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微能源与光学成像技术研讨会
 
 
作者 佚名 摘自 未知 发表 2014-12-10 13:54:35 人气 2569 背景色 杏仁黄 秋叶褐 胭脂红 芥末绿 天蓝 雪青 灰 银河白(默认色) 字号   

微能源与光学成像技术研讨会



主要内容


压电微能源技术

压电非线性效应

三维血管成像术

时间:20141213日(周六)14:30

地点:北京大学微纳电子大厦350会议室

敬请光临!

讲座一

Beyond ZnOmaterials for Piezotronics and Nanogeneration

Dr. Max Migliorato

School of Electrical and ElectronicEngineering, University of Manchester, United Kingdom

Piezotronics is a term coined in by ProfZhong Lin Wang (Georgia Institute of Technology, Atlanta, USA) and describesthe exploitation of strain and deformation internal polarization fields inpolar semiconductors. Such fields already find applications in transducers andmicropositioner devices but are also known to be present in GaN based lightemitting diodes and lasers. Being a property of polar semiconductorspiezoelectricity is present in both III-V and II-VI compounds, such as thetechnologically important ZnO. For many years piezoelectricity was included inthe design of devices only to first order. In recent years a great deal ofevidence, both model and experimental data, has been generated that sucheffects need to be included to at least second order. [1] The inclusion of suchnonlinear effects produces surprising and non-intuitive results, notably thegeneration of fields of opposite polarity compared to the prediction of linearpiezoelectricity and the possibility of enhancing the piezoelectricpolarization by a factor of 5-10 under particular deformations. In thispresentation we will show the evidence for nonlinear effects and discuss thepossible applications to light emitting diodes, quantum dot emitters and energyharvesting devices. Our theory of Non Linearities, based on accurate quantummechanical calculations and a tight binding formulation of the elastic anddielectric properties of zincblende and wurtzite crystals, is capable of highlightingand correctly predicting the polarization properties of several polarsemiconductors under strain.
We observed strong non linearities in the strain dependence of both zincblendeand wurtzite III-V’s III-N and its alloys and even II-VI wurtzitesemiconductors. While revealing much smaller Spontaneous Polarization effectsin nitrides than previously reported, much larger values of the total(spontaneous + strain induced) polarization are observed compared to linearmodels, therefore highlighting the large effect of Non Linear Piezoelectricityin wurtzite semiconductors. Furthermore we will discuss new approach to designing higher outputefficiency nitride based LEDs through the introduction of a metamorphic layer[2].

Our recent work on III-V wurtzitecore-shell nanowires reveal much increased voltage generation are predicted (to be 3 orders ofmagnitude larger) than the typical values of ±3 V in homogeneous nanowires.Also considering properties such as voltage generation, bandgap discontinuityand mobility, such core-shell nanowires are candidates for high performancecomponents in piezotronics and nanogeneration . [3]

Our continued efforts towards developing anew breed of empirical interatomic potentials, namely MMP potentials, forsemiconductors and very recently, we observed strain induced semiconductinggraphene and submitted a patent application on “Graphene-basedElectronic Structure”. We will discuss the potential for Graphene as a piezoelectricmaterial.

Thesignificance of our work is that by incorporating our unique and well testedability of evaluating strain induced polarization in the design of compositesemiconductor structures we will in the near future be able to propose layoutswhere the piezoelectric fields, i.e. the ‘engine’ inside Energy Harvestingdevices, can be suitably enhanced, hugely increasing the ability of suchdevices to convert mechanical energy into an electrical potential difference.Energy harvesting technology is highly sought after by industry and policymakers because of the potential to reduce the need for 24h charging of portableelectronic devices.

Biography

Max A. Migliorato(Laurea in Physics, 1999, University of Rome “La Sapienza”, Italy, and PhD,2003, University of Sheffield, UK). In 2004 he was awarded a Royal Academy ofEngineering ? EPSRC Research Fellowship at the University of Sheffield. In 2007he was also awarded an RCUK Fellowship at the University of Manchester. Hiswork has always concentrated on atomistic modelling of semiconductornanostructures and he has pioneered the study of non linear polarizationeffects in III-V and II-VI semiconductors.

He is a researcher with 15 years ofexperience in modelling, simulations and characterization of semiconductormaterials and devices. His interests span from IIII-As, III-N, SiGe to Graphene.Over the years he has been awarded 3 EPSRC grants and 2 Research Fellowships.He has authored around 40 journal articles and received around 600 citations. Hisrecent work on Graphene, based on a novel technique of predicting crystaldeformation under external strain, has produced one patent application. He iscurrently the co-chairman of the international conference on Theory, Modellingand Computational methods for Semiconductors (TMCS).

Since March 2011 he is a Lecturer in thesame School, with research in modelling of electronic materials. For moreinformation see his web page: http://www.tmcsuk.org/migliorato/

[1] M. A. Migliorato et al, Phys. Rev. B74, 245332 (2006); R. Garg et al, Appl. Phys. Lett. 95, 041912(2009); J.Pal et al, Phys. Rev. B 84, 085211 (2011); H.Y.S. Al-Zahrani etal, Nano Energy 2 (6),1214 (2013); G Tse et al, J. Appl. Phys. 114 (7),073515 (2013).

[2] J.Pal et al, J. Appl. Phys. 114 (7),073104 (2013)

[3] H.Y.S. Al-Zahrani et al, Nano Energy(2014) (Accepted).

讲座二

术中傅里叶频域光学相干层析术对血管缝合手术的导航和评估

报告人:黄勇(博士)

美国约翰霍普金斯大学电子和计算机工程系

内容简介:

血管缝合手术作为现代整形和重建手术的基石,是很多外科手术医生经常需要实施的手术操作,比如在器官移植、血管修复等手术中血管缝合是一个有机的手术部分。血管缝合手术的难度随着血管直径的下降而上升,尤其对于外直径小于1毫米的血管。吻合口狭窄、血栓形成等问题都会影响手术的长期成功率。在问题严重的情况下,需要对问题血管进行再次手术干预。然而,再次干预的有效性取决于发现血管术后问题的及时性。传统术中显微镜无法提供缝合口处的三维结构和血流信息,只能够提供手术处的表面二维信息。对于缝合血管的目测评估一方面依赖于医生的经验,但受许多不稳定性因素的干扰且具有很大的主观性;另一方面很多间接测量方法被医生用来判断术后效果,比如皮肤温度测量、皮下氧含量测量、激光多普勒、超声多普勒、ICG灌注等,但这些方法存在诸多不确定因素且不能对血管缝合的最关键位置(吻合口)进行高精度的三维成像。术中血管缝合的精确指引和缝合后质量的有效客观评估对手术的长期成功率预测具有十分重要的意义,因此临床中急需一种高分辨率、高速、客观、无损伤、简单可靠的术中三维成像技术帮助医生做出准确的判断。

光学相干层析术(OpticalCoherence Tomography, OCT)是一种高速高分辨率无损伤的三维生物组织光学成像技术。具有1-10微米的轴向分辨率,比传统的超声波探测高1到2个数量级,在生物组织中成像深度可达数毫米量级,高速OCT系统可以实现高达百帧每秒的二维成像速度,在科学研究和医学临床具有着广泛的应用前景,目前的主要应用是活体诊断、医学治疗监测及工业监测等方面。此外,OCT成像技术结合多普勒效应、偏振效应等,可以实现生物组织偏振敏感的OCT成像和多普勒流体流速OCT成像。

本报告将围绕实时傅里叶频域多普勒光学相干层析技术对血管缝合手术的指引和评估展开。主要内容包括:实时傅里叶频域多普勒光学相干层析技术的研究;基于小鼠腿动脉和静脉(血管外径小于0.5毫米)缝合模型的成像系统研究;便于临床应用的手持光学相干层析探头的研究。

报告人简介:

黄勇,2009年毕业于北京大学物理学院凝聚态物理专业,取得理学学士学位;2013年9月毕业于美国约翰霍普金斯大学电子和计算机工程系,取得博士学位;2013年10月至今在美国约翰霍普金斯大学电子和计算机工程系从事博士后研究工作。现阶段研究方向包括:高速高分辨率多功能多形式光学相干层析术系统的设计与研发和其在显微手术特别是血管缝合方面的应用和临床转化研究。

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