Nanowire growth

Solution-Liquid-Solid (SLS) growth of semiconductor nanowires by Wang etal. (2006). The synthesis proceeds by a solution-based catalysed growth mechanism in which nanometer-scale metallic droplets catalyse the decomposition of metallo-organic precursors and crystalline nanowire growth. 

A. Persson, M. Larsson, S. Stenstrom, B. Ohlsson, L. Samuelson, and L. Wallenberg, Solid-phase diffusion mechanism for GaAs nanowire growth. Nature Mater. 3, 677-681 (2004). 

Recently, the VLS growth method has been extended beyond the gas-phase reaction to synthesis of Si nanowires in Si-containing solvent (Holmes et al, 2000). In this case 2.5-nm Au nanocrystals were dispersed in supercritical hexane with a silicon precursor (e.g., diphenylsilane) under a pressure of 200-270 bar at 500°C, at which temperature the diphenylsilane decomposes to Si atoms. The Au nanocrystals serve as seeds for the Si nanowire growth, because they form an alloy with Si, which is in equilibrium with pure Si. It is suggested that the Si atoms would dissolve in the Au crystals until the saturation point is reached then they are expelled from the particle to form a nanowire with a diameter similar to the catalyst particle. This method has an advantage over the laser-ablated Si nanowire in that the nanowire diameter can be well controlled by the Au particle size, whereas liquid metal droplets produced by the laser ablation process tend to exhibit a much broader size distribution. With this approach, highly crystalline Si nanowires with diameters ranging from 4 nm to 5 nm have been produced by Holmes et al. (2000). The crystal orientation of these Si nanowires can be controlled by the reaction pressure. 

Fabrication or InP/InAs/InP core-multishell heterostructure nanowire arrays shown in Fig. 24 has been achieved by selective area metal-organic vapour phase epitaxy.1 These core-multishell nanowires were designed to accommodate a strained InAs quantum well layer in a higher band gap InP nanowire. Precise control over the nanowire growth direction and the heterojunction formation enabled the successful fabrication of the nanostructure in which all the three layers were epitaxially grown without the assistance of a catalyst. 

S. Kodambaka, J. Tersoff, M.C. Renter, F.M. Ross, Germanium Nanowire Growth below the Eutectic Temperature, Science 316 (4) (2007) 729 732. 

Figure 6.62. Silicon nanowire growth from a gold nanocluster catalyst. Shown is (a) the phase diagram for the Au/Si system, showing the eutectic temperature/composition (b) SEM image and (c) high-resolution TEM image of the nanowires grown at a temperature of 450° C. The dark tip of the nanowire is from the gold nanocluster. Reproduced with permission from Hu, J. Odom, T. W. Lieber, C. M. Acc. Chem. Res. 1999, 32, 435. Copyright 1999 American Chemical Society.

The word generally is used, since there are also reports of nanowire growth at temperatures below the eutectic. Eor example, see Adhikari, H. Marshall, A. F. Chidsey, E. D. McIntyre, P. C. Nano Lett. 2006, 6, 318. 

Wang ZL (2008) Oxide nanobelts and nanowires - growth, properties and applications. J Nanosci Nanotechol 8 27-55... 

It is clear from the VLS nanowire growth mechanism that the positions of the nanowires can be controlled by the initial positions of the Au clusters or Au thin films. By creating desired patterns of Au using the lithographic technique it is possible to grow ZnO nanowires of the same designed pattern since they grow... 

The seeds are then added to a growth solution that consists of fresh metal salt, and a surfactant, cetyltrimethylammonium bromide, CTAB, that directs the growth of nanopartides into nanorods and nanowires. Growth is initiated by the addition... 

Oxide-Assisted Growth of Silicon and Related Nanowires Growth Mechanism, Structure and Properties... 

Fundamental aspects of vapor-liquid-solid (VLS) semiconductor nanowire growth are presented here. The synthesis of VLS semiconductor has been extended to different reaction media and pathways from the early chemical vapor deposition (CVD) approach, including solution-liquid-solid (SLS) and supercritical fluid-liquid-solid (SFLS), laser-catalyzed growth, and vapor-liquid-solid-epitaxy. The properties of nanowires grown by these VLS embodiments are compared. In this entry, VLS growth of nanowire heterostructures and oriented and hyperbranched arrays is examined. In addition, surface passivation and functionalization are assessed, and the importance of these techniques in the progress toward VLS produced nanowire devices is detailed. 

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