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1

Digitale Medien

Observation of growth modes during metal-organic chemical vapor deposition of GaN (1999)

Stephenson, G. B. ; Eastman, J. A. ; Thompson, C. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 74 (1999), S. 3326-3328

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We present real-time surface x-ray scattering measurements during homoepitaxial growth of GaN by metal-organic chemical vapor deposition. We observed intensity oscillations corresponding to the completion of each monolayer during layer-by-layer growth. The growth rate was found to be temperature independent and Ga-transport limited. Transitions between step-flow, layer-by-layer, and three-dimensional growth modes were determined as a function of temperature and growth rate. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.123333

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2

Digitale Medien

The vibrational spectra of molecular ions isolated in solid neon. XVI. SO2+, SO2−, and (SO2)2− (2000)

Forney, Daniel ; Kellogg, C. Brian ; Thompson, Warren E. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 113 (2000), S. 86-97

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: When a Ne:SO2 mixture is subjected to Penning ionization and/or photoionization by neon atoms in their first excited states, between 16.6 and 16.85 eV, and the products are rapidly frozen at approximately 5 K, the infrared spectrum of the resulting deposit includes absorptions assigned with the aid of isotopic substitution studies to SO, SO2+, SO2−, (SO2)2−, and, tentatively, SO−. The fundamental and first overtone absorptions of SO lie 0.9 and 1.8 cm−1, respectively, below the gas-phase band centers. Ab initio calculations at the Hartree–Fock level show an instability in the v3 vibration of SO2+ which is avoided by higher-level calculations. The ν3 and ν1 fundamentals of SO2− isolated in solid neon are identified at 1086.2 and 990.8 cm−1, respectively. In agreement with an earlier proposal, the 1042 cm−1 absorption originally assigned to ν3 of SO2− trapped in solid argon is reassigned to MSO2, with M an alkali metal. Near the photodetachment threshold for SO2− isolated in a neon matrix, electron capture by SO2 nearest-neighbor pairs results in growth of infrared absorptions of (SO2)2−, which has been shown by gas-phase studies to have a significantly higher photodetachment threshold than does SO2−. The isotopic substitution studies require that the two sulfur atoms in (SO2)2− be nonequivalent, favoring the linking of the two SO2 units by a S (centered ellipsis) O bond. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.481777

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3

Digitale Medien

Applying molecular theory to steady-state diffusing systems (2000)

Frink, Laura J. Douglas ; Thompson, Aidan

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 112 (2000), S. 7564-7571

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Predicting the properties of nonequilibrium systems from molecular simulations is a growing area of interest. One important class of problems involves steady-state diffusion. To study these cases, a grand canonical molecular dynamics approach has been developed by Heffelfinger and van Swol [J. Chem. Phys. 101, 5274 (1994)]. With this method, the flux of particles, the chemical potential gradients, and density gradients can all be measured in the simulation. In this paper, we present a complementary approach that couples a nonlocal density functional theory (DFT) with a transport equation describing steady-state flux of the particles. We compare transport-DFT predictions to GCMD results for a variety of ideal (color diffusion), and nonideal (uphill diffusion and convective transport) systems. In all cases, excellent agreement between transport-DFT and GCMD calculations is obtained with diffusion coefficients that are invariant with respect to density and external fields. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.481376

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4

Digitale Medien

Equilibrium behavior of symmetric ABA triblock copolymer melts (1999)

Matsen, M. W. ; Thompson, R. B.

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 111 (1999), S. 7139-7146

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Melts of ABA triblock copolymer molecules with identical end blocks are examined using self-consistent field theory (SCFT). Phase diagrams are calculated and compared with those of homologous AB diblock copolymers formed by snipping the triblocks in half. This creates additional end segments which decreases the degree of segregation. Consequently, triblock melts remain ordered to higher temperatures than their diblock counterparts. We also find that middle-block domains are easier to stretch than end-block domains. As a result, domain spacings are slightly larger, the complex phase regions are shifted towards smaller A-segment compositions, and the perforated-lamellar phase becomes more metastable in triblock melts as compared to diblock melts. Although triblock and diblock melts exhibit very similar phase behavior, their mechanical properties can differ substantially due to triblock copolymers that bridge between otherwise disconnected A domains. We evaluate the bridging fraction for lamellar, cylindrical, and spherical morphologies to be about 40%–45%, 60%–65%, and 75%–80%, respectively. These fractions only depend weakly on the degree of segregation and the copolymer composition. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.480006

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5

Digitale Medien

Influence functionals with semiclassical propagators in combined forward–backward time (1999)

Thompson, Keiran ; Makri, Nancy

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 1343-1353

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: In a recent letter [Chem. Phys. Lett. 291, 101 (1998)] we presented a semiclassical methodology for calculating influence functionals arising from many-body anharmonic environments in the path integral formulation of quantum dynamics. Taking advantage of the trace operation associated with the unobservable medium, we express the influence functional in terms of a single propagator along a combined forward–backward system path. This propagator is evaluated according to time-dependent semiclassical theory in a coherent state initial value representation. Because the action associated with propagation in combined forward and backward time is governed by the net force experienced by the environment due to its interaction with the system, the resulting propagator is generally a smooth function of coordinates and thus amenable to Monte Carlo sampling; yet, the interference between forward and reverse propagators is fully accounted for. In the present paper we present a more elaborate version of the semiclassical influence functional formalism, along with algorithms for evaluating the coherent state transform of the Boltzmann operator that enters the influence functional. This factor is evaluated by performing an imaginary time path integral, and various approximations of the resulting expression as well as sampling schemes are discussed. The feasibility of the approach is demonstrated via numerous test calculations involving a two-level system coupled to (a) a dissipative harmonic bath and (b) a ten-dimensional bath of coupled anharmonic oscillators. © 1999 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.478011

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6

Digitale Medien

The rotationally resolved infrared spectrum of the ν1 stretch of the allyl radical (1998)

DeSain, J. D. ; Thompson, R. I. ; Sharma, S. D. ; [weitere]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 109 (1998), S. 7803-7809

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ISSN: 1089-7690

Quelle: AIP Digital Archive

Thema: Physik , Chemie und Pharmazie

Notizen: Transient infrared (IR) laser spectroscopy near 3100 cm−1 was used to observe the ν1 and ν13 transitions of the allyl radical, with their band origins found to lie at 3113.9779(3) cm−1 and near 3110.5 cm−1, respectively. Detailed assignment and analysis of the ν1 transition identified over 1100 transitions, and yielded improved values for ΔK and ΦK ground state centrifugal distortion constants, as well as a new set of excited state (ν1=1) rotational and centrifugal distortion constants, in addition to determining the band origin. Transitions involving states with quantum number up to Ka=11 and N=27 were identified. Strong perturbations were found in the excited state, included global perturbations of the Ka′=3 branch, extensive perturbations in the Ka′=2 and 4 branches, and very localized perturbations in the Ka′=6 branch. The Ka′=9 and 10 branches also appear to be significantly perturbed. Possible sources for these perturbations are discussed. © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.477426

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7

Digitale Medien

Effect of Ge on the segregation of B in Si(100) and Si(110) (1997)

Thompson, P. E. ; Silvestre, C. ; Jernigan, G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 81 (1997), S. 7317-7319

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: The segregation of B from Si1−xGex quantum wells grown using molecular beam epitaxy on Si(100) and Si(110) was investigated using secondary ion mass spectrometry. When a 3 nm B doping slab (n=1019/cm3) was placed in the center of a 6 nm Si1−xGex quantum well, the B profiles had two distinct exponential decay lengths, ΔSiGe, the Ge-controlled B decay length and ΔSi, the B decay length normally measured in Si. ΔSiGe was the same for Si(100) and Si(110) and independent of Ge concentration in the well for 0.1≤x≤0.5. As the Ge concentration was increased in the well, the location of the transition point, from ΔSiGe to ΔSi, which was always found far outside of the SiGe quantum well, increased in distance from the center of the well.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.365359

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8

Digitale Medien

Organic films deposited on Si p-n junctions: Accurate measurements of fluorescence internal efficiency, and application to luminescent antireflection coatings (1996)

Garbuzov, D. Z. ; Forrest, S. R. ; Tsekoun, A. G. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 80 (1996), S. 4644-4648

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Ultraviolet (UV) optical pumping followed by fluorescence wavelength downconversion of thin film organic light emitting materials deposited directly on the surface of Si p-n junction diodes is found to be an accurate and rapid means to determine the film internal fluorescence efficiency. By measuring the photoresponse of the Si detectors in the UV, we find that the organic light emitting films of aluminum tris-(8-hydroxyquinoline) (Alq3), N,N′-diphenyl-N,N′-bis-(3-methylphenyl)- 1,1′-biphenyl-4,4′-diamine, and bis-(8-hydroxyquinaldine)-chlorogallium (Gaq2′Cl), have internal fluorescence efficiencies of 0.30±0.05, 0.35±0.03, and 0.36±0.03, respectively. It has also been found that the organic films can be grown to a thickness which optimizes UV light conversion and can, at the same time, serve as antireflection coatings in the visible spectral region, thereby resulting in enhanced Si photodiode sensitivity extending from the UV to the infrared. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.363447

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9

Digitale Medien

Effect of dry etching and subsequent annealing of Si/SiGe/Si heterostructure (1996)

Swain, P. K. ; Misra, D. ; Thompson, P. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 4402-4406

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Exposure to dry etching can deleteriously affect strained SiGe films by initiation of misfit strain discontinuity in the film as well as at the interface. In this paper annealing behavior of defects generated as a consequence of dry etching of Si/SiGe/Si heterostructure metal–oxide–semiconductor capacitors have been reported. Some samples were wet etched for comparison. Samples were annealed at four different temperatures after being etched, namely, 650, 700, 750, and 800 °C. Results of the investigations using deep-level transient spectroscopy reveal defect levels at 0.62, 0.57, 0.56, and 0.44 eV for the dry-etched samples and at 0.31, 0.43, 0.56, and 0.44 eV for the wet-etched samples annealed at the aforetold temperatures. The results could be explained on the basis of appearance of point defects condensing into dislocation loops which eventually shrink and disappear as the annealing temperature is increased. The estimated size of the dislocation loops agrees quite well with the experimentally measured values obtained for identically processed samples. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.361748

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10

Digitale Medien

Jitterbug spin channel mixing in heterogeneous giant magnetoresistive material : The 40th annual conference on magnetism and magnetic materials (1996)

Gregg, J. F. ; Allen, W. ; Thompson, S. M. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 79 (1996), S. 5593-5595

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A mechanism is described which considers the effect of small magnetic particles on the spin diffusion length in a granular giant magnetoresistive material. Spin depolarization occurs by precession of the spin orientation of the carrier due to the s–d exchange interaction within a magnetic particle. Numerical simulation of this jitterbug effect is found to generate a temperature and field dependence of the distance a carrier may travel within the sample without losing its spin memory. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.362252

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