We report the observation of oscillating features in differential reflectance spectra from the GaAs epilayer grown on Si substrate in the energy range both below and above the fundamental band gap. It is demonstrated that the oscillating features are due to the difference in the interference between two neighboring areas of the sample. The interference arises from two light beams reflected from different interfaces of the sample. The calculated spectra in the nonabsorption region are in good agreement with measured data. It is shown that the interference effect can be used as a sensitive method to characterize the inhomogeneity of the semiconductor heterostructures.
More detailed absorption transitions of C60 in the visible region are observed from the third-order derivative absorption spectra.The spectra are fitted with Lorentzian line shapes,and the transition energies are determined.The assignment of the transitions in visible region is discussed,some vibronic modes are given,and finally the energy gap of C60 molecule is determined.
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