Towards engineered branch placement:
Unreal™ match between VLS-GLAD
nanowire growth and simulation
Supplementary Information
M.T. Taschuk1, R.T. Tucker1, J.M. LaForge1, A.L. Beaudry1, M.R. Kupsta2, M.J. Brett1, 2
1. Department of Electrical and Computer Engineering, University of Alberta, Edmonton, AB T6H 2V4
2. NRC National Institute for Nanotechnology, Edmonton, Alberta, T6G 2M9
Table S1: Best Match Simulation Conditions
Parameter
Value
Branch to Branch Barrier (Eb2b)
0.5 eV
Branch to Droplet Barrier
0.0 eV
Branch to Substrate Barrier (Eb2s)
0.5 eV
Face to Face Barrier
N/A
Cubic Nanowire Nominal Radius (rNW)
17.5 nm
Deposition Angle Alpha
85 degrees
Adatom Volume (VA)
1.58 nm3
Substrate Temperature
513 K
Si Substrate Hopping Barrier (ESi)
0.3 eV
ITO Hopping Barrier (EITO)
0.6 eV
Growth Cone Angle (Δθ1/2)
45 degrees
Vapour Flux Half Angle (Δα1/2)
1.2 degrees
1
Figure S1: Distribution of trunk orientation in a unidirectional and isotropic film. The histograms show a
best fit to a Gaussian function for the angles obtained from each film. The trunk orientation appears to be
confined to polar angles less than 45 degrees. The random azimuthal orientation of trunks will tend to
narrow this distribution as trunk angles are projected on to the SEM imaging plane, and the effects of
competitive growth will also be influencing this distribution.
2
Figure S2: Threshold sensitivity for FIB/SEM analysis results for trunk density and planar area density
based on a threshold value between 0 and 255. The number density is relatively insensitive to large
changes in threshold, but the planar area density is very sensitive, and must be treated with care.
Figure S3: Manual measurement of trunk density compared with the results of the automated process
Figure S4: Trunk orientation histograms as a function of azimuth (top, middle) and scatter plots showing
height-azimuth doublets (bottom; each point is a single trunk) for the (a) unidirectional, (b) periodic, (c)
helical and (d) isotropic structures. The top row is histograms for the experimental structure’s trunk
orientation from Ref. 17, while the middle row is the analogous histograms from the simulated structures.
The bottom row shows competitive growth effects for the unidirectional and periodic nanowires, where
trunks oriented at a 45 degree angle from vapour flux (restricted to azimuths of 0 degrees and 180
degrees) grow taller. However, in the helical and isotropic cases which have no azimuthal vapour flux
restriction, no competitive growth effects are observed.
Figure S5: Sensitivity plot for material flux rate
Figure S6: Sensitivity plot for silicon substrate hopping barrier energy
Figure S7: Sensitivity plot for ITO hopping barrier energy
Figure S8: Sensitivity plot for ITO nanowire trunk radius
Figure S9: Sensitivity plot for flux collimation; a larger angle means less collimated
Figure S10: Sensitivity plot periodic boundary side length
Figure S11: Sensitivity plot for branch to branch energy barrier for mass transport processes
Figure S12: Sensitivity plot for branch to substrate energy barrier
Figure S13: Sensitivity plot for adatom volume
Figure S14: Sensitivity plot for growth angle cone
Figure S15: Sensitivity plot for changes in silicon substrate hopping barrier energy at small heights
Description of Movies
All four movies are for the periodic VLS-GLAD film, produced with alternating, discrete azimuthal vapour
flux positions during film growth.
FIB Reconstruction:
File: taschuk-2013-engineered-branch-placement-supplemental-movie-fib-reconstruction.mpg
Figure M1: This movie shows the reconstructed volume as a three dimensional volume. The threshold is
changed to take advantage of the contrast between the nanotrees and the infilled photoresist. False
coloring is applied (pink corresponds to higher intensity in original SEMs), and the film is rotated into a
plan view. The top surface of the rendered volume is decreased towards the substrate, showing the
internal structure changing and increasing in areal number density as the substrate is approached
(enhanced online)
File: taschuk-2013-engineered-branch-placement-supplemental-movie-fib-plan-section.mpg
Figure M2: This movie shows the same volume held at an oblique angle. The top surface of the
rendered volume is moved down through the film towards the substrate, showing the branches and
increasing density (enhanced online).
File: taschuk-2013-engineered-branch-placement-supplemental-movie-fib-cross-section.mpg
Figure M3: This movie shows the same volume, but with the front surface of the rendered volume
moved through the film. This view shows the structures at all heights, with column extinction and
branch structures visible. At the start of the film, the highly porous nature of the VLS-GLAD structures is
clearly visible (enhanced online).
Simulation
File: taschuk-2013-engineered-branch-placement-supplemental-movie-simulation.mpg
Figure M4: This movie is output from the simulator for the same class of film. The white square on the
left at the start of the film is a marker for the incoming vapour flux. The nanotree branches begin by
growing to the left, switching to the right once the vapour flux switches sides. The periodic branch
growth direction is clearly visible in several of the simulated structures (enhanced online).