共查询到20条相似文献,搜索用时 15 毫秒
1.
While growing a chiral sculptured thin film by physical vapor deposition, a sudden change in the direction of the vapor flux creates a plane of discontinuity. In effect, this is a planar interface between two different structurally chiral materials. Theoretical analysis shows that more than one Dyakonov-Tamm waves, with different phase speeds and degrees of localization to this interface, may propagate in different directions guided by the interface. 相似文献
2.
Reflectances and transmittances of chiral sculptured thin films (STFs) with gain qualitatively differ from those of lossless and lossy chiral STFs, chiefly at the edges of the Bragg regime, for normally incident plane waves. The difference is explained in terms of the photonic density of states. A chiral STF with a central twist defect exhibits a reflection hole if there is no gain and emits narrowband radiation if there is gain, provided the thickness is not large. This narrowband feature diminishes as the thickness increases, and is replaced by an ultranarrowband transmission hole only if the chiral STF has neither gain nor loss. 相似文献
3.
Akhlesh Lakhtakia 《Optik》2008,119(4):175-179
A tightly interlaced chiral sculptured thin film (STF), whose unit cell comprises one structural period each of two otherwise identical chiral STFs but of opposite structural handedness, exhibits a polarization-universal bandgap on axial excitation. This bandgap lies wholly inside the Bragg regime of either constituent chiral STF. 相似文献
4.
5.
Aerospace structures often contain multi-layered metallic components where hidden defects such as fatigue cracks and localized disbonds can develop, necessitating non-destructive testing. Employing standard wedge transducers, high frequency guided ultrasonic waves that penetrate through the complete thickness were generated in a model structure consisting of two adhesively bonded aluminium plates. Interference occurs between the wave modes during propagation along the structure, resulting in a frequency dependent variation of the energy through the thickness with distance. The wave propagation along the specimen was measured experimentally using a laser interferometer. Good agreement with theoretical predictions and two-dimensional finite element simulations was found. Significant propagation distance with a strong, non-dispersive main wave pulse was achieved. The interaction of the high frequency guided ultrasonic waves with small notches in the aluminium layer facing the sealant and on the bottom surface of the multilayer structure was investigated. Standard pulse-echo measurements were conducted to verify the detection sensitivity and the influence of the stand-off distance predicted from the finite element simulations. The results demonstrated the potential of high frequency guided waves for hidden defect detection at critical and difficult to access locations in aerospace structures from a stand-off distance. 相似文献
6.
7.
8.
Gyrotropic chiral sculptured thin films (STFs) exhibit optical activity due to their structural chirality, local anisotropy, and magneto-optic gyrotropy. We adapted two algorithms for nongyrotopic chiral STFs to investigate the circular-polarization-sensitivity of gyrotropic chiral STFs to incident plane waves. The impacts of gyrotropy and oblique angles of incidence on the reflectances and the transmittances were examined, and several conclusions drawn. In particular, we found that the incorporation of gyrotropy results in a blueshift of the Bragg regime. 相似文献
9.
A theoretical study predicts that surface-plasmon-polariton (SPP) waves may propagate along the interface of a columnar thin film (CTF) and a metal over a range of propagation directions relative to the morphology of the CTF. The range of propagation directions depends on the tilt of the columns in the CTF. The phase speed of the SPP wave varies mainly as a function of the tilt of the CTF columns. Both the confinement of the SPP wave to the interface and the decay of the SPP wave along the direction of propagation depend strongly on the direction of propagation relative to the morphologically significant plane of the CTF. The greater the columnar tilt in relation to the interface, the shorter is the range of propagation. Because of CTF porosity and the ability to engineer this biaxial dielectric material, the CTF–metal interface may be more attractive for sensor applications than the traditional dielectric–metal interface used for SPP-wave-based sensors. 相似文献
10.
本文从实验的角度介绍从薄膜导波传播衰减研究光学薄膜损耗的方法,并以一些低损耗的光学薄膜样品的测量结果说明这种方法对损耗研究的灵敏程度及其优越性. 相似文献
11.
Monte Carlo simulations of biaxial structure in thin hybrid nematic film based upon spatially anisotropic pair potential 下载免费PDF全文
Hybrid nematic films have been studied by Monte Carlo simulations
using a lattice spin model, in which the pair potential is spatially
anisotropic and dependent on elastic constants of liquid crystals.
We confirm in the thin hybrid nematic film the existence of a
biaxially nonbent structure and the structure transition from the
biaxial to the bent-director structure, which is similar to the
result obtained using the Lebwohl--Lasher model. However, the
step-like director's profile, characteristic for the biaxial
structure, is spatially asymmetric in the film because the pair
potential leads to K1 ≠ K3. We estimate the upper cell
thickness to be 69 spin layers, in which the biaxial structure can
be found. 相似文献
12.
本文从理论上分析了光学薄膜中的三种基本缺陷:折射率消光系数、表面粗糙度以及折射率不均匀性对薄膜内导波传播衰减的影响.基于这些缺陷对光学薄膜内不同导模传播衰减作用的不同,提出了一种区分薄膜中的吸收与散射损耗的方法. 相似文献
13.
Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small pore structure and size of porous SiO2 thin film produced by sputtered Al-Si thin film and etched Al-Si thin film. The film is prepared by an Al/Si 75:25 at.-% (A175Si25) target with the radiofrequency (RF) power of 66 W at room temperature. A 5 wt.-% phosphoric acid solution is used to etch the Al cylinders. All the A1 cylinders dissolved in the solution after 15 h at room temperature, and the sample is subsequently rinsed in pure water. In this way, the porous SiO2 on the Si substrate is produced. From our results, the values of all lifetime components in the spectra of Al-Si thin film are less than 1 ns, but the value of one of the lifetime components in the spectra of porous SiO2 thin film is τ = 7.80 ns. With these values of lifetime, RTE (Rectangular Pore Extension) model has been used to analyze the pore size. 相似文献
14.
本文指出了在棱镜耦合状态下降低平板波导基模截止厚度的途径,用文中提出的准对称波导法测量了薄的MgO膜的折射率和厚度,并给出了测量结果. 相似文献
15.
ZHANG Zhe QIN Xiu-Bo WANG Dan-Ni YU Run-Sheng WANG Qiao-Zhan MA Yan-Yun WANG Bao-Yi 《中国物理C(英文版)》2009,33(2)
Positron annihilation lifetime and Doppler broadening of annihilation line techniques have been used to obtain information about the small pore structure and size of porous SiO2 thin film produced by sputtered A1-Si thin film and etched Al-Si thin film. The film is prepared by an Al/Si 75:25 at.-% (A175Si25) target with the radiofrequency (RF) power of 66 W at room temperature. A 5 wt.-% phosphoric acid solution is used to etch the A1 cylinders. All the Al cylinders dissolved in the solution after 15 h at room temperature, and the sample is subsequently rinsed in pure water. In this way, the porous SiO2 on the Si substrate is produced. From our results, the values of all lifetime components in the spectra of Al-Si thin film are less than 1 ns, but the value of one of the lifetime components in the spectra of porous SiO2 thin film is T = 7.80 ns. With these values of lifetime, RTE (Rectangular Pore Extension) model has been used to analyze the pore size. 相似文献
16.
17.
基于非平衡格林函数及密度泛函理论第一性原理计算方法,计算了Fe, Al, V和Cu四种阳离子掺杂对氧空位缺陷引起的PbTiO_3铁电薄膜漏电流的调控.研究表明:Fe和Al离子掺杂将会增大由其中氧空位缺陷导致的铁电薄膜的漏电流,而Cu和V离子掺杂对该漏电流的大小具有明显抑制作用.这是因为Cu和V掺杂对氧空位缺陷有明显的钉扎作用.相比于半径更大的Cu离子,由于V的离子半径更小,且更接近于PbTiO_3铁电薄膜中Ti的离子半径,可以预言V离子更可能被掺杂进入薄膜,从而抑制氧空位缺陷引起的漏电流.研究结果对铁电薄膜器件的电学性能控制和优化有一定的理论指导意义. 相似文献
18.
Epitaxy surface effect on the first-order phase transition properties in a ferroelectric thin film 下载免费PDF全文
By modifying the interchange interactions and the transverse fields on the epitaxy surface layer,this paper studies the phase transition properties of an n-layer ferroelectric thin film by the Fermi-type Green’s function technique based on the transverse Ising model with a four-spin interaction.The special attention is given to the effect of the epitaxy surface layer on the first-order phase transition properties in the parameter space constructed by the ratios of the bulk transverse field and the bulk four-spin interaction to the bulk two-spin interaction with the framework of the higher-order decoupling approximation to the Fermi-type Green’s function.The results show that the first-order phase transition properties will be changed significantly due to the modification of interchange interaction and transverse field parameters on the epitaxy surface layer.The dependence of the first-order phase transition properties on the thickness of ferroelectric thin films is also discussed. 相似文献
19.
Muhammad Faryad 《Optics Communications》2011,284(24):5678-5687
The excitation of multiple surface-plasmon-polariton (SPP) waves—of different linear polarization states, phase speeds and spatial profiles—guided by the interface of a metal film and a rugate filter in the Kretschmann configuration was investigated. A plane wave of either of the two linear polarization states was made incident on the metal-capped rugate filter of finite thickness and the absorptances were calculated using a stable algorithm. The excitation of SPP waves was inferred by the presence of those peaks in the absorptance curves that were independent of the thickness of the rugate filter. The absorptance peaks representing the excitation of s-polarized SPP waves are narrower than those representing p-polarized SPP waves. For efficient excitation of multiple SPP waves, the metal film's thickness should be close to the penetration depth of the metal. The solution of a canonical boundary-value problem of SPP-wave propagation guided by a metal film, with a semi-infinite homogeneous dielectric material on one side and a semi-infinite rugate filter on the other side, reinforced the results obtained for the Kretschmann configuration. The thin metal film in the Kretschmann configuration may lead to coupling of its two interfaces. 相似文献
20.
Thin film solar cells have the potential to significantly reduce the cost of photovoltaics. Light trapping is crucial to such a thin film silicon solar cell because of a low absorption coefficient due to its indirect band gap. In this paper, we investigate the suitability of surface plasmon resonance Ag nanoparticles for enhancing optical absorption in the thin film solar cell. For evaluating the transmittance capability of Ag nanoparticles and the conventional antireflection film, an enhanced transmittance factor is introduced. We find that under the solar spectrum AM1.5, the transmittance of Ag nanoparticles with radius over 160 nm is equivalent to that of conventional textured antireflection film, and its effect is better than that of the planar antireflection film. The influence of the surrounding medium is also discussed. 相似文献