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11Modification of diamond by laser radiation: from ablation to single NV-centers formation
Vitali Kononenko
A.M. Prokhorov General Physics Institute of RAS
Diamond is a unique material, the use of which is quite desirable in the different technological advances, from constructive elements operating in hot and aggressive media to the platform for quantum communication and computing. The downside is the extreme hardness of diamond crystal. While the problem of diamond synthesis has been largely solved and (poly)monocrystalline substrates are commercially available, the existing diamond processing techniques are still unable to meet the many application requirements and are in a thorough development process. Here, the fundamental aspects of the laser-diamond interaction are reviewed, focusing on the irreversible structural transformations that affect the physical and optical properties of the crystals.
Experiments with harmonics of the Ti-sapphire laser (100 fs, 266-800 nm) and many other pico-and nanosecond pulsed sources have revealed a number of different laser-stimulated processes developing on the diamond surface. This diversity is due to two fundamental properties of diamond: the ability to graphitize, which completely changes the coordination geometry of the carbon bonds, and the ability to chemically react with ambient gases. Modern pulsed lasers enable both scenarios: (1) heating of the crystal lattice up to ~2000 C with single pulse graphitization and ablation (~10 nm/pulse), and (2) nonlinear photoexcitation of the binding electrons with quite slow surface etching - "nanoablation" (<10-2 nm/pulse). Special attention will be paid to the accumulative regime of the laser effect, when the laser fluence is lower than the single pulse ablation threshold and the graphitization develops with a certain delay - after multi-pulse laser treatment. Both accumulative graphitization and nanoablation are atomic-scale processes that pave the way for photolytic formation of structural defects in diamond.
Effective and controllable generation of color centers is a key problem in diamond-based quantum technologies. To date, several vacancy-based defects have been demonstrated to be created as a result of laser treatment of diamond. The most well-known of these is the nitrogen-vacancy complex (NV center), the formation mechanisms of which are discussed in both the accumulation and nanoablation regime. Luminescence measurements confirm that during long irradiation, e.g. with 266 nm femtosecond pulses, the NV concentration gradually increased and can increase tenfold (Fig. 1). The correlation between the coloration of the diamond and the nanoablation of its surface is demonstrated. Taken together, the results presented here indicate that laser preablation irradiation is a promising tool to precisely control the number of generated vacancies in the lattice and thus the probability of formation of a single NV center at the desired location of a crystal.
This work was supported by Russian Science Foundation, grant 24-12-00137.
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Figure 1. PL spectra of irradiated and original diamond (left) and PL image of 10x10 array with a period of 8 ^m and magnified image of individual pixel in the insert (right). The irradiation was made with a third harmonic of Ti-sapphire laser (100 fs, 266 nm, 0.4 J/cm2, 0.5 million pulses).
