Large-scale and high-quality III-nitride membranes through microcavity-assisted crack propagation by engineering tensile-stressed Ni layers

Epitaxially grown III-nitride alloys are tightly bonded materials with mixed covalent-ionic bonds.This tight bonding presents tremendous challenges in developing III-nitride membranes,even though semiconductor membranes can provide numerous advantages by removing thick,inflexible,and costly substrates.Herein,cavities with various sizes were introduced by overgrowing target layers,such as undoped GaN and green LEDs,on nanoporous templates prepared by electrochemical etching of n-type GaN.The large primary interfacial toughness was effectively reduced according to the design of the cavity density,and the overgrown target layers were then conveniently exfoliated by engineering tensile-stressed Ni layers.The resulting III-nitride membranes maintained high crystal quality even after exfoliation due to the use of GaN-based nanoporous templates with the same lattice constant.The microcavity-assisted crack propagation process developed for the current III-nitride membranes forms a universal process for developing various kinds of large-scale and high-quality semiconductor membranes.

Optical Neural Network Architecture for Deep Learning with Temporal Synthetic Dimension

The physical concept of synthetic dimensions has recently been introduced into optics.The fundamental physics and applications are not yet fully understood,and this report explores an approach to optical neural networks using synthetic dimension in time domain,by theoretically proposing to utilize a single resonator network,where the arrival times of optical pulses are interconnected to construct a temporal synthetic dimension.The set of pulses in each roundtrip therefore provides the sites in each layer in the optical neural network,and can be linearly transformed with splitters and delay lines,including the phase modulators,when pulses circulate inside the network.Such linear transformation can be arbitrarily controlled by applied modulation phases,which serve as the building block of the neural network together with a nonlinear component for pulses.We validate the functionality of the proposed optical neural network for the deep learning purpose with examples handwritten digit recognition and optical pulse train distribution classification problems.This proof of principle computational work explores the new concept of developing a photonics-based machine learning in a single ring network using synthetic dimensions,which allows flexibility and easiness of reconfiguration with complex functionality in achieving desired optical tasks.

双能CT的基本原理、应用和未来展望(英文)

断层影像(CT)的图像对比度与扫描所用的X光源能谱分布有很大关系。传统CT使用具有能谱分布的一个光源进行成像,有时会出现信息模糊致使两种不同材料在CT图像上完全相同。双能CT使用两个不同分布的能谱对物体进行成像,能够消除单能谱情况下的信息模糊。虽然双能CT的基本概念由来已久,但最近商业系统的出现使双能CT迅速成为一个热点。我们首先概述了双能CT的基本物理原理和双能信号处理方法,包括促使双能CT进入现代医学成像的关键技术。其次,双能CT的应用已非常广泛,本文从其在临床应用角度进行了详细介绍使读者有所了解。最后,我们简要探讨了当前的两个技术发展领域:光子技术探测器和技术合成CT。

Learning Convex Optimization Models

A convex optimization model predicts an output from an input by solving a convex optimization problem.The class of convex optimization models is large,and includes as special cases many well-known models like linear and logistic regression.We propose a heuristic for learning the parameters in a convex optimization model given a dataset of input-output pairs,using recently developed methods for differentiating the solution of a convex optimization problem with respect to its parameters.We describe three general classes of convex optimization models,maximum a posteriori(MAP)models,utility maximization models,and agent models,and present a numerical experiment for each.

Metal-Organic Framework Nanocarriers for Drug Delivery in Biomedical Applications

Investigation of metal–organic frameworks(MOFs)for biomedical applications has attracted much attention in recent years.MOFs are regarded as a promising class of nanocarriers for drug delivery owing to well-defined structure,ultrahigh surface area and porosity,tunable pore size,and easy chemical functionalization.In this review,the unique properties of MOFs and their advantages as nanocarriers for drug delivery in biomedical applications were discussed in the first section.Then,state-ofthe-art strategies to functionalize MOFs with therapeutic agents were summarized,including surface adsorption,pore encapsulation,covalent binding,and functional molecules as building blocks.In the third section,the most recent biological applications of MOFs for intracellular delivery of drugs,proteins,and nucleic acids,especially aptamers,were presented.Finally,challenges and prospects were comprehensively discussed to provide context for future development of MOFs as efficient drug delivery systems.

Distributed Majorization-Minimization for Laplacian Regularized Problems

We consider the problem of minimizing a block separable convex function(possibly nondifferentiable, and including constraints) plus Laplacian regularization, a problem that arises in applications including model fitting, regularizing stratified models, and multi-period portfolio optimization. We develop a distributed majorization-minimization method for this general problem, and derive a complete, self-contained, general,and simple proof of convergence. Our method is able to scale to very large problems, and we illustrate our approach on two applications, demonstrating its scalability and accuracy.

Short-Range Optical Wireless Communications for Indoor and Interconnects Applications

Optical wireless communications have been widely studied during the past decade in short-range applications, such as indoor highspeed wireless networks and interconnects in data centers and high-performance computing. In this paper, recent developments in high-speed short-range optical wireless communications are reviewed, including visible light communications （VLCs）, infrared indoor communication systems, and reconfigurable optical interconnects. The general architecture of indoor high-speed optical wireless communications is described, and the advantages and limitations of both visible and infrared based solutions are discussed. The concept of reconfigurable optical interconnects is presented, and key results are summarized. In addition, the challenges and potential future directions of short-range optical wireless communications are discussed.

An 8 Bit 0.8 GS/s 8.352 mW Modified Successive Approximation Register Based Analog to Digital Converter in 65 nm CMOS

We propose a new approach in reducing the power consumption of the successive approximation register Analog to Digital Converter (SAR-ADC) by changing the convergence algorithm of the Digital to Analog converter (DAC) input of the SAR-ADC. Different search algorithms such as binary search tree, moving binary search tree (BST), least significant bit shifter (LSB), adaptive algorithm and split-register moving BST algorithm are designed and analyzed for faster convergence of the DAC input. In this paper, we design a 0.8 GS/s, 8 bit (Effective number of bits (ENOB)—7.42), 8.352 mW SAR ADC with a proposed moving BST algorithm in 65 nm CMOS which ranks amongst the current state of the art ADCs with a FOM 65.25 fJ/step.

Polychromatic metasurfaces for complete control of phase and polarization in the mid-infrared

Multifunctional metasurfaces based on wavelength-decoupled supercells are experimentally demonstrated,enabling new regimes of optical control for arbitrary orthogonal polarizations at different wavelengths.

Fermi Level Unpinning and Schottky Barrier Modification by Ti, Sc and V Incorporation at NiSi2/Si Interface

A new method is proposed to modify the Schottky barrier height （SBH） for nickel silicide/Si contact. Chemical and electrical properties for NiSi2/Si interface with titanium, scandium and vanadium incorporation are investigated by first-principles calculations. The metal/semiconductor interface states within the gap region are greatly decreased, which is related to the diminutions of junction leakage when Ti-cap is experimentally used in nickel silicide/Si contact process. It leads to an unpinning metal/semiconductor interface. The SBH obeys the Schottky-Mort theory. Compared to Ti substitution, the SBH for electrons is reduced for scandium and increases for vanadium.

Functionalization of high-moment magnetic nanodisks for cell manipulation and separation

Synthetic antiferromagnetic （SAF） nanoparticles are layer-structured particles with high single-particle magnetic moments. In order to covalently bind these nanopartides to cells, they were coated with a silica shell followed by conjugation with streptavidin. The silica coating generates both SAF@SiO2 core-shell nano- particles and silica core-free nanopartides. Using a simple magnetic separation, silica nanoparticles were removed and SAF@SiO2 nanoparticles were purified. After streptavidin conjugation, these particles were used to stain lung cancer cells, making them highly magnetically responsive. The stained cells can rotate in response to an external magnetic field and can be captured when a blood sample containing these cells flows through the sifter.

Design and fabrication of silicon-tessellated structures for monocentric imagers

Compared with conventional planar optical image sensors,a curved focal plane array can simplify the lens design and improve the field of view.In this paper,we introduce the design and implementation of a segmented,hemispherical,CMOS-compatible silicon image plane for a 10-mm diameter spherical monocentric lens.To conform to the hemispherical focal plane of the lens,we use flexible gores that consist of arrays of spring-connected silicon hexagons.Mechanical functionality is demonstrated by assembling the 20-μm-thick silicon gores into a hemispherical test fixture.We have also fabricated and tested a photodiode array on a siliconon-insulator substrate for use with the curved imager.Optical testing shows that the fabricated photodiodes achieve good performance;the hemispherical imager enables a compact 160°field of view camera with >80% fill factor using a single spherical lens.

MBE growth of tensile-strained Ge quantum wells anC quantum dots

Germanium （Ge） has gained much interest due to the potential of becoming a direct band gap material and an efficient light source for the future complementary metal-oxide-semiconductor （CMOS） compatible photonic integrated circuits. In this paper, highly biaxial tensile strained Ge quantum wells （QWs） and quantum dots （QDs） grown by molecular beam epitaxy are presented. Through relaxed step-graded InGaAs buffer layers with a larger lattice constant, up to 2.3% tensile-strained Ge QWs as well as up to 2.46% tensile-strained Ge QDs are obtained. Characterizations show the good material quality as well as low threading dislocation density. A strong increase of photoluminescence （PL） with highly tensile strained Ge layers at low temperature suggests the existence of a direct band gap semiconductor.

Full-field interferometric imaging of propagating action potentials

Currently,cellular action potentials are detected using either electrical recordings or exogenous fluorescent probes that sense the calcium concentration or transmembrane voltage.Ca imaging has a low temporal resolution,while voltage indicators are vulnerable to phototoxicity,photobleaching,and heating.Here,we report full-field interferometric imaging of individual action potentials by detecting movement across the entire cell membrane.Using spike-triggered averaging of movies synchronized with electrical recordings,we demonstrate deformations up to 3 nm(0.9 mrad)during the action potential in spiking HEK-293 cells,with a rise time of 4ms.The time course of the optically recorded spikes matches the electrical waveforms.Since the shot noise limit of the camera(~2 mrad/pix)precludes detection of the action potential in a single frame,for all-optical spike detection,images are acquired at 50 kHz,and 50 frames are binned into 1 ms steps to achieve a sensitivity of 0.3 mrad in a single pixel.Using a selfreinforcing sensitivity enhancement algorithm based on iteratively expanding the region of interest for spatial averaging,individual spikes can be detected by matching the previously extracted template of the action potential with the optical recording.This allows all-optical full-field imaging of the propagating action potentials without exogeneous labels or electrodes.

Snapshot Mueller spectropolarimeter imager

We introduce an imaging system that can simultaneously record complete Mueller polarization responses for a set of wavelength channels in a single image capture.The division-of-focal-plane concept combines a multiplexed illumination scheme based on Fourier optics together with an integrated telescopic light-field imaging system.Polarization-resolved imaging is achieved using broadband nanostructured plasmonic polarizers as functional pinhole apertures.The recording of polarization and wavelength information on the image sensor is highly interpretable.We also develop a calibration approach based on a customized neural network architecture that can produce calibrated measurements in real-time.As a proof-of-concept demonstration,we use our calibrated system to accurately reconstruct a thin film thickness map from a four-inch wafer.We anticipate that our concept will have utility in metrology,machine vision,computational imaging,and optical computing platforms.

Multi-dimensional band structure spectroscopy in the synthetic frequency dimension

The concept of synthetic dimensions in photonics provides a versatile platform in exploring multi-dimensional physics.Many of these physics are characterized by band structures in more than one dimensions.Existing efforts on band structure measurements in the photonic synthetic frequency dimension however are limited to either onedimensional Brillouin zones or one-dimensional subsets of multi-dimensional Billouin zones.Here we theoretically propose and experimentally demonstrate a method to fully measure multi-dimensional band structures in the synthetic frequency dimension.We use a single photonic resonator under dynamical modulation to create a multidimensional synthetic frequency lattice.We show that the band structure of such a lattice over the entire multidimensional Brillouin zone can be measured by introducing a gauge potential into the lattice Hamiltonian.Using this method,we perform experimental measurements of two-dimensional band structures of a Hermitian and a non-Hermitian Hamiltonian.The measurements reveal some of the general properties of point-gap topology of the non-Hermitian Hamiltonian in more than one dimensions.Our results demonstrate experimental capabilities to fully characterize high-dimensional physical phenomena in the photonic synthetic frequency dimension.

短期国际资本异常流动控制分析——基于中国的实证

本文从合理渠道与非法隐形渠道角度提出了计算中国短期资本流动量的方法;借鉴水库模型,将资本流动划分为五种测度区间,并提出了相应测度区间控制短期资本流量与流速的思路;在研究了短期资本流入对经济影响有时间滞后性的基础上,本文建立了经济周期不同节点与短期资本流入的匹配关系以及控制短期资本流动的组合思想与方式.最后,在分析与统计中国数据的基础上,预测了目标年度中国短期资本流动水平与异常情况,提出了控制中国短期资本异常流动的建议.

High-efficiency,large-area,topologyoptimized metasurfaces

Metasurfaces are ultrathin optical elements that are highly promising for constructing lightweight and compact optical systems.For their practical implementation,it is imperative to maximize the metasurface efficiency.Topology optimization provides a pathway for pushing the limits of metasurface efficiency;however,topology optimization methods have been limited to the design of microscale devices due to the extensive computational resources that are required.We introduce a new strategy for optimizing large-area metasurfaces in a computationally efficient manner.By stitching together individually optimized sections of the metasurface,we can reduce the computational complexity of the optimization from high-polynomial to linear.As a proof of concept,we design and experimentally demonstrate large-area,high-numerical-aperture silicon metasurface lenses with focusing efficiencies exceeding 90%.These concepts can be generalized to the design of multifunctional,broadband diffractive optical devices and will enable the implementation of large-area,high-performance metasurfaces in practical optical systems.

Higher-order topological insulators in synthetic dimensions

Conventional topological insulators support boundary states with dimension one lower than that of the bulk system that hosts them,and these states are topologically protected due to quantized bulk dipole moments.Recently,higherorder topological insulators have been proposed as a way of realizing topological states with dimensions two or more lower than that of the bulk due to the quantization of bulk quadrupole or octupole moments.However,all these proposals as well as experimental realizations have been restricted to real-space dimensions.Here,we construct photonic higher-order topological insulators(PHOTIs)in synthetic dimensions.We show the emergence of a quadrupole PHOTI supporting topologically protected corner modes in an array of modulated photonic molecules with a synthetic frequency dimension,where each photonic molecule comprises two coupled rings.By changing the phase difference of the modulation between adjacent coupled photonic molecules,we predict a dynamical topological phase transition in the PHOTI.Furthermore,we show that the concept of synthetic dimensions can be exploited to realize even higher-order multipole moments such as a fourth-order hexadecapole(16-pole)insulator supporting 0D corner modes in a 4D hypercubic synthetic lattice that cannot be realized in real-space lattices.

Direct bandgap germanium-on-silicon inferred from 5.7% <100> uniaxial tensile strain [Invited]

We report uniaxial tensile strains up to 5.7%along h100i in suspended germanium(Ge)wires on a silicon substrate,measured using Raman spectroscopy.This strain is sufficient to make Ge a direct bandgap semiconductor.Theoretical calculations show that a significant fraction of electrons remain in the indirect conduction valley despite the direct bandgap due to the much larger density of states;however,recombination can nevertheless be dominated by radiative direct bandgap transitions if defects are minimized.We then calculate the theoretical efficiency of direct bandgap Ge LEDs and lasers.These strained Ge wires represent a direct bandgap Group IV semiconductor integrated directly on a silicon platform.