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We report a method to introduce direct bonding between graphene platelets that enables the transformation of a multilayer chemically modified graphene (CMG) film from a paper mache-like structure into a stiff, high strength material. On the basis of chemical/defect manipulation and recrystallization, this technique allows wide-range engineering of mechanical properties (stiffness, strength, density, and built-in stress) in ultrathin CMG films. A dramatic increase in the Young s modulus (up to 800 GPa) and enhanced strength (sustainable stress /=1 GPa) due to cross-linking, in combination with high tensile stress, produced high-performance (quality factor of 31000 at room temperature) radio frequency nanomechanical resonators. The ability to fine-tune intraplatelet mechanical properties through chemical modification and to locally activate direct carbon carbon bonding within carbon-based nanomaterials will transform these systems into true materials-by-design for nanomechanics., Published in NANO Letters, p4212-, 5 Jul 2012. Sponsored in part by NRL s Nanoscience Institute.

In this article, we review our efforts to continuously tune mechanical and thermal properties in multilayer chemically modified graphene (CMG) films. An alteration of the graphene lattice by functional groups, by defects created during reduction, or by defect re-crystallization is used to control CMG mechanical and thermal properties. We attribute a notable increase in Young s modulus and film strength to an emerging network of sp2 sp3 crosslinks established between graphene layers. Control over the film stress and strength enabled us to dramatically improve the performance of radio frequency CMG resonators by fine tuning the fabrication process., Pub. in Solid State Communications, v152, p1990-1998, 2012.

Nanomechanical resonators with their extremely small mass and high surface/volume ratio present a unique opportunity for mass sensing[1-4]. However, functionalization with selective vapor adsorptive functional groups has been an impediment to the realization of nanomechanical systems for mass sensing. Functional groups that adsorb analytes of interest should be patterned only on the nanoresonator itself, and should not be located on structural elements or micro-channel walls, which would greatly limit the minimum detectible limit of the overall device. Also, traditional spin cast polymer films present the problem of being many times thicker than the nanomechanical resonator, essentially burying the resonator in the adsorptive polymer and completely damping the resonator. To address this, we are using a generic monolayer functionalization scheme based on a UV-mediated reaction between terminal alkenes and a hydrogen terminated silicon surface[5]. Specifically, we report the selective surface functionalization with a vapor adsorptive monolayer of hexafluoro-dimethylcarbinol on polycrystalline silicon nanomechanical resonators., See also ADM002137. Presented at the Proceedings of the 2008 IEEE International Conference on Nanotechnology (8th) held in Arlington, TX on 18-21 Aug 2008. Published in the Proceedings of the 2008 IEEE International Conference on Nanotechnology, Aug 2008. U.S. Government or Federal Rights License

Two-dimensional arrays of coupled nanomechanical plate-type resonators were fabricated in single crystal silicon using e-beam lithography. Collective modes were studied using a double laser setup with independent positioning of the point laser drive and interferometric motion detector. The formation of a wide acoustic band has been demonstrated. Localization due to disorder (mistune) was identified as a parameter that limits the propagation of the elastic waves. We show that all 400 resonators in our 20 x 20 array participate in the extended modes and estimate group velocity and density of states. Applications utilizing the resonator arrays for radio frequency signal processing are discussed., Published in Applied Physics Letters, v88 article ID 143504, 3 Apr 2006. Prepraed in collaboration with SFA Inc., Crofton, MD, and Cornell University, Ithaca, NY.