Structure of plate-shape nanodiamonds synthesized from chloroadamantane- are they still diamonds?

S Stelmakh and K Skrobas and S Gierlotka and B Palosz, JOURNAL OF PHYSICS-CONDENSED MATTER, 33, 175002 (2021).

DOI: 10.1088/1361-648X/abe26a

Atomic structure of plate-shaped nanodiamonds synthesized from chloroadamantane was identified with application of large-Q powder diffraction data. Both reciprocal and real space methods of experimental data analysis were applied. Theoretical atomistic models of nanodiamonds were obtained with application of molecular dynamics (MD) simulations. It was found that examined nanodiamond samples with average grain size from 1.2 up to 2.5 nm are plates build from only six hexagonal carbon layers and they are terminated by (111)B surfaces with three dangling bonds. MD simulations showed that as a result of relaxation of surface stresses there appears a complex system of compressive and tensile strains across and parallel to the surface of the plate-nanodiamonds. Identification of the internal structure of nanodiamond was performed based on the analysis of differential interatomic distance diagrams derived from pair distribution functions G(r). Based on MD simulations an atomic model of plate-grains of diamond was elaborated. Usefulness of lattice parameters determined in a routine diffraction data analysis for characterization of nanodiamonds is questioned. As an alternative the application of the apparent lattice parameter is recommended. A dependence of the overall apparent lattice parameter alp on the size and shape of nanodiamond grains terminated by low index crystal faces is presented.

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