5,307 research outputs found
Percolative Effects on Noise in Pentacene Transistors
The 1/f noise in pentacene thin film transistors has been measured as a
function of device thickness from well above the effective conduction channel
thickness to only two conducting layers. Over the entire thickness range, the
spectral noise form is 1/f, and the noise parameter varies as (gate voltage)-1,
confirming that the noise is due to mobility fluctuations, even in the thinnest
films. Hooge's parameter varies as an inverse power-law with conductivity for
all film thicknesses. The magnitude and transport characteristics of the
spectral noise are well explained in terms of percolative effects arising from
the grain boundary structure.Comment: 13 pages, 4 figures, Publishe
Spiral Evolution in a Confined Geometry
Supported nanoscale lead crystallites with a step emerging from a
non-centered screw dislocation on the circular top facet were prepared by rapid
cooling from just above the melting temperature. STM observations of the top
facet show a nonuniform rotation rate and shape of the spiral step as the
crystallite relaxes. These features can be accurately modeled using curvature
driven dynamics, as in classical models of spiral growth, with boundary
conditions fixing the dislocation core and regions of the step lying along the
outer facet edge.Comment: 4 pages, 3 figures, to be published in Physical Review Letter
The Princeton Variability Survey
The Princeton Variability Survey (PVS) is a robotic survey which makes use of
readily available, ``off-the-shelf'' type hardware products, in conjunction
with a powerful set of commercial software products, in order to monitor and
discover variable objects in the night sky. The main goal of the PVS has been
to devise an automated telescope and data reduction system, requiring only
moderate technical and financial resources to assemble, which may be easily
replicated by the dedicated amateur, a student group, or a professional and
used to study and discover a variety of variable objects, such as stars. This
paper describes the hardware and software components of the PVS device as well
as observational results from the initial season of the PVS, including the
discovery of a new bright variable star.Comment: 22 pages, 5 figures. Revised to fix typos and expand discussion.
Accepted PAS
Development and evaluation of die materials for use in the growth of silicon ribbons by the inverted ribbon growth process, task 2, LSSA project
Silicon sessile drop experiments were performed on a variety of commercially available refractory carbides, nitrides, oxides, and borides to examine the potential of these materials for applications involving either direct contact with molten silicon or as substrates for CVD coatings in the fabrication of dies and crucibles for containing molten silicon. Simultaneous experiments were also conducted with CVD layers of SiC, Si3N4, and SiOxNy. Silicon nitride layers, deposited with NH3:SiH4 ratios ranging from 100:1 down to 5:1, were examined in sessile drop experiments to determine if the layers are degraded as a result of using lower reagent ratios. Preliminary experiments were undertaken on the stability of CVD Si3N4 near the melting point of silicon. Silicon ribbon segments were grown from vitreous carbon dies which had been coated with CVD Si3N4. Depending upon the purity of the die materials, ribbon resistivity values up to 40 Omega cm were obtained
Atomic Structure of Graphene on SiO2
We employ scanning probe microscopy to reveal atomic structures and nanoscale
morphology of graphene-based electronic devices (i.e. a graphene sheet
supported by an insulating silicon dioxide substrate) for the first time.
Atomic resolution STM images reveal the presence of a strong spatially
dependent perturbation, which breaks the hexagonal lattice symmetry of the
graphitic lattice. Structural corrugations of the graphene sheet partially
conform to the underlying silicon oxide substrate. These effects are obscured
or modified on graphene devices processed with normal lithographic methods, as
they are covered with a layer of photoresist residue. We enable our experiments
by a novel cleaning process to produce atomically-clean graphene sheets.Comment: 13 pages, 4 figure
Sampling Time Effects for Persistence and Survival in Step Structural Fluctuations
The effects of sampling rate and total measurement time have been determined
for single-point measurements of step fluctuations within the context of
first-passage properties. Time dependent STM has been used to evaluate step
fluctuations on Ag(111) films grown on mica as a function of temperature
(300-410 K), on screw dislocations on the facets of Pb crystallites at 320K,
and on Al-terminated Si(111) over the temperature range 770K - 970K. Although
the fundamental time constant for step fluctuations on Ag and Al/Si varies by
orders of magnitude over the temperature ranges of measurement, no dependence
of the persistence amplitude on temperature is observed. Instead, the
persistence probability is found to scale directly with t/Dt where Dt is the
time interval used for sampling. Survival probabilities show a more complex
scaling dependence which includes both the sampling interval and the total
measurement time tm. Scaling with t/Dt occurs only when Dt/tm is a constant. We
show that this observation is equivalent to theoretical predictions that the
survival probability will scale as Dt/L^z, where L is the effective length of a
step. This implies that the survival probability for large systems, when
measured with fixed values of tm or Dt should also show little or no
temperature dependence.Comment: 27 pages, 10 figure
Cosmic Rays and Large Extra Dimensions
We have proposed that the cosmic ray spectrum "knee", the steepening of the
cosmic ray spectrum at energy E \gsim 10^{15.5} eV, is due to "new physics",
namely new interactions at TeV cm energies which produce particles undetected
by the experimental apparatus. In this letter we examine specifically the
possibility that this interaction is low scale gravity. We consider that the
graviton propagates, besides the usual four dimensions, into an additional
, compactified, large dimensions and we estimate the graviton
production in collisions in the high energy approximation where graviton
emission is factorized. We find that the cross section for graviton production
rises as fast as , where is the fundamental
scale of gravity in dimensions, and that the distribution of
radiating a fraction of the initial particle's energy into gravitational
energy (which goes undetected) behaves as . The missing
energy leads to an underestimate of the true energy and generates a break in
the {\sl inferred} cosmic ray spectrum (the "kne"). By fitting the cosmic ray
spectrum data we deduce that the favorite values for the parameters of the
theory are TeV and .Comment: 8 pages, 1 figur
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