Nanowire modeling

Fan HJ, Barnard AS, Zacharias M (2007) ZnO nanowires and nanobelts Shape selection and thermodynamic modeling. Appl Phys Lett 90 143116-143119... 

For either conventional polycrystalline semiconductors or nanotubes and nanowires to be successful, the development of model and simulation tools that can be used for device and circuit design as well as for predictive engineering must be available. Since these devices are not necessarily based on single wires or single crystals, but rather on an ensemble of particles, the aggregate behavior must be considered. Initial efforts to provide the necessary physical understanding and device models using percolation theory have been reported.64,65... 

Growth Mechanisms. Growth mechanisms have been investigated, andsev-eral theories have been proposed. There are two general models that are used to explain catalytic synthesis of nanowires or nanotubes. The first is called tip growth, in which... 

However, it is unclear what the growth mechanisms are because no Si feedstock was fed in the gas form, which is required for the tip-growth model to work. In the following, we will discuss the composition and growth mechanisms of the nanowires made in this work, and show that the Co nanoparticles may play a dual-catalytic role by helping form gaseous silicon species and catalyze the growth of Si-based nanowires. 

A schematic of the proposed growth model is shown in Fig. 10.23. In this model, Co nanoparticles play a dual catalytic role. On the one hand, they catalyze silane formation by reacting first with silicon to form Co silicides, and then react with hydrogen to form silane while being reduced to Co metal. The second role of Co nanoparticles is their classic catalytic ability of making nanowires by first dissolving the silane and precipitating out Si nanowires. 

Nanowire systems have attracted a great deal of attention recently due to their technological potential They are of fundamental interest because they exhibit unique quantum confinement effects. In this article, advances in the fabrication of nanowires via template-assisted and laser-assisted approaches are reviewed. The structure and characteristics of different nanowire systems are discussed. To understand and predict the unusual properties of nanowires, we have developed a generalized theoretical model for the band structure of these onedimensional systems. A unique semimetal-semiconductor transition that occurs in bismuth nanowires is described. Transport measurements on bismuth and antimony nanowires illustrate that these novel materials are very different from their bulk counterparts. A transport... 

The electronic states of nanowire systems exhibit a very different spectrum from that of bulk materials. In order to understand their unique electronic properties, we have modeled the band structure of these one-dimensional systems. 

The diffusive transport phenomena in nanowires can be described by a semiclassical model based on the Boltzmann transport equation. For carriers in a one-dimensional subband, important transport coefficients, such as the electrical conductivity, a, the Seebeck coefficient, S, and the thermal conductivity, Ke, are derived as (Sun et al., 1999b Ashcroft and Mermin, 1976a)... 

Sun, X., Zhang, Z., and Dresselhaus, M. S., Theoretical modeling of thermoelectricity in bismuth nanowires. Appl. Phys. Lett. 74,4005 (1999b). 

Transport properties (continued.) semiclassical model, 192-193 temperature-dependent resistivity of nanowires, 193-198 Triplet sites on supports, 63-64 Tungsten species, SiC>2-supported, 63 Turnover numbers (TON), nanostructured materials, 6... 

The chapters in this volume present detailed insights into the synthesis-structure-properties relationships of nanostructured materials. In particular, the catalytic and photocatalytic properties of nanoclusters and nanostructured materials with ultrahigh surface-to-volume ratio are demonstrated. The gas absorption characteristics and surface reactivity of nanoporous and nanocrystalline materials are shown for various separation and reaction processes. In addition, the structural manipulation, quantum confinement effects, transport properties, and modeling of nanocrystals and nanowires are described. The biological functionality and bioactivity of nanostructured ceramic implants are also discussed. 

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