525 research outputs found
Threshold voltage and space charge in organic transistors
We investigate rubrene single-crystal field-effect transistors, whose
stability and reproducibility are sufficient to measure systematically the
shift in threshold voltage as a function of channel length and source-drain
voltage. The shift is due to space-charge transferred from the contacts, and
can be modeled quantitatively without free fitting parameters, using Poisson's
equation, and by assuming that the density of states in rubrene is that of a
conventional inorganic semiconductor. Our results demonstrate the consistency,
at the quantitative level, of a variety of recent experiments on rubrene
crystals, and show how the use of FET measurements can enable the determination
of microscopic parameters (e.g., the effective mass of charge carriers).Comment: 4 pages, 4 figure
Correlation between molecular orbitals and doping dependence of the electrical conductivity in electron-doped Metal-Phthalocyanine compounds
We have performed a comparative study of the electronic properties of six
different electron-doped metal phthalocyanine (MPc) compounds (ZnPc, CuPc,
NiPc, CoPc, FePc, and MnPc), in which the electron density is controlled by
means of potassium intercalation. In spite of the complexity of these systems,
we find that the nature of the underlying molecular orbitals produce observable
effects in the doping dependence of the electrical conductivity of the
materials. For all the MPc's in which the added electrons are expected to
occupy orbitals centered on the ligands (ZnPc, CuPc, and NiPc), the doping
dependence of the conductivity has an essentially identical shape. This shape
is different from that observed in MPc materials in which electrons are also
added to orbitals centered on the metal atom (CoPc, FePc, and MnPc). The
observed relation between the macroscopic electronic properties of the MPc
compounds and the properties of the molecular orbitals of the constituent
molecules, clearly indicates the richness of the alkali-doped
metal-phthalocyanines as a model class of compounds for the investigation of
the electronic properties of molecular systems
Sample-specific and Ensemble-averaged Magnetoconductance of Individual Single-Wall Carbon Nanotubes
We discuss magnetotransport measurements on individual single-wall carbon
nanotubes with low contact resistance, performed as a function of temperature
and gate voltage. We find that the application of a magnetic field
perpendicular to the tube axis results in a large magnetoconductance of the
order of e^2/h at low temperature. We demonstrate that this magnetoconductance
consists of a sample-specific and of an ensemble-averaged contribution, both of
which decrease with increasing temperature. The observed behavior resembles
very closely the behavior of more conventional multi-channel mesoscopic wires,
exhibiting universal conductance fluctuations and weak localization. A
theoretical analysis of our experiments will enable to reach a deeper
understanding of phase-coherent one-dimensional electronic motion in SWNTs.Comment: Replaced with published version. Minor changes in tex
High-performance -type organic field-effect transistors with ionic liquid gates
High-performance -type organic field-effect transistors were developed
with ionic-liquid gates and N,N-bis(n-alkyl)-(1,7 and
1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide)s single-crystals. Transport
measurements show that these devices reproducibly operate in ambient atmosphere
with negligible gate threshold voltage and mobility values as high as 5.0
cm/Vs. These mobility values are essentially identical to those measured in
the same devices without the ionic liquid, using vacuum or air as the gate
dielectric. Our results indicate that the ionic-liquid and -type organic
semiconductor interfaces are suitable to realize high-quality -type organic
transistors operating at small gate voltage, without sacrificing electron
mobility
Double-gated graphene-based devices
We discuss transport through double gated single and few layer graphene
devices. This kind of device configuration has been used to investigate the
modulation of the energy band structure through the application of an external
perpendicular electric field, a unique property of few layer graphene systems.
Here we discuss technological details that are important for the fabrication of
top gated structures, based on electron-gun evaporation of SiO. We perform
a statistical study that demonstrates how --contrary to expectations-- the
breakdown field of electron-gun evaporated thin SiO films is comparable to
that of thermally grown oxide layers. We find that a high breakdown field can
be achieved in evaporated SiO only if the oxide deposition is directly
followed by the metallization of the top electrodes, without exposure to air of
the SiO layer.Comment: Replaced with revised version. To appear on New Journal of Physic
Photon-assisted electron transport in graphene
Photon-assisted electron transport in ballistic graphene is analyzed using
scattering theory. We show that the presence of an ac signal (applied to a gate
electrode in a region of the system) has interesting consequences on electron
transport in graphene, where the low energy dynamics is described by the Dirac
equation. In particular, such a setup describes a feasible way to probe energy
dependent transmission in graphene. This is of substantial interest because the
energy dependence of transmission in mesoscopic graphene is the basis of many
peculiar transport phenomena proposed in the recent literature. Furthermore, we
discuss the relevance of our analysis of ac transport in graphene to the
observability of zitterbewegung of electrons that behave as relativistic
particles (but with a lower effective speed of light).Comment: 5 pages, 2 figure
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