Showing papers by "Peidong Yang published in 2002"
TL;DR: In this paper, the photoconducting properties of individual semiconductor nanowires are explored and the authors show the possibility of creating highly sensitive nanowire switches by exploring the photocconducting properties.
Abstract: no attention has been given to the photoconducting properties of nanowires despite the exciting possibilities for use in optoelectronic circuits. Here, we show the possibility of creating highly sensitive nanowire switches by exploring the photoconducting properties of individual semiconductor nanowires. The conductivity of the ZnO nanowires is extremely sensitive to ultraviolet light exposure. The light-induced conductivity increase allows us to reversibly switch the nanowires between “OFF” and “ON” states, an optical gating phenomenon analogous to the commonly used electrical gating. [2,3,10]
2,208 citations
TL;DR: In this paper, a survey of recent developments in the rational synthesis of single-crystalline zinc oxide nanowires and their unique optical properties is presented, based on the fundamental understanding of the vapor-liquid-solid (VLS) nanowire growth mechanism, different levels of growth controls have been achieved.
Abstract: This article surveys recent developments in the rational synthesis of single-crystalline zinc oxide nanowires and their unique optical properties. The growth of ZnO nanowires was carried out in a simple chemical vapor transport and condensation (CVTC) system. Based on our fundamental understanding of the vapor–liquid–solid (VLS) nanowire growth mechanism, different levels of growth controls (including positional, orientational, diameter, and density control) have been achieved. Power-dependent emission has been examined and lasing action was observed in these ZnO nanowires when the excitation intensity exceeds a threshold (∼40 kW cm–2). These short-wavelength nanolasers operate at room temperature and the areal density of these nanolasers on substrate readily reaches 1 × 1010 cm–2. The observation of lasing action in these nanowire arrays without any fabricated mirrors indicates these single-crystalline, well-facetted nanowires can function as self-contained optical resonance cavities. This argument is further supported by our recent near-field scanning optical microscopy (NSOM) studies on single nanowires.
1,769 citations
TL;DR: A redshift that is strongly dependent on pump power supports the idea that the electron–hole plasma mechanism is primarily responsible for the gain at room temperature and is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet–blue coherent light sources.
Abstract: There is much current interest in the optical properties of semiconductor nanowires, because the cylindrical geometry and strong two-dimensional confinement of electrons, holes and photons make them particularly attractive as potential building blocks for nanoscale electronics and optoelectronic devices, including lasersand nonlinear optical frequency converters. Gallium nitride (GaN) is a wide-bandgap semiconductor of much practical interest, because it is widely used in electrically pumped ultraviolet-blue light-emitting diodes, lasers and photodetectors. Recent progress in microfabrication techniques has allowed stimulated emission to be observed from a variety of GaN microstructures and films. Here we report the observation of ultraviolet-blue laser action in single monocrystalline GaN nanowires, using both near-field and far-field optical microscopy to characterize the waveguide mode structure and spectral properties of the radiation at room temperature. The optical microscope images reveal radiation patterns that correlate with axial Fabry-Perot modes (Q approximately 10(3)) observed in the laser spectrum, which result from the cylindrical cavity geometry of the monocrystalline nanowires. A redshift that is strongly dependent on pump power (45 meV microJ x cm(-2)) supports the idea that the electron-hole plasma mechanism is primarily responsible for the gain at room temperature. This study is a considerable advance towards the realization of electron-injected, nanowire-based ultraviolet-blue coherent light sources.
1,207 citations
TL;DR: In this article, a hybrid pulsed laser ablation/chemical capor deposition (PLA-CVD) process was proposed for the synthesis of semiconductor nanowires with longitudinal ordered heterostructures.
Abstract: Heterojunction and superlattice formation is essential for many potential applications of semiconductor nanowires in nanoscale optoelectronics. We have developed a hybrid pulsed laser ablation/chemical capor deposition (PLA-CVD) process for the synthesis of semiconductor nanowires with longitudinal ordered heterostructures. The laser ablation process generates a programmable pulsed vapor source, which enables the nanowire growth in a block-by-block fashion with a well-defined compositional profile along the wire axis. Single-crystalline nanowires with longitudinal Si/SiGe superlattice structure have been successfully synthesized. This unique class of heterostructured one-dimensional nanostructures holds great potential in applications such as light emitting devices and thermoelectrics.
1,057 citations
TL;DR: This process reported here is highly promising for producing uniform nanorods, and more importantly it will be useful in resolving the growth mechanism of anisotropic metal nanoparticles due to its simplicity and the relatively slow growth rate of the nanorod.
Abstract: Gold nanorods have been synthesized by photochemically reducing gold ions within a micellar solution. The aspect ratio of the rods can be controlled with the addition of silver ions. This process reported here is highly promising for producing uniform nanorods, and more importantly it will be useful in resolving the growth mechanism of anisotropic metal nanoparticles due to its simplicity and the relatively slow growth rate of the nanorods.
999 citations
TL;DR: The development of photochemical NO2 sensors that work at room temperature and are based on individual single-crystalline SnO2 nanoribbons are reported, which once again demonstrate that seemingly small variations in ligand structure can result in significant improvements in catalysis.
Abstract: A major area of application for nanowires and nanotubes is likely to be the sensing of important molecules, either for medical or environmental health purposes. The ultrahigh surface-to-volume ratios of these structures make their electrical properties extremely sensitive to surface-adsorbed species, as recent work has shown with carbon nanotubes,[1, 2] functionalized silicon nanowires and metal nanowires.[3, 4] Chemical nanosensors are interesting because of their potential for detecting very low concentrations of biomolecules or pollutants on platforms small enough to be used in vivo or on a microchip. Here we report the development of photochemical NO2 sensors that work at room temperature and are based on individual single-crystalline SnO2 nanoribbons. Tin dioxide is a wide-bandgap (3.6 eV) semiconductor. For n-type SnO2 single crystals, the intrinsic carrier concentration is primarily determined by deviations from stoichiometry in the form of equilibrium oxygen vacancies, which are predominantly atomic defects.[5] The electrical conductivity of nanocrystalline SnO2 depends strongly on surface states produced by molecular adsorption that results in space-charge layer changes and band modulation.[6] NO2, a combustion product that plays a key role in tropospheric ozone and smog formation, acts as an electron-trapping adsorbate on SnO2 crystal faces and can be sensed by monitoring the electrical conductance of the material. Because NO2 chemisorbs strongly on many metal oxides,[7] commercial sensors based on particulate or thin-film SnO2 operate at 300 ± 500 C to enhance the surface molecular desorption kinetics and continuously TMclean∫ the sensors.[8] The high-temperature operation of these oxide sensors is not favorable in many cases, particularly in an explosive environment. We have found that the strong photoconducting response of individual singlecrystalline SnO2 nanoribbons makes it possible to achieve equally favorable adsorption ± desorption behavior at room temperature by illuminating the devices with ultraviolet (UV) light of energy near the SnO2 bandgap. The active desorption process is thus photoinduced molecular desorption (Figure 1).[9] In conclusion, we have succeeded in the development of the ruthenium-based metathesis catalyst 4, which exhibits excellent metathesis activity, without any loss of stability in air. These findings once again demonstrate that seemingly small variations in ligand structure can result in significant improvements in catalysis.
913 citations
Patent•
29 Mar 2002TL;DR: One-dimensional nanostructures have uniform diameters of less than approximately 200 nm and are referred to as "nanowires" as mentioned in this paper, which include single-crystalline materials having different chemical compositions.
Abstract: One-dimensional nanostructures having uniform diameters of less than approximately 200 nm. These inventive nanostructures, which we refer to as “nanowires”, include single-crystalline homostructures as well as heterostructures of at least two single-crystalline materials having different chemical compositions. Because single-crystalline materials are used to form the heterostructure, the resultant heterostructure will be single-crystalline as well. The nanowire heterostructures are generally based on a semiconducting wire wherein the doping and composition are controlled in either the longitudinal or radial directions, or in both directions, to yield a wire that comprises different materials. Examples of resulting nanowire heterostructures include a longitudinal heterostructure nanowire (LOHN) and a coaxial heterostructure nanowire (COHN).
650 citations
TL;DR: A novel microfluidic-assisted nanowire integration (MANI) process was developed for the hierarchical assembly of nanowires building blocks into functional devices and systems.
Abstract: Rationally controlled growth of inorganic semiconductor nanowires is important for their applica- tions in nanoscale electronics and photonics. In this article, we discuss the rational growth, physical proper- ties, and integration of nanowires based on the results from the authors× laboratory. The composition, diameter, growth position, and orientation of the nanowires are controlled based on the vapor ± solid ± liquid (VLS) crystal growth mechanism. The thermal stability and optical properties of these semiconductor nanowires are investigated. Particularly, ZnO nanowires with well- defined end surfaces can function as room-temperature ultraviolet nanolasers. In addition, a novel microfluidic- assisted nanowire integration (MANI) process was de- veloped for the hierarchical assembly of nanowire build- ing blocks into functional devices and systems.
441 citations
TL;DR: In this article, the second and third-harmonic generation (SHG, THG) were imaged on single zinc oxide (ZnO) nanowires using near-field scanning optical microscopy (NSOM).
Abstract: The nonlinear optical response of semiconductor nanowires has potential application for frequency conversion in nanoscale optical circuitry. Here, second- and third-harmonic generation (SHG, THG) are imaged on single zinc oxide (ZnO) nanowires using near-field scanning optical microscopy (NSOM). The absolute magnitudes of the two independent (2) elements of a single wire are determined, and the nanowire SHG and THG emission patterns as a function of incident polarization are attributed to the hexagonal nanowire geometry and (2) tensor symmetry. Semiconductor nanowires are of current interest because of their unique electrical and optical properties. 1-3 In particular, their nonlinear optical properties suggest potential applications as frequency converters or logic/routing elements in nanoscale optoelectronic circuitry. A linear optical property of nanowires, photoluminescence (PL) polarization, has recently been studied in single indium phosphide nanowires. 2 In that case, the PL polarization is based upon the classical electromagnetic properties of a dielectric cylinder and averages ca. 91%. In contrast, coherent nonlinear optical phenomena, such as second- and third-harmonic generation (SHG and THG, respectively), depend explicitly on the crystal lattice structure of the medium, which could yield a very high (nearly 100%) polarization selectivity. In addition, the temporal response of the nonresonant harmonic generation is similar to the pulse width of the pump laser, in some cases 20 fs, 4 while incoherent processes are at least 2-4 orders of magnitude slower. Moreover, nonresonant SHG is essentially independent of wavelength below the energy band gap of semiconductor materials, most often including the 1.3-1.5 Im wavelength region typically used in optical fiber
310 citations
Patent•
29 Mar 2002TL;DR: One-dimensional nanostructures have uniform diameters of less than approximately 200 nm and are referred to as "nanowires" as mentioned in this paper, which include single-crystalline materials having different chemical compositions.
Abstract: One-dimensional nanostructures having uniform diameters of less than approximately 200 nm. These inventive nanostructures, which we refer to as “nanowires”, include single-crystalline homostructures as well as heterostructures of at least two single-crystalline materials having different chemical compositions. Because single-crystalline materials are used to form the heterostructure, the resultant heterostructure will be single-crystalline as well. The nanowire heterostructures are generally based on a semiconducting wire wherein the doping and composition are controlled in either the longitudinal or radial directions, or in both directions, to yield a wire that comprises different materials. Examples of resulting nanowire heterostructures include a longitudinal heterostructure nanowire (LOHN) and a coaxial heterostructure nanowire (COHN).
302 citations
TL;DR: In this article, Braun et al. present a survey of the state of the art in the field of bioinformatics with respect to the use of artificial neural networks (ANNs).
Abstract: Received date: August 27, 2001 Final version: October 17, 2001 ± [1] D. Braun, A. J. Heeger, Appl. Phys. Lett. 1995, 66, 2540. [2] J. H. Schön, C. Kloc, A. Dodabalapur, B. Batlogg, Science 2000, 289, 599. [3] N. Karl, J. Lumin. 1976, 12/13, 851. [4] M. Nagawa, M. Ichikawa, T. Koyama, H. Shirai, Y. Taniguchi, A. Hongo, S. Tsuji, Y. Nakano, Appl. Phys. Lett. 2000, 77, 2641. [5] R. Gupta, M. Stevenson, A. Dogariu, M. D. McGehee, J. Y. Park, V. Srdanov, A. J. Heeger, H. Wang, Appl. Phys. Lett. 1998, 73, 3492. [6] M. Berggren, A. Dodabalapur, R. E. Slusher, Appl. Phys. Lett. 1997, 71, 2230. [7] V. G. Kozlov, V. Bulovi, P. E. Burrows, S. R. Forrest, Nature 1997, 389, 362. [8] Y. C. Kim, T.-W. Lee, O. O. Park, C. Y. Kim, H. N. Cho, Adv. Mater. 2001, 13, 646. [9] D. Fichou, S. Delysse, J.-M. Nunzi, Adv. Mater. 1997, 9, 1178. [10] M. D. McGehee, A. J. Heeger, Adv. Mater. 2000, 12, 1655. [11] H. Yanagi, T. Morikawa, Appl. Phys. Lett. 1999, 75, 187. [12] H. Yanagi, T. Morikawa, S. Hotta, K. Yase, Adv. Mater. 2001, 13, 313. [13] a) S. Hotta, H. Kimura, S. A. Lee, T. Tamaki, J. Heterocycl. Chem. 2000, 37, 281. b) S. Hotta, S. A. Lee, T. Tamaki, J. Heterocycl. Chem. 2000, 37, 25. [14] M. G. Liu, M. H. Jiang, X. T. Tao, D. R. Yuan, D. Xu, N. Zhang, Z. S. Shao, J. Mater. Sci. Lett. 1994, 13, 146. [15] S. A. Lee, Y. Yoshida, M. Fukuyama, S. Hotta, Synth. Met. 1999, 106, 39. [16] a) M. R. Unroe, B. A. Reinhardt, Synthesis, 1987, 981. b) W. Kern, W. Heitz, H. O. Wirth, Makromol. Chem. 1960, 40, 189. [17] S. Hotta, Y. Ichino, Y. Yoshida, M. Yoshida, J. Phys. Chem. B 2000, 104, 10 316. [18] S. Hotta, K. Waragai, Adv. Mater. 1993, 5, 896.
TL;DR: An overview of current research activities that center on nanowires whose lateral dimensions fall anywhere in the range of 1-200 nm can be found in this article, where a number of strategies for the hierarchical assembly of nanowire building blocks are discussed.
Abstract: One-dimensional (1D) nanostructures are ideal systems for investigating the dependence of electrical transport, optical properties and mechanical properties on size and dimensionality. They are expected to play an important role as both interconnects and functional components in the fabrication of nanoscale electronic and optoelectronic devices. This article presents an overview of current research activities that center on nanowires whose lateral dimensions fall anywhere in the range of 1–200 nm. It is organized into three parts: The first part discusses various methods that have been developed for generating nanowires with tightly controlled dimensions, orientations, and well-defined properties. The second part highlights a number of strategies that are being developed for the hierarchical assembly of nanowire building blocks. The third part surveys some of the novel physical properties (e.g., optical, electrical, and mechanical) of these nanostructures. Finally, we conclude with some personal perspecti...
TL;DR: The Langmuir-Blodgett technique has been used to assemble one-dimensional nanoscale building blocks and various superstructures can be obtained as a result of different interactions between the individual nanostructures and different surface pressure applied.
Abstract: The Langmuir-Blodgett technique has been used to assemble one-dimensional nanoscale building blocks. Various superstructures can be obtained as a result of different interactions between the individual nanostructures and different surface pressure applied. The general assembly behavior is exemplified here with BaCrO4, BaWO4, Au nanorods, and Mo3Se3 nanowires.
TL;DR: In this article, a template-engaged topotactic reaction was used to synthesize single-crystalline Ag2Se nanowires from trigonal selenium.
Abstract: Single-crystalline Ag2Se nanowires have been successfully synthesized through a template-engaged topotactic reaction in which nanowires of trigonal selenium were transformed into Ag2Se by reacting with aqueous AgNO3 solutions at room temperature (RT). An interesting size-dependent transition between two crystal structures has also been observed for this newly synthesized one-dimensional system: The Ag2Se nanowires adopted a tetragonal structure when their diameters were less than ∼40 nm; an orthorhombic structure was found to be more favorable as the diameter of these nanowires was increased beyond 40 nm. Since this reaction can be carried out at ambient pressure and temperature, it should be straightforward to scale up the entire process for the high-volume production of Ag2Se nanowires with well-controlled sizes and crystal structures. These highly uniform nanowires of single-crystalline Ag2Se are potentially useful as photosensitizers, superionic conductors, magnetoresistive compounds, or thermoelectric materials. This work also represents the first demonstration of a template-engaged process capable of generating single-crystalline nanowires from the solution-phase and at RT.
TL;DR: In this paper, a novel vapor-liquid-solid epitaxy (VLSE) process was developed to synthesize high-density semiconductor nanowire arrays with diameters of 10-200 nm and aspect ratios of 10 -100.
Abstract: A novel vapor-liquid-solid epitaxy (VLSE) process has been developed to synthesize high-density semiconductor nanowire arrays. The nanowires generally are single crystalline and have diameters of 10-200 nm and aspect ratios of 10-100. The areal density of the array can readily approach 1010 cm-2. Results based on Si and ZnO nanowire systems are reported here. Because of their single crystallinity and high surface area, these nanowire arrays could find unique applications in photocatalysis and photovoltaics.
TL;DR: In this article, single-crystalline nanoribbons were used as substrates for the epitaxial growth of different functional thin films deposited by laser ablation techniques.
Abstract: Single-crystalline nanoribbons were used as substrates for the epitaxial growth of different functional thin films deposited by laser ablation techniques. This simple method yields highly crystalline bilayer nanotapes with sharp structural and compositional interfaces. As an example, Co0.05Ti0.95O2@SnO2 nanotapes are shown to be ferromagnetic at room temperature. These composite nanotapes, with their various possible functionalities, represent an important new class of nanoscale building blocks for optoelectronic applications.
TL;DR: In this article, ultraviolet lasing from single zinc oxide nanowires is demonstrated at room temperature, and near-field optical microscopy images quantify the localization and divergence of the laser beam.
Abstract: Ultraviolet lasing from single zinc oxide nanowires is demonstrated at room temperature. Near-field optical microscopy images quantify the localization and the divergence of the laser beam. The linewidths, wavelengths, and power dependence of the nanowire emission characterize the nanowire as an active optical cavity. These individual nanolasers could serve as miniaturized light sources for microanalysis, information storage, and optical computing.
Patent•
14 May 2002TL;DR: In this article, a low-cost, efficient method of preparing hierarchically ordered structures by filling a mold with a self-assembling mixture of hydrolyzed inorganic species and amphiphilic block copolymers was proposed.
Abstract: A low-cost, efficient method of preparing hierarchically ordered structures by filling a mold with a self-assembling mixture of hydrolyzed inorganic species and amphiphilic block copolymers and applying pressure to the mixture. Polymerization of the inorganic species within the mixture results in a mesoscopically structured material having molded features. A mesoporous material can be produced by subsequent thermal removal of the copolymers.
Princeton University1, Cornell University2, Columbia University3, Texas A&M University4, North Carolina State University5, California Institute of Technology6, Rensselaer Polytechnic Institute7, University of Tennessee8, University of California, Davis9, University of Illinois at Urbana–Champaign10, Georgia Institute of Technology11, University of Michigan12, University of Notre Dame13, Massachusetts Institute of Technology14, Stanford University15, Newcastle University16, University of Valencia17, University of California, Los Angeles18, Lawrence Livermore National Laboratory19, University of Houston20, Michigan State University21, University of North Carolina at Chapel Hill22, University of Texas at Austin23, University of Chicago24, National Renewable Energy Laboratory25, University of Arkansas26, Oak Ridge National Laboratory27, United States Naval Research Laboratory28, National Institute of Standards and Technology29, Ohio State University30, University of California, Berkeley31
TL;DR: The second of a series of workshops planned in this topical area was held at NSF headquarters in Arlington, Virginia, in January 1998, and was designed to address the core of the field, describing how it has developed in the US and worldwide in the past decade, and how the members of the community saw the central thrusts of research and education in solid state chemistry proceeding in the next several years as discussed by the authors.
Patent•
14 May 2002
TL;DR: In this paper, a low-cost, efficient method of preparing hierarchically ordered structures by filling a minimold with a microsphere-containing latex suspension, forming an close-packed array of microspheres within the minimold and filling void space in the array with a self-assembling mixture of hydrolyzed inorganic species and amphiphilic block copolymers.
Abstract: A low-cost, efficient method of preparing hierarchically ordered structures by filling a minimold with a microsphere-containing latex suspension, forming an close-packed array of microspheres within the minimold and filling void space in the array with a self-assembling mixture of hydrolyzed inorganic species and amphiphilic block copolymers. A macroporous and mesoporous material can be produced by subsequent thermal removal of the microspheres and copolymers.
25 Aug 2002
TL;DR: In this article, bismuth telluride nanowires are synthesized by electrodeposition into the cavities of porous alumina templates and subjected to measurements of both thermal conductivity and Seebeck coefficient over temperatures ranging from 20 K to 320 K.
Abstract: Theoretical predictions suggest that the thermoelectric properties of nanowires could be greatly enhanced compared with the bulk materials. To investigate these predictions, bismuth telluride nanowires are synthesized by electrodeposition into the cavities of porous alumina templates. Individual nanowires are then isolated, and subjected to measurements of both thermal conductivity and Seebeck coefficient over temperatures ranging from 20 K to 320 K. All measurements are made using a microfabricated device consisting of two suspended membranes with integrated heaters and resistance thermometers. Platinum or carbon films are locally deposited at the wire and the heater pad junctions to enhance the contact conductance. Results show that the thermal conductivity of the measured Bi/sub 2/Te/sub 3/ nanowires varies from wire to wire and show different temperature dependence, probably because the wire composition and crystal structure are not the same.
25 Jun 2002
TL;DR: In this paper, a novel vapor-liquid solid epitaxy (VLSE) process has been developed to synthesize high-density semiconductor nanowire arrays, which generally are single crystalline and have diameters of 10-200 nm and aspect ratios of 10 -100.
Abstract: A novel vapor-liquid-solid epitaxy (VLSE) process has been developed to synthesize high-density semiconductor nanowire arrays. The nanowires generally are single crystalline and have diameters of 10-200 nm and aspect ratios of 10-100. The areal density of the array can be readily approach 1010 cm-2. Results based on Si and ZnO nanowire systems are reported here.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
01 Jan 2002
TL;DR: In this article, the design, fabrication and testing of a novel thermoelectric device comprised of arrays of silicon nanowires embedded in a polymer matrix was discussed, where parylene, a low thermal conductivity and extremely conformal polymer, was embedded within the arrays.
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 high figure of merit should result. Arrays were first synthesized using a vapor-liquid-solid (VLS) process leading to one-dimensional growth of single-crystalline nanowires. To provide both structural support and 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 microscopy pictures illustrate the results of the fabrication processes. Using the 3ω technique, the effective thermal conductivity of the nanowire matrix was measured.Copyright © 2002 by ASME
TL;DR: In this paper, the photoconducting properties of individual semiconductor nanowires are explored and the authors show the possibility of creating highly sensitive nanowire switches by exploring the photocconducting properties.
Abstract: no attention has been given to the photoconducting properties of nanowires despite the exciting possibilities for use in optoelectronic circuits. Here, we show the possibility of creating highly sensitive nanowire switches by exploring the photoconducting properties of individual semiconductor nanowires. The conductivity of the ZnO nanowires is extremely sensitive to ultraviolet light exposure. The light-induced conductivity increase allows us to reversibly switch the nanowires between “OFF” and “ON” states, an optical gating phenomenon analogous to the commonly used electrical gating. [2,3,10]
TL;DR: In this paper, the authors discuss the rational growth, physical proper-ties, and integration of nanowires based on the results from the authors× laboratory, and a novel microfluidic-assisted nanowire integration (MANI) process was developed for the hierarchical assembly of Nanowire build- ing blocks into functional devices and systems.
Abstract: Rationally controlled growth of inorganic semiconductor nanowires is important for their applica- tions in nanoscale electronics and photonics. In this article, we discuss the rational growth, physical proper- ties, and integration of nanowires based on the results from the authors× laboratory. The composition, diameter, growth position, and orientation of the nanowires are controlled based on the vapor ± solid ± liquid (VLS) crystal growth mechanism. The thermal stability and optical properties of these semiconductor nanowires are investigated. Particularly, ZnO nanowires with well- defined end surfaces can function as room-temperature ultraviolet nanolasers. In addition, a novel microfluidic- assisted nanowire integration (MANI) process was de- veloped for the hierarchical assembly of nanowire build- ing blocks into functional devices and systems.
24 Jul 2002
TL;DR: In this paper, the zinc oxide (ZnO) nanowires grown on a sapphire substrate are discussed for room-temperature optical energy conversion and stimulated UV light emission.
Abstract: One-dimensional nanostructures hold the promise of becoming critical elements for next generation nanoscale electronic and photonic devices. While significant efforts have been devoted to the development of nanotube or nanowire based transistors, little has been done on their photonic counterpart. Here we summarize our recent efforts on one-dimensional crystalline nanostructures, in particular, the zinc oxide (ZnO) nanowires grown on a sapphire substrate. ZnO is a wide bandgap (3.37 eV) compound semiconductor that is especially suitable for blue and ultraviolet (UV) optoelectronic applications. Room-temperature optical energy conversion and stimulated UV light emission from ZnO nanowires are emphasized, along with a discussion of potential applications of nanoscale lasers.
01 Jan 2002
TL;DR: In this article, the size effect on the nanowire thermal conductivity has been investigated and the authors also solved the Boltzmann transport equation (BTE) and showed that the MD results fit reasonably well with the BTE solutions.
Abstract: One-dimensional (1D) materials such as various kinds of nanowires and nanotubes have attracted a lot of attention recently because of their potential applications in nanoelectronic and energy conversion devices [1–3]. As the size of low dimensional materials is confined to be comparable to the phonon mean free path, the thermal conductivity can be reduced due to boundary scattering. A theoretical study [4] further suggests that as the diameter of a Si nanowire becomes smaller than 20 nm, the phonon dispersion relation can be modified due to the boundary confinement and the phonon group velocities will be less than that of the bulk, which will also tend to reduce the thermal conductivity. A molecular dynamics (MD) simulation [5] has shown that for nanowires of cross sections ranging from 2.58 to 28.62 nm2 , the thermal conductivity could be two orders of magnitude smaller than those of bulk Si crystals in a temperature range from 200 K to 500 K. In their paper, the authors also solved the Boltzmann transport equation (BTE) and showed that the MD results fit reasonably well with the BTE solutions. It is very important to experimentally verify the theoretical predictions and provide experimental data for the device design in nanoelectronic and nanoscale energy conversion devices. However, no systematic experimental studies of the size effect on the nanowire thermal conductivity have been published.Copyright © 2002 by ASME