5,301 research outputs found
Convection and chemistry effects in CVD: A 3-D analysis for silicon deposition
The computational fluid dynamics code FLUENT has been adopted to simulate the entire rectangular-channel-like (3-D) geometry of an experimental CVD reactor designed for Si deposition. The code incorporated the effects of both homogeneous (gas phase) and heterogeneous (surface) chemistry with finite reaction rates of important species existing in silane dissociation. The experiments were designed to elucidate the effects of gravitationally-induced buoyancy-driven convection flows on the quality of the grown Si films. This goal is accomplished by contrasting the results obtained from a carrier gas mixture of H2/Ar with the ones obtained from the same molar mixture ratio of H2/He, without any accompanying change in the chemistry. Computationally, these cases are simulated in the terrestrial gravitational field and in the absence of gravity. The numerical results compare favorably with experiments. Powerful computational tools provide invaluable insights into the complex physicochemical phenomena taking place in CVD reactors. Such information is essential for the improved design and optimization of future CVD reactors
Conductivity of Silicon Inversion Layers: comparison with and without in-plane magnetic field
A detailed comparison is presented of the temperature dependence of the
conductivity of dilute, strongly interacting electrons in two-dimensional
silicon inversion layers in the metallic regime in the presence and in the
absence of a magnetic field. We show explicitly and quantitatively that a
magnetic field applied parallel to the plane of the electrons reduces the slope
of the conductivity versus temperature curves to near zero over a broad range
of electron densities extending from to deep in the metallic regime where
the high field conductivity is on the order of . The strong
suppression (or "quenching") of the metallic behavior by a magnetic field sets
an important constraint on theory.Comment: 4 pages, 4 figure
Plasma-Like Negative Capacitance in Nano-Colloids
A negative capacitance has been observed in a nano-colloid between 0.1 and
10^-5 Hz. The response is linear over a broad range of conditions. The
low-omega dispersions of both the resistance and capacitance are consistent
with the free-carrier plasma model, while the transient behavior demonstrates
an unusual energy storage mechanism. A collective excitation, therefore, is
suggested.Comment: 3 pages, 3 figure
Estado nutricional e teor de glicosídeos cianogênicos em plantas de seringueira.
A presença de altos teores de glicosídeos cianogênicos pode predispor a planta ao secamento de painel. O objetivo deste trabalho foi verificar a influência do estado nutricional na formação dos glicosídeos cianogênicos na seringueira, utilizando dois experimentos: a) jardim clonal com copa de híbridos de Hevea pauciflora e H. guianensis var. marginata (CPAA C 01) e de H. rigidifolia (CPAA C 81); e b) viveiro com H. brasiliensis. No jardim clonal foram coletadas ao acaso, folhas de 23 plantas, enquanto no viveiro, foi realizado experimento em delineamento inteiramente casualisado com cinco repetições, com tratamentos em esquema fatorial 2 x 4, com duas doses de nitrogênio - N (0,8 e 1,6%, fonte: uréia) e quatro de manganês - Mn (0, 10, 50 e 100 mg kg-1). Na seringueira, independentemente da idade e da espécie de Hevea, os teores foliares de N, Mn e clorofila tiveram correlação positiva com o HCNp das folhas novas e diagnóstico, podendo assim serem utilizados em futuros processos de seleção. Em concentrações baixas de N (0,8%), as doses de Mn influenciaram a absorção de N, P, K, Ca, S, Fe e Mn pelas plantas de seringueira (Hevea brasiliensis), na fase de viveiro. Nutritional status and glycoside cyanogenic concentration in rubber tree plants. The presence of high cyanogenic glycosides concentrations may predispose plant to the tapping panel dryness (TPD). The aim of this work was to evaluate the effect of nutritional status in formation of cyanogenic glycosides in rubber tree. Two experiments were carried out: a) clonal nursery with crow clones hybrids of Hevea pauciflora x H. guianensis var. Marginata (CPAA C 01) and H. rigidifolia (CPAA C 81); and b) nursery with H. brasiliensis. In clonal nursery, twenty three foliar samples were collected, while in nursery, the experiment was carried out using a completely randomized design in factorial scheme 2 x 4 with five replicates. Two nitrogen doses (0.8 and 1.6%, urea as source) and four manganese doses (0, 10, 50 and 100 mg kg-1, MnSO4 as source) were used. Regardless of age and species of Hevea, only the N, chlorophyll and Mn concentrations showed relationship with the HCNp in young leaves. These variables should be used in future selection processes. At low N (0.8%) concentration, the Mn doses influenced the N, P, K, Ca, S, Fe and Mn uptake by rubber tree (Hevea brasiliensis) in the nursery condition
Modulation of the high mobility two-dimensional electrons in Si/SiGe using atomic-layer-deposited gate dielectric
Metal-oxide-semiconductor field-effect transistors (MOSFET's) using
atomic-layer-deposited (ALD) AlO as the gate dielectric are fabricated
on the Si/SiGe heterostructures. The low-temperature carrier
density of a two-dimensional electron system (2DES) in the strained Si quantum
well can be controllably tuned from 2.5cm to
4.5cm, virtually without any gate leakage current.
Magnetotransport data show the homogeneous depletion of 2DES under gate biases.
The characteristic of vertical modulation using ALD dielectric is shown to be
better than that using Schottky barrier or the SiO dielectric formed by
plasma-enhanced chemical-vapor-deposition(PECVD).Comment: 3 pages Revtex4, 4 figure
Trust as an antecedent to knowledge sharing in virtual communities of practice
2007-2008 > Academic research: refereed > Publication in refereed journalAccepted ManuscriptPublishe
Quantum oscillations observed in graphene at microwave frequencies
We have measured the microwave conductance of mechanically exfoliated
graphene at frequencies up to 8.5 GHz. The conductance at 4.2 K exhibits
quantum oscillations, and is independent of the frequency
Self-dual Vortices in the Abelian Chern-Simons Model with Two Complex Scalar Fields
Making use of -mapping topological current method, we discuss the
self-dual vortices in the Abelian Chern-Simons model with two complex scalar
fields. For each scalar field, an exact nontrivial equation with a topological
term which is missing in many references is derived analytically. The general
angular momentum is obtained. The magnetic flux which relates the two scalar
fields is calculated. Furthermore, we investigate the vortex evolution
processes, and find that because of the present of the vortex molecule, these
evolution processes is more complicated than the vortex evolution processes in
the corresponding single scalar field model.Comment: 9 pages, no figure
Thermodynamic Study of Excitations in a 3D Spin Liquid
In order to characterize thermal excitations in a frustrated spin liquid, we
have examined the magnetothermodynamics of a model geometrically frustrated
magnet. Our data demonstrate a crossover in the nature of the spin excitations
between the spin liquid phase and the high-temperature paramagnetic state. The
temperature dependence of both the specific heat and magnetization in the spin
liquid phase can be fit within a simple model which assumes that the spin
excitations have a gapped quadratic dispersion relation.Comment: 5 figure
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