ABSTRACT
Energy dissipation by internal friction is a property of fundamental interest for probing the effects of scale on mechanical behavior in nanocrystalline metallic films and for guiding the use of these materials in the design of high-Q micro/nanomechanical resonators. This paper describes an experimental study to measure the effects of frequency, annealing and grain size on internal friction at room temperature in sputter-deposited nanocrystalline aluminum films with thicknesses ranging from 60 to 120 nm. Internal friction was measured using a single-crystal silicon microcantilever platform that calibrates dissipation against the fundamental limits of thermoelastic damping. Internal friction was a weak function of frequency, reducing only by a factor of two over three decades of frequency (70 Hz to 44 kHz). Annealing led to significant grain growth and the average grain size of 100 nm thick films increased from 90 to 390 nm after annealing for 1 h at 450 (∘)C. This increase in grain size was accompanied by a decrease in internal friction from 0.05 to 0.02. Taken together, these results suggest that grain-boundary sliding, characterized by a spectrum of relaxation times, contributes to internal friction in these films.
ABSTRACT
Semiconducting nanowires (NWs) are important "building blocks" for potential electrical and electromechanical devices. Here, we report on the mechanical properties of supercritical fluid-grown Ge NWs with radii between 20 and 80 nm. An analysis of the bending and tensile stresses during deformation and failure reveals that while the NWs have a Young's modulus comparable to the bulk value, they have an ultimate strength of 15 GPa, which is the maximum theoretical strength of these materials. This exceptional strength is the highest reported for any conventional semiconductor material and demonstrates that these NWs are without defect or flaws that compromise the mechanical properties.
