Paper TF-TuP7
Initial Growth of Pentacene Thin Film on Si(001) Substrate

Tuesday, December 4, 2018, 4:00 pm, Room Naupaka Salon 1-3

Initial growth process of the pentacene molecules on the clean Si(001)-2×1 substrate were investigated by Scanning Tunneling Microscopy (STM) at room temperature (RT). The pentacene molecules were deposited onto the clean Si(001) surface held at RT, using a quartz crucible. We found that the wetting layer forms first by increasing the amount of the deposited pentacene molecules before starting the formation of the first layer, which is not crystalized, but disorder, where the molecules adsorb flatly. It does not have any ordered domain structure. The first pentacene layer that is crystalized with the standing-up pentacene molecules grows on the disordered wetting layer by increasing the deposited amount of the molecules more. The first layer consists of three domains at least, which have different crystal structures from each other: the ‘α’, the ‘β’ and the ‘γ’ domains. Among them, the ‘β’ domain has a new pentacene crystal structure that can form only on the first layer. The first layer does not have a dendritic shape at least at a field of view of 2 μm. Second pentacene layer starts to form on top of the first layer by increasing the deposited amount more again, before the first layer completely covers the substrate surface. In contrast, the second layer has only single domain. The all other crystal structures found in the present study except for that of the ‘β’ domain, are similar to those of the four polymorphs reported previously [1]. Moreover, we investigated electronic properties of the various pentacene layers by the I-V measurements. The pentacene layers are semiconducting with a gap of about 4 eV from -1 eV to +3 eV.

Reference

[1] M. Kitamura, Y. Arakawa, J. Phys.: Condens. Matter 20, 184011 (2008), and references therein.