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Molecular beam epitaxy (MBE) grown AlN thin layer on sapphire substrates have been implanted with Cr+ ions for various dose from 1013 to 1015 cm−2. The analyses were carried out by an X-ray diffractometer (XRD), Raman spectroscopy, a spectrophotometer and spectroscopic ellipsometry (SE) for structural and optical analyses. E2(high) and A1(LO) Raman modes of AlN layer have been observed and analyzed. The behavior of Raman shift and the variation in intensity and in peak width of Raman modes as a function of ions flux are explained on the basis of chromium substituting aluminum atom and implantation-induced lattice damage. Both Raman and X-ray analyses reveal that the incorporation of chromium atoms increases in the host lattice with the increasing of Cr ions fluence. The band gap energy was determined by using transmission spectra. It was found that the band gap energy decreases as the ion dose increases. The band gap of the unimplanted AlN is 6.02 eV and it decreases down to 5.92 eV for the Cr+-implanted AlN with a ion dose of 1×1015 cm−2. Optical properties such as optical constants of the samples were examined by using a spectroscopic ellipsometer. It was observed that the refractive index (n) decreases with the increasing of ion dose. 相似文献
244.
Abstract This article gives a new reflective filter that consists of material with the continuous periodic change of refractive index obtained by applying the ultrasonic wave generated by an attached ultrasonic generator. Using the characteristic matrix of a thin film, a method to calculate the reflectance of this coating and analyze its optics performance is given. Computer simulations show the very high peak reflectance and very narrow band gap of reflectance spectrum. It is also found that the reflectance spectrum is different at different acoustic pressures and wave numbers. This reflectance spectrum can be easily modulated by changing the acoustic pressure and wave number. 相似文献
245.
R.J. Grant C.G. Johnson D.H. Wilkinson 《International Journal of Heat and Fluid Flow》1983,4(4):239-245
A single stage model turbine has been provided with a set of three special inlet sections which include backward facing steps to produce casing separations of varying size upstream of the stator blades. In addition each inlet section is equipped so as tc be able to emit a swirling jet which simulates the tip leakage jet from a preceeding stage. It is demonstrated that there is a substantial efficiency penalty associated with the stepped casing and its attendant separation and that a small mitigation is brought about by the tip leakage jet, by re-energising the fluid in the separation zone 相似文献
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本文将光子晶体的概念应用于土层结构设计,并利用传输矩阵法计算了p波在土层结构中的传播特性。结果表明,这种土层结构可以全部反射特定频率范围内入射的p波,从而可以减少p波对地上建筑的破坏。此外,还考察了土层的物理特性对反射频带的影响。 相似文献
248.
Zhengqiang Zhan Peijun Wei 《Acta Mechanica Solida Sinica》2010,23(2):181-188
Band gaps of 2D phononic crystal with orthotropic cylindrical fillers embedded in the isotropic host are studied in this paper. Two kinds of periodic structures, namely, the square lattice and the triangle lattice, are considered. For anisotropic phononic crystal, band gaps not only depend on the periodic lattice but also the angle between the symmetry axis of orthotropic material and that of the periodic structure. Rotating these cylindrical fillers makes the angle changing continuously; as a result, pass bands and forbidden bands of the phononic crystal are changed. The plane wave expansion method is used to reduce the band gap problem to an eigenvalue problem. The numerical example is given for YBCO/Epoxy composites. The location and the width of band gaps are estimated for different rotating angles. The influence of anisotropy on band gaps is discussed based on numerical results. 相似文献
249.
《Wave Motion》2016
Numerical procedure based on plane wave expansion and stiffness matrix method is developed to calculate the transmission factor of a micro two-dimensional phononic plate. Calculations of the dispersion curve have been achieved by introducing particular functions which transform motion equations into an eigenvalue problem. The state vector has been generalized to a phononic material, it leads to a comparatively convenient matrix formulation. The influence of the layer number on the transmission factor is studied. In addition, our interest is focused on the observed gap and how it behaves when phononic structure undergoes a slight change. The result shows that if the central phononic layer is replaced by one or two homogeneous layers, guided modes originate inside the frequency band gaps. 相似文献
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