Investigation of perfluoropentacene thin films on substrates with different chemical structures

Thesis Type: Doctorate

Institution Of The Thesis: Middle East Technical University, Graduate School of Natural and Applied Sciences, Turkey

Approval Date: 2020

Thesis Language: English


Principal Supervisor (For Co-Supervisor Theses): Mehmet Fatih Danışman

Co-Supervisor: Selçuk Yerci


Due to their promising properties in electronic device applications, organic semiconductors (OSs) are being studied heavily. In this study, we aimed to investigate the structural properties of PerFluoroPentacene (PFP) thin films on flat and vicinal Au(111), and Ag(111) surfaces grown by the Supersonic Beam Deposition(SMBD) technique as a function of film thickness, metal surface step density, the effect of chemical and electronic properties of substrate, molecular flux (deposition rate), and energy during film growth which will enable us to determine the growth parameters that yield the highest quality PFP films. This study consists of two stages. In the first stage, we used conventional techniques such as Atomic Force Microscopy (AFM), Contact Angle measurements (CAs) and X-Ray Photoelectron Spectroscopy (XPS) for PFP film characterization. In the second stage, we aimed to present the design and construction of a new He diffraction system and the investigation of crystallographic properties of PFP films with this setup. The results indicate that PFP molecules arrange in standing-up orientation in the first layer and upper layers on all surfaces. The first layer of PFP thin films tends to wet the substrate surfaces, and after the first layer is almost completely covered, the second and other layers start to grow with needle-like grains which indicate a layer plus island (Stranski–Krastanow) growth mode. Substrate surface hydrophobicity and deposition rate directly affect the mean grain size and dendriticy of the first layer grains. The film formation is observed to be faster when the PFP molecules were seeded in lighter carrier gas resulting in higher kinetic energy PFP molecules. Construction of the new helium diffraction system was completed, and the performance of all parts of the system was tested. After a final optimization and minor modifications, the system is ready to collect diffraction data.