Spectroscopy of Oxide Surface/Interface
With the development of epitaxial growth of oxides, many exciting and unexpected physical phenomena are being discovered at oxides interfaces. However, their physical understanding is hampered by a dearth of characterization tools capable of probing the buried interfaces.
Second-order nonlinear spectroscopy, such as sum-frequency generation, is ideally suited for such study beause bulk contribution from inversion-symmetric materials, such as many oxides, are forbidden due to symmetry requirement. Such nonlinear spectroscopy therefore has unique surface sensitivity although the number of atoms on the surface can be less than one billionth of that in the bulk. Optical spectroscopy also has a distinct advantage in that photon can penerate the materials and probe buried interface, where other wonderful surface techniques, such as scanning tunneling microscopy, will fail.
Fig. 1 shows a schematic diagram of surface sum-frequency generation. We will apply this powerful tool to investigate the electronic structure, vibrations and coupling between charge and lattice at oxide interfaces.