Five‐Nanometer Diamond with Luminescent Nitrogen‐Vacancy Defect Centers

Abstract

Various types of luminescent color centers made in diamond by substitution of carbon with nitrogen, [1] nickel, [2] silicon, [3] and/or a vacancy have been of interest for applications in many fields. One of the most widely used ways for making diamond luminescent involves substitution of one carbon atom with nitrogen and creation of a vacancy at a location adjacent to the nitrogen atom, thus forming a nitrogen-vacancy (NV) color center. [1] NV-photoluminescent diamonds are extremely photostable, [4] biocompatible, [5] exhibit amiable surface chemistry, [6] and show optically detectable sensitivity to magnetic fields. [1] Although the production of 25-nm luminescent diamond based on high-temperature high-pressure (HTHP) synthesis [7,8] has already brought exciting results in quantum physics [1,9] and the life sciences, [4,7,10] crystals no larger than a few nanometers will break ground in these applications [3,6,11] and other fields. [12,13] Functionalized single-digit nanodiamonds (SNDs) may be used to track biomolecules with minimal steric and biochemical perturbations, are small enough to show detectable quantum interactions between NV centers located in different crystals, [14] and will facilitate the realization of high-resolution magnetic [12,15] and near-field optical microscopes. [13] SNDs have recently been produced by breaking detonation-synthesized nanodiamonds [16] into 5-nm primary crystals [17] but no progress has yet been reported towards embedding NV centers into SNDs. Furthermore, there is growing concern that NV centers in SNDs cannot form due to physical barriers, such as the proximity to surface traps and reduced stability of defects. [3,18,19] A study of NV centers in similar-scale diamond grains created with chemical vapor deposition found no NV centers in crystals smaller than 20 nm. [18] Furthermore, theoretical work suggests that nitrogen becomes less energetically stable in the core of nanodiamonds as they become smaller. [20] It has also been suggested that luminescence may be quenched by nearby surface defects, [18] and that high levels of oxygen and other impurities in detonation-synthesized diamond may affect the formation of NV centers. Intrinsic short-lived luminescence from surface defects in SNDs further confounds the issue. [21] Herein, we examine the properties of weakly bound clusters of SNDs by using spectrally and temporally resolved luminescence detection, electron paramagnetic resonance (EPR) spectroscopy, and transmission electron microscopy (TEM), and present the first report of the successful detection of NV centers in 5-nm diamond. Furthermore, we provide a simple physical argument on why the probability of creating a color center in a small crystal scales as the fifth power of the crystal size.NV centers in diamonds were created by high-energy proton irradiation followed by thermal annealing (see Experimental Section). For luminescence measurements, samples containing equal weights of 55-nm HTHP diamonds and SNDs were uniformly distributed on quartz substrates. Prist...

Fluorescence and Spin Properties of Defects in Single Digit Nanodiamonds

“…The probability of a vacancy to diffuse to the surface instead of binding to a nitrogen atom scales as r 2 (r is nanodiamond radius). 20 Therefore, one expects a significantly lower yield for NV formation in small nanocrystals as compared to the bulk because the vacancies are mostly expected to anneal to the surface. The fact that this is not observed in our experiments suggests that the vacancies do not diffuse far before com- www.acsnano.org bining with a nitrogen or interstitial carbon created by the irradiation process and, therefore, do not have time to reach the surface.…”

“…Attempts to observe stable luminescence from very small 5 nm nanodiamonds synthesized by explosive growth have so far only been successful for aggregates but not for single nanodiamonds. 20 This raised the question of whether stable photoluminescence defects are observable at all in single nanometer-sized nanocrystals and if so how much lower would be the *Address correspondence to j.wrachtrup@physik.uni-stuttgart.de.…”

Near-field microscopy with a single-photon point-like emitter: Resolution versus the aperture tip?

“…In the nanodiamond-based NSOM probe [9], the optical behavior originates from the point-like transition dipole associated with the radiative transition of the NV colorcenter. We here neglect the finite extension of the host nanocrystal since current trends in nanodiamond processing indicate that it can be diminished down to a few nms only [19,20]. Therefore, we expect the point-like model outlined above to apply to this tip and we will indeed describe the nanodiamond-based tip as a single point-like dipole.…”

Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds

“…Although nitrogen-vacancy centres have been observed in aggregated detonation nanodiamonds 5 and milled nanodiamonds 6 , they have not been observed in very small isolated nanodiamonds 7 . Here, we report the first direct observation of nitrogen-vacancy centres in discrete 5-nm nanodiamonds at room temperature, including evidence for intermittency in the luminescence (blinking) from the nanodiamonds.…”