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Summer Internship 1997
Summer interns for 1997 include, (back) Chris Leitz, Bunmi Adekore, Ian Appelbaum, Miro Schverdinovsky, Andrew Reed, (front) Jenny Cutler, Jeff Gore, Jennifer Craft.This year's group of MPC/CMSE-sponsored undergraduates participated in research spanning the full spectrum of materials science and engineering. During the ten weeks between June 9 and August 8, the students worked on such diverse applications as shape memory alloy blood pressure cuffs, gel sensors, lattice-mismatched electronic thin films, optical tweezers, anisotropic magnetic films, quantum computers, photonic crystals, and ceramic microturbines. The projects were selected by the students themselves after a whirlwind tour of 24 laboratories and presentations by CMSE and MPC-affiliated faculty supervisors. Bababunmi Adekore, now a junior at North Carolina State University, Raleigh in Materials Science and Engineering, performed research with Prof. Caroline Ross to develop an understanding of the mechanisms causing magnetic anisotropy in Cr/CoCrTa alloy recording films layered over Al/NiP and Si substrates. This knowledge should then lead to optimization of process design for the manufacturing of computer hard drives. Much of the research involved varying different processing parameters and examining the effect on the microstructure of the plasma-sputtered chromium and cobalt alloy layers using x-ray diffraction and atomic force microscopy. Process parameters that were chosen as variables included sputtering temperature, sputtering pressure, substrate chemistry, and substrate texture. Their effects on grain size, grain shape and grain orientation in the thin films and resultant effects on coercivity indicated optimization at higher temperatures and pressures, and a strong effect on grain alignment and coercivity with substrate texturing. The research suggests further work to be performed with different texture periodicities and geometries. Bunmi says that he has found the project to be very instructive in the crystal chemistry class he is now taking. Ian Appelbaum, who will be graduating this year from Rensselaer Polytechnic Institute in Physics and Math, worked with Prof. John Joannopoulos to verify the feasibility of measuring experimentally the power-density profile of selected propogating modes (Eigen modes) in photonic crystals. Photonic crystals are hoped to be the building block for the next generation of optoelectronic devices, leading to high speed telecommunication and other applications. Much work has been done to theoretically model the operation of these devices, but physical measurement, required for manufacturing quality control and design development, remains exceedingly difficult due to their small size and high containment. Ian modeled transmission spectra and mode profiles beginning with an infinite planar geometry, leading to multiple finite planar geometries demonstrating reflection interference, and finally encorporating crystal interaction with the optical fiber tip employed in Near-Field Scanning Optical Microscopy (NFSOM). His models indicate a quantifiable correlation between the actual local near-field intesity and what would be the measured flux, showing good promise for experimental measurement. However, he also notes that this correlation is presently undetermined, due to some higher order effects or computational artifacts which remain to be resolved. Ian plans to continue his research on this project while at Rensselaer. Jennifer Craft, previously at Mississippi State University and now a junior at Virginia Tech in Chemical Engineering, performed research with Prof. Toyoichi Tanaka on swelling transitions in macroporous hydrogels. Hydrogels have shown great potential for use as sensors or actuators because of their ability to reversibly change volume with changing temperature, pH, light, or electric field. The difficulty in their use is the dependence of the transition rate on gel size; for large monolithic gels, the transition period can be on the order of days. In order to obtain faster response from larger gels, sponge-like gels with continuous porosity (hence increased accessible surface area), have been suggested. Jennifer proposed and tested an innovative method for increasing the surface area of the gel, and consequently its reaction rate, using NaCl as a non-reactive, completely removable casting medium for the formation of macropores in the gel. With the porous gel, Jennifer was able to reduce the transition time between states to less than a minute. Throughout the summer, she continued to work optimizing pore size and examining transition dependence on gel diameter. She was able to prove that, where pores were determined to be interconnecting, the volume of gel between pores rather than total gel volume drove the hydrogel kinetics. Says Jen of her experience this summer, "It was great... The 'no pressure' atmosphere allowed me to focus not only on my research but on the experience as a whole. I appreciated the program's emphasis on exploration, exposure, and learning - This aspect enabled me to gain direction for a future graduate career. Jenny Cutler, a junior in Mechanical Engineering at Brigham Young University, worked with Prof. Ian Hunter to design and test an NiTi (nitinol) shape memory alloy blood pressure cuff. This device is one part of a larger project known as the SIMSUIT, sponsored by the Total Home Automation Consortium. The SIMSUIT is a piece of clothing designed to monitor vital signs such as blood pressure, respiration, heart rate, and so forth. It was conceived as a way to compensate for the occurrence of "white-coat hypertension", where patients become intimidated by the doctor's office environment, and also for those patients who require continuous monitoring. Ambulatory blood pressure monitoring has become a common medical practice, with measurement taken up to once every 15 minutes, but many of the present cuffs are bulky. By using a lightweight, highly controllable shape memory alloy such as nitinol, accurate measurements could be made with a device that could conceivibly be incorporated almost imperceptibly into a patient's clothing. However, difficulties in design arise because of the temperature at which shape change is activated and because of the relatively small contraction and expansion capability of the material. Over the summer, Jenny created a design and produced a working prototype of the cuff, accentuating contraction geometrically by combining braiding of multiple wires with mechanical spacers. Through careful correlation of energy input, pulse time and degree of contraction, she also created a system model that allowed her to optimize the cuff efficiency while maximizing control of the degree of contraction and force and minimizing mass. Jenny found the project to be stimulating - "It allowed me to do system level thinking and implementing... I found the freedom to experiment to be a great catalyst to the learning process." Jeffrey Gore, a junior in Physics and Math here at MIT, performed research with Prof. David Cory to aid in the design and modelling of a nuclear magneto resonance (NMR) ensemble quantum computer using a two-spin molecule, 2,3-dibromothiophene. Quantum computing has been proposed as a means of increasing the computational speed of computers exponentially by employing superposition of electron spin states of molecules as bits in the place of electrical switches. Jeff's work involved developing simulation models of the two-spin logic gate, including error corrections to compensate for relaxation and loss of magentization in the molecular system, then checking the simulation with experiments on the NMR spectrometer. His research this summer suggests that, in ensemble quantum computing, the linear contributions from errors may be suppressed, but at the cost of some sensitivity. Jeff is continuing his work on quantum error correction through the autumn semester. Christopher Leitz, a senior in Materials Science and Engineering at Pennsylvania State University, worked with Prof. Gene Fitzgerald to analyze reciprocal space mapping as a means of characterizing lattice-mismatched thin films. Lattice-mismatched films, such as InGaAs on GaAs or Si/Ge on Si, allow for the direct integration of photonic devices with electronic devices by interfacing light-carrying materials with electron-carrying materials. The band structure necessary for the efficient transmission of light requires a very different lattice constant from those transmitting electrical signals, thus making the integration of the two materials difficult; the lattice-mismatch produces many defects that render the materials useless unless the defects are introduced in a controlled manner. Part of the research involved in trying to produce good films and interfaces includes the ability to analyze the film quality; defects become apparent through analyses of composition, strain, and surface roughness. Initially, Chris used Atomic Force Microscopy (AFM) and a rocking curve analysis of triple axis X-ray diffrractometry to examine material characteristics. However, the rocking curves failed to provide accurate information on film relaxation and composition. Chris then utilized a slower method of x-ray diffraction employing reciprocal space mapping. The new procedure required a substantial amount of refinement, as well as derivation and modification of analytical formulae. By the end of the summer, Chris had compiled a large database of thin film characteristics from his X-ray scans. Says Chris, "I expected to learn a great deal about my project, but I didn't expect to learn so much about how research is done." Andrew Read, a senior in Ceramic Engineering and Physics at the University of Illinois, Urbana-Champaign, performed research with Prof. Michael Cima to develop a manufacturing process for the fabrication of ceramic microturbines. The project is part of MIT's Microengine Project, sponsored by the ARO and DARPA, with the goal of constructing a millimeters-sized electric power generating system capable of producing 50 Watts of power. The approach for fabricating the alumina microturbine utilized a new forming technique developed at the Ceramics Processing Research Laboratory, capable of producing micron-scale features. Much of the challenge in this technique involved obtaining slurry properties that would provide the high feature definition required of the microturbine while simultaneously producing a crack-free green body. Andy made early attempts at process improvement using multiple layers of slurry with different composition, but was able to obtain the best combined results using a single-step casting process with a single slurry composition. He then optimized the solvent composition and solvent, plasticizer and ceramic powder ratios of the slurry to obtain a uniform green part with no cracks and well defined features. Miroslav Shverdinovsky, a senior at Cornell in Applied Physics, worked with Prof. Ian Hunter to design and construct an optical tweezers apparatus. This device uses argon ion laser light and the principle of photon momentum to manipulate micron-sized particles suspended in fluid, and has numerous potential applications in microbiology, colloidal physics and other disciplines. Miro constructed the tweezers using a large aperture microscope objective to focus the beam, and a 3-axis manipulating stage with computer controlled microstep motors to move the target chamber. He also constructed an accompanying imaging system so that the particles and the operation of the tweezers could be viewed on a video display. Using the apparatus, Miro successfully entrapped micron-sized glass beads, PMM spheres, and yeast cells. He conducted further experiments, using a liquid crystal tuneable filter to perform spectroscopic analyses on the fluorescing target particles, and using a dynamic light scattering technique to quantitatively measure the entrapment force applied by the tweezers. In addition, Miro developed a computer program to correlate interferometric data to the displacement of the target for a feedback control system that would help to stabilize the target manipulation. |
