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.

Dielectric loaded graphene plasmon waveguide (DLGPW) is proposed and investigated. An analytical model based on effective-index method is presented and verified by the finite element method simulations. The mode effective index, propagation loss, cutoff wavelength of higher order modes and single-mode operation region were derived at mid-infrared spectral region. By changing Fermi energy level, the propagation properties of fundamental mode could be tuned flexibly. The structure of the DLGPW is simple and easy for fabrication. It provided a new freedom to manipulate the graphene surface plasmons, which may led to new applications in actively tunable integrated optical devices.

A crystal structure has a profound influence on the physical properties of the corresponding material. By synthesizing crystals with particular symmetries, one can strongly tune their properties, even for the same chemical configuration (compare graphite and diamond, for instance). Even more interesting opportunities arise when the structural phases of crystals can be changed dynamically through external stimulations. Such abilities, though rare, lead to a number of exciting phenomena, such as phase-change memory effects. In the case of trilayer graphene, there are two common stacking configurations (ABA and ABC) that have distinct electronic band structures and exhibit very different behaviors. Domain walls exist in the trilayer graphene with both stacking orders, showing fascinating new physics such as the quantum valley Hall effect. Extensive efforts have been dedicated to the phase engineering of trilayer graphene. However, the manipulation of domain walls to achieve precise control of local structures and properties remains a considerable challenge. Here, we experimentally demonstrate that we can switch from one structural phase to another by laser irradiation, creating domains of different shapes in trilayer graphene. The ability to control the position and orientation of the domain walls leads to fine control of the local structural phases and properties of graphene, offering a simple but effective approach to create artificial two-dimensional materials with designed atomic structures and electronic and optical properties.

CommuniCationoptical absorption in experiment for monolayer graphene based subwavelength structures in the near-infrared. Peak absorptions over 99% at wavelength around 1.5 μm with full-width at half maximum (FWHM) about 20 nm are demonstrated from mono layer graphene coupled with different subwavelength gratings on top of a back gold mirror. The experimental results are in excellent quantitative agreement with the simulation results obtained by using finite-element method, which confirm convincingly the theoretical prediction of complete optical absorption for monolayer graphene in the near-infrared range.The schematic image of the absorption structure under investigation in this work is demonstrated in Figure 1a. The structure comprises a monolayer graphene which is sandwiched between a 1D polymethy1-methacrylate (PMMA) grating and a silica layer, and a gold layer is coated in the back side of the silica layer. The absorption structure shown in Figure 1a supports several resonant modes which could be excited by outside incident waves under phase matching conditions. When the incident wave is coupled with a resonant mode, the absorption of the structure could be enhanced due to the field enhancement in the structure. And complete absorption can be obtained when the reflection wave is canceled by the emission wave of the resonant mode since the transmission of the structure is blocked by the gold layer.The monolayer graphene based absorption structures shown in Figure 1a were fabricated on a silicon substrate, and an optical image of our fabricated sample is shown in Figure 1b. The fabrication processes are listed as follows. A 4 nm chromium (Cr) layer was first deposited on a 2 cm size silicon substrate by using electron-beam evaporation, and a 200 nm gold layer was deposited on the Cr layer by using magnetron sputtering. Then, a 520 nm silica layer was deposited by plasmaenhanced chemical vapor deposition on the gold layer. And next, a 1 cm size monolayer graphene (ACS MATERIAL) was transferred on the top of the silica layer. Finally, a PMMA layer was spin coated on the substrate and grating patterns with different periods were formed in the PMMA layer by using E-beam lithography. From Figure 1b we can see that the grating patterns with different periods have different diffraction colors, and the area of the sample with graphene has a slight difference in color from that of the area without graphene. The topview scanning electron microscope (SEM) image of a fabricated pattern is shown in Figure 1c, and the white bar in the figure represents 5 μm. We measured the Raman spectrum of the monolayer graphene after the device fabrication, and compared it with the Raman spectrum of the monolayer graphene before being transferred to our sample (provided by the ACS The copyright line of this paper was changed 13 October 2016 after initial publication.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, pr...

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.