Metal Nanostructures Synthesized by Photoexcitation
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The current interest in the structural control of metal and semiconductor materials in the nanoscale region has been rapidly promoted in terms of construction of ultrasensitive and low-energy-consumption devices. Recently developed nanodevice technologies using scanning probe microscopy have allowed us to construct ultrasmall structures on an atomic scale. However, this method is not adaptable to mass production because it is too slow, especially for sizes of more than a few nanometers. This situation, together with the limitation of the size control to about a hundred nanometers for conventional photolithographic techniques, clearly indicates that the creation of nanodevices sized between a few nanometers and tens of nanometers remains an undeveloped aspect of the present nanotechnology. Thus we should develop methods of effective and high-speed construction of desirable nanostructure in this size region.
To solve the problem, we have proposed the idea of applying localized photoexcitation at metal nanostructures for the structural controls. Generally, metal nanoparticles such as Au, Ag, and Cu show characteristic surface plasmon absorption in the visible–near-infrared wavelength region. The electric field induced by excited surface plasmons is highly localized, and the direction of its polarization can be controlled by changing the wavelength and polarization of illumination light. Thus if the localized field can be utilized to induce electrochemical reactions, such as metal dissolution and deposition, the effect can be applied to change and control the metal nanostructures.