Structural characterization of alkylsilane and fluoroalkylsilane self-assembled monolayers on SiO2 by molecular dynamics simulations

Otello Maria Roscioni (1) , Luca Muccioli (1, 2, 3, 4) , Alexander Mityashin (5) , Jérôme Cornil (6) , Claudio Zannoni (1)

1 Dipartimento di Chimica Industriale ‘‘Toso Montanari’’
2 LCPO - Laboratoire de Chimie des Polymères Organiques
3 Team 4 LCPO : Polymer Materials for Electronic, Energy, Information and Communication Technologies
4 ISM - Institut des Sciences Moléculaires
5 IMEC - IMEC
6 Univ Mons, Lab Chem Novel Mat, Belgium

We present molecular dynamics simulations of self-assembled monolayers (SAMs) chemisorbed on an atomically flat amorphous silicon dioxide substrate. We model two prototypical SAM-forming alkylsilanes, octadecyltrichlorosilane (OTS) and 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS), that find widespread use in organic electronic applications. Crucially, our model does not rely on an explicit bonding between the alkylsilane and the substrate, thus allowing for the spontaneous organization of molecules into regular structures, which we studied as a function of coverage. By comparing the calculated tilt angle, film thickness, and lattice parameters with experiments, we conclude that the simulated morphologies are quantitatively consistent with the experimental evidence, demonstrating the accuracy of the simulation methodology. We take advantage of the atomistic resolution of the calculations for carrying out a detailed one-to-one comparison between the structure and the electronic properties of the two SAMs. In particular, we find that OTS molecules show a coverage-dependent tilt, while FDTS molecules are always vertically oriented, regardless of the coverage. More importantly for organic electronic applications, we observe that OTS SAMs do not alter the electrostatic potential of silica, while FDTS SAMs induce a negative voltage shift which increases with coverage and saturates at about -2 V

Mots clés: Amorphous silicon; Electronic properties; Molecular dynamics; Molecules; Monolayers; Silica; Silicon oxides; Substrates; View at Publisher| Export | Download | Add to List| More... Journal of Physical Chemistry C Volume 120; Issue 27; 14 July 2016; Pages 14652-14662 Structural characterization of alkylsilane and fluoroalkylsilane self-assembled monolayers on SiO2 by molecular dynamics simulations (Article) Roscioni; O.M.a; Muccioli; L.abc; Mityashin; A.d; Cornil; J.e; Zannoni; C.a a Dipartimento di Chimica Industriale Toso Montanari; Università di Bologna; Bologna; Italy b Laboratoire de Chimie des Polymères Organiques; UMR 5629; Université de Bordeaux; Pessac; France c Institut des Sciences Molécularies; UMR 5255; Talence; France View additional affiliations View references (81) Abstract We present molecular dynamics simulations of self-assembled monolayers (SAMs) chemisorbed on an atomically flat amorphous silicon dioxide substrate. We model two prototypical SAM-forming alkylsilanes; octadecyltrichlorosilane (OTS) and 1H; 1H; 2H; 2H-perfluorodecyltrichlorosilane (FDTS); that find widespread use in organic electronic applications. Crucially; our model does not rely on an explicit bonding between the alkylsilane and the substrate; thus allowing for the spontaneous organization of molecules into regular structures; which we studied as a function of coverage. By comparing the calculated tilt angle; film thickness; and lattice parameters with experiments; we conclude that the simulated morphologies are quantitatively consistent with the experimental evidence; demonstrating the accuracy of the simulation methodology. We take advantage of the atomistic resolution of the calculations for carrying out a detailed one-to-one comparison between the structure and the electronic properties of the two SAMs. In particular; we find that OTS molecules show a coverage-dependent tilt; while FDTS molecules are always vertically oriented; regardless of the coverage. More importantly for organic electronic applications; we observe that OTS SAMs do not alter the electrostatic potential of silica; while FDTS SAMs induce a negative voltage shift which increases with coverage and saturates at about -2 V. © 2016 American Chemical Society. Indexed keywords Engineering controlled terms: Amorphous silicon; Substrates Atomistic resolution; Electrostatic potentials; Experimental evidence; Molecular dynamics simulations; Octadecyltrichlorosilane; Perfluorodecyltrichlorosilane; Simulation methodology; Structural characterization; Self assembled monolayers

Domaines: Polymères

Otello Maria Roscioni, Luca Muccioli, Alexander Mityashin, Jérôme Cornil, Claudio Zannoni. Structural characterization of alkylsilane and fluoroalkylsilane self-assembled monolayers on SiO2 by molecular dynamics simulations. Journal of Physical Chemistry C, 2016, 120 (27), pp.14652-14662. ⟨10.1021/acs.jpcc.6b03226⟩. ⟨hal-01416651⟩