LIGHT-SCATTERING OBSERVATION OF SURFACE ACOUSTIC MODES IN HIGH-ORDER BRILLOUIN ZONES OF A SI(001) GRATING

In Brillouin light-scattering (BLS) measurements of an ion-milled Si(001) surface grating with grating wavelength Lambda(G) =0.35 mu m, we have observed numerous high-order zone-folded surface acoustic modes between the second and third zone boundaries associated with the grating. A surprisingly intense signal from a zone-folded longitudinal resonance was observed in the absence of direct hybridization with the Rayleigh modes. The relative intensities of all of the modes have been calculated by allowing for coupling between modes related by up to two grating reciprocal-lattice vectors, and for a grating profile with nonzero first and second Fourier amplitudes. The Fourier amplitudes inferred from the BLS measurements and calculations agree very well with those obtained from a direct measurement of the grating profile using atomic-force microscopy.