SiV0 centres in diamond: effect of isotopic substitution in carbon and silicon

The neutrally charged silicon-vacancy defect (SiV0) is a colour centre in diamond with spin S = 1, a zero-phonon line (ZPL) at 946 nm and long spin coherence, which makes it a promising candidate for quantum network applications. For the proper performance of such colour centres, all of them must have identical optical characteristics. However, in practice, there are factors that influence each individual centre. One of these factors is non-uniform isotope composition for both carbon atoms in diamond lattice and silicon atoms of dopant. In this work, we studied the isotopic shifts of SiV0 centres for CVD-grown epitaxial layers of isotopically enriched 12C and 13C diamonds, as well as for diamond with natural isotope composition but doped only with one isotope of Si (28Si, 29Si and 30Si). The detected shift was 1.60 meV for 12C/13C couple and 0.33 meV for 28Si/29Si and 29Si/30Si couples, which are close to the previously obtained values of the isotopic shift for the negatively charged silicon vacancy (SiV-), which indicates a similar model of interaction with the environment for these two charge states of the SiV colour centres. This article is part of the Theo Murphy meeting issue 'Diamond for quantum applications'.

Multispectral meta-film design: simultaneous realization of wideband microwave absorption, low infrared emissivity, and visible transparency

There is a huge challenge to target multispectral compatible designs to satisfy the conflicting parametric requirements according to specific engineering requirements. In this work, a novel design method of multispectral compatible integration based on a lossy capacitive multispectral meta-film (MMF) is proposed. The simple guidelines from the impedance matching conditions of MMF derived from the transmission line model were employed to guide and analyze the broadband microwave absorption behavior. An autonomous optimization platform was constructed to simultaneously realize the customization of low infrared emissivity, as well as the widest microwave absorption bandwidth while ensuring maximum visible transparency. Following the guidance of the design method, a flexible structure with a low infrared emissivity of 0.534, wideband microwave absorption from 8.9 to 16.4 GHz covering X, Ku, and high visible transmission of 70.18% and ultra-thin thickness of 2.3 mm was finally obtained. The experimental results and simulation results were in high agreement, indicating the MMF has great application potential in multispectral stealth on optical windows, further demonstrating the versatility and effectiveness of the design method.

A new approach to precise mapping of local temperature fields in submicrometer aqueous volumes

Nanodiamonds hosting temperature-sensing centers constitute a closed thermodynamic system. Such a system prevents direct contact of the temperature sensors with the environment making it an ideal environmental insensitive nanosized thermometer. A new design of a nanodiamond thermometer, based on a 500-nm luminescent nanodiamond embedded into the inner channel of a glass submicron pipette is reported. All-optical detection of temperature, based on spectral changes of the emission of "silicon-vacancy" centers with temperature, is used. We demonstrate the applicability of the thermometric tool to the study of temperature distribution near a local heater, placed in an aqueous medium. The calculated and experimental values of temperatures are shown to coincide within measurement error at gradients up to 20 °C/μm. Until now, temperature measurements on the submicron scale at such high gradients have not been performed. The new thermometric tool opens up unique opportunities to answer the urgent paradigm-shifting questions of cell physiology thermodynamics.

Core-shell designs of photoluminescent nanodiamonds with porous silica coatings for bioimaging and drug delivery II: application

Recent advances within materials science and its interdisciplinary applications in biomedicine have emphasized the potential of using a single multifunctional composite material for concurrent drug delivery and biomedical imaging. Here we present a novel composite material consisting of a photoluminescent nanodiamond (ND) core with a porous silica (SiO2) shell. This novel multifunctional probe serves as an alternative nanomaterial to address the existing problems with delivery and subsequent tracing of the particles. Whereas the unique optical properties of ND allows for long-term live cell imaging and tracking of cellular processes, mesoporous silica nanoparticles (MSNs) have proven to be efficient drug carriers. The advantages of both ND and MSNs were hereby integrated in the new composite material, ND@MSN. The optical properties provided by the ND core rendered the nanocomposite suitable for microscopy imaging in fluorescence and reflectance mode, as well as super-resolution microscopy as a STED label; whereas the porous silica coating provided efficient intracellular delivery capacity, especially in surface-functionalized form. This study serves as a demonstration how this novel nanomaterial can be exploited for both bioimaging and drug delivery for future theranostic applications.

Wettability of ultrananocrystalline diamond and graphite nanowalls films: a comparison with their single crystal analogs

Dramatic changes in wettability of diamond and graphite are observed when these materials are prepared in nanostructured forms--undoped and nitrogen-doped ultrananocrystalline diamond (UNCD) films, and graphite nanowalls (GNW), respectively. The nanostructured carbon films were deposited on Si by microwave plasma CVD processes. The advancing contact angle theta for water on hydrogenated undoped UNCD films increases to 106 +/- 3 degrees compared to hydrogenated single crystal diamond (theta = 92 degrees). Nitrogen doping (N2 addition to plasma) during UNCD growth makes the film more hydrophilic. The GNW films exhibited superhydrophobic behavior with theta = 144 +/- 3 degrees for water, which is higher than the contact angle of monocrystalline graphite (the basal plane) by a factor of 1.8. No chemical surface treatment is necessary to achieve such high hydrophobicity, it is accomplished solely by a specific (nanoporous, high aspect ratio) surface morphology with very low free surface energy inherent in it. The wetting behaviour of nanostructured films can be described with the Cassie-Baxter equation for heterophase nanoporous surfaces. Oxidation and hydrogenation of UNCD films make it possible to control theta over a much wider range as compared to a single crystal diamond. The influence of diamond grain size on wetting is considered taking into account the surface treatment. The corresponding variation in surface energy has been determined by the modified Young's equation.

Carbon structures with three-dimensional periodicity at optical wavelengths

Porous carbons that are three-dimensionally periodic on the scale of optical wavelengths were made by a synthesis route resembling the geological formation of natural opal. Porous silica opal crystals were sintered to form an intersphere interface through which the silica was removed after infiltration with carbon or a carbon precursor. The resulting porous carbons had different structures depending on synthesis conditions. Both diamond and glassy carbon inverse opals resulted from volume filling. Graphite inverse opals, comprising 40-angstrom-thick layers of graphite sheets tiled on spherical surfaces, were produced by surface templating. The carbon inverse opals provide examples of both dielectric and metallic optical photonic crystals. They strongly diffract light and may provide a route toward photonic band-gap materials.