Synthesis and characterization of Mo6S4.5I4.5 nanowires

We report on the synthesis and characterization of new a nano-wire-like material with chemical formula Mo6S4.5I4.5. The material can be synthesized in a single step reaction from elements in bulk quantities. The material has a fur-like appearance and is composed of nanowires that are weakly bound in bundles. Bundles itself can be dispersed using an ultrasonic bath in various organic solvents and water. Elemental analysis, X-ray diffraction, thermal analysis (TG, DTA), and electron microscopy were used to characterize the new material in the shape of nanowires. Due to their monodisperse and metallic nature, molybdenum-sulphur-iodine nanowires are an interesting alternative to carbon nanotubes for some applications.     

Bioassembled nanocircuits of Mo6S9-xIx nanowires for electrochemical immunodetection of estrone Hapten

We demonstrate a novel and highly sensitive electrochemical detection of estrone based on an immunosensor platform, composed of bioassembled nanocircuits of Mo 6S 9- x I x nanowires (MoSI NWs) covalently connected to anti-estrone antibodies. The one-step, label-free, and quantitative detection of estrone is realized by employing the [Ru(NH 3) 6] (3+/2+) redox ions to sense anti-estrone antibody and estrone interactions. The MoSI NWs/anti-estrone antibody nanocircuit architectures provide an amplification and conductive pathway for the specific electrochemical sensing of estrone hapten. A detection limit of 1.4 pg x mL (-1) was achieved in contrast to previous electrochemical techniques in which the sensitivity was limited to the nanomolar range.     

The triclinic structure of Cu1.8Mo6S8 in the superconducting state

An x-ray powder diffraction analysis at 5 K shows that the structure of Cu_1.8Mo₆S₈ in the superconducting state is a triclinic distorted version of the rhombohedral room temperature structure. The distortion is due to a clustering of the Cu atoms into pairs [d(Cu-Cu) = 2.58 å] as the compound transforms at 270 K from the disordered high-temperature into the ordered low-temperature modification.     

Mo6S9-xIx nanowire recognitive molecular-scale connectivity

We report on a new highly reproducible route to recognitive self-assembly of molecular-scale circuits using sulfur-terminated subnanometer diameter Mo6S9-xIx (MoSIx) molecular nanowires. We demonstrate solution-processed attachment of MoSIx connecting leads to gold nanoparticles (GNPs). We also show that naked nanowires have the potential to bind thiolated proteins such as green fluorescent protein directly, thus providing a universal construct to which almost any protein could be attached. We further demonstrate three-terminal branched circuits with GNPs, opening a self-assembly route to multiscale complex molecular-scale architectures at the single-molecule level.     

Atomic-scale interface structure of a Cr-coated Zircaloy-4 material

Highly adherent, thin Cr coatings on Zr-based nuclear fuel claddings can be potentially used for the development of accident-tolerant fuels in light water reactors. To guarantee the successful implementation of Cr-coated Zr alloys as cladding tubes in nuclear power plants, the adhesive strength of the Cr coatings must be assessed. The interface between Cr and Zr was characterized via high-resolution transmission electron microscopy. We observed the formation of nanometer-thick Zr(Fe, Cr)₂ poly-type, structured Laves phases at the interfacial region that display both C14 and C15 lattice symmetries. Although the crystallinity was preserved throughout the interfacial region, different atomic configurations were observed for all the interfaces studied. In most cases, coherent or semicoherent crystallographic relationships were observed, ensuring the adhesive strength of the coating.     

On the microscopic interaction in the Chevrel compounds Cu2Mo6S8 and Mo6Se8

The available data on the superconducting properties of Cu₂Mo₆S₈ and Mo₆Se₈ are used to gain some insight into their microscopic parameters ² F() and *, the electron-photon spectral density and Coulomb pseudopotential, respectively. While thermodynamic data play a prominent role in the analysis, use is also made of information on the generalized phonon frequency distributionG() and, for the case of Cu₂Mo₆S₈, on the second derivative of current-voltage tunneling data. The parameters obtained are tested against upper critical magnetic field data. The work suggests that the electron mass enhancement parameter may be of order 2 with * unusually large.     

Superconducting tunneling on Cu x Mo6S8 films

Superconducting tunneling junctions were fabricated on sputtered Cu _x Mo₆S₈ films with Al₂O₃ and SiO₂ barriers. The energy gap was determined by the first derivative measurement. The ratio 2_o/k _B T _c obtained in the experiment clearly indicates the strong coupling nature of Cu _x Mo₆S₈. Preliminary results of the second derivative measurements show phonon structure, which agrees reasonably well with inelastic neutron scattering measurements.Work supported by NSF grant DMR 81-08421.     

Tunneling spectroscopy on the superconducting Chevrel-phase compounds Cu1.8Mo6S8 and PbMo6S8

The Chevrel-phase compounds PbMo₆S₈ and Cu_1.8Mo₆S₈ have been investigated by tunneling spectroscopy. These superconductors show a very strong electron-phonon interaction expressed by 42₀/kT _c5. Structures in the tunneling density of states have been observed at most energies where the phonon spectra show maxima. The coupling of high-energy modes of the Mo₆S₈ units and of modes associated with displacements of the Pb (Cu) atoms are discussed.     

Magnetic susceptibility of (rare earth) x Mo6S8

We have studied the susceptibility of all (RE) _x Mo₆S₈ compounds between 1.3 and 300 K (RE = rare earth). In the two superconducting compounds Ho _1.2 Mo ₆ S ₈ and Dy _1.2 Mo₆S₈ magnetic ordering is expected in the temperature range 0.1–1 K. The magnetic transition in CeMo₆S₈ at2.25 K is of antiferromagnetic nature. A second anomaly at 1.6 K in this compound may announce a low-temperature ferromagnetic state.     

Band structure analysis in SiGe nanowires

One of the main challenges for Silicon-Germanium nanowires (SiGe NWs) electronics is the possibility to modulate and engine their electronic properties in an easy way, in order to obtain a material with the desired electronic features. Diameter and composition constitute two crucial ways for the modification of the band gap and of the band structure of SiGe NWs. Within the framework of density functional theory we present results of ab initio calculations regarding the band structure dependence of SiGe NWs on diameter and composition. We point out the main differences with respect to the case of pure Si and Ge wires and we discuss the particular features of SiGe NWs that are useful for future technological applications.     

Critical current and scaling laws in evaporated two-phase Cu2.5Mo6S8

We have measured critical currents I _c of an evaporated Cu _x Mo₆S₈ (x = 2.5±0.3) film as a function of an external perpendicular field B up to the upper critical field B _c2, at several temperatures (T 4.2K). Results for the pinning force per unit length F = I _c B do not obey a scaling law. That is, F = K(T)f (b), where K and f are general functions of the temperature T and the reduced field b = B/B _c2, respectively. By comparing data with other evaporated and sputtered Cu _x Mo₆S₈ with x 2, we have separated the pinning force into two parts, each one obeying a scaling law. The recently published phase diagram of Cu _x Mo₆S₈, along with our results, suggests that critical current and pinning in this material are controlled by two superconducting phases.National Research Council Senior Research Associate, on leave of absence from Department of Physics, Tel Aviv University, Tel Aviv, Israel.     

固氮酶钼铁蛋白单钼铁硫簇(Mo9Fe6S)的理化特性研究

以棕色固氮菌固氮酶钼铁蛋白为研究材料且用碱性二甲基甲酰胺(DMF)作为铁硫簇的提取剂,所获得金属簇为单钥铁硫簇,该簇的分子组成经电感藕合等离子体发射光谱仪(ICP)和质子激发X射线光谱仪(PIXE)等测定后,确定为Mo9Fe6S,不含有机组份。此外,该簇在可见区的光谱特性与双钼铁硫簇(活性中心)的光谱特性相似,但所表达的生物重组活性却明显低于双钼铁硫簇的活性,推测单,双钼铁硫簇在分子结构上存在局部的相似性。     

Preparation,crystal structure and characterization of α-NaSbP2S6 and β-NaSbP2S6 phases

The new phases α-NaSbP₂S₆ and β-NaSbP₂S₆ were synthesized by ceramic and reactive flux methods at 773 K. The structures of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by the single-crystal X-ray diffraction technique. α-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁/c with a = 11.231(2) Å, b = 7.2807(15) Å, c = 11.640(2) Å, β = 108.99(3)°, V = 900.0(3) Å³ and z = 4. β-NaSbP₂S₆ crystallizes in the monoclinic space group P2₁ with a = 6.6167(13) Å, b = 7.3993(15) Å, c = 9.895(2) Å, β = 92.12(3) °, V = 484.10(17) Å³ and z = 2.The α- and β-phases of NaSbP₂S₆ are closely related, the main difference lies in the stacking of the [Sb[P₂S₆]]_nⁿ⁻ layers. The structure of α-NaSbP₂S₆ consists of two condensed layers (MPS₃ type) to give an ABAB… sequence with Na⁺ cations located in the interlayer space. The packing of β-NaSbP₂S₆ is formed by monolayers of [Sb[P₂S₆]]_nⁿ⁻ stacked in an AA… fashion separated by a layer of Na⁺ cations. Both phases are derivates of the M¹⁺M³⁺P₂Q₆ family.The optical band gaps of α-NaSbP₂S₆ and β-NaSbP₂S₆ were determined by UV–vis diffuse reflectance measurements to be 2.17 and 2.25 eV, respectively.     

SnO_2纳米线的合成与结构表征

采用化学气相沉积法在经表面活性剂与硝酸镍的混合溶液处理过的硅衬底上成功制备出了直径均匀可控的二氧化锡(SnO2)纳米线。利用扫描电子显微镜、透射电子显微镜、选区电子衍射、X射线衍射等手段对样品的表面形貌、微结构及成分等进行了表征分析。并在此基础上讨论了纳米线所遵循的生长机理。     

Strain-driven electronic band structure modulation of si nanowires

One of the major challenges toward Si nanowire (SiNW) based photonic devices is controlling the electronic band structure of the Si nanowire to obtain a direct band gap. Here, we present a new strategy for controlling the electronic band structure of Si nanowires. Our method is attributed to the band structure modulation driven by uniaxial strain. We show that the band structure modulation with lattice strain is strongly dependent on the crystal orientation and diameter of SiNWs. In the case of [100] and [111] SiNWs, tensile strain enhances the direct band gap characteristic, whereas compressive strain attenuates it. [110] SiNWs have a different strain dependence in that both compressive and tensile strain make SiNWs exhibit an indirect band gap. We discuss the origin of this strain dependence based on the band features of bulk silicon and the wave functions of SiNWs. These results could be helpful for band structure engineering and analysis of SiNWs in nanoscale devices.     

The anisotropy of the upper critical field of the Chevrel-phase compound Cu1.8Mo6S8

The anisotropy of the upper critical field has been measured on deoxygenated single crystals of the Chevrel-phase Cu_1.8Mo₆S₈. Data were taken with the applied magnetic field pointing in various directions in the hexagonal and (001) planes. The data reflect the low-temperature, triclinic symmetry of the crystal structure. At each of a series of field values, oscillations in the superconducting transition temperature were observed. Since theH _c2 versusT curve is linear in the field region probed, the shape of the anisotropy inT _c at constantH is the same as the anisotropy of the upper critical fieldH _c2 at constantT. Oscillations with pseudo-threefold symmetry have been observed for the first time in the (001) plane. The data are fitted with an expansion of spherical harmonics with triclinic symmetry.     

Crystal structure transfer in core/shell nanowires

Structure engineering is an emerging tool to control opto-electronic properties of semiconductors. Recently, control of crystal structure and the formation of a twinning superlattice have been shown for III-V nanowires. This level of control has not been obtained for Si nanowires, the most relevant material for the semiconductor industry. Here, we present an approach, in which a designed twinning superlattice with the zinc blende crystal structure or the wurtzite crystal structure is transferred from a gallium phosphide core wire to an epitaxially grown silicon shell. These materials have a difference in lattice constants of only 0.4%, which allows for structure transfer without introducing extra defects. The twinning superlattices, periodicity, and shell thickness can be tuned with great precision. Arrays of free-standing Si nanotubes are obtained by a selective wet-chemical etch of the core wire.