1,966 research outputs found
Surfactant controlled growth of GaInP by organometallic vapor phase epitaxy
Journal ArticleThe effect of the surfactant Sb has been studied for GaInP semiconductor alloys grown by organometallic vapor phase epitaxy. Dramatic changes in the optical and electrical properties of GaInP with CuPt ordering have been observed. A small concentration of triethylantimony TESb in the vapor is found to cause Sb to accumulate at the surface. In situ surface photoabsorption analysis indicates that Sb changes the surface bonding by replacing the 1 10 P dimers that are responsible for the formation of the CuPt structure during growth with 1 10 Sb dimers. As a result, the degree of order for the GaInP layers is decreased, as shown by transmission electron diffraction studies. The 20 K photoluminescence spectra show a 131 meV peak energy increase for GaInP layers grown on vicinal substrates when a small amount of Sb Sb/P(v) 4 10 4 is added to the system during growth. The use of surfactants to control specific properties of materials is expected to be a powerful tool for producing complex structures. In this article, the growth of heterostructures by modulating the Sb concentration in the vapor is demonstrated
Adsorption and desorption of the surfactant Sb on GaInP grown by organometallic vapor phase epitaxy
Journal ArticleIt has been determined that ordering has a profound effect on the bandgap energy of many compound semiconductor alloys. Therefore, ordering must be controlled for devices such as solar cells, light emitting diodes and diode lasers. Since ordering depends on the surface properties during organometallic vapor phase epitaxy (OMVPE), the ability to control the surface has been shown to be important for controlling ordering and for producing heterostructures and quantum wells. However, perhaps equally as important as the affect of ordering on the bandgap is the fundamental information that it can provide about the surface during growth. This paper reports on the use of time dependent surface photoabsorption (SPA) measurements to determine the rate of change in the P dimer concentration when TESb is added to and removed from the reactor. In particular, the time constants for the transients are presented and compared with the Langmuir model for adsorption and desorption of the surfactant. Transients in the Sb surface concentration were also indirectly determined from secondary-ion mass spectroscopy (SIMS) measurements on a GaInP heterostructure where TESb was added during growth of one of the layers
The Technology Acceptance Model: Past, Present, and Future
While the technology acceptance model (TAM), introduced in 1986, continues to be the most widely applied theoretical model in the IS field, few previous efforts examined its accomplishments and limitations. This study traces TAM\u27s history, investigates its findings, and cautiously predicts its future trajectory. One hundred and one articles published by leading IS journals and conferences in the past eighteen years are examined and summarized. An open-ended survey of thirty-two leading IS researchers assisted in critically examining TAM and specifying future directions
Calculus of Tangent Sets and Derivatives of Set Valued Maps under Metric Subregularity Conditions
In this paper we intend to give some calculus rules for tangent sets in the
sense of Bouligand and Ursescu, as well as for corresponding derivatives of
set-valued maps. Both first and second order objects are envisaged and the
assumptions we impose in order to get the calculus are in terms of metric
subregularity of the assembly of the initial data. This approach is different
from those used in alternative recent papers in literature and allows us to
avoid compactness conditions. A special attention is paid for the case of
perturbation set-valued maps which appear naturally in optimization problems.Comment: 17 page
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Effect of geometrical constraint condition on the formation of nanoscale twins in the Ni-based metallic glass composite
We investigated the effect of geometrically constrained stress-strain conditions on the formation of nanotwins in -brass phase reinforced Ni59Zr20 Ti16 Si2 Sn3 metallic glass (MG) matrix deformed under macroscopic uniaxial compression. The specific geometrically constrained conditions in the samples lead to a deviation from a simple uniaxial state to a multi-axial stress state, for which nanocrystallization in the MG matrix together with nanoscale twinning of the brass reinforcement is observed in localized regions during plastic flow. The nanocrystals in the MG matrix and the appearance of the twinned structure in the reinforcements indicate that the strain energy is highly confined and the local stress reaches a very high level upon yielding. Both the effective distribution of reinforcements on the strain enhancement of composite and the effects of the complicated stress states on the development of nanotwins in the second-phase brass particles are discussed
Low temperature thermodynamics of charged bosons in a random potential and the specific heat of La_{2-x}Sr_{x}CuO_{4} below Tc
We propose a simple analytical form of the partition function for charged
bosons localised in a random potential and derive the consequent thermodynamics
below the superfluid transition temperature. In the low temperature limit, the
specific heat, C, depends on the localisation length exponent nu: C is linear
for nu1 we find C proportional to T^{1/nu}. This unusual
sub-linear temperature dependence of the specific heat has recently been
observed in La_{2-x}Sr_{x}CuO_{4} below Tc.Comment: Revtex, 6 pages, 4 postscript figure
Valuing lives equally in a benefit-cost analysis of safety projects: a method to reconcile theory and practice
Electronic Correlations Near a Peierls-CDW Transition
Results of a phenomenological Monte carlo calculation for a 2D
electron-phonon Holstein model near a Peierls-CDW transition are presented.
Here the zero Matsubara frequency part of the phonon action is dominant and we
approximated it by a phenomenological form that as an Ising-like Peierls-CDW
transition. The resulting model is studied on a 32 by 32 lattice. The single
particle spectral weight A(k,\omega), the density of states N(\omega), and the
real part of the conductivity \sigma_1(\omega) all show evidence of a pseudogap
which develops in the low-energy electronic degrees of freedom as the
Peierls-CDW transition is approachedComment: 14 pages, 7 figure
D-wave Bose-Einstein condensation and the London penetration depth in superconducting cuprates
We show that bipolaron formation leads to a d-wave Bose-Einstein condensate
in cuprates. It is the bipolaron energy dispersion rather than a particular
pairing interaction which is responsible for the d-wave symmetry. The unusual
low-temperature dependence of the magnetic field penetration depth in cuprates
is explained by the localisation of bosons in the random potential. The
temperature dependence of the penetration depth is linear with positive or
negative slope depending on the random field profile.Comment: 4 pages (RevTeX), 4 figure
A Gaussian Theory of Superfluid--Bose-Glass Phase Transition
We show that gaussian quantum fluctuations, even if infinitesimal, are
sufficient to destroy the superfluidity of a disordered boson system in 1D and
2D. The critical disorder is thus finite no matter how small the repulsion is
between particles. Within the gaussian approximation, we study the nature of
the elementary excitations, including their density of states and mobility edge
transition. We give the gaussian exponent at criticality in 1D and show
that its ratio to of the pure system is universal.Comment: Revtex 3.0, 11 pages (4 figures will be sent through airmail upon
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