Engaging the Public in Constructive Conversations about the Future of Technology

Dec 1, 2014 9:00am ‐ Dec 1, 2014 9:30am

Identification: FF1.03

Public outreach is often framed as a process of developing lesson plans with an aim of convincing the public to believe a series of facts and/or accept a specific viewpoint. These one-way patterns of communication, however, frequently fall short in at least two important ways. First, the public has many sources of information so getting the attention of a number of people is difficult. And second, the organizations that put together such programs are missing a major source of information that could help them to achieve their goals. Over the past several years museum professionals with the Nanoscale Informal Science Education Network (NISE Net) and scholars at Arizona State University’s Center for Nanotechnology in Society have been developing techniques that go beyond this “linear model.” These techniques enable two way conversations in which members of the public learn about scientific achievements in a specific area and then build their own ideas of what they think a better future would like with them. What we have found is that the visitors to science museums in the United States are not only able to participate in constructive conversations, but that they are hungry for them. This talk will outline some of the lessons learned through this partnership and offer suggestions for how they can be implemented in other spheres.

Chemoenvironmental Modulators of Fluidity in the Suspended Biological Cell

Dec 1, 2014 9:00am ‐ Dec 1, 2014 9:15am

Identification: H1.02

Biological cells can be classified as "active soft matter," with mechanical characteristics modulated by external cues such as pharmaceutical dosage or fever temperature. Quantifying the effects of chemical and physical stimuli on a cell's mechanical response informs models of living cells as complex materials. We discuss the mechanical behavior of single cells in terms of fluidity, or hysteresivity normalized to the extremes of an elastic solid or a viscous liquid. This parameter, which complements stiffness when describing whole-cell viscoelastic response, can be determined for a suspended cell within subsecond times. Questions remain, however, about the origin of fluidity as a conserved parameter across timescales, the physical interpretation of its magnitude, and its potential use for high-throughput sorting and separation of interesting cells by mechanical means. We have selected optical stretching, a non-contact tool that deforms cells in the suspended state via photonic pressure, to explore the linear power-law-rheology regime (1% strain, 1 s timescale) of single cells. Cells were probed for several seconds each by applying an oscillatory photonic stress, and machine vision was used to extract time-dependent elongation and phase lag from phase-contrast images. Our experiments employing various chemoenvironmental conditions---temperature, pharmacological agents, pH, and osmolarity---extend familiarity with suspended-cell mechanics in the context of both soft-matter physics and mechanical flow cytometry development. The strong influence of both osmotic volume changes and the cytoskeleton-disassembling drug latrunculin supports the interpretation of fluidity as a reciprocal friction within the actin cytoskeleton, with implications both for cytoskeletal models and for expectations when separating interesting subpopulations by mechanical means in the suspended state.

Graphene Quantum Devices

Dec 1, 2014 9:00am ‐ Dec 1, 2014 9:30am

Identification: K1.03

Graphene quantum dots show Coulomb blockade, excited states and their orbital and spin properties have been investigated in high magnetic fields. Most quantum dots fabricated to date are fabricated with electron beam lithography and dry etching which generally leads to uncontrolled and probably rough edges. We demonstrate that devices with reduced bulk disorder fabricated on BN substrates display similar localized states as those fabricated on the more standard SiO2 substrates. For a highly symmetric quantum dot with short tunnel barriers the experimentally detected transport features can be explained by 3 localized states, 1 in the dot and 2 in the constrictions. A way to overcome edge roughness and the localized states related to this are bilayer devices where a band gap can be induced by suitable top and back gate voltages. By placing bilayer graphene between two BN layers high electronic quality can be achieved as documented by the observation of broken symmetry states in the quantum Hall regime. In addition we observe a Lifshitz transition indicating a tunable topology of the Fermi circle. This can be exploited to achieve smoother and better tunable graphene quantum devices. Work done in collaboration with D. Bischoff, P. Simonet, A. Varlet, Y. Tian, and T. Ihn.

Calculation of Auger Recombination Rate in CdSe Nanocrystals: Demonstration of the Universal Size-Dependence

Dec 1, 2014 9:15am ‐ Dec 1, 2014 9:30am

Identification: II1.02

Auger recombination is the central non-radiative relaxation process affecting all aspects of carrier dynamics in semiconductor nanocrystals. Auger processes, being significantly enhanced in quantum-confined structures, can dominate the decay of multiexcitons, facilitate fluorescence intermittency, induce the efficiency droop in nanocrystal light-emitting diodes, and limit the performance of nanocrystal lasing applications. The mechanism of the Auger rate acceleration is connected with the combined effect of spatial confinement of carriers and the presence of abrupt interfaces in the nanocrystals. These two effects admix high-momentum components into the ground state wavefunctions of the carriers, thereby relaxing the strict momentum conservation rule during the Auger recombination. Based on the experimental data, the existence of a universal material-independent scaling law of the multiexcitonic Auger recombination rate with the nanocrystal size has been proposed.[1] Similar size-dependence of the trion Auger recombination has been measured in CdSe quantum dots.[2] Theoretically, however, this universal scaling has not been explained yet. Previous calculations of the Auger rates in CdS quantum dots[3] predicted a stronger dependence on the nanocrystal size. This previous model incorporated a simplified version of the boundary conditions which enforced continuity of envelope functions across the nanocrystal surface. This, in turn, precluded generation of a sufficient amount of the high-momentum components in the wavefunctions. Here we calculate the rates of the Auger recombination of negatively charged trions in CdSe nanocrystals in the framework of the 8-bandk.p model. We apply the most general form of the boundary conditions, which permit discontinuity of the envelope functions across the nanocrystal interface, thereby enhancing the generation of the high-momentum components in the carriers' wavefunctions. This allows us to explain the experimental size-dependence of the Auger recombination rate. In addition, our calculations demonstrate orders-of-magnitude oscillations of the Auger rate with size caused by a cyclic switching between constructive and destructive interference of the wavefunctions of carriers participating in the Auger process.

[1] I. Robel, R. Gresback, U. Kortshagen, R. D. Schaller, and V. I. Klimov, Phys. Rev. Lett. 102, 177404 (2009).
[2] A. Cohn, J. Rinehart, A. Schimpf, A. Weaver, and D. Gamelin, Nano Lett. 14, 353 (2014).
[3] D. I. Chepic, Al. L. Efros, A. I. Ekimov, M. G. Ivanov, V. A. Kharchenko, I. A. Kudriavtsev, and T. V. Yazeva, J. Lumin. 47, 113 (1990).

Impacts of a Multi-University REU Program

Dec 1, 2014 9:30am ‐ Dec 1, 2014 9:45am

Identification: AAA1.03

For nine years, an REU program placed over 200 undergraduate researchers at Northeastern University, the University of Massachusetts Lowell, and the University of New Hampshire through the NSF-funded Nanoscale Science and Engineering Center for High-rate Nanomanufacturing. The cross-university professional development program included university-based research skills, communication skills with the Boston Museum of Science, and a unique method for researcher evaluation of the societal impact of their decisions. This work presents the impacts of this research program as measured at program end, along with the career progress of the REU participants, recent interviews with REU participants, and reflections by REU program leaders.

Why be Good? The Role of Stakeholder Relations in Corporate Sustainability Practices

Dec 1, 2014 9:30am ‐ Dec 1, 2014 10:00am

Identification: FF1.04

Corporations are the greatest threat to the sustainability of our planet, and yet also promise to be the most effective means of resolving sustainability challenges. What shapes whether they do harm or do good? In this presentation, I focus on the role of a firm's stakeholders in influencing the firm's behaviors. In particular, I outline the role of firm-stakeholder relations in the business case for corporate social responsiblity, and I discuss several studies I've conducted that shed light on the limits of the business case for conditioning firms to engage in socially responsiblity practices.

Super-Long Perfect Carbon Nanotube Growth and Its Properties

Dec 1, 2014 9:30am ‐ Dec 1, 2014 10:00am

Identification: MM1.02

Perfect Carbon nanotubes (CNTs) is ideal nano materials for electronics and thin film application. Recently, it is demonstrated that CNTs can be growth in super-long and perfect structure, it can exhibits excellent electronic and mechanical properties. They are therefore considered as potential materials for flexible electronics application.

We developed a general strategy for fabrication of super-long perfect carbon nanotube by carefully control the operating conditions, and minimalized the deactivation of the catalyst. The super-long CNTs can be more than half meter in length. We realize the visualization and manipulation of individual super-long carbon nanotubes under optical microscopes by deposition of TiO2nanoparticles on them. The CNTs over 1 mm in length exhibited 120 GPa strength, over 1.2 TPa Young’s modulus, and 17% breaking strain. The superlubricity can be realized in centimetres-long perfect double-walled carbon nanotubes (DWCNTs) under ambient conditions. Centimetres-long inner shells can be pulled out continuously from such nanotubes, with an intershell friction lower than 1 nN that is independent of nanotube length. The shear strength of the DWCNTs is only several pascals, four orders of magnitude lower than the lowest reported value in CNTs and graphite. The perfect structure of the super-long DWCNTs used in our experiments is essential for macroscale superlubricity.

Emergent Dynamical Symmetries Predict Universality beyond Power Laws

Dec 1, 2014 9:30am ‐ Dec 1, 2014 9:45am

Identification: NN1.04

Emergent Lorentzian-, parity- and parabolic- symmetries are analytically proven to govern the facet statistics of slightly undercooled crystal-melt interfaces.  Novel translating fronts whose asymptotic inclinations are offset from the thermodynamic Wulff angles are proven to provide the motive ordering force here.

For each thermodynamically unstable crystal interface that undergoes thermo-kinetic spinodal decomposition, we predict and numerically validate that the characteristic facet length is governed by a universal coarsening law, which includes not only a power law dependency on time, but also the dependence on the orientation of the intial unstable interface.


Self-Repairable Polymer Networks

Dec 1, 2014 10:00am ‐ Dec 1, 2014 10:30am

Identification: B2.01

Materials with bio-inspired attributes are excellent candidates for the development of new technologies. Manifested by the ability to respond to stimuli, bio-inspired properties not only extend materials lifetime, but may also minimize environmental footprint. Among particularly impressive properties of bio-inspired materials that recently received significant attention is the ability to self-repair. Recent studies have utilized a variety of non-covalent and covalent chemistries that have led to self-healing polymers. The main challenge is to generate polymer networks that exhibit high glass transition temperature (Tg) with remote self-repairing, triggered by electromagnetic radiation, electric and/or magnetic fields, and environmental/atmospheric changes. This presentation will focus on the recent advances in utilization of coordination chemistries in which catalysts may play a dual role; (1) catalyze crosslinking reactions forming thermosetting networks and (2) serve as self-repairing components. Covalent incorporation of chemically modified polysaccharides into crosslinked polyurethanes offers another opportunity. Upon mechanical damage, followed by UV light exposure, these networks exhibit self-repairing properties. Furthermore, when monosaccharide moieties are crosslinked, self-repairing is achieved in the presence of atmospheric carbon dioxide and water. Unlike plants, these networks require no photo-initiated reactions, thus are capable of repairs in darkness under atmospheric conditions. Physico-chemical processes responsible for this unique self-repair process involve physical diffusion of cleaved network components to damaged area, which lead to the formation of carbonate and urethane linkages.

Corporate Social Responsibility Roundtable

Dec 1, 2014 10:15am ‐ Dec 1, 2014 12:00pm

Identification: FF2