[show abstract][hide abstract] ABSTRACT: In this article, we report the synthesis of single-crystalline nickel silicide nanowires (NWs) via chemical vapor deposition method using NiCl2.6H2O as a single-source precursor. Various morphologies of delta-Ni2Si NWs were successfully acquired by controlling the growth conditions. The growth mechanism of the delta-Ni2Si NWs was thoroughly discussed and identified with microscopy studies. Field emission measurements show a low turn-on field (4.12 V/mum), and magnetic property measurements show a classic ferromagnetic characteristic, which demonstrates promising potential applications for field emitters, magnetic storage, and biological cell separation.
Nanoscale Research Letters 06/2013; 8(1):290. · 2.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: The formation mechanism of SiGe nanorod (NR) arrays fabricated by combining nanosphere lithography and Au-assisted chemical etching has been investigated. By precisely controlling the etching rate and time, the lengths of SiGe NRs can be tuned from 300 nm to 1 μm. The morphologies of SiGe NRs were found to change dramatically by varying the etching temperatures. We propose a mechanism involving a locally temperature-sensitive redox reaction to explain this strong temperature dependence of the morphologies of SiGe NRs. At a lower etching temperature, both corrosion reaction and Au-assisted etching process were kinetically impeded, whereas at a higher temperature, Au-assisted anisotropic etching dominated the formation of SiGe NRs. With transmission electron microscopy and scanning electron microscopy analyses, this study provides a beneficial scheme to design and fabricate low-dimensional SiGe-based nanostructures for possible applications.
Nanoscale Research Letters 02/2012; 7(1):140. · 2.52 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this article, ZnO nanostructures were synthesized via the hydrothermal method which used ZnCl(2) and HMTA mixed solution as the precursor. A multistep growth was adopted to improve the growth restriction of a closed system, not only the length but also the aspect ratio were increased with steps of growth, and the shape of nanorods maintained integrity. Furthermore, photoluminescence spectra which have the near-band-edge-emission (∼3.37 eV) and defect-related emission show the optical properties of ZnO nanostructures. The defect-related emission intensity was greatly enhanced with the increasing surface area of ZnO nanowires. The level of the OH group was attributed to the yellow-light emission (∼580 nm) and the red-shift phenomenon. In addition, we fabricated two types of ultraviolet photodetectors: a single nanowire device and a nanowire-array device, operating at a low bias (less than 5 mV). With the lower energy consumption and the weaker persistent photoconductive effect, our ultraviolet photodetectors have better performance, exhibiting a short response time and higher sensitivity.
[show abstract][hide abstract] ABSTRACT: Well-aligned ZnO nanowires (NWs) were successfully synthesized on Si(100) by the process of carbothermal reduction and vapor-liquid-solid method. Scanning electron microscopy and transmission electron microscopy results confirmed that ZnO NWs were single crystalline wurtzite structures and grew along the  direction. The influences of substrate temperature and total pressure on the growth were discussed. The well-aligned ZnO NWs show good field emission properties, and the emitter constructed of pencil-like ZnO NWs exhibited a low turn-on field (3.82 V μm(-1)) and a high field enhancement factor (β = 2303). Finally, we demonstrated that the as-prepared ZnO NWs with small diameter on the substrate have good photocatalytic activity toward degradation of methylene blue. Using ZnO NWs with Au nanoparticles (NPs) would decrease the recombination rate of hole-electron pairs due to the great shift of the Fermi level to the conduction band. Hence, adding Au NPs was a promising method to enhance the photocatalytic performance of ZnO NWs. It is significant that photocatalyst fabricated by ZnO NWs can apply to the degradation of organic pollution, and solve the environmental issues.
[show abstract][hide abstract] ABSTRACT: The pulsed laser deposition and growth of a high-k dielectric lanthanum aluminate LaAlO3 (LAO) thin film on indium tin oxide/glass substrate at different oxygen partial pressure was studied. Based on the pulsed laser deposition growth mechanism, we explain how a difference in the oxygen partial pressure influences the surface roughness, formation of an interfacial layer, and the transparent resistive switching characteristics of LAO thin films. The micro-structure and oxygen concentration difference inside LAO thin films may be the main reason for the difference in electrical and resistive switching properties. Films grown at higher oxygen partial pressure displayed more reliable resistive switching performance, due to the formation of the interfacial layer and a lower concentration of oxygen vacancies. The interfacial layer serves as a good oxygen reservoir and the involvement of more oxygen ions ensures the switching reliability. The migration of oxygen ions between the interfacial layer and the LAO film under applied bias may be the switching mechanism.
[show abstract][hide abstract] ABSTRACT: One crucial challenge for the integrated circuit devices to go beyond the current technology has been to find the appropriate contact and interconnect materials. NiSi has been commonly used in the 45 nm devices mainly because it possesses the lowest resistivity among all metal silicides. However, for devices of even smaller dimension, its stability at processing temperature is in doubt. In this paper, we show the growth of high-quality nanowires of NiSi(2), which is a thermodynamically stable phase and possesses low resistivity suitable for future generation electronics devices. The origin of low resistivity for the nanowires has been clarified to be due to its defect-free single-crystalline structure instead of surface and size effects.
[show abstract][hide abstract] ABSTRACT: Self-catalyzed β-FeSi2nanowires with a high aspect ratio have been synthesized by a spontaneous chemical vapor transport and reaction method. The as-synthesized single-crystalline β-FeSi2nanowires exhibit photoluminescence at a wavelength of 1.54 μm, which is suitable for Si-based optical communication, at room temperature. The conductivity of a single-stem β-FeSi2nanowire was found to increase with decreasing diameter. The room temperature ferromagnetism and high magnetoresistance performance of 6% at 200 K indicates that β-FeSi2nanowires are potentially applicable for spintronic nanodevices.
Journal of Materials Chemistry 03/2011; 21(15):5704-5709. · 5.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: The highly sensitive nanowire-based Schottky-gate nanosensors for detecting UV, bio-molecules, and gas sensing were demonstrated. The operating mechanism of the Schottky-gate nanosensors is totally distinct from the conventional Ohmic contacted nanosensors. The Schottky-gated device (SGD) has a few merits in comparison to the conventional Ohmic contacted device (OCD). First, it needs no bio-probe to detect molecules; rather, it depends on the absorption of the charged molecules to the junction region. Second, as for the same type of nanowires, such as ZnO, the sensitivity of the SGD is much higher than that of OCD, because a few molecules at the junction region can change the "gate" that effectively tunes the conductance. This Schottky-gate-modulation based sensing principle can be applied to other materials and sensing systems.
[show abstract][hide abstract] ABSTRACT: A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.
[show abstract][hide abstract] ABSTRACT: A new single nanowire based nanosensor is demonstrated for illustrating its ultrahigh sensitivity for gas sensing. The device is composed of a single ZnO nanowire mounted on Pt electrodes with one end in Ohmic contact and the other end in Schottky contact. The Schottky contact functions as a "gate" that controls the current flowing through the entire system. By tuning the Schottky barrier height through the responsive variation of the surface chemisorbed gases and the amplification role played by the nanowire to Schottky barrier effect, an ultrahigh sensitivity of 32,000% was achieved using the Schottky contacted device operated in reverse bias mode at 275 degrees C for detection of 400 ppm CO, which is 4 orders of magnitude higher than that obtained using an Ohmic contact device under the same conditions. In addition, the response time and reset time have been shortened by a factor of 7. The methodology and principle illustrated in the paper present a new sensing mechanism that can be readily and extensively applied to other gas sensing systems.
Journal of the American Chemical Society 12/2009; 131(48):17690-5. · 10.68 Impact Factor
[show abstract][hide abstract] ABSTRACT: We report an external force triggered field-effect transistor based on a free-standing piezoelectric fine wire (PFW). The device consists of an Ag source electrode and an Au drain electrode at two ends of a ZnO PFW, which were separated by an insulating polydimethylsiloxane (PDMS) thin layer. The working principle of the sensor is proposed based on the piezoelectric potential gating effect. Once subjected to a mechanical impact, the bent ZnO PFW cantilever creates a piezoelectric potential distribution across it width at its root and simultaneously produces a local reverse depletion layer with much higher donor concentration than normal, which can dramatically change the current flowing from the source electrode to drain electrode when the device is under a fixed voltage bias. Due to the free-standing structure of the sensor device, it has a prompt response time less than 20 ms and quite high and stable sensitivity of 2%/microN. The effect from contact resistance has been ruled out.
[show abstract][hide abstract] ABSTRACT: Bat-shaped nanorods (nanobats) of Ti5Si4 were grown on titanium foil by a vapor and condensation method without catalysts. The average diameter of the heads and the tails of the nanobats as well as the length of the nanobats are 25, 15, and 350 nm, respectively. The resistivity of the Ti5Si4 nanobat was measured to be 348 Ωμ·cm. Excellent field emission properties were found with the turn-on voltage of the Ti5Si4 nanobats at the current density of 1 μA/cm2 being 1.47 V/μm and field amplification factor being as high as 1350. The possession of remarkable field emission properties indicates that the Ti5Si4 nanobats may be applicable as emitters in flat panel display and vacuum microelectronic devices.
[show abstract][hide abstract] ABSTRACT: UV response of ZnO nanowire nanosensor has been studied under ambient condition. By utilizing Schottky contact instead of Ohmic contact in device fabrication, the UV sensitivity of the nanosensor has been improved by four orders of magnitude, and the reset time has been drastically reduced from ∼ 417 to ∼ 0.8 s. By further surface functionalization with function polymers, the reset time has been reduced to ∼ 20 ms even without correcting the electronic response of the measurement system. These results demonstrate an effective approach for building high response and fast reset UV detectors.
[show abstract][hide abstract] ABSTRACT: Cobalt silicide nanostructures have been synthesized by a spontaneous chemical vapor transport and reaction method. The temperature and the vapor flow rate were shown to critically influence the growth of nanostructures. The effects of two main parameters on the growth of nanostructures were discussed. The phases formed were determined by the Gibbs free energy changes in the reactions. Various phases (CoSi, Co 2 Si) and morphologies, such as single-stem nanowires, three-dimensional (3D) nanowire networks, and aloelike nanostructures, have been synthesized. Very low turn-on field (1.42 V/μm) and good conductance obtained from field-emission and electrical property measurements, respectively, indicate that CoSi nanowires are potentially useful for electronic devices.
[show abstract][hide abstract] ABSTRACT: In this work, the authors study a polycrystalline silicon thin-film transistor (poly-Si TFT) with oxide/nitride/oxide (ONO) stack gate dielectrics and multiple nanowire channels for the applications of both nonvolatile silicon-oxide-nitride-oxide-silicon (SONOS) memory and switch transistor. The proposed device named as nanowire SONOS-TFT has superior electrical characteristics of a transistor such as on/off current ratio, threshold voltage (Vth), and subthreshold slope due to the good gate control ability originated from fringing electrical field effects. Moreover, the proposed device under adequate operation scheme can exhibit high program/erase efficiency and good retention time characteristics at high temperature.
[show abstract][hide abstract] ABSTRACT: A novel poly-Si thin-film transistor with a self-aligned SiGe raised source/drain (SiGe-RSD TFT) has been proposed and fabricated. The SiGe-RSD regions were grown selectively by the ultra-high vacuum chemical vapor deposition (UHVCVD) process designed by us at 550°C. The resultant transistor structure features an ultra-thin active channel region (20 nm) and a self-aligned thick source/drain region (120 nm), and is ideally suited for optimum performance. Significant improvements in electrical characteristics, such as higher turn-on current, lower leakage current and higher drain breakdown voltage have been observed in the SiGe RSD TFT, compared to its conventional TFT counterpart. Moreover, the process is simple and no additional masks are necessary, which is consistent with conventional fabrication processes.
Japanese Journal of Applied Physics 01/2003; 42:1164-1167. · 1.07 Impact Factor