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Graphene has unique properties which make it an ideal material for photonic and optoelectronic devices. However, the low light absorption in monolayer graphene seriously limits its practical applications. In order to greatly enhance the light absorption of graphene, many graphene-based structures have been developed to achieve perfect absorption of incident waves. In this review, we discuss and analyze various types of graphene-based perfect absorption structures in the visible to terahertz band. In particular, we review recent advances and optoelectronic applications of such structures. Indeed, the graphene-based perfect absorption structures offer the promise of solving the key problem which limits the applications of graphene in practical optoelectronic devices. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A kind of graphene-based perfect absorber which can generate low-threshold and high-extinction-ratio optical bistability in the near-IR band is proposed and simulated with numerical methods. The interaction between input light and monolayer graphene in the absorber can be greatly enhanced due to the perfect absorption. The large nonlinear coefficient of graphene and the strong light-graphene interaction contribute to the nonlinear response of the structure, leading to relatively low switching thresholds of less than 2.5 MW/cm2 for an absorber with a Q factor lower than 1000. Meanwhile, the extinction ratio of bistable states in the absorber reaches an ultrahigh value of 47.3 dB at 1545.3 nm. Moreover, the influence of changing the structural parameters on the bistable behaviors is discussed in detail, showing that the structure can tolerate structural parametric deviation to some extent. The proposed bistable structure with ultra-compact size, low thresholds, high extinction ratio, and ultrafast response time could be of great applications for fabricating high-performance all-optical-communication devices. [ABSTRACT FROM AUTHOR]

In this paper, we propose a broadband infrared stealth metamaterial absorber based on an improved metal-dielectric-metal structure where its top pattern consists of multi-layers. The structure uses high-temperature resistant materials instead of traditional low melting point precious metals and achieves selective thermal radiation in the infrared band. The study shows that with the increase of the number of layers, the absorption peak and bandwidth of the non-atmospheric window band expands. When the thickness of the structure is five layers, it can match well with the atmospheric absorption spectra. The polarization sensitivity and infrared stealth performance at different temperatures of the structure with five-layer are studied in detail. Compared with black body, the selective thermal emitter maintains radiation reduction rates greater than 80% in MWIR and LWIR regions. The high temperature resistant heat emitter proposed by us can be used in spectrally selective thermal radiation, thermal management and thermal camouflage, which has a very promising application prospect. [ABSTRACT FROM AUTHOR]

Since the discovery of the quantum Hall effect in 1980, it has attracted intense interest in condensed matter physics and has led to a new type of metrological standard by utilizing the resistance quantum. Graphene, a true two-dimensional electron gas material, has demonstrated the half-integer quantum Hall effect and composite-fermion fractional quantum Hall effect due to its unique massless Dirac fermions and ultra-high carrier mobility. Here, we use a monolayer graphene encapsulated with hexagonal boron nitride and few-layer graphite to fabricate micrometer-scale graphene Hall devices. The application of a graphite gate electrode significantly screens the phonon scattering from a conventional SiO2/Si substrate, and thus enhances the carrier mobility of graphene. At a low temperature, the carrier mobility of graphene devices can reach 3 × 105 cm2/V·s, and at room temperature, the carrier mobility can still exceed 1 × 105 cm2/V·s, which is very helpful for the development of high-temperature quantum Hall effects under moderate magnetic fields. At a low temperature of 1.6 K, a series of half-integer quantum Hall plateaus are well-observed in graphene with a magnetic field of 1 T. More importantly, the ν = ±2 quantum Hall plateau clearly persists up to 150 K with only a few-tesla magnetic field. These findings show that graphite-gated high-mobility graphene devices hold great potential for high-sensitivity Hall sensors and resistance metrology standards for the new Système International d'unités. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Actively tunable metasurfaces have widespread applications in optics from light modulation, beam steering to LiDAR and many others. Recently, lithium niobate (LN) based metasurfaces have attracted significant attention for their great potentials in integrated electro-optically tunable metadevices. However, the hardness and chemical inactivity of LN make it difficult to process, which severely limits the quality (Q) factors and performance of LN based metasurfaces. In this paper, a type of high Q etchless LN resonant metasurface is experimentally demonstrated. The metasurface shows a measured Q factor of 563 around the telecom wavelength and even higher Q factors are expected to be realized using similar designs in the future. This work represents an important progress for LN resonant metasurfaces and paves the way for the development of high performance electro-optically tunable LN metadevices. • Demonstrate a type of high-Q LN resonant metasurface in telecom wavelength range. • Uses a dielectric-loaded design with subwavelength patterns. • The LN is etchless to avoid the fabrication difficulty. • The measured Q factor of 563 is almost one order higher than the previous work. • Paves the way for the development of high performance EO tunable LN metadevices. [ABSTRACT FROM AUTHOR]

ZnO/PdSe 2 core-shell heterojunction nanorod arrays exhibit higher photocurrent (≈0.75 mA cm−2) and faster response (T off/ZnO@PdSe2 =4.5 ms, T on/ZnO@PdSe2 =4.5 ms) than most of reported commercial ZnO and ZnO composite nanomaterials. [Display omitted] • ZnO/PdSe 2 core-shell HNAs were synthesized by a low temperature selenization method for the first time. • ZnO/PdSe 2 core-shell HNAs possess stable structures and superb active interfaces. • Ultrafast response and high photocurrent density were achieved. • A more profound mechanism for the ZnO/PdSe 2 photoelectrochemical (PEC) reaction was proposed. Palladium diselenide (PdSe 2), a group-10 transition metal dichalcogenide with great optoelectronic and electrical properties due to unique structure, has gained increasing attention in the scientific community. Herein, we demonstrate an effective strategy to synthesis of ZnO/PdSe 2 core–shell heterojunction nanorod arrays (HNAs) through a simple two-step method for the first time. A Pd film was deposited on ZnO NAs by an electron beam evaporation method at first. Then, the selenization process was completed by a chemical vapor deposition (CVD) method. Furthermore, the photoelectric performances of electrodes based on ZnO NAs, PdSe 2 film and ZnO/PdSe 2 core–shell HNAs were investigated, respectively. The ZnO/PdSe 2 core–shell HNA represents better responsitivity with higher photocurrent density (1.3 mA cm−2) comparing to the ZnO NA (0.03 mA cm−2), indicating that the ZnO/PdSe 2 samples are more suitable for photoelectric devices. Besides, photoelectric performance of this work is better than most of reported commercial ZnO and ZnO composite nanomaterials. [ABSTRACT FROM AUTHOR]