1,579 research outputs found
Identification of the major cause of endemically poor mobilities in SiC/SiO2 structures
Materials with good carrier mobilities are desired for device applications,
but in real devices the mobilities are usually limited by the presence of
interfaces and contacts. Mobility degradation at semiconductor-dielectric
interfaces is generally attributed to defects at the interface or inside the
dielectric, as is the case in Si/SiO2 structures, where processing does not
introduce detrimental defects in the semiconductor. In the case of SiC/SiO2
structures, a decade of research focused on reducing or passivating interface
and oxide defects, but the low mobilities have persisted. By invoking
theoretical results and available experimental evidence, we show that thermal
oxidation generates carbon di-interstitial defects inside the semiconductor
substrate and that they are a major cause of the poor mobility in SiC/SiO2
structures
Characteristics and Origins of Modern and Enduring Japanese Managerial Practice
Japan was transformed after World War II into an industrial powerhouse. The combination of strategic support from the West, together with a unique set of cultural factors which manifest themselves in the corporate management culture, left many Western managers in awe at what Japan could accomplish in such a short period. Unfortunately the same factors that enabled Japan to become so strong also became impediments to Japanese organizations as globalization develop. Japan addressed these new trends and made efforts towards conforming to new realities; however venerated traditionally-conservative organizations which endured for many years did little to change these managerial practices
Variability of structural and electronic properties of bulk and monolayer Si2Te3
Since the emergence of monolayer graphene as a promising two-dimensional
material, many other monolayer and few-layer materials have been investigated
extensively. An experimental study of few-layer Si2Te3 was recently reported,
showing that the material has diverse properties for potential applications in
Si-based devices ranging from fully integrated thermoelectrics to
optoelectronics to chemical sensors. This material has a unique layered
structure: it has a hexagonal closed-packed Te sublattice, with Si dimers
occupying octahedral intercalation sites. Here we report a theoretical study of
this material in both bulk and monolayer form, unveiling a fascinating array of
diverse properties arising from reorientations of the silicon dimers between
planes of Te atoms. The lattice constant varies up to 5% and the band gap
varies up to 40% depending on dimer orientations. The monolayer band gap is 0.4
eV larger than the bulk-phase value for the lowest-energy configuration of Si
dimers. These properties are, in principle, controllable by temperature and
strain, making Si2T3 a promising candidate material for nanoscale mechanical,
optical, and memristive devices.Comment: 9 pages, 4 figure
Control of Seismic Response of Structures
Safety requirements for structures built in seismic regions have led to techniques for absorbing the energy induced to these structures by earthquakes. Passive isolation systems such as base isolators are suitable for low-rise structures but they provide only a partial solution to the problem. This paper presents three active control techniques for reducing the dynamic response of machine supporting foundations. The concept of active control is discussed and various control strategies are presented. The active tendon system (ATS), active mass damper (AMD), and active base control (ABC) mechanisms are examined. Both optimal and non-optimal control algorithms are described and numerical simulations are performed. It is shown that active control can reduce the dynamic response of turbomachines and their foundations under both normal operation, and emergency conditions such as earthquakes
Mapping the wavefunction of transition metal acceptor states in the GaAs surface
We utilize a single atom substitution technique with spectroscopic imaging in
a scanning tunneling microscope (STM) to visualize the anisotropic spatial
structure of magnetic and non-magnetic transition metal acceptor states in the
GaAs (110) surface. The character of the defect states play a critical role in
the properties of the semiconductor, the localization of the states influencing
such things as the onset of the metal-insulator transition, and in dilute
magnetic semiconductors the mechanism and strength of magnetic interactions
that lead to the emergence of ferromagnetism. We study these states in the GaAs
surface finding remarkable similarities between the shape of the acceptor state
wavefunction for Mn, Fe, Co and Zn dopants, which is determined by the GaAs
host and is generally reproduced by tight binding calculations of Mn in bulk
GaAs [Tang, J.M. & Flatte, M.E., Phys. Rev. Lett. 92, 047201 (2004)]. The
similarities originate from the antibonding nature of the acceptor states that
arise from the hybridization of the impurity d-levels with the host. A second
deeper in-gap state is also observed for Fe and Co that can be explained by the
symmetry breaking of the surface.Comment: 19 pages, 6 figure
Spin-dependent resonant tunneling through quantum-well states in magnetic metallic thin films
Quantum-well (QW) states in {\it nonmagnetic} metal layers contained in
magnetic multilayers are known to be important in spin-dependent transport, but
the role of QW states in {\it magnetic} layers remains elusive. Here we
identify the conditions and mechanisms for resonant tunneling through QW states
in magnetic layers and determine candidate structures. We report
first-principles calculations of spin-dependent transport in epitaxial
Fe/MgO/FeO/Fe/Cr and Co/MgO/Fe/Cr tunnel junctions. We demonstrate the
formation of sharp QW states in the Fe layer and show discrete conductance
jumps as the QW states enter the transport window with increasing bias. At
resonance, the current increases by one to two orders of magnitude. The
tunneling magnetoresistance ratio is several times larger than in simple spin
tunnel junctions and is positive (negative) for majority- (minority-) spin
resonances, with a large asymmetry between positive and negative biases. The
results can serve as the basis for novel spintronic devices.Comment: 4 figures in 5 eps file
Atomic-Scale Dynamics of the Formation and Dissolution of Carbon Clusters in SiO2
Oxidation of SiC produces SiO2 while CO is released. A `reoxidation' step at
lower temperatures is, however, necessary to produce high-quality SiO2. This
step is believed to cleanse the oxide of residual C without further oxidation
of the SiC substrate. We report first-principles calculations that describe the
nucleation and growth of O-deficient C clusters in SiO2 under oxidation
conditions, fed by the production of CO at the advancing interface, and their
gradual dissolution by the supply of O under reoxidation conditions. We predict
that both CO and CO2 are released during both steps.Comment: RevTex, 4 pages, 2 ps figures, to appear in Phys. Rev. Lett. (June
25, 2001
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