In this work, we report the results of studies of the transverse magnetoresistance (MR) of single-crystal Bi nanowires with diameter d<80 nm. The single-crystal nanowire samples were prepared by the Taylor-Ulitovsky technique. Due to the semimetal-to-semiconductor transformation and high density of surface states with strong spin-orbit interactions, the charge carriers are confined to the conducting tube made of surface states. The non monotonic changes of transverse MR that are equidistant in a direct magnetic field were observed at low temperatures in a wide range of magnetic fields up to 14 T. The period of oscillations depends on the wire diameter d as for the case of longitudinal MR. An interpretation of transverse MR oscillations is presented.

In this work, we study glass-coated single-crystal Bi98Sb02 wires obtained by liquid phase casting.

Semimetal Bi98Sb02 nanowires exhibited a "semiconductor" behavior of the temperature dependence R(T) for wire diameters <400 nm, which is significantly higher than the critical diameter (70 nm) for similar dependences R(T) of pure bismuth nanowires. The thermopower sign reversal in the temperature dependence α(T) was found to depend on the wire diameter d. The effect is interpreted in terms of manifestation of the quantum size effect, based on the appearance a new scattering channel stimulated by fluctuations in the diameter d.

The effect of negative magnetoresistance in a perpendicular magnetic field was observed for the first time both at H | | C3 and H | | C2 in magnetic fields of 1 T.

It is shown that a semimetal-semiconductor transition can be controlled using an elastic strain and a strong magnetic field, which lead to a significant shift of the band boundaries of the energy extrema in the bands

The inner composition, defect content and morphology of AlGaAs nanowires (NWs) grown on (111)B-GaAs by Au-catalyzed MOVPE is reported. The NWs grow tapered with their [111] axis normal to the substrate. The Raman spectra of single AlGaAs NWs were measured in non-resonant conditions with sub-μ-meter spatial resolution, allowing determination of the Al content. NWs consist of GaAs for TG<475°C, but show a two-fold compositional structure for TG >475°C, namely an AlxGa1-xAs core surrounded by an AlyGa1-yAs (y<x) shell, ascribed to the combination of Au-catalyzed (axial) and conventional (sidewall) growth. The cross-sectional shape of AlGaAs NWs changes from triangular (for TG=500÷525°C) to almost hexagonal (for TG=550°C), due to an exchange between and {110} planes as the slowest to grow. The NWs have free-electron concentrations ∼1018 cm-3, due to Si contamination of the Al source.

In this work, we report on the microstructural and morphological characterization of III-V semiconductor nanowires (NWs) epitaxially grown on (111)B-GaAs substrates by Au-catalyst assisted metalorganic vapor phase epitaxy. As-grown dense (108-109 cm-2) arrays of few-micron long vertically-aligned (i.e. parallel to the <111> crystallographic axis) GaAs, AlxGa1-xAs and core-shell GaAs-AlxGa1-xAs NWs were investigated, carrying out HRXRD measurements on different (hkl) reflections and by recording reciprocal space maps (RSMs) around the materials (111) reciprocal lattice points (relps). We show that NW diffraction peaks are visible in the RSM by means of characteristic halos. In the case of GaAs NWs, the halo is located at the (111) relp indicating that the NWs are grown along the <111> direction and parallel to the <111> axis of the GaAs substrate. On the contrary, for AlxGa1-xAs NWs or intentional core-shell GaAs-AlxGa1-xAs NWs the halo is displaced (along the momentum transfer normal to the surface, Qz) with respect to the GaAs (111) relp due to the elastic lattice strain associated with the compositional variation, e.g. the Al molar fraction in the AlxGa1-xAs alloy, within the nanostructures.

Vapor-liquid-solid (VLS) method has become one of the few and most powerful bottom-up single crystal nanowire growth techniques in nanotechnology due to its easy scalability from micro to nano feature sizes, high throughput, relatively low cost, and its applicability to various semiconductor materials. On the other hand, control of growth direction and crystal orientation of nanowires, which determine their electrical, optical, and mechanical properties, stand as major issues in VLS technique. In this study, we demonstrate a new vapor-liquid-solid glancing angle deposition (VLS-GLAD) fabrication approach to produce crystalline semiconductor nanowires with controlled geometry. VLS-GLAD is a physical vapor deposition nanowire fabrication approach based on selective deposition of nanowire source atoms onto metal catalyst nanoislands placed on a crystal wafer. In this technique, collimated obliquely incident flux of source atoms selectively deposit on catalyst islands by using “shadowing effect”. Geometrical showing effect combined with conventional VLS growth mechanism leads to the growth of tilted crystalline semiconductor nanowire arrays. In this study, we report morphological and structural properties of tilted single crystal germanium nanowire arrays fabricated by utilizing a conventional thermal evaporation system. In addition to the tilted geometry, by introducing substrate rotation, nanowires with various morphologies including helical, zig-zag, or vertical shapes can be fabricated. Engineering crystalline nanowire morphology by using VLS-GLAD have the potential of enabling control of optical, electrical, and mechanical properties of these nanostructures leading to the development of novel 3D nano-devices.

SiC nanowires were produced from carbon nanotubes and nanosize silicon powder in a tube furnace at temperatures between 1100°C and 1350°C. SiC nanowires had average diameter of 30 nm and very narrow size distribution. The surface of the SiC nanowires is covered by an amorphous layer composed of amorphous SiC and various carbon and silicon compounds. The objective of the research was to modify the surface structure of the SiC nanowires, a step necessary for future surface functionalization. The acid etched nanowires were analyzed using FTIR, TEM, x-ray diffraction, and photoluminescence. The concentration of Si-Ox groups in untreated specimens was estimated to account for 1% of the total mass of a 2 nm thick amorphous layer wrapping around all structures. After treatment in HF this concentration was negligibly small. TEM images show that after treatment the amorphous layer was removed but the diameter of the core remained unchanged. The surface was roughened and multiple pits formed on that surface. X-ray line broadening analysis indicates a significant contribution due to stress caused by dislocations and planar faults. After acid etching line narrowing was observed and attributed to stress reduction and elimination of the smallest wires. The photoluminescence signal from as received samples was very weak but increased greatly after acid treatment, indicating that the signal is related to surface defects. Measurements at low temperatures, 8 K, showed peaks due to point and planar defects.

In this paper, we investigate the morphology variation of Au-assisted epitaxial InSb nanowires (NWs) dependence on growth temperature and growth duration by chemical vapor deposition (CVD). The NW length and tapering factor correlated to the NW morphology are determined as a function of growth temperature (300°C-480°C). Higher density and longer NWs were observed on the substrate as proportional to the growth duration. The growth direction of the NWs is <110> by Transmission Electron Microscopy (TEM) studies. The aim of this study is to gain better understanding of the III-V NWs growth mechanism and achieve control over the growth of InSb NWs.

ZnO nanobridge sensors were selectively grown and electrically connected using lithographically patterned carbonized photoresist (C-PR). As ZnO is known to dissolve in deionized (DI) water, parylene-A was investigated as a moisture barrier and potential functionalization platform. A chemical vapor deposition (CVD) process for parylene-A was developed and it was demonstrated that parylene-A coated ZnO NWs do not show any signs of dissolution after 24 hours in an aqueous solution. The impact of the parylene-A coating on the electrical performance and sensitivity of ZnO nanobridge devices was investigated. A comparison of UV, O2, and H2O sensitivity between uncoated and coated devices revealed that a thin coating of parylene-A attenuated all of these responses, suggesting the ability to modulate environmental sensitivity using this non-covalently bound polymer passivation layer.

Arrays of CdTe nanowires have been grown on conductive, flexible Mo substrates by the vapor-liquid-solid technique. A method of forming the arrays on a largely continuous CdTe film is described. For producing nanowire solar cells, this structure provides the advantage of preventing shunts. Nanowires having diameters in the range 100-500 nm and lengths up to 100 μm were generated. The influence of growth temperature, time and pressure on the morphology of deposited layers was investigated, and a mechanism for the generation of layer/nanowire combinations is postulated. Characterization by SEM, TEM and low temperature photoluminescence is presented.

We present transport properties of silicon nanowires field effect transistors realized on SOI substrates and their application to probe electrical activity of biological objects. Devices are sensitive to short and weak voltage pulses (ms, mV) applied in an electrolyte solution, allowing a future efficient detection of neuronal activity. For that purpose, the organized growth of neuronal cells along chosen patterns has been obtained, leading to an accurate coupling with silicon nanowire field effect transistors. Both network architectures, neural and semiconducting, have been designed to study some aspects of the propagation and the processing of information by the nervous system.

Control of crystal orientation of vertically grown epitaxial Si (111) and (110) nanowire arrays on Si substrate has been demonstrated using a combination of an anodic aluminum oxide (AAO) template and vapor – liquid – solid (VLS) growth method. The crystal orientation of the nanowire was investigated by transmission electron microscopy. A growth direction of the nanowire arrays was guided perpendicular to the surface of the substrate by the AAO template, and the crystal orientation of the nanowire arrays was selected using the single crystal Si substrate properly cut in desired orientation.

We have determined critical parametres that restrict the vapor→liquid drop→solid growth of silicon NWs. We demonstrate that there are maximum and minimum critical radii for NW growth and identify boundary conditions that lead to solvent droplet breakdown and crystal branching.

Surface photovoltage of three-dimensional networks composed of fused indium phosphide (InP) nanowires is discussed. Particular emphasis is given to the dependence of surface photovoltage on the chopping frequency of light that excites the nanowire network as observed in regions which are laterally separated from the excitation. The nanowire network is modeled as a thin film to simplify numerical solutions to transport equations which aids in the interpretation of diffusion and drift of photo-generated carriers within the nanowire network.

We investigated the data transmission performance of indium antimonide (InSb) nanowires (NWs) synthesized on InSb (100) substrate using chemical vapor deposition (CVD) having diameters of 20 nm and below. The results indicate that the data transmission performance of NWs suffer from low mobility values on the order of 10-to-15 cm2V-1s-1 because of the scattering due to their small diameters, crystal defects and oxidation occurs during growth and cooling. The 20 nm NWs can sustain data rates up to 5 mega bits per second (Mbps) without any impedance matching and de-embedding of the parasitic parameters coming from the measurement system with a bit error rate (BER) level of 10-8. The data rate is directly proportional to the diameter of the NWs.

Zinc oxide is a wide band gap material with excellent semiconducting, photonic and piezoelectric properties. In the past ten years zinc oxide nano-structures such as nanowires and nanorods have received great interest due to their unique dimensional and material properties in the area of photonics, electronics, mechanics, energy recovery, etc. In this paper we report the manufacturing process of a new shape, i.e. hollow hexagonal ZnO nano-cones. We grew them on different kinds of substrate using a low pressure, catalyst free, metal organic chemical vapor deposition (MOCVD) process on a FirstNano EasyTube 3000™ MOCVD system. Nitrogen was used as carrier gas to bring the reactants, DEZ and H2O, to the substrate surface. At the right balance of process temperature and carrier/precursor gas flow rate the ZnO nano-structure transitioned into a hollow hexagonal cones growth mode. The both one and two dimensional aspects of these catalyst free hollow hexagonal ZnO nano-cones, which are novel to the best of our knowledge, could lead to new applications in photonics, near field probing, chemical sensors, quantum confinement, electronic, etc.

Single crystalline Indium Antimonide (InSb) nanowires were synthesized by chemical vapor deposition (CVD) technique, using gold (Au) nanoparticles as catalyst, via a vapor liquid solid mechanism. Structural properties of the as-grown InSb nanowires were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Nanowire field effect transistors (NWFETs) were fabricated in back-gate configuration, on Si/SO2 substrates, using SiO2 as gate insulator. The diameter of InSb nanowires used in the fabricated devices varied from 15-80 nm. Current-voltage measurements were conducted to determine the dependence of NWFETs parameters on the InSb nanowire diameter. Carrier mobility was shown to decrease with decrease of nanowire diameter. Temperature dependen current-voltage measurements were conducted to determine the effect of operating temperature on the InSb NWFET device performance.

A maskless method of employing polymer growth inhibitor layers is used to modulate the conflicting parameters of density and alignment of multi-junction nanowires via large-scale low temperature chemical route. This low temperature chemical route is shown to synthesize multi-junction nanostructures without compromising the crystal quality at the interfaces. The final morphology of an optimized multi-junctions nanowire arrays can be demonstrated on various substrates due to substrate independence and low temperature processing. Here, we also follow-up on device demonstrations whereby p-n junction are created by exposure of secondary nanowires to ammonia plasma, converting them to p-type characteristics and also the density modulated multi-junction nanowires were tuned to infiltrate nanoparticles to create a hybrid hierarchically-structured nanowire/nanoparticles solar cell. The fabrication of hierarchically-structured nanowire/nanoparticles composites presents an advantageous structure, one that allow nanoparticles to provide large surface areas for the dye adsorption, whilst the nanowires can enhance the light harvesting, electron transport rate, and also the mechanical properties of the films. This work can be of great scientific and commercial interest since the technique employed is of low temperature (< 90 °C) and economical for large-scale solution processing, much valued in today’s flexible display and photovoltaic industries. In addition, ZnO nanostructures for gas sensing will be presented.

Silicon carbide (SiC) nanostructures attract interest due to their applications in optoelectronic devices, sensors, and high-power/high temperature electronics. The synthesis of SiC nanowires by chemical vapor deposition using hexamethyldisilane (HMDS) as a source material on SiO2/Si substrate has been investigated. Various catalyst materials, including iron (film and nanoparticles), nickel (film and nanoparticles), and cobalt nanoparticles have been used. The growth runs have been carried out at temperatures between 900 and 1100°C under H2 as carrier gas. 3C-SiC nanowires have successfully been grown at even lower temperatures despite the lower efficiency of source decomposition at low temperatures. The SiC nanowire diameters are in the range of 8 nm to 60 nm, as determined by transmission electron microscopy (TEM). In general, the efficiency of nanowire growth has increased with temperature except the growth on Ni film, which has occasionally resulted in SiC flowers. Higher nanowire density at high temperatures can be attributed to more efficient decomposition of the source at higher temperatures. Further, optical properties of the nanowires have been studied by Fourier transform infrared spectroscopy (FTIR). The fabricated nanowires have also been characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and x-ray diffraction (XRD).