Prof. C V Raman‘s fascination for gemstones in general, and for diamonds in particular is well known. Prof. Bhagavantam, for example, in his Biographical Memoirs article on Raman, devotes a subsection to Raman’s interest in diamonds, and says the following, among other things:
In particular, his interest in the study of diamond, and its remarkable physical properties and of its structure has been more or less a lifelong involvement with him…Professor Raman built up his interest in diamonds to such an extent that at one time, every student working in his Department was engaged in studying one aspect or other of the properties of diamond…In the museum at the Raman Research Institute today, are several hundreds of diamonds–some in their natural condition, some cleavage plates, all of which altogether make up a unique collection probably unparalleled anywhere in the world as a laboratory acquisition…His interest in the physics of the diamond was deep seated. It was both scientific and aesthetic.
Raman himself took time to explain his research on diamonds in popular lectures and newspaper articles. In the newspaper article, he even speculates on the reasons as to why South Indian ladies prefer (especially blue) diamonds:
The reason, I believe is that they tend to have rather dark complexions, and these brilliantly flashing blue diamonds naturally show off well against their complexions. When the diamonds flash, as the human eye never likes to look on anything brilliant it turns away and looks at the wearer instead. Diamonds are not meant to be looked at–they are only a foil for the wearer.
Fascinating as these connections between Raman and diamonds are, in this post I want to concentrate on the other Raman connection to diamonds, namely, the Raman spectroscopy of diamonds (with specific reference to diamond polishing, which makes them brilliant in the first place).
In a recent article in the Philosophical magazine, Hird, Bloomfield and Hayward, three researchers from UK, report on their Raman spectroscopic studies on the wear debris and polished surfaces of diamond, in an attempt to understand the mechanisms that lead to the polish. The article itself is lucid with a bit of history thrown in, and I recommend it strongly.
Diamond is the hardest known material; that being the case, it is still possible to polish it by grinding against a rotating cast iron disk filled with oil and diamond grit (A digression: The complete text of Tolkowsky‘s Diamond design is available here). What happens during such a polishing process? Do the faces cleave? Does some chemical reaction occur due to the high temperatures that are achieved during the grinding? Is it a simple mechanical wear at elevated temperatures? Or, is it a combinations of some or all of the mechanisms above? That is precisely the question that Hird et al set out to answer.
The Raman spectroscopic technique comes handy in answering some of these questions since Raman spectrum of every material is a distinct fingerprint of the material. Thus, by fingerprinting the debris of the polishing process and the polished surface, it is possible to detect any material that would have formed due to a chemical reaction, for example. The first phase of study reported in the paper indicates the occurrence of chemical reactions, as well as a mechanical wear mechanism.
Finally, this is not the only diamond-Raman spectroscopy connection. Many high pressure Raman spectroscopic studies of materials are made possible because of the diamond anvil cells which can withstand high pressures, and allow light to pass through them so that the sample can be illuminated using a laser beam, and the Raman scattered light can be collected for analysis.