Principle Scientist(s): Hyunmin Kim (Potma Group) and David Taggart
Hyunmin Kim, David Taggart, Chengxiang Xiang, Reginald M. Penner and Eric O. Potma*, Spatial Control of Coherent Anti-Stokes Emission with Height-Modulated Gold Zig-zag Nanowires, Nano Letters 8 (2008) 2373. pdf.
Surface-enhanced coherent anti-Stokes Raman scattering (SE-CARS) is a nonlinear optical method that offers a route for exploring the coherent vibrational response of molecules. In order to engender a surface-enhancement, the molecules probed by SE-CARS must be located within the immediate vicinity of a metal "amplifier" structure that possesses a plasmon response tuned to the excitation of the molecular resonances of interest. How should these structures be designed? What background will metal structures contribute to the molecular spectra obtained using this technique?
In this paper, we support the efforts of the Potma group to elucidate these issues with regard to one particular metal support system - a linear gold nanowire that has a rectangual cross-section and millimeter-scale length.
Our role has been to prepare gold nanowires that are modulated in height in order that the influence of wire cross-section can be quantitatively explored. David Taggart in our lab developed a procedure (Fig. 1) for fabricating height-modulated gold nanowires using our lithographically patterned nanowire electrodeposition (LPNE) method.
Figure 1. Schematic diagram depicting the process flow for the preparation of height modulated gold nanowires using a varient of LPNE.
Figure 2. (a) Dark-field transmission image of conventional flat gold nanowires. (b) SEM image of conventional nanowires and cross-sectional profile (c) as measured with AFM. (d) Dark-field transmission image of wire Type II, along with SEM image (e) and AFM cross-sectional profile (f).
In the LPNE method, nanowires of programmable height are obtained by depositing a nickel sacrifical electrode that has the desired height profile using through-mask vapor deposition. This approach should work for the fabrication of nanowires having any height program that consists of a series of discrete, flat sections, but it will not enable wires of smoothly varying height to be obtained. The capability of LPNE to produce height-modulated nanowires is unique, as far as we know.
Read more about the spectroscopy and conclusions in our manuscript.
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