Molecular Synthesis of Complex Nitrogen Defects in HPHT Nanodiamond

Abstract

After Antoine Lavoisier's seminal paper demonstrating the elemental composition of diamond as exclusively carbon in 1772, much research has been devoted to the synthesis, characterization, and application of this illustrious material. By the middle of the 20\textsuperscript{th} century, through the ingenuity of H. Tracy Hall, the first artificial diamond synthetic avenue was discovered; through high-pressure, high-temperature means, a micro-crystal of diamond had been made. Industrial techniques such as CVD and detonation are currently employed to fabricate diamond for commercial applications with ranging purity. Moreover, research within the last twenty years on the optically active defects, also known as color centers, within diamond have found that they hold advantageous properties for a myriad of applications like quantum processing, telecommunications, fluorescence imaging, and magnetic sensing. While much has been discovered about diamond, and the $>$ 100 naturally occurring optically active defects within diamond, an outstanding scientific challenge remains in rationally and deterministically incorporating specific defects into synthetic diamond. Precise atomistic control over the formation of these defects remains elusive, especially so with complex heteroatomic defects like the NE8 center, whose properties align itself as an excellent defect for quantum communication applications. In this work, we demonstrate a facile synthetic avenue to deterministically introduce desired defects into HPHT synthesized nanodiamond. The first part of the synthetic scheme includes the selection of an appropriate small molecule that matches the stereochemistry and stoichiometry of the desired defect and incorporating the small molecule into a carbon aerogel matrix to serve as a carbonaceous precursor for the formation of nanodiamond. The second part of this process is to place these doped carbon aerogel samples into a diamond anvil cell to access pressures similar to where diamonds are formed in nature and to drive the phase transformation to diamond through photothermal heating. Also in this work, we demonstrate for the first time the phenomenon of laser cooling at elevated pressures. By placing a rare earth doped ceramic material inside a diamond anvil cell, we leverage the phonon assisted anti-Stokes fluorescence properties of this material to locally cool the surrounding area in the diamond anvil cell chamber. We also investigate the magnitude of cooling between the lower pressure scheelite phase and the higher pressure fergusonite phase.