Four-point bend apparatus for in situ micro-Raman stress measurements

A device for in situ use with a micro-Raman microscope to determine stress from the Raman peak position was designed and validated. The device is a four-point bend machine with a micro-stepping motor and load cell, allowing for fine movement and accurate readings of the applied force. The machine has a small footprint and easily fits on most optical microscope stages. The results obtained from silicon are in good agreement with published literature values for the linear relationship between stress and peak position for the 520.8 cm(-1) Raman peak. The device was used to examine 4H-SiC and a good linear relationship was found between the 798 cm(-1) Raman peak position and stress, with the proportionality coefficient being close to the theoretical value of 0.0025. The 777 cm(-1) Raman peak also showed a linear dependence on stress, but the dependence was not as strong. The device examines both the tensile and compressive sides of the beam in bending, granting the potential for many materials and crystal orientations to be examined.