miércoles, 22 de febrero de 2012

Nanowires.. the most easy way..

Nanowires are grown by a variety of mechanisms, including vapor-liquid-solid, vapor-quasiliquid-solid or vapor-quasisolid-solid, oxide-assisted growth, and self-catalytic growth (SCG) mechanisms. A critical analysis of the suitability of self-catalyzed nanowires, as compared to other nanowires, for next-generation technology development has been carried out. Basic causes of superiority of self-catalyzed (SCG) nanowires over othernanowires have been described. Polytypism in nanowires has been studied, and a model for polytypism has been proposed. The model predicts polytypism in good agreement with available experiments. 

This model, together with various evidences, demonstrates lower defects, dislocations, and stacking faults in SCG nanowires, as compared to those in other nanowires. Calculations of carrier mobility due to dislocation scattering, ionized impurity scattering, and acoustic phonon scattering explain the impact of defects, dislocations, and stacking faults on carrier transports in SCG and other nanowires. Analyses of growth mechanisms for nanowire growth directions indicate SCG nanowires to exhibit the most controlled growth directions. In-depth investigation uncovers the fundamental physics underlying the control of growth direction by the SCG mechanism. Self-organization of nanowires in large hierarchical arrays is crucial for ultra large-scale integration (ULSI). 

Unique features and advantages of self-organized SCG nanowires, unlike other nanowires, for this ULSI have been discussed. Investigations of nanowire dimension indicate self-catalyzed nanowires to have better control of dimension, higher stability, and higher probability, even for thinner structures.Theoretical calculations show that self-catalyzed nanowires, unlike catalyst-mediated nanowires, can have higher growth rate and lower growth temperature. Nanowire and nanotube characteristics have been found also to dictate the performance of nanoelectromechanical systems.Defects, such as stacking faults, dislocations, and nanopipes, which are common in catalyst-mediated nanowires and nanotubes, adversely affect the efficiency of nanowire (nanotube) nanoelectro-mechanical devices. The influence of seed-to-seed distance and collection area radius on the self-catalyzed, self-aligned nanowire growths in large arrays of seeds has been examined. 

A hypothesis has been presented for this. The present results are in good agreement with experiments. These results suggest that the SCG nanowires are perhaps the best vehicles for revolutionary advancement of tomorrow's nanotechnology. 
One of the newest application of this is in the batteries. Higher-density batteries, more efficient thin-film solar cells, and better catalysts may all soon be possible, thanks to a new technique that allows nanowires to be “decorated” with nanoparticles. Using the novel technology, scientists from Stanford University have been able to festoon the outside surfaces of nanowires with intricate chains of metal oxide or noble metal nanoparticles, thereby drastically boosting the effective surface area of the nanowires. Other researchers have previously tried to achieve the same end result, but apparently never with such success.

Noor Mohammad, S. S. (2011). Why self-catalyzed nanowires are most suitable for large-scale hierarchical integrated designs of nanowire nanoelectronics. Journal Of Applied Physics110(8), 084310. doi:10.1063/1.3624585

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