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PRISM/PCCM Seminar Series

Consistent with the mission of PRISM, the seminar series invites speakers from academic institutions, industry and government laboratories to address exciting new interdisciplinary areas of research and development. The series also strives to enhance the educational experience of students attending the lecture.

For a PDF version of the schedule click here

Fall 2010

All seminars are from 12:00 noon-1:00 PM in the Bowen Hall Auditorium (Rm. 222). Preceding the seminar there will be a light lunch at 11:30 AM in the Bowen Hall Atrium. For questions regarding the seminars please contact Sheila Gunning at sheila@Princeton.edu or 609-258-1575. Visitors are welcome.


"Nanogenerator and Nano-Piezotronics"

Z.L. Wang
School of Materials Science & Engineering
Georgia Institute of Technology, Atlanta USA
zlwang@gatech.edu

Abstract
 
Developing wireless nanodevices and nanosystems is of critical importance for sensing, medical science, environmental/infrastructure monitoring, defense technology and even personal electronics. It is highly desirable for wireless devices to be self-powered without using battery. This is a new initiative in today’s energy research for mico/nano-systems in searching for sustainable self-sufficient power sources [1]. It is essential to explore innovative nanotechnologies for converting mechanical energy, vibration energy, and hydraulic energy into electric energy that will be used to power nanodevices. We have invented an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire arrays [2]. The operation mechanism of the nanogenerator relies on the piezoelectric potential created by an external strain; a dynamic straining of the nanowire results in a transient flow of the electrons in the external load due to the driving force of the piezopotential. We have developed the nanogenerator from fundamental science, to engineering integration and to technological scale-up [3-6]. As today, a gentle straining can output 1.2 V from an integrated nanogenerator [6], using which a self-powered nanosensor has been demonstrated [6]. A commercial LED has been lid up [7]. This is a key step for developing a totally nanowire-based nanosystem [6]. Alternatively, by substituting the gate voltage in a field effect transistor (FET) with the piezopotential creating by an external strain, we have fabricated a series of devices that rely on a coupling between semiconductor and piezoelectric properties and are controlled/tuned by externally applied force/pressure, such as diode, strain sensor and strain-gated logic unites, which are a new field called piezotronics [8]. A three way coupling among piezoelectricity, semiconductor and photonic excitation has demonstrated the piezo-phototronic effect [9].
 
[1] Z.L. Wang “Self-powering nanotech”, Scientific American, 298 (2008) 82-87; Z.L. Wang “Towards self-powered nanosystems: from nanogenerators to nanopiezotronics” (feature article), Advanced Functional Materials, 18 (2008) 3553-3567.
[2] Z.L. Wang and J.H. Song “Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays”, Science, 312 (2006) 242-246.
[3] X.D. Wang, J.H. Song J. Liu, and Z.L. Wang “Direct current nanogenerator driven by ultrasonic wave”, Science, 316 (2007) 102-105.
[4] Y. Qin, X.D. Wang and Z.L. Wang ”Microfiber-Nanowire Hybrid Structure for Energy Scavenging”, Nature, 451 (2008) 809-813.
[5] R.S. Yang, Y. Qin, L.M. Daiand Z.L. Wang “Flexible charge-pump for power generation using laterally packaged piezoelectric-wires”, Nature Nanotechnology, 4 (2009) 34-39.
[6] S. Xu, Y. Qin, C. Xu, Y.G. Wei, R.S. Yang, Z.L. Wang* “Self-powered Nanowire Devices”, Nature Nanotechnology, 5 (2010) 366.
[7] G. Zhu, R.S. Yang, S.H. Wang, and Z.L. Wang* “Flexible High-Output Nanogenerator Based on Lateral ZnO Nanowire Array”, Nano Letters, online
[8] Z.L. Wang “Nano-piezotronics”, Adv. Mater., 19 (2007) 889-992.
[9] Y.F. Hu, Y.L. Chang, P. Fei, R.L. Snyder and Z.L. Wang “Designing the electric transport characteristics of ZnO micro/nanowire devices by coupling piezoelectric and photoexcitation effects”, ACS Nano, 4 (2010) 1234–1240.
 
About the Speaker

Dr. Zhong Lin (ZL) Wang is a Regents' Professor, COE Distinguished Professor and Director, Center for Nanostructure Characterization, at Georgia Tech. Dr. Wang is a foreign member of the Chinese Academy of Sciences, member of European Academy of Sciences, fellow of American Physical Society, fellow of AAAS, fellow of Microscopy Society of America and fellow of Materials Research Society. He has received the 2001 S.T. Li prize for Outstanding Contribution in Nanoscience and Nanotechnology, the 2000 and 2005 Georgia Tech Outstanding Faculty Research Author Awards, Sigma Xi 2005 sustain research awards, the 1999 Burton Medal from Microscopy Society of America, and the 2009 Purdy award from American ceramic society. He is an honorable professor of 6 universities worldwide. Dr. Wang is the world’s top 10 most cited authors in nanotechnology and materials science. He has published four scientific reference and textbooks and over 620 peer reviewed journal articles, 45 book chapters, edited and co-edited 14 volumes of books on nanotechnology, and held 28 patents. His entire publications have been cited for over 36,000 times. The H-index of his citations is 92. Details can be found at: http://www.nanoscience.gatech.edu/zlwang

"Coarse-grained simulation studies of mesoscopic membrane phenomena"

Mark Deserno
Department of Physics
Carnegie Mellon University

Abstract
 
Lipid membranes exhibit a large spectrum of fascinating physical behavior, spanning many orders of magnitude both in length- and time scales. To cover this wide range, models of different resolution have been developed, from atomistically resolved lipid representations to triangulated fluid-elastic surfaces. In the intermediate regime of about 100 nanometer length scale and micro- to millisecond time scale mesoscopic coarse-grained models have recently covered much ground. They can approach phenomena in which cooperativity between several proteins are crucial, while still preserving the essence of many lipid degrees of freedom (area density, order, tilt, composition, etc.),
whose coupling is deemed relevant in many biological situations, notably the "raft question". I will describe in more detail a particular solvent-free coarse-grained model developed by us and
illustrate its applicability to a wide variety of phenomena, among them pore-formation by amphipathic peptides, protein aggregation on critically mixed bilayers, and membrane vesiculation driven by
curvature-imprinting proteins.
 
Markus Deserno, "Mesoscopic Membrane Physics: Concepts, Simulations,
and Selected Applications", Macromol. Rapid. Comm. 30, 752-771 (2009).


"Lithographic patterning of organic semiconductors and the manufacturability of organic complementary logic circuits"

Ian Hill
Department of Physics
Dalhousie University

Abstract
 
Patterning of organic semiconductor materials remains one of the main challenges to the widespread adoption of organic electronic devices. In the laboratory, stencil mask patterning of vacuum deposited films is a common method for device fabrication. Stencil mask patterning is not, however, viewed as a viable fabrication technique for the production of large-area, low-cost electronic devices. Traditional photoresists and lithography cannot be used, due to incompatibility of the solvents contained in resists and developers with the organic semiconductor thin films.
 
Much work has been devoted to additive patterning techniques, such as inkjet, Gravure and offset printing, with great success. Vacuum deposition and photolithography are not inherently expensive techniques and can be compatible with continuous roll-to-roll fabrication. If the materials compatibility issues could be resolved, many applications exist where lithographic patterning would be desirable.
 
While a few examples of lithographic patterning of organic thin films are present in the literature, no complete, manufacturable lithographic process capable of producing organic complementary logic circuits has been demonstrated. Our work toward this goal will be presented.

"Engineered Artificial Proteins: Controlling Function and Supramolecular Assemblies"

Jin Montclare
Polytechnic Institute of New York University

Abstract
 
Through centuries of evolution, nature has developed biomacromolecules capable of folding and assembling into discrete structures with a functional consequence.  Inspired by this, our lab focuses on engineering proteins in order to (1) reprogram or alter their function and (2) fabricate entirely new properties and function.  In the first part of my talk, I will discuss our work towards modulating existing protein function via the integration of chemical and genetic diversity using histone acetyltransferases as the target protein.   This will be followed by a description of how we can now engineer new structures and supramolecular assemblies by piecing together natural or nature-derived domains that have never been fused to one another.  The resulting artificial proteins bear potential as therapeutic agents or scaffolds for biotechnology, nanoelectronics and medicine.   


"Combining microrheology and microfluidics for materials engineering"

Eric Furst
Department of Chemical Engineering and
Center for Molecular and Engineering Thermodynamic
University of Delaware, Newark, Delaware, USA

Abstract
 
Continued advances in structural biology and the quantitative understanding of biomacromolecular and cellular behavior have created new opportunities for the rational design of bioactive hydrogel materials. Hydrogel structure, rheology, epitope presentation, growth factor sequestration, and transient properties such as erosion have emerged as key design parameters in tissue scaffold, wound healing and drug delivery applications. Our recent collaborative efforts have focused on engineering new therapeutic materials based on the interactions of proteins and polysaccharides of relevance in the extracellular matrix (ECM) [1]. These matrices are capable of sequestering and controllably delivering high percentages of active growth factors. In order to identify target material properties in a large composition space, we use high-throughput microrheology based on multiple particle tracking [2]. Our approach relies on a recent understanding of gel microrheology as these materials pass through the liquid-solid transition, which enables us to identify the gel point, gelation kinetics and critical scaling exponents of the percolation transition [3]. Our recent work has focused on developing devices capable of producing hundreds of microliter-volume samples, each with a unique composition. Such “m2rheology” reduces the material costs and sample preparation time for rheological measurements, and is particularly suited to emerging materials during their development and before significant production scale-up.
 
[1] N. Yamaguchi et al., J. Am. Chem. Soc., 129:3040, 2007. [2] K. M. Schultz et al., Soft Matter, 5:740–742, 2009; Macromolecules, 42:5310–5316, 2009. [3] T. H. Larsen and E. M. Furst. Phys. Rev. Lett., 100:146001, 2008.

"A Microscopic View of Plastic Deformation and Physical Aging in Amorphous Solids"

Joerg Rottler
Department of Physics and Astronomy
University of British Columbia

Abstract

Amorphous solids such as polymer and metallic glasses, colloidal glasses, foams, emulsions and granular media form a large group of materials with ubiquitous everyday applications. Due to the absence of symmetries, the atomic level carriers of plasticity in these disordered materials are much less understood than in crystals, where plastic flow can be ascribed to dislocations. Additionally, all glasses experience slow relaxation or aging dynamics, which gradually changes their properties and generates a rich array of history-dependent material behavior. Using molecular simulations, we investigate the interplay between structural relaxation and mechanical properties in simple models for polymeric and metallic glasses. We show how physical aging affects the bulk nonlinear creep compliance and yield stress, and that deformation can cause an apparent reversal of aging phenomena. To gain insight into the underlying atomic level mechanisms, we identify individual relaxation (hopping) events and show directly how the nonstationary aging dynamics arises from a broad distribution of relaxation times. This finding validates the popular trap model of aging, where the relaxation dynamics occurs through thermally activated hops in a random energy landscape. When applied to actively deformed glasses, our analysis reveals how the large increases in molecular mobility and the erasure of aging due to plastic flow reported in recent experiments on polymer glasses can be understood from accelerated particle dynamics that depends universally on local strain.

"Finite curvature: ferroelectricity and electronic transport in single- and multi-component nanostructured materials"

Jonathan Spanier
Department of Materials Science & Engineering
Drexel University

Abstract
 
The study of ferroelectric (FE) nanostructures is motivated in part by opportunities for innovation involving effects of finite size, of shape, and of surface chemical environment on the structural and functional phase stability. Recent advances in the syntheses of FE nanostructures, e.g. nanoparticles, nanowires and nanotubes, have renewed interest in the miniaturization of ferroic materials for use as memory elements and for energy applications. In this talk I shall discuss our recent work in the scanned proximal probe-based analyses and model calculation results involving FE polarizations within individual ABO3 oxide perovskite nanoshells and nanocrystals, and the responses of prototype nanoscale memory and transistor devices. A wide range of interesting effects can be observed in the nanoshells and related nanostructures, including finite-size evolution of the FE phase transition temperature and unexpected FE stability, of enhancements in FE properties with finite size and with finite curvature, hysteretic current-voltage characteristics, and ferroelectric gating. These effects can be understood in terms of a mesoscopic symmetry-lowering and resulting strain profile(s), of molecular adsorbates, and of a redox process. Work supported by the ARO and the NSF.
 
Jonathan E Spanier, Dept of Materials Science & Engineering, Drexel University, Philadelphia PA

"Neither crystalline nor amorphous: understanding how disorder and microstructure affects transport in organic semiconductors"

Alberto Salleo
Department of Materials Science & Engineering
Stanford University

Abstract
 
Organic semiconductors have been proposed as fundamental building blocks for electronic devices such as transistors, LEDs and solar cells fabricated using low-cost techniques such as printing enabling electronic systems on flexible plastic foils. The promise of organic electronics is to dial in desirable properties (emission wavelength, mobility, chemical sensitivity) and use the power of organic chemistry to rationally design new synthetic semiconductors without being limited by Nature and the periodic table.
 
In spite of great advances in materials development, if one asks a basic question such as: “What is the mechanism of charge transport in organic semiconductors?” one is likely to receive as many answers as there are scientists in the room!
 
From the fundamental standpoint, these materials are fascinating as they are neither crystalline nor amorphous and their microstructure plays a central role in governing charge transport. We apply classical Materials Science concepts towards understanding how organic semiconductors “work”. Using advanced synchrotron-based X-ray characterization techniques we are able to define and measure structural order at different length-scales. I will show that understanding disorder is the key to determining charge transport mechanism. For instance, static cumulative disorder (e.g. paracrystallinity) –which we can now measure quantitatively– provides a fundamental justification to using a mobility edge model with a distribution of tail states in the gap. Furthermore, we are able to provide a structural interpretation of these trap states, which manifest themselves as a broad sub-threshold region in transistor characteristics. Finally, I will show that engineering the microstructure of organic semiconductors leads to new insights in the physics of charge transport and in particular in the role of grain-boundaries. Understanding the relationship between microstructure and transport is of fundamental importance for the rational design of new synthetic semiconductors.