Chemistry Reference
In-Depth Information
Fig. 14
Left:
MALDI-TOF mass spectra (positive mode) of Au
38-
x
Ag
x
(SR)
24
nanomolecules for
Au:Ag precursor ratios of 1:0 (
black
), 1:0.05 (
red
), 1:0.10 (
blue
), 1:0.15 (
olive
), 1:0.20 (
orange
),
1:0.30 (
purple
), 1:0.35 (
dark yellow
), and 1:0.40 (
brown
) in the starting material. The mass
difference between the peaks in nanoalloys corresponds to the Au (196.97 Da) and Ag
(107.87 Da) mass difference,
Δ
m ¼
89.10 Da. The number of Au and Ag atoms of most dominant
peak is denoted above each distribution of peaks.
Right
: UV-visible spectra of Au
38-
x
Ag
x
(SR)
24
nanomolecules in toluene with Au:Ag precursor ratios of 1:0 (
black
), 1:0.05 (
red
), 1:0.10 (
blue
),
1:0.15 (
olive
), 1:0.20 (
orange
), and 1:0.30 (
purple
) in the starting material. Reproduced from [
69
]
with permission from The Royal Society of Chemistry
was increased in the initial synthesis, the number of silver atoms incorporated also
increased and started to plateau at 1:0.20 Au:Ag mole ratio. The average and
maximum number of silver atoms in 1:0.30 mole ratios remain at ~6 and 10, respec-
tively. Increasing the Au:Ag incoming mole ratio to 1:0.35 and 1:0.40 still forms
Au
38-
x
Ag
x
(SR)
24
, observed at early stages of etching, but decomposes with time
indicating the instability towards further silver incorporations.
Figure
14
(right) shows the modulation of optical properties of Au
38
(SR)
24
upon
silver atom incorporation. Au
38
(SR)
24
nanomolecules have distinct bands at 1,050,
750, 630, and 480 nm. Silver incorporation into Au
38
(SR)
24
leads to blue shift in
UV-visible spectrum. The band at 1,050 nm present in Au
38
(SR)
24
diminishes with
minimum silver incorporation (in 1:0.05, Au:Ag incoming molar ratio) and grad-
ually disappears with increasing number of Ag atoms. This disappearance implies
that the transitions at 1,050 and 675 nm are originating from pure Au
38
(SR)
24
and
thus silver may not facilitate the low energy transitions in Au
23-
x
Ag
x
core. Further-
more, the electronic transitions occurring at 480 and 630 nm seems to be broaden
upon silver incorporation. In conclusion,
the optical features of Au
38
(SR)
24
