4. Methods for Yield Measurements
• 3 SEM photos taken at x 10k zoom for each
nanowire pad.
• Pads P360, D1 – D5 and D1, P360 – P1000
were imaged.
• Number of knocked-over or otherwise
incomplete nanowires counted manually and
used to calculate the fractional yield.
18. Error in Yield Measurements
• The error bars in the following graphs come from
two sources of error (combined in quadrature):
• 1. Yield variation between 3 images for the same
pad. The standard deviation was calculated and
used as an estimate of this error.
• 2. My own ability to replicate yield counting. I
counted the yield for the same pad twice and
concluded an error of about 1 % from the
variation.
22. Comments on Yield Trends
• The yield increases with increasing dose for
1769 (Low As) and 1770 (No As), and reaches
a maximum of approximately 85%. Further
increasing the dose yields no benefit.
• For 1769 (Low As) and 1770 (No As), the yield
of P1000 is significantly lower than that of
P360.
25. Methods for Diameter Measurements
• SEM photos taken at x 40k zoom, 15 degree tilt.
• Pads P360, D1 – D5 and D1, P360 – P1000 were
imaged.
• The diameters of 5 nanowires at the base and tip
were measured with ImageJ for each pad.
• “Base” means the lowest point at which the
nanowire emerges from the hole (NOT the
diameter of the blob left in the hole upon which
the nanowire grows).
30. Error in Diameter Measurements
• Error bars come from two sources of error
(combined in quadrature):
• 1. Variation between nanowires. The standard
deviation of the mean was taken as a measure of
this error.
• 2. My own ability to replicate measurements. I
measured the diameter of a single nanowire
multiple times and took the standard deviation of
these values as a measure of this error.
38. Comments on Diameter Trends
• The diameter increases with increasing dose.
• The diameter increases with increasing pitch
for 1769 (Low As) and 1770 (No As).
• The tip diameter is always greater than the
base diameter
• The base diameter is greatest for 1768 (High
As).
• The tip diameter is greatest for 1770 (No As)
due to the gallium droplet.
43. Observations on 1768 Morphology
• The nanowires are mostly uniform in diameter
along their length.
• The nanowires stand straight up. From the
side view, there is little lean to the left or the
right. From the top-down view, the nanowires
appear as circles.
47. Observations on 1769 Morphology
• There is significant buildup at the base of the
nanowire in the hole.
• The nanowires do not grow straight up. There
is significant lean. From the side view, the
nanowires lean to the left or right. From the
top-down view, both the base and the tip of
each nanowire is visible, i.e. the nanowire has
grown at an angle to the vertical.
51. Observations on 1770 Morphology
• The gallium droplet sits atop each nanowire,
much thicker than the diameter along the rest
of nanowire.
• The nanowires have grown at an angle, as one
can see from the side view and the top-down
view.
53. Other Comments
• For all samples, for larger D, the nanowire
array appears less straight when viewed from
above. This can be seen in the next slide.
• Equivalently, the nanowires favour growth at
the edge of the hole. This is very pronounced
for D5 compared to D1.
