834 research outputs found
Growth of Inclined GaAs Nanowires by Molecular Beam Epitaxy: Theory and Experiment
The growth of inclined GaAs nanowires (NWs) during molecular beam epitaxy (MBE) on the rotating substrates is studied. The growth model provides explicitly the NW length as a function of radius, supersaturations, diffusion lengths and the tilt angle. Growth experiments are carried out on the GaAs(211)A and GaAs(111)B substrates. It is found that 20° inclined NWs are two times longer in average, which is explained by a larger impingement rate on their sidewalls. We find that the effective diffusion length at 550°C amounts to 12 nm for the surface adatoms and is more than 5,000 nm for the sidewall adatoms. Supersaturations of surface and sidewall adatoms are also estimated. The obtained results show the importance of sidewall adatoms in the MBE growth of NWs, neglected in a number of earlier studies
In a nanoscience lab
The production, observation and manipulation of very small objects is a tour
de force, but these objects, which could infiltrate anywhere without being
seen, may arouse suspicion. To assess the situation at best, we describe the
activity of a nanoscience research institution, some of the methods used there,
the spirit of its researchers and their attitude towards risk.Comment: article accept\'e pour publication dans les C.R. Physique. El\'ement
d'un dossier 'Nanosciences et nanotechnologies: esp\'erances et
inqui\'etudes". D'autres articles de ce dossier, ainsi que la version
fran\c{c}aise de cet articles, seront \'egalement soumis \`a HA
The role of angular momentum conservation law in statistical mechanics
Within the limits of Khinchin ideas [A.Y. Khinchin, Mathematical Foundation of Statistical Mechanics. NY, Ed. Dover, 1949] the importance of momentum and angular momentum conservation laws was analyzed for two cases: for uniform magnetic field and when magnetic field is absent. The law of momentum conservation does not change the density of probability distribution in both cases, just as it is assumed in the conventional theory. It is shown that in systems where the kinetic energy depends only on particle momenta canonically conjugated with Cartesian coordinates being their diagonal quadric form,the angular momentum conservation law changes the density of distribution of the system only in case the full angular momentum of a system is not equal to zero. In the gas of charged particles in a uniform magnetic field the density of distribution also varies if the angular momentum is zero [see Dubrovskii I.M., Condensed Matter Physics, 2206, 9, 23]. Two-dimensional gas of charged particles located within a section of an endless strip filled with gas in magnetic field is considered. Under such conditions the angular momentum is not conserved. Directional particle flows take place close to the strip boundaries, and, as a consequence, the phase trajectory of the considered set of particles does not remain within the limited volume of the phase space. In order to apply a statistical thermodynamics method, it was suggested to consider near-boundary trajectories relative to a reference system that moves uniformly. It was shown that if the diameter of an orbit having average thermal energy is much smaller than a strip width, the corrections to thermodynamic functions are small depending on magnetic field. Only the average velocity of near-boundary particles that form near-boundary electric currents creating the paramagnetic moment turn out to be essential
Dnevnik istorkia S. A. Piontkovskogo
https://scholarship.richmond.edu/bookshelf/1099/thumbnail.jp
Damping of field-induced chemical potential oscillations in ideal two-band compensated metals
The field and temperature dependence of the de Haas-van Alphen oscillations
spectrum is studied for an ideal two-dimensional compensated metal. It is shown
that the chemical potential oscillations, involved in the frequency
combinations observed in the case of uncompensated orbits, are strongly damped
and can even be suppressed when the effective masses of the electron- and
hole-type orbits are the same. When magnetic breakdown between bands occurs,
this damping is even more pronounced and the Lifshits-Kosevich formalism
accounts for the data in a wide field range.Comment: 11 pages, 10 figures, to appear in PR
Frequency combinations in the magnetoresistance oscillations spectrum of a linear chain of coupled orbits with a high scattering rate
The oscillatory magnetoresistance spectrum of the organic metal
(BEDO)Ni(CN)3CH(OH) has been studied up to 50 T, in
the temperature range from 1.5 K to 4.2 K. In high magnetic field, its Fermi
surface corresponds to a linear chain of quasi-two-dimensional orbits coupled
by magnetic breakdown (MB). The scattering rate consistently deduced from the
data relevant to the basic and the MB-induced orbits is very
large which points to a significant reduction of the chemical potential
oscillation. Despite of this feature, the oscillations spectrum exhibits many
frequency combinations. Their effective masses and (or) Dingle temperature are
not in agreement with either the predictions of the quantum interference model
or the semiclassical model of Falicov and Stachowiak.Comment: to be published in Eur. Phys. J. B (2007
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