Generation of quantum emitters by introducing color centers inside diamond

Abstract

This thesis explores the generation of nitrogen-vacancy (NV) color centers in diamond, which are solid-state quantum emitters. Quantum emitters are critical for applications in quantum cryptography, sensing, and computing. Due to their stable photoluminescence and long spin coherence times at room temperature, NV centers are particularly worthy of studying in quantum technologies. The study aims to produce NV centers in a controlled manner by using low-energy electron beam irradiation and thermal annealing. The experimental method began with the selection of a nitrogen doped high-pressure high-temperature (HPHT) synthesized type Ib single-crystal plate diamond with a {100} surface orientation, obtained from Element Six. Electron irradiation was carried out using a lithography system at 100 keV with varying doses (0.5–5.0 C/cm²) applied in specific patterns on four corners of this sample. This step aimed to introduce vacancies in a spatially resolved manner. Subsequent annealing at 800 °C under argon flow at 100 CCM was done to induce the migration of these vacancies to nearby substitutional nitrogen atoms. These processes combined lead to the formation of NV centers. A comprehensive characterization process was conducted at each stage using topographical imaging with an optical profilometer, Raman spectroscopy, photoluminescence (PL) spectroscopy, and electron spin resonance (ESR). Raman analysis confirmed the integrity of the diamond lattice post-treatment. It also provided insights into strain–stress relations within the diamond lattice. Shifts in the diamond Raman peak position and changes in full width at half maximum (FWHM) across the sample revealed localized lattice stress. This discovery was important because these stress variations directly influence NV center formation and performance. PL spectroscopy detected distinct zero-phonon line (ZPL) emissions at ~638 nm, indicative of negatively charged NV⁻ centers. The intensity of NV⁻ emission was observed to vary with electron dose, which indicates the ability to control NV center density. Mapping of the PL signal further demonstrated successful spatial control of NVs on the sample. ESR measurements confirmed the spin-related properties of the generated centers and the charge state transition from NV⁰ to NV⁻ following annealing. Overall, this work stands out for its use of low-energy electron irradiation which is preferable due to easier control over defect positioning and potentially lower damage to the host lattice. This thesis contributes to the development of deterministic NV center engineering.