Following the proposal by Miiller, Berlinger and Tosatti on a possible coherent quantum regime in SrTiOs below 40K we have performed elastic measurements to look for possible related anomalies in a near-monodomain crystal. The known anomalies related to the 105 K structural transition were well reproduced. In addition, distinct anomalies were observed below 40 K, both in internal friction and in elastic compliance. The anomalies cannot be explained by phonon interaction with the soft TO mode. A different kind of excitation seems to be required.The features found bear some qualitative resemblance to what is observed in the superfluid phase of 4He.
The self-organised conical needles produced by plasma etching of silicon (Si), known as black silicon (b-Si), create a form-birefringent surface texture when etching of Si orientated at angles of θ i < 50 − 70°(angle between the Si surface and vertical plasma E-field). The height of the needles in the form-birefringent region following 15 min etching was d ∼ 200 nm and had a 100 µm width of the optical retardance/birefringence, characterised using polariscopy. The height of the b-Si needles corresponds closely to the skin-depth of Si ∼λ/4 for the visible spectral range. Reflection-type polariscope with a voltage-controlled liquid-crystal retarder is proposed to directly measure the retardance ∆n × d/λ ≈ 0.15 of the region with tilted b-Si needles. The quantified form birefringence of ∆n = −0.45 over λ = 400 − 700 nm spectral window was obtained. Such high values of ∆n at visible wavelengths can only be observed in the most birefringence calcite or barium borate as well as in liquid crystals. The replication of b-Si into Ni-shim with high fidelity was also demonstrated and can be used for imprinting of the b-Si nanopattern into other materials.
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