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We measure the mechanical response of optical multilayer dielectric (MLD) diffraction gratings, geometries which are constrained in only one transverse direction but free in the other, using nanoindentation. The results are explained using a stress-strain model, which reveals a uniaxial yield stress of 4.1- 4.6 GPa and predicts a similar dependence of yield stress on loads for both fully-elastic and fully-plastic solutions. Following R. Hill’s model of an expanding cavity under internal pressure, we show that the indentation response of the high-aspect ratio “pillar” geometry can be expressed in terms of uniaxial yield stress rather than material hardness.
We characterize “blisters”, defects observed in multilayer dielectric (MLD) coatings after exposure to acid cleaning procedures. Nanoindentation is used to make site-specific indentations across blisters to measure the mechanical response, especially their compliance under different conditions of loading. Two regions of statistically different mechanical response are identified within a blister defect and compared to the undisturbed regions of the MLD coating. The indentation response of blisters can vary across samples, and we suggest reasons for this variation.
Nanoindentation tests and finite element analysis that considers elastic-mesoplastic deformation for single crystals were used to investigate the mechanical properties of CaF2 under spherical indentation. The goal was to gain a better understanding of microfractures and crystalline anisotropy and their effect on the surface quality of CaF2 during manufacturing. In this analysis, indentations of the three main crystallographic planes (100), (110), and (111) were studied and compared to examine the effects of crystalline anisotropy on the load–displacement curves, surface profiles, contact radius, spherical hardness, stress distributions, and cleavage at two stages, namely at the maximum indentation load and after the load had been removed. Our model results were compared with experimental observation of surface microroughness, subsurface damage, and material removal rate in grinding of CaF2.
Thermal conductivity measurements were performed on several amorphous rare earth transition metal thin films of varying microstructure. The thermal conductivity perpendicular to the plane of the film, measured by the thermal comparator method, was compared with the thermal conductivity value measured parallel to the plane of the film. The latter value was obtained by converting electrical conductivity values to thermal conductivity via the Wiedemann–Franz relationship. As expected, the columnar microstructure induced during the sputter deposition of the thin films causes an anisotropy in the thermal conductivity values, with the in-plane values consistently lower than the out-of-plane values. The effect is most pronounced for the more columnar films deposited at higher pressure, for which the in-plane thermal conductivity, 0.3 W/mK, is an order of magnitude lower than the out-of-plane thermal conductivity, 4.3 W/mK. The thermal conductivity out of the plane of the film decreased with increasing deposition pressure, due to the decreasing film density.
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