Ultralong beltlike (or ribbonlike) nanostructures (so-called nanobelts) were successfully synthesized for semiconducting oxides of zinc, tin, indium, cadmium, and gallium by simply evaporating the desired commercial metal oxide powders at high temperatures. The as-synthesized oxide nanobelts are pure, structurally uniform, and single crystalline, and most of them are free from defects and dislocations. They have a rectanglelike cross section with typical widths of 30 to 300 nanometers, width-to-thickness ratios of 5 to 10, and lengths of up to a few millimeters. The beltlike morphology appears to be a distinctive and common structural characteristic for the family of semiconducting oxides with cations of different valence states and materials of distinct crystallographic structures. The nanobelts could be an ideal system for fully understanding dimensionally confined transport phenomena in functional oxides and building functional devices along individual nanobelts.

https://science.sciencemag.org/content/sci/291/5510/1947.full.pdf

Nanobelts of Semiconducting Oxides

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

The ever increasing requirements for electrical performance of on-chip wiring has driven three major technological advances in recent years. First, copper has replaced Aluminum as the new interconnect metal of choice, forcing also the introduction of damascene processing. Second, alternatives for SiO2 with a lower dielectric constant are being developed and introduced in main stream processing. The many new resulting materials needs to be classified in terms of their materials characteristics, evaluated in terms of their properties, and tested for process compatibility. Third, in an attempt to lower the dielectric constant even more, porosity is being introduced into these new materials. The study of processes such as plasma interactions and swelling in liquid media now becomes critical. Furthermore, pore sealing and the deposition of a thin continuous copper diffusion barrier on a porous dielectric are of prime importance. This review is an attempt to give an overview of the classification, the character...

Low dielectric constant materials for microelectronics

There are growing concerns over the environmental, climate, and health impacts caused by using non-renewable fossil fuels. The utilization of green energy, including solar and wind power, is believed to be one of the most promising alternatives to support more sustainable economic growth. In this regard, lithium-ion batteries (LIBs) can play a critically important role. To further increase the energy and power densities of LIBs, silicon anodes have been intensively explored due to their high capacity, low operation potential, environmental friendliness, and high abundance. The main challenges for the practical implementation of silicon anodes, however, are the huge volume variation during lithiation and delithiation processes and the unstable solid-electrolyte interphase (SEI) films. Recently, significant breakthroughs have been achieved utilizing advanced nanotechnologies in terms of increasing cycle life and enhancing charging rate performance due partially to the excellent mechanical properties of nanomaterials, high surface area, and fast lithium and electron transportation. Here, the most recent advance in the applications of 0D (nanoparticles), 1D (nanowires and nanotubes), and 2D (thin film) silicon nanomaterials in LIBs are summarized. The synthetic routes and electrochemical performance of these Si nanomaterials, and the underlying reaction mechanisms are systematically described.

Silicon-based Nanomaterials for Lithium-Ion Batteries - A Review

Monodisperse silicon nanowires were synthesized by exploiting well-defined gold nanoclusters as catalysts for one-dimensional growth via a vapor–liquid–solid mechanism. Transmission electron microscopy studies of the materials grown from 5, 10, 20, and 30 nm nanocluster catalysts showed that the nanowires had mean diameters of 6, 12, 20, and 31 nm, respectively, and were thus well defined by the nanocluster sizes. High-resolution transmission electron microscopy demonstrated that the nanowires have single-crystal silicon cores sheathed with 1–3 nm of amorphous oxide and that the cores remain highly crystalline for diameters as small as 2 nm.

/pdf/diameter-controlled-synthesis-of-single-crystal-silicon-3liaiih7v0.pdf

Diameter-controlled synthesis of single-crystal silicon nanowires

Semiconductor wires with nanometer widths have attracted much attention in recent years for their potential applications in mesoscopic research and nanodevices. Since the 1960s, Si whiskers grown from the vapor-liquid-solid (VLS) reaction have been extensively studied. In the VLS reaction, Au particles are generally used as the mediating solvent on a Si substrate since Au and Si form a molten alloy at a relatively low temperature. Si in the vapor phase diffuses into the liquid-alloy droplet and bonds to the solid Si at the liquid-solid interface, which results in the growth of Si whiskers. The diameter of the whisker is determined by the diameter of the liquid-alloy droplet at its tip. Si whiskers generally grow along ⟨111⟩ directions epitaxially on Si(111) substrates in the form of single crystals by the VLS reaction.In different materials systems, however, a variety of whisker forms can be obtained. For example, GaP whiskers display rotational twins around their ⟨111⟩ growth axes, while GaAs whiskers grow in the form of the wurtzite structure.Thus far, the synthesis of one-dimensional nanostructured materials on a large scale remains a challenge. In recent years, many efforts have been made to synthesize Si nanowires by employing different methods such as photolithography and etching techniques and scanning tunneling microscopy. One method of particular interest is a recently developed laser ablation of metal-containing semiconductor targets, by which bulk quantities of semiconductor nanowires can be readily obtained. Our recent studies show that oxides play a dominant role in the nucleation and growth of high-quality semiconductor nanowires in bulk quantities by laser ablation, thermal evaporation, or chemical vapor deposition. A new growth mechanism called oxide-assisted nanowire growth has therefore been established. The ability to synthesize large quantities of high-purity (no contamination), ultra-long (in millimeters), and uniform-sized semiconductor nanowires (a few nanometers to tens of nanometers in diameter) from this new technique offers exciting possibilities in fundamental and applied research.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S088376940005288X

Oxide-Assisted Semiconductor Nanowire Growth

We report how the structural arrangement of germanium nanowires optimizes surface stability and enables the formation of very thin free-standing crystalline wires. Ge nanowires consisting of a crystalline Ge core and an amorphous ${\mathrm{GeO}}_{2}$ sheath have been formed by laser ablation of a mixture of Ge and ${\mathrm{GeO}}_{2}.$ The crystalline Ge core lies in the axial [211] direction and is terminated by the {111} facets on the surface. The ${\mathrm{GeO}}_{2}$ sheath saturates the surface bonds of the core, adapts to the core surface roughness, and prohibits the growth of the nanowire in the lateral direction. With such a core and sheath, the surface energy of the nanowire is reduced and the formation of very thin nanowires is thereby permitted. Phonon confinement in the Ge nanowires has been observed by Raman scattering.

/pdf/germanium-nanowires-sheathed-with-an-oxide-layer-4eypyj3mw5.pdf

Germanium nanowires sheathed with an oxide layer

Highly pure, ultralong, and uniform-sized semiconductor nanowires in bulk quantity were synthesized by thermal evaporation or laser ablation of semiconductor powders mixed with oxides. Transmission electron microscopy study shows that decomposition of semiconductor suboxides and defect structures play important roles in enhancing the formation and growth of high-quality nanowires. A new growth mechanism is proposed on the basis of microstructure and different morphologies of the nanowires observed.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400053140

Y. H. Tang

Papers

Oxide-Assisted Semiconductor Nanowire Growth

Germanium nanowires sheathed with an oxide layer

Semiconductor nanowires from oxides

Large-scale synthesis of ultrafine Si nanoparticles by ball milling

Bulk-quantity Si nanowires synthesized by SiO sublimation