Thermal Conductivity in Biphasic Silicon Nanowires.

The work unravels the previously unexplored atomic-scale mechanism involving the interaction of phonons with crystal homointerfaces. Silicon nanowires with engineered isotopic content and crystal phases were chosen for this investigation. Crystal polytypism, manifested by the presence of both diamond cubic and rhombohedral phases within the same nanowire, provided a testbed to study the impact of phase homointerfaces on phonon transport.

Reduction of Thermal Conductivity in Nanowires by Combined Engineering of Crystal Phase and Isotope Disorder.

Nanowires are a versatile platform to investigate and harness phonon and thermal transport phenomena in nanoscale systems. With this perspective, we demonstrate herein the use of crystal phase and mass disorder as effective degrees of freedom to manipulate the behavior of phonons and control the flow of local heat in silicon nanowires. The investigated nanowires consist of isotopically pure and isotopically mixed nanowires bearing either a pure diamond cubic or a cubic-rhombohedral polytypic crystal phase.

Phonon Engineering in Isotopically Disordered Silicon Nanowires.

The introduction of stable isotopes in the fabrication of semiconductor nanowires provides an additional degree of freedom to manipulate their basic properties, design an entirely new class of devices, and highlight subtle but important nanoscale and quantum phenomena. With this perspective, we report on phonon engineering in metal-catalyzed silicon nanowires with tailor-made isotopic compositions grown using isotopically enriched silane precursors (28)SiH4, (29)SiH4, and (30)SiH4 with purity better than 99.9%.

Spatially resolved correlation of active and total doping concentrations in VLS grown nanowires.

Controlling axial and radial dopant profiles in nanowires is of utmost importance for NW-based devices, as the formation of tightly controlled electrical junctions is crucial for optimization of device performance. Recently, inhomogeneous dopant profiles have been observed in vapor–liquid–solid grown nanowires, but the underlying mechanisms that produce these inhomogeneities have not been completely characterized. In this work, P-doping profiles of axially modulation-doped Si nanowires were studied using nanoprobe scanning Auger microscopy and Kelvin probe force microscopy in order to distinguish between vapor–liquid–solid doping and the vapor–solid doping.

On-surface formation of metal nanowire transparent top electrodes on CdSe nanowire array-based photoconductive devices.

A simple wet chemical approach was developed for a unique on-surface synthesis of transparent conductive films consisting of ultrathin gold/silver nanowires directly grown on top of CdSe nanowire array photoconductive devices enclosed in polycarbonate membranes. The metal nanowire film formed an ohmic contact to the semiconductor nanowires without additional treatment. The sheet resistance and transparency of the metal nanowire arrays could be controlled by the number of metal nanowire layers deposited, ranging from ∼98-99% transmission through the visible range and several kOhm/sq sheet resistance for a single layer, to 80-85% transmission and ∼100 Ohm/sq sheet resistance for 4 layers.

Diameter and polarization-dependent Raman scattering intensities of semiconductor nanowires.

Diameter-dependent Raman scattering in single tapered silicon nanowires is measured and quantitatively reproduced by modeling with finite-difference time-domain simulations. Single crystal tapered silicon nanowires were produced by homoepitaxial radial growth concurrent with vapor-liquid-solid axial growth. Multiple electromagnetic resonances along the nanowire induce broad band light absorption and scattering.

Silicon nanowire polytypes: identification by Raman spectroscopy, generation mechanism, and misfit strain in homostructures.

Silicon nanowires with predominant 9R, 27T, 2H and other polytype structures with respective hexagonalities of 50, 40 and 35.3% were identified by Raman microscopy. Transmission electron microscopy indicates that intrinsic stacking faults form the basic building blocks of these polytypes.

Obtaining uniform dopant distributions in VLS-grown Si nanowires.

Semiconducting nanowires grown by the vapor-liquid-solid method commonly develop nonuniform doping profiles both along the growth axis and radially due to unintentional surface doping and diffusion of the dopants from the nanowire surface to core during synthesis. We demonstrate two approaches to mitigate nonuniform doping in phosphorus-doped Si nanowires grown by the vapor-liquid-solid process. First, the growth conditions can be modified to suppress active surface doping.

Electrochemical synthesis of morphology-controlled segmented CdSe nanowires.

Morphology, that is, the study of form comprising shape, size, and structure, is important for materials research in general. For nanostructured materials, popularly known as nanomaterials, morphology has a special significance since form, in this case, dictates physical and chemical properties. Unlike bulk materials, properties of nanomaterials are strongly correlated to form.

Pressure-modulated alloy composition in Si((1-x))Ge(x) nanowires.

Si((1-x))Ge(x) nanowires (NWs) constitute promising building blocks for future electronic and optoelectronic devices due to the enhanced tuneability of their physical properties, achieved mainly by controlling their chemical composition. In this study, the pressure dependence of the chemical composition, growth and tapering rates and crystalline structure of Si((1-x))Ge(x) NWs grown by the CVD-VLS technique was investigated. It is demonstrated for the first time, that the composition of single crystal Si((1-x))Ge(x) NWs can be readily modulated between ca.