Bulk quantities of defect-free silicon (Si) nanowires with nearly uniform diameters ranging from 40 to 50 angstroms were grown to a length of several micrometers with a supercritical fluid solution-phase approach. Alkanethiol-coated gold nanocrystals (25 angstroms in diameter) were used as uniform seeds to direct one-dimensional Si crystallization in a solvent heated and pressurized above its critical point. The orientation of the Si nanowires produced with this method could be controlled with reaction pressure. Visible photoluminescence due to quantum confinement effects was observed, as were discrete optical transitions in the ultraviolet-visible absorbance spectra.

http://science.sciencemag.org/content/sci/287/5457/1471.full.pdf

Control of Thickness and Orientation of Solution-Grown Silicon Nanowires

Inorganic nanocrystals with tailored geometries exhibit unique shape-dependent phenomena and subsequent utilization of them as building blocks for the fabrication of nanodevices is of significant interest. Herein, we review the recent developments in the shape control of colloidal nanocrystals with a focus on the scientifically and technologically important semiconductor and metal oxide nanocrystals obtained by nonhydrolytic synthetic methods. Many structurally unprecedented motifs have been discovered including polyhedrons, rods and wires, plates and prisms, and other advanced shapes such as branched rods, stars, inorganic dendrites, and dumbbells. The currently proposed shape-guiding mechanisms are presented and the important pioneering studies on the assembly of shape-controlled nanocrystals into ordered superlattices and the fabrication of prototype advanced nanodevices are discussed.

Shape Control of Semiconductor and Metal Oxide Nanocrystals through Nonhydrolytic Colloidal Routes

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

/pdf/direct-observation-of-vapor-liquid-solid-nanowire-growth-49migr30t8.pdf

Direct Observation of Vapor-Liquid-Solid Nanowire Growth

and Perspectives Sophie Carenco,†,‡,§,∥,⊥ David Portehault,*,†,‡,§ Ced́ric Boissier̀e,†,‡,§ Nicolas Meźailles, and Cleḿent Sanchez*,†,‡,§ †Chimie de la Matier̀e Condenseé de Paris, UPMC Univ Paris 06, UMR 7574, Colleg̀e de France, 11 Place Marcelin Berthelot, 75231 Paris Cedex 05, France ‡Chimie de la Matier̀e Condenseé de Paris, CNRS, UMR 77574, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Chimie de la Matier̀e Condenseé de Paris, Colleg̀e de France, 11 Place Marcellin Berthelot, 75231 Paris Cedex 05, France Laboratory Heteroelements and Coordination, Chemistry Department, Ecole Polytechnique, CNRS-UMR 7653, Palaiseau, France

Nanoscaled metal borides and phosphides: recent developments and perspectives

Xiangfeng Duan and Charles M. Lieber*Department of Chemistry and Chemical BiologyHarVard UniVersity, Cambridge, Massachusetts 02138ReceiVed October 18, 1999Herein we report the bulk synthesis of single crystalline GaNnanowires. Laser ablation of a composite target of GaN and acatalytic metal generates liquid nanoclusters that serve as reactivesites confining and directing the growth of crystalline nanowires.Field emission scanning electron microscopy (FE-SEM) showsthat the product primarily consists of wire-like structures. PowderX-ray diffraction (PXRD) analyses of a bulk nanowire samplecan be indexed to the GaN wurtzite structure, and indicate >95%phase purity. Transmission electron microscopy (TEM), conver-gent beam electron diffraction (CBED), and energy-dispersiveX-ray fluorescence (EDX) analyses of individual nanowires showthat they are GaN single crystals with a [100] growth direction.Nanostructured GaN materials have attracted extensive interestover the past decade due to their significant potential foroptoelectronics.

https://cml.harvard.edu/assets/JACS_122_188.pdf

Laser-Assisted Catalytic Growth of Single Crystal GaN Nanowires

Methanolysis of {t-Bu2In[μ-P(SiMe3)2]}2 (1) in aromatic solvents gives polycrystalline InP fibers (dimensions 10−100 nm × 50−1000 nm) at 111−203 °C. The chemical pathway consists of a molecular component, in which precursor substituents are eliminated, and a nonmolecular component, in which the InP crystal lattices are assembled. The two components working in concert comprise the solution−liquid−solid (SLS) mechanism. The molecular component proceeds through a sequence of isolated and fully characterized intermediates:  1 → [t-Bu2In(μ-OMe)]2 (2) → [t-Bu2In(μ-PHSiMe3)]2 (3) → 2 → [t-Bu2In(μ-PH2)]3 (4). Complex 4, which is alternatively prepared from t-Bu3In and PH3, undergoes alkane elimination, the last steps of which are catalyzed by the protic reagent MeOH, PhSH, Et2NH, or PhCO2H. In the subsequent nonmolecular component of the pathway, the resulting (InP)n fragments dissolve into a dispersion of molten In droplets, and recrystallize as the InP fibers. Important criteria are identified for crystal growt...

Solution−Liquid−Solid Growth of Indium Phosphide Fibers from Organometallic Precursors: Elucidation of Molecular and Nonmolecular Components of the Pathway

Synthesis, Structure, Spectroscopy, and Reactivity of a Metallathiabenzene1

2,6-Dimethoxyphenylphosphirane Oxide and Sulfide and their Thermolysis to Phosphinidene Chalcogenides—Kinetic and Mechanistic Studies

Preparation of volatile molecular lithium-niobium alkoxides. Crystal structures of [Nb(μ-OCH2SiMe3)(OCH2SiMe3)4]2 and [LiNb(μ3-OCH2SiMe3)-(μ2-OCH2SiMe3)2(OCH2SiMe3]2

Alicia M. Beatty

Papers

Solution−Liquid−Solid Growth of Indium Phosphide Fibers from Organometallic Precursors: Elucidation of Molecular and Nonmolecular Components of the Pathway

Synthesis, Structure, Spectroscopy, and Reactivity of a Metallathiabenzene1

2,6-Dimethoxyphenylphosphirane Oxide and Sulfide and their Thermolysis to Phosphinidene Chalcogenides—Kinetic and Mechanistic Studies

Preparation of volatile molecular lithium-niobium alkoxides. Crystal structures of [Nb(μ-OCH2SiMe3)(OCH2SiMe3)4]2 and [LiNb(μ3-OCH2SiMe3)-(μ2-OCH2SiMe3)2(OCH2SiMe3]2

Oligomerization Chemistry of a Metallabenzene Cycloadduct. Synthesis and Structure of an Organometallic Crown Compound1