221 research outputs found
Force Chain Evolution in a Two-Dimensional Granular Packing Compacted by Vertical Tappings
We experimentally study the statistics of force-chain evolution in a
vertically-tapped two-dimensional granular packing by using photoelastic disks.
In this experiment, the tapped granular packing is gradually compacted. During
the compaction, the isotropy of grain configurations is quantified by measuring
the deviator anisotropy derived from fabric tensor, and then the evolution of
force-chain structure is quantified by measuring the interparticle forces and
force-chain orientational order parameter. As packing fraction increases, the
interparticle force increases and finally saturates to an asymptotic value.
Moreover, the grain configurations and force-chain structures become
isotropically random as the tapping-induced compaction proceeds. In contrast,
the total length of force chains remains unchanged. From the correlations of
those parameters, we find two relations: (i) a positive correlation between the
isotropy of grain configurations and the disordering of force-chain
orientations, and (ii) a negative correlation between the increasing of
interparticle forces and the disordering of force-chain orientations. These
relations are universally held regardless of the mode of particle motions
with/without convection
X-ray method to study temperature-dependent stripe domains in MnAs/GaAs(001)
MnAs films grown on GaAs (001) exhibit a progressive transition between
hexagonal (ferromagnetic) and orthorhombic (paramagnetic) phases at wide
temperature range instead of abrupt transition during the first-order phase
transition. The coexistence of two phases is favored by the anisotropic strain
arising from the constraint on the MnAs films imposed by the substrate. This
phase coexistence occurs in ordered arrangement alternating periodic terrace
steps. We present here a method to study the surface morphology throughout this
transition by means of specular and diffuse scattering of soft x-rays, tuning
the photon energy at the Mn 2p resonance. The results show the long-range
arrangement of the periodic stripe-like structure during the phase coexistence
and its period remains constant, in agreement with previous results using other
techniques.Comment: 4 pages, 4 figures, submitted to Applied Physics Letter
Magnetic reconfiguration of MnAs/GaAs(001) observed by Magnetic Force Microscopy and Resonant Soft X-ray Scattering
We investigated the thermal evolution of the magnetic properties of MnAs
epitaxial films grown on GaAs(001) during the coexistence of
hexagonal/orthorhombic phases using polarized resonant (magnetic) soft X-ray
scattering and magnetic force microscopy. The results of the diffuse satellite
X-ray peaks were compared to those obtained by magnetic force microscopy and
suggest a reorientation of ferromagnetic terraces as temperature rises. By
measuring hysteresis loops at these peaks we show that this reorientation is
common to all ferromagnetic terraces. The reorientation is explained by a
simple model based on the shape anisotropy energy. Demagnetizing factors were
calculated for different configurations suggested by the magnetic images. We
noted that the magnetic moments flip from an in-plane mono-domain orientation
at lower temperatures to a three-domain out-of-plane configuration at higher
temperatures. The transition was observed when the ferromagnetic stripe width L
is equal to 2.9 times the film thickness d. This is in good agreement with the
expected theoretical value of L = 2.6d.Comment: 16 pages in PD
Giant Effective G -factor In Pbx Eu1-x Te Epitaxial Films
We investigated Pbx Eu1-x Te films with x≤0.2 by magneto-optical measurements. For x∼0.01, the optical emission is similar to high quality EuTe films with two narrow lines attributed to excitonic recombinations associated with magnetic polarons. For increasing x, the emission becomes dominated by a broader lower energy band, which is very efficient as compared to the binary emission. The magneto-optical properties of the ternary films show various similarities with EuTe results, such as quenchings at similar temperatures and magnetic fields. Most remarkably, they also present a giant effective g -factor that makes this material a strong candidate for spintronic applications. © 2008 American Institute of Physics.933Mauger, A., Godart, C., (1986) Phys. Rep., 141, p. 51Masset, F., (1971) Phys. Rev. B, 3, p. 2364Akimoto, R., Kobayashi, M., Suzuki, T., (1994) J. Phys. Soc. Jpn., 63, p. 4616Heiss, W., Kirchschlager, R., Springholz, G., Chen, Z., Debnath, M., Oka, Y., (2004) Phys. Rev. B, 70, p. 035209Heiss, W., Prechtl, G., Springholz, G., (2001) Phys. Rev. B, 63, p. 165323Heiss, W., Prechtl, G., Springholz, G., (2001) Appl. Phys. Lett., 78, p. 3484Krenn, H., Herbst, W., Pascher, H., Ueta, Y., Springholz, G., Bauer, G., (1999) Phys. Rev. B, 60, p. 8117Springholz, G., Schwarzi, T., Aigle, M., Pascher, H., Heiss, W., (2000) Appl. Phys. Lett., 76, p. 1807Nolting, W., Mathi Jaya, S., Rex, S., (1996) Phys. Rev. B, 54, p. 14455Umehara, M., (2003) Phys. Rev. B, 68, p. 19320
Phonon Side Bands In The Optical Emission Of Zinc-blende-type Semiconductors
A model for the LO-phonon-related structure observed in the luminescence above the gap of InP is presented. The corresponding exciton-phonon quasiparticle spectrum is calculated for zinc-blende-type semiconductors using a Green's function formalism. It is shown that resonances may appear due to the interaction of the exciton continuum with excitations involving a 1s-exciton state plus an LO phonon. The corresponding electron-hole nonequilibrium distribution function is derived by solving the master equation, which depends on the rate of scattering by acoustic and optical phonons. These results enable the evaluation of the dependence of the luminescence intensity on light frequency and temperature. Explicit calculations are presented for InP, CdTe, and GaAs. In the case of InP they reproduce rather well the experimental luminescence profile observed above the gap and its dependence on temperature. The calculations explain why a similar structure has not been observed in the luminescence spectra of GaAs and CdTe. © 1993 The American Physical Society.4885187519
E 1 Gap Of Wurtzite Inas Single Nanowires Measured By Means Of Resonant Raman Spectroscopy
Indium arsenide nanowires were synthesized with an intermixing of wurtzite and zincblende structure by chemical beam epitaxy with the vapor-liquid-solid mechanism. Resonant Raman spectroscopy of the transverse optical phonon mode at 215cm -1 reveals an E 1 gap of 2.47 eV which is assigned to the electronic band gap at the A point in the indium arsenide wurtzite phase. © 2011 American Institute of Physics.1399473474 Int. Union Pure Appl. Phys. (IUPAP C8 Comm.),Korean Ministry of Education, Science and Technology,Seoul Metropolitan Government,Office of Naval Research Global,Korea Tourism OrganizationDick, K.A., (2008) Prog. Cryst. Growth Charact. Mater., 54, pp. 138-173Milnes, A.G., Polyakov, A.Y., (1993) Mater. Sci. Eng. B, 18, pp. 237-259Dayeh, S.A., Susac, D., Kavanagh, K.L., Yu, E.T., Wang, D., (2009) Adv. Mater., 19, pp. 2102-2108Cardona, M., (1961) J. Appl. Phys., 32 (SUPPL.), pp. 2151-2155Antoci, S., Reguzzoni, E., Samoggia, G., (1970) Phys. Rev. Lett., 24, pp. 1304-1307Arguello, C.A., Rousseau, D.L., Porto, S.P.S., (1969) Phys. Rev., 181, pp. 1351-136
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