5,275 research outputs found
Fabrication of large addition energy quantum dots in graphene
We present a simple technique to fabricate graphene quantum dots in a
cryostat. It relies upon the controlled rupture of a suspended graphene sheet
subjected to the application of a large electron current. This results in the
in-situ formation of a clean and ultra-narrow constriction, which hosts one
quantum dot, and occasionally a few quantum dots in series. Conductance
spectroscopy indicates that individual quantum dots can possess an addition
energy as large as 180 meV and a level spacing as large as 25 meV. Our
technique has several assets: (i) the dot is suspended, thus the electrostatic
influence of the substrate is reduced, and (ii) contamination is minimized,
since the edges of the dot have only been exposed to the vacuum in the
cryostat.Comment: Improved version. To appear in Applied Physics Letter
Spectroscopy of Rb dimers in solid He
We present experimental and theoretical studies of the absorption, emission
and photodissociation spectra of Rb molecules in solid helium. We have
identified 11 absorption bands of Rb. All laser-excited molecular states
are quenched by the interaction with the He matrix. The quenching results in
efficient population of a metastable (1) state, which emits
fluorescence at 1042 nm. In order to explain the fluorescence at the forbidden
transition and its time dependence we propose a new molecular exciplex
RbHe. We have also found evidence for the formation of
diatomic bubble states following photodissociation of Rb
Stochastic integration in UMD Banach spaces
In this paper we construct a theory of stochastic integration of processes
with values in , where is a separable Hilbert space and
is a UMD Banach space (i.e., a space in which martingale differences are
unconditional). The integrator is an -cylindrical Brownian motion. Our
approach is based on a two-sided -decoupling inequality for UMD spaces due
to Garling, which is combined with the theory of stochastic integration of
-valued functions introduced recently by two of the authors.
We obtain various characterizations of the stochastic integral and prove
versions of the It\^{o} isometry, the Burkholder--Davis--Gundy inequalities,
and the representation theorem for Brownian martingales.Comment: Published at http://dx.doi.org/10.1214/009117906000001006 in the
Annals of Probability (http://www.imstat.org/aop/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Stochastic evolution equations in UMD Banach spaces
We discuss existence, uniqueness, and space-time H\"older regularity for
solutions of the parabolic stochastic evolution equation dU(t) = (AU(t) +
F(t,U(t))) dt + B(t,U(t)) dW_H(t), t\in [0,\Tend], U(0) = u_0, where
generates an analytic -semigroup on a UMD Banach space and is a
cylindrical Brownian motion with values in a Hilbert space . We prove that
if the mappings and satisfy suitable Lipschitz conditions and is
\F_0-measurable and bounded, then this problem has a unique mild solution,
which has trajectories in C^\l([0,T];\D((-A)^\theta) provided
and satisfy \l+\theta<\frac12. Various extensions of this
result are given and the results are applied to parabolic stochastic partial
differential equations.Comment: Accepted for publication in Journal of Functional Analysi
Detection of low energy single ion impacts in micron scale transistors at room temperature
We report the detection of single ion impacts through monitoring of changes
in the source-drain currents of field effect transistors (FET) at room
temperature. Implant apertures are formed in the interlayer dielectrics and
gate electrodes of planar, micro-scale FETs by electron beam assisted etching.
FET currents increase due to the generation of positively charged defects in
gate oxides when ions (121Sb12+, 14+, Xe6+; 50 to 70 keV) impinge into channel
regions. Implant damage is repaired by rapid thermal annealing, enabling
iterative cycles of device doping and electrical characterization for
development of single atom devices and studies of dopant fluctuation effects
Ito's formula in UMD Banach spaces and regularity of solutions of the Zakai equation
Using the theory of stochastic integration for processes with values in a UMD
Banach space developed recently by the authors, an Ito formula is proved which
is applied to prove the existence of strong solutions for a class of stochastic
evolution equations in UMD Banach spaces. The abstract results are applied to
prove regularity in space and time of the solutions of the Zakai equation.Comment: Accepted for publication in Journal of Differential Equation
- …