the cyanide concentration was further increased to 2.5 Â 10
À3 M, this band completely disappeared within 8 min.
Figure 9.10(a) shows the TEM of 2.5 G 0.5 aspect ratio spheroids (with 17 nm
short axis) before CN
À addition. The solution also contained a significant amount
(@40%) of spheres of similar size (@20–25 nm). Those spheres contributed only a
single absorbance at 526 nm, as they do not have a longitudinal plasmon band.
Figure 9.10(b) shows the TEM corresponding to sets e of Figure 9.9. In set e only
spheres in the size range 10–25 nm were present in the TEM. In set d (TEM not
shown) the percentage of spheroids decreased from 60% to 40%, and size measurement of the spheroids showed that the length decreased but the width remained unchanged. This leads to a reduced average aspect ratio of spheroids from
2.5 G 0.5 to 2.0 G 0.5. In contrast, the spheres present in the solution did not
change in size significantly. In sets f only spheres of diameter 2–5 nm (@90%) and
5–15 nm (10%) were observed. In set g no particles were found in the TEM.
Absorbance vs. time (Figure 9.11) (at both the longitudinal and transverse wavelength bands for the spheroids) and successive UV–visible spectra (Figure 9.12)
were measured during the dissolution process of the gold spheroids. Figures 9.11
and 9.12 corresponds to set f. The rate of decrease in absorbance is faster for the
longitudinal band than the transverse band (Figure 9.11). In the intermediate
stage, the longitudinal plasmon band gradually blue shifts with a simultaneous
decrease in intensity and finally mixes into the transverse band (Figure 9.12).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
250
350
450
550
650
750
850
Wavelength (nm)
Absorbance
g
f
e
d
c
b a
Fig. 9.9. UV–visible spectra of 2.5 G 0.5
aspect ratio gold spheroids with 17 nm short
axis (2.5 Â 10
À4 M in terms of gold) after 1 h
of the addition of various amounts of cyanide
solution. a: 0.0 M, b: 10
À5 M, c: 10
À4 M, d:
2.5 Â 10
À4 M, e: 5 Â 10
À4 M, f: 10
À3 M, g:
2.5 Â 10
À3 M sodium cyanide. Reprinted with
permission from [62]. Copyright (2002)
American Chemical Society.
9 Synthesis, Assembly and Reactivity of Metallic Nanorods
300
À3 M, this band completely disappeared within 8 min.
Figure 9.10(a) shows the TEM of 2.5 G 0.5 aspect ratio spheroids (with 17 nm
short axis) before CN
À addition. The solution also contained a significant amount
(@40%) of spheres of similar size (@20–25 nm). Those spheres contributed only a
single absorbance at 526 nm, as they do not have a longitudinal plasmon band.
Figure 9.10(b) shows the TEM corresponding to sets e of Figure 9.9. In set e only
spheres in the size range 10–25 nm were present in the TEM. In set d (TEM not
shown) the percentage of spheroids decreased from 60% to 40%, and size measurement of the spheroids showed that the length decreased but the width remained unchanged. This leads to a reduced average aspect ratio of spheroids from
2.5 G 0.5 to 2.0 G 0.5. In contrast, the spheres present in the solution did not
change in size significantly. In sets f only spheres of diameter 2–5 nm (@90%) and
5–15 nm (10%) were observed. In set g no particles were found in the TEM.
Absorbance vs. time (Figure 9.11) (at both the longitudinal and transverse wavelength bands for the spheroids) and successive UV–visible spectra (Figure 9.12)
were measured during the dissolution process of the gold spheroids. Figures 9.11
and 9.12 corresponds to set f. The rate of decrease in absorbance is faster for the
longitudinal band than the transverse band (Figure 9.11). In the intermediate
stage, the longitudinal plasmon band gradually blue shifts with a simultaneous
decrease in intensity and finally mixes into the transverse band (Figure 9.12).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
250
350
450
550
650
750
850
Wavelength (nm)
Absorbance
g
f
e
d
c
b a
Fig. 9.9. UV–visible spectra of 2.5 G 0.5
aspect ratio gold spheroids with 17 nm short
axis (2.5 Â 10
À4 M in terms of gold) after 1 h
of the addition of various amounts of cyanide
solution. a: 0.0 M, b: 10
À5 M, c: 10
À4 M, d:
2.5 Â 10
À4 M, e: 5 Â 10
À4 M, f: 10
À3 M, g:
2.5 Â 10
À3 M sodium cyanide. Reprinted with
permission from [62]. Copyright (2002)
American Chemical Society.
9 Synthesis, Assembly and Reactivity of Metallic Nanorods
300