Stability of Polymer Ultrathin Films (<7 nm) Made by a Top-Down Approach

• Published in: ACS nano 2015-08, Vol.9 (8), p.8184-8193
• Main Authors: Bal, Jayanta Kumar, Beuvier, Thomas, Unni, Aparna Beena, Chavez Panduro, Elvia Anabela, Vignaud, Guillaume, Delorme, Nicolas, Chebil, Mohamed Souheib, Grohens, Yves, Gibaud, Alain
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Dewetting; Film thickness; Polymers; Polystyrene resins; Rinsing; Silicon substrates; Solvents; Stability; Thin films
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.5b02381

In polymer physics, the dewetting of spin-coated polystyrene ultrathin films on silicon remains mysterious. By adopting a simple top-down method based on good solvent rinsing, we are able to prepare flat polystyrene films with a controlled thickness ranging from 1.3 to 7.0 nm. Their stability was scrutinized after a classical annealing procedure above the glass transition temperature. Films were found to be stable on oxide-free silicon irrespective of film thickness, while they were unstable (2.9 nm) on 2 nm oxide-covered silicon substrates. The Lifshitz–van der Waals intermolecular theory that predicts the domains of stability as a function of the film thickness and of the substrate nature is now fully reconciled with our experimental observations. We surmise that this reconciliation is due to the good solvent rinsing procedure that removes the residual stress and/or the density variation of the polystyrene films inhibiting thermodynamically the dewetting on oxide-free silicon.