| 1. |
- Johansson, Jonas, et al.
(författare)
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Effects of Supersaturation on the Crystal Structure of Gold Seeded III-V Nanowires
- 2009
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Ingår i: Crystal Growth & Design. - : American Chemical Society (ACS). - 1528-7483 .- 1528-7505. ; 9:2, s. 766-773
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Tidskriftsartikel (refereegranskat)abstract
- We present results that provide fundamental insights on how to experimentally tailor the planar defect density and even the crystal structure in III-V metal particle seeded nanowires, where zinc blende is the stable bulk crystal structure. We have grown GaP nanowires with metal-organic vapor phase epitaxy under different conditions: pulsing of the Ga source, and continuous growth with and without In background. The dominant crystal structure of the nanowires is zinc blende, which when grown under continuous conditions has a high density of twin planes perpendicular to the growth direction. Using pulsed growth, we observed that the twin plane separations were much longer than those observed for continuous growth with an In background. On the other hand, during continuous growth, under In-free conditions, a considerable amount of the wurtzite phase forms. We explain the importance of the In background during growth. With classical nucleation modeling we qualitatively relate the density of planar defects in a nanowire to the growth conditions. For low supersaturations, we predict a low twin plane density, consistent with our experimental observations of pulsed nanowire growth. In addition, we suggest that under certain conditions, it might be possible to grow wires with almost perfect wurtzite structure.
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| 2. |
- Wacaser, Brent, et al.
(författare)
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Preferential Interface Nucleation: An Expansion of the VLS Growth Mechanism for Nanowires
- 2009
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Ingår i: Advanced Materials. - : Wiley. - 1521-4095 .- 0935-9648. ; 21:2, s. 153-165
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Forskningsöversikt (refereegranskat)abstract
- A review and expansion of the fundamental processes of the vapor-liquid-solid (VLS) growth mechanism for nanowires is presented. Although the focus is on nanowires, most of the concepts may be applicable to whiskers, nanotubes, and other unidirectional growth. Important concepts in the VLS mechanism such as preferred deposition, supersaturation, and nucleation are examined. Nanowire growth is feasible using a wide range of apparatuses, material systems, and growth conditions. For nanowire growth the unidirectional growth rate must be much higher than growth rates of other surfaces and interfaces. It is concluded that a general, system independent mechanism should describe why nanowires grow faster than the surrounding surfaces. This mechanism is based on preferential nucleation at the interface between a mediating material called the collector and a crystalline solid. The growth conditions used mean the probability of nucleation is low on most of the surfaces and interfaces. Nucleation at the collector-crystal interface is however different and of special significance is the edge of the collector-crystal interface where all three phases meet. Differences in nucleation due to different crystallographic interfaces can occur even in two phase systems. We briefly describe how these differences in nucleation may account for nanowire growth without a collector. Identifying the mechanism of nanowire growth by naming the three phases involved began with the naming of the VLS mechanism. Unfortunately this trend does not emphasize the important concepts of the mechanism and is only relevant to one three phase system. We therefore suggest the generally applicable term preferential interface nucleation as a replacement for these different names focusing on a unifying mechanism in nanowire growth.
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