Special Seminar

Junghoon Lee, Seoul National University

Friday June 6, 2008, 2:00pm, NST 1.104

"Mechanical Response of Biomolecules and Cells"

Mechanochemistry has been known as a key principle behind various biochemical processes such as ligand-receptor recognitions and cellular responses to stimuli. Recent progress in microscale and nanoscale fabrication technologies enabled the measurement and use of the mechano-chemical forces on molecular and cellular levels. In this talk I will introduce micro/nano platforms developed in our lab for understanding the molecular interaction and cellular responses via mechanochemistry. Thin membrane technology can be used to detect biochemical interactions such as DNA hybridization and protein recognition with the chemical-mechanical coupling through surface forces. Cells grown on flexible substrates with varying stiffness respond differently, showing, for example, migrations (fibroblasts) and self-beating at different periods (cardiac cells). I will also discuss the molecular detection with DNA-carbon nanotube hybrids, and cell proliferation and differentiation on surface-grown carbon nanotubes. 

Optical profilometer view of thin membrane transducer fabricated, and schematic diagram illustrating chemo-mechanical sensing of DNA hybridization.

Schematic diagram illustrating the precipitation of DNA solubilized SWNTs with complementary single-strand DNA.

Milan Mrksich, University of Chicago

Wednesday January 16, 2008, 12:00pm, NST 1.104

“Engineering Active Interfaces Between Cells and Materials”

This lecture will describe a chemical approach to integrating mammalian cells and electrical components. The strategy is based on self-assembled monolayers of alkanethiolates on gold that are modified with peptide ligands which promote cell adhesion. The monolayers are then engineered with electroactive moieties such that application of an electrical potential to the gold film results in modulation of the activities of immobilized ligands. In one example, an electroactive monolayer could turn on the migration of fibroblast cells that were originally confined to circular patterns on the substrate. This example, which was based on a monolayer that could be switched from an inert state to a state that promotes cell adhesion, establishes the feasibility of engineering active interfaces that can translate electrical signals into biological signals. A second example demonstrated an active monolayer that could selectively release immobilized ligands, and even individual cells. The lecture will describe these and several other strategies for creating functional interfaces between cells and electronics, and will address the opportunities for applying these strategies to creating hybrid devices comprising electrical and cellular components.

Harry Tuller, MIT

Wednesday January 23, 2008, 12:00pm, NST 1.104

“Micro-Ionics: A Revolution in Portable Power Generation and Environmental Sensing”

Ionic conductors have long been known to be the basis of electrochemical devices ranging from batteries and fuel cells to chemical sensors.   In this presentation, I examine options for embedding miniaturized solid state ionic thin film structures as sensors or power sources together with MEMS components in the same wafer platform. 

By applying microelectronics process technology, one accesses means for tailoring electrolyte and electrode geometry with exceptionally high dimensional reproducibility.  Lower process temperatures commonly lead to films with nanoscale dimensions with implications for performance including higher sensitivity in sensors and improved energy densities and shorter charge/discharge in batteries and fuel cells.  But one must temper these advantages with potentially more rapid degradation. Attention is focused on the special challenges that integration of nanostructured solid state ionic materials entails as well recent materials breakthroughs achieved enabling operation of micro-devices to elevated temperatures in harsh environments. Attention will be focused particularly on micro-sensor arrays and micro-solid oxide fuel cells (mSOFC).

Xiaoyang Zhu, University of Minnesota

Wednesday February 6, 2008, 12:00pm, NST 1.104

"Charge Carriers in Organic Semiconductors"

Charge carrier generation and transport are central to the operation of all organic electronic and optoelectronic devices, such as organic light-emitting diodes (OLEDs), field effect transistors (OFETs), and photovoltaic cells (OPVs). A fundamental distinction from their inorganic counter parts is the localized nature of charge carriers and electronic excitations in organic semiconductors. Localization is a fundamental character resulting from the narrowness of the electronic band, the flexibility of the organic molecule, the deformability of the van der Waals bonded lattice, and the low dielectric constants of organic materials. This is in addition to the prevalence of structural and chemical defects that form the bulk of charge carrier traps in organic semiconductors. We study the localization problem in organic semiconductors using two spectroscopic approaches. The first approach relies on in situ IR and NIR spectroscopy to directly monitor molecular vibrations and electronic transitions associated with charge carriers in gate-doped organic semiconductors. The second approach relies on femtosecond time-resolved two-photon photoemission (TR-2PPE) spectroscopy to follow the formation and decay of excitons and small polarons in organic semiconductors. These experiments are beginning to answer the following critical questions: How do charge carriers separate at organic heterojunctions in an OPV? How does a charge carrier move in an OFET? What is the mechanism for the metal-to-insulator transition in a gate doped conducting polymer?

Moungi Bawendi, MIT

Wednesday February 20, 2008, 12:00pm, NST 1.104

“Science and Technology of Semiconductor Nanocrystal Quantum Dots”

Semiconductor nanocrystals, aka quantum dots, have become the prototypical material for the emergence of new properties when dimensions are reduced to the nanometer range. In the case of quantum dots it is the exciton radius in the bulk that determines the size transition from bulk-like electronic behavior to the size dependent properties that have made quantum dots a popular nanomaterial. In the size range of ~2 to 10 nm, the electronic structure of quantum dots becomes discrete at room temperature, leading to the size dependence of their band gap and of their fluorescence. The size dependent properties of excitons and multiexcitons in quantum dots, coupled with a material that can be processed from solution, has led to potential applications in fields that include emissive displays, solar energy conversion, and biological and biomedical fluorescence imaging. A fundamental understanding of exciton processes is critical for any of these applications to become realized. Synthesis of well characterized materials is obviously key, not only of the functional inorganic particle itself, but also the ligand shell that protects it and couples it chemically to molecules and matrices of interest. This talk will introduce the chemistry and photophysics of quantum dots and then explore the fundamential properties and challenges behind broadly applying quantum dots as light emitters and light absorbers in devices and for biological imaging.

Erich Stach, Purdue University

Wednesday February 27, 2008, 12:00pm, NST 1.104

“Understanding the onset of plasticity in materials using quantitative in-situ nanoindentation”

Nanoindentation is widely accepted as the preferred technique to study localized mechanical deformation phenomena in materials. However, the mechanisms of deformation can only be inferred from the load -displacement data obtained during a typical instrumented nanoindentation test. In order to elucidate the underlying physics of these process, we have developed and exploited a new technique, that of in-situ nanoindentation in a transmission electron microscope (TEM). In this technique, a voltage-actuated piezoceramic tube is used to position a sharp diamond in plane with the edge of an electron transparent sample. The tip is driven into the material in order to induce deformation and the corresponding deformation is observed in real time and at high spatial resolution. In this talk, I will review the details of our experimental technique, as well as summarize our results from selected materials systems. In particular, we have studied thin films of aluminum deposited on top of microfabricated wedges of silicon, allowing us to observe such effects as initial deformation modes, size effects on hardening, grain boundary motion and dislocation nucleation, as well as the effects of solute additions on both dislocation propagation and grain boundary movement. Additionally, experiments on harder materials have permitted the observation of unexpected deformation modes. In the case of single crystal silicon, we have found a size-dependent transition from pressure-induced phase transformation to room temperature deformation by dislocation nucleation and propagation.

Portfolio Student Presentations - Spring 2008 Graduates

Wednesday April 16, 2008, 12:00-2:30pm, NST 1.104

1st Place - Alexander Khajetoorians - "Tuning Surface Energy Landscapes of Quantum Metal Thin Films with Alkali Adsorbates"

2nd Place - John H. Slater - "Engineering Endothelial Cell Adhesion and Behavior via Cell-Surface Interactions with Chemically-Defined Fibronection Nanopatterns"Dayne Fanfair - "Twin-Related Branching of Solution-Grown ZnSe nanowires"

Ryan Fitzpatrick - "CVD Boron Carbo-Nitride as a Potential Passivation Layer for Germanium"

J. Ruben Morones - "Novel Synthesis of Polymer-Metal nanocompostites: Tailoring Properties for Applications from Biocides to Optical Switches in Drug Delivery Systems"

Se-Hyuk Im - "Dynamics of Wrinkling in Elastic Thin Films on Soft Substrates"

Anastassios Mavrokefalos - "Thermoelectric and structural characterization of individual nanowires and patterned thin films”

G.P. Li, University of California, Irvine

Wednesday October 10 , 2007, 12:00pm, NST 1.104

"Life Chips Research and Development at UC Irvine"

Concurrent revolutions in biology, medicine, physical sciences and engineering at the micro and nano scale, accompanied by advances in instrumentation, are bringing these historically separate disciplines into convergence. This exciting trend has the potential to bring about dramatic and important changes to life science and micro/nanoelectronics technology: in the results of research, in the way that research is performed, and in the development of a new hybrid industry based on this convergence.

LifeChips is the study of nature’s 3 billion years of evolution ( technology of life), and development of micro- and nano-scale technologies, systems and devices that combines methods developed by life scientists and technologists to help solve fundamental problems in the life sciences and in engineering (technology for life). LifeChips represents a new research paradigm that has driven the need for collaborations among researchers from traditionally different backgrounds and cultures, namely life scientists (biologists, medical researchers) and technologists (physical scientists, engineers). It also represents the fusion of two major industries, the microelectronic chip industry with the life science industry.

UC Irvine is spearheading development in LifeChips on many fronts: initiating graduate training programs, developing design methodologies, defining new applications, promoting commercialization, creating research programs, and pursuing novel LifeChips manufacturing techniques. LifeChips research projects at UC Irvine provide excellent examples of potential new science discovery and engineering products, including implantable microdevices, minimally invasive devices, cell analysis chips, and biosensors. In addition to utilizing micro/nano chip technologies, each project and device has unique requirements for its design, manufacture and deployment. These requirements (and limitations) drive the need for advances in nano/micro fabricaiton and system-integration at manufacturing level, building the foundations for a new LifeChips industry. We will discuss several projects at UC Irvine to illustrate the flavor of LifeChips research.

Chris Dames, University of California Riverside

Wednesday October 17 , 2007, 12:00pm, NST 1.104

"Thermal Properties of Nanostructures: Thermoelectric Applications"

Thermoelectric energy conversion using the Seebeck and Peltier effects is an established technology for refrigeration and power generation. Thermoelectrics are appealing because of their reliability, compact size, and lack of moving parts. However, because of their low efficiency, traditional thermoelectric materials have largely been limited to niche applications. Recent research has shown that nanostructured thermoelectrics can be dramatically more efficient than their bulk counterparts, greatly broadening the pool of possible applications.

In this talk we explore the fundamental size effects on electrons and phonons that can be used to enhance the thermoelectric performance of nanostructures. Emphasis is placed on the thermal properties of nanowires, nanotubes, and self-assembled superlattices, studied using both modeling and experimental approaches.

"Nanomaterials and Nanostructures" - UT - France Workshop

Monday October 22 and Tuesday October 23, NST 1.104

Anatoly Frenkel, Yeshiva University

Wednesday October 17 , 2007, 12:00pm, NST 1.104

"Negative Thermal Expansion and Other Anomalies in Supported Metal Nanoparticles"

Negative thermal expansion (NTE), a peculiar effect reported in 1996 in zirconium tungstate and other framework solids and not expected in fcc metals, was recently observed in alumina-supported Pt nanoparticles. In the smallest particles studied (0.9nm in diameter) the Pt-Pt distance decreased gradually by 0.04 Å over the 500 K range. Such effect was attributed to the charge transfer between the cluster and support. Recently, more experimental information on structure and dynamics of Pt clusters was obtained for different sizes, support materials and atmospheres. Experimental results combined with the first principles, real-time calculations uncovered dynamic structure of supported metal clusters that exhibit large dynamic fluctuations. This dynamic behavior, previously unaccounted for by ground state DFT calculations, is characterized by very peculiar electronic and structural properties in these supported clusters that can explain their various unusual phenomena, including the NTE, large disorder and red-shift of the x-ray absorption edge.

Jan Liphardt, University of California, Berkeley

Wednesday November 7 , 2007, 12:00pm, NST 1.104

"Plasmonics, Radiating Nanowires, and Light-Powered E.Coli"

In the last decade, new materials such as quantum dots and semiconductor nanowires have been developed. Now, methods are needed to efficiently and accurately integrate these pieces into larger heterostructures that collect, emit, and control light. I will discuss several complementary ways of putting small things together, including self-assembly, optical trapping, DNA hybridization, and the use of re-programmed bacteria. Then, I'll discuss the physics of what happens when certain combinations of materials interact with light. Examples will include tuning of the electrical field using plasmon coupling and nonlinear optical processes occurring inside optically trapped potassium niobate nanowires.

Michael Sheetz, Columbia University

Wednesday November 14, 2007, 12:00pm, NST 1.104

"Shaping Cells by Force and Rigidity Through Protein Stretching"

Mechanical factors are critical in determining the observed cell shape and fate. At the microscope level, the integral of many stereotypical cell movements determines the shape. Thus, mechanical factors (external force and substrate rigidity) control cell movements (Vogel and Sheetz, 2006. Nature Rev. Mol. Cell Biol., 7:265). A prominent example is the substrate rigidity response wherein transformed cells can grow on soft agar whereas normal cells die, showing that transforming proteins are involved in cell mechanics (reviewed in Giannone and Sheetz, 2006. Trends Cell Biol. 16:213). Our working model for rigidity sensing postulates that rearward pulling of the cytoskeleton and linked matrices produces force to prime substrate for phosphorylation and possibly displace it from kinase if the surface is soft. In spreading on a rigid fibronectin substrate, cells pull periodically, establish early adhesion complexes, condense the lamellipodial actin and commence the next cycle (Giannone et al., 2007. Cell 128:561). In correlation, mechanical stretching of p130Cas primes it for tyrosine phosphorylation by active Src family and Abl kinases and the unfolded, phosphorylated form of p130Cas is found in the periphery of spreading cells (Sawada et al., 2006. Cell 127:1015). Further, in neurons as well as fibroblasts, movement on rigid fibronectin causes increased tyrosine phosphorylation of p130Cas by Fyn (Kostic and Sheetz, 2006. Mol Biol Cell 17:2864 and Kostic et al 2007. schJ Cell Sci In Press). This reinforces the hypothesis that the unfolding of cytoskeleton-associated proteins is a major force-sensing mechanism in many cell movements. At a general level, mechanical (rigidity and force) and biochemical steps are linked in cell movements, which is hard to duplicate in vitro. Consequently, stereotypical cell movements should be described by the forces, displacements, velocities, times as well as biochemical processes involved in each distinct step of the function, such as periodic contraction or earlier spreading movements. Stereotypical cell movements constitute the tools that cells can use to test and modify the mechanical and chemical aspects of their environment.

Jürgen P. Rabe, Humboldt University Berlin

Joint Atomic & Molecular IGERT/Portfolio Seminar

Wednesday November 28 , 2007, 12:00pm, NST 1.104

"A Workbench for Single Molecular Nanostructures"

Macromolecular and supramolecular nanostructures constitute modules in living systems which most efficiently perform key elementary functions in sensors, actuators, and for energy conversion. The understanding of structure-property relationships on the level of single molecular nanostructures is promising insight that may lead to new concepts for artificial biomimetic systems. We developed a workbench for single molecular nanostructures to determine and correlate structure and dynamics with mechanical, electronic, optical properties. The workbench consists of an inert, conductive, single crystalline substrate, covered with a weakly bound fluid or nanostructured molecular layer, and a scanning tip of a scanning probe microscope. It is used for both the assembly of molecular nanocomposites and the determination of their properties (e.g. Barner et al. Angew. Chem. 2003; Ecker et al. Macromolecules 2004; Jahnke et al. Angew. Chem. 2006). A key role can be played by the physisorbed molecular layer, which together with the forces exerted by a scanning force microscope probe may be employed to bend, stretch, overstretch and finally break dsDNA, as well as to control structure and orientation of single polyelectrolytes (Severin et al. Nano Lett. 2004 & 2006). At solid-liquid interfaces, scanning tunneling microscopy and spectroscopy have been used to develop concepts for single molecule rectifyers and a single molecule transistor with nanometer-sized gates (Jäckel et al. Phys. Rev. Lett. 2004 & Müllen & Rabe, Acc. Chem. Res. in press). Finally, insights into processes on the single molecule level may be related to thin films relevant, e.g., for organic electronic devices (Koch et al., Org. Electron. 2006 & 2007).

Portfolio Student Presentations

Wednesday December 5, 2007, 12:00pm, NST 1.104

1st Place - Yaoyu Pang - "Surface Evolution and Self Assembly of Epitaxial Thin Films: Nonlinear and Anisotropic Effects"

Hongki Min - "Pseudospin Magnetism in Graphene"

Ted Gaubert - "NOBIL and its Applications for Studying Nanoscale Cell Surface Interactions"

Samaresh Guchhait - "Group IV Magnetic Semiconductor Alloys"

Arvind Battula - "Optical Near-Field Enhancement for Submicron Patterning and Plasmonic Optical Devices"

Zhong Lin Wang, Georgia Institute of Technology

Thursday August 9, 2007, 3:00pm, NST 1.104

"From Nanogenerators to Nano-Piezotronics"

Developing novel technologies for wireless nanodevices and nanosystems are of critical importance for in-situ, real-time and implantable biosensing, biomedical monitoring and biodetection. It is highly desired for wireless devices and even required for implanted biomedical devices to be self-powered without using battery. Therefore, it is essential to explore innovative nanotechnologies for converting mechanical energy (such as body movement, muscle stretching), vibration energy (such as acoustic/ultrasonic wave), and hydraulic energy (such as body fluid and blood flow) into electric energy that will be used to power nanodevices without using battery. We have demonstrated an innovative approach for converting nano-scale mechanical energy into electric energy by piezoelectric zinc oxide nanowire (NW) arrays. We have recently developed DC nanogenerator driven by ultrasonic wave, which is a gigantic step towards application in practice.

Jacob Israelachvili, University of California, Santa Barbara

Thursday August 9, 2007, 3:30pm, WRW 102

"Adhesion, Friction, and Failure of Surfaces: Nano- and Micro-Scale Studies on the Transition from Liquid-Like to Solid-Like Behavior"

Recent experiments using the Surface Forces Apparatus and various surface imaging techniques have been conducted to study the adhesion, friction and fracture processes of various polymer and material surfaces and films. The aim was to investigate the transition between pure liquid/ductile and solid/brittle behavior. Both cross-linked and uncross-linked polymers were studied over a large range of molecular weights and viscoelastic properties, and sugars over a range of temperatures, thereby spanning the purely liquid- or ductile-like (T > glass transition temperature, Tg) to the glassy, elastomeric and brittle regimes (T < Tg). We investigated how the deformations and pathways of failing junctions change on passing through Tg, starting with liquid-like rupture at high T (determined by surface tension and viscous forces) and ending up with fracture via micro-cracks, determined by completely different material properties.