Ran Hao

Bio: Ran Hao is an academic researcher from Zhejiang University. The author has contributed to research in topics: Graphene & Slow light. The author has an hindex of 25, co-authored 84 publications receiving 1663 citations. Previous affiliations of Ran Hao include Capital Medical University & China Jiliang University.

Full-Polarization 3D Metasurface Cloak with Preserved Amplitude and Phase.

Abstract: A full-polarization arbitrary-shaped 3D metasurface cloak with preserved amplitude and phase in microwave frequencies is experimentally demonstrated. By taking the unique feature of metasurfaces, it is shown that the cloak can completely restore the polarization, amplitude, and phase of light for full polarization as if light was incident on a flat mirror.

Ultra-compact optical modulator by graphene induced electro-refraction effect

Abstract: We report a highly tunable graphene embedded waveguide which overall modal index is in linear relationship with the in-plane permittivity of graphene and the electro-refraction effect has been significantly enhanced after graphene is embedded. An eight-layer graphene embedded Mach-Zender modulator has been theoretically demonstrated with the advantage of ultra-compact footprint (4 × 30 μm2), high modulation efficiency (20 V·μm), fast modulation speed, and large extinction ratio (35 dB). Our results may promote various on-chip active components, boosting the utilization of graphene in optical applications.

Gradient Chiral Metamirrors for Spin-Selective Anomalous Reflection

Abstract: Metasurfaces, the phase-engineered quasi-2D interfaces, have attracted intensive interest due to their great capabilities in manipulating the reflection, refraction and transmission of electromagnetic waves. Here, we demonstrate the design and realization of a gradient chiral metamirror tailored for spin-selective anomalous reflection based on the theory of Pancharatnam-Berry phase. Asymmetric split ring resonators are employed as the basic meta-atoms for strong circular dichroism. Dispersionless phase discontinuities are achieved by adjusting the orientation of the meta-atoms, and spin-dependent absorption is realized by introducing a chiral resonance. Theoretical results predict both broadband beam deflection and spin-selective absorption for circularly polarized waves in a designer metamirror. Experimental verification of this bifunctional performance is implemented at microwave frequencies and the measured results agree well with the simulation ones. Such chiral metamirrors could pave an avenue towards spin-selective modulation of the wavefront and might find promising applications in planar electromagnetic devices.

Enhanced performance of a graphene/GaAs self-driven near-infrared photodetector with upconversion nanoparticles.

Abstract: Near-infrared photodetectors (NIRPDs) have attracted great attention because of their wide range of applications in many fields. Herein, a novel self-driven NIRPD at the wavelength of 980 nm is reported based on the graphene/GaAs heterostructure. Extraordinarily, its sensitivity to light illumination (980 nm) is far beyond the absorption limitation of GaAs (874 nm). This means that the photocurrent originates from the separation of photo-induced carriers in graphene, which is caused by the vertically built-in electric field formed through the high quality van der Waals contact between graphene and GaAs. Moreover, after introducing NaYF4:Yb3+/Er3+ upconversion nanoparticles (UCNPs) onto the graphene/GaAs heterojunction, the responsivity increases to be as superior as 5.97 mA W-1 and the corresponding detectivity is 1.1 × 1011 cm Hz0.5 W-1 under self-driven conditions. This dramatic improvement is mainly ascribed to the radiative energy transfer from UCNPs to the graphene/GaAs heterostructure. The high-quality and self-driven UCNPs/graphene/GaAs heterostructure NIRPD holds significant potential for practical application in low-consumption and large-scale optoelectronic devices.

Crystallinity of inorganic films grown by atomic layer deposition: Overview and general trends

Abstract: Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Binary bat algorithm

Abstract: Bat algorithm (BA) is one of the recently proposed heuristic algorithms imitating the echolocation behavior of bats to perform global optimization. The superior performance of this algorithm has been proven among the other most well-known algorithms such as genetic algorithm (GA) and particle swarm optimization (PSO). However, the original version of this algorithm is suitable for continuous problems, so it cannot be applied to binary problems directly. In this paper, a binary version of this algorithm is proposed. A comparative study with binary PSO and GA over twenty-two benchmark functions is conducted to draw a conclusion. Furthermore, Wilcoxon's rank-sum nonparametric statistical test was carried out at 5 % significance level to judge whether the results of the proposed algorithm differ from those of the other algorithms in a statistically significant way. The results prove that the proposed binary bat algorithm (BBA) is able to significantly outperform others on majority of the benchmark functions. In addition, there is a real application of the proposed method in optical engineering called optical buffer design at the end of the paper. The results of the real application also evidence the superior performance of BBA in practice.

Nanoscale Magnetic Resonance Imaging

Abstract: We have combined ultrasensitive magnetic resonance force microscopy (MRFM) with 3D image reconstruction to achieve magnetic resonance imaging (MRI) with resolution <10 nm. The image reconstruction converts measured magnetic force data into a 3D map of nuclear spin density, taking advantage of the unique characteristics of the “resonant slice” that is projected outward from a nanoscale magnetic tip. The basic principles are demonstrated by imaging the 1H spin density within individual tobacco mosaic virus particles sitting on a nanometer-thick layer of adsorbed hydrocarbons. This result, which represents a 100 million-fold improvement in volume resolution over conventional MRI, demonstrates the potential of MRFM as a tool for 3D, elementally selective imaging on the nanometer scale.

2D Materials for Optical Modulation: Challenges and Opportunities.

Abstract: Owing to their atomic layer thickness, strong light–material interaction, high nonlinearity, broadband optical response, fast relaxation, controllable optoelectronic properties, and high compatibility with other photonic structures, 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, have been attracting increasing attention for photonic applications. By tuning the carrier density via electrical or optical means that modifies their physical properties (e.g., Fermi level or nonlinear absorption), optical response of the 2D materials can be instantly changed, making them versatile nanostructures for optical modulation. Here, up-to-date 2D material-based optical modulation in three categories is reviewed: free-space, fiber-based, and on-chip configurations. By analysing cons and pros of different modulation approaches from material and mechanism aspects, the challenges faced by using these materials for device applications are presented. In addition, thermal effects (e.g., laser induced damage) in 2D materials, which are critical to practical applications, are also discussed. Finally, the outlook for future opportunities of these 2D materials for optical modulation is given.