Plasmonic sensors provide a means of detecting chemical and biological species through the observation of spectral features by measurement techniques such as surface enhanced Raman spectroscopy (SERS) or surface plasmon resonance (SPR). In order to develop a full-scale plasmonic sensor, periodic nanostructures must be replicated over large-area surfaces, such as six-inch silicon wafers. By incorporating hybrid top-down and bottom-up synthesis, a versatile approach has been demonstrated for fabricating large-area plasmonic sensors. The ability to fine tune nanostructure features over large areas renders this technique highly adaptable, thereby opening up new opportunities for plasmonic sensor applications. |
Reviewed by Jeff Morse, PhD, National Nanomanufacturing Network
- Dhawan JW, Du Y, Batchelor D, Wang HN, Leonard D, Misra V, Ozturk M, Vo-Dinh T. 2011. Hybrid Top-Down and Bottom-Up Fabrication Approach for Wafer-Scale Plasmonic Nanoplatforms. Small7(6):727-731. DOI: 10.1002/smll.201002186.
Plasmonic sensors provide a means of detecting chemical and biological species through the observation of spectral features by measurement techniques such as surface enhanced Raman spectroscopy (SERS) or surface plasmon resonance (SPR). Plasmonically active SERS substrates, such as metallic gratings or periodic metal nanowire arrays, have sub-wavelength features that enable direct coupling of normally incident electromagnetic (EM) radiation to surface plasmons. The high detection sensitivity of these methods is facilitated by EM field enhancements in the vicinity of the metallic nanostructures. Field enhancements can be achieved by controlling the spacing between nanostructures as well as the features along the length of individual nanostructures. In order to develop a full-scale plasmonic sensor, periodic nanostructures must be replicated over large-area surfaces, such as six-inch silicon wafers. One of the key challenges here is developing a cost effective approach to fabricate nanoscale structures over macroscale length scales with adequate uniformity and fidelity. Furthermore, process approaches must enable fine-tuning of the nanostructures in order to optimize field enhancement and reproducibility for the final sensor device configuration.
Finally, the DNW structures are coated with a 20-100 nm film of plasmonically active metal, such as gold or silver, by sputter deposition or electron beam evaporation. Utilizing the precise control of the crystal growth process, spacings between the DNW structures of <10 nm have been observed. Further control of nanowire spacing is facilitated by the use of conformal ALD coatings applied after the crystal growth step. The rate limited growth provided by ALD enables highly uniform, precise control of the DNW spacing in order to optimize the plasmonic structures for a given application. Experimental and modeled performance of the resulting plasmonic sensor exhibited both high sensitivity and specificity. By incorporating hybrid top-down and bottom-up synthesis, a versatile approach has been demonstrated for fabricating large-area plasmonic sensors. The ability to fine tune nanostructure features over large areas renders this approach highly adaptable, thereby opening up new opportunities for plasmonic sensor applications.
Image reproduced with permission from Dhawan JW, et. al. 2011. Small7(6):727-731. DOI: 10.1002/smll.201002186.
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