科研之友
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摘要
High quality single crystalline PbTe thin films have been grown on BaF2 (1 1 1) by using molecular beam epitaxy ( MBE) Raman scattering measurements have revealed the vibration modes of oxide on the surface, longitudinal optical(LO) phonon at Brillouin center q approximate to 0, and coupled plasmon-phonon. With the variation of the focusing-depth(FD) of the pumping laser beam, the integrated intensities, peak positions and line widths of the observed Raman peaks showed different behaviors. When FD changed I from 3 mu m above the top-surface to 3 mu m below the bottom-surface, the PbTe LO phonon frequency shifted from 119 to 124 cm(-1). Different Raman scattering results were also observed by comparison of the freshly surface-etched and the as grown PbTe samples. These phenomena originated from the different vibration modes. The frequency shift of LO phonon is explained by the fact that the strain relaxation caused by the lattice mismatch between PbTe and BaF2 is as high as 4.2%.
