Seminars
Physics Graduate Student Seminar
Date: Friday, March 6, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Qiaohui Zhang will speak on "Fabrication of Crosslinked Porous Film in Strain Transducer -- Demonstration of a Plastic-Friendly Process for Flexible Electronics."
Abstract: In the past few decades, flexible (or plastic) electronics have been attracting significant attentions due to potential applications in the foldable solar panel, RFID tag, and electronic newspaper. However, the development is constantly impeded by the lack of appropriate materials and processes. Finding materials that are electrically functional and mechanically robust when flexed is one of the critical issues in this area. In addition, conventional semiconductor processes require high temperature and high-energy plasma, which tend to deform or blur the plastic substrates. This presentation demonstrates a new low-temperature process which appears to be promising to the fabrication of flexible electronics, and is applicable to plastic substrate and many other delicate electronic materials. In particular, as a proof-of-concept, a flexion sensor fabricated by this process is illustrated. Such sensor involves a porous dielectric layer (nanospring) which contributes to the sensitivity to the strain. It is also shown that the porous film can be thermally crosslinked to obtain a satisfactory cyclic response. The crosslinked porous film acts as an “artificial rubber” at nanoscale. Both simulation and experimental data show that the bending of the sample results in the deformation of the porous film and increasing of the current. It is hypothesized that the electric conduction is a combination of tunneling and ionic currents through the thin polymeric film. Compare to the commercial products, the transducer consumes zero power in idle situation and makes pixel sensing possible.
Physics Graduate Student Seminar
Date: Friday, February 27, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Ionel Halaciuga will speak on "Coated Polymer Particles for Electronic Packaging."
Abstract: Miniaturization and robustness are key factors in today’s electronics industry when considering manufacturing new devices. Anisotropic conductive adhesives (ACA) that conduct electricity along only one direction are widely used to provide electrical connection in electronic packages. Using such adhesives instead of soldering and other traditional methods provides for a more efficient use of the boards and for more flexible and reliable connections. Typically, the ACA consists of electrically conductive particles and an insulating binder. Using polymer spheres coated with a metal film as electrically conductive particles provides a lower cost and a higher bonding area between components due to the elasticity of the polymer particles. The metal film consists in general of an inner layer of nickel and an outer layer of gold. Nickel is used to improve connection between gold and the polymer particles’ surface, and gold is used for its high electrical conductivity and corrosion resistance. Experimentally, the ultimate goal of this research is to prepare well dispersed metal coated polymer particles of various sizes having a relatively smooth surface to satisfy the demands of the current electronic materials market. A novel method was developed to coat polymer spheres with metal film and the parameters that influence the plating were studied. We found that by varying certain experimental parameters the coating can be improved and applied successfully to different size polymer spheres with various surface functionalities.Physics Graduate Student Seminar
Date: Friday, February 20, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Irina Dokukina will speak on "Fibroblast Motility on Substrates with Different Rigidities."
Abstract: Cell motility is extremely important for many aspects of life from embryonic development and immunity response to wound healing and diseases. It is not fully understood how cells coordinate overall motility, but it is well known that cell ability to sense environment is crucial to cell functioning. Mechanosensitivity of cell to extracellular matrix is one of many mechanisms that direct cell behavior. It was identified experimentally that given a choice between 'soft' and 'stiff' substrates, a cell prefers to crawl over 'stiff' substrate, turning away from the boundary that separates two substrates. We develop a discrete model for cell locomotion on substrates with different rigidities. The model allows us to understand the relationship between cell-substrate sensing and cell internal function. Our model exhibits experimentally observed cell rigidity sensing and allows us to make additional insights into cell mechanosensitivity. We consider only the role of cell mechanics in cell-substrate rigidity sensing, however, it is also sharpened by the chemical signaling inside the cell.
Physics Graduate Student Seminar
Date: Friday, January 30, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Alexey Nikolaev will speak on "Simple Model for Controlled DNA Translocation through a Nanopore."
Abstract: The goal of this research is to study the effect of the layered semiconductor membrane on DNA translocation through a nanopore. Previously calculated electrostatic potentials of thin electrically tunable membranes composed of two layers of n-type and p-type semiconductor materials are used to study distinct electrostatic potential landscapes. The membrane-DNA system is immersed in an electrolyte solution under bias to induce DNA translocation. A simple charges-and-springs model is used to model the DNA molecule. We compare electrostatic potential landscapes in the nanopore with one and more potential extrema and show how the landscape can be used to alter the dynamics of the molecule translocation. In particular, we specify different conditions under which DNA nucleotides can translocate through the nanopore in one by one fashion in both directions as well as be paused in the nanopore.
Physics Graduate Student Seminar
Date: Friday, January 23, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Oleksandr Gromenko will speak on "Random Sequential Adsorption: Modern Status"
Abstract: Random sequential adsorption (RSA) model has attracted a lot of attention and has a long history. Applications can be found in many fields, ranging from surface science to polymers, biology, device physics, and physical chemistry. Traditionally, the RSA model assumed that particles are transported to a substrate, which is a continuous surface or a lattice. Modern status and recent theoretical development in the RSA will be discussed.
Physics Graduate Student Seminar
Date: Friday, January 9, 2009
Time: 11 a.m.
Location: B.H. Snell Hall, Room 177
Igor Sevonkaev will speak on "Investigation of NaMgF3 and MgF2 Nanoparticle Growth on Short Time Scales"
Abstract: Over the past several decades a large number of dispersions, consisting of uniform particles of simple and composite nature, have been reported in the literature. In principle, the most versatile method to produce such dispersions is by precipitation in solutions. The latter process may involve different mechanisms of formation, such as polymerization of solutes in liquid media, diffusional growth following the nucleation stage, or aggregation of preformed nanosize precursors. In this study we investigated initial stages of particles growth prepared by precipitation. Specifically, the stopped-flow and continued-flow methods were developed for observations of particle synthesis kinetics at short time scales. We also utilized TEM and laser diffraction techniques to obtain broader characterization details. Our results yield novel data for theoretical models, in the regime of behavior not probed by earlier experiments.