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Observation of hypersonic phononic crystal effects in porous silicon superlattices
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Image of FIG. 1.
FIG. 1.

(a) Cross-sectional scanning electron micrograph of a SL. The bright (dark) regions correspond to layers with a porosity of 0.56 (0.46). (b) Scattering geometry. The wavevectors of the probed phonon and the incident (scattered) light are and , respectively.

Image of FIG. 2.
FIG. 2.

Spectra collected from (a) a 0.59/0.52 superlattice, (b) a 0.59/0.52 superlattice, (c) a 0.59/0.52 superlattice, and (d) a 0.56/0.46 superlattice (smoothed using three-point averaging). The arrow indicates a weak feature that was difficult to fit to a Lorentzian and, hence, has a large uncertainty in frequency shift. This and similar features in other spectra appear in Fig. 3 and are indicated by large frequency-axis error bars.

Image of FIG. 3.
FIG. 3.

Phonon frequency vs modulation wavelength for superlattices with constituent layer porosities of (a) 0.59 and 0.52 and (b) 0.56 and 0.46. Thick (thin) broken lines: calculated curves for the longitudinal (transverse) mode; shaded region: values of for which the probing light is in a photonic bandgap. Arrows mark the approximate values of for which coincides with the edges of the first, second, and third phononic Brillouin zones, respectively. Open symbols: experimental data; diamonds: duplicate sample. The frequency scale on both plots is the same.


Generic image for table
Table I.

Porosity, refractive index, and bulk acoustic phonon velocities for single layer porous silicon films.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Observation of hypersonic phononic crystal effects in porous silicon superlattices