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ZnO thin film has been epitaxially grown on the (111) plane of the diamond substrate by rf magnetron sputtering at substrate temperature as low as 260 °C. The crystallinity was examined by x-ray diffraction and reflection high-energy electron diffraction. It was found that the smallest standard deviation angle estimated from the x-ray rocking curve of the ZnO(0002) peak was 0.27° whereas the mismatch of the lattice parameter between film and substrate is 28.8%. The epitaxial relationship between ZnO film and the diamond is determined as [112̄0] ZnO//[1̄01] diamond.

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Research and development have been carried out to apply the CVD diamond film to surface acoustic wave (SAW) devices. Several kinds of layered structures including a diamond layer have been investigated by the calculations and experiments, and it has been found that the diamond SAW has great advantages for the application of high-frequency SAW devices with high SAW velocity, small temperature coefficient and high power durability. Practical SAW devices have been successfully fabricated with ZnO/diamond/Si and SiO 2 /ZnO/diamond/Si structures whose characteristics are superior to those with conventional SAW materials.

In the slow-roll inflationary scenario, the amplitude of the curvature perturbations approaches a constant value soon after the modes leave the Hubble radius. However, relatively recently, it was shown that the amplitude of the curvature perturbations induced by the canonical scalar field can grow at super-Hubble scales if there is either a transition to fast roll inflation or if inflation is interrupted for some period of time. In this work, we extend the earlier analysis to the case of a non-canonical scalar field described by the Dirac-Born-Infeld action. With the help of a specific example, we show that the amplitude of the tachyonic perturbations can be enhanced or suppressed at super-Hubble scales if there is a transition from slow roll to fast roll inflation. We also illustrate as to how the growth of the entropy perturbations during the fast roll regime proves to be responsible for the change in the amplitude of the curvature perturbations at super-Hubble scales. Furthermore, following the earlier analysis for the canonical scalar field, we show that the power spectrum evaluated in the long wavelength approximation matches the exact power spectrum obtained numerically very well. Finally, we briefly comment on an application of this phenomenon.