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Journal of Materials Research, 23 (4), ISSN:0884-2914, ISSN:2044-5326

The deformation behavior of single- and polycrystalline gold pillars with diameters in the 150–1000 nm range was investigated at room temperature by compression testing. The pillars were produced by nanoimprinting and focused ion-beam (FIB) milling, and characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). No significant differences in the flow strength level or scaling behavior were observed when nanoimprinted pillars were compared with FIB-milled pillars with comparable diameters. These observations justify the use of FIB milling for the study of scaling behavior in this material system. Weibull statistics were used to analyze the distribution of strength levels, and a minimum in experimental scatter was identified at intermediate pillar size in comparison with their microstructural length scales.

A series of amorphous Ti–Ni–Cu based thin films with compositional spread and different thicknesses was produced at room temperature using a magnetron sputtering device and crystallized by means of different heat treatments. Phase composition and crystallographic orientation of the films were characterized using a Multi-Axial X-ray Diffraction approach and their mechanical properties were assessed using nanoindentation. The results show that the addition of Cu and thermal treatments can be used to significantly alter the phase composition, the texture and the microstructure of the films. Film thickness plays an important role in determining of the amount of martensitic phase at room temperature as well as the amount of Ti-rich and Ni-rich phases. In particular a thickness threshold between 350 nm and 800 nm was shown to be critical for the triggering of the texture in the austenitic phase.

Microstructure control of thin films is of particular importance for improving the reliability of microdevices in terms of electromigration, fatigue damage and hillocking. High-energy ion bombardment has turned out to be an appropriate modification instrument as it leads to selective grain growth, resulting in single-crystal-like structures. The current work addresses the effect of 7 MeV Au+ and 1.5 MeV N+ irradiation at high fluences (up to 45 × 1016 ions cm−2) on the microstructure and the mechanical properties of 500 nm Au thin films of small initial grain size (70–90 nm). The following microstructure changes were observed: selective grain growth, texture changes, sputtering, interfacial degradation, formation of geometrically necessary dislocations, and defect clusters. Hardening behavior was found to be a consequence of grain growth (Hall–Petch effect) and the formation of ion-induced defects.

Scaling in material properties is of great importance in microsystems and microelectronics where the device dimensions continuously shrink. Recently, compression tests of micron-sized pillars produced using a focused-ion beam (FIB) have become standard in the investigation of scaling effects. The influence of the fabrication process on the mechanical properties of the samples has, however, not been conclusively resolved. In this study, 130 silver pillars were fabricated using a novel embossing technique that does not pose the issues associated with FIB milling, i.e. surface amorphization and gallium contamination. Displacement-controlled compression tests on pillars with diameters of 130–3000 nm reveal for submicrometer samples an inverse proportionality of flow strength to diameter, which is associated with a wide strength distribution and a deformation taking place in large discrete strain bursts. The largest pillars show instead near bulk-like behavior. Unlike studies on other fcc materials, mechanical...

Natural materials exhibit outstanding properties compared to their single constituents because of their hierarchical alignment. Therefore, they can be used as a guide to enhance the properties of artificial nanocomposite materials, which eventually could excel compared to their biological counterparts. In this study, seashells of five species with different microstructures were compared by correlating the sizes and aspect ratios of the building blocks to their mechanical behavior. The analyzed nacreous seashells were Trochus maculatus, Haliotis rufescens and Pteria penguin; the non-nacreous seashells were Meretrix lusoria and Pecten maximus. The results were used to determine the optimal values for the shape, size and volume fraction of the structural elements with regards to hardness, Young’s modulus and fracture toughness. Surprisingly, the aspect ratio of the mineral phase in all seashells investigated was found to be close to the optimal value for strength as predicted by theory.

Understanding the mechanical properties of materials with external dimensions on the nanometer scale is crucial for the design and fabrication of nanoelectronics and nanosystems. Metal thin films exhibit a size-dependent hardening effect that scales inversely with the film thickness down to 200 nm. The thickness range below 200 nm is mostly unexplored and initial experiments indicate a change in the scaling law. Here, the mechanical properties of single-crystalline Au films are investigated in the thickness range from 31 to 858 nm by nanoindentation. Maximum shear stresses at the onset of plasticity are determined by the finite element method. While the hardness increases with decreasing film thickness, as expected from macroscopic experiments, the onset of plasticity shifts to lower shear stresses for thinner films. These observations are interpreted with respect to detailed observations of the microstructures of the films investigated.

Bulk nanocrystalline cobalt was prepared from reducing flame-spray-derived cobalt nanopowders exclusively in the face-centred cubic (fcc) modification. Compacts of approximately 60% density were obtained from uniaxial compression at room temperature and showed a strong resistance towards grain growth upon subsequent sintering to 90% relative density. The nanocrystalline structure remained stable well above 1000 degrees C and resulted in a pore-rich metal with about 10(15) nanovoids cm(-3). These sintered compacts displayed an up to three times higher bulk hardness if compared to conventional cobalt and local ductility as evidenced from scanning electron microscopy and nanoindentation. The strong grain-growth resistance and consequent increase in material hardness are discussed in respect of the presence of nanovoids, twin boundaries and material contamination.