Impact of strain relaxation of AlmGa1−mN layer on 2-DEG sheet charge density and current voltage characteristics of lattice mismatched AlmGa1−mN/GaN HEMTs

An accurate charge control model to investigate the effect of aluminum composition, strain relaxation, thickness and doping of the Al_mGa_1−mN barrier layer on the piezoelectric and spontaneous polarization induced 2-DEG sheet charge density, threshold voltage and output characteristics of partially relaxed Al_mGa_1−mN/GaN HEMTs is proposed. The strain relaxation of the barrier imposes an upper limit on the maximum 2-DEG density achievable in high Al content structures and is critical in determining the performance of lattice mismatched Al_mGa_1−mN/GaN HEMTs. The model incorporates the effects of field dependent mobility, parasitic source/drain resistance and velocity saturation to evaluate the output characteristics of Al_mGa_1−mN/GaN HEMTs. Close proximity with published results confirms the validity of the proposed model.     

Regional eigenvalue-clustering robustness of linear output feedback systems with both time-varying structured and unstructured uncertainties as well as nonlinear actuators

This paper investigates the regional eigenvalue-clusteringrobustness of linear output feedback systems with both time-varyingstructured (elemental) and unstructured (norm-bounded) parameteruncertainties as well as nonlinear actuators. A sufficient conditionis proposed for ensuring that all the eigenvalues of outputfeedback systems with both time-varying structured and unstructuredparameter uncertainties as well as nonlinear actuators remaininside the specified region. No restriction is imposed on theshapes of the specified region. The proposed method is applicableto both the continuous-time case and the discrete-time case.When all the eigenvalues are just required to locate in thestable region, the proposed criterion will become the stabilityrobustness criterion. Two numerical examples are given to illustratethe application of the proposed sufficient condition.     

Acoustically induced dynamic potential dots

Mobile potential dots (dynamic dots, DDs) formed by surface acoustic waves (SAWs) are used to transport photogenerated electrons and holes in GaAs quantum wells (QWs). We investigate the interaction between the transported carriers and microscopic trap centers in the QW plane using spatially and time-resolved photoluminescence (PL) spectroscopy. The carriers recombine at the trap site emitting short (width0.6 ns) light pulses at a repetition rate corresponding to the SAW frequency. The dependence of the PL intensity from the traps on the number of carriers transported per DD n exhibits a well-defined, distinct plateau for n in the range from 5–20, which is attributed to the emission of a well-defined number of photons.     

基于PZT厚膜驱动的微喷芯片的设计

设计了一种基于双压电薄膜驱动的微喷芯片,该芯片中每个流体单元结构主要是由进样室、微管道、喷口以及集成了PZT驱动器的主副贮液室组成,其中主驱动器提供喷射液体的驱动力,副驱动器抑制液体回流;采用计算流体力学模拟(CFD-simulation)对其进行了结构设计、进样模拟和喷样模拟,结果表明,液体能成功进样及喷样。同时当微管道尺寸小于40μm时,喷样过程中微管道内将不再产生回流,证明双PZT驱动器的芯片设计合理,为该芯片的制作打下基础。     

压电智能挠性板的主动振动控制研究

对挠性悬臂矩形板的主动振动控制进行了研究。给出了悬臂板的压电敏感器和致动器的布置准则，并推导了悬臂板的（包括弯曲和扭转振动模态）基于分布式压电致动器的压电致动方程，可以根据该方程设计悬臂板压电主动振动抑制的控制器。该文在控制方法上采用应变律反馈控制和线性二次型（LQR）控制，计算机数字仿真结果表明：设计的控制律对于悬臂板的弯曲和扭转振动是有效的。     

硅基PZT压电驱动微开关的设计和优化

采用压电多层微悬臂梁理论分析模型，研究了一种新型PZT压电复合多层膜微悬臂梁驱动微开关的机械性能，提出了一种新的硅基PZT压电复合多层薄膜微悬臂梁驱动微开关的制作方法。利用有限元分析软件ANSYS7.O对微悬臂梁结构进行了模态分析，探讨了结构参数与微悬臂梁运动特性的关系及影响压电薄膜微开关性能的因素，进一步模拟了0．3V工作电压下微开关的位移。结果表明，经优化后的压电薄膜微开关可进一步应用到集成化芯片系统中。     

Surface integral determination of built-in electric fields and analysis of exciton binding energies in nitride-based quantum dots

We present a simple analytical approach to calculate the built-in strain-induced and spontaneous piezoelectric fields in nitride-based quantum dots (QDs) and then apply the method to describe the variation of exciton, biexciton and charged exciton energy with dot size in GaN/AlN QDs. We first present the piezoelectric potential in terms of a surface integral over the QD surface, and confirm that, due to the strong built-in electric field, the electrons are localised near the QD top and the holes are localised in the wetting layer just below the dot. The strong localisation and smaller dielectric constant results in much larger Coulomb interactions in GaN/AlN QDs than in typical InAs/GaAs QDs, with the interaction between two electrons, J_ee, or two holes, J_hh, being about a factor of three larger. The electron–hole recombination energy is always blue shifted in the charged excitons, X⁻ and X⁺, and the biexciton, and the blue shift increases with increasing dot height. We conclude that spectroscopic studies of the excitonic complexes should provide a useful probe of the structural and piezoelectric properties of GaN-based QDs.     

Self‐Healing Graphene Oxide Based Functional Architectures Triggered by Moisture

Self‐healing materials are capable of spontaneously repairing themselves at damaging sites without additional adhesives. They are important functional materials with wide applications in actuators, shape memorizing materials, smart coatings, and medical treatments, etc. Herein, this study reports the self‐healing of graphene oxide (GO) functional architectures and devices with the assistance of moisture. These GO architectures can completely restore their mechanical‐performance (e.g., compressibility, flexibility, and strength) after healing their broken sites using a little amount of water moisture. On the basis of this effective moisture‐triggered self‐healing process, this study develops GO smart actuators (e.g., bendable actuator, biomimetic walker, rotatable fiber motor) and sensors with self‐healing ability. This work provides a new pathway for the development of self‐healing materials for their applications in multidimensional spaces and functional devices.     

Piezocatalytic Techniques in Environmental Remediation

As a consequence of rapid industrialization throughout the world, various environmental pollutants have begun to accumulate in water, air, and soil. This endangers the ecological environment of the earth, and environmental remediation has become an immediate priority. Among various environmental remediation techniques, piezocatalytic techniques, which uniquely take advantage of the piezoelectric effect, have attracted much attention. Piezoelectric effects allow pollutant degradation directly, while also enhancing photocatalysis by reducing the recombination of photogenerated carriers. In this Review, we provide a comprehensive summary of recent developments in piezocatalytic techniques for environmental remediation. The origin of the piezoelectric effect as well as classification of piezoelectric materials and their application in environmental remediation are systematically summarized. We also analyze the potential underlying mechanisms. Finally, urgent problems and the future development of piezocatalytic techniques are discussed.