285 research outputs found
Observation of individual molecules trapped on a nanostructured insulator
For the first time, ordered polar molecules confined in monolayer-deep
rectangular pits produced on an alkali halide surface by electron irradiation
have been resolved at room temperature by non-contact atomic force microscopy.
Molecules self-assemble in a specific fashion inside pits of width smaller than
15 nm. By contrast no ordered aggregates of molecules are observed on flat
terraces. Conclusions regarding nucleation and ordering mechanisms are drawn.
Trapping in pits as small as 2 nm opens a route to address single molecules
Using exchange bias to extend the temperature range of square loop behavior in [Pt/Co] multilayers with perpendicular anisotropy
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The temperature dependence of the magnetic properties of [Pt/Co]multilayers (ML), exhibiting perpendicular anisotropy, with and without exchange biasing with an antiferromagnet(AFM) has been investigated. Upon heating, a loss of the out-of-plane anisotropy and, consequently, of the remanence to saturation ratio is observed in these systems. However, such effect occurs at higher temperatures in the [Pt/Co] ML exchange coupled to the AFM than for the unbiased ML. This is attributed to the additional anisotropy induced to the ML by the ferromagnetic-antiferromagnetic exchange coupling
Theory of Current and Shot Noise Spectroscopy in Single-Molecular Quantum Dots with Phonon Mode
Using the Keldysh nonequilibrium Green function technique, we study the
current and shot noise spectroscopy of a single molecular quantum dot coupled
to a local phonon mode. It is found that in the presence of electron-phonon
coupling, in addition to the resonant peak associated with the single level of
the dot, satellite peaks with the separation set by the frequency of phonon
mode appear in the differential conductance. In the ``single level'' resonant
tunneling region, the differential shot noise power exhibit two split peaks.
However, only single peaks show up in the ``phonon assisted''
resonant-tunneling region. An experimental setup to test these predictions is
also proposed.Comment: 5 pages, 3 eps figures embedde
Measurement of the conductance of a hydrogen molecule
Recent years have shown steady progress in research towards molecular
electronics [1,2], where molecules have been investigated as switches [3-5],
diodes [6], and electronic mixers [7]. In much of the previous work a Scanning
Tunnelling Microscope was employed to address an individual molecule. As this
arrangement does not provide long-term stability, more recently
metal-molecule-metal links have been made using break junction devices [8-10].
However, it has been difficult to establish unambiguously that a single
molecule forms the contact [11]. Here, we show that a single H2 molecule can
form a stable bridge between Pt electrodes. In contrast to results for other
organic molecules, the bridge has a nearly perfect conductance of one quantum
unit, carried by a single channel. The H2-bridge provides a simple test system
and a fundamental step towards understanding transport properties of
single-molecule devices.Comment: 6 pages, 4 figure
Coherent electron-phonon coupling and polaron-like transport in molecular wires
We present a technique to calculate the transport properties through
one-dimensional models of molecular wires. The calculations include inelastic
electron scattering due to electron-lattice interaction. The coupling between
the electron and the lattice is crucial to determine the transport properties
in one-dimensional systems subject to Peierls transition since it drives the
transition itself. The electron-phonon coupling is treated as a quantum
coherent process, in the sense that no random dephasing due to electron-phonon
interactions is introduced in the scattering wave functions. We show that
charge carrier injection, even in the tunneling regime, induces lattice
distortions localized around the tunneling electron. The transport in the
molecular wire is due to polaron-like propagation. We show typical examples of
the lattice distortions induced by charge injection into the wire. In the
tunneling regime, the electron transmission is strongly enhanced in comparison
with the case of elastic scattering through the undistorted molecular wire. We
also show that although lattice fluctuations modify the electron transmission
through the wire, the modifications are qualitatively different from those
obtained by the quantum electron-phonon inelastic scattering technique. Our
results should hold in principle for other one-dimensional atomic-scale wires
subject to Peierls transitions.Comment: 21 pages, 8 figures, accepted for publication in Phys. Rev. B (to
appear march 2001
International Geomagnetic Reference Field: the eleventh generation
The eleventh generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2009 by the International Association of Geomagnetism and Aeronomy Working Group V-MOD. It updates the previous IGRF generation with a definitive main field model for epoch 2005.0, a main field model for epoch 2010.0, and a linear predictive secular variation model for 2010.0-2015.0. In this note the equations defining the IGRF model are provided along with the spherical harmonic coefficients for the eleventh generation. Maps of the magnetic declination, inclination and total intensity for epoch 2010.0 and their predicted rates of change for 2010.0-2015.0 are presented. The recent evolution of the South Atlantic Anomaly and magnetic pole positions are also examine
Mobile Criminals, Immobile Crime: The Efficiency of Decentralized Crime Deterrence
In this paper we examine a class of local crimes that involve perfectly mobile criminals, and perfectly immobile criminal opportunities. We focus on local non-rival crime deterrence that is more efficient against criminals pursuing domestic crimes than criminals pursuing crimes elsewhere. In a standard case of sincerely delegated politicians and zero transfers to other districts, we show that centralized deterrence unambiguously dominates the decentralized deterrence. With strategic delegation and voluntary in-kind transfers, the tradeoff is exactly the opposite: Decentralization achieves the social optimum, whereas cooperative centralization overprovides for enforcement. This is robust to various cost-sharing modes. We also examine the effects of the growing interdependence of districts, stemming from criminals' increasing opportunities to strategically displace. Contrary to the supposition in Oates's decentralization theorem, increasing interdependence makes centralization less desirable
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