Nanogap fabrication by Joule heating of electromechanically spun suspended carbon nanofibers

Abstract

We present Suspended Carbon Nanofibers featuring a central nanometric gap fabricated by integration of Electro-Mechanical Spinning, pyrolysis of ultraviolet-cured microstructures and a Joule heating process. Photopatterned walls were used to suspend polymeric electrospun fibers based on a solution of SU-8. After pyrolysis, the complete structure was converted into a monolithic carbon microstructure featuring stable ohmic contact between the suspended fibers and the supporting walls without the need of further processing. By applying an electrical bias through the electrodes, the wire can be gradually thinned by excessive Joule heating, eventually forming a nanogap. The maximum supported current density in the fibers was found to be of the order of 10 5 A/cm 2 . Furthermore, the electrical characteristics of carbon nanofibers and the dimensions of the nanogaps were demonstrated to be dependent on the length of the fiber and atmosphere conditions, i.e. air or vacuum. A finite element simulation was used to gain insight into the influence of length on nanogap size. The shorter fibers modeled portrayed a significantly steeper temperature gradient, which agrees with the experimental observation of smaller gaps.The presented method facilitates an inexpensive manufacturing technique of nanogaps as small as 12 nm, holding potential for the preparation molecular electronics devices.

Tailoring the Diameters of Electro-Mechanically Spun Fibers by Controlling Their Deborah Numbers

“…For all cases, the increase of λ c is proportional to the addition of both additives. This dependence between λ c and concentration is in agreement with previous reports where the relaxations times were determined for a wide number of PEO aqueous solutions with different molecular weight and concentrations [ 12 , 28 ].…”

Pyrolysis-induced shrinking of three-dimensional structures fabricated by two-photon polymerization: experiment and theoretical model

“…Nonetheless, a notable advantage of these structures is that they are seamlessly embedded within two posts in a single piece (support wall-wire-support wall). This “monolith” configuration is expected to result in a highly stable ohmic contact 3 , which can be straightforwardly used as a platform to produce nanogap-sized electrodes 28 . In this prospect, the combination of TPP with pyrolysis is expected to be particularly useful, since it can routinely provide a fine control over nanowire length, and hence, over nanogap size 28 .…”

“…Moreover, the improved biocompatibility and mechanical strength of glassy carbon microstructures can be readily used for transdermal drug delivery, offering better stability and stiffness than most polymers 27 . In addition to these advantages, photoresist-derived glassy carbon has been used to fabricate conductive microstructures that have ohmic contacts 3,28,29 —a desirable feature in functional microdevices. Despite the importance in analyzing the inherent volumetric shrinkage experienced during pyrolysis of TPP structures, no studies to date have experimentally and theoretically assessed how the different geometrical building blocks, such as nanorods or micro/nanowires 30 , and bars 4,24 , transform upon carbonization.…”

Nano‐spaced Gold on Glassy Carbon Substrate for Controlling Cell Behavior

“…[ 21 ] It is easy to fabricate by pyrolyzing precursors such as SU8 and polyacrylonitrile among other polymers. [ 22,23 ] It is widely used in carbon microelectromechanical systems (C‐MEMS) such as for the fabrication of carbon interdigitated electrode arrays for redox amplification, [ 24,25 ] dielectrophoretic devices, [ 26 ] biosensors, [ 27 ] nanogap electrodes, [ 28 ] and supercapacitors [ 29 ] among many other applications. Being inert also entails limitations as chemical and biological sensing typically require physical or chemical attachments of reactive species on the GC surface.…”