ZnO is an attractive II-VI compound semiconductor material for various optoelectronic devices. Recently, growth of various nanostructures of ZnO such as nanorod, nanobelt, nanowall, etc. has been reported, and ZnO has been considered as a promising material for nanodevices. We have studied on fabrication of aligned ZnO nanorods by a low-pressure thermal chemical vapor deposition (CVD) method cooperated with laser ablation of Mn pellet. In this paper, we report on fabrication of ZnO/ZnS/ZnO multilayer structured nanorods and particularly on effects of laser ablation on the morphology of the nanorods intending to develop a new electroluminescent device including ZnO nanorods. The fabrication method of ZnO/ZnS/ZnO multilayer structured nanorods is almost same method used in our previous study. Metal Zn vapor and O2 gas or H2S are used as precursors to synthesize ZnO or ZnS, and N2 is used as carrier gas. A Mn pellet is placed near a Si(111) substrate in a deposition chamber and ablated by a pulsed Nd:YAG laser beam (wavelength =1.064 mm, pulse width = 8 ns, repetition frequency = 10 shots/sec). The pressure is 13.3 Pa and the temperature is 550 C. When ZnO is grown, O2 of 0.88 SCCM mass flow rate is used as a precursor. When ZnS is grown, on the other hand, H2S of 2.0 SCCM mass flow rate is used as a precursor. The growth time is 15 min for each layer. Firstly, ZnO nanorods are grown. Laser ablation of Mn is executed for initial 3 min and only CVD is performed for remaining 12 min. The vertically aligned ZnO nanorods with 100 nm diameter and 1500 nm height are grown. Secondly, ZnS nanorod is grown on the top surface of the first ZnO nanorods. In this process, the morphology is not so dependent on execution of laser ablation of Mn for initial 3 min in this growth process. Finally, ZnO layer is again grown on ZnS/ZnO nanorods described above. When the laser ablation of Mn for initial 3 min is not executed, many fine ZnO whiskers with long length are grown with random directions on the top surface and on the side surfaces of ZnS/ZnO nanorods. When the laser ablation of Mn for initial 3 min is executed, on the other side, a thick whisker is grown on top surface of ZnS/ZnO nanorods. The shape is not nanorod. The diameter is abruptly decreased and the tip is very sharp. The growth of ZnO whisker on the side surface of ZnS/ZnO nanorods is not almost observed. It is found that the laser ablation of Mn for initial 3 min in the third ZnO growth strongly influences the morphology of the third ZnO layer. We estimate that the Mn species that are ablated from a Mn pellet and reaches the surface of ZnS/ZnO nanorods change any quality of the surface of ZnS/ZnO nanorods. We are now studying of finding the growth conditions of the third ZnO layer with morphology of nanorod on ZnS/ZnO nanorods that is considered to be suitable for electroluminescent devices.

The photoluminescence of MBE-grown InGaN/GaN vertical heterostructures on c-axis oriented GaN nanocolumns is investigated. Nanocolumnar InGaN heterostructures exhibit luminescence efficiencies greater than 20% for peak emission wavelengths as long as 540 nm. Compared to otherwise identical InGaN samples with larger median column diameters, the luminescence is blue-shifted and exhibits reduced efficiency for diameters less than about 50 nm. Growth of InGaN on GaN columns with a broad distribution of diameters results in broad-band photoluminescence that appears white to the eye and has efficiency as high as 23%.

Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique three-dimensional structures of helical or zigzagged GaN, ZnGa2O4 and Zn2SnO4 nanowires. The helical GaN nanowires adopt a helical structure that consists of six equivalent <0-111> growth directions with the axial [0001] direction. The ZnGa2O4 nanosprings have four equivalent <011> growth directions with the [001] axial direction. The zigzagged Zn2SnO4 nanowires consisted of linked rhombohedrons structure having the side edges matched to the <011> direction, and the [111] axial direction.

Nanocrystalline silicon (nc-Si) micro-bridges are melted and crystallized through Joule heating by applying high-amplitude short duration voltage pulses. Full crystallization of nc-Si bridges is achieved by adjusting the voltage-pulse amplitude and duration. If the applied pulse cannot deliver enough energy to the bridges, only surface texture modification is observed. On the contrary, if the pulse is not terminated after the entire bridge melts, molten silicon diffuses on to the contact pads and the bridge tapers in the middle. Melting of the bridges can be monitored through current-time (I-t) and voltage-time (V-t) measurements during the electrical stress. Conductance of the bridges is enhanced after the electrical stress.

In this paper the deposition and morphological characterization of gallium island structures on silicon and first results of silicon wire growth assisted by the created gallium droplets is presented. The islands and wires were grown on (111)-oriented single crystalline p-doped silicon substrates by microwave plasma enhanced chemical vapor deposition (MW PECVD) using trimethylgallium (TMGa) and silane (SiH4) as precursors for island and wire growth, respectively. The samples were investigated by SEM, EDS, XPS, and AFM.

We have measured the yield strength of gold nanowires with diameters in the range from 30 to 70 nm fabricated by electro-deposition into porous alumina templates. All nanowire sizes showed yield strengths much greater than polycrystalline gold with the 30 nm specimens having a yield strength of 1.4 GPa. We found no significant work hardening at plastic strains up to 30%. The strength of the nanowires as a function of wire diameter follows the same trend as has been found for the compression strength of larger gold pillars reported in the literature. TEM observations of deformed wires are consistent with mechanisms of dislocation induced deformation. The strength of nanoporous gold nanowires measured by uniaxial compression test is also reported here. Although two different mechanisms are thought to operate in gold nanowires and nanoporous gold respectively, their strengths show very similar dependence on wire or ligament diameter. However the nanoporous material shows significant strain hardening.

We found that novel amphiphilic tetrathiafulvalene (TTF; 1) organized into supramolecular assemblies by the addition of electron acceptor 2,3,5,6-tetrafluoro-7,7'f,8,8'f-tetracyano-p-quinodimethane (F4TCNQ) at the air-water interface. The assemblies on the air-water interface can be transferred onto the surface of mica and the morphologies of transferred films were investigated by AFM. The morphology of Langmuir-Blodgett films strongly depended on the ratio between 1 and F4TCNQ. Film of 1:1 mixture of 1 and F4TCNQ formed nanoscopic wires having an average dimension of 5.0 (height) × 70 (width) × 3000 (length) nm. On the other hand, the film of 2:1 mixture of 1 and F4TCNQ showed the mixed domains of wires and flat monolayers. Thus, the completely charge-transferred complex (1+)(F4TCNQ-) formed one-dimensional nanowires having a micrometer length. Room temperature electrical conductivities of cast film for 1:1 and 2:1 mixed layers of 1 and F4TCNQ were 2.4 × 10−4 and 8.0 × 10−5 S cm−1, respectively.

TiO2 nanostructures with various morphologies and crystal structures were obtained by calcination of alkaline hydrothermal synthesized hydrogen titanate at different temperatures. The photocatalytic activities of the as-prepared samples were investigated by degradation of methyl orange aqueous solution under ultraviolet irradiation. The effects of the phase composition, crystallinity, surface area and shape of the nanostructures were evaluated. The results showed that high crystallinity, pure anatase phase and nanowire structure are favorable for the photocatalysis. The dependence of the photocatalytic activity on the surface area is not significant as usually expected.

Catalyst-free vapor-solid GaN nanowire growth occurs when ammonia flows over Ga first forming a GaN matrix, the top layer of which is composed of hexagonal platelets. Multiphase nanowire growth occurs at nanoscale nucleation sites on the GaN platelets. Lower layers of the matrix are Ga rich, upper ones are stoichiometrically GaN. Gallium for later stages of growth is sourced from the decomposition of GaN particles and Ga rich GaN. Growth temperature exerts a strong influence on nucleation site formation. Scanning electron microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) was used to characterize the matrix.

We report here the growth of ultra thin ZnSe nanowires at low temperatures by Au-catalyzed molecule beam epitaxy and structural characterization of the nanowires. ZnSe nanowires may contain a high density of stacking faults and twins from low temperature growth and show a phase change from cubic to hexagonal structures. Ultra thin ZnSe nanowires can grow at a temperature below the eutectic point, and the relationship between the growth rates and nanowire diameters is V = 1/dn + C0 (C0 is a constant and n is a fitting parameter). The growth rate of the ultra thin nanowires at low temperatures can be elucidated based on the model involving interface incorporation and diffusion, in which the catalyst is solidified, and the nanowire growth is controlled through the diffusion of atoms into the interface between catalyst and the nanowire. The growth rate of ZnSe ultra-thin nanowires has been simulated.

Sub-monolayer coverages of the rare-earth metal Ho were deposited onto Si(001) substrates at elevated temperatures resulting in the formation of rare-earth silicide nanowires. Between the nanowires the substrate area reconstructs into either a 2×4 or 2×7 reconstruction depending on the specific preparation conditions. We have studied the structural and electronic properties of both the nanowires and the reconstructed areas with the complementary techniques of scanning tunneling microscopy (STM) and metastable de-excitation spectroscopy (MDS) revealing the electronic similarities between the 2×4 and 2×7 phases. Evidence for the presence of hybridized Si 3s3p-Ho 6s5d bonds suggests that these reconstructions form as a precursor to nanowire growth.

We describe electrochemical synthesis of a bulk metamaterial, consisting of silver nanowires in Porous Anodic Alumina membrane and its characterization. We have found that the quality of the synthesized metamaterial depends on the metal used as a working electrode at the optimal conditions of the electroplating process. The dissolution of the thin layer of working electrode is occurred during the electrochemical reaction. It suggests an important role of interfacial phenomena taking place between the working electrode and the sample holder.

The oxidation of suspended Si nanowires is studied under wet and dry conditions. The nanowire characteristics are extracted from Electron Microscopy images. In parallel, the Deal and Grove model is extended to cylindrical geometry. The used model also assumes that stress effects reduce the oxidation rate and predicts the retardation of oxide growth on curved surface, leading to a self-limited process. The model predictions show a good agreement with experiments.

Thin films composed of poly(ethylene imine)-functionalized single-walled carbon nanotubes (CNTs) were formed through a vacuum filtration process and decorated with Au nanoparticles, roughly 40 nm in diameter. The Au nanoparticles, on the surface of the CNT fabric, accommodated the growth of GaAs nanowires (NWs), according to the vapour-liquid-solid (VLS) mechanism, in a gas-source molecular beam epitaxy (GS-MBE) system. Structural analysis indicated that the nanowires, up to 2.5 μm in length, were not preferentially oriented at specific angles with respect to the substrate surface. The NWs grew in the energetically favored [0001] direction of the wurtzite lattice while stacking faults, characterized as zincblende insertions, were observed along their lengths. Micro-photoluminescence spectroscopy demonstrated bulk-type optical behaviour. Current-voltage behaviour of the core-shell pn-junction heterostructured NWs exhibited asymmetric rectification. Thus, the potential for the incorporation of such hybrid NW/CNT architectures into an emerging class of flexible opto-electronic devices is demonstrated.

The density of threading dislocations in GaN/(0001)sapphire films grown by molecular beam epitaxy can be reduced to about 108 cm−2 by growing an intermediate nanorod layer. This paper examines the growth of the nanorods and proposes that threading defects in the overlayer arise either through grain boundaries formed when nanorods coalesce, or through the propagation of dislocation dipoles seen during nanorod growth. Results showing that the latter often terminate or develop into voids during growth are discussed.

We reported the aqueous chemical method to fabricate the well-aligned ZnO/Al2O3 core-shell nanorod arrays (NRAs). The shell is composed of α-Al2O3 nanocrystals in amorphous Al2O3 layers. The photoluminescence (PL) measurements showed that the enhancement of near-band-edge emission in ZnO NRAs arrays due to the addition of Al2O3 shell was observed. The Al2O3 shell layer resulting in flatband effect near ZnO surface leads to a stronger overlap of the wavefunctions of electrons and holes in the ZnO core, further enhancing the NBE emission.

ZnO nanowires are directly integrated into a working device by a single-step chemical vapor deposition (CVD) method. Gold catalyst is patterned on a quartz glass substrate using a comb-shaped shadow mask and then ZnO is grown on the patterned substrate by CVD. Thick ZnO layers formed on the gold-patterned areas serve as native electrodes. Ultra-long (˜100 μm) ZnO nanowires grown across the gap between the ZnO electrodes and the nanowires serve as the sensing elements of the device. The device exhibits high sensitivity and fast response to UV illumination in air. Our method can be used to fabricate other metal oxide semiconductor bridging nanowire devices, which have promising applications in photodetection and gas sensing.

A novel inorganic thin-film electroluminescence (TFEL) device exhibiting bright EL emission when driven by a low DC voltage is demonstrated. The DC-TFEL device is based on a composite layer in which aluminum-doped ZnO nanorods are vertically embedded in ZnS:Mn as an EL phosphor. The DC driving voltage is then applied laterally to the composite layer via two side electrodes set 3.5 mm apart. The aluminum-doped ZnO nanorods were synthesized on a glass substrate by low-pressure thermal chemical vapor deposition combined with laser ablation, and the composite layer was formed by electron-beam deposition of ZnS:Mn onto the ZnO nanorods. The thickness of the composite layer was about 160 nm. After electrical modification to breakdown a basal conduction ZnO path, the lateral DC-TFEL device exhibited bright EL emission without avalanche breakdown, achieving a luminance of 747 cd/m2 at 4200 V with a luminous efficiency of 9.2×10−3 lm/W.

Recently, we have experimentally demonstrated a very simply structured unipolar accumulation-type metal oxide semiconductor field effect transistor (AMOSFET) using grow-in-place silicon nanowires. The AMOSFET consists of a single doping type nanowire, metal source and drain contacts which are separated by a partially gated region. Despite its simple configuration, it is capable of high performance thereby offering the potential of a low manufacturing-cost transistor. Since the quality of the metal/semiconductor ohmic source and drain contacts impacts AMOSFET performance, we repot here on initial exploration of contact variations and of the impact of thermal process history. With process optimization, current on/off ratios of 106 and subthreshold swings of 70 mV/dec have been achieved with these simple devices

We functionalized nanowires with three different probe peptide nucleic acid (PNA) sequences, and assembled the three populations onto a lithographically patterned chip. Electrofluidic assembly enabled positioning each set of nanowires to span a different pair of guiding electrodes. Fluorescence imaging was used to probe whether the PNA on the individual nanowires remained able to selectively bind complementary DNA targets following assembly and integration of the positioned nanowires onto the chip surface.