FY2010 - Oak Ridge National Laboratory

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Seed Money Fund— Measurement Science and Systems Engineering Division fields (electromagnetic waves) is based on the detection of the force on electrically charged nanomechanical oscillators. Nanoscale mechanical structures have already proven potentially useful for the detection of small (attonewton) forces, which will enable the measurement of small electric and electromagnetic fields. To achieve both high dynamic range and wide spectral response, we need to design a system where the cantilever operating frequency is tunable. During the project, we will design and fabricate a nanomechanical oscillator for E-field detection. In addition, we will characterize the fabricated nanomechanical oscillators by measuring their responses to time varying electric and electromagnetic fields. Mission Relevance Highly sensitive nanomechacical E-field detectors will have a tremendous impact in many applications, such as the detection of small strength fields from global positioning system signals inside buildings. Specific Department of Defense needs for electric field sensing are described in the recent Defense Advanced Research Projects Agency (DARPA) BAA 09-34. DARPA program manager Dr. Devanand Shenoy has expressed great interest in utilizing micro/nanomechanical systems for electric field sensing. The great promise of these devices in detecting both static and time varying electric fields stems from this initial feasibility study. Other implications of this technology can be envisioned in environmental science, homeland security, and DOE applications. A more efficient electric grid may be a result of the accurate and inexpensive detectors of low frequency E-fields surrounding power lines. In addition, technologies capable of identifying centrifuge locations as well as other counterproliferation technologies are likely to result from this study. Results and Accomplishments The following research tasks were completed during FY 2010 to demonstrate the unique advantages of the present dual wavelength imaging technique and to show the feasibility of the approach. The FY 2010 tasks focused primarily on fabrication and testing of nanomechanical oscillators and their adaptation for detection for constant and time varying electric fields. We evaluated several designs of microfabricated oscillators, including pillar-shaped and cantilever-shaped resonator structures. Gold-coated cantilever structures fabricated using silicon nitride as a structural material were found to be most promising for creating one-dimensional arrays of E-field detectors. Implemented devices relied on a straightforward technological sequence suitable for scaled-up fabrication. We assembled a test rig based on optical readout and tested a series of cantilever resonators in the frequency range 1 kHz to 30 MHz. An electrical charge on the cantilever tips was created by applying a DC bias between the metal layer on the cantilever and a metal counter electrode at 1–5 mm away from the cantilever. The value of the charge located on the tip was evaluated using finite-element analysis modeling. Consistent with our analytical predictions, less stiff cantilevers showed higher sensitivity and were selected for subsequent, more detailed studies. In summary, we demonstrated the feasibility of the innovative concept of a cantilever-based E-field detector that integrates an antenna, a high Q resonator, and a frequency mixer on a very compact platform. Using heterodyning, we achieved detectability of E-fields in the sub-millivolt per meter range in the kilohertz to megahertz frequency range. Further improved sensitivity can be obtained by integrating a high charge density electrete into the resonating element. Information Shared Datskos, P., S. Rajic, N. Lavrik, and T. Thundat. 2010. “Nanomechanical Electric and Electromagnetic Field Sensors.” UT-Battelle Invention Disclosure 201002376, DOE S-115,422. Patent application in preparation. 234
05858 Fabrication of Ultrathin Graphite/Graphene Films Ivan Vlassiouk, Nickolay V. Lavrik, Sheng Dai, and Panos Datskos Seed Money Fund— Measurement Science and Systems Engineering Division Project Description Since its first introduction in 2004, graphene quickly has become a wonder nanomaterial of unexhausting interest to many researchers due to its unique properties. Despite graphene`s high potential for unlimited applications, a reliable source of graphene is still a bottleneck for further development. Recent advances in chemical vapor deposition (CVD) growth and in chemical techniques based on reduction of graphene oxide appear promising in providing the routes for the desired high throughput supply of graphene. In this project we intended to investigate a new, low temperature technique for consistent ultrathin graphite/graphene membranes fabrication with a large surface area. We relied on graphene synthesis through a CVD technique. Several approaches were used (different carbon sources/temperature ranges) with the purpose of understanding whether technologically attractive low temperature CVD graphene growth could provide graphene that possesses high electronic and thermal conductivities suitable for the majority of applications. Mission Relevance The project outcome will constitute a cornerstone for a successful development of various applications based on a single layer of graphite. Graphene shows a gigantic potential virtually in every DOE mission area, such as membranes technologies, energy, computing, and waste treatment. Graphene possesses unique electronic properties with membranes of this material showing high potential for separation and filtration. Graphene can be used as a substitute for indium tin oxide in various solar applications, construction of diverse nanoelectromechanical systems, etc. Currently we are working on follow up funding from the Defense Advanced Research Projects Agency. Results and Accomplishments We have shown that CVD growth of continuous monolayer graphene on copper foils or thin films can be performed at temperatures as low as 800°C, similar to those for CVD growth on nickel. Despite some structural defects, such monolayer graphene possesses high electrical and thermal conductivities that justify its utilization in numerous applications where its thermal management, transparency, and conductance are desired. Structural disorder, as evaluated from the Raman G-band and D-band ratio (I G /I D ), gradually increases with lowering the deposition temperature and can be related to a decreasing size of monocrystalline graphene domains, L a . The corresponding decline in the electrical conductivity is close to a linear function of L a , while the thermal conductivity (as evaluated from the relative anti-Stokes intensity) is a much weaker function of L a , with an apparent power dependence K ~ L 1/3 a . The thermal conductivities measured from the temperature dependence of the G-band position result in almost orderof-magnitude greater values. Depending on the disorder degree, CVD graphene shows high thermal (K ~ 1200 WK -1 m -1 , measured using temperature-induced G band position shift) and electrical (5 10 -4 ohms -1 , for doping levels of 10 12 cm -2 ) conductivities suitable for various applications. Optical absorbance has a nondetectable dependence on the disorder and equal to 0.023 (pi times fine structure constant) for a single graphene layer. 235
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NEUTRON SCIENCES ..................
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NATIONAL SECURITY SCIENCE AND TECHN
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FY2010 - Oak Ridge National Laboratory

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