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InAs nanowires (NWs) were grown on silicon substrates by gas source molecular beam epitaxy using five different growth modes: (1) Au-assisted growth, (2) positioned (patterned) Au-assisted growth, (3) Au-free growth, (4) positioned Au-assisted growth using a patterned oxide mask, and (5) Au-free selective-area epitaxy (SAE) using a patterned oxide mask. Optimal growth conditions (temperature, V/III flux ratio) were identified for each growth mode for control of NW morphology and vertical NW yield. The highest yield (72%) was achieved with the SAE method at a growth temperature of 440 °C and a V/III flux ratio of 4. Growth mechanisms are discussed for each of the growth modes. [ABSTRACT FROM AUTHOR]

Abstract: Patterned arrays of gold-assisted vapor–liquid–solid (VLS) nanowires (NWs) were grown on Si(111) substrates by gas source molecular beam epitaxy (MBE). GaAs/GaP heterostructures were grown with periodic modulation of the group V composition. Study of these oscillations by high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) enabled the measurement of the instantaneous growth rate throughout the NW. Novel transient growth behavior, NW dissolution, droplet purging, and droplet refilling were observed to occur at the GaAs/GaP hetero-interface. These behaviors were linked to the large change in chemical potential difference between the liquid droplet and the crystal solid when switching between As and P. [Copyright &y& Elsevier]

Abstract: InAs nanowires were grown on GaAs substrates by the Au-assisted vapour–liquid–solid (VLS) method in a gas source molecular beam epitaxy (GSMBE) system. Passivation of the InAs nanowires using InP shells proved difficult due to the tendency for the formation of axial rather than core–shell structures. To circumvent this issue, Al x In1−x As or Al x In1−x P shells with nominal Al composition fraction of x=0.20, 0.36, or 0.53 were grown by direct vapour–solid deposition on the sidewalls of the InAs nanowires. Characterisation by transmission electron microscopy revealed that the addition of Al in the shell resulted in a remarkable transition from the VLS to the vapour–solid growth mode with uniform shell thickness along the nanowire length. Possible mechanisms for this transition include reduced adatom diffusion, a phase change of the Au seed particle, and surfactant effects. The InAs–AlInP core-shell nanowires exhibited misfit dislocations, while the InAs–AlInAs nanowires with lower strain appeared to be free of dislocations. [Copyright &y& Elsevier]