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Resonant Raman scattering in GaN single crystals and GaN-based heterostructures: feasibility for laser cooling

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Chinese Optics Letters 2013年第1期11卷 63-71页

作者： Yujie J. Ding Jacob B. Khurgin Department of Electrical and Computer Engineering Lehigh University Department of Electrical and Computer Engineering The Johns Hopkins University

The recent progress on Raman scattering in GaN single crystals and GaN/A1N heterostructures is re- viewed. Anti-Stokes Raman scattering is used to determine electron-phonon scattering time and decay time constant for longitudinal-opticat phonons. In a typical high electron mobility transistor based on GaN/A1N heterostructures, strong resonances are reached for the first-order and second-order Raman scattering processes. Therefore, both Stokes and anti-Stokes Raman intensities are dramatically enhanced. The feasibility for laser cooling of a nitride structure is studied. A further optimization will enable us to reach the threshold for laser cooling. Raman scattering have potential applications in up-conversion lasers and laser cooling of nitride ultrafast electronic and optoelectronic devices.

关键词： GaN Ra Resonant Raman scattering in GaN single crystals and GaN-based heterostructures feasibility for laser cooling

Coulomb drag between in-plane graphene double ribbons and the impact of the dielectric constant

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Nano Research 2013年第12期6卷 897-905页

作者： Hongyan Chen Joerg Appenzeller Electrical and Computer Engineering Department Purdue University West Lafayette IN 47907 USA

With recent developments in the search for novel device ideas, understanding electron-electron interaction in low dimensional systems is of particular interest. Coulomb drag measurements can provide critical insights in this context. In this article, we present a novel planar graphene double ribbon structure that shows for the first time that Coulomb drag is observable in two adjacent monolayer ribbons in the same plane at room temperature. Moreover, our planar devices enable experimentally study of the impact of the dielectric constant on Coulomb drag which is difficult to explore in the typically used double layer graphene structures. Our experimental findings indicate in particular that the drag resistance is proportional to the dielectric constant （~） and does not, as recently reported, show an increasing trend of interaction strength for small C-values. In fact, we find that the drag resistance follows approximately an ~l.2-dependence. The exponent of ＂1.2＂ is consistent with the theory considering the carrier concentration in our samples, and positions our results in between the weak and strong coupling limits.

关键词： Coulomb drag graphene ribbon dielectric scattering electron-electroninteractions

LITTLEWOOD-PALEY THEOREM FOR SCHR DINGER OPERATORS

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Analysis in Theory and Applications 2006年第4期22卷 353-361页

作者： Shijun Zheng University of South Carolina Columbia Department of MathematicsUniversity of South Carolina Columbia SC 29208 USA

Let H be a Schroedinger operator on R^n. Under a polynomial decay condition for the kernel of its spectral operator, we show that the Besov spaces and Triebel-Lizorkin spaces associated with H are well defined. We further give a Littlewood-Paley characterization of Lp spaces in terms of dyadic functions of H. This generalizes and strengthens the previous result when the heat kernel of H satisfies certain upper Gaussian bound.

关键词： functional calculus SchrSdinger operator Littlewood-Paley theory

Resonant pitch and roll silicon gyroscopes with sub-micron-gap slanted electrodes:Breaking the barrier toward high-performance monolithic inertial measurement units

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Microsystems & Nanoengineering 2017年第1期3卷 332-340页

作者： Haoran Wen Anosh Daruwalla Farrokh Ayazi School of Physics Georgia Institute of Technology837 State StreetAtlantaGA 30332USA Department of Electrical and Computer Engineering Georgia Institute of Technology777 Atlantic Drive NWAtlantaGA 30332USA

This paper presents the design,fabrication,and characterization of a novel high quality factor(Q)resonant pitch/roll gyroscope implemented in a 40μm(100)silicon-on-insulator(SOI)substrate without using the deep reactive-ion etching(DRIE)*** featured silicon gyroscope has a mode-matched operating frequency of 200 kHz and is the first out-of-plane pitch/roll gyroscope with electrostatic quadrature tuning capability to fully compensate for fabrication non-idealities and variation in SOI *** quadrature tuning is enabled by slanted electrodes with sub-micron capacitive gaps along the(111)plane created by an anisotropic wet *** quadrature cancellation enables a 20-fold improvement in the scale factor for a typical fabricated *** measurement of quadrature-cancelled mode-matched devices shows an angle random walk(ARW)of 0.63°√h^(−1) and a bias instability of 37.7°h^(−1),partially limited by the noise of the interface *** elimination of silicon DRIE in the anisotropically wet-etched gyroscope improves the gyroscope robustness against the process variation and reduces the fabrication *** use of a slanted electrode for quadrature tuning demonstrates an effective path to reach high-performance in future pitch and roll gyroscope designs for the implementation of single-chip high-precision inertial measurement units(IMUs).

关键词： anisotropic wet etching MEMS resonant pitch/roll gyroscope quadrature cancellation slanted electrode

Nanoporous membrane device for ultra high heat flux thermal management

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Microsystems & Nanoengineering 2018年第1期4卷 474-483页

作者： Daniel F.Hanks Zhengmao Lu Jay Sircar Todd R.Salamon Dion S.Antao Kevin R.Bagnall Banafsheh Barabadi Evelyn N.Wang Massachusetts Institute of Technology 77 Massachusetts AvenueCambridgeMA 02139USA Nokia Bell Labs 600 Mountain AvenueNew ProvidenceNJ 07974USA

High power density electronics are severely limited by current thermal management solutions which are unable to dissipate the necessary heat flux while maintaining safe junction temperatures for reliable *** designed,fabricated,and experimentally characterized a microfluidic device for ultra-high heat flux dissipation using evaporation from a nanoporous silicon ***~100 nm diameter pores,the membrane can generate high capillary pressure even with low surface tension fluids such as pentane and *** suspended ultra-thin membrane structure facilitates efficient liquid transport with minimal viscous pressure *** fabricated the membrane in silicon using interference lithography and reactive ion etching and then bonded it to a high permeability silicon microchannel array to create a biporous wick which achieves high capillary pressure with enhanced *** back side consisted of a thin film platinum heater and resistive temperature sensors to emulate the heat dissipation in transistors and measure the temperature,*** experimentally characterized the devices in pure vaporambient conditions in an environmental ***,we demonstrated heat fluxes of 665±74 W/cm^(2) using pentane over an area of 0.172mm×10mm with a temperature rise of 28.5±1.8 K from the heated substrate to ambient *** heat flux,which is normalized by the evaporation area,is the highest reported to date in the pure evaporation regime,that is,without nucleate *** experimental results are in good agreement with a high fidelity model which captures heat conduction in the suspended membrane structure as well as non-equilibrium and sub-continuum effects at the liquid–vapor *** work suggests that evaporative membrane-based approaches can be promising towards realizing an efficient,high flux thermal management strategy over large areas for high-performance electronics.

关键词： high thermal ambient

Expanding the top rungs of the extremity reconstructive ladder:targeted muscle reinnervation,osseointegration,and vascularized composite allotransplantation

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Plastic and Aesthetic Research 2020年第2期7卷 1-20页

作者： Saïd C.Azoury Andrew Bauder Jason M.Souza John T.Stranix Sammy Othman Christine M.cAndrew Scott M.Tintle Stephen J.Kovach Lawrence Scott Levin Division of Plastic Surgery Department of SurgeryUniversity of PennsylvaniaPennsylvaniaPA 19104USA Department of Orthopaedic Surgery Walter Reed National Military Medical CenterBethesdaMD 20889USA Department of Plastic Surgery University of VirginiaCharlottesvilleVA 22908USA Department of Orthopaedic Surgery University of PennsylvaniaPennsylvaniaPA 19104USA

Osseointegration(OI),targeted muscle reinnervation(TMR),and vascularized composite allotransplantation(VCA)are just a few ways by which our reconstructive ladder is *** is important to recognize that amputation does not necessarily denote failure,but surgeons should strive to find ways to provide these patients with means for obtaining better satisfaction and quality of life *** and OI have added options for mutilating lower extremity injuries that necessitate *** recently,the senior author(Levin LS)described the"penthouse"floor of the reconstructive ladder being *** the advances in VCA over the last 20 years,there are many challenges that face this discipline including indications for patient selection,minimizing immunosuppressive regimens,standardizing outcome measures,establishing reliable protocols for monitoring,and diagnosing and managing ***,the authors review TMR,OI,and VCA as additional higher rungs of the reconstructive ladder.

关键词： Targeted muscle reinnervation osseointegration vascularized composite allotransplantation salvage reconstruction

Broadband 200-nm second-harmonic generation in silicon in the telecom band

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Light(Science & Applications) 2020年第1期9卷 1844-1850页

作者： Neetesh Singh Manan Raval Alfonso Ruocco Michael R.Watts Research Laboratory of Electronics Massachusetts Institute of Technology77 Massachusetts AvenueCambridgeMA 02139USA

Silicon is well known for its strong third-order optical nonlinearity,exhibiting efficient supercontinuum and four-wave mixing processes.A strong second-order effect that is naturally inhibited in silicon can also be observed,for example,by electrically breaking the inversion symmetry and quasi-phase matching the pump and the *** generate an efficient broadband second-harmonic signal,however,the most promising technique requires matching the group velocities of the pump and the *** this work,we utilize dispersion engineering of a silicon waveguide to achieve group velocity matching between the pump and the signal,along with an additional degree of freedom to broaden the second harmonic through the strong third-order *** demonstrate that the strong self-phase modulation and cross-phase modulation in silicon help broaden the second harmonic by 200 nm in the ***,we show a waveguide design that can be used to generate a second-harmonic signal in the entire nearinfrared *** work paves the way for various applications,such as efficient and broadband complementarymetal oxide semiconductor based on-chip frequency synthesizers,entangled photon pair generators,and optical parametric oscillators.

关键词： waveguide synthesizer harmonic

Advancing on-chip Kerr optical parametric oscillation towards coherent applications covering the green gap

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Light(Science & Applications) 2024年第10期13卷 2212-2220页

作者： Yi Sun Jordan Stone Xiyuan Lu Feng Zhou Junyeob Song Zhimin Shi Kartik Srinivasan Microsystems and Nanotechnology Division Physical Measurement LaboratoryNational Institute of Standards and TechnologyGaithersburgMDUSA Joint Quantum Institute NIST/University of MarylandCollege ParkMDUSA Reality Labs Research MetaRedmondWAUSA

Optical parametric oscillation(OPO)in Kerr microresonators can efficiently transfer near-infrared laser light into the visible *** date,however,chromatic dispersion has mostly limited output wavelengths to>560 nm,and robust access to the whole green light spectrum has not been *** fact,wavelengths between 532 nm and 633 nm,commonly referred to as the“green gap”,are especially challenging to produce with conventional laser ***,there is motivation to extend the Kerr OPO wavelength range and develop reliable device ***,we experimentally show how to robustly access the entire green gap with Kerr OPO in silicon nitride microrings pumped near 780 *** microring geometries are optimized for green-gap emission;in particular,we introduce a dispersion engineering technique,based on partially undercutting the microring,which not only expands wavelength access but also proves robust to variations in resonator *** just four devices,we generate>150 wavelengths evenly distributed throughout the green gap,as predicted by our dispersion ***,we establish the usefulness of Kerr OPO to coherent applications by demonstrating continuous frequency tuning(>50 GHz)and narrow optical linewidths(<1 MHz).Our work represents an important step in the quest to bring nonlinear nanophotonics and its advantages to the visible spectrum.

关键词： tuning pumped coherent

Visual interpretability for deep learning：a survey

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Frontiers of Information Technology & Electronic Engineering 2018年第1期19卷 27-39页

作者： Quan-shi ZHANG Song-chun ZHU University of California Los Angeles California 90095 USA

This paper reviews recent studies in understanding neural-network representations and learning neural networks with interpretable/disentangled middle-layer *** deep neural networks have exhibited superior performance in various tasks,interpretability is always Achilles' heel of deep neural *** present,deep neural networks obtain high discrimination power at the cost of a low interpretability of their black-box *** believe that high model interpretability may help people break several bottlenecks of deep learning,e.g.,learning from a few annotations,learning via human–computer communications at the semantic level,and semantically debugging network *** focus on convolutional neural networks(CNNs),and revisit the visualization of CNN representations,methods of diagnosing representations of pre-trained CNNs,approaches for disentangling pre-trained CNN representations,learning of CNNs with disentangled representations,and middle-to-end learning based on model ***,we discuss prospective trends in explainable artificial intelligence.

关键词： Artificial intelligence Deep learning Interpretable model