7,152 research outputs found
Asymptotic solution of a model for bilayer organic diodes and solar cells
The current voltage characteristics of an organic semiconductor diode made by placing together two materials with dissimilar electron affinities and ionisation potentials is analysed using asymptotic methods. An intricate boundary layer structure is examined. We find that there are three regimes for the total current passing through the diode. For reverse bias and moderate forward bias the dependency of the voltage on the current is similar to the behaviour of conventional inorganic semiconductor diodes predicted by the Shockley equation and are governed by recombination at the interface of the materials. There is then a narrow range of currents where the behaviour undergoes a transition. Finally for large forward bias the behaviour is different with the current being linear in voltage and is primarily controlled by drift of charges in the organic layers. The size of the interfacial recombination rate is critical in determining the small range of current where there is rapid transition between the two main regimes. The extension of the theory to organic solar cells is discussed and the analogous current voltage curves derived in the regime of interest
Direct-write, focused ion beam-deposited,7 K superconducting C-Ga-O nanowire
We have fabricated C-Ga-O nanowires by gallium focused ion beam-induced
deposition from the carbon-based precursor phenanthrene. The electrical
conductivity of the nanowires is weakly temperature dependent below 300 K, and
indicates a transition to a superconducting state below Tc = 7 K. We have
measured the temperature dependence of the upper critical field Hc2(T), and
estimate a zero temperature critical field of 8.8 T. The Tc of this material is
approximately 40% higher than that of any other direct write nanowire, such as
those based on C-W-Ga, expanding the possibility of fabricating direct-write
nanostructures that superconduct above liquid helium temperaturesComment: Accepted for AP
Thermodynamics of glasses: a first principle computation
We propose a first principle computation of the thermodynamics of simple
fragile glasses starting from the two body interatomic potential.
A replica formulation translates this problem into that of a gas of
interacting molecules, each molecule being built of atoms, and having a
gyration radius (related to the cage size) which vanishes at zero temperature.
We use a small cage expansion, valid at low temperatures, which allows to
compute the cage size, the specific heat (which follows the Dulong and Petit
law), and the configurational entropy.Comment: Latex, 13 pages, 4 figure
The Glassy Potts Model
We introduce a Potts model with quenched, frustrated disorder, that enjoys of
a gauge symmetry that forbids spontaneous magnetization, and allows the glassy
phase to extend from down to T=0. We study numerical the 4 dimensional
model with states. We show the existence of a glassy phase, and we
characterize it by studying the probability distributions of an order
parameter, the binder cumulant and the divergence of the overlap
susceptibility. We show that the dynamical behavior of the system is
characterized by aging.Comment: 4 pages including 4 (color) ps figures (all on page 4
Numerical study of a short-range p-spin glass model in three dimensions
In this work we study numerically a short range p-spin glass model in three
dimensions. The behaviour of the model appears to be remarkably different from
mean field predictions. In fact it shares some features typical of models with
full replica-symmetry breaking (FRSB). Nevertheless, we believe that the
transition that we study is intrinsically different from the FRSB and basically
due to non-perturbative contributions. We study both the statics and the
dynamics of the system which seem to confirm our conjectures.Comment: 20 pages, 15 figure
An Improved Red Spectrum of the Methane or T-dwarf SDSS 1624+0029: Role of the Alkali Metals
A Keck~II low resolution spectrum shortward of ome-micron is presented for
SDSS 1624+0029, the first field methane or T dwarf discovered in the Sloan
Digital Sky Survey. Significant flux is detected down to the spectrum's short
wavelength limit of 6200\AA. The spectrum exhibits a broad absorption feature
centered at 7700\AA, which we interpret as the K~I 7665/7699 resonance doublet.
The observed flux declines shortward of 7000\AA, due most likely to the red
wing of the Na~I doublet. Both Cs~I doublet lines are detected more strongly
than in an earlier red spectrum. Neither Li~I absorption nor H emission
are detected. An exploratory model fit to the spectrum suggests that the shape
of the red spectrum can be primarily accounted for by the broad wings of the
K~I and Na~I doublets. This behavior is consistent with the argument proffered
by Burrows, Marley and Sharp that strong alkali absorption is principally
responsible for depressing T dwarf spectra shortward of 1m. In particular,
there seems no compelling reason at this time to introduce dust or an
additional opacity source in the atmosphere of the SDSS object. The width of
the K~I and strengths of the Cs~I lines also indicate that the Sloan object is
warmer than Gl~229B.Comment: accepted March 3, 2000 for Ap.J. Letters, LaTeX, 2 figure
Glassiness in a model without energy barriers
We propose a microscopic model without energy barriers in order to explain
some generic features observed in structural glasses. The statics can be
exactly solved while the dynamics has been clarified using Monte Carlo
calculations. Although the model has no thermodynamic transition it captures
some of the essential features of real glasses, i.e., extremely slow
relaxation, time dependent hysteresis effects, anomalous increase of the
relaxation time and aging. This suggests that the effect of entropy barriers
can be an important ingredient to account for the behavior observed in real
glasses.Comment: 11 Pages + 3 Figures, Revtex, uufiles have been replaced since figure
2 was corrupted in the previous submissio
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