[Show abstract][Hide abstract] ABSTRACT: SnO2@carbon nanostructure composites are prepared by a simple hydrothermal method. The composite exhibits unique structure, which consists of a mesoporous SnO2 core assembled of very small nanoparticles and a carbon shell with 10 nm thickness. The mesoporous SnO2@carbon core-shell nanostructures manifest superior electrochemical performance as an anode material for lithium ion batteries. The reversible specific capacity of the composite is about 908 mAh g(-1) for the first cycle and it can retain about 680 mAh g(-1) after 40 charge/discharge cycles at a current density of 0.3 C. Moreover, it shows excellent rate capability even at the high rate of 4.5 C. The enhanced performance was attributed to the mesoporous structure and a suitable carbon coating.
[Show abstract][Hide abstract] ABSTRACT: Composite Zn Sn O <sub>3</sub> nanowires are synthesized via a one-step thermal evaporation method. The nanowires are of core-shell structures with the presence of grain boundary and out-of-phase boundaries. Transport through individual nanowires shows nonlinear current-voltage (I-V) characteristics in the range of the voltage from -3 to 3 V . Such a behavior can be attributed to the presence of the barrier at the grain boundary, and the effective barrier height is estimated to be about 0.22 eV by analyzing the I-V curves at various temperatures. The current at -3 V jumps from 0.12 to 6.0 μ A within 30 s at 300 K as exposed to UV illumination. Such jump can be well explained in terms of effective barrier height and depletion width.
[Show abstract][Hide abstract] ABSTRACT: Individual β- Ga <sub>2</sub> O <sub>3</sub> nanowires as solar-blind photodetectors are investigated. The detectors show encouraging advantages to 254 nm light. The dark current is on the order of pA. The conductance of the nanowire increases by about three orders of magnitude under 254 nm ultraviolet illumination. The upper limits of the response and recovery time are 0.22 and 0.09 s , respectively. These results indicate that β- Ga <sub>2</sub> O <sub>3</sub> nanowires have potential applications in realizing future miniaturized solar-blind photodetectors.
[Show abstract][Hide abstract] ABSTRACT: Positive temperature coefficient of resistance is observed on single Cd-doped ZnO nanowires. The current along the nanowire increases linearly with the bias and saturates at large biases. The conductance is greatly enhanced either by ultraviolet illumination or infrared illumination. However, the conductance decreases with increasing temperature, in contrast to the reported temperature behavior either for ZnO nanostructures or for CdO nanoneedles. The increase of the conductance under illumination is related to surface effect and the decrease with increasing temperature to bulk effect. These results show that Cd doping does not change surface effect but affects bulk effect. Such a bulk effect could be used to realize on-chip temperature-independent varistors.
[Show abstract][Hide abstract] ABSTRACT: Optoelectronic properties of single CdS nanobelts are investigated by performing transport measurements with different laser ON/OFF circles. The current increases linearly with the bias voltage in the dark, and superlinearly under illumination. The superlinear increase can be related to the enhanced mobility due to the partial release of surface adsorbates under illumination. The current jumps up by five orders of magnitude upon turning on the laser with an intensity of 0.3 W / cm <sup>2</sup> within 91 ms and decreases by five orders 6 ms just after turning off the laser. The high sensitivity and fast response in the visible range indicate potential applications of CdS nanobelts in realizing optoelectronic switches.
[Show abstract][Hide abstract] ABSTRACT: Mass production of single-crystalline CdS nanobelts is achieved by thermal evaporation of CdS powders with the presence of Au catalyst. The as-synthesized CdS nanobelts are usually hundreds of nanometers to tens of micrometers in width, tens of nanometers in thickness, and several hundreds of micrometers in length. CdS nanobelts have a pronounced increase in conductance of up to four orders of magnitude upon exposure to white light, and also very fast response time about 1–3 s. The photoconductivity mechanism of CdS nanobelts is discussed. The results demonstrate the potential of fabricating nanosized photoconductors and optical switches using the integrity of a single CdS nanobelt.
[Show abstract][Hide abstract] ABSTRACT: We present experimental evidence of in situ growth of carbon nanowires on the tip of a carbon nanotube under an applied voltage of 150 V. The grown nanowires with the well-defined geometry and diameter less than ten nanometers are structurally amorphous in nature and result in the solid carbon nanotube-nanowire junction with minimum junction size. The as-generated carbon nanotube-nanowire junction with a distinctive morphology clearly shows evidence of the bonding between the carbon atoms at the tip of carbon tube. The carbon nanotube could be used as a template for in situ growth of the carbonate nanowires under a strong electric field. The measured current-voltage (I‐V) characteristic of the nanotube-nanowire contact shows a nonlinear relation between the current and applied bias voltage due to the saturated sp3 bonds formed at the junction. The detected I‐V behavior suggests the formation of the metal∕insulator∕metal structure at the nanotube-nanowire junction.
[Show abstract][Hide abstract] ABSTRACT: Sensing mechanisms of ZnO nanowire films are investigated by performing transient photocurrent measurements. The current jumps upon ultraviolet or green laser illumination. The amplitude in the jump is strongly dependent on the ambient atmosphere. The decay rate is much more sensitive to the ambient atmosphere than the rise rate. The fast rise is due to rapid photogenerated carriers and the slow decay is controlled by slow surface process. Our experimental results indicate that the oxygen physisorption rate is slower than the chemisorption rate.
[Show abstract][Hide abstract] ABSTRACT: Individual ZnO nanowire transistors are fabricated, and their sensing properties are investigated. The transistors show a carrier density of 2300 μm−1 and mobility up to 6.4 cm2∕V s, which are obtained from the ISD−VG curves. The threshold voltage shifts in the positive direction and the source-drain current decreases as ambient oxygen concentration increases. However, the opposite occurs when the transistors are under illumination. Surface adsorbates on the ZnO nanowires affect both the mobility and the carrier density. Our data are helpful in understanding the sensing mechanism of the gas sensors.
[Show abstract][Hide abstract] ABSTRACT: We report on field emission from SnO2 nanobelt arrays with the length of about 90 μm grown on silicon substrates. The turn-on field of the nanobelt arrays at the current density of 1 μA∕cm2, is 4.5, 3.0, 2.4, and 2.3 V∕μm as the distance between anode and cathode (d) is 0.1, 0.2, 0.35, and 0.5 mm, respectively. The current density rapidly reaches 2.1 mA∕cm2 at the electrical field of 4.4 V∕μm at d=0.35 mm. The current density is higher than or comparable to those of the carbon nanotubes and other one-dimensional nanostructured materials. We also discuss the mechanism of high current densities and estimate the enhancement factor according to both the Fowler–Nordheim law and the reported model on micrometer-long of carbon nanotubes.
[Show abstract][Hide abstract] ABSTRACT: Thin film transistors are fabricated by in situ growth of SnO2 nanobelts on Au∕Pt electrodes. A linear correlation in the output characteristics is observed at zero gate voltage, indicating Ohmic contacts between the nanobelts and the electrodes. The transistors exhibit n-type behaviors and have a mobility of 1.85 cm2∕V s with a current on∕off ratio above 103. The conductance increases as the pressure in the device chamber is reduced, which indicates that the transistors are promising for oxygen detecting.
[Show abstract][Hide abstract] ABSTRACT: Stable field emission is realized from well-separated tetrapod-like ZnO nanostructures with high purity. The ZnO nanostructures are painted on a highly doped silicon substrate covered by a Au layer with a thickness of 300 nm . An emission current density of 18 mA / cm <sup>2</sup> is obtained and degradation was not observed over a three day period. The fluctuations of the emission current are less than 2%. These experimental results indicate that tetrapod-like ZnO nanostructures are promising materials as cold cathodes for mass production.
[Show abstract][Hide abstract] ABSTRACT: Transport properties of a single multiwalled carbon nanotube (MWNT) have been investigated in vacuum at room temperature. The MWNTs show the large current carrying capacity at large bias due to the ballistic transport. The conductance for a single MWNT around zero bias is 0.4G0, and increases almost linearly with the applied voltage until it reaches its acmes. Being the signature of the ballistic transport for MWNTs, the conductance acmes are observed at the bias of +/-5.8 V equal to +/-2gamma0/e, where gamma0 is the pi bonding energy for carbon nanotubes. Our calculation shows a similar curve to our experimental results, which further indicates the ballistic transport through the single MWNT.