It is well-known that physical properties of matter can be either extensive or intensive, i.e. dependent or independent on the amount of material in a particular system. However, it is up until recent times, that progress in scientific instrumentation and analytical techniques has made it possible to study matter at nanoscales. As a result of this, extensive research and efforts have been focused on unveiling the hidden properties of materials that become only accessible at nanoscales, understanding their emerging mechanisms and developing far-reaching technological applications.
The intriguing optical properties exhibited by metal nanoparticles (1 – 100 nm) are a good example of this. Such properties are linked to the phenomenon known as surface plasmon resonance (SPR). When such nanoparticles are stimulated with light a resonant oscillation of electron in the conduction band is induced, and as a result, some of their properties such as absorption and scattering are enhanced. This has very promising application in diverse field of science and technology including optoelectronics and biomedicine. In addition, it has been found that the interaction of metal nanoparticles with light largely depends on their morphology and size as well as the dielectric environment. The plasmonic properties of the metal nanoparticles can be tuned by varying their morphology. For instance, by inducing the formation of interconnected porosity inside metal nanoparticles (i.e. increasing surfacevolume ratio), the emerging of new surface and optical properties can be controlled. Such applications require that the porous structure is stable at high temperatures. A way to prevent thermal degradation is by using metal oxides such as SiO2 or TiO2 as passivation.
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SEM image to show the morphology of Au nanoparticles
Gold nanoparticles are a typical example in which the phenomenon of SPR appears. In this application example, Au/Ag alloy nanoparticles on a Si substrate with SiO2 as passivation is presented.
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