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We review some of our recent experimental results on charge transport in organic nanostructures such as self-assembled monolayer and monolayers of organic semiconductors. We describe a molecular rectifying junction made from a sequential self-assembly on silicon. These devices exhibit a marked current-voltage rectification behavior due to resonant transport between the Si conduction band and the π...
We review the unusual structural, transport and magnetic properties of highly conducting polyaniline, doped with boron trifluoride. Our studies establish the unique conducting state of this system, which is in distinct contrast with the conventional proton-doped polyaniline samples.
By suitable design it is possible to achieve quasi-ballistic transport in semiconductor nanostructures over times up to the ps-range. Monte-Carlo simulations reveal that under these conditions phase-coherent real-space oscillations of an electron ensemble, generated by fs-pulses become possible in wide potential wells. Using a two-color pump-and-probe technique we have been able to observe this new...
Soft matter, like colloidal suspensions and surfactant gels, exhibit strong response to modest external perturbations. This paper reviews our recent experiments on the nonlinear flow behaviour of surfactant worm-like micellar gels. A rich dynamic behaviour exhibiting regular, quasi-periodic, intermittency and chaos is observed. In particular, we have shown experimentally that the route to chaos is...
Highly ordered composite nanowires with multilayer Ni/Cu and NiFe/Cu have been fabricated by pulsed electrodeposition into nanoporous alumina membrane. The diameter of wires can be easily varied by pore size of alumina, ranging from 30 to 100 nm. The applied potential and the duration of each potential square pulse determine the thickness of the metal layers. The nanowires have been characterized...
We shall discuss magnetization and transport measurements in materials exhibiting a broad first-order transition. The phase transitions would be caused by varying magnetic field as well as temperature, and we concentrate on ferro- to antiferromagnetic transitions in magnetic materials. We distinguish between metastable supercooled phases and metastable glassy phase.
Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0...
Surface photovoltage (SPV) spectroscopy has been used for the first time to explore Landau levels of a two-dimensional electron gas (2DEG) in modulation doped InP/InGaAs/InP QW in the quantum Hall regime. The technique gives spectroscopically distinct signals from the bulk Landau levels and the edge states. Evolution of the bulk Landau levels and the edge electronic states is investigated at 2.0 K...
The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of research for almost 100 years. The role of dipolar interactions and anistropy are important to obtain, the otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monlayers). We have demonstrated that conventional low-temperature...
By subjecting materials to high pressures one can significantly reduce interatomic and intermolecular distances. This causes drastic changes in the nature of electronic and vibrational states and also in bonding, bringing about several unusual structural, electronic and magnetic phase transitions. In addition, these studies provide a very useful data about the equation of state of the materials of...
We discuss specular reflectivity and off-specular scattering of neutrons and X-rays from magnetic films. Both these techniques are capable of providing information about the morphology of the chemical and magnetic roughness and the magnetic domain structure. The use of neutrons with polarization analysis enables the spatial distribution of different vector components of the magnetization to be determined,...
The understanding of mesoscopic transport has now attained an ultimate simplicity. Indeed, orthodox quantum kinetics would seem to say little about mesoscopics that has not been revealed — nearly effortlessly — by more popular means. Such is far from the case, however. The fact that kinetic theory remains very much in charge is best appreciated through the physics of a quantum point contact. While...
Organic solar cells using the CuPc and PTCBI semiconductor layers were studied. A high open circuit voltage of 1.15 V was obtained in a device with ITO/PEDOT:PSS/CuPc (15 nm)/PTCBI (7 nm)/Al structure. Results were interpreted in terms of a modified CuPc-Al Schottky diode for the thin PTCBI case and a CuPc-PTCBI heterojunction for the thick PTCBI case. Also, the formation of a thin aluminum oxide...
A simple method, based on the proximity effect of electron beam lithography, alleviated by exposing various shapes in the pattern of incident electron exposures with various intensities, was applied to fabricate silicon point-contact devices. The drain current (Id) of the device oscillates against gate voltage. The electrical characteristics of the single-electron transistor were observed to be consistent...
Nickel substitution at the cobalt site in Na0.75CoO2 induces an upturn in the resistivity on lowering the temperature, with the metal-to-insulator transition temperature (TMIT) increasing with the Ni content. Low temperature far infrared measurements on polycrystalline samples of Na0.75CoO2 and Na0.75Co0.95Ni0.05O2, the latter having TMIT ∼ 175 K, have been carried out. Dramatic changes in the Na...
The discovery of organic- and molecule-based magnets has led to design and synthesis of several families with magnetic ordering temperatures as high as ∼125°C. Examples of soft and hard magnets with coercivities as high as 27 kOe have also been reported. Examples from our laboratory of organic-based magnets using the tetracyanoethylene radical anion, [TCNE]•−, are discussed. In addition, several molecule-based...
Langmuir Blodgett (LB) process is an important route to the development of organized molecular layered structures of a variety of organic molecules with suitably designed architecture and functionality. LB multilayers have also been used as templates and precursors to develop nano-structured thin films. In this article, studies on the molecular packing and three-dimensional structure of prototypic...
A national facility for neutron beam research is operated at the research reactor Dhruva at Trombay in India. The research activities involve various nanoscale structural, dynamical and magnetic investigations on materials of scientific interest and technological importance. Thermal neutron has certain special properties that enable, e.g., selective viewing of parts of an organic molecule, hydrogen...
The Center for Nanoscale Science and Engineering (CeNSE) at the University of Kentucky is a multidisciplinary group of faculty, students, and staff, with a shared vision and cutting-edge research facilities to study and develop materials and devices at the nanoscale. Current research projects at CeNSE span a number of diverse nanoscience thrusts in bio-engineering and medicine (nanosensors and nanoelectrodes,...
Bose-Einstein condensation and superfluidity are well known to occur in the dilute gaseous as well as in the dense liquid state of matter having a fixed number of Bose particles. Very recently, experimental evidence has been obtained for the probable realization of BEC and superfluidity in 4He in the solid state too, as revealed through its non-classical rotational moment of inertia — smaller than...
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