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We studied the temperature-dependent electrical transport properties of individual ZnO nanowires with metal contacts. We used temperature dependent gate response curves to obtain the carrier mobility and the carrier concentration of ZnO nanowires as function of temperature; these were estimated from the modified transconductance equation to subtract the unavoidable contact resistance effect. As the temperature was lowered from 300 K, the carrier concentration decreased and the carrier mobility increased until it reached a maximum at 150 K. An increase in the carrier mobility upon cooling occurred due to a decrease in the electron-phonon scattering rate; the scatterings from defects and impurities became dominant at temperatures below 150 K. The intrinsic conduction of the ZnO nanowire itself, neglecting the contact effect, followed the thermal activation process related to zinc interstitials, ZnI , rather than a variable range hopping behavior.

Growth of GaN nanowires by using a vapor-liquid-solid (VLS) mechanism with Pt catalysts was investigated. Single-crystal GaN nanowires with diameters of ∼100 nm and lengths of ∼5 μm were grown with Pt and with the well-known VLS catalyst of Ni. The growth rate of nanowires with Pt was lower than that with Ni under identical processing conditions. Pt-Ga alloy globules were observed by Transmission electron microscopy at the ends of the nanowires which lead the growth by the VLS mechanism. Electrical data from individual nanowires indicated high conductivity associated with high electron concentration in the Pt-GaN nanowires.

We report on synthesis of Mn-doped Ge nanowires and their magnetic and electrical properties. The nanowires were grown on the silicon substrate by vapor−liquid−solid mechanism using Au as catalyst and GeCl4 and MnCl2 as precursor. Anomalous X-ray scattering measurement makes it clear that Mn atoms are substitutionally incorporated with the diamond network of host Ge sites. Superconducting quantum interference device characterization indicated that the nanowires possess ferromagnetism up to room temperature. X-ray magnetic circular dichroism spectra at Mn L2,3-edges showed that doped Mn has local spin moment with the 3d5 electronic configuration above room temperature, meaning that the ferromagnetism originates from doped Mn2+ ions. Electrical characterization of a nanowire field effect transistor revealed the improved p-type behavior with hole mobility of 4.95 cm2/V·s.

This paper presents a review of our current experimental research on GaP nanowires grown by a vapor deposition method. Their structural, electrical, opto-electric transport, and gas-adsorption properties are reviewed. Our structural studies showed that a GaP nanowire consisted of a core–shell structure with a single-crystalline GaP core and an outer Ga2O3 layer. The individual GaP nanowires exhibited n-type field effects. Their electron mobilities were in the range of about 6 to 22 cm2/V s at room temperature. When the nanowires were illuminated with an ultraviolet light source, an abrupt increase of conductance occurred resulting from carrier generation in the nanowire and de-adsorption of adsorbed OH- or O2 - ions on the Ga2O3 surface shell. Using an intrinsic Ga2O3 shell layer as a gate dielectric, top-gated GaP nanowire field-effect transistors were fabricated and characterized. Like other metal oxide nanowires, the carrier concentration and mobility of GaP nanowires were significantly affected by the surface molecular adsorption of OH or O2. The GaP nanowire devices were fabricated as sensors for NO2, NH3, and H2 gases by using a simple metal decoration technique.

The electrical transport properties of high quality ZnO nanorods, synthesized by catalyst-free metalorganic chemical vapour deposition, were studied as a function of temperature by fabricating field effect transistors based on single ZnO nanorods. The thermally activated Schottky emission was found to be a ruling transport mechanism in the temperature regime of 70?293?K over a wide range of electric fields with an effective barrier height of ~120?meV. In contrast, the Fowler?Nordheim tunnelling dominated at low temperatures (

Growth behaviors of ZnO nanorods synthesized by catalyst-free metalorganic chemical vapor deposition were studied as functions of various growth parameters such as growth temperature, precursor ratio and substrate type. We found that their sizes, shapes and alignment nature were strongly dependent on such parameters. However, individual ZnO nanorods were of single-crystalline nature as well as of high optical quality. Field effect transistors (FETs) using single ZnO nanorods were fabricated to study their electrical properties. Ultraviolet illumination and vacuum environment resulted in a significant increase of mobile electrons. Investigation on temperature-dependent electrical transport revealed that thermionic emission dominated as a current transport mechanism in the FETs.

Size-tuned ZnO nanorod arrays (NRAs), aligned well vertically and laterally, were synthesized by catalyst-free, metalorganic chemical vapor deposition on GaN-buffered Al2O3 (0001) substrates by adjusting the O/Zn precursor ratio in the reactor. Their electrical transport properties were investigated using field effect transistors based on individual ZnO nanorods. We find that the carrier concentrations and mobilities in the nanorods are not very sensitive to the change of the precursor ratio. This suggests that altering the precursor ratio is a way of fabricating size-tuned ZnO NRAs with quite consistent electrical properties.

Vertically aligned carbon-nanotube (CNT) arrays were fabricated in the thin-film anodic aluminum oxide (AAO) templates on silicon wafers utilizing a niobium (Nb) thin film as the source electrode. The average diameter of the CNTs was 25 nm, and the number density was 3 x 10(10) cm(-2). The CNT arrays synthesized at 700 degrees C and above exhibited Schottky behavior even at 300 K, with energy gaps between 0.2 eV and 0.3 eV. However, individual CNTs obtained by removal of the template behaved as resistors at 300 K. The CNT/Nb oxide/Nb junction is thought to be responsible for the Schottky behavior. This structure can be a useful cornerstone in the fabrication of nanotransistors operating at room temperature.

On a single GaN nanowire, obtained by chemical vapour deposition, several Schottky-junction diodes were fabricated and their electrical transport properties were studied. Alternately attached metal electrodes of Al and Ti/Au formed a Schottky barrier junction (for Al) or an ohmic contact (for Ti/Au), resulting in several diodes on a single nanowire. The current–voltage measurements exhibited clear rectifying behaviour and no reverse-bias breakdown was observed up to the measured voltage, −5 V. The forward-bias threshold voltage was observed to decrease linearly with temperature, from 0.4 V at 280 K to 1 V at 10 K.

Electronic transport properties of a heterostructure junction made of two different multiwall carbon nanotubes are studied. Independent measurement of the current–voltage characteristics of each nanotube revealed that both of them were lightly p-doped semiconductors with energy gaps whose magnitudes are widely different from each other. The current–voltage characteristics measured across the heterojunction show reproducible rectifying diode behavior. The forward bias current across the heterojunction increases rapidly with the application of a positive gate bias voltage, implying an n-type gate response.

We report on the compatibility of various nanowires with hippocampal neurons and the structural study of the neuron–nanowire interface. Si, Ge, SiGe, and GaN nanowires are compatible with hippocampal neurons due to their native oxide, but ZnO nanowires are toxic to neuron due to a release of Zn ion. The interfaces of fixed Si nanowire and hippocampal neuron, cross-sectional samples, were prepared by focused ion beam and observed by transmission electron microscopy. The results showed that the processes of neuron were adhered well on the nanowire without cleft.

This study reports the electrical transport characteristics of Si(1-x)Gex (x=0-0.3) nanowires. Nanowires with diameters of 50-100 nm were grown on Si substrates. The valence band spectra from the nanowires indicate that energy band gap modulation is readily achievable using the Ge content. The structural characterization showed that the native oxide of the Si(1-x)Gex nanowires was dominated by SiO2; however, the interfaces between the nanowire and the SiO2 layer consisted of a mixture of Si and Ge oxides. The electrical characterization of a nanowire field effect transistor showed p-type behavior in all Si(1-x)Gex compositions due to the Ge-O and Si-O-Ge bonds at the interface and, accordingly, the accumulation of holes in the level filled with electrons. The interfacial bonds also dominate the mobility and on- and off-current ratio. The large interfacial area of the nanowire, together with the trapped negative interface charge, creates an appearance of p-type characteristics in the Si(1-x)Gex alloy system. Surface or interface structural control, as well as compositional modulation, would be critical in realizing high-performance Si(1-x)Gex nanowire devices.

We have fabricated a Schottky-junction diode, utilizing gallium nitride (GaN) nanowire, and studied its electrical transport properties. Two kinds of metal electrodes, Al and Ti/Au, were incorporated into an individual GaN nanowire synthesized by chemical vapor deposition method. A Schottky-barrier junction was formed in the Al electrode while ohmic contact was formed in the Ti/Au electrode. The measured current–voltage characteristic exhibited clear rectifying behavior and no reverse bias breakdown was observed up to the measured voltage, −5 V .

We report the effect of an Al layer, covering the central part of the nanotube channel, on the electrical transport properties of carbon nanotube field-effect transistors (CNFETs). The CNFETs, consisting of single-walled carbon nanotube or double-walled carbon nanotube between two Pd electrodes on top of SiO2 layer, which showed p-type or ambipolar transport behaviors, exhibit clear n-type characteristics after the Al deposition. We ascribe such conversions into n-type behaviors to the electron doping in the Al-covered nanotube region, which results in the bending of the nanotube bands nearby the edges of the Al layer. This technique, Al deposition under a high vacuum, may give rise to a practical fabrication method for the n-type CNFET, which may enable us to develop complementary logic nanotube electronic devices.

Vertically well-aligned and epitaxial ZnO nanorod arrays (NRAs) were synthesized by catalyst-free metalorganic chemical vapor deposition on Al2O3 (0001) substrates particularly using an epitaxially grown GaN buffer layer. ZnO NRAs grown directly on Al2O3 (0001) substrates are aligned vertically, but randomly oriented in the lateral direction to the substrates. In sharp contrast, ZnO NRAs grown with a GaN buffer layer show an excellent vertical and epitaxial alignment with mosaic distributions of 0.11° and 1.28° in the out-of- and the in-plane directions, respectively. The electrical measurements using field effect transistors based on individual ZnO nanorods show a pronounced n-type gate modulation with an electron concentration of ∼7.5×1017cm−3 and an electron mobility of ∼25.1cm2∕Vs at a bias voltage of 1 V, while showing quite a high on/off ratio exceeding ∼105. In addition, their high on/off conductivity ratio of ∼103 with UV light gives a potential of their use in nanoscale UV detectors.

We have studied the spin dependent tunneling properties of Mn-doped GaN nanowires with ferromagnetic Co contacts. The magnetoresistances were measured between two ferromagnetic Co electrodes, or Co and Ti∕Au electrodes through Mn-doped GaN nanowires. The magnetoresistances of nanowire with the Co electrode indicate hysteretic behaviors, which are commonly observed in tunnel magnetoresistance devices. The magnetoresistance ratio increases from −0.6% at 20K to −9.4% at 1.74K. It is believed that the hysteretic magnetoresistances originate from the tunnel magnetoresistance effect between the ferromagnetic phases of nanowire and Co electrode.