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Saxonian Institute of Surface Mechanics

Comment on the Paper “Nanotwinned diamond with unprecedented hardness and stability” in Nature

There has been published a paper on nanotwinned diamond in Nature recently which is supposed to be one of the top journals world-wide. The authors Quan Huang et al. claim having measured a Vickers hardness of up to 203 GPa at a load as high as 4.9 N - and now the really interesting part of the measurement comes - without having damaged the indenter tip, “ because no visible plastic deformation of indenter diamond tip was observed”. Does that remind you of former myth? Yes, us too. It is physically impossible that a material harder then the counter body does not damage the counter body at all. But there are also theoretically aspects which have been completely ignored by the authors (a list featuring comments of one of the scientists who has been in touch with Nature's editor):

  1. There is no solution for an ordinary diamond structure with a natural lattice distance. Only from lattice constants being suddenly much smaller than those of ordinary diamond one finds solutions being “mathematically possible”.
  2. However, most of these solutions need the carbon atoms to suck energy from somewhere (“probably the vacuum of which the nature-paper does consist of so obviously”) to be held together this strongly (see blue curve with lowest minimum in Fig. 1).
    Atomic interaction potentials
    Fig. 1: Interaction potentials of diamond (violet plot), hypothetic nanotwinned diamond being permanently fed with energy (blue plot with lowest minimum) and hypothetic nanotwinned diamond with a lattice constant of about 0.885 that of natural diamond (blue plot with middle minimum).
    Only for a lattice constant of about 0.885 times the one of diamond (and lower) one obtains a solution where the carbon atoms do not need to be fed with quantum mechanical energy “from which source ever” (see the blue curve with middle high minimum in Fig. 1).
  3. Only problem, to realize this we have the need of a big diamond crystal suddenly and very surprisingly being compressed by a factor of 1.3 in a phenomenologic region much bigger than the contact area.
    “Of course, it might also be possible that the diamond just shrinks out of pure fun and stays this way without releasing any energy and / or showing any sign of distress.
    This is material science as I so very much like it.”

In addition, we would like to quote an angry scientist who is mad at his slapdash colleagues:

  1. “…and we haven’t even discussed the problems of how on earth they have tested something so much harder than diamond with an ordinary diamond tip. Oh, please don’t come me with that rubbish of the purely compressed tip again! Can’t these people even do a simple contact calculation before telling the world such stupid lies? Well then, but what about the high class reviewers this Journal does have… sorry, should have?”
  2. “What about the foundation and the well known theoretical limits for self-similar indenters like Vickers and Knoop simply not allowing to measure hardnesses for certain materials – like rubber, for instance – because these tips aren’t sharp enough? Nothing of this is answered nothing is covered within this publication. In my humble opinion, this paper is crap and was only pushed through by the editors in order to boost the Journal a bit… End of story!”

Anyways, we would like to refer you to Fischer-Cripps' thorough review of this paper.

And again, the question remains, how the supposed-to-be world-class referees could have been convinced by such an utter nonsense. This is a npn = Nature Publishes Nonsense!

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