• Behn, Dino
• Mews, Alf
• Kjelstrup-Hansen, Jakob
• Tavares, Luciana

Abstract

Organic semiconductors have unique properties that can be tailored via synthetic chemistry for specific applications, which combined with their low price and straight-forward processing over large areas make them interesting materials for future devices. Certain oligomers can self-assemble into crystalline nanofibers by vapor deposition onto muscovite mica substrates, and we have recently shown that such nanofibers can be transferred to different substrates by roll-printing and used as the active material in e.g. organic field-effect transistors (OFETs), organic light-emitting transistors (OLETs), and organic phototransistors (OPTs). However, several device-related issues incl. charge-separation and local band structure remain poorly understood. In this work, we use electrostatic force microscopy (EFM) combined with optical microscopy to study the local surface charge of an individual organic nanofiber upon illumination with a focused laser beam. Under local illumination electron-hole pairs are generated resulting in positive charge accumulation along the entire nanofiber due to the redistribution of the holes, while the electrons presumably migrate into the substrate. This is in agreement with the transport characteristics that show these nanofibers form p-type FET devices. Our current efforts are focused on nanofiber-based transistor devices using scanning photocurrent imaging (SPI) to study the local electronic band structure along the channel and at the contacts.

Topics

• Deposition
• impedance spectroscopy
• surface
• semiconductor
• optical microscopy
• band structure
• field-effect transistor method
• Electrostatic force microscopy