Single photon emitters (SPEs) in hexagonal boron nitride (hBN) have garnered significant attention over the last few years due to their superior optical properties. However, despite the vast range of experimental results and theoretical calculations, the defect structure responsible for the observed emission has remained elusive. Here, by controlling the incorporation of impurities into hBN via various bottom-up synthesis methods and directly through ion implantation we provide direct evidence that the visible SPEs are carbon related. Room temperature optically detected magnetic resonance (ODMR) is demonstrated on ensembles of these defects. We perform ion implantation experiments and confirm that only carbon implantation creates SPEs in the visible spectral range. Computational analysis of the simplest 12 carbon-containing defect species suggest the negatively charged V B C N − defect as a viable 53 candidate and predict that out-of-plane deformations make the defect environmentally sensitive. 54Our results resolve a long-standing debate about the origin of single emitters at the visible range 55 grown epitaxially. 28, 29 The energy detuning between the ZPL of the ensemble and phonon sideband (PSB) peak is ~176 meV on average (Extended Data Fig. 1). 30, 31 X-ray photoelectron spectroscopy (XPS) was used to quantify the incorporation of carbon (Extended Data Fig. 2). Figure 1b(c) demonstrate a near linear correlation between C-B (C-N) bonding and increasing TEB flux, with C-B bonding being roughly an order of magnitude more prevalent than C-N bonding. Preferential formation of C-B bonds follows logically from noting the B species are introduced with three pre-existing bonds to C. PL intensity of the resulting ensemble emission likewise displays a linear correlation with carbon concentration (Extended Data Fig. 3). Based on these results, we advance that the SPE emission at ~580 nm in hBN is likely to originate from a carbon-related defect complex. Figure 1-Photoluminescence from MOVPE hBN Samples. a. MOVPE hBN grown with increasing flow rates of triethyl borane (TEB). As TEB flow increases, the fluorescence of SPE ensembles increases. b. Percentage of B-C bonding with increasing TEB flow evaluated by XPS. c. Percentage of N-C bonding with increasing TEB flow evaluated by XPS. d. Room temperature ODMR displayed as relative contrast, spin-dependent variation in photoluminescence (∆PL/PL), observed from the ~585 nm ensemble emission of MOPVE hBN (TEB 60) at applied fields of 19, 24, and 29 mT respectively. e.
Growth of hexagonal boron nitride (hBN) layers on 2″ sapphire substrate using metal organic vapour phase epitaxy is reported here, where we compare the growth under continuous flow and flow modulation (FM) schemes. hBN films grown under the continuous flow regime exhibit low growth rate and rough surface profiles due to severe parasitic reactions between precursor molecules, which are suppressed by adopting a FM scheme. We also observe spontaneous delamination of hBN films from the substrate when immersed in a water bath and attribute this to be due to relaxation of compressive stress in the films, which was further corroborated using Raman spectroscopy. Carbon is identified as a major impurity which gets incorporated as boron carbide under FM growth and results in large sub-bandgap fluorescence in the range of 1.77–2.25 eV. Overall, hBN films deposited using the FM scheme at low growth rate (~2–3 nm h−1) exhibited the best characteristics in the present study, which will be suitable for applications such as van der Waals epitaxy and 2D hetero-structure devices.
Optically addressable solid-state spins are important platforms for quantum technologies, such as repeaters and sensors. Spins in two-dimensional materials offer an advantage, as the reduced dimensionality enables feasible on-chip integration into devices. Here, we report room-temperature optically detected magnetic resonance (ODMR) from single carbon-related defects in hexagonal boron nitride with up to 100 times stronger contrast than the ensemble average. We identify two distinct bunching timescales in the second-order intensity-correlation measurements for ODMR-active defects, but only one for those without an ODMR response. We also observe either positive or negative ODMR signal for each defect. Based on kinematic models, we relate this bipolarity to highly tuneable internal optical rates. Finally, we resolve an ODMR fine structure in the form of an angle-dependent doublet resonance, indicative of weak but finite zero-field splitting. Our results offer a promising route towards realising a room-temperature spin-photon quantum interface in hexagonal boron nitride.
We investigate the properties of an inexpensive hole-transporting material (HTM), copper phthalocyanine (CuPc), deposited by a solution-processing method in perovskite solar cells (PSCs). Cracks are found to be abundant on the as-deposited CuPc films, which lead to serious shunts and interface recombination. Surprisingly, shunts and interface recombination are significantly reduced and cell performance is greatly improved after heat treatment at 85 °C. We find that the enhancement is due to heat-induced migration of Au particles away from the cracks. Furthermore, Au is found to dope the CuPc film, and the doping effect is greatly enhanced by the heat treatment. Using CuPc and quadruple-cation perovskite, an efficiency of over 20% and negligible hysteresis is achieved after the heat treatment, which is the highest value reported for this structure. Additionally, PSCs employing CuPc and dual-cation perovskite show excellent thermal stability after >2000 h at 85 °C and good light stability at 25 °C.
Liquid dielectrophoresis ͑L-DEP͒, when deployed at microscopic scales on top of hydrophobic surfaces, offers novel ways of rapid and automated manipulation of very small amounts of polar aqueous samples for microfluidic applications and development of laboratory-on-a-chip devices. In this article we highlight some of the more recent developments and applications of L-DEP in handling and processing of various types of aqueous samples and reagents of biological relevance including emulsions using such microchip based surface microfluidic ͑SMF͒ devices. We highlighted the utility of these devices for on-chip bioassays including nucleic acid analysis. Furthermore, the parallel sample processing capabilities of these SMF devices together with suitable on-or off-chip detection capabilities suggest numerous applications and utility in conducting automated multiplexed assays, a capability much sought after in the high throughput diagnostic and screening assays.
Surface microfluidic systems have emerged as an attractive alternative to conventional closed-channel microfluidic devices. In many such systems, electric fields are leveraged for the manipulation and transport of discrete nanoliter droplets on open planar surfaces. The present research work discusses dielectrophoretic liquid and droplet actuations, which provide an attractive methodology for dispensing and manipulating nanoliter and picoliter droplets on planar surfaces. We demonstrate the integration of two independent sample actuation schemes, namely liquid dielectrophoresis (L-DEP) and droplet dielectrophoresis, and furthermore validate its applicability through model biochemical assays (DNA-PicoGreen Ò assay and DNA FRET assay). We also describe and present 'tapering L-DEP' actuation scheme, whereby we demonstrate how to simultaneously create multiple droplets of different sizes and volumes in the range of nanoliter and picoliters, from a given larger parent sample droplet.
metallic nanoparticles (NPs), through plasmonic effects cause enhancement of the local electromagnetic (EM) fields (between gaps of neighboring metallic surfaces), also known as "hot-spots," which consequently amplifies the Raman signals. [3] Hence, over the years, SERS has emerged as a powerful and ultrasensitive diagnostic technique even capable of single molecule detection. [4] Gold and silver are the two most commonly used metals for SERS applications, in terms of ease of fabrication and enhancement effect obtained with commercially available visible laser sources. Between the two, silver gives a higher enhancement effect due to lower interband losses; [5] however, it easily oxidizes in air resulting in loss of SERS activity. [6,7] Despite large enhancement factors, a number of issues arise with use of metal nanoparticles for SERS. These include, charge transfer between metal and adsorbed molecules, metal catalyzed reactions, adsorption induced vibrations which are noncharacteristic of the molecule, photocarbonization and adsorption of carbonaceous species, which lead to nonreproducible and undesired peaks. [8] Li et al. demonstrated that these challenges could be overcome by encapsulating the metal nanoparticles with a thin layer of silica or alumina shell and thus prevent any direct contact between metal and molecule (also known as shell isolated nanoparticle enhanced Raman spectroscopy). [9] While passivation of metallic nanoparticles results in cleaner and reliable Raman signals, a certain minimum thickness (>5 nm) of shell is often needed to form pinhole-free coating. As EM field intensity ("hot spots") decreases exponentially with the distance from nanoparticle surface, passivation with dielectric materials comes at a cost of reduced enhancement.Recently, atomically thin layers of 2D materials, namely graphene and hexagonal boron nitride (hBN), have been used for passivating metallic nanoparticles for SERS applications. [10][11][12][13] Mono-to few layers of graphene and hBN were shown to be highly effective in wrapping around metal nanoparticles and thereby preserving EM "hot spots." Alternately, hBN nanosheets suspensions can be functionalized with metallic nanoparticles and have been used for SERS. [14] Unlike graphene, which oxidizes in air at temperatures above 250 °C, atomically thin hBN (nano) sheets have been shown to be stable at high temperatures in oxidative environments. [15] Recent studies have shown that hBN coatings can protect metals (copper, steel, and Application of atomically thin layers of hexagonal boron nitride (hBN) for passivating gold and silver nanoparticles is investigated and its potential use is demonstrated through surface-enhanced Raman spectroscopy (SERS). Silver nanoparticles readily oxidize in air, resulting in a significant decrease in its SERS activity. hBN is a novel 2D material, well-known for its thermal and chemical stability. In this study, wafer-scale hBN is grown using metal organic vapor phase epitaxy (MOVPE) and centimeter-sized hBN layers are transferred...
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