No abstract

Hexagonal boron nitride (h-BN), an isomorph of graphene, has attracted great attention owing to its potential applications as an ultra-flat substrate or gate dielectric layer in novel graphene-based devices. Besides, h-BN appears to be a promising material for deep ultraviolet (DUV) optoelectronic applications because of its extraordinary physical properties, such as wide band gap and high absorption coefficient. In this work, two-dimensional h-BN with controllable layers was synthesized on Cu foils by ion beam sputtering deposition, and DUV photodetectors were fabricated from the transferred h-BN layers on SiO/Si substrates. The h-BN layers synthesized at the higher substrate temperature possess a lower density of domain boundaries and higher crystalline quality, and the photodetectors based on a 3 nm h-BN layer exhibited high performance with an on/off ratio of >10 under DUV light illumination at 212 nm and a cutoff wavelength at around 225 nm. This work demonstrates that two-dimensional h-BN layers are promising for the construction of high-performance solar-blind photodetectors.

Polar domains arise in insulating ferroelectrics when free carriers are unable to fully screen surface-bound charges. Recently discovered binary and ternary polar metals exhibit broken inversion symmetry coexisting with free electrons that might be expected to suppress the electrostatic driving force for domain formation. Contrary to this expectation, we report the first direct observation of polar domains in single crystals of the polar metal CaRuO. By a combination of mesoscale optical second-harmonic imaging and atomic-resolution scanning transmission electron microscopy, the polar domains are found to possess a quasi-two-dimensional slab geometry with a lateral size of ∼100 μm and thickness of ∼10 nm. Electronic structure calculations show that the coexistence of electronic and parity-lifting orders arise from anharmonic lattice interactions, which support 90° and 180° polar domains in a metal. Using in situ transmission electron microscopy, we also demonstrate a strain-tuning route to achieve ferroelastic switching of polar metal domains.

Plasmonic nanolasers have ushered in a paradigm of deep sub-wavelength coherent optical sources with ultrafast dynamics that exploit the strong confinement capabilities of metals. Although these devices are usually associated with higher thresholds due to absorption in metals, the high gain inorganic II-VI and III-V semiconductor materials have allowed the realization of plasmonic nanolasers operating under ambient conditions. In this work, we introduce single-crystalline lead halide perovskite (CHNHPbI) nanowires as an organic-inorganic semiconducting gain material to the plasmonic laser community. We demonstrate plasmonic laser action using a hybrid geometry whereby the perovskite nanowires are placed on a silver substrate with an insulating spacer layer. We report relatively low threshold operation under ambient conditions (13.5 μJ cm), and the devices work well even at temperatures up to 43.6 °C. The demonstration highlights the high optical gain achievable in perovskite materials and thus provides a solution to high gain materials for plasmonic devices.