100 research outputs found
Electronic and optical properties of electromigrated molecular junctions
Electromigrated nanoscale junctions have proven very useful for studying
electronic transport at the single-molecule scale. However, confirming that
conduction is through precisely the molecule of interest and not some
contaminant or metal nanoparticle has remained a persistent challenge,
typically requiring a statistical analysis of many devices. We review how
transport mechanisms in both purely electronic and optical measurements can be
used to infer information about the nanoscale junction configuration. The
electronic response to optical excitation is particularly revealing. We briefly
discuss surface-enhanced Raman spectroscopy on such junctions, and present new
results showing that currents due to optical rectification can provide a means
of estimating the local electric field at the junction due to illumination.Comment: 19 pages, 8 figures, invited paper for forthcoming special issue of
Journal of Physics: Condensed Matter. For other related papers, see
http://www.ruf.rice.edu/~natelson/publications.htm
Unauthorized Horizontal Spread in the Laboratory Environment: The Tactics of Lula, a Temperate Lambdoid Bacteriophage of Escherichia coli
We investigated the characteristics of a lambdoid prophage, nicknamed Lula, contaminating E. coli strains from several sources, that allowed it to spread horizontally in the laboratory environment. We found that new Lula infections are inconspicuous; at the same time, Lula lysogens carry unusually high titers of the phage in their cultures, making them extremely infectious. In addition, Lula prophage interferes with P1 phage development and induces its own lytic development in response to P1 infection, turning P1 transduction into an efficient vehicle of Lula spread. Thus, using Lula prophage as a model, we reveal the following principles of survival and reproduction in the laboratory environment: 1) stealth (via laboratory material commensality), 2) stability (via resistance to specific protocols), 3) infectivity (via covert yet aggressive productivity and laboratory protocol hitchhiking). Lula, which turned out to be identical to bacteriophage phi80, also provides an insight into a surprising persistence of T1-like contamination in BAC libraries
Transition Voltage Spectroscopy and the Nature of Vacuum Tunneling
Transition Voltage Spectroscopy (TVS) has been proposed as a tool to analyze
charge transport through molecular junctions. We extend TVS to Au-vacuum-Au
junctions and study the distance dependence of the transition voltage V_t(d)
for clean electrodes in cryogenic vacuum. On the one hand, this allows us to
provide an important reference for V_t(d)-measurements on molecular junctions.
On the other hand, we show that TVS forms a simple and powerful test for vacuum
tunneling models
New directions in point-contact spectroscopy based on scanning tunneling microscopy techniques (Review Article)
Igor Yanson showed 38 years ago for the first time a point-contact measurement where he probed the energy
resolved spectroscopy of the electronic scattering inside the metal. Since this first measurement, the pointcontact
spectroscopy (PCS) technique improved enormously. The application of the scanning probe microscopy
(SPM) techniques in the late 1980s allowed achieving contacts with a diameter of a single atom. With the introduction
of the mechanically controlled break junction technique, even spectroscopy on freely suspended chains
of atoms could be performed. In this paper, we briefly review the current developments of PCS and show recent
experiments in advanced scanning PCS based on SPM techniques. We describe some results obtained with both
needle-anvil type of point contacts and scanning tunneling microscopy (STM). We also show our first attempt to
lift up with a STM a chain of single gold atoms from a Au(110) surface
Stabilizing single atom contacts by molecular bridge formation
Gold-molecule-gold junctions can be formed by carefully breaking a gold wire
in a solution containing dithiolated molecules. Surprisingly, there is little
understanding on the mechanical details of the bridge formation process and
specifically on the role that the dithiol molecules play themselves. We propose
that alkanedithiol molecules have already formed bridges between the gold
electrodes before the atomic gold-gold junction is broken. This leads to
stabilization of the single atomic gold junction, as observed experimentally.
Our data can be understood within a simple spring model.Comment: 14 pages, 3 figures, 1 tabl
Major surgery in an osteosarcoma patient refusing blood transfusion: case report
We describe an unusual case of osteosarcoma in a Jehovah's Witness patient who underwent chemotherapy and major surgery without the need for blood transfusion. This 16-year-old girl presented with osteosarcoma of the right proximal tibia requiring proximal tibia resection, followed by endoprosthesis replacement. She was successfully treated with neoadjuvant chemotherapy and surgery with the support of haematinics, granulocyte colony-stimulating factor, recombinant erythropoietin and intraoperative normovolaemic haemodilution. This case illustrates the importance of maintaining effective, open communication and exploring acceptable therapeutic alternative in the management of these patients, whilst still respecting their beliefs
Tunneling Spectra of Individual Magnetic Endofullerene Molecules
The manipulation of single magnetic molecules may enable new strategies for
high-density information storage and quantum-state control. However, progress
in these areas depends on developing techniques for addressing individual
molecules and controlling their spin. Here we report success in making
electrical contact to individual magnetic N@C60 molecules and measuring spin
excitations in their electron tunneling spectra. We verify that the molecules
remain magnetic by observing a transition as a function of magnetic field which
changes the spin quantum number and also the existence of nonequilibrium
tunneling originating from low-energy excited states. From the tunneling
spectra, we identify the charge and spin states of the molecule. The measured
spectra can be reproduced theoretically by accounting for the exchange
interaction between the nitrogen spin and electron(s) on the C60 cage.Comment: 7 pages, 4 figures. Typeset in LaTeX, updated text of previous
versio
Single-molecule sensing electrode embedded in-plane nanopore
Electrode-embedded nanopore is considered as a promising device structure for label-free single-molecule sequencing, the principle of which is based on nucleotide identification via transverse electron tunnelling current flowing through a DNA translocating through the pore. Yet, fabrication of a molecular-scale electrode-nanopore detector has been a formidable task that requires atomic-level alignment of a few nanometer sized pore and an electrode gap. Here, we report single-molecule detection using a nucleotide-sized sensing electrode embedded in-plane nanopore. We developed a self-alignment technique to form a nanopore-nanoelectrode solid-state device consisting of a sub-nanometer scale electrode gap in a 15 nm-sized SiO2 pore. We demonstrate single-molecule counting of nucleotide-sized metal-encapsulated fullerenes in a liquid using the electrode-integrated nanopore sensor. We also performed electrical identification of nucleobases in a DNA oligomer, thereby suggesting the potential use of this synthetic electrode-in-nanopore as a platform for electrical DNA sequencing
Signatures of Molecular Magnetism in Single-Molecule Transport Spectroscopy
Single-molecule transistors provide a unique experimental tool to investigate
the coupling between charge transport and the molecular degrees of freedom in
individual molecules. One interesting class of molecules for such experiments
are the single-molecule magnets, since the intramolecular exchange forces
present in these molecules should couple strongly to the spin of transport
electrons, thereby providing both new mechanisms for modulating electron flow
and also new means for probing nanoscale magnetic excitations. Here we report
single-molecule transistor measurements on devices incorporating Mn12
molecules. By studying the electron-tunneling spectrum as a function of
magnetic field, we are able to identify clear signatures of magnetic states and
their associated magnetic anisotropy. A comparison of the data to simulations
also suggests that electron flow can strongly enhance magnetic relaxation of
the magnetic molecule
Protecting Wild Land from Wind Farms in a Post-EU Scotland
Scotland is one of the places in Europe to have experienced significant wind farm development over recent years. Concern about impacts on wild land has resulted in legal challenges based on European Union (EU) law. This article analyses whether wild land can be protected from wind farms and the differences that the United Kingdom (UK) departure from the EU will make. It considers the concept of 'wild land' compared with 'wilderness', analyses the legal basis (if any) for wild land protection, and examines potential impacts from wind farms. It highlights the significance of EU environmental law, particularly nature conservation and environmental assessment law, and analyses recent Scottish jurisprudence that has applied this. The role of the European Commission and Court of Justice of the EU (CJEU) is emphasised as a key part of EU environmental law. The article asks whether relevant global and regional environmental agreements can effectively replace the content of the substantive law and context of the Commission and CJEU. Four environmental agreements and two related compliance procedures are briefly evaluated. The conclusion is that while EU law does not directly provide protection for wild land, it is considerably stronger than the international environmental agreements that may replace it
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