Diamond nanoparticles behave outstanding chemical, electronic, thermal and optical properties. Such nanoparticles are actively investigated for nanomedecine, energy applications, quantum technologies and advanced lubricants and composites [1-3]. For the major part of these applications, the crystalline quality of the diamond core is essential and the most studied particles are milled from bulk diamond. Nevertheless, these particles exhibit a wide size dispersion, shape anisotropies and variable concentrations of chemical impurities. These aspects strongly affect their properties. It is thus required to develop a synthesis method to grow highly crystalline nanodiamonds with an accurate control of their size, morphology and chemical impurities.

This PhD aims to develop a bottom-up synthesis based on sacrificial templates (silica beads or fibers) on which nanometric diamond seeds will be attached via electrostatic interactions. Diamond growth will be achieved by an exposure of the seeded templates to a micro-wave assisted CVD plasma (MPCVD). The growth set-up is already in use at CEA NIMBE for diamond core-shells synthesis [4]. Growth parameters will be adjusted to select the size, the shape and the concentration of chemical impurities (nitrogen, boron) in nanodiamonds. After CVD growth, nanoparticles will be collected by dissolution of the templates. Their crystalline structure, morphology and surface chemistry will be characterized at CEA NIMBE by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman, infra-red (FTIR) and photoelectrons (XPS) spectroscopies. An external collaboration will allow an investigation of the diamond crystalline quality and the identification of structural defects in CVD grown nanodiamonds by high-resolution transmission electron microscopy (HR-TEM).

Several kinds of nanodiamonds will be grown : first, intrinsic particles (without intentional doping), then boron doped particles. Both types of particles will be then surface modified to get a colloidal stability in water. Photocatalytic performances will be measured in collaboration with ICPEES (Strasbourg University). This original synthesis method will also permit to create colored centers (nitrogen-vacancy or silicon-vacancy) in nanodiamonds to exploit their optical properties (collaboration to initiate).

Références :

[1] N. Nunn, M. Torelli, G. McGuire, O. Shenderova, Current Opinion in Solid State and Materials Science, 21 (2017) 1-9.

[2] Y. Wu, F. Jelezko, M. Plenio,T. Weil, Angew. Chem. Int. Ed. 55 (2016) 6586–6598.

[3] H. Wang, Y. Cui, Energy Applications 1 (2019) 13-18.

[4] A. Venerosy et al., Diam. Relat. Mater. 89 (2018) 122-131.