Photoactive Self-Assembled Monolayers

Figure 10. A self-assembled monolayer comprised of terminal porphyrins, intermediate ferrocences, and surface thiols attached on gold surface. The sold line is the photoaction spectrum, the dashed line is the absorption spectrum. Panels a) and b) show the proposed mechanisms, and c) provides the structure of the thiol ferrocene-porphyrin complex.

Delarache, E., Sundarababu, G. Biebuyck, H., Michel, B., Gerber, C., Sigrist, H., Wolf, H., Ringsdorf, H., Xanthopoulos, N., Mathieu, H. J. (1996). Immobilization of antibodies on a photoactive self-assembled monolayer on gold, Langmuir, 12 1997. 

Since this initial work, many developments of the technique have occurred. SNOM has subsequently been used to expose films of conventional photoresist to UV light emanating from the SNOM probe and to write patterns with line widths well beyond the limitations of diffraction [65]. Despite this success, the key to realising SNOM s full potential in photolithography applications is to minimise the thickness of the photoresist films. This point is critical since the evanescent electric field decays very rapidly with increasing distance from the probe s aperture. As such, the highest resolutions are achieved when self-assembled monolayers (SAMs) of photoactive medium are utilised— rather than standard polymer resists. 

There is a special type of photoelectrochemical devices based on donor/acceptor dyads and triads self-assembled on the metal (gold) or metal oxide (TTO and FTO) electrodes. A multistep photoinduced electron transfer occurring in such devices resembles in some way a natural photosynthetic process. The power conversion efficiencies of such devices are negligibly low because the monolayer of the photoactive material does not absorb much light. However, internal quantum efficiencies (IQEs) of such devices approach 80-90% in many cases. 

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