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Carbon MEMS in Microsystems & Nanoengineering

This special issue on carbon micro and nano fabrication is a testament to the field having reached a level of maturity that sets it apart not only from Si microfabrication but also from efforts in CNT, graphene and fullerenes. By judicious choice of polymer precursors and pyrolysis steps, predetermined shapes and controlled microstructure of the resulting carbon devices are now possible. This field represents a holistic approach to carbon micro- and nanofabrication that, depending on the application at hand, yields the desired carbon shape and microstructure and thus the desired functionality in terms of chemical, electrical, thermal or mechanical properties. (Written by Marc Madou)

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A new approach for controlled ‘writing’ with a microscale plasma stream enables precise and efficient chemical modification of three-dimensional carbon electrodes. Such materials are highly desirable for diverse microelectronics applications, but conventional plasma-based techniques for targeted modification are relatively labor-intensive. Fatimah Ibrahim and colleagues at the University of Malaya have devised a novel strategy in which a controllable conductive microelectrode is used to precisely direct a microplasma discharge at specific sites on the surface of a carbon electrode. As a demonstration, they introduce water vapor into the system, thereby coupling of oxygen molecules to the electrodes. This approach enabled them to increase the amount of surface oxygen by nearly ten-fold, enabling efficient subsequent modification with other chemical groups, and the authors demonstrate that the resulting electrodes could offer superior performance for biosensors and other applications.

Article | Open Access | | Microsystems & Nanoengineering

A two-step process enables the fabrication of miniaturized enzymatic biofuel cells composed of nanomaterials for possible use as power sources in implantable devices. There is growing need for self-powered implanted medical devices. Enzymatic biofuel cells are attractive for this since they rely on bio-compatible and non-toxic materials. However, improvements in power cell density are needed, and agglomeration of nanomaterials on existing devices limits performance. Now, Yin Song and Chunlei Wang from Florida International University report a new process: top–down photolithography creates a high surface area micropillar array, followed by deposition of reduced graphene oxide, carbon nanotubes and enzymes onto the pillars. A maximum power density of 196.04 µW cm−2 at 0.61 V is achieved in the resulting devices, attributed to the combination of nanomaterials and conformal coating of the micropillars.

Article | Open Access | | Microsystems & Nanoengineering

Pyrolytic carbon is a material similar to graphite, and resonators (devices that oscillate with greater amplitude at certain frequencies) made from pyrolytic carbon show considerable promise in the micromechanical thermal analysis (MTA) of nanogram samples of polymers. Thermal analysis is essential for characterizing polymers and drugs, but conventional analytic techniques typically demand several milligrams of the sample, which may be unavailable or excessively expensive. A team headed by Long Quang Nguyen at the Technical University of Denmark was able to develop a simple fabrication process to produce electrically conductive pyrolytic carbon resonators for MTA of polymer samples at the nanogram level. The authors believe that pyrolytic carbon resonators have great potential in MTA; toward expanding those possibilities, they aim in future to examine whether they can enhance the thermal range of the resonators.

Article | Open Access | | Microsystems & Nanoengineering

Evidence suggests that neural implants based on glassy carbon are safe during MRI scans and do not distort scan images. Glassy carbon (GC) is becoming a preferential material in biosensors such as implants for brain wave recording or deep brain stimulation. To be useful, new neural implants should be maintained compatible with MRI scanning, as MRI has previously been known to induce vibration and heating of implants, induce an electrical current in the implant, and distort MR images. Sam Kassegne’s team at San Diego State University & Center for Neurotechnology (CNT) collaborated with Jan Korvink’s team at Karlsruhe Institute of Technology in Germany and pitted GC microelectrodes against conventional platinum microelectrodes. GC microelectrodes exhibited superior compatibility with MRI scanning compared to platinum, producing no significant vibration or induced current, yet were still visible in the images. The team expects further research will find that GC microelectrodes do not significantly heat during MRI scanning.

Article | Open Access | | Microsystems & Nanoengineering