Chapter 4 Properties of nanomaterials
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1- Size<br />
The op;cal proper;es <strong>of</strong> large and small nanopar;cles are markedly different.<br />
Kreibig and Vollmer define two types <strong>of</strong> size effects: extrinsic and intrinsic . The<br />
threshold for the two regimes occurs for diameters <strong>of</strong> around 10 nm in the case <strong>of</strong><br />
Au nanopar;cles.<br />
The op;cal proper;es <strong>of</strong> nanopar;cles with diameters above the threshold are<br />
dominated by extrinsic effects, which are related to the diameter and the bulk<br />
dielectric func;on <strong>of</strong> the metal. A red-shiving and broadening <strong>of</strong> the resonance peak<br />
is seen for increasing radius, due to retarda;on effects.<br />
For nanopar;cles with diameters below the threshold several special considera;ons<br />
must be made due to intrinsic effects. This size range is clearly within the quasi-sta;c<br />
regime, and so electrodynamics effects such as retarda;on do not play a role in the<br />
op;cal proper;es. However, surface scatering <strong>of</strong> electrons occurs due to the<br />
par;cle dimensions being smaller than the mean free path, leading to damping <strong>of</strong><br />
the plasmon oscilla;on and a resul;ng atenua;on and broadening <strong>of</strong> the resonance<br />
peak.
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