Showing papers by "Peidong Yang published in 2004"

Semiconductor nanowires and nanotubes

Abstract: ▪ Abstract Semiconductor nanowires and nanotubes exhibit novel electronic and optical properties owing to their unique structural one-dimensionality and possible quantum confinement effects in two dimensions. With a broad selection of compositions and band structures, these one-dimensional semiconductor nanostructures are considered to be the critical components in a wide range of potential nanoscale device applications. To fully exploit these one-dimensional nanostructures, current research has focused on rational synthetic control of one-dimensional nanoscale building blocks, novel properties characterization and device fabrication based on nanowire building blocks, and integration of nanowire elements into complex functional architectures. Significant progress has been made in a few short years. This review highlights the recent advances in the field, using work from this laboratory for illustration. The understanding of general nanocrystal growth mechanisms serves as the foundation for the rational sy...

Platonic Gold Nanocrystals

Abstract: Thiswork was supported by the Camille and Henry Dreyfus Foundation, Beckman Foundation, the National Science Foundation (CAREER) and Department of Energy. P.Y. isan Alfred P. Sloan Research Fellow.Work at the Lawrence Berkeley National Laboratory was supported by the Office of Science, Basic Energy Sciences, Division of Materials Science of the U.S. Department of Energy. We thank the National Center for Electron Microscopy for the use of their facilities.

Nanoribbon waveguides for subwavelength photonics integration.

Abstract: Although the electrical integration of chemically synthesized nanowires has been achieved with lithography, optical integration, which promises high speeds and greater device versatility, remains unexplored We describe the properties and functions of individual crystalline oxide nanoribbons that act as subwavelength optical waveguides and assess their applicability as nanoscale photonic elements The length, flexibility, and strength of these structures enable their manipulation on surfaces, including the optical linking of nanoribbon waveguides and other nanowire elements to form networks and device components We demonstrate the assembly of ribbon waveguides with nanowire light sources and detectors as a first step toward building nanowire photonic circuitry

Crystallographic alignment of high-density gallium nitride nanowire arrays

Abstract: Single-crystalline, one-dimensional semiconductor nanostructures are considered to be one of the critical building blocks for nanoscale optoelectronics1 Elucidation of the vapour–liquid–solid growth mechanism2 has already enabled precise control over nanowire position and size1,3,4,5,6,7,8, yet to date, no reports have demonstrated the ability to choose from different crystallographic growth directions of a nanowire array Control over the nanowire growth direction is extremely desirable, in that anisotropic parameters such as thermal and electrical conductivity, index of refraction, piezoelectric polarization, and bandgap may be used to tune the physical properties of nanowires made from a given material Here we demonstrate the use of metal–organic chemical vapour deposition (MOCVD) and appropriate substrate selection to control the crystallographic growth directions of high-density arrays of gallium nitride nanowires with distinct geometric and physical properties Epitaxial growth of wurtzite gallium nitride on (100) γ-LiAlO2 and (111) MgO single-crystal substrates resulted in the selective growth of nanowires in the orthogonal [110] and [001] directions, exhibiting triangular and hexagonal cross-sections and drastically different optical emission The MOCVD process is entirely compatible with the current GaN thin-film technology, which would lead to easy scale-up and device integration

Ion Transport in Nanofluidic Channels

Abstract: Theoretical modeling of ionic distribution and transport in silica nanotubes, 30 nm in diameter and 5 μm long, suggest that when the diameter is smaller than the Debye length, a unipolar solution of counterions is created within the nanotube and the colons are electrostatically repelled By locally modifying the surface charge density through a gate electrode, the ion concentration can be depleted under the gate and the ionic current can be significantly suppressed It is proposed that this could form the basis of a unipolar ionic field-effect transistor

Electrochemomechanical Energy Conversion in Nanofluidic Channels

Abstract: When the Debye length is on the order of or larger than the height of a nanofluidic channel containing surface charge, a unipolar solution of counterions is generated to maintain electrical neutrality A pressure-gradient-driven flow under such conditions can be used for ion separation, which forms the basis for electrochemomechanical energy conversion The current−potential (I−φ) characteristics of such a battery were calculated using continuum dynamics When the bulk concentration is large and the channel does not become a unipolar solution of counterions, both the current and potential become small On the other hand, when bulk concentration is so much smaller, the mass diffusion becomes the rate-controlling step and the potential drops rapidly in the high current density region When the Debye length of the solution is about half of the channel height, the efficiency is maximized

Ultrafast Carrier Dynamics in Single ZnO Nanowire and Nanoribbon Lasers

Abstract: Time-resolved second-harmonic generation (TRSHG) and transient photoluminescence (PL) spectroscopy are utilized to probe the ultrafast creation and subsequent relaxation of excited carriers immediately following band-gap excitation in single ZnO nanowire and nanoribbon lasers. The TRSHG signal consists of a 1−5 ps recovery present only during strong lasing and a 10−80 ps intensity-dependent component. The transient PL response from single structures exhibits an 80 ps decay component independent of pump power (free exciton PL), and a < 10 ps power-dependent component (stimulated emission) that shifts to earlier delay by ca. 10 ps at high pump fluence.

Nanowire array and nanowire solar cells and methods for forming the same

Abstract: Homogeneous and dense arrays of nanowires are described. The nanowires can be formed in solution and can have average diameters of 40-300 nm and lengths of 1-3 μm. They can be formed on any suitable substrate. Photovoltaic devices are also described.

Solution-phase synthesis of single-crystalline iron phosphide nanorods/nanowires.

Abstract: A solution-phase route for the preparation of single-crystalline iron phosphide nanorods and nanowires is reported. We have shown that the mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), which are commonly used as the solvents for semiconductor nanocrystal synthesis, is not entirely inert. In the current process, TOP, serving as phosphor source, reacts with Fe precursors to form FeP nanostructures with large aspect ratios. In addition, the experimental results show that both TOP and TOPO are necessary for the formation of FeP nanowires and their ratio appears to control the morphology of the produced FeP structures. A possible growth mechanism is discussed.

Fabrication and characterization of a nanowire/polymer-based nanocomposite for a prototype thermoelectric device

Abstract: This paper discusses the design, fabrication and testing of a novel thermoelectric device comprised of arrays of silicon nanowires embedded in a polymer matrix. By exploiting the low-thermal conductivity of the composite and presumably high-power factor of the nanowires, a thermoelectric figure of merit, higher than the corresponding bulk value, should result. Arrays were first synthesized using a vapor-liquid-solid (VLS) process leading to one-dimensional (1-D) growth of single-crystalline nanowires. To provide structural support while maintaining thermal isolation between nanowires, parylene, a low thermal conductivity and extremely conformal polymer, was embedded within the arrays. Mechanical polishing and oxygen plasma etching techniques were used to expose the nanowire tips and a metal contact was deposited on the top surface. Scanning electron micrographs (SEMs) illustrate the results of the fabrication processes. Using a modification of the 3/spl omega/ technique, the effective thermal conductivity of the nanowire matrix was measured and 1 V characteristics were also demonstrated. An assessment of the suitability of this nanocomposite for high thermoelectric performance devices is given.

Fluidic nanotubes and devices

Abstract: Fluidic nanotube devices (29) are described in which a hydrophilic, non-carbon nanotube (152), has its ends fluidly coupled to reservoirs (154 and 156). Source and drain contacts (164 and 166) are connected to opposing ends of the nanotube, or within each reservoir near the opening of the nanotube. The passage of molecular species can be sensed by measuring current flow (source-drain, ionic, or combination). The tube interior can be functionalized by joining binding molecules (160) so that different molecular species can be sensed by detecting current changes. The nanotube may be a semiconductor (132), wherein a tubular transistor (130) is formed. A gate electrode (146) can be attached between source (136) and drain (138) to control current flow and ionic flow. By way of example an electrophoretic array embodiment is described, integrating MEMs switches. A variety of applications are described, such as: nanopores, nanocapillary devices, nanoelectrophoretic, DNA sequence detectors, immunosensors, thermoelectric devices, photonic devices, nanoscale fluidic bioseparators, imaging devices, and so forth.

Rapid Prototyping of Site-Specific Nanocontacts by Electron and Ion Beam Assisted Direct-Write Nanolithography

Abstract: Rapid prototyping of bottom-up nanostructure circuits is demonstrated, utilizing metal deposition and patterning methodology based on combined focused ion and electron beam induced decomposition of a metal−organic precursor gas. Ohmic contacts were fabricated using electron beam deposition, followed by the faster process of ion beam deposition for interconnect formation. Two applications of this method are demonstrated: three-terminal transport measurements of Y-junction carbon nanotubes and fabrication of nanocircuits for determination of electromechanical degradation of silver nanowires.

Gallium nitride nanowires with a metal initiated metal-organic chemical vapor deposition (MOCVD) approach

Abstract: We have studied structural and electrical properties of one dimensionally grown single crystalline gallium nitride (GaN) nanowires (NWs) for nanoscale devices using a metal-initiated metal-organic chemical vapor deposition (MOCVD). GaN nanowires were formed via the vapor-liquid-solid (VLS) mechanism with gold, iron, or nickel as growth initiators and were found to have triangular cross-sections with widths of 15 ∼ 200 nm and lengths of 5 ∼ 20 μm. TEM confirmed that the nanowires were single crystalline and were well oriented along the [210] or [110] direction on substrate depending on the metal initiators. For electrical transport properties of un-doped GaN nanowires, the back-gated field effect transistors (FET) were also fabricated by standard e-beam lithography. In our electrical measurement, the carrier concentration and mobility were 2 ∼ 4 × 10 18 cm -3 and 60 ∼ 70 cm2/V s, respectively.

Langmuir-blodgett nanostructure monolayers

Abstract: Methods for assembly of monolayers of nanoparticles using the Langmuir-Blodgett technique, as well as monolayers, assemblies, and devices are described The surface properties of these monolayers are highly reproducible and well-defined as compared to other systems These monolayers can readily be used for molecular detection in either an air-borne or a solution environment, and sensors using the monolayer could have significant implications in chemical and biological warfare detection, national and global security, as well as in medical detection applications

Transport Phenomena in Nanofluidic Channels

Abstract: Ion transport in nanoscale channels has recently received increasing attention. Much of that has resulted from experiments that report modulation of ion transport through the protein ion channel, α-hemolysin, due to passage of single biomolecules of DNA or proteins [1]. This has prompted research towards fabricating synthetic nanopores out of inorganic materials and studying biomolecular transport through them [2]. Recently, the synthesis of arrays of silica nanotubes with internal diameters in the range of 5–100 nm and with lengths 1–20 μm was reported [3]. These tubes could potentially allow new ways of detecting and manipulating single biomolecules and new types of devices to control ion transport. Theoretical modeling of ionic distribution and transport in silica nanotubes, 30 nm in diameter and 5 μm long, suggest that when the diameter is smaller than the Debye length, a unipolar solution of counterions is created within the nanotube and the coions are electrostatically repelled [4]. We proposed two different types of devices to use this unipolar nature of solution, i.e. ‘transistor’ and ‘battery’. When the electric potential bias is applied at two ends of a nanotube, ionic current is generated. By locally modifying the surface charge density through a gate electrode, the concentration of counterions can be depleted under the gate and the ionic current can be significantly suppressed. This could form the basis of a unipolar ionic field-effect transistor. By applying the pressure bias instead of electric potential bias, the fluid flow is generated. Because only the counterions are located inside the channel, the streaming current and streaming potential are generated. This could form the basis of an electro-chemo-mechanical battery. In the present study, transport phenomena in nanofluidic channels were investigated and the performance characteristics were evaluated using continuum dynamics.Copyright © 2004 by ASME