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Physics

Behavior of Gold Nanoparticles on Graphene Sheets

Berkley, Scott ('09);  Tanenbaum, David;  Van Der Zande, Arend;  McEuen, Paul

We studied the manner in which gold nanoparticles aggregated on graphene surfaces. Graphene is a plane of carbon bound in a hexagonal pattern that is a single atom thick. Manual exfoliation is used to deposit graphene onto a silicon dioxide surface. A submonolayer of gold particles with diameters of less than 20 nm was then deposited on top of the single or multilayer graphene using electron-beam evaporation. Due to high mobility the gold move across the surface until it collides with other particles. The thickness of the graphene sheet and the pattern of the deposited gold were characterized using an atomic force microscope (AFM). Dendritic and mesh-like patterns were observed. Qualitatively different patterns of gold were observed on sheets of 1-2 layers and those of 3 or more layers with otherwise identical evaporation conditions. The cause of this is unknown but could be due to an interaction with the substrate.
Funding provided by: The Center for Nanoscale Systems (at Cornell University);  National Science Foundation

Working Towards Bose-Einstein Condensation: Creating a Magneto-Optical Trap

Boyd, Alexander ('11);  Stutz, Eric ('10);  Whitaker, Dwight

The ultimate goal of our lab is to create and image a Bose-Einstein Condensate (BEC) of rubidium-87 in order to test theories about the transition to the BEC state. This summer, we focused on creating a Magneto-Optical Trap (MOT). The MOT is the first stage in cooling the 87Rb enough to create a BEC. The MOT uses counterpropagating laser beams along the three principal axes to cool and confine 87Rb atoms. The lasers utilize the Doppler Effect to cool the Rb atoms while an applied magnetic field in combination with the laser light to confines the atoms and holds them up against gravity. It is also necessary to create a very good vacuum to isolate the atoms. This summer, we created the vacuum, set up the magnetic coils, and set up most of the optics to direct the lasers.
Funding provided by: The Norris Foundation

The Biomechanics of Ballistic Seed Dispersal in Impatiens Pallida

Del Campo, Lua ('09);  Whitaker, Dwight

This research analyzes the biomechanics of Impatiens pallida’s intrinsic seed launching mechanism. To study the process, we filmed the plant using a high-speed video camera, recording at a rate of 5,000 frames per second. From our videos we observed that the seed launching process takes place in under 0.01seconds as a result of released elastic potential energy. I. pallida’s fruit is a bean pod, when touched the pod’s valves tear away from each other and curl inwards thus releasing their stored energy. We generated quantitative results for the velocity, acceleration and kinetic energy of the seeds and other components of the fruit. We also deduced a preliminary value of Young’s modulus of 1MPa for the fruit’s valves. This summer we were successful in laying the groundwork for a comprehensive theoretical model of I. pallida’s seed dispersal mechanism. These results provide insights into Impatiens pallida’s evolutionary history.
Funding provided by: The Norris Foundation

Construction of Total Internal Reflection Fluorescence (TIRF) Microscope for the Study of Lipid Doma

Kelley, Kevin ('09);  Kwok, Alfred

Lipid domains, which have been implicated in numerous signal transduction pathways, are cholesterol and sphingolipid rich regions which provide organization in the plasma membrane bilayer such that they form “rafts” on a sea of phospholipids. Subsequently, there has been much effort on the study of lipid domains in model membranes. Yet, there is no current technique that provides quantitative information on the composition of lipid domains. We plan to use Raman spectral-imaging to determine the composition of micron-sized lipid domains in supported bilayers. The noise from Raman scattering from water in our samples will hinder our ability to analyze the lipid spectra. Therefore, we plan to employ total internal reflection (TIR) excitation to maximize our signal to noise ratio. In preparation for this project we constructed a prism based TIRF microscope and have successfully observed fluorescent signal form a bilayer with dye attached to the phospholipid head groups.
Funding provided by: Howard Hughes Medical Institute

Research at Pomona