It is essential to immobilize gold nanoparticles (AuNPs)
firmly
onto a certain substrate in a closely packed manner to apply plasmonic
functions of AuNP in photonic/electronic devices. AuNP-Si systems
are of particular interest for the integration of plasmonics to semiconductor
electronics. Here we report on the arrangement of AuNPs into a 2-D
array that was covalently bonded to a Si substrate without surface
oxide. This process was achieved by simply irradiating visible light
to a hydogen-terminated Si substrate immersed in a solution of AuNPs
covered with a self-assembled monolayer (SAM) of 11-mercaptoundecene
(MUD). These MUD-AuNPs were attached to the substrate by forming Si–C
bonds as a result of the photochemical reaction between Si–H
groups on the substrate and vinyl groups of the MUD-SAMs. The reaction
proceeded most effectively at a wavelength band around 520 nm adjusted
to the plasmonic resonance peak of the MUD-AuNPs(20 nm in diameter)/toluene
solution centered at 535 nm, demonstrating that the photochemical
reaction was assisted by localized surface plasmon, which allowed
the AuNPs to be photon collectors.
Ordered and high-density AuNP structures were successfully immobilized on Si(111) substrates via a photochemical reaction, using the immersion method and the LB method, respectively. Because of partial oxidation of the substrate, island-like structures were formed using the immersion method. While that in the LB method, because AuNPs were immobilized in nitrogen atmosphere and not in liquid solution, oxidation was minimized thus a more compact structure was obtained. Furthermore, the plasmonic properties of the AuNP structure were found to be tunable by controlling the particle density and the interparticle distance.
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