Hierarchical Nanostructures for Photo-Electro-Chemical Cells - Hierarchical Nanostructures for Energy Devices - page 185

organic vapor phase epitaxy (MOVPE) method, decorated with branches
grown from pre-alloyed binary Au-In seed particles on the trunk nanowires
from e-beam patterned Au seed particles as shown in Figure 8.8(c).
Although this process is straightforward, the chamber needs to be opened
between each catalyst deposition step. During this opening step, oxidation
of pre-grown nanomaterials sometimes happens, which is deleterious
to forming an epitaxial

d n 3 r 4 n g | 4

junction between the backbone and branch

nanostructure.

8.4.3 Branch Formation by in situ Catalyst Generation
This method is distinguishable from the previous method in that the catalyst
for the branches is provided in situ during nanowire growth. May et al. 46
synthesized highly branched InAs nanowires on a GaAs(111) substrate
through MOVPE composed of backbone nanowires by VLS growth with a
gold catalyst, and Mn-mediated branches. Self-assembled Mn clusters on
growing nanowires initiated epitaxial branch growth, which results in highly
branched dendritic structures as displayed in Figures 8.9(a) and (b).

.

Figure 8.9 SEM image of (a) top view and (b) side view of InAs nanowire

branches grown from a InAs backbone. Adapted with permission
from ref. 46. (Copyright 2005, WILEY-VCH Verlag GmbH & Co. KGaA,
Weinheim.) (c) A single column of ZnO nanopropeller arrays.
Adapted with permission from ref. 47. (Copyright 2004, AIP Publishing
LLC.) (d) 6-Fold hierarchical ZnO nanonail structures. Adapted from
ref. 48.