8,062 research outputs found
Nanomechanics of a Hydrogen Molecule Suspended between Two Equally Charged Tips
Geometric configuration and energy of a hydrogen molecule centered between
two point-shaped tips of equal charge are calculated with the variational
quantum Monte-Carlo (QMC) method without the restriction of the
Born-Oppenheimer (BO) approximation. Ground state nuclear distribution,
stability, and low vibrational excitation are investigated. Ground state
results predict significant deviations from the BO treatment that is based on a
potential energy surface (PES) obtained with the same QMC accuracy. The quantum
mechanical distribution of molecular axis direction and bond length at a
sub-nanometer level is fundamental for understanding nanomechanical dynamics
with embedded hydrogen. Because of the tips' arrangement, cylindrical symmetry
yields a uniform azimuthal distribution of the molecular axis vector relative
to the tip-tip axis. With approaching tips towards each other, the QMC sampling
shows an increasing loss of spherical symmetry with the molecular axis still
uniformly distributed over the azimuthal angle but peaked at the tip-tip
direction for negative tip charge while peaked at the equatorial plane for
positive charge. This directional behavior can be switched between both stable
configurations by changing the sign of the tip charge and by controlling the
tip-tip distance. This suggests an application in the field of molecular
machines.Comment: 20 pages, 10 figure
Anisotropic Temperature Factors in the Calculation of Low-Energy Electron Diffraction Intensities
Effective calculation of LEED intensities using symmetry-adapted functions
The calculation of LEED intensities in a spherical-wave representation can be substantially simplified by symmetry relations. The wave field around each atom is expanded in symmetry-adapted functions where the local point symmetry of the atomic site applies. For overlayer systems with more than one atom per unit cell symmetry-adapted functions can be used when the division of the crystal into monoatomic subplanes is replaced by division into subplanes containing all symmetrically equivalent atomic positions
Self-induced decoherence approach: Strong limitations on its validity in a simple spin bath model and on its general physical relevance
The "self-induced decoherence" (SID) approach suggests that (1) the
expectation value of any observable becomes diagonal in the eigenstates of the
total Hamiltonian for systems endowed with a continuous energy spectrum, and
(2), that this process can be interpreted as decoherence. We evaluate the first
claim in the context of a simple spin bath model. We find that even for large
environments, corresponding to an approximately continuous energy spectrum,
diagonalization of the expectation value of random observables does in general
not occur. We explain this result and conjecture that SID is likely to fail
also in other systems composed of discrete subsystems. Regarding the second
claim, we emphasize that SID does not describe a physically meaningful
decoherence process for individual measurements, but only involves destructive
interference that occurs collectively within an ensemble of presupposed
"values" of measurements. This leads us to question the relevance of SID for
treating observed decoherence effects.Comment: 11 pages, 4 figures. Final published versio
Influence Of Ch4/h2 Reactive Ion Etching On The Deep Levels Of Si-doped Alxga1-xas (x=0.25)
We study the passivation and recovery of shallow and deep levels in Si-doped AlGaAs exposed to CH4/H2 and H2 reactive ion etching (RIE). The carrier concentration depth profile is determined by capacitance-voltage measurements. The activation energy to recover the silicon donors is found to be 1.1 eV for samples exposed to CH4/H2 RIE and 1.3 eV for samples exposed to H2 RIE. We study the behavior of DX centers in Si-doped AlGaAs layers after RIE exposure and subsequent thermal annealing by using deep level transient spectroscopy. For CH4TH2 RIE a new emission is detected at the high temperature side. We identify this emission as the DX3 center, which is assigned to a DX center with three aluminum atoms surrounding the Si donor. This DX center is only detected on the samples exposed to CH4/H2 RIE. We explain the formation of this deep level to the highly selective removal of Ga atoms in favor of Al atoms. Consequently Al-rich regions are created near the surface. © 1996 American Vacuum Society.14317731779Chevallier, J., Clerjaud, B., Pajot, B., (1991) Semiconductors and Semimetals, 34, p. 449. , Chap. 13Dautremont-Smith, W.C., (1988) Mater. Res. Soc. Symp. Proc., 104, p. 313Pearton, S.J., Dautremont-Smith, W.C., Chevallier, J., Tu, C.W., Cummings, K.D., (1986) J. Appl. Phys., 59, p. 2821Jalil, A., Chevallier, J., Pesant, J.C., Mostefaoui, R., Pajot, B., Murawala, P., Azoulay, R., (1987) Appl. Phys. Lett., 50, p. 439Chevallier, J., Pajot, B., Jalil, A., Mostefaoui, R., Rahbi, R., Boissy, M.C., (1988) Mater. Res. Soc. Symp. Proc., 104, p. 337Pavesi, L., Giannozzi, P., Reinhart, F.K., (1990) Phys. Rev. B, 42, p. 1864Pavesi, L., Giannozzi, P., (1991) Phys. Rev. B, 43, p. 2446Tavendale, A.J., Pearton, S.J., Williams, A.A., Alexiev, D., (1990) Appl. Phys. Lett., 56, p. 1457Yuan, M.H., Wang, L.P., Jin, S.X., Chen, J.J., Qin, G.G., (1991) Appl. Phys. Lett., 58, p. 925Srivastava, P.C., Chandra, S., Singh, U.P., (1991) Semicond. Sci. Technol., 6, p. 1126Cho, H.Y., Kim, E.K., Min, S., Chang, K.J., Lee, C., (1990) J. Appl. Phys., 68, p. 5077Zundel, T., Weber, J., (1989) Phys. Rev. B, 39, p. 13549Roos, G., Johnson, N.M., Herring, C., Harris, J.S., (1991) Appl. Phys. Lett., 56, p. 461Pearton, S.J., Abernathy, C.R., Lopata, J., (1991) Appl. Phys. Lett., 59, p. 3571Morrow, R.A., (1989) J. Appl. Phys., 66, p. 2973Cameron, N.I., Beaumont, S.P., Wilkinson, C.D.W., Johnson, N.P., Kean, A.H., Stanley, C.R., (1990) J. Vac. Sci. Technol. B, 8, p. 1966Cameron, N.I., Beaumont, S.P., Wilkinson, C.D.W., Johnson, N.P., Kean, A.H., Stanley, C.R., (1990) Microelectron. Eng., 11, p. 607Cheung, R., Thorns, S., McIntyre, I., Wilkinson, C.D.W., Beaumont, S.P., (1988) J. Vac. Sci. Technol. B, 6, p. 1911Jackson, G.S., Beberman, J., Feng, M.S., Hsieh, K.C., Holonyak Jr., N., Verdeyen, J., (1988) J. Appl. Phys., 64, p. 5175Dautremont-Smith, W.C., Nabity, J.C., Swaminathan, V., Stavola, M., Chevallier, J., Tu, C.W., Pearton, S.J., (1986) Appl. Phys. Lett., 49, p. 1098Jalil, A., Heurtel, A., Marfaing, Y., Chevallier, J., (1989) J. Appl. Phys., 66, p. 5854Nabity, J.C., Stavola, M., Lopata, J., Dautremont-Smith, W.C., Tu, C.W., Pearton, S.J., (1987) Appl. Phys. Lett., 50, p. 921Morrow, R.A., (1991) J. Appl. Phys., 69, p. 4306Chadi, D.J., Chang, K.J., (1988) Phys. Rev. Lett., 61, p. 873Chadi, D.J., Chang, K.J., (1988) Phys. Rev. B, 39, p. 10063Mooney, P.M., (1990) J. Appl. Phys., 67, pp. R1Chang, K.J., (1990) Proc. 20th Conference on Physics Semiconductor, 1, p. 787. , edited by E. M. Anastassakis and J. D. JoannopoulosCollot, P., Gaonach, C., (1990) Semicond. Sci. Technol., 5, p. 237Constantine, C., Johnson, D., Pearton, S.J., Chakrabarti, U.K., Emerson, A.B., Hobson, W.S., Kinsella, A.P., (1990) J. Vac. Sci. Technol. B, 8, p. 596Pearton, S.J., Chakrabarti, U.K., Hobson, W.S., (1989) J. Appl. Phys., 66, p. 2061Pearton, S.J., Abernathy, C.R., (1989) Appl. Phys. Lett., 55, p. 678Pearton, S.J., Hobson, W.S., Jones, K.S., (1989) J. Appl. Phys., 66, p. 5009Pereira, R., Van Hove, M., De Potter, M., Van Rossum, M., (1990) Electron. Lett., 26, p. 462Pereira, R., Van Hove, M., De Raedt, W., Jansen, Ph., Borghs, G., Jonckheere, R., Van Rossum, M., (1991) J. Vac. Sci. Technol. B, 9, p. 1978Chevallier, J., Dautremont-Smith, W.C., Tu, C.W., Pearton, S.J., (1985) Appl. Phys. Lett., 47, p. 108Hansen, W.L., Haler, E.E., Luke, P.N., (1982) IEEE Trans. Nucl. Sci., NS-29, p. 738Hall, R.N., (1984) IEEE Trans. Nucl. Sci., NS-31, p. 320Mooney, P.M., Theis, T.N., Wright, S.L., (1988) Appl. Phys. Lett., 53, p. 2546Mooney, P.M., Theis, T.N., Calleja, E., (1991) J. Electron. Mater., 20, p. 23Baba, T., Mizuta, M., Fujizawa, T., Yoshino, J., Kukimoto, H., (1989) Jpn. J. Appl. Phys., 28, pp. L891Morgan, T.N., (1991) J. Electron. Mater., 20, p. 6
Raman, infrared and optical spectra of the spin-Peierls compound NaV_2O_5
We have measured polarized spectra of Raman scattering, infrared and optical
transmission of NaV_2O_5 single crystals above the temperature of the
spin-Peierls transition Tsp=35 K. Some of the far-infrared (FIR) phonon lines
are strongly asymmetric, due to the spin-phonon interaction. In addition to the
phonon lines, a broad band was observed in the c(aa)c Raman spectrum and in the
E||a FIR transmission spectrum. A possible origin of these bands is discussed.
The absorption band at 10000 cm-1 1.25 eV is attributed to vanadium d-d
electronic transitions while the absorption edge above 3 eV is supposed to
correspond to the onset of charge-transfer transitions.Comment: 7 figures, 8 page
Effect of bonding of a CO molecule on the conductance of atomic metal wires
We have measured the effect of bonding of a CO molecule on the conductance of
Au, Cu, Pt, and Ni atomic contacts at 4.2 K. When CO gas is admitted to the
metal nano contacts, a conductance feature appears in the conductance histogram
near 0.5 of the quantum unit of conductance, for all metals. For Au, the
intensity of this fractional conductance feature can be tuned with the bias
voltage, and it disappears at high bias voltage (above 200 mV). The
bonding of CO to Au appears to be weakest, and associated with monotomic Au
wire formation.Comment: 6 figure
Hadronization corrections to helicity components of the fragmentation function
In the hadronic decays of Z, gluon emission leads to the appearance of the
longitudinal component of the fragmentation function, F_L. Measurement of F_L
and the transverse component, F_T, could thus provide an insight into the gluon
fragmentation function. However, hadronization corrections at low x can be
significant. Here we present a method of accounting for such corrections, using
the JETSET event generator as illustration.Comment: 11 pages, 5 figure
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