Hybrid structures composed of photosynthetic system and metal nanoparticles: plasmon enhancement effect

The efficiency of chemical energy production of a photosynthetic system can be strongly enhanced in the presence of metal nanoparticles. Two competing effects contribute to the photosystem efficiency: plasmon enhancement of photon fields inside the light-absorbing chlorophyll molecules and energy transfer from chlorophylls to metal nanoparticles. The first effect can lead to strong enhancement of light absorption by the chlorophylls, whereas the second can somewhat reduce the quantum yield of the system. This paper describes one concrete example of hybrid photosystem that incorporates a photosynthetic reaction center bound to gold and silver nanocrystals. The calculated rate of production of excited electrons inside the reaction center is strongly increased due to plasmon resonance and fast electron-hole separation. In phototransport experiments with photosynthetic reaction centers, the plasma resonance can enhance the photocurrent response. The enhancement mechanism described here can be utilized in energy-conversion devices and sensors.     

A proximity effect model for superconductivity in titanium-transition metal alloys

We present a unified model for the variation in superconducting transition temperature T _c of quenched titanium-transition metal alloys with intermediate-temperature aging. Experimental results on T _c and the low-temperature resistivity of -quenched Ti-27 at % Nb solid solution, a representative system, measured as a function of annealing are given. It is shown that the enrichment of the matrix in Nb as a result of precipitation of a Ti-rich phase is too small to be of any consequence in influencing T _c. Our resistivity data give, for the first time, evidence for the formation of athermal phase in this system. In the light of the present investigation a clear picture has emerged for the interpretation of T _c in terms of varying extent of superconducting proximity effect, which is shown to be intimately related to the microstructural evolution. The result is shown to be general, applicable to any Ti-transition metal alloy system.     

On the proximity effect in a superconductive slab bordered by metal

The first Ginzburg-Landau equation for the order parameter in the absence of magnetic fields is solved analytically for a superconducting slab of thickness 2d bordered by semi-infinite regions of normal metal at each face. The real-valued normalized wave function f=/ depends only on the transversal spatial coordinate x, normalized with respect to the coherence length of the superconductor, provided the de Gennes boundary condition df/dx=f/b is used. The closed-form solution expresses x as an elliptic integral of f, depending on the normalized parameters d and b. It is predicted theoretically that, for b< and dd_c=arctan(1/b), the proximity effect is so strong that the superconductivity is completely suppressed. In fact, in this case, the first Ginzburg-Landau equation possesses only the trivial solution f0.     

A microscopic model for the nonequilibrium proximity effect in superconductor-normal metal junctions

The current-voltage characteristics of a superconductor-normal metal junction are affected by the proximity superconductivity induced on the normal side. We study this effect using the quasiclassical theory. We first present a unified derivation of the previous results obtained by time-dependent Ginzburg-Landau (TDGL) theories. In order to study the effect beyond the scope of the TDGL theory, we approximate the induced order parameter by a step function. The amplitude and the phase of the induced order parameter as well as the width of the step are determined self-consistently. The calculation is made in the pure limit, but no restrictions are set on the temperature or on the transmission coefficient of the junction besides the ones implicit in the step approximation. A time-dependent solution for the order parameter is found at all currents or voltages. It is found that the results in the TDGL region and outside are relatively similar, although different mechanisms are responsible for the conversion from the normal to supercurrent in each case.     

Nanoscale Superconductor-Magnetic Metal Structures: Critical Current Enhancement and Proximity Effect

No Heading We focus on some aspects of proximity effect in coupled superconductor-magnetic metal artificial structures and discuss mechanisms that may enhance superconductivity of such systems. Superconductor-ferromagnet tunnel junctions are considered where an inversion/enhancement of the Josephson current is due to magnetic proximity effect. Special attention has been paid to another way of enhancing superconductivity of a proximity coupled superconductor-magnetic metal system - the field-induced enhancement. This mechanism can be realized if the effective exchange field between the conducting electrons and localized spins of magnetic ions in a magnetic spacer can counteract the effect of an external magnetic field, i.e., an enhancement due to the so-called Jaccarino-Peter compensation effect.PACS numbers: 74.78.Fk, 74.50.+r, 75.70.Cn     

Tomasch effect and superconducting proximity

Tunneling conductance measurements (dI/dV)(V) on thick and clean super-conducting films (S ₁ ) backed by normal metals (M ₂ ) show geometrical resonance effects, which have been associated with the variation (x) of the pair potential near the interface. We analyze both theoretically and experimentally the three factors involved in the resonance effect on S ₁ /M ₁ sandwiches where one of the films is superconducting. The first factor, period, has already received considerable attention and is connected with the ratioV _F ^* /d ₁ of the renormalized Fermi velocity and the thicknessd ₁ of the film S ₁ . We show that generally subharmonic effects, related to multiple interference effects, are expected. This result is demonstrated experimentally on Pb/M ₂ sandwiches. The phase depends on the sign of (x), the detailed shape of its variation, and on the nature of the tunneling process. Unfortunately the interplay among these parameters is difficult to analyze, although directive tunneling is found to fit better with experiments than the generally assumed diffuse tunneling. The amplitude of the resonance should be proportional to the change of (x). The ambiguity in the experimental results is pointed out and an experiment that shows clearly the role of the superconducting proximity mechanisms is described where the proximity on several simultaneously prepared Pb/Al films is controlled by deposition of various third upper layers. The theoretical discussion is an extension of the Ishii matrix formulation, itself based on an application of the Andreev scattering process.     

Nanoscale perspective: Materials designs and understandings in lithium metal anodes

Li metal chemistry is a promising alternative with a much higher energy density than that of state-of-the-art Li-ion counterparts. However, significant challenges including safety issues and poor cyclability have severely impeded Li metal technology from becoming viable. In recent years, nanotechnologies have become increasingly important in materials design and fabrication for Li metal anodes, contributing to major progress in the field. In this review, we first introduce the main achievements in Li metal battery systems fulfilled by nanotechnologies, particularly regarding Li metal anode design and protection, ultrastrong separator engineering, safety monitoring, and smart functions. Next, we introduce recent studies on nanoscale Li nucleation/deposition. Finally, we discuss possible future research directions. We hope this review delivers an overall picture of the role of nanoscale approaches in the recent progress of Li metal battery technology and inspires more research in the future.

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The long-range proximity effect: Pair echoes

Recent experiments on N-N-S junctions with high-temperature cuprate superconductors have shown that superconductivity can be induced in the adjacent, normal metal at distances many times greater than the few hundred Ångstroms range of the conventional proximity effect. We show that this arises in the particular geometry used in these experiments through the constructive interference of the tails of the de Gennes-Saint-James bound and quasi-bound states of the normal metal N that penetrate into the third metal, N. This constructive interference results in the re-appearance of a pair amplitude in this metal which is analogous to the spin echo of NMR and which we name a pair echo.     

Nanoscale leakage current measurements in metal organic chemical vapor deposition crystalline SrTiO3 films

The properties of SrTiO₃ thin films, grown by liquid injection metal organic chemical vapor deposition on Si/SiO₂, using a mixture of precursors, have been investigated at the nanoscale using an Atomic Force Microscope in the so-called Conductive Atomic Force Microscopy mode. Maps of the leakage currents with a nanometric resolution have been obtained on films elaborated at different temperatures and stoichiometries in order to discriminate the role of each parameter on the onset of leakage currents in the resulting layers. It appears that the higher the deposition temperature, the higher the leakage currents of the films. The mapping with a nanometric precision allows to show a heterogeneous behaviour of the surface with leaky grains and insulating boundaries. The study of films elaborated at the same temperature with different compositions supports the assumption that the leakage currents on Ti-rich layers are far higher than on Sr-rich layers.     

Microbial technologies for heavy metal remediation: effect of process conditions and current practices

Clean Technologies and Environmental Policy - Heavy metal (HM) contamination is a persisting environmental problem in many countries. The major sources of soil contamination due to heavy metals...     

Solubility and dissolution enhancement strategies: current understanding and recent trends

Identification of lead compounds with higher molecular weight and lower aqueous solubility has become increasingly prevalent with the advent of high throughput screening. Poor aqueous solubility of these lipophilic compounds can drastically affect the dissolution rate and subsequently the drug absorbed in the systemic circulation, imposing a significant burden of time and money during drug development process. Various pre-formulation and formulation strategies have been applied in the past that can improve the aqueous solubility of lipophilic compounds by manipulating either the crystal lattice properties or the activity coefficient of a solute in solution or both, if possible. However, despite various strategies available in the armor of formulation scientist, solubility issue still remains an overriding problem in the drug development process. It is perhaps due to the insufficient conceptual understanding of solubility and dissolution phenomenon that hinders the judgment in selecting suitable strategy for improving aqueous solubility and/or dissolution rate. This article, therefore, focuses on (i) revisiting the theoretical and mathematical concepts associated with solubility and dissolution, (ii) their application in making rationale decision for selecting suitable pre-formulation and formulation strategies and (iii) the relevant research performed in this field in past decade.     

Critical current measurements: A compendium of experimental results

The results of a programme to evaluate the measurement of the critical current of relatively small (<600 A) practical superconductors are presented. Experimental data showing the effect of various parameters on the measurement are given. Specific areas covered are: experimental design and sample mounting; electric field and resistivity criteria; temporal and spatial variations in the field and current; and temperature and strain effects. The goal of the presentation is to describe the critical current measurement process and its pitfalls in sufficient detail to serve as a guide for those relatively new to the field of practical superconductors.     

Field effect studies on p-type PbTe metal/insulator/semiconductor structures

Field effect studies on metal/insulator/semiconductor structures of Ag/mica/p-PbTe were made in the temperature range 120–300 K. It was observed that the effect of a negative voltage is to decrease the Hall coefficient, the Hall mobility and the defect scattering mobility. A positive gate voltage has the opposite effect and to a smaller extent. These results are explained on the basis of accumulation and depletion of charges induced by the field at the surface.     

Strong coupling theory and the Josephson current into proximity high-T c junctions

The correlation between the order parameter and the energy gap is studied. Josephson junctions containing proximity systems are described within the framework of the strong coupling theory. The value of the current is affected by the difference between the order parameter at zero frequency and the energy gap. The proximity effect leads to depression of the Josephson current for the high-critical-temperature junctions.     

Critical current studies on metal clad R1Ba2Cu3O7−x wires

Silver clad wires of R₁Ba₂Cu₃O_7−x (R=Y, Gd, Sm, Dy and Ho) have been fabricated following the powder-in-tube method and cold-rolling. The critical current densityJ _c at 77 K and zero magnetic field is restricted to 66 A.cm⁻². In a separate experiment we have studied the effect of silver sheath thickness onJ _c of the Y₁Ba₂Cu₃O_7−x wires. Interestingly,J _c is higher for larger sheath thickness indicating that large sheath thickness prevents oxygen loss during sintering. Uniaxial pressing of the wires into flat tapes results in an increase of theJ _c . MaximumJ _x is, however, limited to 169 A.cm⁻². No grain alignment is found in the core material of our wires which is essential for highJ _c . Several options are being tried.     

Nanoscale Joule heating, Peltier cooling and current crowding at graphene-metal contacts

The performance and scaling of graphene-based electronics is limited by the quality of contacts between the graphene and metal electrodes. However, the nature of graphene-metal contacts remains incompletely understood. Here, we use atomic force microscopy to measure the temperature distributions at the contacts of working graphene transistors with a spatial resolution of ~ 10 nm (refs 5-8), allowing us to identify the presence of Joule heating, current crowding and thermoelectric heating and cooling. Comparison with simulation enables extraction of the contact resistivity (150-200 Ω μm2) and transfer length (0.2-0.5 μm) in our devices; these generally limit performance and must be minimized. Our data indicate that thermoelectric effects account for up to one-third of the contact temperature changes, and that current crowding accounts for most of the remainder. Modelling predicts that the role of current crowding will diminish and the role of thermoelectric effects will increase as contacts improve.     

Superconducting nucleation fields and proximity effect of normal-superconducting-normal triple layers

Superconducting nucleation fields for normal-superconducting-normal (nsn) triple layers are calculated when the static magnetic field is applied parallel to thens boundaries, thes layer is of arbitrary thickness, and then metals are identical and very thick. Comparing these results with experiments by Jain and Tilley on Cu-Pb-Cu triple layers, one finds that Zaitsev's microscopicns boundary conditions apply (at least approximately) over a wide range of temperatures at the nucleation field. This implies thatp _FG is continuous across ans boundary for diffuse and _G for specular electron scattering (_G is the Gor'kov pair potential, p_F the Fermi momentum). Furthermore, the magnitudes of the order parameters on thens boundary are similar for Cu and Pb over a wide range of temperatures in large magnetic fields.