Suresh Shankarappa Vagarali

Isotopically pure diamond anvil for ultrahigh pressure research

Large gem quality type IIa crystal of isotopically pure 12C diamond (364 mgm) was evaluated for applications as an anvil in ultrahigh pressure research. Raman microprobe and photoluminescence studies on 12C diamond were compared with a typical type Ia natural diamond anvil used in high pressure research. Visible fluorescence in the isotopically pure diamond is an order of magnitude lower as compared to natural diamond and is ideal for spectroscopic studies in diamond cell devices. Low intrinsic strain, high purity and crystal perfection of 12C diamond anvil offer better performance under extreme stresses.

Isotopically pure 12C diamond anvil at megabar pressure

The optical properties of a 0.15 carat isotopically pure (isopure) 12C diamond anvil were studied to 250 GPa by micro‐raman and photoluminescence spectroscopy. At ambient pressure, the laser excited fluorescence from the isopure diamond is an order of magnitude lower than that from the best selected type Ia natural diamonds. We find that the fluorescence of the isopure diamond remains low up to pressures as high as 200 GPa, in contrast to type I and type II natural diamond anvils that show rapid increase in fluorescence above 100 GPa. Pressures in this experiment were characterized by ruby fluorescence, micro‐raman analysis of the diamond tip, and x‐ray diffraction on Cu pressure standard. We conclude that the isopure diamond anvils are ideal for spectroscopic studies in the ultrahigh pressure regime (100–400 GPa).

Nitrogen in the isotopically enriched 12C diamond

An electron paramagnetic resonance (EPR) characterization study of isotopically enriched 12C diamond grown by General Electric has been carried out. While other commonly used techniques detect no nitrogen in this diamond, the clear EPR spectrum consistently measured a nitrogen concentration of about 0.05 ppm by calibration against a few standards. The concentration is about 2 orders of magnitude lower than that of a few natural IIa diamonds and over 4 orders of magnitude smaller than that of a typical yellow Ib diamond. The 12C diamond is evaluated to be ideal for research of diamonds under high pressure as well as irradiated diamonds. Both the experimental line shape and second moment do not support a random nitrogen distribution in this diamond. Instead, we found that nitrogen atoms tend to stay apart from one another. This uniformly dispersed nitrogen distribution is a new state of nitrogen found in diamond.