IJVS Volume 4 Edition 2 - editorial

This edition has been edited by Professor ZQ Tian of the University of Xiamen in China. I have known Tian for many years – he and his lady wife Dr. Bing Wei Mao were research students at Southampton and I have always admired Tian’s poineering work on S.E.R.S.

This edition is a milestone for the Journal – it contains the most up-to-date accounts available anywhere on the SERS effect, its progress since its discovery, current thinking and its application. I recommend it to everyone interested in vibrational spectroscopy. If you are not particularly attracted by the field do read Tian’s first piece – it reviews the situation and is a ‘tour de force’.

Tian asked me to reminise on the discovery of SERS. It was a long time ago and only Jim McQuillan of the trio of folks involved are fully functional – Martin Fleischmann and I are at least partially retired. Anyway here goes – an entirely idiosyncratic account of the matter ...

Raman Spectroscopy at electrode – electrolyte interfaces

Back in years gone by, Martin Fleischmann who was Professor of Electrochemistry and I enjoyed regular brainstorming (no – not brainwashing!) sessions when we were both at Southampton. Crazy improbable ideas and waves of excitement ebbed and flowed and sometimes (rarely!?) a good idea materialised.

Back in 1972 we discussed and argued over the possibility of recording Raman spectra from an electrode surface. Problem, of course, is that the amount of material present is minimal.
So what system to use? My knowledge of electrochemistry just about includes the car battery, so I wasn’t much help until the mercury/calomel system was mentioned. My ears duly flapped because Calomel (Hg₂Cl₂) is nearly the strongest Raman scatterer known to man (C₆₀ is better!), Martin came up with the idea of generating a high area mercury surface – so we were hopefully ‘in business’.

The mercury layer – over a Pt foil – was made as tiny droplets so that the area was maximised. Martin’s skill in devising and Jim McQuillan’s in producing this electrode was the key. The surface was set at 45º inclination inside a glass cell and the laser beam came in from below and glanced along it. The Raman scatter was collected horizontally and hey presto included the characteristic Hg-Hg stretch at 168cm^-1. Lowering the electrode potential removed the band so it seemed to us, it must indeed be the surface layer. We then ran the bromide and oxide systems and found

So we were convinced that electrode electrolyte interfaces were accessible to Raman spectroscopy in situ[1] . This note seems to have been ignored by the community probably because it doesn’t have any pictures in it!!

Now as everyone knows – get a result – just one and apply for money leads to success. Get several results and the funding bodies tell you that you’ve done the job and don’t need any more cash. We had only 3 spectra …. And got the money!

It took ages to get the next data. I remember that nothing seemed to really work. High area surface treatments were devised and many, many electrolytes were scanned, all selected because they would give strong Raman bands, but spectra were few and far between.

The next success was pyridine over silver. Why this combination? Silver roughened nicely and Martin & Jim had sorted this out really well. My modest contribution was to suggest pyridine. Back in the late 60’s, I had started a lot of work on the Raman spectra of species adsorbed to catalyst surfaces (silica aluminas etc) and pyridine was used as a tell-tale molecule. Sorbed to an acidic oxide surface, the spectrum told us how the pyridine was reacting to Lewis or other acidic sites [2-4]. As you will see my folk were still playing around with pyridine in 1974. Thought – rumour tells us that pyridine has a nasty effect on the virility of young men – didn’t work in my case – I have 4 children!

Well, as we all know, the pyridine/silver system demonstrated massive enhancement of the Raman intensity, not that this was obvious to us at the time. We thought initially the surface of the silver might be covered with silver chloride and the pyridine was sorbed to it. Somehow the surface enhancement didn’t arise – not at first.

We regarded the pyridine silver system as ‘interesting’ but not crucial. Martin & Jim were electrochemists – they wanted results off Platinum and other transition metals. Jim left us after achieving some results off copper and returned to New Zealand, but it took almost three more years before Ralph Cooney arrived as a post-doc, and further results appeared. Progress in 1976/7 was rapid. After further developing their roughening techniques, the following systems gave spectra: Iodine/Platinum [5], Chloride/Lead [6], CNS^–/Ag [7], CO/Pt [8] and again more on Iodine over platinum [9]

As a Raman spectroscopist, I was a fish out of water! I still kept some work going on catalysts, my work on polymers was expanding fast, we had recorded Raman spectra of flames at about the time the whole electrochemical business started and I couldn’t see much of a future in it.

Further, my contribution was becoming minimal because my knowledge of electrochemistry still hadn’t progressed much beyond the car battery!

So – I dropped out and left it to Martin and an array of others. Oh well, I suppose you can’t be right all the time!

Acknowledgement

For a very long time the U.S. Navy Office of Naval Research provided us with financial support. The rate of funding was modest but it was steady and continuous. Good ideas would be tried because funds were available. We didn’t have to think of the idea, request the funds, wait for a response only to see some other idiot do the job while we were waiting! Good heartfelt thanks are due!

References

1. M. Fleischmann, P.J. Hendra & A.J. McQuillan, J.Chem.Soc.Chem.Comm, 80 (1970)
2. P.J.H. and E.J. Loader. Trans. Faraday Soc., 67 828 (1970)
3. P.J.H and J.R. Harder, J. Chem. Soc. A., 1766 (1971)
4. P.J.H., M.Stacey and I.D.M. Turner, J. Phys. Chem, 31, 300 (1974)
5. P.J.H., M.F., R. Cooney & E. Reid, J.Anal.Chem.Soc., 99, 2022 (1977)
6. P.J.H., M.F., R. Cooney & E. Reid, J. Electroanal. Chem, 86, 485 (1977)
7. P.J.H., M.F., R. Cooney & E. Reid, J. Chem. Soc. Faraday Trans 1, 73, 1691 (1977)
8. P.J.H., M.F., R. Cooney, J. Chem. Soc, Chem Commun. 7, 235, (1977)
9. P.J.H., M.F., R. Cooney, J. Raman Spect, 6 264, (1977)

Patrick Hendra

Assistant Editorial

Just a quick note to say that we have also published the spectra of various chemical compounds with kind permission from Geoffrey Dent from Avecia Ltd, UK. All you have to do is
click here.

The files are all .pdf’s which means they are for reference only (see my comments in Dear Readers). To read them you will need Adobe Reader, which is available to download FREE-OF-CHARGE from Adobe’s website – www.adobe.com.

If anyone else out there has any spectra which they are happy to share, then please let us know and we will publish them on the web.