S3 Seminar: A. Cassinese

Foto: Prof. Cassinese (©


Modena - 06.06.2017 - S3 Seminar: A. Cassinese
Prof. Antonio Cassinese, CNR-SPIN and Physics Department, University of Naples, Italy

"Organic Films Deposited by Supersonic Molecular Beam Deposition"

6/6/2017 - 15.00 - Seminar Room, S3 Cnr Nano, Physics Building, Unimore
Host: Arrigo Calzolari

In a Supersonic Molecular Beam Deposition (SuMBD) system, molecules are seeded in a hyperthermal carrier gas flow which, in specific conditions, is able to strongly accelerate them. In this way, the kinetic energy Ek of the molecules can reach several eV, being, at least, one order of magnitude higher than that characterizing the classical Organic Molecular Beam Deposition (OMBD) process based on Knudsen cells. In this talk I will summarize the main results obtained in the last years by using this technique. Then I will focus my attention on the deposition of (PDIF-CN2) films on HMDS-treated SiO2 dielectric barriers for the fabrication of bottom-contact bottom-gate organic thin-film transistors. During the film growth, the substrates were kept at room temperature, the molecular kinetic energy (Ek) was 17 eV and the growth rate (Drate) was finely tuned from 0.01 to 0.22 nm/min. In these conditions combining high kinetic energies and very low deposition rates, we found that the film growth mode has a largely dominant 3D character. Indeed, immediately after the deposition, the condensate is not compact being formed by rounded islands with a diameter of about 150 nm. The surface density of these islands changes with Drate which, consequently, affects the related degree of interconnectivity. Quite surprisingly, however, through AFM microscopy we observed the occurrence during the post-deposition period of a spontaneous slow wetting process of the condensate that ends with the formation of a continuous film1. This exotic phenomenon evolves with unusually long time scales (from days to months) which are also dependent on the deposition rate used for the film growth. In parallel with the film morphology evolution, an increase by orders of magnitude of the device charge mobility (m) was recorded over time, until getting maximum values of ~ 0.2 cm2/volt*sec for Drate~0.08 nm/min. This unconventional spreading effect, which cannot be observed for OMBD-deposited films, was systematically analyzed for a period of one year.the data will be discussed existing models. Finally a part of the talk will be dedicated to summarize the other activities existing in Naples , mainly concerning the mianiaturization of organic devices at nanoscale level
1  F.Chiarella, F. Chianese, M. Barra, L. Parlato, T.Toccoli, A. Cassinese, Journ. of Physical Chemistry C ,120 pp. 26076-26082 (2016) 

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