לוח שנה משולב

Thirty-five years of SERS
Martin Moskovits
Department of Chemistry and Biochemistry
University of California, Santa Barbara
Scientists do not read the scientific literature. This is because, time, unlike other currencies that may be plentiful for awhile, then scarce, then plentiful again, time diminished monotonically, so that the triage one needs to make for professional success in science is simple: one either reads them, or writes them. SERS, whose inordinate enhancement was discovered by Jeanmaire and Van Duyne in 1977, has had a particularly rocky time in achieving mechanistic steady state. This is not due to the absence of a working model that was both explicative and predictive, and therefore useful in constructing new experiments. Such a model was already in place in the 1980s and supported by some excellent and sophisticated theory. (I mention the work of Metiu and Nitzan, as examples.) That model is the plasmonic model, which not only guided most of the successful experiments in SERS to date, but begat the field of Plasmonics in the bargain.
Rather, the notion that SERS lacked a sound fundamental understanding was due to an inexplicable hostility to the plasmonic model of SERS by a few prominent workers, together with a reinforcement of the rejection of the plasmonic model following the announcement of single-molecule SERS (SM-SERS), since people (forgetting that Aravind, Nitzan and Metiu in 1981 predicted a 1010 enhancement factor in the hot spot between two, almost touching silver nanoparticles) could not fathom how so great an enhancement could arise from the concentration of electromagnetic fields as to permit single-molecule Raman detection. Following the announcement of SM-SERS, and stimulated by initiatives in nanotechnology, many entered the field of SERS. The fact that most SERS experiments involve rather simple chemistry, but somewhat subtle physics, did not help. It merely granted facile entry into the field, and allowed some to generate a great deal of interesting experimental observations and publish them with only a passing understanding of the underlying mechanism.
By 1985, I believe most of us understood the way SERS worked rather well. Certainly well enough for me to have been able to state (based on the aggregate work of some two a dozen major contributors to SERS at that time) “… the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparation required to produce the effect …is now understood to be necessary as a means for producing surfaces with appropriate
electromagnetic resonances that may couple electromagnetic fields either by generating rough films or by placing small metal particles in close proximity to one another.”
Still, even today, the mention of SERS still engenders comments such as “a phenomenon whose mechanism is not fully understood”, stated with the implication being that (unlike most other fields of science about which one can make that statement in the sense that one can always understand more) SERS is unusual in that after 35 years of work, people still apparently do random experiments wholly unguided by a successful theory. To be sure, the technology needed to nano-engineer plasmonic substrates, the computer power and the theories and codes needed to make regular nanostructures and carry out meaningful computations has improved enormously in the intervening 35 years. So that whereas 30 years ago one might have excused such a statement. Today the notion that SERS lacks a fundamental understanding is ludicrous.
Of course, the theory of SERS is incomplete since a fully quantum theory of the effect is only partially developed.
I have had the good fortune of witnessing the development of SERS from its inception. The talk will focus on some of the key people, experiments, insights and ideas, as well as some of the Quixotic individuals and notions that permeated SERS over the years, and how they led to our current understanding of SERS, and to our celebrating Chanukah at the Dwek School on Nanoplasmonics, at the Weizmann Institute in the year 5773.

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