9,032 research outputs found
Mathematical model for a radioactive marker in silicide formation
A mathematical model is constructed to interpret the profiles of radioactive (^31)Si tracers in a
computer simulation proposed by R. Pretorius and A. P. Botha [Thin Solid Films 91, 99 (1982)].
This model assumes that only Si moves in the silicide, that the Si moves interstitially and
convectively, and that the moving Si can exchange sites with the stationary Si in the silicide lattice.
An analytical solution of this model is given and confirms the published computer simulation
data. However, it is shown that the model is physically inadequate. Solutions of another model
which assumes that metal, instead of Si, is the moving species for silicide formation (either
interstitially, or substitutionally, or both), with self-diffusion of (^31)Si in the silicide during silicide
formation. Almost all the experimental data can be fitted by solutions of both models. These
examples demonstrate that radioactive tracer experiments alone are insufficient to determine the
moving species when a solid binary compound film forms by reaction of adjacent elemental layers.
Both inert marker and tracer data are needed to identify the moving species and the mechanisms
A structure marker study for Pd_2Si formation: Pd moves in epitaxial Pd_2Si
A sample with the configuration Si (111)/single crystalline Pd_2Si/polycrystalline Pd_2Si/Pd is used to study the dominant moving species during subsequent Pd_2Si formation by annealing at 275 °C. The interface between monocrystalline and polycrystalline Pd_2Si is used as a marker to monitor the dominant moving species. The result shows that Pd is the dominant moving species in the monocrystal
Finite-Size Scaling in Two-dimensional Continuum Percolation Models
We test the universal finite-size scaling of the cluster mass order parameter
in two-dimensional (2D) isotropic and directed continuum percolation models
below the percolation threshold by computer simulations. We found that the
simulation data in the 2D continuum models obey the same scaling expression of
mass M to sample size L as generally accepted for isotropic lattice problems,
but with a positive sign of the slope in the ln-ln plot of M versus L. Another
interesting aspect of the finite-size 2D models is also suggested by plotting
the normalized mass in 2D continuum and lattice bond percolation models, versus
an effective percolation parameter, independently of the system structure (i.e.
lattice or continuum) and of the possible directions allowed for percolation
(i.e. isotropic or directed) in regions close to the percolation thresholds.
Our study is the first attempt to map the scaling behaviour of the mass for
both lattice and continuum model systems into one curve.Comment: 9 pages, Revtex, 2 PostScript figure
Model for Anisotropic Directed Percolation
We propose a simulation model to study the properties of directed percolation
in two-dimensional (2D) anisotropic random media. The degree of anisotropy in
the model is given by the ratio between the axes of a semi-ellipse
enclosing the bonds that promote percolation in one direction. At percolation,
this simple model shows that the average number of bonds per site in 2D is an
invariant equal to 2.8 independently of . This result suggests that
Sinai's theorem proposed originally for isotropic percolation is also valid for
anisotropic directed percolation problems. The new invariant also yields a
constant fractal dimension for all , which is the same
value found in isotropic directed percolation (i.e., ).Comment: RevTeX, 9 pages, 3 figures. To appear in Phys.Rev.
CO2 emissions from Biofuels and District Heating in Zero Emission Buildings (ZEB)
Carbon Debt and Carbon Payback time have recently been introduced into the Norwegian debate on greenhouse gas emissions, challenging the established view that Biofuels are carbon neutral. This report demonstrates that these new concepts are primarily a reflection of how the temporal system boundaries for CO2 emissions from biofuels are viewed. In a short term perspective it is possible that CO2 emissions from biofuels may have a non-zero short term climate effect, even though biofuels will be carbon neutral on the order of a century. Two alternative, more useful new concepts for analysis of climate effects of biofuels are described in this report: The Global Warming Potential (GWP) index for biofuels and the Albedo effect. In particular, one should be aware that the Albedo effect may overshadow the effects of CO2 emissions from biofuels. Finally, the report describes how waste incineration based District Heating systems may have greenhouse gas emissions on the same order as natural gas.publishedVersio
Observing Coherence Effects in an Overdamped Quantum System
It is usually considered that the spectrum of an optical cavity coupled to an
atomic medium does not exhibit a normal-mode splitting unless the system
satisfies the strong coupling condition, meaning the Rabi frequency of the
coherent coupling exceeds the decay rates of atom and cavity excitations. Here
we show that this need not be the case, but depends on the way in which the
coupled system is probed. Measurements of the reflection of a probe laser from
the input mirror of an overdamped cavity reveal an avoided crossing in the
spectrum which is not observed when driving the atoms directly and measuring
the Purcell-enhanced cavity emission. We understand these observations by
noting a formal correspondence with electromagnetically-induced transparency of
a three-level atom in free space, where our cavity acts as the absorbing medium
and the coupled atoms play the role of the control field
Exploring effective co-teaching models
The research question addressed in this project was, what is an effective co-teaching model between mainstream and special education teachers and the impact on the kindergarten classroom environment? It documents one teacher\u27s exploration of the five models of co-teaching. The author documents the benefits of co-teaching and full inclusion. She documents details of the surveys, lesson plans, and outcomes of the three models of co-teaching that were used in two kindergarten classrooms. She concludes that: (1) it is important to gather background information from participating colleagues, (2) students with disabilities and at risk learners benefit most from co-teaching, and (3) students\u27 abilities determine which co-teaching model is effective
Improvement of thermally formed nickel silicide by ion irradiation
A significant improvement of the lateral uniformity of thermally formed Ni_(2)Si layers has been observed after low‐dose (10^(13)~3 × 10^(14) ion/cm^2) Xe irradiation of an As‐deposited Ni film. Measurements have also been made on samples that contained a thin impurity layer formed intentionally between the silicon substrate and the evaporated nickel film. The impurity layer was thick enough to prevent thermal silicide formation in unirradiated samples, but in irradiated samples, the silicide formation was not prevented. Similar results were obtained for As implantations. We attribute this effect to ion mixing of the interfacial layer. These results demonstrate that a low‐dose irradiation can render the process of silicide formation by thermal annealing more tolerant to interfacial impurities. The concept is of potential significance to VLSI technology
Sensitivity limits of a Raman atom interferometer as a gravity gradiometer
We evaluate the sensitivity of a dual cloud atom interferometer to the
measurement of vertical gravity gradient. We study the influence of most
relevant experimental parameters on noise and long-term drifts. Results are
also applied to the case of doubly differential measurements of the
gravitational signal from local source masses. We achieve a short term
sensitivity of 3*10^(-9) g/Hz^(-1/2) to differential gravity acceleration,
limited by the quantum projection noise of the instrument. Active control of
the most critical parameters allows to reach a resolution of 5*10^(-11) g after
8000 s on the measurement of differential gravity acceleration. The long term
stability is compatible with a measurement of the gravitational constant G at
the level of 10^(-4) after an integration time of about 100 hours.Comment: 19 pages, 20 figure
- …