In situ micromechanical testing inside the scanning electron microscope at subambient temperatures

In material science, the measurement of mechanical material properties as a function of temperature is of great interest, as it allows determining the activation parameters of the underlying deformation mechanism. In the case of nanostructured materials or MEMS devices, it is interesting to probe local properties by means of micromechanical experiments. However, in the case of nanograined metals, testing at elevated temperatures is not possible due to heat induced grain growth and thus changes in the microstructure during testing. We developed a device that allows performing micromechanical tests at low temperatures down to -150°C inside a scanning electron microscope. A cold finger connected to the sample and tip holders by copper braids is cooled by circulating nitrogen. Independent thermal management of the indenter and the sample allows minimizing temperature differences and thereby drift. Local cooling, thermal isolation of the cold regions, and a closed loop frame temperature control reduce frame drift, noise, and the need for a temperature-dependent calibration. A symmetric design of the cooling bodies was chosen in order to minimize bending moments on the indenter and the sample, which increases the accuracy of the measurements. The high vacuum environment minimizes condensation of water vapor and hydrocarbons on the indenter and sample. Positioning as well as in situ observation is made possible by the use inside a scanning electron microscope. For validation of the system, indentations in Cu were performed down to -150°C. Please click Additional Files below to see the full abstract