Fabrication of a nickel nanowire mesh electrode suspended on polymer substrate

Realization of Nanolene: A Planar Array of Perfectly Aligned, Air-Suspended Nanowires

Air suspension and alignment are fundamental requirements to make the best use of nanowires' unique properties; however, satisfying both requirements is very challenging due to the mechanical instability of air-suspended nanowires. Here, a perfectly aligned air-suspended nanowire array called "nanolene" is demonstrated, which has a high mechanical stability owing to a C-channel-shaped cross-section of the nanowires. The excellent mechanical stability is provided through geometrical modeling and finite element method simulations. The C-channel cross-section can be realized by top-down fabrication procedures, resulting in reliable demonstrations of the nanolenes with various materials and geometric parameters. The fabrication process provides large-area uniformity; therefore, nanolene can be considered as a 2D planar platform for 1D nanowire arrays. Thanks to the high mechanical stability of the proposed nanolene, perfectly aligned air-suspended nanowire arrays with an unprecedented length of 1 mm (aspect ratio ≈5100) are demonstrated. Since the nanolene can be used in an energy-efficient nanoheater, two energy-stringent sensors, namely, an air-flow sensor and a carbon monoxide gas sensor, are demonstrated. In particular, the gas sensor achieves sub-10 mW operations, which is a requirement for application in mobile phones. The proposed nanolene will pave the way to accelerate nanowire research and industrialization by providing reliable, high-performance nanowire devices.

The Roles of Biofilm Conductivity and Donor Substrate Kinetics in a Mixed-Culture Biofilm Anode

We experimentally assessed the kinetics and thermodynamics of electron transfer (ET) from the donor substrate (acetate) to the anode for a mixed-culture biofilm anode. We interpreted the results with a modified biofilm-conduction model consisting of three ET steps in series: (1) intracellular ET, (2) non-Ohmic extracellular ET (EET) from an outer membrane protein to an extracellular cofactor (EC), and (3) ET from the EC to the anode by Ohmic-conduction in the biofilm matrix. The steady-state current density was 0.82 ± 0.03 A/m² in a miniature microbial electrochemical cell operated at fixed anode potential of -0.15 V versus the standard hydrogen electrode. Illumina 16S-rDNA and -rRNA sequences showed that the Geobacter genus was less than 30% of the community of the biofilm anode. Biofilm conductivity was high at 2.44 ± 0.42 mS/cm, indicating that the maximum current density could be as high as 270 A/m² if only Ohmic-conduction EET was limiting. Due to the high biofilm conductivity, the maximum energy loss for Ohmic-conduction EET was negligible, 0.085 mV. The energy loss in the second ET step also was small, only 20 mV, and the potential for the EC involved in the second ET was -0.15 V, a value documenting that >99% of the EC was in the oxidized state. Monod kinetics for utilization of acetate were relatively slow, and at least 87% of the energy loss was in the intracellular step. Thus, intracellular ET was the main kinetic and thermodynamic bottleneck to ET from donor substrate to the anode for a highly conductive biofilm.

Controlling film topography to form highly hydrophobic waterborne coatings

Coatings have a tremendous impact on economy as they reduce corrosion that has an estimated cost of 3% of the world's GDP. Hydrophobic coatings are particularly efficient for this purpose and the challenge is to produce cost effective and environmentally friendly, highly hydrophobic, cohesive and non-porous coatings applicable to large and irregular surfaces. This work shows that this goal can be achieved by forming wrinkles on the surface of waterborne coatings through fine-tuning of the film forming conditions. The proof of concept was demonstrated by using waterborne dispersions of copolymers of 1H,1H,2H,2H-perfluorodecyl acrylate and 2-ethylhexyl acrylate, and using the temperature and hardness of the copolymer as control variables during film formation. This allowed the formation of transparent films with a wrinkled surface that had a contact angle of 133°, which represents an increase of 20° with respect to the film cast under standard conditions.

Highly Hydrophobic Coatings from Waterborne Latexes

This work reports on the formation of highly hydrophobic coatings from waterborne latexes able to form films at ambient temperature. The contact angle of film forming copolymers of 2-ethylhexyl acrylate and perfluorodecyl acrylate (PFDA) was limited to 114° because flat surfaces were obtained. Attempts to increase the roughness of the film using blends of film-forming latexes with the latex of PFDA homopolymer (which is not film forming) were not successful under regular casting conditions because the PFDA particles accumulated at the film-substrate interface. Film formation engineering allowed modifying the morphology of the film obtaining a contact angle of 137°.

Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers

We report on the synthesis and magnetic characterization of ultralong (1 cm) arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes). Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene-ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications.