The mechanical properties of SU-8 at microscale were measured under both micropillar compression and nanoindentation on a film on a substrate. To the best of our knowledge, this paper reports the first set of results for microcompression of SU-8 micropillars for measurement of mechanical properties using viscoelastic analysis. The effects of loading rate and micropillar size are examined. It was determined that the SU-8 exhibits viscoelastic properties at room temperature, the time-average Young's modulus increases in general with the loading rate. The average Young's modulus determined by compression of a micropillar was 4.1 GPa at a strain rate near 10 −3 s −1 . For nanoindentation on a SU-8 film supported by a silicon substrate, the default output from the nanoindenter for the Young's modulus was approximately 6.0 GPa with the consideration of elastic-plastic behavior of the SU-8. When the viscoelastic effects were considered, the time-average Young's modulus at a given strain rate was determined to be near 3.6 GPa, which agrees with the reported values in the literature obtained from tension and bending, and also correlates reasonably well with data from microcompression. This work indicates that viscoelastic analysis is necessary to extract the valid mechanical properties at nano/microscales for SU-8.

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Graphene-derived macroscopic assemblies feature hierarchical nano- and microstructures that provide numerous routes for surface and interfacial functionalization achieving unconventional material properties. We report that the microstructural hierarchy of pristine chemically modified graphene films, featuring wrinkles, delamination of close-packed laminates, their ordered and disordered stacks, renders remarkable negative Poisson’s ratios ranging from −0.25 to −0.55. The mechanism proposed is validated by the experimental characterization and theoretical analysis. Based on the understanding of microstructural origins, pre-strech is applied to endow chemically modified graphene films with controlled negative Poisson’s ratios. Modulating the wavy textures of the inter-connected network of close-packed laminates in the chemically modified graphene films also yields finely-tuned negative Poisson’s ratios. These findings offer the key insights into rational design of films constructed from two-dimensional materials with negative Poisson’s ratios and mechanomutable performance.

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