| AVS 56th International Symposium & Exhibition | |
| Surface Science | Friday Sessions |
| Session SS1-FrM |
| Session: | Nanoclusters, Organics and Beam Induced Chemistry |
| Presenter: | J.T. Sadowski, Brookhaven National Laboratory |
| Authors: | J.T. Sadowski, Brookhaven National Laboratory A. Al-Mahboob, Tohoku University, Japan Y. Fujikawa, Tohoku University, Japan T. Sakurai, Tohoku University, Japan |
| Correspondent: | Click to Email |
The growth mode, morphology, crystallinity and electronic structure of thin rubrene (5,6,11,12–tetraphenylnaphthacene: C42H28) films grown in ultra-high vacuum (UHV) conditions have been studied in situ in the low-energy electron microscope (LEEM).
Rubrene is attracting a considerable attention since it has shown promise in OTFT’s, with field-effect mobilities of the single-crystal FET devices surpassing that of amorphous silicon and even pentacene. However, still little is known how the electronic and chemical properties of the substrate affect the crystallinity of rubrene thin films.
When rubrene is deposited on clean semiconductor surfaces, such as Si(111)-7x7, its reacts with the dangling bonds, partially dissociating and forming a disordered wetting layer. The nucleation of the crystalline islands follows, but high nucleation density and slow surface diffusion, due to a rough and disordered interface, result in a poor crystallinity of the films.
A completely different growth mechanism is observed upon rubrene deposition on semi-metallic Bi(0001) surface. In this case rubrene islands nucleate immediately, without formation of any wetting layer. Keeping the substrate temperature at 400K results in nucleation of large, single-crystalline rubrene islands preferentially oriented along the surface terraces. Low-energy electron diffraction (LEED) patterns indicate formation of a new rubrene phase. Most interestingly, this phase is characterized by chiral ordering of the molecules within single crystalline domains having sizes in the range of tenths of micrometers. Such chiral ordering has a great potential for improvement of the crystallinity of rubrene films, and thus performance of rubrene-based devices.