| Control of pentacene thin film growth by supersonic molecular beam deposition (2008) | |||||||||||||||
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| Abstract of PhD Thesis: In this thesis, we present a series of fundamental studies of pentacene thin film growth on SiOx aimed at understanding its growth mechanism by means of surface morphology analysis. The novel aspect of our investigation is that we employed an unconventional organic thin film growth technique - supersonic molecular beam deposition (SuMBD); this is a relatively new method for growing thin pentacene layers if compared to the more commonly employed organic molecular beam deposition (OMBD). Three main achievements have been presented in this thesis: I) we demonstrated that the kinetic energy of pentacene landing on SiOx is the key factor to determine the surface morphology, which include the nucleation density, molecular island structure, critical nucleus size and growth mode of deposited pentacene (sub)-monolayers, and the crystal quality of pentacene first monolayer. The better quality of pentacene first monolayer composed by the large single crystal grains (spanning ~ 10 m) with flat surface and very few grain boundaries were achieved by the SuMBD with applying a kinetic energy of 6.4 eV; II) we discovered that the sticking coefficient of pentacene on SiOx surface is strongly influenced by the molecular kinetic energy, the incidence angle of the molecular beam and the applied substrate temperature. Additionally, these different growth conditions also have strong impaction on the nucleation density, island size and the formation of critical nucleus due to different molecular surface diffusivity and molecule-surface scattering; III) we succeeded in producing high quality pentacene ultrathin films for application in field effect transistors with the bottom contact Au electrodes. This was the first time that a high quality pentacene monolayer was produced at the interface between Au and SiOx. The morphology transition area, which is normally observed in the vicinity of a bare Au electrode and characterized by isolated 3D grains with high concentration of grain boundaries, was completely eliminated in our devices. The field effect transistors constructed with such ultrathin pentacene films show much better electronic and transfer characteristics. | |||||||||||||||
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