Nanowire diameter control

Cui, Y. Lauhon, L. I Gudiksen, M. S. Wang, J. Lieber, C. M. 2001. Diameter-controlled synthesis of single-crystal silicon nanowires. Appl. Phys. Lett. 78 2214-2216. 

For CVD-VLS nanowire growth, colloidal particles are first size-selected in solution and then drop cast or spun cast onto the substrate prior to nanowire deposition. Nanowire diameter control is very important, as the optical, electronic, and mechanical properties of nanowire depend on the nanowire diameter. The histograms shown in Fig. 5B illustrate that the nanowire diameter... 

Cui Y Lauhon LJ, Gudiksen MS, Wang J, Lieber CM. Diameter-controlled synthesis of single-crystal sihcon nanowires. Appl Phys Lett 2001 78 2214. 

Huang J, Chiam SY, Tan HH, Wang S, Chim WK (2010b) Fabrication of sihcon nanowires with precise diameter control using metal nanodot arrays as a hard mask blocking material in chemical etching. Chem Mater 22 4111—4116... 

Li C, Zhang D, Han S, Liu TT, Zhou C (2003a) Diameter-controlled growth of single-crystaUine In Oj nanowires and their electronic properties. Adv Mater 15 143-146... 

Tang et al., 1999) and correspond to broad distributions of wire diameters and lengths. Therefore, it would be important to devote future research efforts toward controlling the wire diameter, length, morphology, and assembly in such synthesis in order to utilize the nanowires derived effectively for potential electronic applications. 

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. 

In this section advanced developments of the PLD technique are shortly described, e.g., the combinatorial approach and laser MBE. Because of the increasing research interest in ZnO-based nanostructures, the established PLD (at background gas pressure 10-4—3 mbar) was extended to much higher pressures of 50-200 mbar to grow arrays of free-standing ZnO nanowires. This unique high-pressure PLD process allows the growth of ZnO-based nanostructures with controlled shape and diameter and excellent optical properties. 

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