Examination of cross-sections of nanoindents with the transmission electron microscope has recently become feasible owing to the development of focused ion beam milling of site-specific electron transparent foils. Here, we discuss the development of this technique for the examination of nanoindents and survey the deformation behaviour in a range of single crystal materials with differing resistances to dislocation flow. The principal deformation modes we discuss, in addition to dislocation flow, are phase transformation (silicon and germanium), twinning (gallium arsenide and germanium at 400 °C), lattice rotations (spinel), shear (spinel), lattice rotations (copper) and lattice rotations and densification (TiN/NbN multilayers). The magnitude of the lattice rotation, about the normal to the foil, was measured at different positions under the indents. Indents in a partially recrystallized metallic glass Mg ₆₆ Ni ₂₀ Nd ₁₄ were also examined. In this case a low-density porous region was formed at the indent tip and evidence of shear bands was also found. Further understanding of indentation deformation will be possible with three-dimensional characterization coupled with modelling which takes account of the variety of competing deformation mechanisms that can occur in addition to dislocation glide. Mapping the lattice rotations will be a particularly useful way to evaluate models of the deformation process.

When prepared as a thin foil by rapid solidification, the Mg₈₅Cu₅Y₁₀ amorphous alloy undergoes a ‘ductile’/brittle transition upon bending after ageing at room temperature. This macroscopic behaviour arises from structural relaxation, which lowers the enthalpic content of the system and increases the elastic constants (i.e. the Young modulus and the shear modulus) as a function of ageing time. Since the shear modulus is found to increase faster than the Young modulus, the Poisson ratio decreases as the alloy ages and, at a critical value of ν ∼ 0.32, the ‘ductile’/brittle transition occurs. The results are discussed in terms of the annihilation of different types of defect, which characterize the disordered structure of a metallic glass.

The increasing energy demand and the ever more pressing need for clean technologies of energy conversion pose one of the most urgent and complicated issues of our age. Thermoelectricity, namely the direct conversion of waste heat into electricity, is a promising technique based on a long-standing physical phenomenon, which still has not fully developed its potential, mainly due to the low efficiency of the process. In order to improve the thermoelectric performance, a huge effort is being made by physicists, materials scientists and engineers, with the primary aims of better understanding the fundamental issues ruling the improvement of the thermoelectric figure of merit, and finally building the most efficient thermoelectric devices. In this Roadmap an overview is given about the most recent experimental and computational results obtained within the Italian research community on the optimization of composition and morphology of some thermoelectric materials, as well as on the design of thermoelectric and hybrid thermoelectric/photovoltaic devices.