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  • PANGAEA  (215)
  • American Institute of Physics (AIP)  (107)
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  • 11
    Electronic Resource
    Electronic Resource
    Picosecond optical nonlinearities in a strained InAs/GaAs hetero n-i-p-i structure (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 929-932 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear optical properties of a n-i-p-i structure containing strained superlattice quantum wells in the intrinsic regions are studied using picosecond pump and probe pulses of the same photon energy. For pump fluences as low as 1.1 μJ/cm2, a blue shift of the excitonic resonance, caused by the screening of the built-in space-charge field and the accompanying reduction in the quantum-confined Stark effect, is clearly observed. At higher fluences, the onset of bleaching of the excitonic absorption is observed. The nonlinearities associated with the quantum confined Stark effect in the hetero n-i-p-i are directly compared to those arising from excitonic bleaching in identical strained superlattice quantum wells under flatband conditions. The picosecond time resolution allows a more accurate estimation of the carrier density in the hetero n-i-p-i by ignoring the density-dependent recombination and a quantitative comparison between the strength of the nonlinearities in the two structures. Although such comparisons depend on the optical fluence and structure of the hetero n-i-p-i, we find that the magnitudes of the nonlinearities in these two specific structures are comparable on a per carrier basis, although their spectral signatures are quite distinct.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351315
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  • 12
    Electronic Resource
    Electronic Resource
    Optical nonlinearities and ultrafast charge transport in all-binary InAs/GaAs strained hetero n-i-p-i's (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6891-6897 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We use picosecond differential spectroscopy to temporally and spectrally resolve the formation and decay of nonlinearities and space-charge fields in a hetero n-i-p-i that contains quantum wells in the intrinsic regions that are composed of all-binary InAs/GaAs short-period strained-layer superlattices. The evolution of the optical response is determined by competition between excitonic bleaching and the excitonic shift caused by screening of the built-in electric field of the n-i-p-i. The relative contributions of the two resulting optical nonlinearities are complicated functions of fluence, time, and wavelength, with the detailed dynamics determined by thermionic emission from the wells, picosecond charge transport over nanometer dimensions, screening, and recombination. At low fluences, excitonic bleaching is the source of an ultrafast nonlinear response that can be turned on and off in 〈10 ps. This initial excitonic bleaching gives way to a blue shift of the exciton as the carriers escape the wells in ∼3 ps and drift to screen the built-in field in 〈10 ps. The blue shift persists until the carriers recombine nonexponentially on microsecond time scales. At higher fluences, excitonic bleaching and the blue shift are observed simultaneously, since only a fraction of the carriers are required to screen the field and the wells remain partially occupied. On the time scale of ∼10 ns, the bleaching contribution disappears as the carriers within the wells recombine, leaving only the persistent blue shift.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349813
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  • 13
    Electronic Resource
    Electronic Resource
    Velocity selective rotational rainbows for normal incidence/normal detection gas–surface scattering (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 6178-6180 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Velocity selected rotational state distributions of N2 molecules scattered from Ag(111) have been measured. These measurements have been made at normal incidence and normal detection for incident energies of 0.25 and 0.75 eV. This new technique allows us to rapidly study the cross correlation between the exit rotational state and its velocity distribution. A pronounced difference between the rotational distributions of fast and slow scattered molecules is observed, and this difference is much more pronounced for high incident kinetic energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461587
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  • 14
    Electronic Resource
    Electronic Resource
    Photodissociation near a rough metal surface: Effect of reaction fields (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 9106-9112 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The modification of the photochemical dissociation rate of molecules in the presence of a rough metal surface is explored. Classical electromagnetic calculations are presented for the photodissociation rate of a point dipole near a rough surface modeled as a hemispheroidal bump on a semi-infinite flat plane. A correction is introduced by accounting for the reaction fields due to the dipole–substrate system radiating photons and coupling to delocalized surface plasmons. The effects of the shape and size of the bump, and the separation of the molecule from the bump on the rate of photodissociation of the molecule, are studied numerically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459201
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  • 15
    Electronic Resource
    Electronic Resource
    Linear and nonlinear optical properties of small silicon clusters (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7427-7438 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic contributions to the optical properties of small silicon clusters are examined. Geometries and the electronic structures of the clusters are established using the tight-binding model, and linear as well as nonlinear polarizabilities of the clusters are evaluated using one-electron density matrix techniques. Kleinman's conjecture for hyperpolarizabilities is shown to be violated in the frequency-degenerate case, which is of practical importance. The nonlinear polarizabilities are found to depend primarily on the symmetry of the cluster and prove to be high for the low-symmetry clusters. Possible experiments and applications are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459417
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  • 16
    Electronic Resource
    Electronic Resource
    Structure of the Si45 cluster (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 8552-8560 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Six structures for the Si45 cluster are compared using a tight-binding model. Two new structures are proposed which appear to be the low-energy isomers and to explain much of the existing experimental data. Cluster reactivity is distinguished from cluster stability, and several reasons are discussed which may lead to a reactive or unreactive species. These criteria are applied to the Si45 isomers, and the results are also correlated with experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461813
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  • 17
    Electronic Resource
    Electronic Resource
    Nonlocal and quasilocal potentials in the spontaneous emission of molecular exciplexes coupled to the phonon bath of a solid matrix (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1048-1060 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular exciplexes coupled to the phonon bath of a solid matrix are treated by a two-state model allowing for radiative relaxation from the excited to ground state and thermal relaxation from each of the states to the phonon bath. Molecular dynamics is considerably simplified by a canonical (Duke–Soules) transformation on the model Hamiltonian. This transformation (i) renormalizes the bath-free exciplex potential surfaces to phonon-dressed surfaces, and (ii) combines the radiative and phonon couplings into a single effective coupling. This leads to an effective nonlocal potential whose kernel is a product of radiative and nonradiative parts, and which can be interpreted pictorially in an intuitive manner when individual terms in the Born series solution of the corresponding Schrödinger equation are linked to special "Feynman diagrams.'' Under the small phonon energy and the weak correlation (between phonon and nuclear degrees of freedom) approximations, a thermally averaged wave function for nuclear motion can be constructed, and the nonlocal potential reduces to a quasilocal potential in which the phonon bath "filters out'' certain nonlocal transitions between the exciplex states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456158
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  • 18
    Electronic Resource
    Electronic Resource
    Photoabsorption of molecules at corrugated thin metal films (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 7472-7477 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A phenomenological study has been carried out for the photoabsorption of molecules in the vicinity of a corrugated thin metal film. In particular, perturbative results for a grating silver film have been obtained to first order in the corrugation parameter, where the effect of the incident field coupled with the long-range surface plasmon is observed. Based on the different coupling nature between the radiations from the incident plane wave and from the molecular dipole to the substate film, it is proposed that, through control of the various parameters of the film, enhanced selective photoabsorption may be achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456226
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  • 19
    Electronic Resource
    Electronic Resource
    Semiempirical study of rare gas and rare gas–hydrogen ionic clusters: R+n, (RnH)+, and (RnH2)+ for R≡Ar, Xe (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8925-8938 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ionic rare gas clusters Ar+n and Xe+n and rare gas–hydrogen clusters (ArnH)+, (ArnH2)+, (XenH)+ and (XenH2)+ are studied by the semiempirical diatomics-in-ionic-systems (DIIS) method. The Ar+n clusters (n〉3) are seen to have a structure of a linear Ar+3 core surrounded by n−3 neutral or almost neutral Ar atoms. For Xe+n (n〉3), a symmetrical Xe+4 ionic core with the geometry of regular pyramid is formed. The rare gas–hydrogen clusters with one H atom have a simple Rk(RH)+ structure with k neutral rare gas atoms attracted to the (RH)+ molecule by polarization forces. Two H atoms can bind with Ar atoms to form quasistable clusters ArnH+2 which dissociate to (n−1)Ar+H+(ArH)+ through a high barrier of roughly 0.75 eV. Two H atoms and one Xe+ ion are shown to form a collinear valence-bound (XeHH)+ cluster whose dissociation energy is 0.46 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459231
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  • 20
    Electronic Resource
    Electronic Resource
    Electronic states of the XenHCl systems in gas and condensed phases (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3071-3078 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Systems formed by one Cl, one H, and one or several Xe atoms are considered by the semiempirical diatomics-in-ionic-systems (DIIS) method, which takes into account the charge delocalization in ionic states and the coupling between the neutral and ionic states. Calculations are performed both for gas-phase systems, such as van der Waals complexes and clusters XenHCl (n=1,2,4,8,12) and ionic molecules (HXen)+Cl−, and for systems formed in Xe solids doped by HCl molecules. The calculations give the structure of the systems, dissociation energies, and energies of electronic transitions. The calculations show, in particular, the existence of the ground-state ionic molecule (HXe)+Cl−, the decrease of the HCl electronic excitation energy in clusters and solids, and the increase of the emission photon energy of the ionic HXe+nCl− systems as compared to the Xe+nCl− molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454963
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