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Properties of Nanodiamonds

TEM-Image of Nanodiamonds, which were modified with wet method (Scaling: 100nm)
TEM-Image of Nanodiamonds, which were modified with wet method (Scaling: 100nm)

Nanodiamonds are allotropes (sp3) of carbon and possess a series of distinct properties compared to other carbon–based materials. Their outstanding characteristics include extreme hardness, high thermal conductivity, transparency at all optical wavelengths, biocompatibility, and chemical robustness [1]. Pure diamond is an electric insulator while doped diamond is a semiconductor with a large bandgap (5.5 eV at room temperature). In addition doped impurities can create optically active defects – also called color centers – within the diamond. A nitrogen vacancy center (NV) consists of two adjacent positions in the atomic lattice of a diamond one replaced by a nitrogen atom while the other remains vacant. Under excitation with an appropriate light source, NV centers are a reliable single-photon source. The emitted photons carry defined spin information related to the spin state of the NV center. During the production of nanodiamonds by detonation of TNT-hexogen mixtures nitrogen defects are added. [2].
Although nanodiamonds are sp3 allotropes of carbon materials many residual groups, such as hydroxyl, carboxyl, lactone, ketone, exist on nanodiamonds due to their high surface energy. These groups provide initial functional sites for further modification.

Functional groups of a nanodiamonds, which was modified with wet method
Functional groups of a nanodiamonds, which was modified with wet method

The surface modification of the nanodiamonds can be divided into two main categories: wet methods [3, 4] and dry methods [5, 6].The dry methods usually employ gas plasma or high temperatures to remove the surface impurities and embedded functional radicals. The wet methods usually employ mineral acids to oxidize the surface and then further conjugate the oxidized surfaces with other groups by non-covalent or covalent interaction.
Both procedures modify the nanodiamonds surface by introducing carboxyl or amino groups to enable an attachment. For our project, we used nanodiamonds that were already modified by wet method by Tanja Weil's group from Ulm Univeristy.


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