baranger@phy.duke.eduNanoscience at Duke: nano-Duke
(Jan. 2000)Overview The astounding changes in our world that have resulted from the widespread use of computers, lasers, and novel materials represent only the early stages of a radical transformation of our material culture. The future holds the promise of tiny sensors and computers embedded in everyday objects, interfaces between physical devices and biological systems at the cellular and molecular level, lightweight materials with unprecedented strength, and tiny machines that operate on sub-cellular scales. These will have profound effects on everyday life as well as on physical sciences, biological sciences and engineering disciplines. All of this will be made possible by coordinated advances in the emerging interdisciplinary field called ``Nanoscience'', the science of physical systems about a billionth of a meter (a ``nanometer'') in size. To quote NSF Assistant Director Eugene Wong, the nanometer is a ``magical point on the scale of length, for this is the point where the smallest man-made devices meet the atoms and molecules of the natural world.''
Nanoscience: A Field in Transition
Nanoscience is a field in transition. The study of small bits of solid is, of course, not new. But a set of systems and problems has been extensively studied: the properties of electrons in structures made by physical lithography. Currently, the field is greatly expanding its view as it turns to other issues, notably ones motivated by biology, and other kinds of nanostructures. The field has begun to blossom rapidly for two reasons. First, spectacularly precise and versatile probes have recently been developed. Instruments such as the atomic force microscope and scanning tunneling microscope can directly observe the arrangements of individual atoms on a surface. They can be used to probe reversibly the folding of proteins. And they are essential for accurately characterizing nanostructures used in many domains, from biomedical engineering to physics. Second, the rapid development of new growth and synthesis techniques for the creation of nanostructures, such as quantum dot growth by self-assembly, is opening up fundamentally new types of structures. The field is poised for rapid growth in the foreseeable future, as new nanostructure materials are developed and as nanostructuring processes are applied to existing inorganic, organic, and hybrid materials.
The Breadth of Nanoscience
Perhaps the best way to indicate the scope of Nanoscience is to briefly summarize some of the current work in the area here at Duke in various departments.
Physics-- Nanophysics probes the interface between the quantum micro world and the classical macro world. On the one hand, new phenomena occur which require new concepts: novel many-body states in quantum wires and dots, for instance. On the other hand, the microscopic basis for bulk phenomena can be probed: exploring friction by pushing a single atom tip along an atomically flat surface is a recent example. The primary current focus of Nanophysics is on many-body phenomena in low-dimensional systems. Future topics include, for instance, transport through single molecules, magnetic nanoparticles, dissipation in quantum systems and quantum computing, the interplay of nanosystems with membranes and supramolecular structures, and optical properties of nanostructured materials. [Baranger and Matveev (theory), Finkelstein (experiment)]
Chemistry-- Nanochemistry focuses on the preparation and manipulation of materials with nanometer scale dimensions. Materials of this size often exhibit unique chemical properties which promise to be important for technological applications. For example, it is known that carbon nanotubes can be either metallic or semiconductive depending on their diameter and atomic orientation. This richness in electronic properties makes carbon nanotubes ideal candidates for interconnections and even functional devices in molecular electronics. Current research in the Chemistry department includes probing the formation mechanisms of carbon nanotubes and nanoparticles, manipulating individual nano-objects through chemically guided assembly, and using AFM lithography to assemble biological macromolecules. These approaches will allow us to design and synthesize nanostructures in pre-designed patterns to form functional nanodevices and nanobiosensors. [Liu]
Computer Science-- The possibility of using DNA to fabricate nanoscale computational elements of several sorts is being investigated theoretically and experimentally. Due to its easily programmable molecular association rules (base pairing) and the vast infrastructure developed for molecular biology, DNA is attractive for bottom-up construction of nano-scale objects and devices. Specifically designed DNA molecules are able to self-assemble into complex structural components which, in turn, associate specifically with neighboring components to form superstructures. Sets of DNA molecules can be designed to form only superstructures which represent valid solutions to computational problems (for example, n-bit addition). Other sets of DNA have been used to form structures which self-assemble into micron-scale, periodic lattices with nano-scale feature precision. Currently, we are optimizing known chemical protocols to ``grow'' nano-scale gold wires using self-assembled DNA lattices as templates. Similarly, self-assembled DNA structures are being used as frameworks upon which to immobilize electrically active organic chemicals in an attempt to construct molecular-scale circuitry. [LaBean and Reif]
Bio-Medical Engineering-- Biology works to a large extent on the nanometer scale. With advances in the ability to characterize and create molecular constructs, and to genetically control protein structure/function, researchers are now engineering biology at the molecular level. Several technical hurdles remain: for both multi-analyte biosenseing and biomaterials, for example, site-specific immobilization of biomacromolecules at the nanometer scale is needed. In fact, the era of bioactive biomaterials has emerged through greater understanding of the molecular events of wound healing, cell adhesion, and ligand binding. In tissue engineering, for example, it is desired to have cells bind to degradable polymeric scaffolds so that they will grow into organized, functionally distinct tissues. This requires knowledge of matrix-cellular signaling that encourages the directed growth and differentiation of cells. One strategy is to identify the density and composition of extra-cellular matrix proteins that lead to tissue growth, and reproduce this pattern through nanometer scale immobilization, which in turn requires nanoscale patterning. [Chilkoti and Reichert]
Electrical Engineering-- A variety of nanostructures are readily prepared with the group III-V compound semiconductors by molecular-beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). These structures have tens of nanometers dimensions as quantum wells or quantum dots. Because these structures are prepared as readily controlled layers within cladding layers of similar semiconductors, subsequent nanometer patterning is not required. Many properties of these quantum structures may be investigated with ultra-fast laser excitation; our present measurements use differential transmission of sub 100 fs pulses to probe the carrier dynamics in these nanostructures. Many issues remain to be resolved concerning the behavior of quantum wells and dots, and it is currently a very active research area. [Casey, Everitt, and Teitsworth]
Materials Science-- A Nanoscience program in the general area of ``Biological and other Soft Wet Materials'' focuses on coating and encapsulation of particles in the colloidal size range (10 nanometers to 10 micrometers). It essentially comprises two related areas. One deals with the material properties of lipid monolayers, bilayer membranes, hydrogels, emulsions, and cells. And the other is concerned with adhesion and repulsion involving molecular structures at interfaces, including water-soluble polymers and receptor-mediated cell adhesion. Two focuses of current research are molecular exchange and defect formation in lipid vesicle membranes, and the measurement of the local compliance of cellular interfaces and bond strengths for receptor-ligand bonds in response to cell activation. Information gained in this work is directed towards improved image contrast agents and drug delivery systems that use lipids and polymers to create micro- and nano-capsules and monolayer coatings. These systems are being tested pre-clinically with collaborators in the Duke Medical Center. [Needham]
Cell Biology-- As stated above, biology works primarily at the nanometer scale. For example, protein motor molecules move along microtubules and actin filaments in 1-10 nm steps. Methodology is in place to track the forces generated for this movement. On another scale, atomic force microscopy has recently been developed to unfold single proteins by mechanical stretching, relating the piconewton force to the energy and kinetics of unfolding. These technologies are ready for exploitation in further understanding biophysics at the nanometer level, and perhaps for exploitation in nanomachines. An important expertise in the Cell Biology department is electron microscopy (EM). At present it is used primarily for imaging cells and single protein molecules at a 1-2 nm resolution. EM structural analysis continues to be important in characterizing new proteins, and should be an invaluable resource in development of arrays or nanomachines. [Erickson]
Last modified: 11-Aug-00