Can Europium Atoms form Luminescent Centres in Diamond: A combined Theoretical-Experimental Study

The incorporation of Eu into the diamond lattice is investigated in a combined theoretical-experimental study. The large size of the Eu ion induces a strain on the host lattice, which is minimal for the Eu-vacancy complex. The oxidation state of Eu is calculated to be 3+ for all defect models considered. In contrast, the total charge of the defect-complexes is shown to be negative -1.5 to -2.3 electron. Hybrid-functional electronic-band-structures show the luminescence of the Eu defect to be strongly dependent on the local defect geometry. The 4-coordinated Eu substitutional dopant is the most promising candidate to present the typical Eu3+ luminescence, while the 6-coordinated Eu-vacancy complex is expected not to present any luminescent behaviour. Preliminary experimental results on the treatment of diamond films with Eu-containing precursor indicate the possible incorporation of Eu into diamond films treated by drop-casting. Changes in the PL spectrum, with the main luminescent peak shifting from approximately 614 nm to 611 nm after the growth plasma exposure, and the appearance of a shoulder peak at 625 nm indicate the potential incorporation. Drop-casting treatment with an electronegative polymer material was shown not to be necessary to observe the Eu signature following the plasma exposure, and increased the background luminescence.Comment: 12 pages, 7 figures, 5 table

Laser writing of individual atomic defects in a crystal with near-unity yield

Atomic defects in wide band gap materials show great promise for development of a new generation of quantum information technologies, but have been hampered by the inability to produce and engineer the defects in a controlled way. The nitrogen-vacancy (NV) color center in diamond is one of the foremost candidates, with single defects allowing optical addressing of electron spin and nuclear spin degrees of freedom with potential for applications in advanced sensing and computing. Here we demonstrate a method for the deterministic writing of individual NV centers at selected locations with high positioning accuracy using laser processing with online fluorescence feedback. This method provides a new tool for the fabrication of engineered materials and devices for quantum technologies and offers insight into the diffusion dynamics of point defects in solids.Comment: 16 pages, 8 figure

Catalyst Stability Benchmarking for the Oxygen Evolution Reaction: The Importance of Backing Electrode Material and Dissolution in Accelerated Aging Studies

In searching for alternative oxygen evolution reaction (OER) catalysts for acidic water splitting, fast screening of the material intrinsic activity and stability in half-cell tests is of vital importance. The screening process significantly accelerates the discovery of new promising materials without the need of time-consuming real-cell analysis. In commonly employed tests, a conclusion on the catalyst stability is drawn solely on the basis of electrochemical data, for example, by evaluating potential-versus-time profiles. Herein important limitations of such approaches, which are related to the degradation of the backing electrode material, are demonstrated. State-of-the-art Ir-black powder is investigated for OER activity and for dissolution as a function of the backing electrode material. Even at very short time intervals materials like glassy carbon passivate, increasing the contact resistance and concealing the degradation phenomena of the electrocatalyst itself. Alternative backing electrodes like gold and boron-doped diamond show better stability and are thus recommended for short accelerated aging investigations. Moreover, parallel quantification of dissolution products in the electrolyte is shown to be of great importance for comparing OER catalyst feasibility

Rare Isotope-Containing Diamond Color Centers for Fundamental Symmetry Tests

Detecting a non-zero electric dipole moment (EDM) in a particle would unambiguously signify physics beyond the Standard Model. A potential pathway towards this is the detection of a nuclear Schiff moment, the magnitude of which is enhanced by the presence of nuclear octupole deformation. However, due to the low production rate of isotopes featuring such "pear-shaped" nuclei, capturing, detecting, and manipulating them efficiently is a crucial prerequisite. Incorporating them into synthetic diamond optical crystals can produce defects with defined, molecule-like structures and isolated electronic states within the diamond band gap, increasing capture efficiency, enabling repeated probing of even a single atom, and producing narrow optical linewidths. In this study, we used density functional theory (DFT) to investigate the formation, structure, and electronic properties of crystal defects in diamond containing $^{229}$Pa, a rare isotope that is predicted to have an exceptionally strong nuclear octupole deformation. In addition, we identified and studied stable lanthanide-containing defects with similar electronic structures as non-radioactive proxies to aid in experimental methods. Our findings hold promise for the existence of such defects and can contribute to the development of a quantum information processing-inspired toolbox of techniques for studying rare isotopes

Impact of methane concentration on surface morphology and boron incorporation of heavily boron-doped single crystal diamond layers

The methane concentration dependence of the plasma gas phase on surface morphology and boron incorporation in single crystal, boron-doped diamond deposition is experimentally and computationally investigated. Starting at 1%, an increase of the methane concentration results in an observable increase of the B-doping level up to 1.7 x 10(21) cm(-3), while the hole Hall carrier mobility decreases to 0.7 +/- 0.2 cm(2) V-1 s(-1). For B-doped SCD films grown at 1%, 2%, and 3% [CH4]/[H-2], the electrical conductivity and mobility show no temperature-dependent behavior due to the metallic-like conduction mechanism occurring beyond the Mott transition. First principles calculations are used to investigate the origin of the increased boron incorporation. While the increased formation of growth centers directly related to the methane concentration does not significantly change the adsorption energy of boron at nearby sites, they dramatically increase the formation of missing H defects acting as preferential boron incorporation sites, indirectly increasing the boron incorporation. This not only indicates that the optimized methane concentration possesses a large potential for controlling the boron concentration levels in the diamond, but also enables optimization of the growth morphology. The calculations provide a route to understand impurity incorporation in diamond on a general level, of great importance for color center formation. (C) 2020 Elsevier Ltd. All rights reserved.</p

Elucidation of the Growth Mechanism of Sputtered 2D Hexagonal Boron Nitride Nanowalls

Abstract: Hexagonal boron nitride nanowall thin films were deposited on Si(100) substrates using a Ar(51%)/N-2(44%)/H-2(5%) gas mixture by unbalanced radio frequency sputtering. The effects of various target-to-substrate distances, substrate temperatures, and substrate tilting angles were investigated. When the substrate is close to the target, hydrogen etching plays a significant role in the film growth, while the effect is negligible for films deposited at a farther distance. The relative quantity of defects was measured by a non-destructive infrared spectroscopy technique that characterized the hydrogen incorporation at dangling nitrogen bonds at defect sites in the deposited films. Despite the films deposited at different substrate tilting angles, the nanowalls of those films were found to consistently grow vertical to the substrate surface, independent of the tilting angle. This implies that chemical processes, rather than physical ones, govern the growth of the nanowalls. The results also reveal that the degree of nanowall crystallization is tunable by varying the growth parameters. Finally, evidence of hydrogen desorption during vacuum annealing is given based on measurements of infrared stretching (E-1u) and bending (A(2u)) modes of the optical phonons, and the H-N vibration mode

Dataset: Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield

This archive contains the underlying data used in the preparation of the manuscript: YC Chen et al, "Laser writing of individual nitrogen-vacancy defects in diamond with near-unity yield" Optica 6 (5), 662-667 (2019). There is photoluminessence data from a confocal microscope taken to analyse the orientation, positioning accuracy and number of nitrogen vacancy defects written in three different arrays inside diamond. There is also included the photoluminessence feedback signal recorded when laser writing each of the defects. Matlab and Origin are required to open some of the files