William Angerer - Department of Physics and Astronomy - University ...

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6.1 Nonlinear Optical Spectroscopy as a Probe of Condensed Matter
Systems
Nonlinear optical spectroscopy is a unique probe of condensed matter systems as a
result of its sensitivity to surfaces and interfaces, its long penetra.tion depth. and its
non-destructive nature. One application of nonlinear optical spectroscopy has been
the investigation of the symmetry and structure of surfaces and interfaces. This includes
the determination of the bonding angle of a molecule to a surface [6], the
measurement of the pretilt angle of a liquid crystal [9], the observation of Angstrom
scale roughness at the Si(100)/Si0 2 interface [97], and the observation ofSi-O bonding
arrangements at kinks on vicinal Si(l11) surfaces [98]. Nonlinear optical spectroscopy
has also been used to measure electronic properties at the interfaces between solid
materials. Examples of these investigations include the spectral identification of antisite
defects in Au/GaAs [10], the measurement of new bonding states at the CaF 2/Si
interface [3], the observation of an interface quantum well state in ZnSejGaAs [2].
and the observation of a strain induced two photon resonances from Si-Si0 2 interfaces
[4]. Our nonlinear optical investigations reveal both structural and electronic features
of bulk GaN thin films. In addition, we did not observe any strain induced interface
states by second-harmonic rotational symmetry measurements.
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