Poster Presentation 26th ACMM “2020 Visions in Microscopy”

Using high pressure and pulse laser heating to transform glassy carbon into diamond (#224)

Brenton A Cook 1 , Thomas B Shiell 2 , David R McKenzie 3 , Matthew R Field 4 , Bianca Haberl 5 , Reinhard Boehler 5 , Jodie E Bradby 6 , Dougal G McCulloch 1 4
  1. School of Science, Physics, RMIT University, Melbourne, VIC, Australia
  2. Geophysical Laboratory, Carnegie Institution of Washington, NW Washington, DC, USA
  3. School of Physics, The University of Sydney, Sydney, NSW, Australia
  4. RMIT Microscopy and Microanalysis Facility, RMIT University, Melbourne, VIC, Australia
  5. Chemical and Engineering Materials Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
  6. Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT, Australia

The synthesis pathway to diamond from graphitic precursors using high pressures and temperatures has been studied and applied for many decade [1]. Industrial manufacturing methods require temperatures up to 1500 K, pressures between 5-6 GPa, and the use metallic catalysts [1]. Without these catalysts the pressure and temperature conditions required are far more extreme to overcome kinetic energy barriers. In recent times, there has been considerable interest in the synthesis of diamond and other novel forms of carbon from non-crystalline precursors. Recently, an amorphous form of diamond is synthesised from GC following compression to 50 GPa and laser heating to ~1800 K [2].  However, previous work has only investigated the compression of non-crystalline precursors to a limited number of temperatures resulting in an incomplete understanding the transformation pathways. There is a need for a more thorough study of the effects of high temperature and high pressure on non-crystalline graphitic materials, particularly for temperatures above ~3000 K.  

In this study, GC was loaded into a diamond anvil cell with an Ar pressure medium and compressed to 16 GPa. A pulse laser was used to heat the samples to temperatures ranging from 1900-4500 K. A total of 15 samples were made for ex-situ analysis using raman spectroscopy, scanning electron microscopy and transmission electron microscopy. At low temperatures (1900-2200 K), the GC was found to transformed into an oriented graphitic material in which its graphene layers are preferentially aligned perpendicular to the compression axis. Nanodiamonds (~10-200 nm) begin to form near the surface at temperatures of ~2200 K. These nanodiamonds increase in size and density as the temperature increases. Interestingly, above ~3500 K voids were observed in the microstructure. This observation supports the proposition that at these high temperatures, the GC may have melted prior to the formation of diamond.

  1. [1] F.P. Bundy, W.A. Bassett, M.S. Weathers, R.J. Hemley, H.U. Mao, A.F. Goncharov, The pressure-temperature phase and transformation diagram for carbon; updated through 1994, Carbon N. Y. 34 (1996) 141–153. doi:10.1016/0008-6223(96)00170-4.
  2. [2] Z. Zeng, L. Yang, Q. Zeng, H. Lou, H. Sheng, J. Wen, D.J. Miller, Y. Meng, W. Yang, W.L. Mao, H. Mao, Synthesis of quenchable amorphous diamond, Nat. Commun. 8 (2017) 322. doi:10.1038/s41467-017-00395-w.