单晶金刚石外延层生长工艺研究

目的研究高质量单晶金刚石外延生长工艺。方法使用X射线白光形貌束分析了等离子体表面刻蚀处理前后单晶金刚石位错密度的变化,随后使用等离子体刻蚀预处理工艺,通过改变沉积温度研究了其对金刚石质量的影响。为了表征温度对单晶金刚石质量的影响程度,使用拉曼光谱和X射线衍射摇摆曲线等方法分析了单晶金刚石质量以及位错密度的变化情况,进而确定沉积高质量单晶金刚石最佳的沉积温度。结果X射线白光形貌束结果显示,未进行氢氧等离子体表面刻蚀的籽晶生长之后,由于表面微加工、抛光引入的位错或者微裂纹,导致生长层位错增多;同时,氢氧等离子体表面刻蚀实验结果显示,刻蚀时间并非越长越好;使用刻蚀处理过的单晶金刚石籽晶进行不同温度外延生长实验,籽晶刻蚀后生长的金刚石拉曼峰位均在1332.5 cm^(?1)附近,半高宽为2~3 cm^(?1)之间。在900℃沉积之后,X射线摇摆曲线半高宽仅为0.009。结论使用氢氧微波等离子体刻蚀单晶金刚石,800℃刻蚀40 min,可以基本消除因微加工或者抛光引入的位错或者缺陷。经过刻蚀处理的籽晶在900℃制备出的单晶金刚石质量最高,位错最少,可以满足高质量单晶金刚石的制备。

Fabrication of 3D Templates Using a Large Depth of Focus Femtosecond Laser

We report the use of a large depth of focus Bessel beam in the fabrication of cell structures. Two axicon lenses are investigated in the formation of high aspect ratio line structures. A sol-gel resin, with good mechanical strength, is polymerised in a modified two-photon polymerisation system. Examples of different two-dimensional grids are presented to show that the lateral resolution can be maintained even in the rapid fabrication of high-sided structures.

Approach for Grid Connected PV Management:Advance Solar Prediction and Enhancement of Voltage Stability Margin Using FACTS Device

The uncertainty in solar energy is different from conventional,dispatchable generation fuels and difficult to incorporate into the standard system operating procedures.In the first part of this work,the machine learning algorithm is used to train models based on solar irradiance data and different meteorological weather information to predict the solar irradiance for different cities to validate the forecasting model.Again,the intermittent and inertialess nature of photovoltaic(PV)systems can produce significant power oscillations that can cause significant problems with dynamic stability of the power system and also limit the penetration capacity of PV into the grid.In the second part,it is shown that the residue-based power oscillation damping(POD)controller obviously improves the inter-area oscillation damping.The validity and effectiveness of the proposed controller are demonstrated on the three-machine two-area test system that combines the conventional synchronous generator and flexible alternating current transmission systems(FACTS)device using simulations.This report overall puts an in-depth analysis with regard to the challenges of solar resources with integrating,planning,operating,and particularly the stability of the rest of the power grid,including existing generation resources,customer requirements,and the transmission system itself that will lead to an improved decision making in resource allocations and grid stability.

Integrated silicon ohotonic MEMS

Silicon photonics has emerged as a mature technology that is expected to play a key role in critical emerging applications,including very high data rate optical communications,distance sensing for autonomous vehicles,photonic-accelerated computing,and quantum information processing.The success of silicon photonics has been enabled by the unique combination of performance,high yield,and high-volume capacity that can only be achieved by standardizing manufacturing technology.Today,standardized silicon photonics technology platforms implemented by foundries provide access to optimized library components,including low-loss optical routing,fast modulation,continuous tuning,high-speed germanium photodiodes,and high-effciency optical and electrical interfaces.However,silicon's relatively weak electro-optic effects result in modulators with a significant footprint and thermo-optic tuning devices that require high power consumption,which are substantial impediments for very large-scale integration in silicon photonics.Microelectromechanical systems(MEMS)technology can enhance silicon photonics with building blocks that are compact,low-loss,broadband,fast and require very low power consumption.Here,we introduce a silicon photonic MEMS platform consisting of high-performance nano-opto-electromechanical devices fully integrated alongside standard silicon photonics foundry components,with wafer-level sealing for long-term reliability,flip-chip bonding to redistribution interposers,and fibre-array attachment for high port count optical and electrical interfacing.Our experimental demonstration of fundamental silicon photonic MEMS circuit elements,including power couplers,phase shifters and wavelength-division multiplexing devices using standardized technology lifts previous impediments to enable scaling to very large photonic integrated circuits for applications in telecommunications,neuromorphic computing,sensing,programmable photonics,and quantum computing.

Unlocking the monolithic integration scenario: optical coupling between GaSb diode lasers epitaxially grown on patterned Si substrates and passive SiN waveguides

Silicon(Si)photonics has recently emerged as a key enabling technology in many application fields thanks to the mature Si process technology,the large silicon wafer size,and promising Si optical properties.The monolithic integration by direct epitaxy of III-V lasers and Si photonic devices on the same Si substrate has been considered for decades as the main obstacle to the realization of dense photonics chips.Despite considerable progress in the last decade,only discrete III-V lasers grown on bare Si wafers have been reported,whatever the wavelength and laser technology.Here we demonstrate the first semiconductor laser grown on a patterned Si photonics platform with light coupled into a waveguide.A mid-IR GaSb-based diode laser was directly grown on a pre-patterned Si photonics wafer equipped with SiN waveguides clad by SiO_(2).Growth and device fabrication challenges,arising from the template architecture,were overcome to demonstrate more than 10 mw outpower of emitted light in continuous wave operation at room temperature.In addition,around 10%of the light was coupled into the SiN waveguides,in good agreement with theoretical calculations for this butt-coupling configuration.This work lft an important building block and it paves the way for future low-cost,large-scale,fully integrated photonic chips.

Evaluating the performance of nanostructured materials as lithium-ion battery electrodes

The performance of the lithium-ion cell is heavily dependent on the ability of the host electrodes to accommodate and release Li＋ ions from the local structure. While the choice of electrode materials may define parameters such as cell potential and capacity, the process of intercalation may be physically limited by the rate of solid-state Li＋ diffusion. Increased diffusion rates in lithium-ion electrodes may be achieved through a reduction in the diffusion path, accomplished by a scaling of the respective electrode dimensions. In addition, some electrodes may undergo large volume changes associated with charging and discharging, the strain of which, may be better accommodated through nanostructuring. Failure of the host to accommodate such volume changes may lead to pulverisation of the local structure and a rapid loss of capacity. In this review article, we seek to highlight a number of significant gains in the development of nanostructured lithium-ion battery architectures （both anode and cathode）, as drivers of potential next-generation electrochemical energy storage devices.

Coupling strategies for silicon photonics integrated chips[Invited]

Over the last 20 years, silicon photonics has revolutionized the field of integrated optics, providing a novel and powerful platform to build mass-producible optical circuits. One of the most attractive aspects of silicon photonics is its ability to provide extremely small optical components, whose typical dimensions are an order of magnitude smaller than those of optical fiber devices. This dimension difference makes the design of fiberto-chip interfaces challenging and, over the years, has stimulated considerable technical and research efforts in the field. Fiber-to-silicon photonic chip interfaces can be broadly divided into two principle categories:in-plane and out-of-plane couplers. Devices falling into the first category typically offer relatively high coupling efficiency, broad coupling bandwidth(in wavelength), and low polarization dependence but require relatively complex fabrication and assembly procedures that are not directly compatible with wafer-scale testing.Conversely, out-of-plane coupling devices offer lower efficiency, narrower bandwidth, and are usually polarization dependent. However, they are often more compatible with high-volume fabrication and packaging processes and allow for on-wafer access to any part of the optical circuit. In this paper, we review the current state-of-the-art of optical couplers for photonic integrated circuits, aiming to give to the reader a comprehensive and broad view of the field, identifying advantages and disadvantages of each solution. As fiber-to-chip couplers are inherently related to packaging technologies and the co-design of optical packages has become essential, we also review the main solutions currently used to package and assemble optical fibers with silicon-photonic integrated circuits.

Metal-assisted chemical etching of silicon and the behavior of nanoscale silicon materials as Li-ion battery anodes

This review outlines the developments and recent progress in metal-assisted chemical etching of silicon, summarizing a variety of fundamental and innovative processes and etching methods that form a wide range of nanoscale silicon structures. The use of silicon as an anode for Li-ion batteries is also reviewed, where factors such as film thickness, doping, alloying, and their response to reversible lithiation processes are summarized and discussed with respect to battery cell performance. Recent advances in improving the performance of silicon-based anodes in Li-ion batteries are also discussed. The use of a variety of nanostructured silicon structures formed by many different methods as Li-ion battery anodes is outlined, focusing in particular on the influence of mass loading, core-shell structure, conductive additives, and other parameters. The influence of porosity, dopant type, and doping level on the electrochemical response and cell performance of the silicon anodes are detailed based on recent findings. Perspectives on the future of silicon and related materials, and their compositional and structural modifications for energy storage via several electrochemical mechanisms, are also provided.

Towards a Wireless Sensor Platform for Energy Efficient Building Operation

Currently, the IT-support for energy performance rating of buildings is insufficient. So-called IT-platforms often 'built' of an ad-hoc, inconsistent combination of off-the-shelf building management compo-nents, distributed data metering equipment and several monitoring software tools. A promising approach to achieve consistent, holistic performance data management is the implementation of an integrated, modular wireless sensor platform. This paper presents an approach of how wireless sensors can be seamlessly integrated into existing and future intelligent building management systems supporting improved building performance and diagnostics with an emphasis on energy management.

Ultralow-crosstalk,strictly non-blocking microring-based optical switch

We report on the first monolithically integrated microring-based optical switch in the switch-and-select architecture. The switch fabric delivers strictly non-blocking connectivity while completely canceling the first-order crosstalk. The 4 × 4 switching circuit consists of eight silicon microring-based spatial(de-)multiplexers interconnected by a Si/SiN dual-layer crossing-free central shuffle. Analysis of the on-state and off-state power transfer functions reveals the extinction ratios of individual ring resonators exceeding 25 dB, leading to switch crosstalk suppression of up to over 50 dB in the switch-and-select topology. Optical paths are assessed, showing losses as low as 0.1 dB per off-resonance ring and 0.5 dB per on-resonance ring. Photonic switching is actuated with integrated micro-heaters to give an ～24 GHz passband. The fully packaged device is flip-chip bonded onto a printed circuit board breakout board with a UV-curved fiber array.

Optical information processing using dual state quantum dot lasers: complexity through simplicity

We review results on the optical injection of dual state InAs quantum dot-based semiconductor lasers.The two states in question are the so-called ground state and first excited state of the laser.This ability to lase from two different energy states is unique amongst semiconductor lasers and in combination with the high,intrinsic relaxation oscillation damping of the material and the novel,inherent cascade like carrier relaxation process,endows optically injected dual state quantum dot lasers with many unique dynamical properties.Particular attention is paid to fast state switching,antiphase excitability,novel information processing techniques and optothermally induced neuronal phenomena.We compare and contrast some of the physical properties of the system with other optically injected two state devices such as vertical cavity surface emitting lasers and ring lasers.Finally,we offer an outlook on the use of quantum dot material in photonic integrated circuits.

Direct visualization of phase-matched efficient second harmonic and broadband sum frequency generation in hybrid plasmonic nanostructures

Second harmonic generation and sum frequency generation(SHG and SFG)provide effective means to realize coherent light at desired frequencies when lasing is not easily achievable.They have found applications from sensing to quantum optics and are of particular interest for integrated photonics at communication wavelengths.Decreasing the footprints of nonlinear components while maintaining their high up-conversion efficiency remains a challenge in the miniaturization of integrated photonics.Here we explore lithographically defined AlGaInP nano(micro)structures/Al_(2)O_(3)/Ag as a versatile platform to achieve efficient SHG/SFG in both waveguide and resonant cavity configurations in both narrow-and broadband infrared(IR)wavelength regimes(1300-1600 nm).The effective excitation of highly confined hybrid plasmonic modes at fundamental wavelengths allows efficient SHG/SFG to be achieved in a waveguide of a cross-section of 113 nm×250 nm,with a mode area on the deep subwavelength scale(λ2/135)at fundamental wavelengths.Remarkably,we demonstrate direct visualization of SHG/SFG phase-matching evolution in the waveguides.This together with mode analysis highlights the origin of the improved SHG/SFG efficiency.We also demonstrate strongly enhanced SFG with a broadband IR source by exploiting multiple coherent SFG processes on 1μm diameter AlGaInP disks/Al_(2)O_(3)/Ag with a conversion efficiency of 14.8%MW^(−1) which is five times the SHG value using the narrowband IR source.In both configurations,the hybrid plasmonic structures exhibit>1000 enhancement in the nonlinear conversion efficiency compared to their photonic counterparts.Our results manifest the potential of developing such nanoscale hybrid plasmonic devices for state-of-the-art on-chip nonlinear optics applications.

Development of a facile block copolymer method for creating hard mask patterns integrated into semiconductor manufacturing

Our goal is to develop a facile process to create patterns of inorganic oxides and metals on a substrate that can act as hard masks. These materials should have high etch contrast （compared to silicon） and so allow high-aspect-ratio, high- fidelity pattern transfer whilst being readily integrable in modem semiconductor fabrication （FAB friendly）. Here, we show that ultra-small-dimension hard masks can be used to develop large areas of densely packed vertically and horizontally orientated Si nanowire arrays. The inorganic and metal hard masks （Ni, NiO, and ZnO） of different morphologies and dimensions were formed using microphase- separated polystyrene-b-poly（ethylene oxide） （PS-b-PEO） block copolymer （BCP） thin films by varying the BCP molecular weight, annealing temperature, and annealing solvent（s）. The self-assembled polymer patterns were solvent-processed, and metal ions were included into chosen domains via a selective inclusion method. Inorganic oxide nanopatterns were subsequently developed using standard techniques. High-resolution transmission electron microscopy studies show that high-aspect-ratio pattern transfer could be affected by standard plasma etch techniques. The masking ability of the different materials was compared in order to create the highest quality uniform and smooth sidewall profiles of the Si nanowire arrays. Notably good performance of the metal mask was seen, and this could impact the use of these materials at small dimensions where conventional methods are severely limited.

Review of current methods of acousto-optical tomography for biomedical applications

The field of acousto-optical tomography （AOT） for medical applications began in the 1990s and has since developed multiple techniques for the detection of ultrasound-modulated light. Light becomes frequency shifted as it travels through an ultrasound beam. This ＂tagged＂ light can be detected and used for focused optical imaging. Here, we present a comprehensive overview of the techniques that have developed since around 2011 in the field of biomedical AOT. This includes how AOT has advanced by taken advantage of the research conducted in the ultrasound, as well as, the optical fields. Also, simulations and reconstruction algorithms have been formulated specifically for AOT imaging over this time period. Future progression of AOT relies on its ability to provide significant contributions to in vivo imaging for biomedical applications. We outline the challenges that AOT still faces to make in vivo imaging possible and what has been accomplished thus far, as well as possible future directions.

The origin of the lattice thermal conductivity enhancement at the ferroelectric phase transition in GeTe

The proximity to structural phase transitions in IV-VI thermoelectric materials is one of the main reasons for their large phonon anharmonicity and intrinsically low lattice thermal conductivityκ.However,theκof GeTe increases at the ferroelectric phase transition near 700 K.Using first-principles calculations with the temperature dependent effective potential method,we show that this rise inκis the consequence of negative thermal expansion in the rhombohedral phase and increase in the phonon lifetimes in the high-symmetry phase.Strong anharmonicity near the phase transition induces non-Lorentzian shapes of the phonon power spectra.To account for these effects,we implement a method of calculatingκbased on the Green-Kubo approach and find that the Boltzmann transport equation underestimatesκnear the phase transition.Our findings elucidate the influence of structural phase transitions onκand provide guidance for design of better thermoelectric materials.

Giant thermoelectric power factor in charged ferroelectric domain walls of GeTe with Van Hove singularities

Increasing the Seebeck coefficient S in thermoelectric materials usually drastically decreases the electrical conductivity σ,making significant enhancement of the thermoelectric power factor σS^(2) extremelly challenging.Here we predict,using first-principles calculations,that the extraordinary properties of charged ferroelectric domain walls(DWs)in GeTe enable a five-fold increase ofσS^(2) in the DW plane compared to bulk.The key reasons for this enhancement are the confinement of free charge carriers at the DWs and Van Hove singularities in the DW electronic band structure near the Fermi level.

Wavelength stability in a hybrid photonic crystal laser through controlled nonlinear absorptive heating in the reflector

The need for miniaturized,fully integrated semiconductor lasers has stimulated significant research efforts into realizing unconventional configurations that can meet the performance requirements of a large spectrum of applications,ranging from communication systems to sensing.We demonstrate a hybrid,silicon photonicscompatible photonic crystal(PhC)laser architecture that can be used to implement cost-effective,high-capacity light sources,with high side-mode suppression ratio and milliwatt output output powers.The emitted wavelength is set and controlled by a silicon PhC cavity-based reflective filter with the gain provided by a Ⅲ–Ⅴ-based reflective semiconductor optical amplifier(RSOA).The high power density in the laser cavity results in a significant enhancement of the nonlinear absorption in silicon in the high Q-factor PhC resonator.The heat generated in this manner creates a tuning effect in the wavelength-selective element,which can be used to offset external temperature fluctuations without the use of active cooling.Our approach is fully compatible with existing fabrication and integration technologies,providing a practical route to integrated lasing in wavelength-sensitive schemes.

Impact of surface hydroxylation in MgO-/SnO-nanocluster modified TiO_2 anatase(101) composites on visible light absorption, charge separation and reducibility

Surface modification with metal oxide nanoclusters has emerged as a candidate for the enhancement of the photocatalytic activity of titanium dioxide. An increase in visible light absorption and the suppression of charge carrier recombination are necessary to improve the efficiency. We have studied Mg4O4 and Sn4O4 nanoclusters modifying the（101） surface of anatase TiO2 using density functional theory corrected for on-site Coulomb interactions（DFT ＋ U）. Such studies typically focus on the pristine surface, free of the point defects and surface hydroxyls present in real surfaces. We have also examined the impact of partial hydroxylation of the anatase surface on a variety of outcomes such as nanocluster adsorption, light absorption, charge separation and reducibility. Our results indicate that the modifiers adsorb strongly at the surface, irrespective of the presence of hydroxyl groups, and that modification extends light absorption into the visible range while enhancing UV activity. Our model for the excited state of the heterostructures demonstrates that photoexcited electrons and holes are separated onto the TiO2 surface and metal oxide nanocluster respectively. Comparisons with bare TiO2 and other TiO2-based photocatalyst materials are presented throughout.

Nanophase separation and structural evolution of block copolymer films： A ＂green＂ and ＂clean＂ supercritical fluid approach

Thin films of block copolymers （BCPs） are widely accepted as potentially important materials in a host of technological applications including nano- lithography. In order to induce domain separation and form well-defined structural arrangements, many of these are solvent-annealed （i.e. solvent swollen） at moderate temperatures. The use of solvents can be challenging in industry from an environmental point of view as well as having practical/cost issues. However, a simple and environmentally friendly alternative to solvo-thermal annealing for the periodically ordered nanoscale phase separated structures is described herein. Various asymmetric polystyrene-b-poly（ethylene oxide） （PS-b-PEO） thin films were annealed in a compressible fluid, supercritical carbon dioxide （scCO2）, to control nanodomain orientation and surface morphologies. For the first time, periodic well defined, hexagonally ordered films with sub-25 nm pitch size were demonstrated using a supercritical fluid （SCF） process at low temperatures and pressures. Predominant swelling of PEO domains in scCO2 induces nanophase separation, scCO2 serves as green alternative to the conventional organic solvents for the phase segregation of BCPs with complete elimination of any residual solvent in the patterned film. The depressurization rate of scCO2 following annealing was found to affect the morphology of the films. The supercritical annealing conditions could be used to define nanoporous analogues of the microphase separated films without additional processing, providing a one-step route to membrane like structures without affecting the ordered surface phase segregated structure. An understanding of the BCP self- assembly mechanism can be realized in terms of the deviation in glass transition temperature, melting point, viscosity, interaction parameter and volume fraction of the constituent blocks in the scCO2 environment.

A Low-Cost, Portable Optical Sensing System With Wireless Communication Compatible of Real-Time and Remote Detection of Dissolved Ammonia

A low-cost and portable optical chemical sensor based ammonia sensing system that is capable of detecting dissolved ammonia up to 5 ppm is presented. In the system, an optical chemical sensor is designed and fabricated for sensing dissolved ammonia concentrations. The sensor uses eosin as the fluorescence dye which is immobilized on the glass substrate by a gas-permeable protection layer. A compact module is developed to hold the optical components, and a battery powered micro-controller system is designed to read out and process the data measured. The system operates without the requirement of laboratory instruments that makes it cost effective and highly portable. Moreover, the calculated results in the system can be transmitted to a PC wirelessly, which allows the remote and real-time monitoring of dissolved ammonia.