Silver nanoparticles (AgNPs) with diameters in the range
40–80
nm have been synthesized by the hydrothermal route and the low temperature
heating–stirring method. The influences of reaction time, reactant
concentration, and temperature on the AgNP growth have been systemically
studied. Experimental surface enhanced Raman scattering (SERS) results
show that AgNPs prepared under different temperature and time exhibit
a large difference in enhanced SERS signals for rhodamine 6G (10–6 M). Ag@C core–shell NPs have been proved to
be formed by using the above two methods, and the carbon shell thickness
is gradually increased with increasing reaction time and temperature.
It is found that Ag@C NPs with a thick shell (more than 3 nm) have
a very low SERS activity, while those with an ultrathin film (less
than 1 nm) have a high SERS activity, indicating that carbon shell
thickness is a key factor affecting the SERS, which has also been
evaluated by finite-difference time-domain simulation. The existence
of an ultrathin carbon shell around the AgNP can decrease its surface
electric property; then Ag@C NP aggregates are easily formed which
may produce the higher hot spots than the bare AgNPs. In addition,
this kind of Ag@C NPs exhibits a long SERS-active shelf life (6 months),
because the carbon shell can protect AgNPs from oxidation.
The surface plasmon resonances of silver nanoshell particles are studied by Green’s function. The nanoshell system of plasmon resonances results from the coupling of the inner and outer shell surface plasmon. The shift of the nanoshell plasmon resonances wavelength is plotted against with different dielectric environments, several different dielectric cores, the ratio of the inner and outer radius, and also its assemblies. The results show that a red- and blue-shifted localized surface plasmon can be tuned over an extended wavelength range by varying dielectric environments, the dielectric constants and the radius of nanoshell core respectively. In addition, the separation distances, the distribution of electrical field intensity, the incident directions and its polarizations are also investigated. The study is useful to broaden the application scopes of Raman spectroscopy and nano-optics.
Silver nanoparticle (AgNP) film is a kind of useful material in biochemical and biomedical fields as it can be used as a sensor based on its surface plasmon resonance for surface enhanced Raman scattering (SERS) analysis. In this work, a uniform AgNP film with controlled nanoparticle size, shape, and density have been prepared on TiO 2 film in a AgNO 3 solution by photocatalysis reduction method. The influences of TiO 2 film thickness and morphology on the AgNP's growth have been systemically studied. It is found that a thicker TiO 2 film with nanocrystalline morphology leads to a higher AgNP's growth rate, while a thinner TiO 2 film with membrane morphology leads to a lower AgNP's growth rate. Experimental SERS results show that the AgNP film prepared with different TiO 2 films and ultraviolet light irradiation time exhibit different SERS signals of rhodamine 6G (10 −6 M). Atomic force microscope and scanning electron microscope analysis reveal that the size effect is a key factor affecting the SERS of our prepared AgNP films, which has also been evaluated by finitedifference time-domain simulation. It is found that the larger the average AgNP's size (≤λ/4) and roughness, the higher the Raman enhancement. The SERS mapping images exhibit a good uniform Raman enhanced results in our prepared TiO 2catalyzed AgNP film with a low relative standard deviation of approximately 10%.
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