3, RIKEN, Wako, Saitama, Japan
2, CSIRO, Parkville, Victoria, Australia
4, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan
5, NanoCarbon Research Institute Ltd., Ueda, Nagano, Japan
Elementary particles of detonation nanodiamond (EPDND) were first revealed by DFT calculations, consisting of some patches of sp2(G-patch), a mantle of sp2+x(F-mantle), and a core of sp3 carbons (D-core). However, its emprical confirmation has been delayed because of difficulties in isolating pure samples. The elaborate attrition milling of nanodiamond (ND) agglutinates by NanoCarbon Research Institute (NCR) produced a pure well-dispersed solution of single-nano(~3nm) sized EPDND, thus giving us its evidence. Korepanov demonstrated by the phonon confinement analysis of Raman spectra that G-core from the solution is nearly 1.6 nm in size and Tristan confirmed the G-patches only in the solution by X-ray absorption. We consider that the solution contains the EPDND that are predicted by the calculations. Hence, any further experimental evidence is appreciated.
Laser desorption ionization mass spectra (LDI MS) demonstrate herein that a G-core of EPDND contains nearly 1000 sp3 carbon atoms. The positive ion mass peak of ~12k Da (~C1000) was first reported three years ago  and, among five positive-peaks (<0.5kDa: Cn+, 1~5kDa: C2n+, ~12kDa: broad, ~40kDa: broad, ~120kDa:broad) observed, it was assigned to a remnant D-core after losing all the G-patches and F-mantles[6,7]. Abundant Cn+ and C2n+peaks are the fragments from the G-patches or F-mantles through thermal or photochemical decomposition at their surfaces because they were observed with the lower laser power threshold which cannot give G-core ions. Little change in the D-core peak from a linear to a reflector mode also indicates the stability of D-core ions as the remnant. Although the solution was dried before measurements, G-core ions were observed from the solution and not from raw agglutinates without milling. We think that D-core ion is generated from the micro colloidal crystals that can be precipitated at air-drying only from the well-dispersed solution. Such a stable D-core ion furthermore should be the cubic diamond that corresponds to be one of the energy-minimized model structures simulated by DFT calculations. The high sp3 content of the cube reaching 76% is unique in the structures, thus explaining the size and stability observed.
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