299 research outputs found
Steering effects on growth instability during step-flow growth of Cu on Cu(1,1,17)
Kinetic Monte Carlo simulation in conjunction with molecular dynamics
simulation is utilized to study the effect of the steered deposition on the
growth of Cu on Cu(1,1,17). It is found that the deposition flux becomes
inhomogeneous in step train direction and the inhomogeneity depends on the
deposition angle, when the deposition is made along that direction. Steering
effect is found to always increase the growth instability, with respect to the
case of homogeneous deposition. Further, the growth instability depends on the
deposition angle and direction, showing minimum at a certain deposition angle
off-normal to (001) terrace, and shows a strong correlation with the
inhomogeneous deposition flux. The increase of the growth instability is
ascribed to the strengthened step Erlich Schwoebel barrier effects that is
caused by the enhanced deposition flux near descending step edge due to the
steering effect.Comment: 5 page
d0 Ferromagnetic Interface Between Non-magnetic Perovskites
We use computational and experimental methods to study d0 ferromagnetism at a
charge- imbalanced interface between two perovskites. In SrTiO3/KTaO3
superlattice calculations, the charge imbalance introduces holes in the SrTiO3
layer, inducing a d0 ferromagnetic half-metallic 2D electron gas at the
interface oxygen 2p orbitals. The charge imbalance overrides doping by
vacancies at realistic concentrations. Varying the constituent materials shows
ferromagnetism to be a gen- eral property of hole-type d0 perovskite
interfaces. Atomically sharp epitaxial d0 SrTiO3/KTaO3, SrTiO3 /KNbO3 and
SrTiO3 /NaNbO3 interfaces are found to exhibit ferromagnetic hysteresis at room
temperature. We suggest the behavior is due to high density of states and
exchange coupling at the oxygen t1g band in comparison with the more studied d
band t2g symmetry electron gas.Comment: 5 pages, 5 figure
Effects of deposition dynamics on epitaxial growth
The dynamic effects, such as the steering and the screening effects during
deposition, on an epitaxial growth (Cu/Cu(001)), is studied by kinetic Monte
Carlo simulation that incorporates molecular dynamic simulation to rigorously
take the interaction of the deposited atom with the substrate atoms into
account.
We find three characteristic features of the surface morphology developed by
grazing angle deposition:
(1) enhanced surface roughness, (2) asymmetric mound, and (3) asymmetric
slopes of mound sides.
Regarding their dependence on both deposition angle and substrate
temperature, a reasonable agreement of the simulated results with the previous
experimental ones is found.
The characteristic growth features by grazing angle deposition are mainly
caused by the inhomogeneous deposition flux due to the steering and screening
effects, where the steering effects play the major role rather than the
screening effects.
Newly observed in the present simulation is that the side of mound in each
direction is composed of various facets instead of all being in one selected
mound angle even if the slope selection is attained, and that the slope
selection does not necessarily mean the facet selection.Comment: 9 pages, 10 figure
Vicinal Surfaces, Fractional Statistics and Universality
We propose that the phases of all vicinal surfaces can be characterized by
four fixed lines, in the renormalization group sense, in a three-dimensional
space of coupling constants. The observed configurations of several Si surfaces
are consistent with this picture. One of these fixed lines also describes
one-dimensional quantum particles with fractional exclusion statistics. The
featureless steps of a vicinal surface can therefore be thought of as a
realization of fractional-statistics particles, possibly with additional
short-range interactions.Comment: 6 pages, revtex, 3 eps figures. To appear in Physical Review Letters.
Reference list properly arranged. Caption of Fig. 1 slightly reworded. Fig 3
(in color) is not part of the paper. It complements Fig.
Quasiparticle dynamics in ferromagnetic compounds of the Co-Fe and Ni-Fe systems
We report a theoretical study of the quasiparticle lifetime and the
quasiparticle mean free path caused by inelastic electron-electron scattering
in ferromagnetic compounds of the Co-Fe and Ni-Fe systems. The study is based
on spin-polarized calculations, which are performed within the
approximation for equiatomic and Co- and Ni-rich compounds, as well as for
their constituents. We mainly focus on the spin asymmetry of the quasiparticle
properties, which leads to the spin-filtering effect experimentally observed in
spin-dependent transport of hot electrons and holes in the systems under study.
By comparing with available experimental data on the attenuation length, we
estimate the contribution of the inelastic mean free path to the latter.Comment: 10 pages, 10 figure
Opportunities and challenges for spintronics
This is the author accepted manuscript. The final version is available from EDP Sciences via the DOI in this recordConventional electronics use the flow of electric charges and are based on standard semiconductors. Spintronic devices exploit the electrons- spin to generate and control currents and to combine electric and magnetic signals. Today there is a strong effort worldwide to integrate spintronic devices with standard CMOS technology towards hybrid spin-CMOS chips, offering advantages in terms of power consumption, compactness, and speed. Recent results (from SAMSUNG [1], TSMC [2], etc.) confirm the merit of this approach
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Theory of spin-polarized bipolar transport in magnetic p-n junctions
The interplay between spin and charge transport in electrically and
magnetically inhomogeneous semiconductor systems is investigated theoretically.
In particular, the theory of spin-polarized bipolar transport in magnetic p-n
junctions is formulated, generalizing the classic Shockley model. The theory
assumes that in the depletion layer the nonequilibrium chemical potentials of
spin up and spin down carriers are constant and carrier recombination and spin
relaxation are inhibited. Under the general conditions of an applied bias and
externally injected (source) spin, the model formulates analytically carrier
and spin transport in magnetic p-n junctions at low bias. The evaluation of the
carrier and spin densities at the depletion layer establishes the necessary
boundary conditions for solving the diffusive transport equations in the bulk
regions separately, thus greatly simplifying the problem. The carrier and spin
density and current profiles in the bulk regions are calculated and the I-V
characteristics of the junction are obtained. It is demonstrated that spin
injection through the depletion layer of a magnetic p-n junction is not
possible unless nonequilibrium spin accumulates in the bulk regions--either by
external spin injection or by the application of a large bias. Implications of
the theory for majority spin injection across the depletion layer, minority
spin pumping and spin amplification, giant magnetoresistance, spin-voltaic
effect, biasing electrode spin injection, and magnetic drift in the bulk
regions are discussed in details, and illustrated using the example of a GaAs
based magnetic p-n junction.Comment: 36 pages, 11 figures, 2 table
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