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seeds and, therefore, influence the relative proportions of different Ag
seeds. For example, Cl– is a stronger ligand, the Cl–/O 2 pair dissolve
both multiply twinned and singly twinned seeds. Close monitoring of
the reaction process by UV–Visible spectroscopy and electron micros
copy revealed that twinned particles are formed first but later dis
solved by oxidative etching. Thus, after a certain reaction time,
singlecrystal seeds with a spherical profile predominate, and continue
growing into nanocubes with all facets being {100}.72,92 Meanwhile,
Br – is slightly weaker than Cl–, the Br – /O 2 pair will only dissolve mul
tiply twinned seeds, resulting in a right bipyramids dominated
solution.
3.2. Physical Methods
The major challenge of wetsynthesis lies in controlling the position
and orientation of nanoparticles with sufficiently high resolution
when nanoparticles placed on substrates. Unlike chemical synthesis,
lithography, deposition, and other forms of nanofabrication offer pre
cise control over deliberately varied shapes and configurations and
therefore open avenues to both fundamental investigations and appli
cations.^93 Conventional lithographic techniques such as electron beam
lithography (EBL) or focused ion beam lithography (FIB) utilize
polymeric resists to fabricate masks for deposition or etching of metal
with high resolution.94,95 Take EBL for example, a focused electron
beam is scanned over a substrate coated with a thin layer of resist
(EBL usually used PMMA as resist), exposing specific regions accord
ing to a programmed pattern.96,97 Halas and Nordlander et al. utilize
EBL to organize nanostructures with precise size and shape and to
generate complex optical phenomenon like Fano resonance.98–101
4. Technic to Detect Localized Surface
Plasmon Resonance
As a typical plasmon spectroscopy technique, darkfield microscopy
(DFM) coupled with spectrometer was developed for the observation
of metal nanoparticles. The primary advantage of this technique is
