A Strategy for the Maximum Fluorescence Enhancement Based on Tetrahedral Amorphous Carbon-Coated Metal Substrates

Recently metal-enhanced fluorescence (MEF) has been reported. However, the bare metal would always quench the emission if the separation between the fluorophore and metal is very close. In order to get maximum fluorescence enhancement, the key point is to allow the maximum local electric field of plasmonic substrate at the interface to be used, and at the same time the quenching should be efficiently reduced. We demonstrate for the first time that by coating with an ultrathin dielectric layer of tetrahedral amorphous carbon (ta-C), an optically transparent material in the visible, the metal nanostructures can be used to realize the maximum enhancement in MEF. This result can be attributed to the well control of two competitive mechanisms of the local field enhancement and quenching. It is found that a 10 angstrom ta-C layer can modify plasmon resonance of the metal to produce a higher local electric field than uncoated metal and can also reduce the quenching. The coated metal substrate has higher mechanical stability, chemical inertness, and technological compliance and may be useful, for example, to enhance TiO2 photocatalysis and solar-cell efficiency and to design the surface plasmon laser with fluorophores as gains by the surface plasmons.