Deterministic and versatile approaches to sample preparation on nanoscopic scales are important in many fields including photonics, electronics, biology and material science. However, challenges exist in meeting many nanostructuring demands–particularly in emerging optical materials and component architectures. Here, we report a nanofabrication workflow that overcomes long-standing challenges in deterministic and top-down sample preparation procedures. The salient feature is a carbon mask with a low sputter yield that can be readily shaped using high resolution electron beam processing techniques. When combined with focused ion beam processing, the masking technique yields structures with ultra-smooth, near-vertical side walls. We target different material platforms to showcase the broad utility of the technique. As a first test case, we prepared nanometric gaps in evaporated Au. Gap widths of 7 plus/minus 2 nm, aspect ratios of 17, and line edge roughness values of 3sigma = 2.04 nm are achieved. Furthermore, the gap widths represent an order of magnitude improvement on system resolution limits. As a second test case, we designed and fabricated dielectric resonators in the ternary compounds MnPSe3 and NiPS3; a class of van der Waals material resistant to chemical etch approaches. Nanoantenna arrays with incrementally increasing diameter were fabricated in crystalline, exfoliated flakes. The optical response was measured by dark field spectroscopy and is in agreement with simulations. The workflow reported here leverages established techniques in material processing without the need for custom or specialized hardware. It is broadly applicable to functional materials and devices, and extends high speed focused ion beam milling to true sub-10 nm length scales.

Deterministic and versatile approaches to sample preparation on nanoscopic scales are important in many fields including photonics, electronics, biology and material science. However, challenges exist in meeting many nanostructuring demands─particularly in emerging optical materials and component architectures. Here, we report a nanofabrication workflow that overcomes long-standing challenges in deterministic and top down sample preparation procedures. The salient feature is a carbon mask with a low sputter yield that can be readily shaped using high resolution electron beam processing techniques. When combined with focused ion beam processing, the masking technique yields structures with ultrasmooth, near-vertical sidewalls. We target different material platforms to showcase the broad utility of the technique. As a first test case, we prepared nanometric gaps in evaporated Au. Gap widths of 7 ± 2 nm, aspect ratios of 17, and line edge roughness values of 3σ = 2.04 nm are achieved. Furthermore, the gap widths amount to an order of magnitude improvement on system resolution limits. As a second test case, we designed and fabricated dielectric resonators in the ternary compounds MnPSe3 and NiPS3; a class of van der Waals material resistant to chemical etch approaches. Nanoantenna arrays with incrementally increasing diameter were fabricated in crystalline, exfoliated flakes. The optical response was measured by dark field spectroscopy and is in agreement with simulations. The workflow reported here leverages established techniques in material processing without the need for custom or specialized hardware. It is broadly applicable to functional materials and devices, and extends high speed focused ion beam milling to true sub-10 nm length scales.

Hexagonal boron nitride (hBN) is gaining interest as a wide bandgap van der Waals host of optically active spin defects for quantum technologies. Most studies of the spin-photon interface in hBN focus on the negatively charged boron vacancy (VB-) defect, which is typically fabricated by ion irradiation. However, VB- fabrication methods often lack robustness and reproducibility when applied to thin flakes (less than 10 nm) of hBN. Here we identify mechanisms that both promote and inhibit VB- generation and optimize ion beam parameters for site-specific fabrication of optically active VB- centers. We emphasize conditions accessible by high resolution focused ion beam (FIB) systems, and present a framework for VB- fabrication in hBN flakes of arbitrary thickness for applications in quantum sensing and quantum information processing.

Focused ion beam (FIB) techniques are employed widely for nanofabrication and processing of materials and devices. However, ion irradiation often gives rise to severe damage due to atomic displacements that cause defect formation, migration, and clustering within the ion-solid interaction volume. The resulting restructuring degrades the functionality of materials and limits the utility of FIB ablation and nanofabrication techniques. Here we show that such restructuring can be inhibited by performing FIB irradiation in a hydrogen plasma environment via chemical pathways that modify defect binding energies and transport kinetics, as well as material ablation rates. The method is minimally invasive and has the potential to greatly expand the utility of FIB nanofabrication techniques in processing functional materials and devices.

Monoclinic β-Ga2O3 nanowires were fabricated using chemical vapor deposition and doped with nitrogen using remote plasma. The monoclinic phase and high crystallinity of the nanowires were confirmed by XRD and TEM, while nitrogen incorporation into the nanowires was confirmed by X-ray absorption and Raman spectroscopies. Temperature-resolved cathodoluminescence characterisation revealed a green luminescence band at 2.5 eV due to the N incorporation. The UV emission at 3.4 eV associated with self-trapped holes and its temperature-dependant behaviour were found to be identical for the undoped and N-doped nanowires. The experimental findings will be discussed in context of theoretical calculations for N-doped Ga2O3.

Nitrogen (N) is a promising candidate currently being pursued for p-type doping in Ga2O3. In this work, the results of detailed investigations into N-doped fiGa2O3 nanowires using microstructural, chemical, and optical analyses are described. Monoclinic fi-Ga2O3 nanowires are grown by chemical vapor deposition using a metallic gallium (Ga) precursor and subsequently doped with N by remote plasma by exploiting their nanoscale cross sections and large surface-to-volume ratios. The N incorporation into fi-Ga2O3 is confirmed by X-ray absorption near-edge and Raman spectroscopies without changes in the nanowire morphology. N is found to exist mainly as molecular N2 and N-O chemical states, but a significant portion of N substitutes on oxygen (O) sites. Concurrent temperature-resolved cathodoluminescence measurements of the undoped and N-doped fi-Ga2O3 are used to track the temperature dependences of their intrinsic ultraviolet (UV) luminescence and defect-related visible bands from 80 to 480 K. The blue and green bands increase in intensity relative to the UV after N doping; however, their intensity variations with temperature are found to be identical for the undoped and N-doped fi-Ga2O3, indicating that these bands originate from existing recombination pathways in Ga2O3 rather than from radiative N-related centers. The enhancement in defect-related luminescence in N-doped fiGa2O3 is explained by an increase in the concentration of O vacancies as a result of the compensation of N-O acceptors.

Quantum microscopes based on solid-state spin quantum sensors have recently emerged as powerful tools for probing material properties and physical processes in regimes not accessible to classical sensors, especially on the nanoscale. Such microscopes have already found utility in a variety of problems, from imaging magnetism and charge transport in nanoscale devices, to mapping remanent magnetic fields from ancient rocks and biological organisms. However, applications of quantum microscopes have so far relied on sensors hosted in a rigid, three-dimensional crystal, typically diamond, which limits their ability to closely interact with the sample under study. Here we demonstrate a versatile and robust quantum microscope using quantum sensors embedded within a thin layer of a van der Waals (vdW) material, hexagonal boron nitride (hBN). To showcase the capabilities of this platform, we assemble several active vdW heterostructures, with an hBN layer acting as the quantum sensor. We demonstrate time-resolved, simultaneous temperature and magnetic imaging near the Curie temperature of a vdW ferromagnet as well as apply this unique microscope to map out charge currents and Joule heating in graphene. By enabling intimate proximity between sensor and sample, potentially down to a single atomic layer, the hBN quantum sensor represents a paradigm shift for nanoscale quantum sensing and microscopy. Moreover, given the ubiquitous use of hBN in modern materials and condensed matter physics research, we expect our technique to find rapid and broad adoption in these fields, further motivated by the prospect of performing in-situ chemical analysis and noise spectroscopy using advanced quantum sensing protocols.

Spin-dependent optical transitions are attractive for a plethora of applications in quantum technologies. Here we report on utilization of high quality ring resonators fabricated from TiO2 to enhance the emission from negatively charged boron vacancies (V-B(-)) in hexagonal Boron Nitride. We show that the emission from these defects can efficiently couple into the whispering gallery modes of the ring resonators. Optically coupled V-B(-) showed photoluminescence contrast in optically detected magnetic resonance signals from the hybrid coupled devices. Our results demonstrate a practical method for integration of spin defects in 2D materials with dielectric resonators which is a promising platform for quantum technologies.

Ion beams are used routinely for processing of semiconductors, particularly sputtering, ion implantation and direct-write fabrication of nanostructures. However, the utility of ion beam techniques is limited by crystal damage and surface roughening. Damage can be reduced or eliminated by performing irradiation at elevated temperatures. However, at these conditions, surface roughening is highly problematic due to thermal mobility of adatoms and surface vacancies. Here we solve this problem using hydrogen gas, which we use to stabilize surface mass flow and suppress roughening during ion bombardment of elemental and compound semiconductors. We achieve smooth surfaces during ion-beam processing, and show that the method can be enhanced by radicalizing H2 gas using a remote plasma source. Our approach is broadly applicable, and expands the utility of ion beam techniques for the processing and fabrication of functional materials and nanostructures.

Nanoscale fabrication and characterization techniques critically underpin a vast range of fields, including nanoelectronics and nanobiotechnology. Focused ion beam (FIB) techniques are appealing due to their high spatial resolution and widespread use for processing of nanostructured materials. Here, we introduce FIB-induced fluorescence spectroscopy (FIB-FS) as a nanoscale technique for spectroscopic detection of atoms sputtered by an ion beam. We use semiconductor heterostructures to demonstrate nanoscale lateral and depth resolution and show that it is limited by ion-induced intermixing of nanostructured materials. Sensitivity is demonstrated qualitatively by depth profiling of 3.5, 5, and 8 nm quantum wells and quantitatively by detection of trace-level impurities present at parts-per-million levels. The utility of the FIB-FS technique is demonstrated by characterization of quantum wells and Li-ion batteries. Our work introduces FIB-FS as a high-resolution, high-sensitivity, 3D analysis and tomography technique that combines the versatility of FIB nanofabrication techniques with the power of diffraction-unlimited fluorescence spectroscopy.

Resonance fluorescence from a quantum emitter is an ideal source to extract indistinguishable photons. By using the cross-polarization to suppress the laser scattering, we observed resonance fluorescence from GeV color centers in diamond at cryogenic temperature. The Fourier-transform-limited line width emission with T2/2T1 ∼ 0.86 allows for two-photon interference based on single GeV color center. Under pulsed excitation, the separated photons exhibit a Hong-Ou-Mandel quantum interference above classical limit, whereas the continuous-wave excitation leads to a coalescence time window of 1.05 radiative lifetime. In addition, we demonstrated a single-shot readout of spin states with a fidelity of 74%. Our experiments lay down the foundation for building a quantum network with GeV color centers in diamond.

3-D vertical nanoelectrode arrays (NEAs) have found applications in several biomedical and sensing applications, including high-resolution neuronal excitation and measurement and single-molecule electrochemical biosensing. There have been several reports on high-density nanoelectrodes in recent years, with the filling ratio of electrodes reaching close to 0.002 (assuming the electrode diameter of 200 nm and pitch of 4 μm). Still, it is well below the nanowire filling ratio required to form interconnected neuronal networks, i.e., more than 0.14 (assuming the electrode diameter of 200 nm and pitch of 1.5 μm). Here, we employ a multi-step, large-area electron beam lithography procedure along with a targeted, focused ion beam based metal deposition technique to realize an individually addressable, 60-channel nanoelectrode chip with a filling ratio as high as 0.16, which is well within the limit required for the formation of interconnected neuronal networks. Moreover, we have designed the NEA chip to be compatible with the commercially available MEA2100-System, which can, in the future, enable the chip to be readily used for obtaining data from individual electrodes. We also perform an in-depth electrochemical impedance spectroscopy characterization to show that the electrochemical behavior and the charge transfer mechanism in the array are significantly influenced by changing the thickness of the SU-8 planarization layer (i.e., the thickness of the exposed platinum surface). In addition to neural signal excitation and measurement, we propose that these NEA chips have the potential for other future applications, such as high-resolution single-molecule level electrochemical and bio-analyte sensing.

Two-dimensional hexagonal boron nitride (hBN) has attracted much attention as a platform for studies of light-matter interactions at the nanoscale, especially in quantum nanophotonics. Recent efforts have focused on spin defects, specifically negatively charged boron vacancy (V-B(-)) centers. Here, we demonstrate a scalable method to enhance the V-B(-) emission using an array of SiO2 nanopillars. We achieve a 4-fold increase in photoluminescence (PL) intensity, and a corresponding 4-fold enhancement in optically detected magnetic resonance (ODMR) contrast. Furthermore, the V-B(-) ensembles provide useful information about the strain fields associated with the strained hBN at the nanopillar sites. Our results provide an accessible way to increase the emission intensity as well as the ODMR contrast of the V-B(-) defects, while simultaneously form a basis for miniaturized quantum sensors in layered heterostructures.

Spin defects in hexagonal boron nitride, and specifically the negatively charged boron vacancy (VB - ) centers, are emerging candidates for quantum sensing. However, the VB - defects suffer from low quantum efficiency and, as a result, exhibit weak photoluminescence. In this work, a scalable approach is demonstrated to dramatically enhance the VB - emission by coupling to a plasmonic gap cavity. The plasmonic cavity is composed of a flat gold surface and a silver cube, with few-layer hBN flakes positioned in between. Employing these plasmonic cavities, two orders of magnitude are extracted in photoluminescence enhancement associated with a corresponding twofold enhancement in optically detected magnetic resonance contrast. The work will be pivotal to progress in quantum sensing employing 2D materials, and in realization of nanophotonic devices with spin defects in hexagonal boron nitride.

Diamond is known to possess a range of extraordinary properties that include exceptional mechanical stability. In this work, it is demonstrated that nanoscale diamond pillars can undergo not only elastic deformation (and brittle fracture), but also a new form of plastic deformation that depends critically on the nanopillar dimensions and crystallographic orientation of the diamond. The plastic deformation can be explained by the emergence of an ordered allotrope of carbon that is termed O8-carbon. The new phase is predicted by simulations of the deformation dynamics, which show how the sp3 bonds of (001)-oriented diamond restructure into O8-carbon in localized regions of deforming diamond nanopillars. The results demonstrate unprecedented mechanical behavior of diamond, and provide important insights into deformation dynamics of nanostructured materials.

Graphene is often used as an acceptor in highly efficient energy transfer processes between its electrons and neighbouring optical emitters such as quantum dots, fluorescent molecules and color centres in crystals. Here we demonstrate that graphene can act not only as an acceptor in energy transfer processes, but also an acceptor of charge donated by photoexcited quantum emitters. Specifically, we use heterostructures comprised of graphene and hexagonal boron nitride (hBN) to demonstrate a reversible charge transfer process from quantum emitters in hBN to graphene. The process acts as a controllable, energy-resolved filter that quenches quantum emitters with ground states located above the Fermi level of graphene. Our findings shed light on the positions of hBN defect states within the bandgap of hBN, and are important for the design of devices based on 2D heterostructures, opening new avenues to technologies based on electrical excitation, manipulation, and readout of the quantum states of optical emitters.

Quantum technologies require robust and photostable single photon emitters (SPEs). Hexagonal boron nitride (hBN) has recently emerged as a promising candidate to host bright and optically stable SPEs operating at room temperature. However, the emission wavelength of the fluorescent defects in hBN has, to date, been shown to be uncontrolled, with a widespread of zero phonon line (ZPL) energies spanning a broad spectral range (hundreds of nanometers), which hinders the potential development of hBN-based devices and applications. Here we demonstrate chemical vapor deposition growth of large-area, few-layer hBN films that host large quantities of SPEs: ∼100-200 per 10 × 10 μm2. More than 85% of the emitters have a ZPL at (580 ± 10) nm, a distribution that is an order of magnitude narrower than reported previously. Furthermore, we demonstrate tuning of the ZPL wavelength using ionic liquid devices over a spectral range of up to 15 nm-the largest obtained to date from any solid-state SPE. The fabricated devices illustrate the potential of hBN for the development of hybrid quantum nanophotonic and optoelectronic devices based on two-dimensional materials.

Single crystals of bis(kappa S-2,S'-di(isopropyl)dithiocarbamato) nickel(II) were utilized as a single source precursor for the formation of NiS via thermolysis. The complex decomposed at - 250 degrees C to form alpha-NiS exclusively with no beta-NiS detected. Analysis of the thermolysis regime using in situ techniques showed that the thermolysis occurs in a single step with the major volatile side-products being isopropyl-isothiocyanate and carbon disulfide. The resultant NiS was examined using SEM and TEM to reveal a retention of precursor crystal edge-length and angle relationships.

Quantum emitters in layered materials are promising candidates for applications in nanophotonics. Here we present a technique based on charge transfer to graphene for measuring the charge transition levels ($\rm E_t$) of fluorescent defects in a wide bandgap 2D material, and apply it to quantum emitters in hexagonal boron nitride (hBN). Our results will aid in identifying the atomic structures of quantum emitters in hBN, as well as practical applications since $\rm E_t$ determines defect charge states and plays a key role in photodynamics.

PbS submicron crystals were formed by thermolysis of two different lead dithiocarbamate complexes. These precursors were readily synthesized and fully characterized, and in situ synchrotron powder diffraction experiments were performed to characterize their decomposition. The structure and purity of resultant PbS was examined using scanning electron and transmission electron microscopies, powder X-ray diffraction, and infrared spectroscopy. Submicron crystalline PbS was used to create a new PbS thermistor with excellent sensitivity and an ultrarapid thermal response time.