You were asked to construct a nanostructure consisting of two 100 nm diameter go

Question

You were asked to construct a nanostructure consisting of two 100 nm diameter gold nano-spheres suspended in water. Initially, the two nano-spheres can keep an arbitrary distance from each other. Upon application of a chemical or physical signal, however, they must form a dumbbell-like dimer structure with a 68 nm separation between the nano-spheres. Explain (a) a possible steps to fabricate such a nanostructure and (b) a possible scheme for such an active control on particle-to-particle separation.(c) If the gold nano-sphere dimer with 68 nm separation is capable of enhancing the electric field in its ambience by a factor of 200, how much enhancement can you expect when it is used as the site for SERS (surface-enhanced Raman scattering)?

Explanation / Answer

(A) There's a technique gives one layer of nanostructures from one unit process including exposure, development, deposition and lift-off steps, but we can also fabricate three-dimensional (3D) nanostructures by repeating this unit process on the same position of the substrate, i.e. stacking the individual two-dimensional (2D) layers.

To build elaborate 3D nanostructures using EBL overlays, reducing the alignment errors is certainly the most critical factor.

(B) Electron beam lithography is the best technique for actiive controlon particle-to-particle separation. Widely used cross-type and circle-type alignment marks can easily lose their alignment spot due to other fabrication steps such as photoresist development and pattern transfer, and thus EBL is considered as one of the gine methods.

(c) In surface enhanced Raman scattering, the surface to volume ratio is very high for nanopartcles. So, if electric field is enhanced by a factor of 200, more electrons will be forced to remain presenrt on surface, however a portion of eletric energy is used to overcome the threshold energies. So, there will be an enhancement of about 100 to 150 times when itwill be used as a site for SERS.

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