Strain mechanism of LiNbO3/sapphire heterostructures grown by pulsed laser deposition

Thin LiNbO3 films are deposited on (001) sapphire substrates by a pulsed laser deposition technique. The epitaxial growth of the films is confirmed by high-resolution X-ray diffraction action (HRXRD) and high-resolution transmission electron microscopy (TER I) analyses. The lattice parameters and thermal expansion coefficients of the films are determined by an XRD technique. The deposited films are strained at room temperature; that is, the a-axis is longer and the c-axis is shorter than those of LiNbO3 single crystals. On the contrary, the films are not strained at the deposition temperature of 735 degrees C, The strain of the films is caused by the large differences in the thermal expansion coefficients between LiNbO3 and sapphire substrates.