193 research outputs found
Impurity-induced diffusion bias in epitaxial growth
We introduce two models for the action of impurities in epitaxial growth. In
the first, the interaction between the diffusing adatoms and the impurities is
``barrier''-like and, in the second, it is ``trap''-like. For the barrier
model, we find a symmetry breaking effect that leads to an overall down-hill
current. As expected, such a current produces Edwards-Wilkinson scaling. For
the trap model, no symmetry breaking occurs and the scaling behavior appears to
be of the conserved-KPZ type.Comment: 5 pages(with the 5 figures), latex, revtex3.0, epsf, rotate, multico
Pathway to the PiezoElectronic Transduction Logic Device
The information age challenges computer technology to process an
exponentially increasing computational load on a limited energy budget - a
requirement that demands an exponential reduction in energy per operation. In
digital logic circuits, the switching energy of present FET devices is
intimately connected with the switching voltage, and can no longer be lowered
sufficiently, limiting the ability of current technology to address the
challenge. Quantum computing offers a leap forward in capability, but a clear
advantage requires algorithms presently developed for only a small set of
applications. Therefore, a new, general purpose, classical technology based on
a different paradigm is needed to meet the ever increasing demand for data
processing.Comment: in Nano Letters (2015
Shape Transition in the Epitaxial Growth of Gold Silicide in Au Thin Films on Si(111)
Growth of epitaxial gold silicide islands on bromine-passivated Si(111)
substrates has been studied by optical and electron microscopy, electron probe
micro analysis and helium ion backscattering. The islands grow in the shape of
equilateral triangles up to a critical size beyond which the symmetry of the
structure is broken, resulting in a shape transition from triangle to
trapezoid. The island edges are aligned along directions. We have
observed elongated islands with aspect ratios as large as 8:1. These islands,
instead of growing along three equivalent [110] directions on the Si(111)
substrate, grow only along one preferential direction. This has been attributed
to the vicinality of the substrate surface.Comment: revtex version 3.0, 11 pages 4 figures available on request from
[email protected] - IP/BBSR/93-6
Te covered Si(001): a variable surface reconstruction
At a given temperature, clean and adatom covered silicon surfaces usually
exhibit well-defined reconstruction patterns. Our finite temperature ab-initio
molecular dynamics calculations show that the tellurium covered Si(001) surface
is an exception. Soft longitudinal modes of surface phonons due to the strongly
anharmonic potential of the bridged tellurium atoms prevent the reconstruction
structure from attaining any permanent, two dimensional periodic geometry. This
explains why experiments attempting to find a definite model for the
reconstruction have reached conflicting conclusions.Comment: 4 pages, 3 gif figure
Reversed anisotropies and thermal contraction of FCC (110) surfaces
The observed anisotropies of surface vibrations for unreconstructed FCC metal
(110) surfaces are often reversed from the "common sense" expectation. The
source of these reversals is investigated by performing ab initio density
functional theory calculations to obtain the surface force constant tensors for
Ag(110), Cu(110) and Al(110). The most striking result is a large enhancement
in the coupling between the first and third layers of the relaxed surface,
which strongly reduces the amplitude of out-of-plane vibrations of atoms in the
first layer. This also provides a simple explanation for the thermal
contraction of interlayer distances. Both the anisotropies and the thermal
contraction arise primarily as a result of the bond topology, with all three
(110) surfaces showing similar behavior.Comment: 13 pages, in revtex format, plus 1 postscript figur
Towards the fabrication of phosphorus qubits for a silicon quantum computer
The quest to build a quantum computer has been inspired by the recognition of
the formidable computational power such a device could offer. In particular
silicon-based proposals, using the nuclear or electron spin of dopants as
qubits, are attractive due to the long spin relaxation times involved, their
scalability, and the ease of integration with existing silicon technology.
Fabrication of such devices however requires atomic scale manipulation - an
immense technological challenge. We demonstrate that it is possible to
fabricate an atomically-precise linear array of single phosphorus bearing
molecules on a silicon surface with the required dimensions for the fabrication
of a silicon-based quantum computer. We also discuss strategies for the
encapsulation of these phosphorus atoms by subsequent silicon crystal growth.Comment: To Appear in Phys. Rev. B Rapid Comm. 5 pages, 5 color figure
Vicinal Surface with Langmuir Adsorption: A Decorated Restricted Solid-on-solid Model
We study the vicinal surface of the restricted solid-on-solid model coupled
with the Langmuir adsorbates which we regard as two-dimensional lattice gas
without lateral interaction. The effect of the vapor pressure of the adsorbates
in the environmental phase is taken into consideration through the chemical
potential. We calculate the surface free energy , the adsorption coverage
, the step tension , and the step stiffness by
the transfer matrix method combined with the density-matrix algorithm. Detailed
step-density-dependence of and is obtained. We draw the roughening
transition curve in the plane of the temperature and the chemical potential of
adsorbates. We find the multi-reentrant roughening transition accompanying the
inverse roughening phenomena. We also find quasi-reentrant behavior in the step
tension.Comment: 7 pages, 12 figures (png format), RevTeX 3.1, submitted to Phys. Rev.
Transverse-spin dependence of the p-p total cross section ΔσT from 0.8 to 2.5 GeV/c
The difference ΔσT=σ(↓↑)-σ(↑↑) between the proton-proton total cross sections for protons in pure transverse-spin states, was measured at incident momenta 0.8 to 2.5 GeV/c in experiments performed at the Los Alamos Clinton P. Anderson Meson Physics Facility and the Argonne Zero Gradient Synchrotron. In agreement with other data, peaks were observed at center-of-mass energies of 2.14 and 2.43 GeV/c2, where 1D2 and 1G4 dibaryon resonances have been proposed
Structure determination of the (1×2) and (1×3) reconstructions of Pt(110) by low-energy electron diffraction
The atomic geometry of the (1×2) and (1×3) structures of the Pt(100) surface has been determined from a low-energy electron-diffraction intensity analysis. Both structures are found to be of the missing-row type, consisting of (111) microfacets, and with similar relaxations in the subsurface layers. In both reconstructions the top-layer spacing is contracted by approximately 20% together with a buckling of about 0.17 Å in the third layer and a small lateral shift of about 0.04 Å in the second layer. Further relaxations down to the fourth layer were detectable. The surface relaxations correspond to a variation of interatomic distances, ranging from -7% to +4%, where in general a contraction of approximately 3% for the distances parallel to the surface occurs. The Pendry and Zanazzi-Jona R factors were used in the analysis, resulting in a minimum value of RP=0.36 and RZJ=0.26 for 12 beams at normal incidence for the (1×2) structure, and similar agreement for 19 beams of the (1×3) structure. The (1×3) structure has been reproducibly obtained after heating the crystal in an oxygen atmosphere of 5×10-6 mbar at 1200 K for about 30 min and could be removed by annealing at 1800 K for 45 min after which the (1×2) structure appeared again. Both reconstructed surfaces are clean within the detection limits of the Auger spectrometer. CO adsorption lifts the reconstruction in both structures. After desorption at 500 K the initial structures appear again, indicating that at least one of the reconstructions does not represent the equilibrium structure of the clean surface and may be stabilized by impurities
A phase II study of sequential 5-fluorouracil, epirubicin and cyclophosphamide (FEC) and paclitaxel in advanced breast cancer (Protocol PV BC 97/01)
Sequential administration of the association of 5-fluorouracil, epirubicin and cyclophosphamide (FEC) and paclitaxel could be better tolerated than the association of an anthracycline and paclitaxel while having a similar antitumour effect. 69 patients with advanced breast cancer previously untreated with anthracyclines or paclitaxel entered a phase II multicentre study in which FEC was followed by paclitaxel. Both regimens were administered 4 times every 21 days. The median follow-up is 20 months and 38/69 patients have died. Grade III–IV toxicity was acceptable. Leukopenia occurred in 26% of patients, thrombocytopenia in 2% and anaemia in 4%. One patient had reversible heart failure during FEC therapy. Peripheral neuropathy and arthralgia-myalgia occurred in 9% and 4% of patients, respectively and one patient had respiratory hypersensitivity during paclitaxel treatment. 9 patients did not complete therapy because of: treatment refusal (n= 1), cardiac toxicity (n= 1), early death during FEC chemotherapy (n= 1), major protocol violations (n= 4), hypersensitivity reaction (n= 1) and early death during paclitaxel chemotherapy (n= 1). The overall response rate was 65% (95% CI = 53–76), and 7% of patients had stable disease. Therapy was defined as having failed in 28% of patients because they were not evaluable (13%) or had progressive disease (15%). The median time to progression and survival are 13.2 and 23.5 months, respectively. Sequential FEC-paclitaxel is a suitable strategy for patients with metastatic breast cancer who have not been previously treated with anthracyclines and/or taxanes. In fact, it avoids major haematologic toxicity and has a good antitumour effect. © 2001 Cancer Research Campaign http://www.bjcancer.co
- …