The interaction between superconductivity and ferromagnetism, which entails incompatible spin order, is one of the problems of fundamental interest in condensed-matter physics. In general, when a ...ferromagnet is placed in contact with a superconductor, the Cooper pairs from the superconductor are not expected to survive beyond at most a few nanometres into the ferromagnet. Here we present a systematic study of single-crystal ferromagnetic cobalt nanowires sandwiched between superconducting electrodes. Surprisingly, we find that a cobalt wire as long as 600 nm attains zero resistance at low temperatures. For even longer nanowires, the transition to incomplete superconductivity is foreshadowed by a strikingly large and sharp resistance peak near the superconducting transition temperature of the electrodes. Although the origin of the 'critical peak' remains mysterious, our analysis strongly points against charge or spin imbalance as its underlying cause. PUBLICATION ABSTRACT
Although the main Raman features of semiconducting transition metal dichalcogenides are well known for the monolayer and bulk, there are important differences exhibited by few layered systems which ...have not been fully addressed. WSe2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe2, MoSe2, WS2 and MoS2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E', E″ and E2g modes shift to lower frequencies, and the A'1 and A1g modes shift to higher frequencies. Second, new high frequency first order A'1 and A1g modes appear, explaining recently reported experimental data for WSe2, MoSe2 and MoS2. Third, splitting of modes around A'1 and A1g is found which explains those observed in MoSe2. Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD.
Combinatorial methods were used to search for active alloy electrocatalysts for use in enzyme-free amperometric glucose sensors. Electrode arrays (715-member) containing combinations of Pt, Pb, Au, ...Pd, and Rh were prepared and screened by converting anodic current to visible fluorescence. The most active compositions contained both Pt and Pb. Bulk quantities of catalysts with compositions corresponding to those identified in the screening experiments were prepared and characterized. The best alloy electrocatalysts catalyzed glucose oxidation at substantially more negative potentials than pure platinum in enzyme-free voltammetric measurements. They were also insensitive to potential interfering agents (ascorbic and uric acids, and 4-acetamidophenol), which are oxidized at slightly more positive potentials. Rotating disk electrode (RDE) experiments were carried out to study the catalytic mechanism. The improvement in catalytic performance was attributed to the inhibition of adsorption of oxidation products, which poison Pt electrodes.
Ordered mesoporous polymers have been prepared by replication of colloidal crystals made from silica spheres 35 nanometers in diameter. The pores in the colloidal crystals were filled with ...divinylbenzene (DVB), ethyleneglycol dimethacrylate (EDMA), or a mixture of the two. Polymerization and subsequent dissolution of the silica template leaves a polycrystalline network of interconnected pores. When mixtures of DVB and EDMA are used, the pore size of the polymer replicas can be varied continuously between 35 and 15 nanometers because the polymer shrinks when the silica template is removed.
The coverage of Au surfaces with Au nanowires by linking them with DNA offers great prospects for the assembly of wire structures with particular connectivity. This work presents the first example of ...using DNA hybridization to control the assembly of micrometer‐size inorganic particles on surfaces. The Figure shows the optical microscopy image of Au nanowires modified with DNA.
Free‐standing SiO2 nanotubes have been synthesized by surface sol–gel replication of the pores of alumina membranes. The nanotubes are very flexible (as shown in the Figure) and their walls are ...smooth and uniformly thick along their length. SiO2‐insulated nanowires were also grown, by electroplating gold inside the SiO2‐coated pores of the membrane, and their I–V characteristics were examined.
Combinatorial screening of electrochemical catalysts by current-voltage methods can be unwieldy for large sample sizes. By converting the ions generated in an electrochemical half-cell reaction to a ...fluorescence signal, the most active compositions in a large electrode array have been identified. A fluorescent acid-base indicator was used to image high concentrations of hydrogen ions, which were generated in the electrooxidation of methanol. A 645-member electrode array containing five elements (platinum, ruthenium, osmium, iridium, and rhodium), 80 binary, 280 ternary, and 280 quaternary combinations was screened to identify the most active regions of phase space. Subsequent "zoom" screens pinpointed several very active compositions, some in ternary and quaternary regions that were bounded by rather inactive binaries. The best catalyst, platinum(44)/ruthenium(41)/osmium(10)/iridium(5) (numbers in parentheses are atomic percent), was significantly more active than platinum(50)/ruthenium(50) in a direct methanol fuel cell operating at 60°C, even though the latter catalyst had about twice the surface area of the former.
Metal nanowires coated with multilayer films of (TiO2/W12O41)3(PAN/SWNT)3PAN (12 nm thick; PAN: Polyaniline; SWNT: single‐walled carbon nanotube) are synthesized using different, templated, ...layer‐by‐layer assembly techniques. Their I–V characteristics indicate a built‐in p–n junction at the TiO2/PAN interface (rectification ratio >120 at 3 V). Films grown on planar substrates have similar thickness, morphology, and electrical properties.
Small‐scale synthetic motors capable of generating their own motive forces by exploiting the chemical free energy of their environment represent an important step in developing practical ...nanomachines. Catalytic particles are capable of generating concentration and other gradients that can be used to self‐propel small objects. However, the autonomous movement of catalytic nanoparticles by self‐generated forces is a relatively unexplored area in colloid and interfacial chemistry. This paper explores the potential of catalytically self‐generated forces for propulsion of small objects through fluids.
Minute Motors: Small‐scale synthetic motors capable of generating their own motive forces by exploiting the chemical free energy of their environment represent an important step in developing practical nanomachines. A Pt/Au nanorod that can act as a nanomotor is illustrated here schematically.
We measured the electronic properties and gas sensing response of nanowires containing segments of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS) that were synthesized using ...anodic aluminum oxide (AAO) membranes. The nanowires have a “striped” structure of gold-PEDOT/PSS-gold and are typically 8
μm long (1
μm-6
μm-1
μm for each section, respectively) and 220
nm in diameter. Dielectrophoretic assembly was used to position single nanowires on pre-fabricated gold electrodes. A polymer conductivity of 11.5
±
0.7
S/cm and a contact resistance of 27.6
±
4
kΩ were inferred from resistance measurements of nanowires of varying length and diameter. When used as gas sensors, the wires showed a resistance change of 10.5%, 9%, and 4% at the saturation vapor pressure of acetone, methanol and ethanol, respectively. Sensor response and recovery were rapid (seconds) with excellent reproducibility in time and across devices. “Striped” template-grown nanowires are thus intriguing candidates for use in electronic nose vapor sensing systems.
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