantum wells
- 2001
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 63:3, s. 333031-333034
-
Journal article (peer-reviewed)abstract
- Three independent experimental techniques, namely, time-resolved photoluminescence (PL) spectroscopy, PL polarization, and optically detected cyclotron resonance, are employed to determine the band alignment of GaNxAS1-x/GaAs quantum structures with a low-N composition. It is concluded that band lineup is type I based on the following experimental results: (i) comparable radiative decay time of the GaNAs-related emission measured from single GaNAs epilayers and from GaNAs/GaAs quantum well (QW) structures, (ii) polarization of the GaNAs-related emission, and (iii) spatial confinement of the photoexcited holes within the GaNAs layers under resonant excitation of the GaNAs QW's.
|
|
| 58. |
- Carling, K. M., et al.
(author)
-
Vacancy concentration in Al from combined first-principles and model potential calculations
- 2003
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 67:5
-
Journal article (peer-reviewed)abstract
- We present a comprehensive study of vacancy formation enthalpies and entropies in aluminum. The calculations are done in the framework of the local-density and generalized-gradient approximations in the density-functional formalism. To assess anharmonic contributions to the formation free energies, we use an interatomic potential with parameters determined from density-functional-theory calculations. We find that the binding energy for the nearest-neighbor divacancy is negative, i.e., it is energetically unstable. The entropy contributions slightly stabilize the divacancy but also the binding free energy at the melting temperature is found to be negative. We show that the anharmonic atomic vibrations explain the non-Arrhenius temperature dependence of the vacancy concentration in contrast to the commonly accepted interpretation of the experimental data in terms of the monovacancy-divacancy model.
|
|
| 59. |
- Carlson, S., et al.
(author)
-
High-Pressure Transitions of Trigonal α-ZrMo2O8
- 2000
-
In: Physical review B Condensed matter and materials physics. - : American Physicl Society. - 1098-0121. ; 61:17, s. 11209-11212.
-
Journal article (peer-reviewed)abstract
- High-pressure synchrotron x-ray powder-diffraction studies show that trigonal α-ZrMo2O8 transforms to a monoclinic symmetry phase (δ-ZrMo2O8) at 1.06–1.11 GPa. The space group was determined to C2/m. A further high-pressure transition from the monoclinic δ to a triclinic ε phase occur at 2.0–2.5 GPa (space group P1 or P1¯). Both transformations are reversible. The volume compressibilities are similar for the α and δ phase, and five times lower for the ε phase.
|
|
| 60. |
- Carniato, S., et al.
(author)
-
Ab initio study of the Cu 2p and 3s core-level XPS spectra of copper phthalocyanine
- 2002
-
In: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 66:4
-
Journal article (peer-reviewed)abstract
- The x-ray photoelectron spectra (XPS) of copper tetraazaporphyrin (CuTAP), used as a model of copper phthalocyanine(CuPc) are studied by theoretical simulations. The nature of the main and satellite features observed in the XPS Cu 2p and Cu 3s photoelectron spectra are discussed based on the results of the charge-transfer (CT) model and of ab initio calculations in the sudden approximation limit. It is shown that the two descriptions of the core level final states can be derived from the two types of approaches. The final-state wave functions given by the CT model are described in a shakedown scenario. This process produces a well-screened final 2p(5)3d(10)(L) under bar configuration ((L) under bar denotes a ligand hole) on the Cu atom together with the core hole, resulting in the main spectral peak. On the other hand, the process where the outer electron stays on the ligand corresponds to the satellite with a poorly-screened 2p(5)3d(9) character. The ab initio calculations, performed on an isolated copper tetraazaporphyrin molecule at the Hartree-Fock (HF) level, the multi-configuration self-consistent field level, and the hybrid density-functional-theory levels show that the core hole final states (satellite/main peak) can be attributed to valence-valence transitions. We show that a correct intensity distribution of the different features, including the so-called white line and the satellite structures, can be obtained when the electronic relaxation and correlation and the overlap between the ground-state and final-state Slater determinants are explicitly taken into account. It is found that the nature of the main peak is strongly depending on the Ligand-to-Metal charge transfer, on the exchange interaction and on the core-hole-3d-hole interaction energies.
|
|
