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(0 01) surface grating with grating wavelength Lambda(G) =0.35 mu m, we h ave observed numerous high-order zone-folded surface acoustic modes be tween the second and third zone boundaries associated with the grating . A surprisingly intense signal from a zone-folded longitudinal resona nce was observed in the absence of direct hybridization with the Rayle igh modes. The relative intensities of all of the modes have been calc ulated by allowing for coupling between modes related by up to two gra ting reciprocal-lattice vectors, and for a grating profile with nonzer o 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 atomi c-force microscopy.