Showing papers by "Peidong Yang published in 2007"

Shaping binary metal nanocrystals through epitaxial seeded growth.

Abstract: Morphological control of nanocrystals has become increasingly important, as many of their physical and chemical properties are highly shape dependent. Nanocrystal shape control for both single- and multiple-material systems, however, remains empirical and challenging. New methods need to be explored for the rational synthetic design of heterostructures with controlled morphology. Overgrowth of a different material on well-faceted seeds, for example, allows for the use of the defined seed morphology to control nucleation and growth of the secondary structure. Here, we have used highly faceted cubic Pt seeds to direct the epitaxial overgrowth of a secondary metal. We demonstrate this concept with lattice-matched Pd to produce conformal shape-controlled core-shell particles, and then extend it to lattice-mismatched Au to give anisotropic growth. Seeding with faceted nanocrystals may have significant potential towards the development of shape-controlled heterostructures with defined interfaces.

Platinum Nanoparticle Shape Effects on Benzene Hydrogenation Selectivity

Abstract: Benzene hydrogenation was investigated in the presence of a surface monolayer consisting of Pt nanoparticles of different shapes (cubic and cuboctahedral) and tetradecyltrimethylammonium bromide (TTAB). Infrared spectroscopy indicated that TTAB binds to the Pt surface through a weak C-H...Pt bond of the alkyl chain. The catalytic selectivity was found to be strongly affected by the nanoparticle shape. Both cyclohexane and cyclohexene product molecules were formed on cuboctahedral nanoparticles, whereas only cyclohexane was produced on cubic nanoparticles. These results are the same as the product selectivities obtained on Pt(111) and Pt(100) single crystals in earlier studies. The apparent activation energy for cyclohexane production on cubic nanoparticles is 10.9 +/- 0.4 kcal/mol, while for cuboctahedral nanoparticles, the apparent activation energies for cyclohexane and cyclohexene production are 8.3 +/- 0.2 and 12.2 +/- 0.4 kcal/mol, respectively. These activation energies are lower, and corresponding turnover rates are three times higher than those obtained with single-crystal Pt surfaces.

Nanowire Photonics

Abstract: The manipulation of optical energy in structures smaller than the wavelength of light is key to the development of integrated photonic devices for computing, communications and sensing. Wide band gap semiconductor nanostructures with near-cylindrical geometry and large dielectric constants exhibit two-dimensional ultraviolet and visible photonic confinement (i.e. waveguiding). Combined with optical gain, the waveguiding behavior facilitates highly directional lasing at room temperature in controlled-growth nanowires with favorable resonant feedback. We have further explored the properties and functions of individual ultralong crystalline oxide nanoribbons that act as subwavelength optical waveguides, nonlinear frequency converter and assess their applicability as nanoscale photonic elements and scanning probes. Semiconductor nanowires offer a versatile photonic platform due to the ability to specify material size, shape, and composition. The integration of multiple unique materials with distinct optical properties promises to enable advances for several applications ranging from solid state lighting, biochemical sensing to imaging and spectroscopy.

Complete composition tunability of InGaN nanowires using a combinatorial approach

Abstract: The III nitrides have been intensely studied in recent years because of their huge potential for everything from high-efficiency solid-state lighting and photovoltaics to high-power and temperature electronics. In particular, the InGaN ternary alloy is of interest for solid-state lighting and photovoltaics because of the ability to tune the direct bandgap of this material from the near-ultraviolet to the near-infrared region. In an effort to synthesize InGaN nitride, researchers have tried many growth techniques. Nonetheless, there remains considerable difficulty in making high-quality InGaN films and/or freestanding nanowires with tunability across the entire range of compositions. Here we report for the first time the growth of single-crystalline In(x)Ga(1-x)N nanowires across the entire compositional range from x=0 to 1; the nanowires were synthesized by low-temperature halide chemical vapour deposition and were shown to have tunable emission from the near-ultraviolet to the near-infrared region. We propose that the exceptional composition tunability is due to the low process temperature and the ability of the nanowire morphology to accommodate strain-relaxed growth, which suppresses the tendency toward phase separation that plagues the thin-film community.

Tunable nanowire nonlinear optical probe

Abstract: One crucial challenge for subwavelength optics has been the development of a tunable source of coherent laser radiation for use in the physical, information and biological sciences that is stable at room temperature and physiological conditions. Current advanced near-field imaging techniques using fibre-optic scattering probes have already achieved spatial resolution down to the 20-nm range. Recently reported far-field approaches for optical microscopy, including stimulated emission depletion, structured illumination, and photoactivated localization microscopy, have enabled impressive, theoretically unlimited spatial resolution of fluorescent biomolecular complexes. Previous work with laser tweezers has suggested that optical traps could be used to create novel spatial probes and sensors. Inorganic nanowires have diameters substantially below the wavelength of visible light and have electronic and optical properties that make them ideal for subwavelength laser and imaging technology. Here we report the development of an electrode-free, continuously tunable coherent visible light source compatible with physiological environments, from individual potassium niobate (KNbO3) nanowires. These wires exhibit efficient second harmonic generation, and act as frequency converters, allowing the local synthesis of a wide range of colours via sum and difference frequency generation. We use this tunable nanometric light source to implement a novel form of subwavelength microscopy, in which an infrared laser is used to optically trap and scan a nanowire over a sample, suggesting a wide range of potential applications in physics, chemistry, materials science and biology.

Interfacing silicon nanowires with mammalian cells

Abstract: We present the first demonstration of a direct interface of silicon nanowires with mammalian cells such as mouse embryonic stem (mES) cells and human embryonic kidney (HEK 293T) cells without any e...

Tunable plasmonic lattices of silver nanocrystals.

Abstract: Silver nanocrystals are ideal building blocks for plasmonic materials that exhibit a wide range of unique and potentially useful optical phenomena. Individual nanocrystals display distinct optical scattering spectra and can be assembled into hierarchical structures that couple strongly to external electromagnetic fields. This coupling, which is mediated by surface plasmons, depends on the shape and arrangement of the nanocrystals. Here we demonstrate the bottom-up assembly of polyhedral silver nanocrystals into macroscopic two-dimensional superlattices using the Langmuir–Blodgett technique. Our ability to control interparticle spacing, density and packing symmetry allows for tunability of the optical response over the entire visible range. This assembly strategy offers a new, practical approach to making novel plasmonic materials for application in spectroscopic sensors, subwavelength optics and integrated devices that utilize field-enhancement effects.

ZnO-TiO2 Core-Shell Nanorod/P3HT Solar Cells

Abstract: We evaluate an ordered organic−inorganic solar cell architecture based on ZnO−TiO2 core−shell nanorod arrays encased in the hole-conducting polymer P3HT. Thin shells of TiO2 grown on the ZnO nanorods by atomic layer deposition significantly increase the voltage and fill factor relative to devices without shells. We find that the core−shell cells must be exposed to air to reproducibly attain efficiencies higher than 0.05%. Cells stored in air for 1 month are 0.29% efficient.

Very High Frequency Silicon Nanowire Electromechanical Resonators

Abstract: We demonstrate very high frequency (VHF) nanomechanical resonators based upon single-crystal silicon nanowires (SiNWs), which are prepared by the bottom-up chemical synthesis. Metallized SiNW resonators operating near 200 MHz are realized with quality factor Q ≈ 2000−2500. Pristine SiNWs, with fundamental resonances as high as 215 MHz, are measured using a VHF readout technique that is optimized for these high resistance devices. The pristine resonators provide the highest Q's, as high as Q ≈ 13 100 for an 80 MHz device. SiNWs excel at mass sensing; characterization of their mass responsivity and frequency stability demonstrates sensitivities approaching 10 zeptograms. These SiNW resonators offer significant potential for applications in resonant sensing, quantum electromechanical systems, and high frequency signal processing.

Shape, size, and assembly control of PbTe nanocrystals.

Abstract: In this communication, we demonstrate an approach for shape control of PbTe nanocrystals. We succeeded in synthesizing three different shapes of PbTe nanoparticles, including cubes, cuboctahedra, and octahedra. These morphologies were prepared by changing the molar ratio between the Pb and Te precursors and also by changing the surfactant. Langmuir−Blodgett films were prepared using these PbTe nanocrystals.

One‐Step Patterning of Aligned Nanowire Arrays by Programmed Dip Coating

Abstract: A fundamental step in the construction of nanowire devices is transfer of the nanowires from their stock to the substrate on top of which the device will be built. Therefore, alignment and controlled positioning of the nanowires are highly desirable, especially for the large-scale (e.g., on a 4-inch (10-cm) wafer) fabrication of parallel device arrays. Nanowires are normally synthesized and processed in solution. Therefore, any subsequent patterning technique would inevitably involve a dewetting step. Herein we show that nanowires can be aligned and selectively deposited at the edge of a drying droplet as a result of evaporation-induced capillary flow. This contact-line deposition can be regulated with a simple dip-coating setup to create massive nanowire arrays with predefined spacing and tunable wire density. It also enables the selective placement of the nanowire arrays directly onto prefabricated electrode arrays, thus providing a facile and inexpensive method for the large-scale fabrication of nanowire-based devices. Although it is possible to integrate nanowires directly into some specific device platforms during synthesis, it is more common to make nanowire devices starting from a nanowire suspension with a subsequent patterning process. A few methods have been developed to make aligned nanowire arrays on a substrate, for example, Langmuir–Blodgett, microfluidic, 7] electric-field-assisted assembly, and optical trapping. For all these patterning processes, nanowires are either made or processed within a solvent. As a result, any such technique would eventually encounter solvent evaporation before the final dried nanowire pattern is obtained. Therefore, it should be of great interest and technological importance to explore the full extent of the dewetting process for assembling nanostructures. 12] Herein we report our observation of contact-line deposition and alignment of nanowires in an evaporating droplet. These findings are then employed and tailored for large-scale patterning of nanowires by dip coating. Ring-shaped stains are often observed when a droplet of colloidal solution (e.g., coffee) is dried. An outward capillary flow of the solvent is necessary to compensate the loss of solvent at the perimeter, which also carries the dispersed materials to the solvent–substrate contact line and leads to highly selective deposition along the perimeter of the droplet. We have discovered that in a drying droplet containing nanowires, this capillary flow also sorts the nanowires along the radial direction (Figure 1a), especially when the solvent is volatile (e.g., methylene chloride or chloroform). Figure 1b shows a typical ring-shaped stain obtained from drying a droplet of nanowire dispersion in methylene

Multifunctional Nanowire Evanescent Wave Optical Sensors

Abstract: Compact, reusable chemical sensors are highly desirable for on-site detection in the field, including the identification of water contaminants, hazardous biochemical compounds, or blood serum content. Ideally, such a sensing platform should be portable, and employ several complementary sensing modalities that allow quantitative chemical identification of extremely small sample volumes. Optical spectroscopy is a powerful analytical tool for characterizing biological and chemical systems, but making a standard optical laboratory transportable is a major challenge. However, with recent advances in the synthesis and assembly of nanomaterials, [1] it is timely to begin integrating these materials into functional device architectures for sensing and monitoring. Of the well-studied inorganic nanostructures, chemically synthesized 1D semiconductor systems have gained significant interest from the photonics community as passive and active components for miniaturized spectroscopic devices. This is due, in part, to their ability to guide a significant portion of the confined electromagnetic energy outside the measurement cavity (i.e., in the evanescent field) while operating below the diffraction limit of light. [2] Because the evanescent field efficiently travels through fluidic and air dielectrics, [3] it is possible to integrate the waveguides into microfluidic devices and sense molecules located near the surface of the cavity. We demonstrate this by performing absorbance, fluorescence, and surface-enhanced Raman spectroscopy (SERS) measurements on sub-picoliter volumes of solution. The chemical specificity of SERS is obtained by decorating the waveguide with silver nanocubes, thus enhancing the field around the nanoribbon. Our nanowire optical sensing platform complements nanowire field-effect sensors [4] with the ability to monitor optical attenuation across the wire element. However, the use of photons instead of electrons allows optical spectroscopy to be carried out on the analyte. Fiber-based detection is a unique alternative to free-space sensing, because it localizes chemical recognition at the surface of a waveguide. Among the most popular sensing schemes that rely on the evanescent field of a fiber are absorption [5–7] and fluorescence. [8–11] Typically, these set-ups involve multimode silica fibers with diameters much larger than the free-space wavelength of light. The evanescent field in these experiments has been used to measure refractive indices of liquids, [12] monitor volatile compounds in water, [13] and detect shifts in localized surface-plasmon resonances of coupled metal colloids. [14] Recently, the use of subwavelength silica fibers in a Mach–Zehnder-type interferometer to detect index changes caused by molecules interacting with the surface of the fibers has been proposed. [15] Although these various sensing configurations are promising for high sensitivity, fast cycling times, and reversibility, they do not provide versatility in their spectroscopic detection, nor enable a chemical read-out of the analyte. To move beyond fiber sensors that operate solely as on/off detectors it is vital to develop materials that can sustain multiple analytical modes for chemical identification.

Synthesis and Thermoelectrical Characterization of Lead Chalcogenide Nanowires

Abstract: Thermoelectricity is the phenomenon of conversion between thermal and electrical energy. Compared with other technologies, thermoelectric (TE) devices offer distinct advantages: they have no moving parts, contain no chlorofluorocarbons, and have a long lifetime of reliable operation. However, current TE materials have found limited commercial application due to their low efficiency. TE efficiency is related to a material-dependent coefficient, Z, and is often expressed as the dimensionless figure-of-merit, ZT, given by ZT= rS 2 T/j, where Tis the absolute temperature, r is the electrical conductivity, S is the Seebeck coefficient, and j is the total thermal conductivity. It becomes difficult to improve ZT beyond a certain point since the material properties S, r, and j are inter-dependent. [1] Presently, simple bulk materials have reached an upper limit of ZTat approximately 1. Hicks and Dresselhaus proposed that conversion of bulk materials to low dimensional materials might significantly enhance TE performance through phonon scattering and electron confinement effects. [2] Dimensional reduction has since been shown to increase boundary scattering of phonons and reduce lattice thermal conductivity, [3] possibly without negatively affecting the electrical conductivity or Seebeck coefficient. The positive effects of low-dimensionality on ZT have already been demonstrated through several theoretical [2,4–6] and experimental [7] investigations, a few of which were based on lead chalcogenide systems. [8,9] Harman et al. achieved an especially high ZTof 2.0 at 300 K with PbSeTe/PbTe quantum dot superlattices. [10] Bulk

One-step Polyol Synthesis and Langmuir-Blodgett Monolayer Formation of Size-tunable Monodisperse Rhodium Nanocrystals with Catalytically Active (111) Surface Structures

Abstract: Size-tunable monodisperse Rh nanocrystals can offer unique properties for many heterogeneous catalytic reactions (such as hydrogenation, hydroformylation, and hydrocarbonylation) of both scientific and technological interest. In this article, we report the synthesis of monodisperse, well-shaped Rh nanocrystals in a range of 5−15 nm by a one-step polyol reduction at temperatures of 170−230 °C under Ar, using rhodium(III) acetylacetonate [Rh(acac)3] as the source of metal ions, 1,4-butanediol as the reducing solvent, and poly(vinylpyrrolidone) as the capping agent. Two-dimensional projects of the nanocrystals are polygons, dominated by hexagons, pentagons, and triangles with catalytically active (111) surfaces (>65% yield). Over 45% of the polygons are multiple (111) twinned particles (hexagons and pentagons), favored by thermodynamics. To achieve size uniformity, adjustment of the reduction kinetics of Rh(acac)3 in the nucleation and crystal growth stages has been shown to depend upon several synthetic par...

Growth and Electrical Characteristics of Platinum-Nanoparticle-Catalyzed Silicon Nanowires

Abstract: Silicon nanowires (Si NWs) will likely revolutionize a wide variety of applications ranging from field-effect transistors (FETs) and other nanoelectronics to chemical and biological sensing, and even solar cells. These nanowire devices must be integrated with more traditional electronic or optical components to make a complete usable system, which will probably require standard silicon clean-room processing. Nearly all Si NWs are made using a gold (or gold-based) catalyst and the well-known vapor–liquid–solid (VLS) growth mechanism first discovered by Wagner and Ellis. Because Au creates mid-gap trap states in silicon, it poisons device performance and typically is not allowed for use in electronicsfabrication labs and clean rooms. Therefore a new, electronics-friendly catalyst is critical not only for nanowire electronics, but also for integrated devices incorporating Si NWs in any capacity. Several groups have successfully grown Si NWs with alternative catalyst thin films such as Ti, Al, Pt, and PtSi but extensive electrical characterization that is very important for many device applications has not been conducted. In this report, Pt was chosen as a catalyst because it has a high melting point, can be made into nanoparticles with a tight size distribution and shows orders-of-magnitudelower leakage current when incorporated into silicon diodes compared to gold. We have developed a chemical-vapor-deposition (CVD) synthesis based on our previous experience with gold catalysts to grow high-quality single-crystalline size-controlled epitaxial Si NWs from various sized Pt nanoparticles. The nanowires were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to determine their size distribution, growth direction, and alignment, whereas their electrical properties were tested by making planar FETs. Unlike the Au–Si system, Pt does not form a simple eutectic with Si; rather, there are several stable platinum silicide compounds in the 800–1000 °C temperature range where Si-NW growth occurs. There is a eutectic formed between PtSi and Si at 979 °C, so at temperatures above this point and at high Si concentrations, it is thermodynamically favorable to precipitate pure Si. Si-NW growth below 979 °C can be explained by two possible mechanisms. First, because the Pt nanoparticles begin melting (at least surface melting) around 600 °C, which is about 1000 °C lower than the bulk melting point, the bulk phase diagram may not accurately represent the phase transitions occurring in the catalyst nanoparticle tip. In a very simplistic view, all the phase boundaries should shift down in temperature, with the Pt-rich phases being affected more strongly than the Si-rich phases. With a shift of over 1000 °C at the pure platinum side of the phase diagram, a 180 °C shift for the PtSi–Si eutectic down to 799 °C at 67 % Si seems likely. Several reports also show that Pt nanoparticles annealed in a hydrogen atmosphere at temperatures as low as 600 °C on silica substrates form PtxSiy [21,22] Additionally, Wagner and Ellis found that even Pt thin films as thick as 100 nm on Si formed a liquid surface layer at temperatures as low as 850 °C, further supporting a significant temperature decrease of the PtSi eutectic point from the bulk value. The second possible explanation is that the Pt nanoparticles do not completely melt and instead act as an active site for rapid SiCl4 decomposition and diffusion, leading to a vapor– solid–solid (VSS) rather than VLS growth mechanism. The VSS mechanism has been proposed to explain the growth of several other semiconducting nanowires, particularly III–V compounds, that were originally thought to grow according to the VLS mechanism. In a recent report, Pt thin films deposited on Si were annealed at 800 °C in a hydrogen atmosphere to form PtSi islands which in turn were used to catalyze Si-NW growth at temperatures between 500 and 700 °C through a proposed VSS mechanism. Considering the strong in situ TEM evidence from the literature mentioned above that the Pt nanoparticles begin melting well below their reaction temperatures, the island formation observed for Pt/Si films near 800 °C, and the evidence of strong eutectic-point depression seen for Pt thin films on Si, the Si NWs in this study most likely grow via the VLS mechanism. However, the VSS mechanism cannot be ruled out without in situ TEM evidence. Pt nanoparticle catalysts with average diameters of (9.3± 1.2) nm were used to synthesize Si NWs with average diameters of (11.3± 1.6) nm (Fig. 1). The standard deviations of the starting colloid and the resulting wire diameters were C O M M U N IC A TI O N

Suspended Mechanical Structures Based on Elastic Silicon Nanowire Arrays

Abstract: We demonstrate a bottom-up/top-down combined method for the fabrication of horizontally suspended, well-oriented and size-controlled Si nanowire arrays. Mechanical beamlike structures composed of multiple ordered arrays consecutively linked by transversal microspacers are obtained by this method. Such structures are used to investigate the mechanical elasticity of the nanowire arrays by atomic force microscopy. Our results point out important differences in the morphology and mechanical behavior of the fabricated nanowire-based structures with respect to equivalent bulk material structures.

Microfabricated monolithic multinozzle emitters for nanoelectrospray mass spectrometry.

Abstract: Mass spectrometry is the enabling technology for proteomics. To fully realize the enormous potential of lab-on-a-chip in proteomics, a major advance in interfacing microfluidics with mass spectrometry is needed. Here, we report the first demonstration of monolithic integration of multinozzle electrospray emitters with a microfluidic channel via a novel silicon microfabrication process. These microfabricated monolithic multinozzle emitters (M3 emitters) can be readily mass-produced from silicon wafers. Each emitter consists of a parallel silica nozzle array protruding out from a hollow silicon sliver with a conduit size of 100 x 10 mum. The dimension and number of freestanding nozzles can be systematically and precisely controlled during the fabrication process. Once integrated with a mass spectrometer, M3 emitters achieved sensitivity and stability in peptide and protein detection comparable to those of commercial silica-based capillary nanoelectrospray tips. These M3 emitters may play a role as a critical component in a fully integrated silicon/silica-based micro total analysis system for proteomics.

Probing the local coordination environment for transition metal dopants in zinc oxide nanowires.

Abstract: It is hypothesized that a highly ordered, relatively defect-free dilute magnetic semiconductor system should act as a weak ferromagnet. Transition-metal-doped ZnO nanowires, being single crystalline, single domain, and single phase, are used here as a model system for probing the local dopant coordination environments using X-ray absorption spectroscopy and diffraction. Our X-ray spectroscopic data clearly show that the dopant resides in a uniform environment, and that the doping does not induce a large degree of disorder in the nanowires. This homogeneous nature of the doping inside the oxide matrix correlates well with observed weakly ferromagnetic behavior of the nanowires.

High-brightness gallium nitride nanowire UV-blue light emitting diodes

Abstract: We report on high-brightness GaN nanowire UV–blue light emitting diodes (LEDs), which are fabricated by coupling of n-GaN nanowires and p-GaN substrates using two assembly methods, random dispersion (RD) and dielectrophoresis assisted assembly deposition (DAAD). These GaN nanowire LEDs have bright UV–blue emission (411–437 nm) from the n-GaN nanowire/p-GaN substrate junction and the light emission is strong enough to be observed with the naked eye even for a single GaN nanowire LED. The results reported here should have significant implications for the fabrication of highly efficient, low-cost UV–blue LEDs with low power consumption, as compared to conventional thin-film based GaN LEDs.

Trapping and Transport of Silicon Nanowires Using Lateral-Field Optoelectronic Tweezers

Abstract: We present a new optoelectronic tweezers device that produces electric fields parallel to the plane of the device. This device is capable of trapping and transporting p-type silicon nanowires at velocities of 20 mum/s.

Inorganic nanotubes and devices fabricated therefrom

Abstract: Nanofluidic devices are taught incorporating inorganic nanotubes fluidly coupled to channels or nanopores for supplying a fluid containing chemical or biochemical species. In one aspect, two channels are fluidly interconnected with a nanotube. Electrodes on opposing sides of the nanotube establish electrical contact with the fluid therein. A bias current is passed between the electrodes through the fluid, and current changes are detected to ascertain the passage of select molecules, such as DNA, through the nanotube. In another inventive aspect, a gate electrode is located proximal the nanotube between the two electrodes thus forming a nanofluidic transistor. The voltage applied to the gate controls the passage of ionic species through the nanotube selected as either or both ionic polarities. In either of these aspects the nanotube can be modified, or functionalized, to control the selectivity of detection or passage.

Chemical sensing with nanowires using electrical and optical detection

Abstract: Chemical nanosensors based on inorganic nanowires hold promise for the extremely sensitive, direct detection of pollutants, toxins and biomolecules on platforms small enough to be integrated on optoelectronic chips or even deployed in living organisms. This paper discusses two approaches to nanowire-based chemical and biological detection. First we review the development of electrically-driven nanowire gas sensors that function by an adsorbate-mediated conductivity mechanism. We then describe an alternative sensing strategy that exploits the excellent waveguiding ability of high-refractive-index nanowires to create subwavelength evanescent wave sensors that operate in solution with an optical, rather than electrical, readout.

Semiconductor nanowire manipulation using optoelectronic tweezers

Abstract: We demonstrate, for the first time, the trapping and manipulation of individual Si nanowires by light-induced dielectrophoresis, or optoelectronic tweezers (OET). Trapping of single Si nanowires, with a diameter of 100 nm and length of 15 mum, is reported using OET with an optical power density of 100 W/cm2 . We show that OET can separate two adjacent Si nanowires and transport a single nanowire at a speed of 135 mum/s. Array patterns of Si nanowires have also been demonstrated.

Method of non-catalytic formation and growth of nanowires

Abstract: A method for the non-catalytic growth of nanowires is provided. The method includes a reaction chamber with the chamber having an inlet end, an exit end and capable of being heated to an elevated temperature. A carrier gas with a flow rate is allowed to enter the reaction chamber through the inlet end and exit the chamber through the exit end. Upon passing through the chamber the carrier gas comes into contact with a precursor which is heated within the reaction chamber. A collection substrate placed downstream from the precursor allows for the formation and growth of nanowires thereon without the use of a catalyst. A second embodiment of the present invention is comprised of a reaction chamber, a carrier gas, a precursor target, a laser beam and a collection substrate. The carrier gas with a flow rate and a gas pressure is allowed to enter the reaction chamber through an inlet end and exit the reaction chamber through the exit end. The laser beam is focused on the precursor target which affords for the evaporation of the precursor material and subsequent formation and growth of nanowires on the collection substrate.

In situ Raman Measurement of an Individual Silicon Nanowire Trapped Using Optoelectronic Tweezers (OET)

Abstract: We demonstrate in-situ Raman measurement of individual silicon nanowires (100 nm diameter, 10-20 μm in length) which are trapped using optoelectronic tweezers (OET).

Nanowires for Subwavelength Waveguides

Abstract: One dimensional semiconducting and metal nanostructures were demonstrated as optical or plasmonic waveguides for subwavelength photonic integration. Model structures built from these subwavelength waveguides are used to illustrate electromagnetic coupling between semiconducting and metallic cavities.

Propagation of Guided Modes in Curved Nanoribbon Waveguides

Abstract: Author(s): Yang, P. | Abstract: The authors develop a plane-wave-based transfer matrix method in curvilinear coordinates to study the guided modes in curved nanoribbon waveguides. The problem of a curved structure is transformed into an equivalent one of a straight structure with spatially dependent tensors of dielectric constant and magnetic permeability. The authors investigate the coupling between the eigenmodes of the straight part and those of the curved part when the waveguide is bent. The authors show that curved sections can result in strong oscillations in the transmission spectrum similar to the recent experimental results of Lawet al.