Two-dimensional materials, such as graphene and monolayer hexagonal BN (h-BN), are attractive for demonstrating fundamental physics in materials and potential applications in next-generation electronics. Atomic sheets containing hybridized bonds involving elements B, N and C over wide compositional ranges could result in new materials with properties complementary to those of graphene and h-BN, enabling a rich variety of electronic structures, properties and applications. Here we report the synthesis and characterization of large-area atomic layers of h-BNC material, consisting of hybridized, randomly distributed domains of h-BN and C phases with compositions ranging from pure BN to pure graphene. Our studies reveal that their structural features and bandgap are distinct from those of graphene, doped graphene and h-BN. This new form of hybrid h-BNC material enables the development of bandgap-engineered applications in electronics and optics and properties that are distinct from those of graphene and h-BN.

With advances in exfoliation and synthetic techniques, atomically thin films of semiconducting transition metal dichalcogenides have recently been isolated and characterized. Their two-dimensional structure, coupled with a direct band gap in the visible portion of the electromagnetic spectrum, suggests suitability for digital electronics and optoelectronics. Toward that end, several classes of high-performance devices have been reported along with significant progress in understanding their physical properties. Here, we present a review of the architecture, operating principles, and physics of electronic and optoelectronic devices based on ultrathin transition metal dichalcogenide semiconductors. By critically assessing and comparing the performance of these devices with competing technologies, the merits and shortcomings of this emerging class of electronic materials are identified, thereby providing a roadmap for future development.

Unencapsulated, exfoliated black phosphorus (BP) flakes are found to chemically degrade upon exposure to ambient conditions. Atomic force microscopy, electrostatic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are employed to characterize the structure and chemistry of the degradation process, suggesting that O2 saturated H2O irreversibly reacts with BP to form oxidized phosphorus species. This interpretation is further supported by the observation that BP degradation occurs more rapidly on hydrophobic octadecyltrichlorosilane self-assembled monolayers and on HSi(111), versus hydrophilic SiO2. For unencapsulated BP field-effect transistors, the ambient degradation causes large increases in threshold voltage after 6 hours in ambient, followed by a ~10 3 decrease in FET current on/off ratio and mobility after 48 hours. Atomic layer deposited AlOx overlayers effectively suppress ambient degradation, allowing encapsulated BP FETs to maintain high on/off ratios of ~10 3 and mobilities of ~100 cm 2 V -1 s -1 for over two weeks in ambient. This work shows that the ambient degradation of BP can be managed effectively when the flakes are sufficiently passivated. In turn, our strategy for enhancing BP environmental stability will accelerate efforts to implement BP in electronic and optoelectronic applications. On increased ambient exposure, the bubble density eventually decreases, evolving into wider and taller bubbles. These bubbles occur in BP, regardless of flake thickness (Fig. S2). In Fig. 2, we therefore use X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy to assess whether chemical modifications, such as the formation of additional chemical bonds or a change in oxidation state, occur in BP upon ambient exposure. Fig. 2A shows P 2p core level XPS spectra of as-exfoliated BP flakes on SiO2 for 0 hrs, 13 hrs, 1, day, 2 days, and 3 days, respectively, of ambient exposure. All spectra are calibrated to the binding energy of adventitious carbon (284.8 eV), and electrostatic charging is compensated using an Ar + flood gun (see Supporting Information for details). At 0 hrs of ambient exposure (black spectrum in Fig. 2A), the exfoliated BP exhibits a single spin-orbit split doublet at ~130 eV, consistent with previous XPS measurements on BP bulk crystals. 27, 28 Note that these spectra do not match those for red phosphorus (~129.8 eV), white phosphorus, or amorphous P-H. 27 A broad, s photoelectronSi satellite from the substrate 300 nm SiO2 appears at ~126.5 eV. After 13 hrs of ambient exposure (maroon spectrum), the full-width at half-maximum (FWHM) for the BP increases, characteristic of some loss of long range order. After 1, 2, and 3 days in ambient (green, navy, and gray spectra, respectively), an additional doublet appears at ~134 eV. This feature is best assigned to phosphate species, 9, 29 although many oxidized phosphorus compounds exhibit peaks near ~134-135 eV. 30, 31 The la...