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Nanotechnology

The 'shrinking' of traditional engineering is driven largely by chip technology and by the microfabrication of nanostructures in Physics. For soft materials, access to subcellular organelles is facilitated by developments in optics and protein chemistry.

Nanotechnology research is conducted in the Department of Physics in conjunction with the Laboratory for Research on the Structure of Matter (LRSM) where investigations of nanotubes and 'buckyballs' are in progress. The Pennsylvania Muscle Institute (PMI) and Department of Physiology have a program in Molecular Motors (See under "Cell Motility" above) of the cytoskeleton using purified cell proteins. Optical images of living cell components are generated by fluorescent gene constructs (GFP) transfected into cells and rendered 3-dimensional for dynamics studies at the Optical Imaging Laboratory of the Institute for Medicine and Engineering (IME).

Manipulations of Single Molecules (PMI)

A very recent area of research concentration at the Pennsylvania Muscle Institute is nanotechnology. The Instituteís involvement has been in development of techniques to manipulate and study single functioning protein molecules. In many enzyme and polynucleotide systems, important elementary events at the molecular level are obscured within the average behavior of a molecular population. Studying enzymes one at a time has only recently become technically feasible but new information, not otherwise available, can be gained from such an approach. Work in this area will allow, for the first time, measurements of time-resolved structural information, forces, elasticity and molecular displacements on single biomolecules.

Carbon Tubules and Fullerides (Drs. Harris, Kamien, Kane, Mele)

Over the last few years a spectrum of new solid phases of carbon have been discovered which are derived from the carbon molecule C60, and more recently from carbon nanotubules which are formed by wrapping graphitic sheets into compact cylindrical forms. These solids span an impressive range of electronic behavior: by moderately varying the degree of doping in the fullerides one finds phases with insulating, magnetic, and even superconducting ground states. New methods have been developed for controlling the growth of solid phases of single wall carbon nanotubes, and these structures hold great promise for new applications which exploit their unique electronic and elastic properties. We are actively investigating the electronic properties in these molecular solids, with a focus on understanding the phase equilibrium in these systems, and the effects of the underlying molecular symmetry, the orientational registry in the solid phase, and the quenched disorder in the condensed phases on their macroscopic electronic properties. The work is carried out in close collaboration with experimental work in the Department of Physics and Astronomy and the Department of Materials Science and Engineering on these systems.

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Carbon nanotubules and fullerenes (Drs. Heiney, Johnson)

Carbon buckeyballs and nanotubes are but two of the "fullerenes", a family of beautiful, atomically perfect, and potentially useful macromolecules made of pure carbon. With the 1985 Kroto-Smalley discovery of the C60 molecule ("buckeyball") and subsequent methods for large-scale production of fullerenes, research into the chemistry, physics and materials science of these materials simply exploded. Solid forms of C60 can be metallic, semiconducting, insulating, or even superconducting depending on the degree of doping. In contrast, the electrical properties of single-walled carbon nanotubes (a single graphene sheet folded into a flawless cylinder) are strongly influenced by the geometric structure of the tube, allowing metallic, semiconducting or insulating ground states in the absence of doping. Penn researchers discovered a striking orientational ordering transition in crystalline C60: at temperatures above 250K, the molecular centers of mass are fixed but the molecules rotate freely, while at low temperatures the molecules lock into a three dimensional gear structure. We are measuring the astounding mechanical and electrical properties of perfect single-walled nanotubes. X-ray scattering measurements essential to this research are performed using in-house central facilities and synchrotron facilities at Brookhaven National Laboratory. We will use the Argonne Advanced Photon Source when it becomes operational. These projets involve collaboration among scientists from Physics and Astronomy, Chemistry, and Materials Science and Engineering.

Nanostructure physics and quantum transport (Drs. Burstein, Johnson, Kikkawa)

Confinement-induced quantization profoundly alters the electronic, optical, mechanical, and magnetic properties of a nanostructure, whether it is a quantum dot formed by surface gates in a Ga[Al]As heterostructure, a carbon nanotube, or an organic macromolecule. Research projects at Penn focus on nanostructures fabricated both "from the top down" using optical and electron-beam lithography (e.g., 100nm quantum dots defined in a GaAs wafer), and "from the bottom up", where the nanostructure is a macromolecule or cluster created via a chemical reaction. We measure the electrical properties of nanostructures using low-noise transport from room temperature to the millikelvin regime, and magnetic fields up to 14 Tesla. Scanned probe technologies, including Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM), at temperatures as low as1.4 Kelvin, are used to determine local physical and electronic properties of nanostructures. Our newest facility allows the study of quantum spin transport by combining femtosecond nonlinear optics with low-temperature methods to explore the dynamics of spin-related phenomena in solids.

Extremely sensitive tests of our understanding of nanostructures can be done through experiments on single nanostructures or intentionally fabricated arrays, rather than random collections. With this idea in mind, we are developing techniques to electrically contact single nanostructures and macromolecules, using a combination of high-resolution electron beam lithography and chemically-controlled self-assembly. Pennís new Center for Advanced Imaging and Micromanipulation is developing novel instruments where individual molecules can be used as luminescence probes for scanning near-field optical microscopy or manipulated with optical tweezers and simultaneously probed with optical excitation and advanced microscopy.

For more information on the Institute for Medicine and Engineering, please visit http://www.med.upenn.edu/ime/

For more information on the Laboratory for Research on the Structure of Matter, please visit http://www.lrsm.upenn.edu/

For more information on The Pennsylvania Muscle Institute, please visit http://www.med.upenn.edu/pmi/

For more information on the Department of Physics, please visit http://www.physics.upenn.edu/

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Biological Engineering Network at the University of Pennsylvania
1010 Vagelos Research Labs / 3340 Smith Walk / Philadelphia PA 19104-6383
tel. 215-573-6813 ~ fax. 215-573-6815 ~ e-mail: ben-penn@pobox.upenn.edu