L. Liao

Multifunctional CuO nanowire devices: p-type field effect transistors and CO gas sensors

We report the properties of a field effect transistor (FET) and a gas sensor based on CuO nanowires. CuO nanowire FETs exhibit p-type behavior. Large-scale p-type CuO nanowire thin-film transistors (10(4) devices in a 25 mm(2) area) are fabricated and we effectively demonstrate their enhanced performance. Furthermore, CuO nanowire exhibits high and fast response to CO gas at 200 degrees C, which makes it a promising candidate for a poisonous gas sensing nanodevice.

Direct growth of SnO2nanorod array electrodes for lithium-ion batteries

SnO2nanorod arrays have been prepared on large-area flexible metallic substrates (Fe–Co–Ni alloy and Ni foil) via a hydrothermal process for the first time and have been demonstrated as a high-performance anode material for lithium ion batteries. Electrochemical behavior is found to depend crucially on the structural parameters of the array. An array consisting of SnO2nanorods of average 60 nm in diameter and 670 nm in length delivers a reversible capacity of as high as 580 mAh g−1 after 100 cycles (at 0.1C) and shows excellent rate capability (350 mAh g−1 at the 5C rate). Structural disintegration and agglomeration were not observed for SnO2 arrays even after 50 cycles.

Synthesis, structure and ferromagnetic properties of Mn-doped ZnO nanoparticles

Nanosized Mn-doped ZnO particles were synthesized by a rheological phase reaction precursor method and the thermal decomposition of the oxalate precursors was studied by thermogravimetry and differential thermal analysis in air atmosphere. X-ray analysis reveals that the Mn-doped ZnO crystallizes in a wurtzite structure. The lattice constants of Zn1−xMnxO increase slightly when Mn is doped into ZnO. TEM analysis shows that the average diameter of the nanoparticles is about 10–13 nm. In addition, magnetization measurements under field cooling conditions reveal that the Mn-doped ZnO nanoparticles show ferromagnetic behaviour at room temperature and both the susceptibility and coercive force of Zn0.95Mn0.05O are larger than those of Zn0.97Mn0.03 and Zn0.93Mn0.07. This work demonstrates that Mn can be doped into nanosized ZnO by the method of rheological phase reaction, which represents an important method to synthesize a nanosized diluted magnetic semiconductor.

A novel gas sensor based on field ionization from ZnO nanowires: moderate working voltage and high stability

We report a kind of gas sensor using ZnO nanowires as the field ionization anode. The sharp tips of nanowires generate very high electric fields at relatively low voltages. The sensors show good sensitivity and selectivity. Moreover, the detection limitation of the field ionization based ZnO nanowire gas sensors is about 5%. More importantly, a sensor with ZnO nanowires as the anode exhibits an impressive performance with respect to stability and anti-oxidation behavior, which are significantly better than those of carbon nanotubes (CNTs) as electrodes. Therefore, the simple, low-cost, sensors described here could be deployed for a variety of applications.

P-type electrical, photoconductive, and anomalous ferromagnetic properties of Cu2O nanowires

Cu2O nanowires are synthesized by reduction of CuO nanowires with hydrogen gas. Strong green photoluminescence dominated by band-edge emission is observed. Field effect transistors fabricated from individual Cu2O nanowires present high on-off ratio (>106) and high mobility (>95 cm2/V s). Furthermore, the device demonstrates a fast photoelectric response to blue illumination in air at room temperature. In addition, anomalous ferromagnetism appears in Cu2O nanowires, which may originate from the defects in Cu2O nanowires. This work shows the application potentials of the Cu2O nanowires, especially in an electrical and photonic device.

Ferroelectric Transistors with Nanowire Channel: Toward Nonvolatile Memory Applications

We report the fabrication and characterization of ZnO nanowire memory devices using a ferroelectric Pb(Zr(0.3)Ti(0.7))O(3) (PZT) film as the gate dielectric and the charge storage medium. With a comparison to nanowire transistors based on SiO(2) gate oxide, the devices were evaluated in terms of their electric transport, retention, and endurance performance. Memory effects are observed as characterized by an eminent counterclockwise loop in I-V(g) curves, which is attributed to the switchable remnant polarization of PZT. The single-nanowire device exhibits a high (up to 10(3)) on/off ratio at zero gate voltage. Our results give a proof-of-principle demonstration of the memory application based on a combination of nanowires (as channels) and ferroelectric films (as gate oxide).

Field emission property improvement of ZnO nanowires coated with amorphous carbon and carbon nitride films

In this paper, we report an approach to prepare a new type of field emitter made up of ZnO nanowires coated with an amorphous carbon (a-C) or carbon nitride film (a-CNx). The coated ZnO nanowires form coaxial nanocables. The best field emission properties, which showed a very low turn-on electric field of 1.5?V??m?1 and an emission current density of 1?mA?cm?2 (enough to produce a luminance of 300?cd?m?2 from a VGA FED with a typical high-voltage phosphor screen efficacy of 9?lm?W?1) under the field of only 2.5?V??m?1, have been obtained from the a-CNx coated ZnO nanowire field emitter among three kinds of emitters: a-C coated ZnO nanowires, a-CNx coated ZnO nanowires and uncoated ZnO nanowires. Microstructures and crystal configuration were investigated by scanning electron microscopy, x-ray diffraction and transmission electron microscopy. Band edge transition without any significant photoluminescence peak relating to intrinsic defects has been observed by photoluminescence measurement. The superior properties of the field emission are attributed to the low work function of the coated carbon nitride film and good electron transport property of the ZnO nanowires with an extremely sharp tip.

Effects of temperature on the ferromagnetism of Mn-doped ZnO nanoparticles and Mn-related Raman vibration

Mn-doped ZnO nanoparticles were synthesized by a rheological phase-reaction–precursor method and the thermal decomposition of the oxalate precursors was studied by thermogravimetry and differential thermal analysis in air. The Mn-doped ZnO obtained at lower temperature crystallizes in a wurtzite structure and a new phase appears at higher temperature. The lattice parameters of Zn1−xMnxO (0.09≤x≤0.1) increase gradually with increasing temperature up to 650 °C and then decrease. X-ray photoelectron spectroscopy indicates that there are different Mn valence bonds in Mn-doped ZnO nanoparticles. Furthermore, two additional Raman peaks were observed. One peak is considered to have an origin related to the incorporation of Mn ions into the Zn site of the ZnO lattice; the other may be attributed to the ZnMnO3 phase. Magnetization measurements under field cooling conditions reveal that the Zn1−xMnxO nanoparticles exhibit ferromagnetic behaviour, and the Curie temperatures of some samples are above room temperature. The difference of the ferromagnetic properties of the Mn-doped ZnO nanoparticles is primarily attributed to the Mn2+ content.

Self-assembly of aligned ZnO nanoscrews: Growth, configuration, and field emission

We report the syntheses of self-catalyst-grown and self-assembled ZnO nanoscrews (ZNS). The morphology and microstructures were characterized by using scanning electron microscopy, transmission electron microscopy and x-ray diffraction. The results reveal that the aligned ZNS are single crystalline grown along the c axis, with 18 sides on their tops but six sides on their stems, while the whole exhibits sixfold symmetry. The formation of such a special-shaped ZNS that may have potential applications in fabrication of nanodevices, is related to the increase of the oxygen supply during the growth followed by a rapidly cooling down process. The growth kinetics of the ZNS is discussed. The field-emission studies show a good stability of the emission current and a low turn-on electrical field.

Morphology-controlled synthesis and a comparative study of the physical properties of SnO2 nanostructures: from ultrathin nanowires to ultrawide nanobelts.

Controlled synthesis of one-dimensional materials, such as nanowires and nanobelts, is of vital importance for achieving the desired properties and fabricating functional devices. We report a systematic investigation of the vapor transport growth of one-dimensional SnO(2) nanostructures, aiming to achieve precise morphology control. SnO(2) nanowires are obtained when SnO(2) mixed with graphite is used as the source material; adding TiO(2) into the source reliably leads to the formation of nanobelts. Ti-induced modification of crystal surface energy is proposed to be the origin of the morphology change. In addition, control of the lateral dimensions of both SnO(2) nanowires (from approximately 15 to approximately 115 nm in diameter) and nanobelts (from approximately 30 nm to approximately 2 microm in width) is achieved by adjusting the growth conditions. The physical properties of SnO(2) nanowires and nanobelts are further characterized and compared using room temperature photoluminescence, resonant Raman scattering, and field emission measurements.