Controlling thermal radiation in nanoscale is critical for verifying the Planck's law in subwavelength limit, and is the key for a range of innovative technologies including energy, display and security. Benefit from the superior electronic, thermal, and mechanical properties, electrically biased graphene has been recently demonstrated as promising thermal emitter with only one-atom thickness. Here, we show an enhancement of Joule heating effect in graphene by confining the current flow through narrow constrictions. The lattice temperature distribution of graphene shows a well localized "hot spot" at the middle of the constriction. Hexagonal boron nitride encapsulated graphene devices can sustain high lattice temperature up to ∼1600 K, enabling localized light emission from the constriction in air. The spectrum of graphene emitter is drastically modified to visible range by the photonic cavity composed of SiO 2 and hBN dielectrics. The intensity of emission can be tuned by changing the applied bias voltage. A 4 × 4 graphene emitters array is realized using chemical vapor deposited graphene and atomic layer deposited Al 2 O 3 capping layer to demonstrate the scalability and compatibility to Si platform of this technique. The results explore one potential "killer application" of graphene-based devices as electrically driven thermal emitters, paving the way for future nano-optoelectronics.

Subwavelength perfect optical absorption structures based on monolayer-graphene are analyzed and demonstrated experimentally. The perfect absorption mechanism is a result of critical coupling relating to a guided mode resonance of a low index two-dimensional periodic structure. Peak absorption over 99% at wavelength of 1526.5 nm with full-width at half maximum (FWHM) about 18 nm is demonstrated from a fabricated structure with period of 1230 nm, and the measured results agree well with the simulation results. In addition, the influence of geometrical parameters of the structure and the angular response for oblique incidence are analyzed in detail in the simulation. The demonstrated absorption structure in the presented work has great potential in the design of advanced photo-detectors and modulators.

Broadband optical absorption structures in the near infrared by coupling monolayer-graphene with periodical metal structures are proposed and demonstrated numerically. Optical absorption of graphene with over-50%-absorption bandwidth up to hundreds of nanometer caused by magnetic dipole resonances and magnetic coupling effect are investigated in detail, and the demonstrated bandwidths are one order higher than those caused by dielectric guiding mode resonances. In addition, the influences of geometrical parameters of structures are fully analyzed and these demonstrated structures show angular-insensitive absorption for oblique incidence in a large angular range. The demonstrated absorption structures in this work provide new design ideas in the realization of advanced graphene-based optoelectronic devices.

2D semiconductors with atomically thin body thickness have attracted tremendous research interest for high-performance nanoelectronics and optoelectronics. Most of the 2D semiconductors grown by chemical vapor deposition (CVD) methods suffer from rather low carrier mobility, small single-crystal size, and instability under ambient conditions. Here, we develop an improved CVD method with controllable reverse-gas flow to realize the direct growth of quality Bi2O2Se 2D single crystals on a mica substrate. The applied reverse flow significantly suppresses the random nucleation and thus promotes the lateral size of 2D Bi2O2Se crystals up to ∼750 μm. The Bi2O2Se field-effect transistors display high-room-temperature electron mobility up to ∼1400 cm2·V–1·s–1 and a well-defined drain current saturation. The on/off ratio of the Bi2O2Se transistor is larger than 107, and the sub-threshold swing is about 90 mV·dec–1. The responsivity, response time, and detectivity of Bi2O2Se photodetectors approach up to 60 A·W–1, 5 ms, and 2.4 × 1010 Jones at room temperature, respectively. Our results demonstrate large-size and high-quality Bi2O2Se grown by reverse-flow CVD as a high-performance channel material for next-generation transistors and photodetectors.

A very attractive advantage of graphene is that its Fermi level can be regulated by electrostatic bias doping. It is of great significance to investigate and control the spatial location of graphene emission for graphene thermal emitters, in addition to tuning the emission intensity and emission spectrum. Here, we present a detailed theoretical model to describe the graphene emission characteristics versus gate voltages. The experimentally observed movement of the emission spot and temperature distribution of graphene emitters are basically in agreement with those from the theoretical model. Our results provide a simple method to predict the behavior of graphene emitters that is beneficial for achieving the spatial dynamic regulation of graphene infrared emission arrays.