Showing papers by "Peidong Yang published in 2001"

Room-temperature ultraviolet nanowire nanolasers

Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 03 nanometer The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis

Catalytic Growth of Zinc Oxide Nanowires by Vapor Transport

Abstract: nanoparticles in dimethylsulfoxide onto the PLL film for about 20 min, after which it was rinsed in dimethylsulfoxide and then dichloromethane. From the molecular weight, the average length of the PLL is about 30 nm. Therefore, each polymer can accommodate about seven or eight nanoparticles. [20] L. Clarke, M. N. Wybourne, M. Yan, S. X. Cai, J. F. W. Keana, Appl. Phys. Lett. 1997, 71, 617. [21] A. A. Middleton, N. S. Wingreen, Phys. Rev. Lett. 1993, 71, 3198. [22] G. Y. Hu, R. F. O'Connell, Phys. Rev. B 1994, 49, 16 773. [23] A. J. Rimberg, T. R. Ho, J. Clarke, Phys. Rev. Lett. 1995, 74, 4714. [24] L. Clarke, M. N. Wybourne, M. Yan, S. X. Cai, L. O. Brown, J. Hutchison, J. F. W. Keana, J. Vac. Sci. Technol. B 1997, 15, 2925. [25] The capacitance matrix was calculated for different chain lengths using the software package FastCap MIT (1992). We used the nanoparticle dimensions given in the text and a ligand shell dielectric constant of 3. For nanoclusters away from the end of the chains we obtain Cdd » 0.04 aF and Cg » 0.17 aF. As expected, the value of Cg is slightly larger than the value calculated for an isolated metal sphere of radius a coated with a dielectric shell, Cg» (4pee0a)/(1 + (a/d)(e±1)) = 0.14 aF, where d is the total radius of the core plus ligand shell. [26] Simulations were carried out using both MOSES (Monte-Carlo SingleElectronics Simulator, R. H. Chen) and SIMON (Simulation of Nano Structures, C. Wasshuber). [27] S. Chen, R. S. Ingram, M. J. Hostetler, J. J. Pietron, R. W. Murray, T. G. Schaaff, J. T. Khoury, M. M. Alvarez, R. L. Whetton, Science 1998, 280, 2098. [28] L. Y. Gorelik, A. Isacsson, M. V. Voinova, B. Kasemo, R. I. Shekhter, M. Jonson, Phys. Rev. Lett. 1998, 80, 4526. [29] O. D. Häberlen, S. C. Chung, M. Stener, N. Rösch, J. Chem. Phys. 1997, 106, 5189. [30] Y. Awakuni, J. H. Calderwood, J. Phys. D: Appl. Phys. 1972, 5, 1038. [31] G. Markovich, C. P. Collier, J. R. Heath, Phys. Rev. Lett. 1998, 80, 3807. [32] C. P. Collier, R. J. Saykally, J. J. Shiang, S. E. Hendrichs, J. R. Heath, Science 1997, 277, 1978. [33] N. Mott, Metal Insulator Transitions, Taylor and Francis, London 1990.

Direct Observation of Vapor-Liquid-Solid Nanowire Growth

Abstract: Nanotubes and semiconductor nanowires are of fundamental importance to the study of sizeand dimensionality-dependent chemical and physical phenomena. 1,2 How to rationally synthesize these 1-dimensional nanostructures has been a major challenge, although several strategies have been pursued recently. 3-16 For example, carbon nanotubes have been prepared via condensation of hot carbon plasmas in the presence of certain metals, although the real growth mechanism has been elusive. 3-5 Recently, semiconductor nanowires with different compositions have been successfully synthesized using either vapor 6-12 or solution-based methodologies. 13-16 One key feature of these syntheses is the promotion of anisotropic crystal growth using metal nanoparticles as catalysts. The growth mechanism has been extrapolated from the vapor -liquid-solid (VLS) mechanism which was proposed in the 1960s -1970s for large whisker growth, 17-19 although an oxide-assisted growth mechanism has also been proposed. 2,20

Room-Temperature Ultraviolet Nanowire Nanolasers.

Abstract: Room-temperature ultraviolet lasing in semiconductor nanowire arrays has been demonstrated. The self-organized, oriented zinc oxide nanowires grown on sapphire substrates were synthesized with a simple vapor transport and condensation process. These wide band-gap semiconductor nanowires form natural laser cavities with diameters varying from 20 to 150 nanometers and lengths up to 10 micrometers. Under optical excitation, surface-emitting lasing action was observed at 385 nanometers, with an emission linewidth less than 0.3 nanometer. The chemical flexibility and the one-dimensionality of the nanowires make them ideal miniaturized laser light sources. These short-wavelength nanolasers could have myriad applications, including optical computing, information storage, and microanalysis.

Langmuir-Blodgett nanorod assembly.

Abstract: Techniques for directing the assembly of metal or semiconductor quantum dots into novel superstructures have been extensively pursued over the past decades.1-3 Recent interest has been drawn toward 1-dimensional nanoscale building blocks such as nanotubes, nanowires, and nanorods.4-14 If these one-dimensional nanoscale building blocks can be ordered and rationally assembled into appropriate 2-dimensional architectures, they will offer fundamental scientific opportunities for investigating the influence of size and dimensionality with respect to their collective optical, magnetic, and electronic properties, as well as many other technologically important applications. Currently, efforts have been focused on the development of new synthetic methodologies for making nanorods with uniform sizes and aspect ratios.4-14 Few studies addressed the organization of these anisotropic building blocks except the 3-dimensional spontaneous superlattice formation of BaCrO4, FeOOH,13 CdSe,4 Ag,6 and Au12 nanorods. Herein, we report 2-dimensional nanorod monolayer assembly using the Langmuir-Blodgett technique. Pressure-induced isotropic-nematic-smectic phase transitions as well as transformation from monolayer to multilayer nanorod assembly were observed. Uniform BaCrO4 nanorods were prepared by using published procedures.7 Briefly, Barium bis(2-ethylhexyl)sulfosuccinate (Ba(AOT)2) reverse micelles were added to sodium chromate (Na2CrO4)-containing NaAOT microemulsion droplets, to give final molar ratios of [Ba]:[CrO4] ) 1 and water content [H2O]: [NaAOT] ) 10. The as-made yellow precipitate consists of ribbonlike and rectangular superstructures made of uniform nanorods. The nanorods were uniform in length (∼20 nm) and diameter (∼5 nm). Energy-dispersive X-ray analysis and electron diffraction patterns indicated that the nanorods were single crystalline BaCrO4 with an orthorhombic unit cell (a ) 0.91 nm, b ) 0.55 nm, c ) 0.73 nm). These as-made nanorods generally are stabilized with AOT surfactant molecules. They were diluted and redispersed into isooctane to make a stable nanorod colloidal suspension, which is used as stock solution for subsequent Langmuir-Blodgett studies. The nanorod colloidal suspension was spread dropwise (typically 1 mL of 2.5 mg/mL concentration) on the water surface of a Langmuir-Blodgett trough (Nima Technology, M611). The nanorod surface layer was then compressed slowly while the surface pressure was monitored with a Wilhelmy plate. Due to the presence of noncovalently bonded surfactant molecules, the compression starts with a nonzero surface pressure. In addition, since AOT is partially soluble in subphase water, the surface pressure decays with the time. In general, it was observed that the surface pressure increases during the compression. At different stages of compression, the nanorod assemblies at the water-air interface were transferred carefully onto transmission electron microscope (TEM) grids covered with continuous carbon thin film using the Langmuir-Schäffer horizontal liftoff procedure. Nanorod assemblies were examined systematically by using TEM. Initially, at low surface pressure, individual nanorods (generally 3 to 5 rods) form raft-like aggregates. These aggregates disperse on the subphase surface in a mostly isotropic state (Figure 1a). The surface pressure remains unchanged until the nanorods start forming a monolayer and when the monolayer was compressed to a surface pressure of ∼30 mN/m.15 During this process, monolayer of nanorods in a nematic arrangement are first obtained where the directors of these nanorods (or nanorod rafts) are qualitatively aligned presumably dictated by the barrier of the trough. Figure 1b shows such a partial nematic region with an orientational order parameter S of 0.83. The regularity of sideby-side inter-rod distance is reflected in the Fourier transform of the region (Figure 1b, inset). This nematic ordering, however, only occurs within a quite narrow pressure range. With further compression (surface pressure about ∼35 mN/m), nanorod (1) Collier, C. P.; Vossmeyer, T.; Heath, J. R. Annu. ReV. Phys. Chem. 1998, 49, 371-404. (2) Sun, S.; Murray, C. B.; Weller, D.; Folks, L.; Moser, A. Science 2000, 287, 1989-1992. (3) Chung, S. W.; Markovich, G.; Heath, J. R. J. Phys. Chem. B 1998, 102, 6685-6687. (4) Peng, X.; Manna, L.; Yang, W.; Wickham, J.; Scher, E.; Kadavanich, A.; Alivisatos, A. P. Nature 2000, 404, 59-61. (5) Chang, S.; Shih, C.; Chen, C.; Lai, W.; Wang, C. R. C. Langmuir 1999, 15, 701-709. (6) Korgel, B. A.; Fitzmaurice, D. AdV. Mater. 1998, 10, 661-665. (7) Li, M.; Schnablegger, H.; Mann, S. Nature 1999, 402, 393-395. (8) Park, S. J.; Kim, S.; Lee, S.; Khim, Z. G.; Char, K.; Hyeon, T. J. Am. Chem. Soc. 2000, 35, 8581-8582. (9) Tanori, J.; Pileni, M. P. Langmuir 1997, 13, 639-646. (10) Martin, B. R.; Dermody, D. J.; Reiss, B. D.; Fang, M.; Lyon, A.; Natan, M. J.; Mallouk, T. E. AdV. Mater. 1999, 11, 1021-1025. (11) Chen, C.; Chao, C.; Lang, Z. Chem. Mater. 2000, 12, 1516-1519. (12) Nikoobakht, B.; Wang, Z. L.; El-Sayed, M. A. J. Phys. Chem. B 2000, 104, 8635-8640. (13) Maeda, H.; Maeda, Y. Langmuir 1996, 12, 1446-1452. (14) Gabriel, J. C. P.; Davidson, P. AdV. Mater. 2000, 12, 9-20. (15) The free surfactants in the system can form Langmuir films themselves and may interfere with the formation of the nanorod monolayers. Consequently, the actual surface pressure during the compression may differ from the observed value. Figure 1. Transmission electron microscopy images of the nanorod assemblies at the water/air interface at different stages of compression: (a) isotropic distribution at low pressure; (b) monolayer with partial nematic arrangement; (c) monolayer with smectic arrangement; and (d) nanorod multilayer with nematic configuration. Insets in panels b and c are the Fourier transform of the corresponding image. 4360 J. Am. Chem. Soc. 2001, 123, 4360-4361

Bismuth nanotubes: a rational low-temperature synthetic route.

Abstract: The discovery of carbon nanotubes has initiated an exciting, intellectually challenging, and rapidly expanding research field for one-dimensional (1D) nanostructures. 1 Over the past several years, considerable efforts have been placed on the synthesis of nanotubes or nanowires. A particularly significant breakthrough in MX2 (M: Mo or W, X: S or Se) nanotube synthesis was made by Tenne and co-workers. 2 Various approaches to other nanotubes, such as BN, 3 BxCyNz, NiCl2, vanadium oxide, 6 and InS7 have also been reported, which implies that substances possessing layered structures might be able to form nanotubes under favorable conditions. Here we report the synthesis of bismuth metal nanotubes with diameters ∼5 nm and lengths ranging between 0.5-5 μm. A low-temperature hydrothermal reduction method with bismuth nitrate [Bi(NO3)3] and aqueous hydrazine solution (N2H4‚H2O) at 120°C has been successfully used to synthesize large quantities of nested bismuth nanotubes. The resulting Bi nanotubes were characterized by X-ray powder diffraction, transmission electron microscopy and composition analysis. Metallic bismuth ( R-Bi) (Figure 1a) has a pseudolayered structure very similar to that of rhombohedral graphite and black phosphorus. 8 In each layer, one Bi atom is connected with three other Bi atoms according to the 8N rule and thus forms a trigonal pyramid. These pyramids further form a folded bismuth layer by vertex-sharing. The distances between one Bi atom and its three neighbors in the same layer and the neighboring layer are 3.072 and 3.529 Å, respectively, and the Bi -Bi-Bi bonding angle is 95.5°. The analogy between the layered structures of R-Bi (Figure 1a) and graphite/phosphorus suggests that the Bi nanotubes (Figure 1b) may also exist. In fact, theoretical simulation indeed indicates that phosphorus nanotubes are stable. 9 More recently, both theoretical and experimental studies have established the existence of multishell gold nanotubes. 10 Here, we report the synthesis of the Bi-nanotubes (NT) with uniform diameters of 5 nm and lengths ranging between 0.5 -5 μm. Bismuth’s small effective mass ( ∼0.001m0) and large mean free path ( ∼0.4 mm at 4 K) make Bi nanotube an interesting system for studying quantum confinement effects. 11 In addition, nanoscaled bismuth materials have recently been suggested to have enhanced thermoelectric properties at room temperature. 12

Single Nanowire Lasers

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.

Single-Crystalline Nanowires of Ag2Se Can Be Synthesized by Templating against Nanowires of Trigonal Se

Abstract: Template-directed synthesis represents a straightforward approach to generating one-dimensional (1D) nanostructures. In this approach, the template serves as a scaffold against which other materials are assembled with a morphology similar (or complementary) to that of the template. A variety of 1D templates have been successfully demonstrated for use with this process, and examples include channels in porous materials, 1 hexagonal assemblies of surfactants or block copolymers, 2 and 1D nanostructures synthesized using other chemical methods. 3,4 These templating processes, although very versatile, often led to the formation of polycrystalline 1D nanostructures that are limited in use for device fabrication or property measurements. Highly crystalline nanowires were only produced at temperatures around 800-1200°C when carbon nanotubes were allowed to react with proper chemicals under carefully controlled conditions. 3 A template-directed process that could generate single-crystalline nanowires in the solution phase and at room temperature is yet to be demonstrated. Here we describe a template-directed reaction, in which single-crystalline nanowires of trigonal Se ( t-Se) were quantitatively converted into single-crystalline nanowires of Ag2Se by reacting with aqueous AgNO 3 solutions at room temperature. The single-crystalline 1D morphology of the wire-like templates was retained in the final products with high fidelity. Silver selenide exhibits many interesting and useful properties. 5

Melting and Welding Semiconductor Nanowires in Nanotubes

Abstract: and deformations are obtained after removal of the silica matrix using aqueous HF. Our study indicates that mesoporous silicas such as C16MCM-41, C22MCM-41, and SBA-15 can act as good templates for the synthesis of Pd nanowires. Moreover, a significantly depressed melting point of the Pd nanowires is observed around 300 C. To the best of our knowledge, this is the first report on the synthesis and thermal behavior of Pd nanowires of less than 10 nm diameter. Along with our matrix-assisted process, in particular, our low-temperature CVI approach is attractive because it can be carried out under conditions mild enough to avoid any disruption of both the desired material and the template structure. The combined matrix-assisted and CVI process can be extended not only to other sizes of nanowires but also to multidimensional structures using appropriate host architectures.

Patterning Porous Oxides within Microchannel Networks

Abstract: A continuing challenge for materials chemists and engineers is the ability to create multifunctional composite structures with well-defined superimposed structural order from nanometer to micrometer length scales. Materials with three-dimensional structures ordered over multiple length scales can be prepared by carrying out colloidal crystallization and inorganic/organic cooperative self-assembly within microchannel networks. The resulting materials show hierarchical ordering over several discrete and tunable length scales ranging from several nanometers to micrometers. These patterned porous materials hold promise for use as advanced catalysts, sensors, low-k dielectrics, optoelectronic and integrated photonic crystal devices.

Metal Nanowire Formation Using Mo3Se3- as Reducing and Sacrificing Templates

Abstract: Recent research in the field of nanometer-scale electronics has focused on two fundamental issues: the operating principles of small-scale devices1 and schemes that lead to their realization and eventual integration into useful circuits.2 The availability of a nanoscale toolbox is the key for this field of research. Among the many potential building blocks within this nanoscale toolbox, nanowires are considered one of the key components because they can be used as interconnects and other functional devices in nanoelectronics.3 Unfortunately, although several processes have been developed for the syntheses of semiconductor nanowires,4 few methods have been developed for preparing free-standing, uniform metal nanowires. Among them, template synthesis (in porous matrixes such as porous Al2O3 films5 and mesoporous silica6) and step-edge decoration7 are considered as effective approaches. The step-edge decoration method was recently employed to produce Mo nanowires of 100 nm thickness.7 Metal nanowires have also been prepared by using DNA8 and carbon nanotubes as templates.9 Herein we report a simple chemical process for synthesizing long, free-standing metal nanowires. LiMo3Se3 nanowires are used as both reducing agents and sacrificial templates in this study to yield continuous metal nanowires. The metal nanowires generally have diameters of 10100 nm and lengths of several micrometers. These metal nanowires display small ohmic resistances at room temperature, indicating that these wires could prove useful as interconnects in nanoelectronic circuits. Previously, DNA has been used as a biotemplate for making metallic nanowires,8 although the continuity of the resulting metal nanowires has been problematic. Since DNA itself does not possess any reducing/oxidizing capability, the synthesis generally is a two-step process, which involves metal activation followed by chemical reduction. Nevertheless, the construction of electronic circuits based only on native DNA remains problematic, mainly due to the high resistance of DNA that limits its potential applications in this regard. Recently, Braun and co-workers presented a new approach by fixing DNA between two contacts and utilizing it as a template for the construction of a silver nanowire.8 This technique uses the molecular recognition properties of the molecule for the defined buildup of a nanostructure and installs its electrical functionality by the directed construction of a metallic wire on the biotemplate. However, the reported 100 nm thick silver wires displayed a nonconducting gap for small bias voltages. In this study, we choose [Mo3Se3]∞ molecular chains as our experimental system for two important reasons. First, these molecular chains are obtained by dissolution of crystals of quasi1D materials LiMo3Se3 in polar solvent.10 Each chain is made of staggered stacks of triangular Mo3Se3 with a diameter of 0.5 nm. The molecular chain itself is a reducing agent and can be readily oxidized. Second, these individual molecular wires form uniform nanowire bundles with diameters of 2-100 nm in certain polar solvents such as methanol and DMSO. Hence, these nanowires possess dual functionalities, being reductive one-dimensional templates. In fact, the redox chemistry of LiMo3Se3 was previously studied by Tarascon, and it was demonstrated that insertion and extraction of Li/Mo6Se6 is reversible.11 To form uniform metal nanowires, a redox reaction is carried out using LiMo3Se3 nanowires as the reducing agents to reduce aqueous metal ions (e.g., AuCl4, Ag+, PdCl4, PtCl4). Metal ions are reduced and deposited directly on the nanowire templates, while the nanowire templates are oxidized into Mo3Se3 and eventually dissolve in water (Figure 1). Consequently, metal nanowires with diameters of 2-100 nm can be obtained through this cooperative chemical templating process. Metal nanowires of Au, Ag, Pt, and Pd can be readily synthesized. In a typical experiment, a LiMo3Se3 solution was prepared by dissolving 5 mg of LiMo3Se3 in 20 mL of DMSO. A 2 mL drop of metal ion solution (0.005 wt %) was added to this DMSO solution. Using the Au nanowire system as an example, evidence of the reaction is apparent immediately after the solution mixing. The overall solution color develops a pink tint, and a peak at 526 nm appears in the UV-vis absorption spectra, indicating that Au nanocluster nucleation and growth has occurred. Figure 2 shows transmission electron microscopy images taken before (a) and after (b-d) the templating reaction for the Au nanowire system. Before the reaction, the LiMo3Se3 molecular chains self-assemble into nanowire bundles of 10-100 nm in diameter. After the redox reaction, Au nanowires of similar diameters and morphology are obtained. These Au nanowires are continuous and polycrystalline. Figure 2d shows a high-resolution TEM image of an individual Au nanowire with diameter of 15 nm. It can be seen that the Au nanocrystalline domains fuse together at the interface and form a continuous and robust (1) Dekker: C. Phys. Today 1999, 52, 22. (2) (a) Hu, T.; Odom, W.; Lieber, C. M. Acc. Chem. Res. 1999, 32, 435. (b) Collier, C. P.; Wong, E. W.; Behloradsky, M.; Raymo, F. M.; Stoddart, J. F.; Kuekes, P. J.; Williams, R. S.; Heath, J. R. Science 1999, 285, 391. (c) Rueches, T.; Kim, K.; Joselevich, E.; Tseng, G. Y.; Cheung, C.; Lieber, C. M. Science 2000, 289, 94. (3) Huang, M. H.; Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. Science 2001, 292, 1897. (4) Wu, Y.; Yang, P. J. Am. Chem. Soc. 2001, 123, 3165. (5) (a) Foss, C. A.; Tierney, M. J.; Martin, C. R. J. Phys. Chem. 1992, 96, 9001. (b) Preston, C. K.; Moskovits, M. J. Phys. Chem. 1993, 97, 8495. (c) Whitney, T. M.; Jiang, J. S.; Searson, P. C.; Chien, C. L. Science 1993, 261, 1316. (6) Huang, M.; Choudrey, A.; Yang, P. Chem. Commun. 2000, 12, 1603. (7) Zach, M. P.; Ng, K. H.; Penner, R. M. Science 2000, 290, 2120 and references therein. (8) Braun, E.; Eichen, Y.; Sivan, U.; Ben-Yoseph, G. Nature 1998, 391, 775. (9) Zhang, Y.; Dai, H. Appl. Phys. Lett. 2000, 77, 3015. (10) Tarascon, J. M.; DiSalvo, F. J.; Carrol, C. H. J.; Walsh, M.; Rupp, L. J. Solid State Chem. 1985, 58, 290. (11) Tarascon, J. M.; Hull, G. W.; DiSalvo, F. J. Mater. Res. Bull. 1984, 19, 915. Figure 1. Schematic illustration of metal nanowire templating reaction between LiMo3Se3 nanowires and metal ions. 10397 J. Am. Chem. Soc. 2001, 123, 10397-10398

Patterned Block-Copolymer-Silica Mesostructures as Host Media for the Laser Dye Rhodamine 6G

Abstract: Rhodamine 6G-doped mesostructured silica is prepared by an acidic sol−gel route using poly-b-poly(propylene oxide)-b-poly(ethylene oxide) (EOx−POy−EOx) block copolymer surfactants. Using low-refrac...

Synthesis of Mesocellular Silica Foams with Tunable Window and Cell Dimensions

Abstract: Polystyrene microspheres coated with cationic surfactants are easily prepared by microemulsion polymerization. These microspheres can be used in place of surfactants to synthesize porous silica foams. The nature of the foams depends strongly upon the synthesis conditions. Under basic catalysis, “closed-cell” foams are obtained. Under acidic catalysis, open-cell foams are obtained. The windows that connect the cells of the open-cell foams are believed to arise from direct contact between adjacent spherical templates. These silica foams resemble dense aerogels.

MMo3Se3 (M = Li+, Na+, Rb+, Cs+, NMe4+) Nanowire Formation via Cation Exchange in Organic Solution

Abstract: Currently, there is intensive research driving toward developing suitable one-dimensional (1D) conducting molecular wires because of their potential use as building blocks for molecular-scale electronic devices. 1 One appealing approach for obtaining molecular wires is the disassembly of quasi-1D crystals 2,3 such as LiMo3Se3 into structurally and electronically identical molecular wires. These linear chain compounds display a unique variety of physical properties including highly anisotropic conductivity, superconductivity and semiconducting behavior, depending on the identity of the interstitial cation separating the molecular chains [Mo3Se3]∞. Therefore [Mo3Se3]∞ nanowires with different cations represent a collection of different 1D building blocks for molecular devices. Unfortunately, due to the high-temperature nature of traditional solid-state cation-exchange processes, most MMo3Se3 (M ) Na+, Rb+, Cs+, Tl+) are prepared as single crystals and are insoluble in any polar solvent. 2 Only LiMo3Se3 is accessible in the nanowire/molecular wire form due to its solubility in polar solvents. 2a Recently, we have demonstrated surfactant-induced self-assembly of these inorganic LiMo 3Se3 molecular units into different mesophases. 5 Herein we report the formation of MMo3Se3 nanowires of different cations M using low-temperaturechimie doucesolution chemistry. X-ray diffraction, transmission electron microscopy studies, and elemental analysis on these nanowires indicate that different cations have been successfully intercalated into the nanowires. LiMo3Se3 crystals and 12-crown-4 were dissolved in propylene carbonate (PC), and the solution was sonicated fo r 1 h for complete dissolution of LiMo 3Se3. Appropriate amounts of alkali iodide (M ) Na, K, Rb, Cs) and NMe 4Cl were dissolved in 10 mL of PC and mixed with the LiMo 3Se3 in PC solution. The mixture was stirred fo r 5 h at 135-145°C. The resulting reddish product was centrifuged down, collected, and dried under vacuum for X-ray diffraction (XRD) analysis. X-ray diffraction taken on the exchanged sample indicates that the parent LiMo3Se3 structure2 is maintained after the reaction. Figure 1a shows the XRD patterns for the starting LiMo 3Se3 nanowires and the resulting MMo 3Se3 product. Upon cation exchange, the (100) peak shifts to lower angles, indicating an expansion of the interwire spacing. Figure 1b shows the lattice constanta obtained from the XRD for samples prepared using cations of different radius. It was found that the a lattice spacing is linearly correlated to the ionic radius of the exchanged cations within a given periodic group, while NMe 4 yields the largest interwire spacing (11 Å). 6 That thea spacing to ionic radius ratio for NMe4 is not collinear with the alkali counterions is not surprising, given the nonspherical shape of the ion and the resulting decrease in registry between the counterion and the surface of the [Mo3Se3]∞ frame. Cross-polarized optical microscopy studies indicate that the products consist of well-aligned microscopic fiber bundles. This is also clearly shown in the field emission scanning electron microscope (FESEM). Figure 2a shows one such image recorded on the CsMo3Se3 sample. We found that the molecular wires form nanowire bundles with diameters of 10 -200 nm. These molecular wire bundles were deposited on copper grids and examined using a transmission electron microscope (TEM). It was found that the individual molecular wires are aligned along the bundle axis and are evenly spaced (Figure 2b). The observed interwire spacing matches well with the XRD data. Similar results have been obtained in the systems of Rb +, Cs+, NMe4. In addition, elemental analysis was carried out for these exchanged compounds. It was found that the exchange is complete in most cases with the notable exception of the K + system. For example, the composition of Li x(NMe4)1-xMo3Se3 was obtained, with x ) 0.07. It was reported in an early paper that no cation exchange was observed via the simple addition of an alkali metal halide to a DMSO solution of LiMo3Se3. We have observed the same results when no 12-crown-4 is present in the solution. This observation clearly indicates the importance of the addition of 12-crown-4 to the currentchimie doucereaction. The 12-crown-4 molecules could complex with Li ions in the PC solvent and effectively shield their positive charge, consequently reducing the electrostatic interaction between the negatively charged [Mo 3Se3]∞ backbone with these Li ions. Cations of different sizes can then associate (1) (a) Hu, J.; Odom, T. W.; Lieber, C. M. Acc. Chem. Res . 1999, 32, 435. (b) Dekker, C.Phys. Today1999, 52, 22. (2) (a) Tarascon, J. M.; DiSalvo, F. J.; Cheve, C. H.; Carroll, J.; Walsh, M.; Rupp, L.J. Solid State Chem . 1985, 58, 290. (b) Golden, J. H.; DiSalvo, F. J.; Frechet, J. M. J.; Silcox, J.; Thomas, M.; Elman, J. Science, 1996, 273, 782. (c) Golden, J. H.; DiSalvo, F. J.; Frechet, J. M. J. Chem. Mater . 1995, 7, 232. (3) Davidson, P.; Gabriel, J. C.; Levelut, A. M.; Batail, P. Europhys. Lett. 1993, 21, 317. (4) Tarascon, J. M.; DiSalvo, F. J.; Waszczak, J. V. S olid State Commun. 1984, 52, 227. (5) Messer, B.; Song, J. H.; Huang, M.; Wu, Y.; Kim, F.; Yang, P. AdV. Mater. 2000, 12, 1526. (6) Huheey, J. E.; Keiter, E. A.; Keiter, R. L. Inorganic Chemistry: Principles of Structure and Reacti Vity, 4th ed.; HarperCollins College Publishers: New York, 1993. Figure 1. (a). X-ray diffraction patterns for the exchanged nanowire samples, from top to bottom, Li +, Na+, Cs+, NMe4. (b). Lattice constant a of the exchanged MMo 3Se3 sample (M) Li+, Na+, Rb+, Cs+, NMe4) vs the ionic radius of the exchanged ions. 9714 J. Am. Chem. Soc. 2001,123,9714-9715

Nanowire optoelectric switching device and method

Abstract: A nanowire switching device and method. The device has a nanowire structure comprising an elongated member having a cross-sectional area ranging from about 1 nanometers but less than about 500 nanometers, but can also be at other dimensions, which vary or are substantially constant or any combination of these. The device also has a first terminal coupled to a first portion of the nanowire structure; and a second terminal coupled to a second portion of the nanowire structure. The second portion of the nanowire structure is disposed spatially from the first portion of the nanowire structure. An active surface structure is coupled to the nanowire structure. The active surface structure extends from the first portion to the second portion along the elongated member.

Inorganic/block copolymer-dye composites and dye doped mesoporous materials for optical and sensing applications

Abstract: A method for preparing transparent mesostructured inorganic/block-copolymer composites or inorganic porous solids containing optically responsive species with selective optical, optoelectronic, and sensing properties resulting therefrom. Mesoscopically organized inorganic/block copolymer composites doped with dyes or complexes are prepared for use as optical hosts, chemical/physical/biological sensors, photochromic materials, optical waveguides, tunable solid-state lasers, or optoelectronic devices. The materials can be processed into a variety of different shapes, such as films, fibers, monoliths, for novel optical and sensing applications.