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.

A MoS 2 /graphene hybrid aerogel synthesized with two-dimensional MoS 2 sheets coating a high surface area graphene aerogel scaffold is characterized and used for ultrasensitive NO 2 detection. The combination of graphene and MoS 2 leads to improved sensing properties with the graphene scaffold providing high specifi c surface area and high electrical and thermal conductivity and the single to few-layer MoS 2 sheets providing high sensitivity and selectivity to NO 2 . The hybrid aerogel is integrated onto a low-power microheater platform to probe the gas sensing performance. At room temperature, the sensor exhibits an ultralow detection limit of 50 ppb NO 2 . By heating the material to 200 °C, the response and recovery times to reach 90% of the fi nal signal decrease to <1 min, while retaining the low detection limit. The MoS 2 / graphene hybrid also shows good selectivity for NO 2 against H 2 and CO, especially when compared to bare graphene aerogel. The unique structure of the hybrid aerogel is responsible for the ultrasensitive, selective, and fast NO 2 sensing. The improved sensing performance of this hybrid aerogel also suggests the possibility of other 2D material combinations for further sensing applications.