18,994 research outputs found
Sum rules for correlation functions of ionic mixtures in arbitrary dimension
The correlations in classical multi-component ionic mixtures with spatial
dimension are studied by using a restricted grand-canonical ensemble
and the associated hierarchy equations for the correlation functions. Sum rules
for the first few moments of the two-particle correlation function are derived
and their dependence on is established. By varying continuously near
it is shown how the sum rules for the two-dimensional mixture are related
to those for mixtures at higher .Comment: 19 page
Twisted Open Strings from Closed Strings: The WZW Orientation Orbifolds
Including {\it world-sheet orientation-reversing automorphisms}
in the orbifold program, we construct the operator
algebras and twisted KZ systems of the general WZW {\it orientation orbifold}
. We find that the orientation-orbifold sectors corresponding
to each are {\it twisted open} WZW strings, whose
properties are quite distinct from conventional open-string orientifold
sectors. As simple illustrations, we also discuss the classical (high-level)
limit of our construction and free-boson examples on abelian .Comment: 65 pages, typos correcte
Organic Single-Crystal Field-Effect Transistors
We present an overview of recent studies of the charge transport in the field
effect transistors on the surface of single crystals of organic
low-molecular-weight materials. We first discuss in detail the technological
progress that has made these investigations possible. Particular attention is
devoted to the growth and characterization of single crystals of organic
materials and to different techniques that have been developed for device
fabrication. We then concentrate on the measurements of the electrical
characteristics. In most cases, these characteristics are highly reproducible
and demonstrate the quality of the single crystal transistors. Particularly
noticeable are the small sub-threshold slope, the non-monotonic temperature
dependence of the mobility, and its weak dependence on the gate voltage. In the
best rubrene transistors, room-temperature values of as high as 15
cm/Vs have been observed. This represents an order-of-magnitude increase
with respect to the highest mobility previously reported for organic thin film
transistors. In addition, the highest-quality single-crystal devices exhibit a
significant anisotropy of the conduction properties with respect to the
crystallographic direction. These observations indicate that the field effect
transistors fabricated on single crystals are suitable for the study of the
\textit{intrinsic} electronic properties of organic molecular semiconductors.
We conclude by indicating some directions in which near-future work should
focus to progress further in this rapidly evolving area of research.Comment: Review article, to appear in special issue of Phys. Stat. Sol. on
organic semiconductor
Field-Effect Transistors on Tetracene Single Crystals
We report on the fabrication and electrical characterization of field-effect
transistors at the surface of tetracene single crystals. We find that the
mobility of these transistors reaches the room-temperature value of $0.4 \
cm^2/Vs$. The non-monotonous temperature dependence of the mobility, its weak
gate voltage dependence, as well as the sharpness of the subthreshold slope
confirm the high quality of single-crystal devices. This is due to the
fabrication process that does not substantially affect the crystal quality.Comment: Accepted by Appl. Phys. Lett, tentatively scheduled for publication
in the November 24, 2003 issu
Intense field stabilization in circular polarization: 3D time-dependent dynamics
We investigate the stabilization of a hydrogen atom in circularly polarized
laser fields. We use a time-dependent, fully three dimensional approach to
study the quantum dynamics of the hydrogen atom subject to high intensity,
short wavelength laser pulses. We find enhanced survival probability as the
field is increased under fixed envelope conditions. We also confirm wavepacket
dynamics seen in prior time-dependent computations restricted to two
dimensions.Comment: 4 pages, 3 figures, submitte
Influence of the gate leakage current on the stability of organic single-crystal field-effect transistors
We investigate the effect of a small leakage current through the gate
insulator on the stability of organic single-crystal field-effect transistors
(FETs). We find that, irrespective of the specific organic molecule and
dielectric used, leakage current flowing through the gate insulator results in
an irreversible degradation of the single-crystal FET performance. This
degradation occurs even when the leakage current is several orders of magnitude
smaller than the source-drain current. The experimental data indicate that a
stable operation requires the leakage current to be smaller than $10^{-9} \
\mathrm{A/cm}^2$. Our results also suggest that gate leakage currents may
determine the lifetime of thin-film transistors used in applications.Comment: submitted to Appl. Phys. Let
Space Charge Limited Transport and Time of Flight Measurements in Tetracene Single Crystals: a Comparative Study
We report on a systematic study of electronic transport in tetracene single
crystals by means of space charge limited current spectroscopy and time of
flight measurements. Both - and time of flight measurements show that the
room-temperature effective hole-mobility reaches values close to
cm/Vs and show that, within a range of temperatures, the mobility increases
with decreasing temperature. The experimental results further allow the
characterization of different aspects of the tetracene crystals. In particular,
the effects of both deep and shallow traps are clearly visible and can be used
to estimate their densities and characteristic energies. The results presented
in this paper show that the combination of - measurements and time of
flight spectroscopy is very effective in characterizing several different
aspects of electronic transport through organic crystals.Comment: Accepted by J. Appl. Phys.; tentatively scheduled for publication in
the January 15, 2004 issue; minor revisions compared to previous cond-mat
versio
- …