Large-scale controllable patterning growth of aligned organic nanowires through evaporation-induced self-assembly

Organic one-dimensional nanostructures are attractive building blocks for electronic, optoelectronic, and photonic applications. Achieving aligned organic nanowire arrays that can be patterned on a surface with well-controlled spatial arrangement is highly desirable in the fabrication of high-performance organic devices. We demonstrate a facile one-step method for large-scale controllable patterning growth of ordered single-crystal C(60) nanowires through evaporation-induced self-assembly. The patterning geometry of the nanowire arrays can be tuned by the shape of the covering hats of the confined curve-on-flat geometry. The formation of the pattern arrays is driven by a simple solvent evaporation process, which is controlled by the surface tension of the substrate (glass or Si) and geometry of the evaporation surface. By sandwiching a solvent pool between the substrate and a covering hat, the evaporation surface is confined to along the edge of the solvent pool. The geometry of the formed nanowire pattern is well defined by a surface-tension model of the evaporation channel. This simple method is further established as a general approach that is applicable to two other organic nanostructure systems. The I-V characteristics of such a parallel, organic, nanowire-array device was measured. The results demonstrate that the proposed method for direct growth of nanomaterials on a substrate is a feasible approach to device fabrication, especially to the fabrication of the parallel arrays of devices.     

Fabrication of hexaphenylsilole nanowires and their morphology-tunable photoluminescence.

Immersion of nanoporous alumina membranes into saturated solutions of hexaphenylsilole with subsequent solvent evaporation affords aligned organic nanowires. The luminescent properties of the hexaphenylsilole nanowires can be manipulated by varying their morphologies, which were controlled by changing the channel sizes of the alumina templates.     

Covalent Modification of MoS2 with Poly(N‐vinylcarbazole) for Solid‐State Broadband Optical Limiters

New soluble MoS₂ nanosheets covalently functionalized with poly(N‐vinylcarbazole) (MoS₂–PVK) were in situ synthesized for the first time. In contrast to MoS₂ and MoS₂/PVK blends, both the solution of MoS₂–PVK in DMF and MoS₂–PVK/poly(methyl methacrylate) (PMMA) film show superior nonlinear optical and optical limiting responses. The MoS₂–PVK/PMMA film shows the largest nonlinear coefficients (β_eff) of about 917 cm GW^?1 at λ=532 nm (cf. 100.69 cm GW^?1 for MoS₂/PMMA and 125.12 cm GW^?1 for MoS₂/PVK/PMMA) and about 461 cm GW^?1 at λ=1064 nm (cf. ?48.92 cm GW^?1 for MoS₂/PMMA and 147.56 cm GW^?1 for MoS₂/PVK/PMMA). A larger optical limiting effect, with thresholds of about 0.3 GW cm^?2 at λ=532 nm and about 0.5 GW cm^?2 at λ=1064 nm, was also achieved from the MoS₂–PVK/PMMA film. These values are among the highest reported for MoS₂‐based nonlinear optical materials. These results show that covalent functionalization of MoS₂ with polymers is an effective way to improve nonlinear optical responses for efficient optical limiting devices.     

Optical and field emission properties of thin single-crystalline GaN nanowires

Thin high-quality gallium nitride (GaN) nanowires were synthesized by a catalytic chemical vapor deposition method. The synthesized GaN nanowires with hexagonal single-crystalline structure had thin diameters of 10-50 nm and lengths of tens of micrometers. The thin GaN nanowires revealed UV bands at 3.481 and 3.285 eV in low-temperature PL measurements due to the recombination of donor-bound excitons and donor-acceptor pairs, respectively. The blue shifts of UV bands in the low-temperature PL measurement were observed, indicating quantum confinement effects in the thin GaN nanowires which have smaller diameters than the exciton Bohr radius, 11 nm. For field emission properties of GaN nanowires, the turn-on field of GaN nanowires was 8.5 V/microm and the current density was about 0.2 mA/cm(2) at 17.5 V/microm, which is sufficient for the applications of field emission displays and vacuum microelectronic devices. Moreover, the GaN nanowires indicated stronger emission stability compared with carbon nanotubes.     

Structure and electronic transport properties of the Misfit layer compound (LaSe)1.14(NbSe2)2, „LaNb2Se5”︁

The new misfit layer compound (LaSe)_1.14(NbSe₂)₂ has been synthesized from the elements at 1050- and its structure has been determined by a composite approach. The structure has an alternating stacking sequence of [LaSe] and two [NbSe₂] layers along the c direction. The misfit of the two different layers is occurring along the a direction: a₁(LaSe)=6.0191 Å and a₂(NbSe₂)=3.4372 Å therefore yielding a ratio of 1.751 which is very close to 7/4. An investigation of electrical resistivity was done. The crystal shows superconducting properties at 5.3 K.     

Growth of well-aligned gamma-MnO2 monocrystalline nanowires through a coordination-polymer-precursor route

A new coordination-polymer-precursor route has been developed to synthesize nanowires under hydrothermal conditions. In the present work, well-aligned gamma-MnO(2) nanowires, growing along the [0 0 2] axis, have successfully been prepared by selecting an appropriate coordination polymer [[Mn(SO(4))(4,4'-bpy)(H(2)O)(2)](n)] as precursor. In comparison with the experimental results from other coordination-polymer precursors, it is found that only [[Mn(SO(4))(4,4'-bpy)(H(2)O)(2)](n)] is appropriate for the formation of gamma-MnO(2) crystal lattices during the process of oxidization. The IR absorption spectra of as-obtained precipitates at different reaction intervals minutely describe the reaction process, due to the different coordination abilities of ligands in the coordination polymer. More evidence about the mechanism will be further explored in the future study. Further observations show the ordered alignment of nanowires' tops and such well-aligned nanowires provide more possible applications in lithium batteries.     

Characterization and field emission properties of ZnMgO nanowires fabricated by thermal evaporation process

In this paper, we investigate the roles of gold catalyst using modified thermal evaporation set-up in the growth process of ZnMgO nanowires. ZnMgO nanowires are fabricated on silicon substrates using different thickness of gold catalyst. A simple horizontal double-tube system along with chemical vapor diffusion of the precursors, based on Fick’s first law, is used to grow the ZnMgO nanowires. Field emission scanning electron microscopy images show that the ZnMgO nanowires are tapered. The optical properties of the ZnMgO nanowires are characterized by room temperature photoluminescence (PL) measurements. The PL studies demonstrate that the ZnMgO nanowires grown using this method have good crystallinity with excellent optical properties and have a larger band-gap in comparison to the pure ZnO nanowires. Field emission characterization shows that the turn-on field for the nanowires grown on the thinner gold film is lower than those grown on the thicker gold film.     

Coordination Adducts of Niobium(V) and Tantalum(V) Azide M(N3)5 (M=Nb,Ta) with Nitrogen Donor Ligands and their Self‐Ionization

Several new donor–acceptor adducts of niobium and tantalum pentaazide with N‐donor ligands have been prepared from the pentafluorides by fluoride–azide exchange with Me₃SiN₃ in the presence of the corresponding donor ligand. With 2,2′‐bipyridine and 1,10‐phenanthroline, the self‐ionization products [MF₄(2,2′‐bipy)₂]⁺[M(N₃)₆]^?, [M(N₃)₄(2,2′‐bipy)₂]⁺[M(N₃)₆]^? and [M(N₃)₄(1,10‐phen)₂]⁺[M(N₃)₆]^? were obtained. With the donor ligands 3,3′‐bipyridine and 4,4′‐bipyridine the neutral pentaazide adducts (M(N₃)₅)₂?L (M=Nb, Ta; L=3,3′‐bipy, 4,4′‐bipy) were formed.