Nitrogen-vacancy Centers In Nanodiamonds Research Articles

Near-zero-field microwave-free magnetometry with nitrogen-vacancy centers in nanodiamonds

Near-zero-field microwave-free magnetometry with nitrogen-vacancy centers in nanodiamonds

Sensing the Spin State of Room-Temperature Switchable Cyanometallate Frameworks with Nitrogen-Vacancy Centers in Nanodiamonds.

Room-temperature magnetically switchable materials play a vital role in current and upcoming quantum technologies, such as spintronics, molecular switches, and data storage devices. The increasing miniaturization of device architectures produces a need to develop analytical tools capable of precisely probing spin information at the single-particle level. In this work, we demonstrate a methodology using negatively charged nitrogen vacancies (NV-) in fluorescent nanodiamond (FND) particles to probe the magnetic switching of a spin crossover (SCO) metal-organic framework (MOF), [Fe(1,6-naphthyridine)2(Ag(CN)2)2] material (1), and a single-molecule photomagnet [X(18-crown-6)(H2O)3]Fe(CN)6·2H2O, where X = Eu and Dy (materials 2a and 2b, respectively), in response to heat, light, and electron beam exposure. We employ correlative light-electron microscopy using transmission electron microscopy (TEM) finder grids to accurately image and sense spin-spin interacting particles down to the single-particle level. We used surface-sensitive optically detected magnetic resonance (ODMR) and magnetic modulation (MM) of FND photoluminescence (PL) to sense spins to a distance of ca. 10-30 nm. We show that ODMR and MM sensing was not sensitive to the temperature-induced SCO of FeII in 1 as formation of paramagnetic FeIII through surface oxidation (detected by X-ray photoelectron spectroscopy) on heating obscured the signal of bulk SCO switching. We found that proximal FNDs could effectively sense the chemical transformations induced by the 200 keV electron beam in 1, namely, AgI → Ag0 and FeII → FeIII. However, transformations induced by the electron beam are irreversible as they substantially disrupt the structure of MOF particles. Finally, we demonstrate NV- sensing of reversible photomagnetic switching, FeIII + (18-crown-6) ⇆ FeII + (18-crown-6)+ •, triggered in 2a and 2b by 405 nm light. The photoredox process of 2a and 2b proved to be the best candidate for room-temperature single-particle magnetic switching utilizing FNDs as a sensor, which could have applications into next-generation quantum technologies.

Atomically Precise Detection and Manipulation of Nitrogen-Vacancy Centers in Nanodiamonds.

Nitrogen-vacancy (NV) centers in nanodiamonds are a promising quantum communication system offering robust and discrete single photon emission, but a more thorough understanding of properties of the NV centers is critical for real world implementation in functional devices. The first step to understanding how factors such as surface, depth, and charge state affect NV center properties is to directly characterize these defects on the atomic scale. Here we use Angstrom-resolution scanning transmission electron microscopy (STEM) to identify a single NV center in a ∼4 nm natural nanodiamond through simultaneous acquisition of electron energy loss and energy dispersive X-ray spectra, which provide a characteristic NV center peak and a nitrogen peak, respectively. In addition, we identify NV centers in larger, ∼15 nm synthetic nanodiamonds, although without the single-defect resolution afforded by the lower background of the smaller natural nanodiamonds. We have further demonstrated the potential to directly position these technologically relevant defects at the atomic scale using the scanning electron beam to "herd" NV centers and nitrogen atoms across their host nanodiamonds.

Detecting the metabolism of individual yeast mutant strain cells when aged, stressed or treated with antioxidants with diamond magnetometry

Free radicals play a key role in the ageing process. However, free radicals are small, reactive and short lived and thus challenging to measure. We utilize a new technique called diamond magnetometry for this purpose. We make use of nitrogen vacancy centers in nanodiamonds. Via a quantum effect these defects convert a magnetic resonance signal into an optical signal. While this method is increasingly popular for its unprecedented sensitivity in physics, we use this technique here for the first time to measure free radicals in living cells. Our signals are equivalent to T1 signals in conventional MRI but from nanoscale voxels from single cells with sub-cellular resolution. With this powerful tool we are able to follow free radical generation after chemically inducing stress. In addition, we can observe free radical reduction in presence of an antioxidant. We were able to clearly differentiate between mutant strains with altered metabolism. Finally, the excellent stability of our diamond particles allowed us to follow the ageing process and differentiate between young and old cells. We could confirm the expected increase of free radical load in old wild type and sod1Δ mutants. We further applied this new technique to investigate tor1Δ and pex19Δ cells. For these mutants an increased lifespan has been reported but the exact mechanism is unclear. We find a decreased free radical load in, which might offer an explanation for the increased lifespan in these cells.

Tailored light emission from color centers in nanodiamond using self-assembled photonic crystals

The defect centers in solid-state materials especially the nitrogen-vacancy (NV) centers in diamond have shown a tremendous potential for their utilization in quantum technology applications. However, they exhibit certain drawbacks such as the feeble zero phonon line with huge phonon contribution and the higher lifetime values. Here, we present a novel approach to control the spontaneous emission from NV centers in nanodiamond using engineered self-assembled photonic crystals. Using two complimentary emission measuring geometries at room temperature, we show a 63% suppression and 17% enhancement of NV center emission intensity using photonic stopgap, supported with simulations. The emission rates are modified in a broad spectral range of NV center emission and are consistent with the Barnett–Loudon sum rule. The results are crucial for emerging quantum technologies using NV centers in diamond.

Nanodiamond-Quantum Sensors Reveal Temperature Variation Associated to Hippocampal Neurons Firing.

Temperature is one of the most relevant parameters for the regulation of intracellular processes. Measuring localized subcellular temperature gradients is fundamental for a deeper understanding of cell function, such as the genesis of action potentials, and cell metabolism. Notwithstanding several proposed techniques, at the moment detection of temperature fluctuations at the subcellular level still represents an ongoing challenge. Here, for the first time, temperature variations (1 °C) associated with potentiation and inhibition of neuronal firing is detected, by exploiting a nanoscale thermometer based on optically detected magnetic resonance in nanodiamonds. The results demonstrate that nitrogen‐vacancy centers in nanodiamonds provide a tool for assessing various levels of neuronal spiking activity, since they are suitable for monitoring different temperature variations, respectively, associated with the spontaneous firing of hippocampal neurons, the disinhibition of GABAergic transmission and the silencing of the network. Conjugated with the high sensitivity of this technique (in perspective sensitive to < 0.1 °C variations), nanodiamonds pave the way to a systematic study of the generation of localized temperature gradients under physiological and pathological conditions. Furthermore, they prompt further studies explaining in detail the physiological mechanism originating this effect.

Revealing Capillarity in AFM Indentation of Cells by Nanodiamond-Based Nonlocal Deformation Sensing.

Nanoindentation based on atomic force microscopy (AFM) can measure the elasticity of biomaterials and cells with high spatial resolution and sensitivity, but relating the data to quantitative mechanical properties depends on information on the local contact, which is unclear in most cases. Here, we demonstrate nonlocal deformation sensing on biorelevant soft matters upon AFM indentation by using nitrogen-vacancy centers in nanodiamonds, providing data for studying both the elasticity and capillarity without requiring detailed knowledge about the local contact. Using fixed HeLa cells for demonstration, we show that the apparent elastic moduli of the cells would have been overestimated if the capillarity was not considered. In addition, we observe that both the elastic moduli and the surface tensions are reduced after depolymerization of the actin cytoskeleton in cells. This work demonstrates that the nanodiamond sensing of nonlocal deformation with nanometer precision is particularly suitable for studying mechanics of soft biorelevant materials.

Stacked metasurfaces for enhancing the emission and extraction rate of single nitrogen-vacancy centers in nanodiamond

Dielectric metasurfaces with unique possibilities of manipulating light–matter interaction lead to new insights in exploring spontaneous emission control using single quantum emitters. Here, we study the stacked metasurfaces in one- (1D) and two-dimensions (2D) to enhance the emission rate of a single quantum emitter using the associated optical resonances. The 1D structures with stacked bilayers are investigated to exhibit Tamm plasmon resonance optimized at the zero phonon line (ZPL) of the negative nitrogen-vacancy (NV−) center. The 2D stacked metasurface comprising of two-slots silicon nano-disks is studied for the Kerker condition at ZPL wavelength. The far-field radiation plots for the 1D and 2D stacked metasurfaces show an increased extraction efficiency rate for the NV− center at ZPL wavelength that reciprocates the localized electric field intensity. The modified local density of optical states results in large Purcell enhancement of 3.8 times and 25 times for the single NV− center integrated with 1D and 2D stacked metasurface, respectively. These results have implications in exploring stacked metasurfaces for applications such as single photon generation and CMOS compatible light sources for on-demand chip integration.

Comparison of back focal plane imaging of nitrogen vacancy centers in nanodiamond and core-shell CdSe/CdS quantum dots

We report on the characterization of the angular-dependent emission of two different single-photon emitters based on nitrogen-vacancy centers in nanodiamond and on core-shell CdSe/CdS quantum dot nanoparticles. The emitters were characterized in a confocal microscope setup by spectroscopy and Hanbury-Brown and Twiss interferometry. The angular-dependent emission is measured using a back focal plane imaging technique. A theoretical model of the angular emission patterns of the 2D dipoles of the emitters is developed to determine their orientation. Experiment and model agree well with each other.

Charge state depletion nanoscopy with a nitrogen-vacancy center in nanodiamonds.

The development of super-resolution imaging has driven research into biological labeling, new materials' characterization, and nanoscale sensing. Here, we studied the photoinduced charge state conversion of nitrogen-vacancy (NV) centers in nanodiamonds (NDs), which show the potential for multifunction sensing and labeling at the nanoscale. Charge state depletion (CSD) nanoscopy is subsequently demonstrated for the diffraction-unlimited imaging of NDs in biological cells. A resolution of 77 nm is obtained with 50 nm NDs. The depletion laser power of CSD nanoscopy is approximately 1/16 of stimulated emission depletion (STED) microscopy with the same resolution. The results can be used to improve the spatial resolution of biological labeling and sensing with NDs and other nanoparticles.

Sample fabrication and metrological characterization of single-photon emitters based on nitrogen vacancy centers in nanodiamonds

Quantum metrology requires a stable single-photon emission and a high single-photon purity. Since nitrogen-vacancy (NV-) centers provide both features at room temperature, they are promising candidates for the application in this field [1, 2]. The knowledge about a suitable sample preparation technique is crucial, because the quality of the single-photon emission strongly depends on the sample purity and on the spatial resolvability of the emitters. This work presents the comparison and optimization of various sample fabrication techniques of nitrogen vacancy center doped nanodiamonds on standard cover glasses. The preparation is followed by a comparative characterization of the centers of the various samples. The sample fabrication includes the removal of contaminants on the cover glass surface. This was carried out by using peroxymonosulfuric acid (piranha solution, H2SO5) in comparison to the commercially available lye Hellmanex III (by Hellma Analytics). After cleaning the cover glasses, volumes of various nanodiamond dilutions were applied via spin coating. In subsequent steps, the nanodiamonds themselves were cleaned with peroxymonosulfuric acid, too, to remove contaminants resulting from the manufacturing process, e.g. graphite. The samples were analyzed by using a confocal laser scanning microscope with an oil immersion objective. Single-photon purity was determined by measuring the second order correlation function with a Hanbury Brown and Twiss setup. Spectral analysis revealed the presence of NV−- and NV°-centers. It was shown that a suitable cleansing method has an immense impact on single-photon emission, as was proven by a comparative characterization of differently manufactured nanodiamonds.

Enhancing spontaneous emission using structural resonances of self-assembled monolayers

Self-assembled monolayers made using sub-micron dielectric spheres are analogous to atomic monolayers that have proved to be a modern workhorse in condensed matter physics. Here, we discuss the origin of optical resonances associated with sub-micron dielectric monolayers through experiments that are further supported by theory and simulation. These resonances are used to enhance the emission rate of nitrogen-vacancy centers in nanodiamonds. Emission decay rate measurements confirm a 14% decrease in the excited state lifetime, which implies an enhanced emission rate at the resonances. The increase in measured decay rates is supported by the calculated local density of optical states. Our results provide a platform to tailor light transport and emission for applications in photonics and quantum technology using these monolayers.

Engineering the collapse of lifetime distribution of nitrogen-vacancy centers in nanodiamonds

Abstract

Purcell effect of nitrogen-vacancy centers in nanodiamond coupled to propagating and localized surface plasmons revealed by photon-correlation cathodoluminescence

We measured the second-order correlation function of the cathodoluminescence intensity and investigated the Purcell effect by comparing the lifetimes of quantum emitters with and without metal structure. The increase in the electromagnetic local density of state due to the coupling of a quantum emitter with a plasmonic structure causes a shortening of the emitter lifetime, which is called the Purcell effect. Since the plasmon-enhanced electric field is confined well below the wavelength of light, the quantum emitter lifetime is changed in the nanoscale range. In this study, we combined cathodoluminescence in scanning (transmission) electron microscopy with Hanbury Brown-Twiss interferometry to measure the Purcell effect with nanometer and nanosecond resolutions. We used nitrogen-vacancy centers contained in nanodiamonds as quantum emitters and compared their lifetime in different environments: on a thin SiO2 membrane, on a thick flat silver film, and embedded in a silver film. The lifetime reductions of nitrogen-vacancy centers were clearly observed in the samples with silver. We evaluated the lifetime by analytical calculation and numerical simulations and revealed the Purcell effects of emitters coupled to propagating and localized surface plasmons. This is the first experimental result showing the Purcell effect due to the coupling between nitrogen-vacancy centers in nanodiamonds and surface plasmon polaritons with nanometer resolution.

Magnetically Modulated Fluorescence of Nitrogen-Vacancy Centers in Nanodiamonds for Ultrasensitive Biomedical Analysis.

The negatively charged nitrogen-vacancy center in fluorescent nanodiamonds (FNDs) is a point defect with unique magneto-optical properties. It emits far-red fluorescence at ∼700 nm, and its intensity can be magnetically modulated with a depth of more than 10% at a field strength of 30 mT. We have closely examined this property and illustrated its practical use in biomedicine by applying a periodic, time-varying magnetic field to FNDs deposited on a surface or dispersed in a solution with a lock-in detection method. We achieved selective and sensitive detection of 100 nm FNDs on a nitrocellulose membrane at a particle density of 0.04 ng/mm2 (or ∼2 × 104 particles/mm2) and in an aqueous solution with a particle concentration of 1 ng/mL (or ∼1 fM) in 10 s as the detection limits. The utility and versatility of the technique were demonstrated with an application to background-free detection of FNDs as reporters for FND-based lateral flow immunoassays as well as selective quantification of FNDs in tissue digests for in vivo studies.

Monitoring Dark-State Dynamics of a Single Nitrogen-Vacancy Center in Nanodiamond by Auto-Correlation Spectroscopy: Photonionization and Recharging.

In this letter, the photon-induced charge conversion dynamics of a single Nitrogen-Vacancy (NV) center in nanodiamond between two charge states, negative (NV−) and neutral (NV0), is studied by the auto-correlation function. It is observed that the ionization of NV− converts to NV0, which is regarded as the dark state of the NV−, leading to fluorescence intermittency in single NV centers. A new method, based on the auto-correlation calculation of the time-course fluorescence intensity from NV centers, was developed to quantify the transition kinetics and yielded the calculation of transition rates from NV− to NV0 (ionization) and from NV0 to NV− (recharging). Based on our experimental investigation, we found that the NV−-NV0 transition is wavelength-dependent, and more frequent transitions were observed when short-wavelength illumination was used. From the analysis of the auto-correlation curve, it is found that the transition time of NV− to NV0 (ionization) is around 0.1 μs, but the transition time of NV0 to NV− (recharging) is around 20 ms. Power-dependent measurements reveal that the ionization rate increases linearly with the laser power, while the recharging rate has a quadratic increase with the laser power. This difference suggests that the ionization in the NV center is a one-photon process, while the recharging of NV0 to NV− is a two-photon process. This work, which offers theoretical and experimental explanations of the emission property of a single NV center, is expected to help the utilization of the NV center for quantum information science, quantum communication, and quantum bioimaging.

High ensemble concentration of photo-stable NV centers in Type Ib nanodiamonds by thermal assisted migration of native vacancies

Ion implantation and subsequent vacuum annealing is a conventional technique to fabricate nitrogen vacancy (NV) centers in nanodiamonds (NDs) for different applications where high emission collection is required. In this work, we have explored as-grown lattice vacancies for creation of NV centers in NDs by making them migrate using high temperature isothermal heat treatment. The concentration of NV centers is maximized at optimized fabrication parameters of heat treatment (1000 °C with residual time of 1 h in vacuum environment) and subsequent air oxidation (575 °C, 2 h). The results show that optimized NV fabrication parameters lead to high photo-stability of NDs both at ensemble as well as individual ND particle level. The obtained NV− concentration of ~6.7 ppm is comparable to that of the sample irradiated by He2+ ions having beam energy of 50 keV and fluence of 1013 ions/cm2 (~12.5 ppm), with higher ensemble photo-stability than the later. Our results, which demonstrate that high concentration NV centers with high photo-stability is achievable by low cost processing without employing the ion implantation, thus can contribute to the fields of optical bio-imaging and ensemble magnetometry which require bright emission from NV centers.

Robust integration of nitrogen-vacancy centers in nanodiamonds to optical fiber and its application in all-optical thermometry

In this Letter, we developed a robust method for integrating nanodiamonds (NDs) to optical fiber. The NDs, containing nitrogen-vacancy (NV) centers, were uniformly mixed with UV adhesive before coating the end surface of a multimode fiber as a hemispherical film. The excitation and collection efficiency of NV fluorescence can be enhanced by increasing the thickness of UV adhesive film and additional aluminum film deposition. The fiber-based quantum sensor was also experimentally demonstrated for all-optical thermometry application. The variation of the refractive index of UV adhesive under different temperatures will also affect the NV collection efficiency by changing the light confinement. The demonstrated facile integration approach paves the way for developing fiber-based quantum thermometry and magnetometry.

In Situ Studies of Stress Environment in Amorphous Solids Using Negatively Charged Nitrogen Vacancy (NV–) Centers in Nanodiamond

Amorphous solids, which show characteristic differences from crystals, are common in daily usage. Glasses, gels, and polymers are familiar examples, and polymers are particularly important in terms of their role in construction and crafting. Previous studies have mainly focused on the bulk properties of polymeric products, and the local properties are less discussed. Here, we designed a distinctive protocol using the negatively charged nitrogen vacancy center in nanodiamond to study properties inside polymeric products in situ. Choosing the curing of poly dimethylsiloxane and the polymerization of cyanoacrylate as subjects of investigation, we measured the time dependence of local pressure and strain in the materials during the chemical processes. From the measurements, we were able to probe the local shear stress inside the two polymeric substances in situ. By regarding the surprisingly large shear stress as the internal tension, we attempted to provide a microscopic explanation for the ultimate tensile strength of a bulk solid. Our current methodology is applicable to any kind of transparent amorphous solids with the stress in the order of MPa and to the study of in situ properties in nanoscale. With better apparatus, we expect the limit can be pushed to sub-MPa scale.

Characterization of the angular-dependent emission of nitrogen-vacancy centers in nanodiamond

We report on the characterization of the angular-dependent emission of single-photon emitters based on single nitrogen-vacancy (NV-) centers in nanodiamond at room temperature. A theoretical model for the calculation of the angular emission patterns of such an NV-center at a dielectric interface will be presented. For the first time, the orientation of the NV-centers in nanodiamond was determined from back focal plane images of NV-centers and by comparison of the theoretical and experimental angular emission pattern. Furthermore, the orientation of the NV-centers was also obtained from measurements of the fluorescence intensity in dependence on the polarization angle of the linearly polarized excitation laser. The results of these measurements are in good agreement. Moreover, the collection efficiency in this setup was calculated to be higher than 80% using the model of the angular emission of the NV-centers.