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Arthur Barnard
Applied Engineering & Physics
I am studying the mechanical and electronic properties of the world’s thinnest film — a one-atom-thick honeycomb of carbon atoms known as a graphene film— using devices (waveguides) that precisely direct and confine light. Because of its atomic thickness, this material is all surface and thus challenging to study. The waveguides will allow me to learn precisely how light interacts with both mechanical vibrations and electric charge on graphene membranes. Understanding these interactions will enable us to better design and manipulate graphene devices, thereby laying the groundwork for new, highly sensitive chemical or biological detectors. |
Faculty Advisor:
Paul McEuen
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Ted Gudmundsen
Physics
Inside your hard drive are billions of tiny nanomagnets that save your data as 0's and 1's. To read those 1's and 0's, we make nanomagnet sandwiches, with two nanomagnets on the ends and a metal spacer in the middle. The physics underlying this process, known as giant magnetoresistance, won the 2007 Nobel Prize and revolutionized the computer industry. In the last few years, we’ve learned that replacing the metal spacer in the middle of the sandwich with a very thin layer of MgO — an insulator —makes the difference between the ‘1’ and ‘0’ states more pronounced. This allows us to make the bits smaller, which in turn promises faster, more efficient computers. I study the interface between nanomagnets and MgO barriers, trying to understand how we can manipulate these materials to suit our engineering needs while preserving the fundamental properties of the interface that make MgO-nanomagnet sandwiches so promising. |
Faculty Advisor:
Dan Ralph
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Scanning electron micrograph of a single nanomagnet sandwich
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Mark Levendorf
Chemistry and Chemical Biology
I am trying to develop new devices, such as solar cells, that capitalize on the unusual properties of nanoscale materials. For example, electrons in nanoscale rods or sheets can only move in one (rods) or two (sheets) directions. On extremely small length scales this “confinement” effect can alter both the physical and electrical properties of the material. In order to take advantage of these characteristics, new fabrication techniques are necessary. In one series of experiments, I have been growing semiconducting nanowires (/e.g.,/ silicon nanowires) using a focused laser with the aim of making nanoscale solar cells. In a second set of experiments, I have been producing single-atom-thick sheets of graphite (so-called “graphene” films) and then testing the quality of the films electronically. For example, the image below shows an array of graphene-based transistors used to test film quality. Our ultimate goal is the reproducible growth of perfect, atomically-thin films that are many inches in size — the first step in the development of new, ultrasensitive microscopies. |
Faculty Advisor:
Jiwoong Park |
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Optical brightfield image of an array of atomically-thin graphite transistors with
source (S), drain (D), and top-gate (TG) electrodes shown. |
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Alexander Melville
Materials Science and Engineering
I am trying to understand the subtle interactions that give rise to interesting electronic and magnetic phenomena by growing thin films of “unnatural” oxide-based materials in an atom-by-atom fashion. For example, we can grow thin films of the semiconductor EuO that have slightly elongated or slightly compressed bonds; we can then characterize the effects of the bond distortion on the material’s properties. Additionally, we can change the density of charge carriers (e.g., electrons) in the oxide by replacing a few of the Eu atoms with either La or Gd atoms, each of which provide an additional electron. Computer simulations have previously predicted that the magnetic properties of EuO could be improved by subtle changes in bond lengths and carrier density. We are testing these predictions. By growing EuO on top of another material, SrO, we hope to also trap a thin layer of electrons at the interface of the two materials, thereby creating a “spin-polarized electron gas” with interesting properties. |
Faculty Advisor:
Darrell Schlom |
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Colorized scanning electron
microscope image with a schematic drawing of spin-polarized electrons
flowing from La-doped EuO epitaxial thin film (orange) to the
patterned niobium superconducting film (blue).
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John Mergo
Applied Physics
I am studying the fundamental physics of crystal growth by watching micron-sized beads (colloids) crystallize under an optical microscope in real-time. This model system allows us to visualize processes that have been predicted to occur during the crystallization of atoms and molecules. For example, we can watch colloids crystallize in different geometries by using specially designed surfaces that act as patterns for the growing crystal. This technique allows us to alter the strain and symmetry of the growing crystal and record their effects on crystal growth. Using these experiments, we hope to understand the dynamics of defect and crack formation and perhaps eventually enable the growth of self-assembled colloidal electronics. |
Faculty Advisor:
Itai Cohen
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Single-layer colloidal crystal imaged during the start of coalescence (merging) with another crystal.
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Joanna Tan
Chemistry and Chemical Biology
I am trying to understand the conduction of electrons at the smallest possible length scale — through single molecules! We are particularly interested in studying the properties of molecules that contain one or more metal atoms, because they readily accept or lose a single electron and have a rigid linear geometry. As a result, metal-containing molecules conduct electricity in a sequential process in which individual electrons hop from one metal atom to another much like a person crossing a river by hopping from stone to stone. For example, the molecule pictured below has four metal atoms (in red) embedded in a molecule that also contains carbon, hydrogen and nitrogen atoms (in grey, white, and blue, respectively). We can tune the properties of these molecules by varying the atoms that connect and surround the metal atoms. Our goal is to understand the subtle chemical effects that control electron conduction in these systems. |
Faculty Advisor:
Héctor D. Abruña |
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Model of a molecular wire suspended between gold electrodes
Image by Stephen Burkhardt |
