Phonon polaritons in thin films and microcrystals of MnO

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Abstract
The infrared spectra of the MnO bulk, thin-film and microcrystal specimens are measured at room temperature by reflection and transmission methods. The reststrahlen reflectivity spectrum of MnO bulk crystal is analysed by means of a two-damped-oscillator dispersion model and the lattice vibrational properties of MnO are discussed. The virtual mode spectra of MnO thin film are analysed by means of the virtual mode theory of the anharmonic ionic crystal slab and the upper branch of the polariton dispersion curve of MnO at room temperature is determined experimentally for the first time. The extinction spectrum of MnO microcrystals is discussed in the light of the theory for the surface phonon polaritons in ionic microcrystals. The effects of the microcrystal-substrate interaction and the aggregation of microcrystals are also discussed.