Visualizing Local Morphology and Conductivity Switching in Interface-Assembled Nanoporous C₆₀ Thin Films

Abstract

Carbon materials promise a revolution in optoelectronics, medical applications, and sensing provided that their morphology can be controlled down to the nanometer scale. Nanoporous materials are particularly appealing as they offer a drastically enlarged interfacial area compared to the corresponding planar materials. Entire fields such as organic solar cells, catalysis, or sensing may profit from an enlarged interface and facilitated molecular interaction between a carbon material and the environment. Nanoporous fullerene thin films obtained by the deposition of suspended nanoclusters of fullerene were already reported but suffered from the limitation of the size of these particles to over 100 nm. We study here a complementary method based on interfacial self-assembly forcing C clusters to spontaneously form 2D percolating monolayers with most morphological features in the 5-20 nm range. Analysis of these films by means of electron microscopy and scanning probe microscopy proved their morphology to be a nanocomposite of crystalline beads embedded in an amorphous matrix of fullerenes. When contacted between two gold electrodes, these films show an intrinsic conductivity switching behavior. Their electrical conductivity could be reversibly switched on by applying a threshold electrical current and switched off by exposure to oxygen. Interestingly, the on-state exhibits an astonishing conductivity of over 10 S/m. Kelvin probe force microscopy (KFM) was used to observe local changes in the distribution of electrical potential upon switching, on the relevant length scale of a few nanometers.

Nanoporous Organic Field‐Effect Transistors Employing a Calixarene Dielectric for Sub‐ppb Gas Sensing

“…[7,14] These templates require cross-linking prior to pattern transfer to the OSC using chlorinated solvents, [7] making their specific chemical functionalization toward gas sensing challenging. In the approach that we follow here, nanoporous films of 6,13-bis(triisopropylsilyle thynyl)pentacene (TIPS-Pn) were interfacially self-assembled on a water-air interface, [15,16] allowing facile deposition on a sensitive 4-tert-butylcalix [6]arene gate dielectric. Calixarenes are cyclic molecules allowing specific supramolecular interactions through molecular engineering of the functional moieties decorating the rims of the chalice.…”