Hetero nano-interface

Keywords Hetero nano-interface Localized surface plasmon Ordered array structure Organic core/shell type hybridized nanocrystals Reprecipitation method... 

Well now, the proposed co-reprecipitation method [45] and visible-light-driven photocatalytic reduction method [53] have been established for the purpose of these kinds of core/shell type hybridized NCs composed of PDA NC and noble metal NP, and both processes have been further improved to extend to another type hybridized NCs, respectively [50, 54], Typical core/shell type hybridized NPs were first reported by Halas and Caruso research groups [70, 71, 73, 84, 87]. A great number of fine gold (Au) NPs as Au shell were deposited densely on the surface of silica NPs, which are spherical and uniform size. The LSP speetra were continuously blue-shifted with increasing the thickness of Au shell, and some optoelectronic applications have been now presented such as a substrate for surface enhanced Raman spectrum (SERS) measurement, chemical- and bio-sensors, etc. Silica NPs, however, are core as a template to fabricate core/sheU type hybridized nanostructure, and there is no something like optoelectronic interaction through core/shell hetero nano-interface in this case. 

This characteristic LSP damping without changing resonance frequency was qualitatively speculated to occur by the following experimental conditions at that time [45] (1) the energy level of LSP of metal core is near the exciton level (or between band gap) of PDA shell, (2) metal core should be in direct contact with PDA shell at hetero nano-interface in hybridized NCs, and (3) the core/shell volume ratio should also be optimized experimentally. 

One can imagine from these experimental results that PDA chains inside poly(DCHD)shell may contact with some points on the surface of Ag core [47,49]. These contact points at hetero nano-interface might be anchors to disturb and depress the plasma oscillation, and then diminish the mean-free-path of conduction free electrons in VB of Ag core. In other words, the LSP of Ag core would damp simply without changing the resonance frequency, owing to the reduction of electronic conductive domain induced by locally and strongly physicochemical interaction at the core/shell interface in the hybridized NCs [103,105]. 

In addition, there are some advantageous factors in surface-specific reduction of Ag+ on PDA core. The first is the electrostatic adsorption between [Ag(NH3)2] and PDA-core having negative -potential (ca. -40mV) [14], the second is the self-catalytic property [118] of already-deposited Ag NPs to reduce [Ag (NH3)2, and the final is the suppression of electron-hole recombination, because of rapid carrier separation at hetero nano-interface. 

Electron and excitation transfer in hetero-supramolecular assemblies and at molecule-nano-particle interfaces, P. Piotrowiak, K. Deshayes, Z. S. Romanova, C. Pagba, S. Hore, G. Zordan, 1. Place, A. Farran, Pure Appl. Chem., 2003, 75, 1061-1068. 

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