Small Scale Thermomechanics in Si with an Account of Surface Stress Measurements

Abstract

Multiscale experiments and models have repeatedly shown that thermal and mechanical properties of materials are a strong function of the length scale of measurement. This work uses a newly established nanomechanical Raman spectroscopy approach to analyze creep deformation of microscale Si cantilevers as a function of temperature and mechanical strain. This research reports in-situ creep properties of silicon micro-cantilevers in this temperature range under uniaxial compressive stress. The experimental setup consists of micro-scale mechanical loading platform and localized heating module. The results reveal that in the stress range of 50–150 MPa, the strain rate of the silicon cantilever increases linearly as a function of applied stress. The strain rate also increases a function of temperature increase. However, the strain rate increase slows down with increase in temperature. The strain rate of the microscale silicon cantilever (0.2–2.5 × 10⁻⁶ s⁻¹) was comparable to literature values for bulk silicon reported in temperature range 1100–1300 °C but with only one tenth of the applied stress level. The relaxation of the near-surface atoms also contributes to the creep of the material. Analyses are also used to establish a surface stress relation in one dimensional nanostructures subjected to mechanical loading at high temperatures.