Fluorescent milled nanodiamonds are one of the most promising physical bases for quantum devices. The nitrogen vacancy (NV) center in diamond acts a room temperature, optically addressable quantum system which significantly decreases the infrastructure costs of developing quantum devices. Since nanodiamonds are nontoxic and colloidally stable, the nanoparticles are particularly attractive to the fields of sensing and nanomedicine where environmental changes must be detected with nanoscale resolution. Particle to particle irregularity, however, alters the spin and optical properties of each nanodiamond and complicates their integration into more complex systems. In this dissertation, we address the inhomogeneity of nanodiamonds and provide multiple paths towards fully utilizing these quantum emitters. First, we develop a technique for the self-assembly of nanodiamonds into arrays. We then utilize these arrays to perform a statistical study of the nanodiamonds and characterize the impact of the material’s surface and crystalline structure on the NV center’s optical and spin properties. Next, we establish a surface modification method that both improves the general properties of the nanodiamonds and enables chemical conjugation reactions. Together, these results deliver a newfound level of control and uniformity over an otherwise uncontrollable and polydisperse material.
Fluorescent milled nanodiamonds are one of the most promising physical bases for quantum devices. The nitrogen vacancy (NV) center in diamond acts a room temperature, optically addressable quantum system which significantly decreases the infrastructure costs of developing quantum devices. Since nanodiamonds are nontoxic and colloidally stable, the nanoparticles are particularly attractive to the fields of sensing and nanomedicine where environmental changes must be detected with nanoscale resolution. Particle to particle irregularity, however, alters the spin and optical properties of each nanodiamond and complicates their integration into more complex systems. In this dissertation, we address the inhomogeneity of nanodiamonds and provide multiple paths towards fully utilizing these quantum emitters. First, we develop a technique for the self-assembly of nanodiamonds into arrays. We then utilize these arrays to perform a statistical study of the nanodiamonds and characterize the impact of the material’s surface and crystalline structure on the NV center’s optical and spin properties. Next, we establish a surface modification method that both improves the general properties of the nanodiamonds and enables chemical conjugation reactions. Together, these results deliver a newfound level of control and uniformity over an otherwise uncontrollable and polydisperse material.
Diamond is unique. Whether mechanical, thermal, electrical or optical, its properties are within the most extreme compared to those of any other material. This, together with the fact that in the last fifty years the synthesis of artificial diamond has become a reality, makes it very attractive for engineering and technological purposes. The range of diamond-based applications is very diverse and, among the others, includes its use in mechanical machining, high-power high-frequency electronics and high transmissivity optics. -- Diamond is also host to a wide variety of crystallographic defects. Appropriately controlled, they can be used to tune the characteristics of the material, but even more interestingly they often possess attractive optical properties on their own. In particular, nitrogen-vacancy (NV) centres in diamond have been the subject of extensive study in the last few years. They possess unique room-temperature optical and spin properties which make them promising systems for solid-state qubits in quantum information technologies and for emerging applications in biotechnology, nanomedicine and high resolution magnetometry, such as drug delivery, fluorescent biomarking and spin imaging. -- This thesis is focused on NV centres in diamond. I first present an extensive review on diamond as a material, describing in detail its physical properties, the methods that have been developed to synthesise it and some of its possible applications. I then move the attention specifically to NV centres in nanodiamonds (NDs), i.e. diamond crystals in the nanometre size range (0-100 nm). They are a potential candidate for emerging technologies including high-resolution magnetometry and biomedical imaging. For these applications, specific material requirements, such as the small size of the diamond nanocrystals and the optical stability of the hosted NV centres, are crucial. The NV stability with respect to the nanodiamond size and surface is the central theme of this thesis. I analyse the optical behaviour of NV centres in nanodiamond while varying a number of key parameters such as size, surface termination and diamond origin. Based on the measurements, I conclude whether the nanodiamond size and the NV surface proximity are factors that must be taken into consideration in order to control the material and realise nanotechnologies based on NV centres in nanodiamonds.
Nitrogen-vacancy centers (NVs) are an atomic defect in diamond which possess remarkable fluorescence and spin properties which can be used for multiple metrological applications, particularly when the NV is hosted in nanodiamond, which can be easily integrated with a variety of nanoscale systems. A new class of nanodiamond hybrid nanostructures was developed using bottom-up synthesis methods. In this work, coupling between NV centers and plasmonic, excitonic and magnetic nanoparticles in these nanodiamond hybrid nanostructures is investigated using fluorescence lifetime measurements, spin relaxometry measurements and modeled using finite element method (FEM) and Monte Carlo simulations. This work not only characterizes the properties of these nanodiamond-hybrid nanostructures but also facilitates design guidelines for future hybrid structures with enhanced metrological and imaging capabilities.
The NV defect center in diamond forms a pseudo-atomic quantum system with discreet optically excitable transitions between ground and excited states in the gap between valence and conduction bands, making the NV center a deep-level defect center in diamond. For the negatively charged NV center (NV-), both the ground and excited states are spin triplets (S=1) and coupling between optical and spin states provides unique opportunities for optical detection of magnetic resonance (ODMR) and quantum metrology under ambient conditions. As an atomically sized point defect that is stable in single nanodiamonds as small as a few nanometers, the NV center enables spin based imaging of temperature, electric fields, magnetic fields and mechanical strain with nanoscale spatial resolution. Made of carbon, nanodiamonds are also ideal nanoparticles for use in biological systems, exhibiting extremely low cytotoxicity, no photo bleaching and exceptional contrast in transmission electron and light microscopy. With the ability to act as both a passive, non perturbing sensor (e.g. a diamagnetic material used for sensing magnetic fields) and a connection point for two way, direct coupling of far field optics to NV− spins and indirectly to the highly localized neighborhood of atoms, electronic states and phonon modes in the local vicinity, NV diamond provides a route to nanoscale field sensing and spin based optical microscopy. These sensors are also stable in nanodiamonds. For nanoparticles, the reduction in particle diameter dramatically enhances the proportion of the material that is surface exposed, enhancing any surface related properties. Nitrogen Vacancy centers in nanodiamonds provide another example of material properties that vary with particle size. In chapter 5, evidence that modulation of nanodiamonds fluorescent emissions by electrical perturbations in their surrouding environment allows transduction of local electrodynamics into a far field optical signal capable of mapping action potentials in cardiomyocytes in presented. The unifying theme for all of the work presented in this dissertation is to enable the use of magnetic resonance signals and interactions for imaging and sensing in previously inaccessible regimes. The specific focus is on methods and techniques to enable nanoscale physical sensing and functional imaging in live tissues, with the ultimate aim to lay the predicate for the combination of both without compromise.
A quantum system with discrete, resolvable energy levels is an ideal system for sensing applications, taking into account that it can strongly interact with its environment. Although the strong response with the target properties such as magnetic or electric field is ideal, it can be a disadvantage when the system is interacting with other physical changes (noise) at the same time. However, the benefits of the strong coupling as well as small size of the sensor has motivated many researchers to explore quantum systems for measuring very small physical quantities. For instance, Nitrogen vacancy center in diamond is a unique quantum system enabling sensing of magnetic field from single molecules or electrons at room temperature.
This thesis has focused on two different quantum emitters: NV centers in nanodiamonds and quantum emitters in hexagonal Boron Nitride (hBN). In the first part a new assembly technique based on electron beam induced deposition and crosslinking chemistry is developed. It is demonstrated that fluorescent nanodiamonds containing NV centers can be assembled into arrays of various size and shapes on any substrate. The produced array is ideal for device fabrication due to its outstanding robustness. A potential application of such arrays as magnetic field sensor with high spatial resolution is shown.
The superior properties of quantum emitters in hBN has been studied in the second part of this thesis, where is has been shown that these emitters are not only stable but also maintain their single photon purity at elevated temperature. The highest measured quantum emission at 800 K in this study is the highest reported temperature for a quantum emitter so far, makes them a suitable candidate for temperature sensing. In addition, the level structure of emitters in hBN has been investigated in detail which reveals the unique photophysical properties of a class of these emitters which result in a nonlinear increase in the emission upon co-excitation with two lasers of different wavelength. Finally the photophysic property of these emitters has been employed to introduce a new modality of super-resolution microscopy with resolution down to about 70 nm. These findings will extend our understanding of quantum emitters in hBN and introduce a new functionality for them which paves the way toward their application in biology and sensing.
Progress in controlling diamond synthesis has made it possible to produce very pure crystals and to incorporate and control atomic impurities and carbon vacancies in the crystal lattice. The appropriate impurity-vacancy combinations can give rise to special defects known as color centers, such as the nitrogen-vacancy (NV) or the silicon-vacancy (SiV), which exhibit exceptional quantum properties with spins that are optically addressable. The use of diamond containing color centers has paved the way for the development of innovative quantum technologies, such as very high-resolution magnetometry and quantum information processing. Nevertheless, the development of quantum sensors at the nanometric scale remains one of the most interesting challenges. In this context, the development of a reliable nanoparticle synthesis technique that allows the desired defects to be incorporated and their quantum optical properties to be modulated is crucial. In this seminar, an efficient and recent method to produce diamond nanoparticles containing NV, SiV and germanium-vacancy (GeV) centers is proposed through direct plasma assisted chemical vapour deposition (CVD) growth. This technique allows good control of both nanoparticle growth processes and color centers formation. The optimization of the CVD nanodiamond growth process is presented, showing the impact of different plasma parameters and gas phasecomposition on nanoparticle crystallinity, size and shape. Morphological characterizations reveal the production of small (around 100 nm) and well faceted nanodiamond particles. In addition, the SiV and GeV color centers incorporation can be tuned within this material by varying the gas phase composition which emphasizes the high flexibility of the CVD growth technique. Finally, the quantum properties of the incorporated color centers have been successfully investigated under extreme pressure conditions (up to ~ 180 GPa) showing a monotonic blue shift of their optical zero-phonon line. Since their luminescence remains stable, SiV and GeV centers emerge as high-pressure nanosensors.
Unlocking the quantum potential of nitrogen-vacancy (NV) centers in diamonds has led to innovative advancements in sensing applications. By coupling NV centers with plasmonic nanostructures, ultrasensitive biolabels are envisioned. To this end, we exploit DNA self-assembly to create hybrid plasmonic nanodiamonds, featuring a closed nanocavity encapsulating a single nanodiamond. Correlated spectroscopy reveals enhanced brightness and emission rates, crucial for quantum sensing. This synergy between plasmonics and diamond fluorescence augments photon emission intensity and accelerates emission rates, enabling improved temporal resolution. These nanodiamonds hold promise as stable single-photon sources and versatile platforms for probing quantum effects in biology. This talk highlights the development, properties, and potential applications of these nanodiamonds, bridging quantum sensing and biomedicine, and fostering transformative changes in biophotonics.