Purification, fabrication and shape engineering of diamond materials for applications ranging from anti-counterfeiting to biofilm inhibition

Abstract

Diamond materials have demonstrated various applications from basic science to industrial fields because of their extraordinary properties, e.g., exceptional biocompatibility, high chemical inertness, excellent optical properties, etc. Particularly, the optically active impurity defects discovered in diamond crystal, e.g., nitrogen-vacancy (NV) centers and silicon-vacancy (SiV) centers, have been utilized in advanced quantum technologies due to their exceptional spin characteristics. However, the current most available diamonds (such as detonation, high-pressure high-temperature (HPHT), and chemical vapor deposition (CVD) synthesized) are not suitable for demanding applications which require superior material properties, e.g., stable and sound surface functionalities, high crystalline quality, high emissive and stable color centers, controllable geometric features, etc. Here, this thesis focused on the engineering of diamond materials in terms of nanodiamonds (NDs) purification, high-quality diamond fabrication and diamond shape engineering, to advance the practical applications of diamond materials, e.g., ultrasensitive thermometry, unclonable anti-counterfeiting, and biofilm inhibition.

Firstly, a new purification technique for NDs called salt-assisted air oxidation (SAAO) was developed, which requires mixing NDs with salt crystals, such as sodium chloride, before conventional oxidation. The addition of chloride salts would create a “salt-assisted etching atmosphere” at high temperature that would effectively remove non-diamond impurities and speed up the oxidation process of NDs. With this technique, clean NDs could be produced on a larger scale, and their shape could be transformed from shard-like to rounded, making them more suitable for practical applications that require stable and robust surface functionalities.

Secondly, the purified and rounded SAAO NDs were proved useful as CVD seeds to fabricate high-quality microdiamonds (MDs) on a silicon substrate. The as-grown MDs contain SiV centers with excellent properties, for example, the photoluminescence (PL) signals were enhanced, and the linewidths were reduced. These outstanding features make them ideal for various practical applications, e.g., ultrasensitive all-optical thermometry.

Thirdly, the feasibility of arbitrary morphology transformation of MDs and NDs via air oxidation was demonstrated. Notably, a series of unique shapes, including “flower” shaped, “hollow” structured, “pyramids” patterned on the surface, were achieved for the diamond particles. These results could pave the way for diamond-based devices in various fields such as nanophotonics, quantum computing, quantum sensing, etc.

Lastly, a reliable anti-counterfeiting strategy based on our high-quality MDs on silicon substrates was presented. These diamond labels boasted exceptional properties in terms of capacity, diversity, safety, manufacturability, stability, and compatibility, making them ideal candidates for immediate use in various anti-counterfeiting applications. Additionally, it was shown that NDs could be utilized to prevent the formation of biofilm and disrupt pre-existing biofilms of orally and systemically important organisms. This discovery could advance our understanding of how NDs affect oral microbes and facilitate their clinical use.