中央研究院 原子與分子科學研究所

Extreme ultraviolet (EUV) radiation with wavelengths of 10 – 121 nm has drawn considerable attention recently for its use in photolithography to fabricate nanoelectronic chips.  This study demonstrates, for the first time, fluorescent nanodiamonds (FNDs) with nitrogen-vacancy (NV) centers as scintillators to image and characterize EUV radiations.  The FNDs employed are ~100 nm in size; they form a uniform and stable thin film on an indium tin oxide-coated slide by electrospray deposition.  The film is non-hygroscopic, photostable, and can emit bright red fluorescence from NV⁰ centers when excited by EUV light.  An FND-based imaging device has been developed and applied for beam diagnostics of 50 nm and 13.5 nm synchrotron radiations, achieving a spatial resolution of 30 μm using a film of ~1 μm thickness.  The noise equivalent power density is 29 μW/cm²Hz^1/2 for the 13.5 nm radiation.  The method is generally applicable to imaging EUV radiations from different sources. 

 
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The negatively charged nitrogen-vacancy (NV^–) center in fluorescent nanodiamond (FND) 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 surface or dispersed in solution with a lock-in detection method.  We achieved selective and sensitive detection of 100-nm FNDs on nitrocellulose membrane at a particle density of 0.04 ng/mm² (or ~2 × 10⁴ particles/mm²) and in 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.

Fluorescent nanodiamond (FND) containing nitrogen-vacancy (NV) centers as built-in fluorophores exhibits a nearly constant emission profile over 550 – 750 nm upon excitation by vacuum-ultraviolet (VUV), extreme ultraviolet (EUV), and X- radiations from a synchrotron source over the energy (wavelength) range of 6.2 – 1450 eV (0.86 – 200 nm).  The photoluminescence (PL) quantum yield of FND increases steadily with the increasing excitation energy, attaining a value as great as 1700% at 700 eV (1.77 nm).  Notably, the yield curve is continuous, having no gap in the VUV to X-ray region.  In addition, no significant PL intensity decreases were observed for hours.  Applying the FND sensor to measure the absorption cross sections of gaseous O₂ over 110 – 200 nm and comparing the measurements with the sodium-salicylate scintillator, we obtained results in agreement with each other within 5%.  The superb photostability and broad applicability of FND offer a promising solution for the long-standing problem of lacking a robust and reliable detector for VUV, EUV, and X- radiations.

Containing an ensemble of nitrogen-vacancy centers in crystal matrices, fluorescent nanodiamonds (FNDs) are a new type of photostable markers that have found wide applications in light microscopy.  The nanomaterial also has a dense carbon core, making it visible to electron microscopy.  Here, we show that FNDs encapsulated in biotinylated lipids (bLs) are useful for sub-diffraction imaging of antigens on cell surface with correlative light-electron microscopy (CLEM).  The lipid encapsulation enables not only good dispersion of the particles in biological buffers but also high specific labeling of live cells.  By employing the bL-encapsulated FNDs to target CD44 on HeLa cell surface through biotin-mediated immunostaining, we obtained the spatial distribution of these antigens by CLEM with a localization accuracy of ~50 nm in routine operations.  A comparative study with dual-color imaging, in which CD44 was labeled with FND and MICA/MICB was labeled with Alexa Fluor 488, demonstrated the superior performance of FNDs as fluorescent fiducial markers for CLEM of cell surface antigens.

The nitrogen-vacancy (NV) centers in diamond are among the most thoroughly investigated defects in the solid state of matter; however, our understanding of their properties upon far-UV excitation of the host matrix is limited.  The knowledge is crucial for the identification of NV as the carrier of extended red emission (ERE) bands detected in a wide range of astrophysical environments.  Here, we report a study on the photoluminescence spectra of NV-containing nanodiamonds excited with synchrotron radiation over the wavelength range of 125 – 350 nm.  We observed, for the first time, the emission at 520 – 850 nm with a quantum yield greater than 20 %.  Our results share multiple similarities with the ERE phenomena, suggesting that nanodiamonds are a common component of dust in space.