A nanometric cushion for enhancing scratch and wear resistance of hard films

Abstract

SummaryScratch 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.

Thickness measurement of thin films using atomic force microscopy based scratching

“…In order to scratch harder materials, it is necessary to apply larger normal loads and use stiff and wear resistive AFM probes with diamond and diamond-like carbon coatings. Such approach enabled successful AFM scratching experiments on metals (nickel [81], copper [81], gold [81,82], aluminium [83,84], nickel-iron [85], platinum [86] and silver [87]), semiconductors (silicon [88][89][90], gallium arsenide [91,92] and silicon carbide [93]) and even on very hard materials such as titania [94], Cr 2 N/Cu films [95] and carbon films [96][97][98][99]. The maximal depth of scratched domains is the main difference when comparing soft and hard materials.…”

Nanomechanics of Biomaterials – from Cells to Shells

“…[5] We have exploited the "hard yet compliant" phenomenon to engineer and study friction reduction by coating a thin titania layer on PDMS. [10] But such simple, engineered structures cannot compete with the performance levels of natural ones: Optimization of the elasticity index is inherent in mandibles of West Indian dry-wood termites which have a resistance to irreversible deformation which is almost two times greater than that of human enamel, despite the fact that the mandible hardness is 1/3 that of hydrated enamel. [5] This natural engineering feat lies in stark contrast to much of materials research which is focussed on producing harder and stiffer materials for mechanical applications.…”

Engineered TiO2 and SiO2‐TiO2 films on silica‐coated glass for increased thin film durability under abrasive conditions

“…Thin film durability is a key factor for products exposed to severe conditions such as abrasive wear. The applications of thin films to give an extra function to a substrate, or to protect it from external factors are growing . Abrasive wear performance evaluations in the automotive sector are already established by special standards…”

“…The applications of thin films to give an extra function to a substrate, [1][2][3][4] or to protect it from external factors are growing. [5][6][7][8][9][10] Abrasive wear performance evaluations in the automotive sector are already established by special standards. 11 In the last decades, TiO 2 has become more relevant for the industry due to its wide range of applications in selfcleaning surfaces, 12 antibacterial coatings, 13 optical filters, 14 electrodes in solar cells, 15 sensors, 16 among others.…”