中央研究院 原子與分子科學研究所

Nanoscale quantum sensing is playing an increasingly critical role across diverse areas of research, particularly in the rapidly evolving field of semiconductor nanoelectronics.  In this work, ultrathin fluorescent nanodiamond (FND) films are developed to function as quantum sensors for in operando measurements of magnetic fields and temperature in semiconductor devices.  FNDs are electrically insulating carbon nanomaterials containing nitrogen-vacancy (NV) centers, renowned for their exceptional photostability and distinctive quantum properties.  An electrospray deposition method is first established to produce uniform, near-monolayer FND films on bipolar junction transistors (BJTs) and field-effect transistors (FETs) without compromising their performance.  Then, optically detected magnetic resonance (ODMR)s is employed to detect magnetic fields and monitor temperature increases as electrical currents are passed through the FND-coated semiconductor chips.  Finally, we introduce a technique called FND-based lock-in photoluminescence (PL) thermography, which enables wide-field, real-time temperature sensing and imaging of these actively operating BJTs and FETs with nanometric spatial and millisecond temporal resolution.  In comparison to ODMR, this innovative PL thermography method offers enhanced practicality and ease of implementation, making it well-suited for diagnostic applications in semiconductor devices. 

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.