An important challenge of modern materials science and nanoscience is to develop ways to alter the mechanical properties of an interface in a controlled fashion. Doing this while preserving the bulk properties of a material and maintaining a fixed chemical composition and reactivity of the interface is particularly attractive. In this work, the creation of substrates with tunable stiffness has been achieved by coating a soft polymer with an adherent, crack-free oxide overlayer whose thickness is varied from 8 to 70 nm. Specifically, amorphous titania with controlled, variable, thickness was deposited on polydimethylsiloxane (PDMS), and the surface mechanical properties were characterized using atomic force microscope (AFM)-based nanoindentation. The force/deformation curves can be quantitatively reproduced using a finite element analysis (FEA) modeling protocol. The FEA modeling facilitates predictability and enables the design of surfaces with independently customized chemical and mechanical properties.

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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.

Focused ion beam (FIB) is an extremely valuable tool in nanopatterning and nanofabrication for potentially high-resolution patterning, especially when refers to He ion beam microscopy. The work presented here demonstrates an 'out-of-the-box' method of writing using FIB, which enables creating very large matrices, up to the beam-shift limitation, in short times and with high accuracy unachievable by any other writing technique. The new method allows combining different shapes in nanometric dimensions and high resolutions for wide ranges.