Vapour–liquid–solid route and its vari­ants are rou­tinely used for scal­able syn­thesis of semi­con­ducting nanowires, yet the fun­da­mental growth processes remain unknown. Here we employ atomic-​​scale com­pu­ta­tions based on model poten­tials to study the sta­bility and growth of gold-​​catalysed sil­icon nanowires. Equi­lib­rium studies uncover seg­re­ga­tion at the solid-​​like sur­face of the cat­a­lyst par­ticle, a liquid AuSi droplet, and a silicon-​​rich droplet–nanowire inter­face enveloped by het­ero­ge­neous trun­cating facets. Super­sat­u­ra­tion of the droplets leads to rapid one-​​dimensional growth on the trun­cating facets and much slower nucleation-​​controlled two-​​dimensional growth on the main facet. Sur­face dif­fu­sion is sup­pressed and the excess Si flux occurs through the droplet bulk which, together with the Si-​​rich inter­face and con­tact line, lowers the nucle­ation bar­rier on the main facet. The ensuing step flow is mod­i­fied by Au dif­fu­sion away from the step edges. Our study high­lights key inter­fa­cial char­ac­ter­is­tics for mor­pho­log­ical and com­po­si­tional con­trol of semi­con­ducting nanowire arrays.


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