Fig. S1 Cross-sectional TEM images of Ni catalyzed Ge nanowires grown at 0.75 GeH4
partial pressure at various growth temperatures – (a) 300C (b) 330C (c) 345C (d)
360C and (e) 375C
Fig. S2 Cross-sectional TEM images of Ni catalyzed Ge nanowires grown at 330 C and
various GeH4 partial pressures – (a) PGeH4 = 0.5 torr (b) PGeH4 = 0.6 torr (c) PGeH4 = 0.75
torr and (d) PGeH4 = 1.0 torr
Supporting Information S3:
In order to further confirm the hypothesis that both VSS and VLS nanowire growth
kinetics in the higher temperature regime are limited by vapor phase transport (e.g. of
GeH4 precursor to the nanowires) for the typical operating conditions of our CVD reactor
a rough estimate was made of the amount of Ge deposited per unit substrate area in the
form of nanowires. This estimate was performed for both Au-catalyzed VLS growth and
Ni-catalyzed VSS growth of Ge nanowires at the same growth temperature and GeH4
partial pressure. To compare the amount of Ge deposited, samples grown at 345C and
0.75 torr GeH4 partial pressure using Au and Ni nanoparticles were considered. To
estimate the amount of Ge deposited on Au-catalyzed VLS-grown sample, the average
nanowire densities (#/m2), diameters and lengths of the nanowires were calculated from
SEM and TEM images of the samples. For Ni-catalyzed VSS growth, only the volume of
Ge nanowires with straight morphology were included in the estimation. In equation 2, L
denotes the average length of the nanowires; r and R denote the nanowire radii at the tip
and the base of the nanowires. Taking into account the wire taper, the volume of Ge
deposited per unit area (/m2) for both the samples was estimated as –
V ( /#
m)x V
2
G
e
N
(1)
W
V 13RRrr 
2
N
2
(2)
W

For Au catalyzed VLS-grown sample, the volume was calculated as 7x107 nm3/m2 in the

form of Ge nanowires. For Ni catalyzed VSS grown sample, the corresponding Ge
volume was estimated as 2x106 nm3/m2. A significant amount of Ge is also deposited in
the form of kinked nanowires on the VSS-grown sample, which was not included in the
calculation here. These estimates indicate that a comparable amount of Ge is deposited
for both VSS and VLS, in spite of the much smaller axial length of VSS-grown (546 nm
for the straight wires) versus VLS-grown (6250 nm) Ge nanowires at 345°C. This further
supports the conclusion that, in the higher temperature VSS growth regime, the vapor
phase transport is rate limiting, rather than factors associated with the catalyst.