36,027 research outputs found
Electron transport in semiconducting carbon nanotubes with hetero-metallic contacts
We present an atomistic self-consistent study of the electronic and transport
properties of semiconducting carbon nanotube in contact with metal electrodes
of different work functions, which shows simultaneous electron and hole doping
inside the nanotube junction through contact-induced charge transfer. We find
that the band lineup in the nanotube bulk region is determined by the effective
work function difference between the nanotube channel and source/drain
electrodes, while electron transmission through the SWNT junction is affected
by the local band structure modulation at the two metal-nanotube interfaces,
leading to an effective decoupling of interface and bulk effects in electron
transport through nanotube junction devices.Comment: Higher quality figures available at http://www.albany.edu/~yx15212
Schottky barriers at metal-finite semiconducting carbon nanotube interfaces
Electronic properties of metal-finite semiconducting carbon nanotube
interfaces are studied as a function of the nanotube length using a
self-consistent tight-binding theory. We find that the shape of the potential
barrier depends on the long-range tail of the charge transfer, leading to an
injection barrier thickness comparable to half of the nanotube length until the
nanotube reaches the bulk limit. The conductance of the nanotube junction shows
a transition from tunneling to thermally-activated transport with increasing
nanotube length
Scaling analysis of Schottky barriers at metal-embedded semiconducting carbon nanotube interfaces
We present an atomistic self-consistent tight-binding study of the electronic
and transport properties of metal-semiconducting carbon nanotube interfaces as
a function of the nanotube channel length when the end of the nanotube wire is
buried inside the electrodes. We show that the lineup of the nanotube band
structure relative to the metal Fermi-level depends strongly on the metal work
function but weakly on the details of the interface. We analyze the
length-dependent transport characteristics, which predicts a transition from
tunneling to thermally-activated transport with increasing nanotube channel
length.Comment: To appear in Phys.Rev.B Rapid Communications. Color figures available
in PRB online versio
Neutrino masses and mixings
We propose a novel theoretical understanding of neutrino masses and mixings,
which is attributed to the intrinsic vector-like feature of the regularized
Standard Model at short distances. We try to explain the smallness of Dirac
neutrino masses and the decoupling of the right-handed neutrino as a free
particle. Neutrino masses and mixing angles are completely related to each
other in the Schwinger-Dyson equations for their self-energy functions. The
solutions to these equations and a possible pattern of masses and mixings are
discussed.Comment: LaTex 11 page
Mechanical modulation of single-electron tunneling through molecular-assembled metallic nanoparticles
We present a microscopic study of single-electron tunneling in nanomechanical
double-barrier tunneling junctions formed using a vibrating scanning nanoprobe
and a metallic nanoparticle connected to a metallic substrate through a
molecular bridge. We analyze the motion of single electrons on and off the
nanoparticle through the tunneling current, the displacement current and the
charging-induced electrostatic force on the vibrating nanoprobe. We demonstrate
the mechanical single-electron turnstile effect by applying the theory to a
gold nanoparticle connected to the gold substrate through alkane dithiol
molecular bridge and probed by a vibrating platinum tip.Comment: Accepted by Phys. Rev.
Safety and Socio-Economic Issues Raised by Modern Biotechnology
Modern new biotechnology has the potential to provide major economic and other benefits, but at the same time it poses potential hazards for human health, the environment, the ‘natural’ biological order and can have adverse socio-economic consequences. The application of such technology frequently violates traditional ethical, moral and religious values. This paper after outlining possible benefits of modern new biotechnologies, discusses the type of biosafety risks which they pose, their possible adverse consequences for the sustainability of biodiversity and agriculture and their potential impacts on socioeconomic welfare and traditional cultures. Particular concern is expressed about the possible consequences of such technologies for developing countries and the practice in some developed countries of issuing patents conferring very broad rights over the use of genetically engineered material. Because these rights are so broad in some cases they have the potential to establish powerful multinational monopolies in the hands of private companies. Global debate about these issues suggest that more emphasis should be given globally to the socio-economic consequences of such technology than in the past. The need for this is highlighted by the North-South divide. Developing countries lag considerably in this new technological field, are placed in a dependant position and have weak institutional structures to control the application of such technologybiotechnology, socio-economic policy, genetic engineering, biodiversity, biosafety, patents, Environmental Economics and Policy, Research and Development/Tech Change/Emerging Technologies,
Transonic blade-vortex interactions noise: A parametric study
Transonic Blade-Vortex Interactions (BVI) are simulated numerically and the noise mechanisms are investigated. The 2-D high frequency transonic small disturbance equation is solved numerically (VTRAN2 code). An Alternating Direction Implicit (ADI) scheme with monotone switches is used; viscous effects are included on the boundary and the vortex is simulated by the cloud-in-cell method. The Kirchoff method is used for the extension of the numerical 2-D near field aerodynamic results to the linear acoustic 3-D far field. The viscous effect (shock/boundary layer interaction) on BVI is investigated. The different types of shock motion are identified and compared. Two important disturbances with different directivity exist in the pressure signal and are believed to be related to the fluctuating lift and drag forces. Noise directivity for different cases is shown. The maximum radiation occurs at an angle between 60 and 90 deg below the horizontal for an airfoil fixed coordinate system and depends on the details of the airfoil shape. Different airfoil shapes are studied and classified according to the BVI noise produced
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