One-pot synthesis of ultranarrow single crystal ZnSe nanowires

High-quality wurtzite-type ultranarrow single crystal ZnSe nanowires were synthesized via a one-pot, solution-based method for the first time. The as-prepared nanowires have diameters ranging from 1.0 nm to 3.5 nm and lengths up to 300 nm. The optical characterizations indicate that the as-synthesized ZnSe nanowires have a band gap of 3.31 eV, whose absorbance spectra are different from recent literatures. Both the quantum confinement and the vacancies of Zn in ZnSe or impurities were accounted for the phenomenon. The solvent employed in the synthesis is also playing a dominant role in the size and morphology control of the ZnSe nanowires. A reasonable mechanism was proposed to describe the function of solvent. The excellent properties of the ZnSe nanowires would render it a promising alternative functional material which might be widely used in short-wavelength lasers and other photoelectronic devices.     

Size dependent breakdown of superconductivity in ultranarrow nanowires

Below a certain temperature T(c) (typically cryogenic), some materials lose their electric resistance R entering a superconducting state. Following the general trend toward a large scale integration of a greater number of electronic components, it is desirable to use superconducting elements in order to minimize heat dissipation. It is expected that the basic property of a superconductor, i.e., dissipationless electric current, will be preserved at reduced scales required by modern nanoelectronics. Unfortunately, there are indications that for a certain critical size limit of the order of approximately 10 nm, below which a "superconducting" nanowire is no longer a superconductor in a sense that it acquires a finite resistance even at temperatures close to absolute zero. In the present paper we report experimental evidence for a superconductivity breakdown in ultranarrow quasi-1D aluminum nanowires.     

Hierarchical assembly of ultranarrow alkylamine-coated ZnS nanorods: a synchrotron surface X-ray diffraction study

The packing of anisotropic ultranarrow nanoparticles ( r 相似文献   

High ferromagnetic transition temperature in PbS and PbS:Mn nanowires

Spontaneous magnetization measured in the temperature range 5-300 K with high ferromagnetic transition temperature (T(c)) has been observed in both undoped and Mn doped (2-8 mol %) PbS nanowires (diameter 30 nm) in polymer. For undoped sample, we find T(c) ~ 290 K while for doped samples T(c) varies between 310-340 K depending on Mn concentrations. Both T(c) and coercive fields are critically dependent on Mn concentrations. Coercive fields show a T(0.5) dependence with temperature for a moderate concentration of Mn (4 mol %) in PbS while it deviates from T(0.5) behavior for higher Mn concentrations. Anionic defects arising out of nonstoichiometric growth is solely responsible for the observed magnetism in undoped PbS nanowires. The role of intrinsic strain along with reduced dimensionality in determining such high T(c) and overall magnetizations has been discussed.     

Synthesis of platinum dendrites and nanowires via directed electrochemical nanowire assembly

Directed electrochemical nanowire assembly is a promising high growth rate technique for synthesizing electrically connected nanowires and dendrites at desired locations. Here we demonstrate the directed growth and morphological control of edge-supported platinum nanostructures by applying an alternating electric field across a chloroplatinic acid solution. The dendrite structure is characterized with respect to the driving frequency, amplitude, offset, and salt concentration and is well-explained by classical models. Control over the tip diameter, side branch spacing, and amplitude is demonstrated, opening the door to novel device architectures for sensing and catalytic applications.     

Effect of point defects and impurities on the electronic transport of Au tipped ultranarrow PbS nanorods

Electronic transport through single nanowire/nanorod directly probes the fundamental limits of semiconductor device miniaturization. Point defects or impurity centers form easily during the growth of nanorods/nanowires which may strongly affect the electronic transport efficiencies. Existing models of electronic transport are often unable to determine the role of defects and impurities at the nanoscale because there are significant differences between nanostructures and bulk materials arising from unique geometries and confinement. The effect of defect and impurities on the conductance of a model ultranarrow PbS rod was modeled using density functional theory. It was observed that the introduction of defects and Au impurities modified the orbital energies of PbS nanorods and reduced the conductance compared to the defect-free rod. The conductance for the nanorods with defects and impurities were limited by the number of available conduction channels required for efficient electronic conduction.     

Fabrication of luminescent silver doped PbS nanowires in polymer

We report here fabrication of silver (0 to 1.76 mol%) doped PbS nanowires (radius r approximately 1.75 nm) in polymer by a simple wet chemical process. An X-ray photoelectron spectroscopy study clearly confirms the possibility of silver (Ag) doping in PbS nanowires. Both absorption and photoluminescence spectra reveal very strong quantum confinement effect in PbS nanowires as expected for a r/Bohr radius ratio approximately 0.0972 nm. Visible excitonic emission is observed at room temperature in the photoluminescence spectra of undoped and silver doped PbS nanowires in polymer. The excitonic emission is appreciably blue-shifted when doped by silver (1.76 mol%) indicating strong modification of the electronic states by magnetic silver ions. While Ag2+ centers at the substitutional lattice site show an emission band around 525 nm, Ag0 at the interstitial site act as nonradiative recombination centers. Effect of silver doping on the luminescence intensity is also discussed.     

Designing and building nanowires: directed nanocrystal self-assembly into radically branched and zigzag PbS nanowires

Lead sulfide nanowires with controllable optoelectronic properties would be promising building blocks for various applications. Here, we report the hot colloidal synthesis of radically branched and zigzag nanowires through self-attachment of star-shaped and octahedral nanocrystals in the presence of multiple surfactants. We obtained high-quality single-crystal nanowires with uniform diameter along the entire length, and the size of the nanowire can be tuned by tailoring the reaction parameters. This slow oriented attachment provides a better understanding of the intricacies of this complex nanocrystal assembly process. Meanwhile, these self-assembled nanowire structures have appealing lateral conformations with narrow side arms or highly faceted edges, where strong quantum confinement can occur. Consequently, the single-crystal nanowire structures exhibit strong photoluminescence in the near-infrared region with a large blue-shift compared to the bulk material.     

Layer-by-layer assembly of nanowires for three-dimensional, multifunctional electronics

We report a general approach for three-dimensional (3D) multifunctional electronics based on the layer-by-layer assembly of nanowire (NW) building blocks. Using germanium/silicon (Ge/Si) core/shell NWs as a representative example, ten vertically stacked layers of multi-NW field-effect transistors (FETs) were fabricated. Transport measurements demonstrate that the Ge/Si NW FETs have reproducible high-performance device characteristics within a given device layer, that the FET characteristics are not affected by sequential stacking, and importantly, that uniform performance is achieved in sequential layers 1 through 10 of the 3D structure. Five-layer single-NW FET structures were also prepared by printing Ge/Si NWs from lower density growth substrates, and transport measurements showed similar high-performance characteristics for the FETs in layers 1 and 5. In addition, 3D multifunctional circuitry was demonstrated on plastic substrates with sequential layers of inverter logical gates and floating gate memory elements. Notably, electrical characterization studies show stable writing and erasing of the NW floating gate memory elements and demonstrate signal inversion with larger than unity gain for frequencies up to at least 50 MHz. The ability to assemble reproducibly sequential layers of distinct types of NW-based devices coupled with the breadth of NW building blocks should enable the assembly of increasing complex multilayer and multifunctional 3D electronics in the future.     

Growth,coalescence,and etching of two-dimensional overlayers on metals modulated by near-surface Ar nanobubbles

The synthesis of high-quality ultrathin overlayers is critically dependent on the surface structure of substrates,especially involving the overlayer-substrate i...     

Hyperbranched PbS and PbSe nanowires and the effect of hydrogen gas on their synthesis

We report a chemical vapor deposition (CVD) synthesis of hyperbranched single-crystal nanowires of both PbS and PbSe using PbCl2 and S/Se as precursors under hydrogen flow. Multiple generations of nanowires grow perpendicularly from the previous generation of nanowires in an epitaxial fashion to produce dense clusters of a complex nanowire network structure. The flow rate and duration of the hydrogen co-flow in the argon carrier gas during the CVD reactions are found to have a significant effect on the morphology of the PbS/PbSe grown, from hyperbranched nanowires to micrometer-sized cubes. No intentional catalyst was employed for the nanowire synthesis, but it is suggested that elemental lead that has been reduced from the vapor by the hydrogen might serve as a vapor-liquid-solid (VLS) catalyst for the anisotropic growth of PbS/PbSe. The nanowires were also investigated with Raman spectroscopy. These PbS and PbSe nanostructures can have applications in photovoltaics because multiple exciton generation has been demonstrated in nanocrystals of both materials.     

Controlled assembly of spherical nanoparticles: nanowires and spherulites

A large variety of nanoparticles hold extraordinary promise for practical applications in catalysis, materials science, medicine, and so on. It is, however, necessary to assemble them into supramolecular aggregates with desired structural properties. In this work we explore the self-assembly of spherical nanoparticles induced by interactions that, due to entropic effects, may become anisotropic. The spherical nanoparticles considered attract each other via square-well potentials, mimicking dispersive interactions. To induce anisotropic effects, short polymer brushes are bound to the nanoparticles but only on the equatorial plane. The brushes are treated as tangent-hard-sphere chains. Nanoparticles with such morphology could be synthesized experimentally. Monte Carlo calculations are conducted to assess the properties of the self-assembled nanostructures as a function of the length of the brushes and of the depth of the particle-particle square-well potential. Our results indicate that for strongly attractive particle-particle interactions it is possible to obtain supramolecular spherulites (employing short brushes) or uniform dispersions (using long brushes). At some intermediate lengths of the polymer brushes, the formation of one-dimensional wires occurs. Our results are useful for designing responsive nanoparticles that reversibly assemble yielding uniform dispersions, nanowires, or spherulites depending on the solution conditions.     

Conductance, surface traps, and passivation in doped silicon nanowires

We perform ab initio calculations within the Landauer formalism to study the influence of doping on the conductance of surface-passivated silicon nanowires. It is shown that impurities located in the core of the wire induce a strong resonant backscattering at the impurity bound state energies. Surface dangling bond defects have hardly any direct effect on conductance, but they strongly trap both p- and n-type impurities, as evidenced in the case of H-passivated wires and Si/SiO2 interfaces. Upon surface trapping, impurities become transparent to transport, as they are electrically inactive and do not induce any resonant backscattering.     

Surfactant mediated assembly of gold nanowires on surfaces

The potential of surfactant interactions to direct both the placement and orientation of gold nanowires onto surfaces from solution has been investigated. Gold nanowires were synthesized by template electrodeposition in porous aluminum oxide membranes. Their assembly onto surfaces was controlled by functionalizing the nanowires and surfaces with self-assembled monolayers of thiol based surfactants. Nanowires were assembled from solution onto patterned functional surfaces, and after excess solvent had evaporated the arrangement of nanowires on the surface was observed. A variety of assembly techniques, based upon wettability, electrostatic, or chemical interactions have been studied. Nanowire assembly onto surfaces with patterned wettability resulted in the placement of nanowires on hydrophilic regions with a specific orientation. Hydrogen bonding and carboxylate salt attachment of mercaptoundecanoic acid functionalized nanowires to reactive regions of patterned surfaces has been demonstrated, with unbound wires removed by washing. Similarly, electrostatic interactions between charged nanowires and surfaces have been demonstrated to preferentially assemble nanowires onto oppositely charged surface regions. Although selective attachment of nanowires to reactive surface regions was achieved by both chemical and electrostatic assembly techniques, these methods did not control the orientation of assembled nanowires.     

Aligned nanowires and nanodots by directed block copolymer assembly

The directed self-assembly of block copolymers (BCPs) is a promising route to generate highly ordered arrays of sub-10 nm features. Ultradense arrays of a monolayer of spherical microdomains or cylindrical microdomains oriented parallel to the surface have been produced where the lateral ordering is guided by surface patterning and the lattice defined by the patterning can be commensurate or incommensurate with the natural period of the BCP. Commensurability between the two can be used to elegantly manipulate the lateral ordering and orientation of the BCP microdomains so as to form well-aligned arrays of 1D nanowires or 2D addressable nanodots. No modification of the substrate surface, aside from the patterning, was used, making the influence of lattice mismatch and pattern amplification on the size, shape and pitch of the BCP microdomains more transparent. A skew angle between incommensurate lattices, defining a stretching or compression of the BCP chains to compensate for the lattice mismatch, is presented.     

Probe based manipulation and assembly of nanowires into organized mesostructures

A convenient approach to patterning inorganic and organic nanowires using a novel probe manipulator is presented. The system utilizes an electrochemically etched tungsten wire probe mounted onto a 3D actuator that is directed by a 3D controller. When it is engaged by the user, the movement of the probe and the forces experienced by the tip are simultaneously reported in real time. Platinum nanowires are manipulated into organized mesostructures on silicon chip substrates. In particular, individual nanowires are systematically removed from aggregates, transferred to a chosen location, and manipulated into complex structures in which selected wires occupy specific positions with defined orientations. Rapid prototyping of complex mesostructures, by pushing, rotating and bending conjugated polymer, i.e., polyfluorene, nanowires into various configurations, is also achieved. By exploiting the strong internal axial alignment of polymer chains within the polyfluorene nanowires, mesostructures tailored to exhibit distinctly anisotropic optical properties, such as birefringence and photoluminescence dichroism, are successfully assembled on fused silica substrates.     

Synthesis and characterization of srilankite nanowires

We describe the synthesis and characterization of srilankite (Ti2ZrO6) nanowires. The nanowires are produced via hydrothermal synthesis with a TiO2/ZrO2 mixture under alkaline conditions. The zirconium titanate nanowires have median diameters of 60 nm and median lengths of 800 nm with the (022) axis along the length of the nanowire. Electron microscopy, energy dispersive X-ray spectroscopy, powder X-ray diffraction, and electron diffraction are used to characterize the phases and compare nanowires produced with varying molar ratios of Ti and Zr. Electron diffraction patterns produced from single nanowires show highly crystalline nanowires displaying a compositional-ordering superlattice structure with Zr concentrated in bands within the crystal structure. This is in contrast to naturally occurring bulk srilankite where Zr and Ti are randomly substituted within the crystal lattice. Streaking is observed in the electron diffraction patterns suggesting short-range ordering within the superlattice structure.