title: Direct imaging of defect formation in strained organic flexible electronics by Scanning Kelvin Probe Microscopy.
abstract: The development of new materials and devices for flexible electronics depends crucially on the understanding of how strain affects electronic material properties at the nano-scale. Scanning Kelvin-Probe Microscopy (SKPM) is a unique technique for nanoelectronic investigations as it combines non-invasive measurement of surface topography and surface electrical potential. Here we show that SKPM in non-contact mode is feasible on deformed flexible samples and allows to identify strain induced electronic defects. As an example we apply the technique to investigate the strain response of organic thin film transistors containing TIPS-pentacene patterned on polymer foils. Controlled surface strain is induced in the semiconducting layer by bending the transistor substrate. The amount of local strain is quantified by a mathematical model describing the bending mechanics. We find that the step-wise reduction of device performance at critical bending radii is caused by the formation of nano-cracks in the microcrystal morphology of the TIPS-pentacene film. The cracks are easily identified due to the abrupt variation in SKPM surface potential caused by a local increase in resistance. Importantly, the strong surface adhesion of microcrystals to the elastic dielectric allows to maintain a conductive path also after fracture thus providing the opportunity to attenuate strain effects.
authors.affiliation: Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Italy.
authors.forename: Tobias
authors.initials: T
authors.lastname: Cramer
authors.affiliation: Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Italy.
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Travaglini
authors.affiliation: Department of Electric and Electronic Engineering, University of Cagliari, Piazza d'Armi, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Lai
authors.affiliation: DICAM, University of Bologna, Viale Risorgimento 2, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Patruno
authors.affiliation: DICAM, University of Bologna, Viale Risorgimento 2, Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: de Miranda
authors.affiliation: Department of Electric and Electronic Engineering, University of Cagliari, Piazza d'Armi, Italy.
authors.forename: Annalisa
authors.initials: A
authors.lastname: Bonfiglio
authors.affiliation: Department of Electric and Electronic Engineering, University of Cagliari, Piazza d'Armi, Italy.
authors.forename: Piero
authors.initials: P
authors.lastname: Cosseddu
authors.affiliation: Department of Physics and Astronomy, University of Bologna, Viale Berti Pichat 6/2, Italy.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Fraboni