Nanoindentation pop-in effects of Bi2Te3 thermoelectric thin films

• Bi2Te3 films are deposited on c-plane sapphire substrates using PLD.
• The mechanical properties of Bi2Te3 films are measured by nanoindentation.
• The dislocation loops in Bi2Te3 films is estimated by classical dislocation theory.

The structural, surface morphological and nanomechanical characteristics of Bi2Te3 thin films are investigated by means of X-ray diffraction (XRD), atomic force microscopy (AFM) and nanoindentation techniques. The Bi2Te3 thin films are deposited on c-plane sapphire substrates using pulsed laser deposition (PLD). The XRD result showed that Bi2Te3 thin film had a c-axis preferred orientation and a smoother surface feature from AFM observation. Nanoindentation results exhibit the discontinuities (so-called multiple “pop-ins” event) in the loading segments of the load–displacement curves, indicative of the deformation behavior in the hexagonal-structured Bi2Te3 thin film is the nucleation and propagation of dislocations. Based on this scenario, an energetic estimation of nanoindentation-induced dislocation resulted from pop-in effects is made. Furthermore, the hardness and Young’s modulus of Bi2Te3 thin films were measured by a Berkovich nanoindenter operated with the continuous contact stiffness measurements (CSM) mode. The obtained values of the hardness and Young’s modulus are 5.7 ± 0.8 GPa and 158.6 ± 6.2 GPa, respectively.