ZnO nanowires
As a II-VI compound semiconductor with wide band gap (3.37 eV), zinc oxide (ZnO) has been broadly used in optical applications, for example, optical waveguide, transparent conducting layer, surface acoustic wave device. Recently one-dimensional ZnO nanostructures, such as nanowire, nanoneedle, and nanobelt, are attracting more and more attention. Their optical, mechanical, field emission and magnetic properties have been studied. ZnO nanowire (NW) is expected to be one of the candidates for nanoscale ultra-violet (UV) lasing, light emitting and photodetection. However, electrical transport properties through ZnO NWs have not yet been broadly investigated. Here we report the transport studies on field effect transistors (FET) made of individual ZnO NWs synthesized via chemical vapor deposition (CVD) method. The effects of oxygen adsorption on NW’s electrical behavior are investigated and the oxygen sensing property is characterized. The results indicate that ZnO NWs can serve as potential building blocks for nanoscale electronic and sensing devices.
nami administrator
Fe2O3 Nanowires
Quasi-one-dimensional (Q1D) materials, such as nanotubes and nanowires, are considered as highly promising nanoscale building blocks for integrated electronic and photonic circuits. In this regard, the control of electron (n-type) and hole (p-type) doping in these nanostructures is of paramount importance. The doping approach is usually implemented by incorporating impurity elements during the synthesis procedures. In our work, α-Fe2O3 nanobelts are configured as field effect transistors (FETs), followed by a controlled in-situ doping method using zinc (Zn) as the impurity element to achieve p- or enhanced n- type semiconducting property. Carrier concentrations and mobilities are obtained from electrical transport studies. Furthermore, the mechanism of p- and n-type doping using only one impurity element is discussed.
Ga2O3 Nanowires
Gallium oxide (Ga2O3), a trivalent metal oxide semiconductor, exhibits a wide band gap (4.9eV) and electrically insulating behavior in normal circumstances. Its remarkable thermal and chemical stability renders it suitable for many potential applications. Ga2O3 thin film has been extensively studied and implemented as high temperature oxygen sensor, insulating barrier in spin tunneling junction, and UV-transparent conductive oxide (TCO). In recent years, low dimensional structures have become the rising stars that draw intensive attention because of their unique properties resulted from the high aspect ratio. Quasi-one-dimensional structures of Ga2O3, such as nanowires and nanobelts, have been synthesized and characterized. However, the electrical transport studies on Ga2O3 nanowires demonstrate poor conductivity at room temperature, making it impractical for device applications. With the aim to enhance the charge carrier density, this report describes the synthesis and a p-type doping method. The electrical and optical properties of Ga2O3 nanowires are characterized.
GaN nanowires
GaN is a direct wide band-gap semiconductor at room temperature. It is a prominent candidate for optoelectronic devices at blue and near ultra-violet wavelengths. In addition, it exhibits high thermal conductivity and little radiation damage, suitable for high temperature and high power microelectronic devices. GaN nanowires have been synthesized by several groups using different methods. In order to perform electrical transport measurements, one needs well dispersed nanowires on a substrate. Here we report a method to synthesize completely dispersed single crystal GaN nanowires with a diameter distribution of 20-70 nm, and we present the surface electric potential distribution on individual, electrical biased nanowire.
Ag-TCNQ Nanowire
Our group is also investigating nanowires based on organic semiconductor TCNQ complexes. Charge transfer complexes using TCNQ (tetracyanoquinodimethane) as organic acceptor hold unique electrical properties. TTF (tetrathiafulvalene)-TCNQ thin film shows potential for electrically NO2 gas sensing, TMTSF (tetramethyltetraserenafulvalene) - TCNQ has been tried to fabricate field effect transistor. Metal-TCNQ complexes such as Cu-TCNQ, K-TCNQ and Ag-TCNQ exhibit electrical switching and photochromic properties, which indicate metal-TCNQ complexes could be potential materials for electrical and optical memory devices. Besides electrical switching, optoelectronic switching of Metal-TCNQ thin film has also been reported, this unique property may be used to build optically controlled solid-state devices with potential applications in optical communications. In addition, TCNQ complexes are organic semiconductor and they could form p-conjugated molecules and lamellar structures, organic semiconductor system has been studied for spin transport.
B Nanowires
Miniaturization of electronic devices is continuously progressing. One-dimensional (1D) systems, such as nanotube and nanowire, are the possible building blocks for the next generation devices. They offer the opportunities for us to test and understand fundamental concepts on the importance of dimensionality and size in electrical, optical, magnetic, and mechanical properties. Boron-based 1D structures are predicted to have high conductivity, good refractoriness, high chemical stability and mechanical strength. These predications suggest that boron-based 1D structures can be a good choice for building nanoelectronic devices.
FMSET
For decades, electronic devices have been relying on the transport of electronic charge. The electron spin degree of freedom, however, was often ignored. A new technology called spin electronics (Spintronics) has emerged since the discovery of giant magnetoresistance (GMR) effect in 1988. Today, GMR read head has become the key for high-density magnetic information storage. At the same time, much progress has been made in making magnetic random access memory (MRAM) based on the tunneling magnetoresistance (TMR) effect. The ability to manipulate electron spin states is critical to extremely high-density information storage, electron-spin-based quantum computing, magneto-electronic sensors, and perhaps future spin electronic devices and systems yet to be imagined. As the trend of device miniaturization continues, such applications require a good understanding of the fundamental physics of spin dependent transport in nanoscale structures.
The proposed project is to combine the recent developments in spin tunnel junctions and single electron transistors, to fabricate and characterize nanoscale hybrid junction structures that reveal new physical aspects of quantum states and dynamic behavior of single electron spins. Several interesting effects have been predicted for spin-dependent transport in ferromagnet (FM)/metal/FM and FM/superconductor/FM single electron transistors. The project is aimed to experimentally verify these theoretical predictions. The approach of this study is to fabricate hybrid junction devices using ebeam lithography and shadow evaporation techniques. This work contributes to the current research in spintronics community and provides more comprehensive understanding of the spin dynamics in order to develop innovative spin based nanoelectronic devices.
Magnetic nanostructure
Development of novel magnetic materials has played an important role in modern-day science and technology. Ferromagnetic nanowires are good candidates for studying one dimensional electron spin dynamics, magnetic domain wall dynamics, and their interaction properties. Technologically, vertical magnetic nanowire arrays embedded in insulating matrix may serve as high density patterned perpendicular magnetic medium with superior signal-to-noise ratio and reduced transition position jitter. On the other hand, magnetic nanotubes with very small wall thickness are predicted to reveal quantum-mechanical effects, such as spin-dependent electron transport with quantization around the tube circumference. Hereby, we present the synthesis of Co nanowires and nanotubes using template-assisted method, and show a systematic characterization of these nanostructures.
