Laboratory for Surface Modification (LSM)

Seminars Archives

March 2017 | April 2017 | June 2017

Thursday, April 06, 2017
Phase Transformations of Nanoscale Systems Using in situ TEM
Judy Cha
Yale University
12:00 Noon CHEM 260

Many nanoscale systems rely on phase transformations for switching their functionalities in response to stimuli. Thus, investigation of such phase transformations and subsequent correlation to changes in materials’ properties are critical. Here, we use in situ transmission electron microscopy (TEM) as a tool to study directly how phase transformations occur, deviate, and be controlled at the nanoscale under either thermal or electrical stimuli. I will discuss two examples: the IBM’s new confined phase change memory (PCM) device and metallic glass nanostructures. In the PCM device case, nanosecond voltages are used to switch the Ge-Sb-Te alloy between the crystalline and amorphous states. Our in situ TEM studies reveal how we can avoid void formation inside the Ge-Sb-Te alloy, which is one of the most common failure mechanisms for the PCM device. In the metallic glass nanostructure case, we will show that the crystallization kinetics deviates greatly from the bulk at the nanoscale. These two examples highlight that in situ TEM is a powerful way to examine the intricate structure-property relationships of nanoscale materials.
Thursday, April 13, 2017
Using Bio-inspired Water-responsive Materials to Harvest Energy from Evaporation
Xi Chen
CUNY Advanced Science Research Center
City College of New York
Department of Chemical Engineering
12:00 Noon CHEM 260

Biological organisms have developed interesting nanoscale structures to facilitate their functions. Water-responsive nanostructures in many plants can effectively harness changes in relative humidity (RH) to power vital tasks, suggesting the potential of using these materials for mechanical actuators and energy harvesting devices. Bacillus spores are microscale water-responsive materials that expand and contract with changing RH. We found that spores demonstrate energy densities significantly higher than those of existing actuator materials and artificial muscles. The energy densities were measured by an environment-controlled atomic force microscope (AFM), which was used to apply periodically varying forces and RH on individual spores. The experiments also showed an extremely fast response of spores to changes in RH (<0.1 s). We then created hygroscopy-driven artificial muscles (HYDRAs) by depositing spores into patterns on thin plastic films. These HYDRAs can lift 50 times their own weight and quadruple their length while exchanging less than 5% moisture by weight. Using HYDRAs, we developed two kinds of evaporation-driven engines that can self-start and continuously convert evaporation into mechanical motions, and subsequently into electricity, when placed at air-water interfaces. The energy harvested from evaporation is enough to power a small light source as well as a miniature car. These studies illustrate that further investigation and development of nanostructured water-responsive materials will contribute to new types of renewable energy, energy storage, actuators, and medical technologies.
Thursday, April 20, 2017
Microengineered Physiological Biomimicry: Human Organ-on-Chips
Dan Dongeun Huh
Department of Bioengineering
University of Pennsylvania
12:00 Noon CHEM 260

Human organs are complex living systems in which specialized cells and tissues are assembled in various patterns to carry out integrated functions essential to the survival of the entire organism. A paucity of predictive models that recapitulate the complexity of human organs and physiological systems poses major technical challenges in virtually all areas of life science and technology. This talk will present interdisciplinary research efforts to develop microengineered biomimetic models that reconstitute complex structure, dynamic microenvironment, and physiological function of living human organs. Specifically, I will talk about i) bioinspired microsystems that mimic the structural and functional complexity of the living human lung in health and disease, ii) an organ-on-chip microdevice that emulates the ocular surface of the human eye, and iii) microengineered physiological models of human reproductive organs.
Thursday, April 27, 2017
Plasmonic Interferometry: Physics and Applications
Domenico Pacifici
Brown University
School of Engineering
12:00 Noon CHEM 260

Surface Plasmon Polaritons (SPPs) are fluctuations of the free electron density in metals coupled to electromagnetic waves. SPPs at optical frequencies show a significant momentum mismatch with respect to the light incident upon a flat metal/dielectric interface, therefore coupling strategies generally rely on prisms (Kretschmann configuration) or metal gratings to excite them. In this talk I will show alternative methods to generate SPPs at optical frequencies using light diffraction by individual nano-corrugations etched in metal films. In particular, I will show how nanometer-scale slits, grooves and holes can be used as efficient, localized sources of SPPs. Spatial localization of the source of SPPs allows for control of the SPP propagative phase, thus enabling researchers to perform "plasmonic interferometry," i.e., optical interferometry at nano- and micro-meter length scales using SPPs as the interfering waves. By properly varying the nanoscatterer separation distance and in-plane distribution, the optical interference of SPPs can be spatially modulated and spectrally tuned. This property, together with the highly confined nature of SPPs, can be employed to enhance the optical absorption in thin film solar cells, and improve the sensitivity and selectivity of biochemical sensors. I will also discuss how Plasmonic Interferometers can be designed to measure the coherence length of light sources with sub-wavelength resolution, as well as determine the optical functions of dielectric materials adsorbed on metal surfaces.

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