Possible Operation of Periodically Layered Nanocrystalline Porous Silicon as an Acoustic Band Crystal Device

Abstract

It is shown that the periodic stacked structures of nanocrystalline porous silicon (nc-PS) layers with controlled densities and elastic properties act as an acoustic band crystal (ABC) device. Supposing that the periodic nc-PS layers are formed by conventional modulated anodization technique to fabricate the multi-layered distributed Brag reflection mirror, the acoustic wave propagation modes are investigated theoretically for various structural parameters. According to the calculation results, a significant acoustic band gaps are generated in the ultrasonic regions due to a big contrast in the elastic constant produced between low-porosity and compact nc-PS layers. The propagation of acoustic wave can be completely suppressed in the characteristic band determined from designed parameters. The present result suggests further possibility of the nc-PS layer as a key component of ABC devices.

Off-axis phonon and photon propagation in porous silicon superlattices studied by Brillouin spectroscopy and optical reflectance

“…Due to the porosity dependence of the sound velocities V j (either longitudinal (L) or transverse (T)) and mass densities q j , the resulting structure has a periodicity in the elastic impedance and the corresponding dispersion relation is again mathematically similar to that of the Kronig-Penney model. 1,2,8 It is assumed that V 2 > V 1 and q 2 > q 1 . In the case that the elastic impedances are approximately the same or, more specifically, V 2 % V 1 and q 2 % q 1 , the phonon dispersion relation can be approximated as 33,34…”

“…Multilayered mesoporous silicon films with a spatial modulation in the porosity, and hence in the elastic impedance, exhibit rich acoustic phonon band structures. [1][2][3][4][5][6][7][8][9][10] The resulting bulk acoustic dispersion curves contain multiple zone-folded branches which may be accompanied by the appearance of forbidden phonon frequency bands, or in analogy to photonic crystals, phononic band gaps. Recent ultrasonic measurements along the modulation direction of films with square-wave, 4,7 sinusoidal, 5 and linearly graded modulation 10 variations in the porosity have reported the existence of one-dimensional phononic band gaps in the bulk longitudinal acoustic phonon band structure; these band gaps were centered at frequencies on the order of 1 GHz.…”

Localization of acoustic modes in periodic porous silicon structures

“…PS is known as a versatile material with applications in light emission, sensing, and photonic devices [ 18 ]. The possibility of producing acoustic band gaps in PS was proposed in 2005 [ 19 ], and detailed calculations of predicted bandwidths were subsequently published [ 20 ]. Recently, experimental results of Brillouin light scattering suggested the existence of zone-folded phonons and phononic band gaps in PS multilayers [ 21 ].…”

Silicon Nanocrystals in Porous Silicon and Applications

“…Only two reports exist in the literature. In the first one, the band structure of a simple acoustic multilayer reflector was calculated [248]. The influence of porosity and velocity contrast was studied.…”