THE ELASTIC BEHAVIOR OF FINITE-STAGE QUASI-PERIODIC FIBONACCI A-SI-H A-SI1-XCXH MULTILAYERS/

The Brillouin light scattering technique has been exploited in order t o study the elastic properties of finite-stage a-Si:H/a-Si1-xCx:H semi conductor quasiperiodic Fibonacci multilayers, deposited by plasma enh anced chemical vapour deposition on crystalline silicon, fused quartz and coming glass substrates. Detection of the Rayleigh surface acousti c mode enabled us to study the evolution of the phase velocity of this mode as the number of Fibonacci stages is increased from eight to twe lve and to evaluate the effective elastic constant c44. The values obt ained in these finite-stage Fibonacci structures are consistent with t hose calculated, by means of the effective modulus model, for an infin ite quasiperiodic structure. In contrast to the anomalous elastic beha viour previously found in metallic superlattices, no elastic anomaly h as been observed in the a-Si:H/a-Si1-xCx:H amorphous semiconductor mul tilayers, in agreement with recent theoretical models, which predict t he presence of elastic anomalies in cases of symmetry difference and l attice mismatch between adjacent crystalline layers. Moreover, a sligh t decrease of the Rayleigh mode velocity has been observed on changing the substrate from c-Si to coming glass or fused quartz.