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CO2 hydrogenation to olefins and ethylene oligomerization was investigated in efforts to improve catalyst composition and reaction conditions needed for scale-up. The hydrogenation of CO2 to hydrocarbons is investigated over -alumina-supported iron-based catalysts modified with manganese and potassium promoters and a silica-stabilized coating under fixed-bed reactor conditions to produce unsaturated hydrocarbons as feedstock chemicals for jet fuel synthesis. The stabilizer is introduced by impregnating the K/Mn/Fe on Al2O3 catalyst with tetraethylorthosilicate (TEOS) to minimize the deactivating effects of water on catalyst activity in CO2 hydrogenation. The K/Mn/Fe on Al2O3 catalyst modified with the TEOS and reduced in CO produced a lighter end fraction of olefins compared with the catalyst reduced in H2. To increase the chain length of the olefins formed in the CO2 hydrogenation step, investigation of oligomerization reaction is conducted in a separate experiment, where pure ethylene is used as a model olefin. Ethylene oligomerization over pelletized amorphous silica-alumina (ASA)- supported Ni catalysts demonstrated high conversion and selectivity towards the jet fuel fraction (C8-C16) at very low MHSV., Published in Energy & Fuels, 14 Aug 2013. The original document contains color images. Prepared in collaboration with NRL's Chemistry and Acoustics Divisions, Washington, DC. Prepared in cooperation with Nova Research Inc., Alexandria, VA. Sponsored in part by ONR.

Graphene films grown on Cu foils have been fluorinated with xenon difluoride (XeF2) gas on one or both sides. When exposed on one side the F coverage saturates at 25% (C4F), which is optically transparent, over 6 orders of magnitude more resistive than graphene, and readily patterned. Density functional calculations for varying coverages indicate that a C4F configuration is lowest in energy and that the calculated band gap increases with increasing coverage, becoming 2.93 eV for one C4F configuration. During defluorination, we find hydrazine treatment effectively removes fluorine while retaining graphene's carbon skeleton. The same films may be fluorinated on both sides by transferring graphene to a silicon-on-insulator substrate enabling XeF2 gas to etch the Si underlayer and fluorinate the backside of the graphene film to form perfluorographane (CF) for which calculated the band gap is 3.07 eV. Our results indicate single-side fluorination provides the necessary electronic and optical changes to be practical for graphene device applications., Published in NANO Letters, v10 p3001-3005, 2010.

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( = 185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit (fxQ > 10(exp 11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite., Published in Nano Letters, v8 n10 p3441-3445, 2008.

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.