TiO 2 /Au Janus nanoparticles have been shown to exhibit catalytic activity in the reduction of 4nitrophenol to 4-aminophenol by sodium borohydride, with 99 % conversion achieved in 6 min. [11] Many synthetic approaches have been developed for the fabrication of Janus structures, including self-assembly, [12][13][14][15][16][17] microfluidics, [18][19][20] biphasic electrified jetting, [21][22][23] olefin metathesis, [24] protonation-deprotonation cycling, [25] etc. [26][27][28][29] Notably, several reviews describing synthetic procedures, properties, and applications of Janus structures from different viewpoints have been reported. [8,26,[30][31][32][33][34][35][36] These concentrated on the fabrication methods and self-assembly of polymeric Janus particles, [35,37,38] the synthetic strategies and self-assembly of both polymeric and inorganic Janus particles, [2, 8,26,30] or the design and preparation of Janus structures with different morphologies (e.g. patchy, multicompartmental, ellipsoidal, snowman-like). It is noteworthy that none of them concen-trated on perfectly biphasic Janus structures consisting of two completely dissimilar materials. [26,[30][31][32][33][34] Strictly biphasic Janus structures can be divided into three categories depending on the composition: soft (i.e. polymeric), hard (i.e. inorganic), and hybrid soft/hard. In addition, they can also be classified according to their architecture and dimensionality into spherical Janus particles (i.e. J-1, Scheme 1 a), dumbbell-like (J-2, Scheme 1 b), rodlike (J-3, Scheme 1 c, and J-4, Scheme 1 d), disclike (J-5, Scheme 1 e, and J-6, Scheme 1 f), and sheetlike (or ribbon-like; J-7, Scheme 1 g). This Review seeks to summarize the preparation strategies for strictly biphasic Janus structures, highlight their unique Janus structures, named after the ancient two-faced Roman god Janus, comprise two hemistructures (e.g. hemispheres) with different compositions and functionalities. Much research has been carried out over the past few years on Janus structures because of the intriguing properties and promising potential applications of these unusually shaped materials. This Review discusses recent progress made in the synthesis, properties, and applications of strictly biphasic Janus structures possessing symmetrical structures but made of disparate materials. Depending on the chemical compositions, such biphasic structures can be categorized into soft, hard, and hybrid soft/hard Janus structures of different architectures, including spheres, rodlike, disclike, or any other shape. The main synthetic routes to soft, hard, and hybrid soft/hard Janus structures are summarized and their unique properties and applications are introduced. The perspectives for future research and development are also described. From the Contents 1. Introduction 5525 2. Synthesis of Strictly Biphasic Janus Structures 5526 3. Properties and Applications of Strictly Biphasic Janus Structures 5533 4. Summary and Outlook 5535Scheme 1. Overview of strictly biphasic Janus architectures. a...
Interlayer grating-to-grating optical interconnect coupling efficiency is simulated and optimized using rigorous coupled-wave analysis (RCWA) for the case of binary rectangular-groove gratings. The "equivalent index slab (EIS)" concept is proposed to alleviate the numerical sensitivity problem inherent in the RCWA-leaky-wave approach, making the method applicable to any multilayer structure that has an arbitrary grating profile, large refractive-index differences, and a limited grating length. The method is easy to implement and computationally efficient and can provide optimal designs based on the system designer's need. To determine the viability of the RCWA-EIS approach, results are compared to those obtained using the finite-difference time-domain method, and an excellent agreement is found.
The grating coupling efficiencies for interlayer connection (overlaid chips) were previously calculated using the new rigorous coupled-wave analysis equivalent-index-slab (RCWA-EIS) method. The chip-to-chip coupling efficiencies were determined for rectangular-groove (binary) gratings. In the present work, the search algorithms used in the RCWA-EIS method are optimized giving rise to improved definition of equivalent indices. Further, the versatility of the RCWA-EIS method is demonstrated by extending it to (nonbinary) parallelogramic gratings, sawtooth gratings, and volume gratings. The finite-difference time-domain method is used to verify the results. This demonstrates the flexibility of the RCWA-EIS method in analyzing arbitrary 1D gratings.
The interlayer waveguide grating coupling efficiencies under angular (rotational) misalignments are simulated using the 3D rigorous coupled-wave analysis (3D-RCWA) together with the RCWA equivalent-index-slab (RCWA-EIS) method. As examples of conical diffraction, rotations about the two coordinate axes, x and z, defined by the vectors [1 0 0] and [0 0 1], respectively, as well as an arbitrary axis, defined by the vector [2 2 1], are simulated for binary rectangular-groove gratings. The interlayer grating coupling efficiency is approximated by the product of the top- and bottom-grating diffraction efficiencies (DEs). It is found that the bottom-grating DEs decrease about 25% when the bottom grating is rotated ±0.1 rad (5.73°) about the z-axis. DEs slightly increase (5% to 10% depending on the grating structures) when the bottom grating is rotated ±0.1 rad about the x-axis. This is consistent with the diffraction behavior of an over-modulated grating. When the bottom grating is rotated about the vector [2 2 1], the change in DEs is asymmetric with a 100% decrease at a rotation angle -0.1 rad and a 67% decrease at a rotation angle +0.1 rad. The method is shown to be computationally efficient and numerically stable for grating structures with optimized parameters, and the resulting bottom-grating diffraction efficiencies demonstrate similar trends as those calculated by the 3D finite-difference time-domain simulations. The procedure presented can be directly used in the analysis and design of interlayer waveguide grating coupling for optical interconnects in high-density integrated electronics.
Applying reflectors adds 30%~40% to the diffraction efficiencies of binary waveguide gratings. The greatest angular misalignment sensitivity occurs for rotations about the grating groove axis and rotation should be limited to ±3°.
A grating-assisted-cylindrical-resonant-cavities (GARC) interlayer coupler made of Si/SiO is designed and simulated to achieve efficient and broadband interlayer coupling. This coupler consists of three cylindrical resonant cavities: two waveguide cavities in the horizontal direction and one cylindrical via cavity in the vertical direction. The resonant strengths of the two cylindrical waveguide cavities are enhanced by circular Bessel-function-defined gratings and distributed Bragg reflectors. The interlayer coupling efficiency of this Si/SiO GARC coupler is simulated as η=68%(-1.7 dB) for transverse electric polarization at 1.55 μm wavelength, which is generally higher than those of conventional rectangular silicon-on-insulator gratings with additional features such as reflectors, overlayers, chirped periods, dual gratings, etc. The GARC couplers are predicted to have favorable attributes compared to previous couplers, including wider operational bandwidth (δ=270 nm), larger tolerance to inplane misalignment (±2 μm for 1 dB extra loss), easier grating patterning (wider grating ridges), smaller footprint (20 μm in diameter), and more flexible choices of interlayer distances (2-5 μm). A sensitivity analysis is also provided as a guide in fabrication. In general, it is found that the vertical dimensions of the GARC couplers need to be carefully controlled while the horizontal dimensions are less critical.
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