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Switchable tribological properties of ferroelectrics offer an alternative route to visualize and control ferroelectric domains. Here, we observe the switchable friction and wear behavior of ferroelectrics using a nanoscale scanning probe—down domains have lower friction coefficients and show slower wear rates than up domains and can be used as smart masks. This asymmetry is enabled by flexoelectrically coupled polarization in the up and down domains under a sufficiently high contact force. Moreover, we determine that this polarization-sensitive tribological asymmetry is widely applicable across various ferroelectrics with different chemical compositions and crystalline symmetry. Finally, using this switchable tribology and multi-pass patterning with a domain-based dynamic smart mask, we demonstrate three-dimensional nanostructuring exploiting the asymmetric wear rates of up and down domains, which can, furthermore, be scaled up to technologically relevant (mm–cm) size. These findings demonstrate that ferroelectrics are electrically tunable tribological materials at the nanoscale for versatile applications. The interaction of flexoelectric polarization arising from strain gradients with ferroelectricity impacts tribological properties and facilitates fine physical lithography without masks or chemicals, with potential applications in various fields. [ABSTRACT FROM AUTHOR]

A size effect study was conducted on [001] oriented vanadium nanopillars that were synthesized from both a thin film and a bulk crystal. The results indicate that a size-dependent deformation behavior exists for vanadium; the smaller nanopillars displayed discrete strain bursts and higher stresses during deformation. The size effect exponent is found to be 0.79, and the results are compared with previous reports on other body-centered cubic (bcc) metals: Nb, Ta, Mo and W. [ABSTRACT FROM AUTHOR]

Abstract: Multilayer thin films with bilayer thicknesses in the nanometer range have been reported to have very high strengths. A previous study has shown that Al–Al3Sc multilayers, with bilayer thicknesses as small as 6nm, have hardnesses as high as ∼3GPa as measured by sharp tip nanoindentation. In the present study, we have avoided some of the complications associated with sharp tip nanoindentation by directly measuring the yield strengths and strain hardening/softening properties of Al–Al3Sc multilayers using microcompression testing methods with a nanoindenter. The results show the expected trend of increasing yield strength with decreasing bilayer thickness, and compare favorably with estimates of the yield strengths based on sharp tip nanoindentation. During deformation, the Al–Al3Sc multilayer pillars with smaller bilayer spacings experience considerable strain softening, resulting in a “flat-top mushroom” shape after deformation. We have developed a numerical model to account for this inhomogeneous deformation behavior and to calculate stress–strain relationships during strain softening. A new transmission electron microscopy study of a deformed pillar shows that the softening is a result of destruction of the layered structure due to shearing and rotation. [Copyright &y& Elsevier]

Abstract: The size-dependent strength of face-centered cubic (fcc) metals, as revealed by uniaxial compression of nanopillars, suggests that plasticity is dislocation source-controlled, with fewer sources in smaller pillars producing a “smaller is stronger” effect. To further investigate this phenomenon we have studied the effects of prestraining and annealing on the deformation properties of [001] Au nanopillars. By making pillars from an epitaxial film of [001] Au on [001] MgO, using focused ion beam machining, we are able to create both puck-shaped pillars that can be stably prestrained and pillars with a high aspect ratio, which can be tested in uniaxial compression. We find that prestraining dramatically reduces the flow strength of nanopillars while annealing restores the strength to the pristine levels. These unusual effects are not seen in bulk fcc metals, which behave in the opposite way. We discuss their possible causes in terms of dislocation densities using transmission electron microscopy. [Copyright &y& Elsevier]

Abstract: External stresses are applied during operation or storage in flexible electronics, which makes understanding time-dependent plastic deformation of nanobuilding blocks more crucial for ensuring the reliability of the devices. Here, we systematically explored the time-dependent nanoscale plasticity of single-crystal ZnO nanorods and its size effects. A series of compression creep tests under different low stresses (in elastic regime) were performed on vertically oriented rods having equivalent diameters in the range of ∼200 to ∼2000nm. It was revealed that creep indeed occurs in the rods even at ambient temperature, and is more pronounced in smaller nanorods. Analyzing the stress exponent and the activation volume suggests that the enhanced plasticity may be controlled by the diffusion creep (through the “space-charge layer” near the surface and/or along the interface between the punch and the top surface of the rod), which is supported by the results from in situ creep tests under electron-beam irradiation and in situ electric measurements. [Copyright &y& Elsevier]

Abstract: Indium columnar structures with diameters near 1μm were deformed by uniaxial compression at strain rates of approximately 0.01 and 0.001s−1. Defect density evolution in the nanopillars was evaluated by applying synchrotron Laue X-ray microdiffraction (μSLXRD) on the same specimens before and after deformation. Results of the μSLXRD measurements indicate that the dislocation density increases as a result of mechanical deformation and is a strong function of strain rate. These results suggest that the rate of defect generation during the compression tests exceeds the rate of defect annihilation, implying that plasticity in these indium nanostructures commences via dislocation multiplication rather than nucleation processes. This is in contrast with the behaviors of other materials at the nanoscale, such as, gold, tin, molybdenum, and bismuth. A hypothesis based on the dislocation mean-free-path prior to the multiplication process is proposed to explain this variance. [Copyright &y& Elsevier]