Session J37: SPS Undergraduate Research IV

Life as a Hiltern

The Mather Policy Intern Program, conducted through the Society of Physics Students, is an innovative internship encouraging physics students to get involved in science policy. Funded by the John and Jane Mather Foundation for Science and the Arts and the American Institute of Physics, Mather Interns spend a summer at the Capitol, working as congressional interns for a representative or committee. As the first female student inducted into the Mather Policy Intern program, the author presents Life as a Hilltern, detailing her summer working with Representative Rush Holt, the only physicist currently serving in the U.S. House of Representatives.   

Zinc Oxide Coated Carbon Nanotubes for Energy Harvesting Applications

Small scale electrical devices depend on bulky batteries that require recharging or replacement. In biomedical monitoring, where sensors could be implanted inside the body, maintenance of batteries presents a problem. It would be beneficial if small scale devices could generate their own power and alleviate their dependence on batteries. Piezoelectric nanogenerators have proven themselves as a viable means for ambient energy harvesting. Piezoelectric materials, such as zinc oxide (ZnO), produce a voltage difference when subjected to mechanical strain. Manipulation of this voltage can allow for the storage of energy to power small scale devices. The objective of this research is to manufacture a piezo-generator that can transduce mechanical vibrations into electrical energy. Carbon nanotubes, selected for their strong, flexible, and conductive properties, are used as a structural backbone for a ZnO piezoelectric coating and a Ag electrode coating. A Schottky diode interface is used to rectify the current output of the device. The devices yielded an average current output of .79 microAmps. SEM imagining was used to characterize the fabrication process. A Keithley 2700 digital multimeter was used to characterize the current output of the devices.   

Influence of carbon nanotubes diameter on thermal conductivity of polyester based nanocomposites

Carbon nanotubes (CNTs) are considered good candidates to improve the physical properties of polymeric materials. It is well known that CNTs have one of the highest thermal conductivities in nature. However, it has been found that thermal resistance between polymer matrix and CNTs, at nanometric scale, could imply a disadvantage to obtain high thermal conductivity nanocomposites. In this work, the effect of CNTs diameter on the effective thermal conductivity of composites based on polyester resin is studied. In particular, the effects of CNT's diameter and volume fraction are analyzed. The thermal conductivity of the nanocomposites is obtained determining the thermal diffusivity by photothermal radiometry and from the values of their specific heat capacity.   

Electrical characterization of field effect transistors made from C-nanotubes covered with poly(3-hexylthiophene)

Organic transistors were fabricated using a thin film of regio-regular poly(3-hexylthiophene-2,5-diyl) spun from a 0.5 wt{\%} solution in CHCl$_{3}$ on doped Si/SiO$_{2}$ substrates with and without CNT's. The performance of devices with percolating networks of CVD grown single-wall carbon nanotubes (SWNT's) between the source (S) and drain (D) electrodes and without SWNT's are compared. Nanotubes are used as a way to shorten the effective mean distance between the S/D terminals while retaining the wide spacing macroscopic shadow mask technique for S/D fabrication. We found that devices made with SWNT's do not exhibit S/D current saturation but have a charge mobility of 1.2x10$^{-2}$ cm$^{2}$/V-s and an on/off ratio of 9, while the device without SWNT's show clear saturation with a charge mobility of 8.6x10$^{-4}$ cm$^{2}$/V-s and an on/off ratio of 870. The devices made with nanotubes possess a larger off state current although they show a $\sim $14X increase in the mobility which can thus be increased without using sophisticated lift-off techniques to shorten the S/D distance.   

Physical Manipulation of the Na/K Pump

It has been demonstrated that a well-designed oscillating electric field can synchronize and modulate the functions of the Na+/K+ ATPase pump, a ubiquitous active transporter in the cell membrane. Current work aims to improve this technique in order to synchronize the individual steps in the pumping cycle, allowing all of the individual pumps to run simultaneously. Using frog skeletal muscle fibers and the double Vaseline-gap voltage clamp technique, we are working to design wave pulses, which will isolate the voltage dependent steps of the active ion transport. This will improve the signal-to-noise ratio and provide insight into the protein conformation changes that occur during active transport.   

Characterization of the GaN-MgO Transistor Interface: More Power and Efficiency

In this age of high-energy consumption, the development of more efficient and more reliable devices is indispensable. Gallium nitride (GaN)-based devices are an option in achieving this goal. GaN's wide bandgap of 3.4 eV allows the device to handle large amount of current before leakage makes its energy consumption inefficient. The characteristics of GaN, in conjunction with those of Magnesium oxide (MgO), would allow for improvement of different electronic applications such as mobile phone communication technology. In this work, the fabrication of the GaN/MgO device was done by Molecular Beam Epitaxy. This device was grown under a variety of parameters where the growth temperature, growth chamber pressure, and the rate of material deposition were changed. To determine the optimal growth parameters, current-voltage and capacitance-voltage measurements were conducted on to evaluate the effects of these growth conditions. Atomic Force Microscopy was also used in characterizing the crystallinity and morphology of the samples. A conclusion of the research is that by improving the roughness of the substrate, the breakdown voltage of the MgO layer and the overall performance of the device can be improve, yielding a device with very low energy loss in the current transmission process.   

Generating more electricity from water

The Kelvin water drop generator is an ingenious method of using naturally occurring water to induce charge separation in water droplets by allowing them to fall through cross-wired conductors. While being a simple and clean source of energy, the generator has never been considered practical due to its low current output. The goal of this experiment was to discover what conditions were required to obtain maximum voltage. Manipulating where a water stream breaks into droplets inside the conductor, we were able to take advantage of the conductor's geometry and electric field to induce the largest charge separation inside the water droplets. We also explored methods on how to reduce charge cancellation during the operation of the apparatus.