title: A nanometric cushion for enhancing scratch and wear resistance of hard films.
abstract: Scratch resistance and friction are core properties which define the tribological characteristics of materials. Attempts to optimize these quantities at solid surfaces are the subject of intense technological interest. The capability to modulate these surface properties while preserving both the bulk properties of the materials and a well-defined, constant chemical composition of the surface is particularly attractive. We report herein the use of a soft, flexible underlayer to control the scratch resistance of oxide surfaces. Titania films of several nm thickness are coated onto substrates of silicon, kapton, polycarbonate, and polydimethylsiloxane (PDMS). The scratch resistance measured by scanning force microscopy is found to be substrate dependent, diminishing in the order PDMS, kapton/polycarbonate, Si/SiO2. Furthermore, when PDMS is applied as an intermediate layer between a harder substrate and titania, marked improvement in the scratch resistance is achieved. This is shown by quantitative wear tests for silicon or kapton, by coating these substrates with PDMS which is subsequently capped by a titania layer, resulting in enhanced scratch/wear resistance. The physical basis of this effect is explored by means of Finite Element Analysis, and we suggest a model for friction reduction based on the "cushioning effect" of a soft intermediate layer.
authors.affiliation: Department of Chemistry and Institute of Nanotechnology & Advanced Materials, Bar Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Katya
authors.initials: K
authors.lastname: Gotlib-Vainshtein
authors.affiliation: Department of Chemistry and Institute of Nanotechnology & Advanced Materials, Bar Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Olga
authors.initials: O
authors.lastname: Girshevitz
authors.affiliation: Department of Chemistry and Institute of Nanotechnology & Advanced Materials, Bar Ilan University, Ramat-Gan 52900, Israel.
authors.forename: Chaim N
authors.initials: CN
authors.lastname: Sukenik
authors.affiliation: Department of Mechanical Engineering, Ben Gurion University, Beer Sheva, Israel.
authors.forename: David
authors.initials: D
authors.lastname: Barlam
authors.affiliation: Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel.
authors.forename: Sidney R
authors.initials: SR
authors.lastname: Cohen
keywords: finite element analysis; hard coating; scanning probe microscopy; scratch; thin films; tribology