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1.
The effect of the spatial structure of an interface in multilayer metallic films on the spectrum of x-ray specular scattering
is studied. Two types of interface structural defects are considered. One type is steps resulting in a variable layer thickness,
and the other is the mixing of unlike metal atoms during epitaxial growth. These defects are shown to have different effects
on the specular-scattering spectra. The mixing significantly decreases the Bragg-peak height, especially the height of higher
order peaks. The interface roughness results in broadening of the Bragg peaks and in the disappearance of intermediate peaks
between them. 相似文献
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Ba(0.9)Sr(0.1)TiO(3) (BST)-based and PbZr(0.4)Ti(0.6)O(3)-based quasi-periodic multilayers consisting of dense and porous ferroelectric layers have been fabricated by solgel technique using chemical solutions containing polyethylene glycol (PEG) or polyvinylpyrrolidone k30 (PVP). All multilayers exhibit good performance as dielectric mirrors. For each multilayer, the maximum peak reflectivity is over 90% and the photonic stopband width is no less than 30 nm at room temperature. The reflection-band position can be easily tuned by varying the thickness of the bilayer. With the same processing conditions and number of periods, the Bragg reflection performance is almost the same for quasi-periodic PZT multilayers derived from two precursors containing different polymers. The BST multilayers deposited by using a PVP-containing precursor are superior in optical properties, including peak reflectivities and stop-band width, to those deposited by using the PEG-containing solution. 相似文献
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A. Aschentrup W. Hachmann T. Westerwalbesloh Y.C. Lim U. Kleineberg U. Heinzmann 《Applied Physics A: Materials Science & Processing》2003,77(5):607-611
We present a method of deriving single layer thickness fluctuations of Mo/Si EUV multilayers from cross-sectional high-resolution transmission electron microscopy micrographs. The obtained thickness values for each layer are used in a layer model to calculate the grazing-incidence X-ray reflectivity (GIXRR) and the corresponding at-wavelength-reflectivity curves. Comparison with XRR measurements shows the strong effect of thickness fluctuations on the intensity of the secondary Kiessig fringes and the main Bragg maxima. This model results in substantially better reflectivity simulations than the standard periodic four-layer model or the assumption of statistically distributed (random) thickness errors. Results for reflectivity curves at 13-nm wavelength are discussed in terms of peak reflectivity, peak shift and further changes in the shape of the reflectivity curve. PACS 68.65.Ac; 68.37.Lp; 41.50.+h 相似文献
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We present studies on the optical properties of periodic metallic-dielectric (MD) multilayers and numerical results show that there exists, insensitive to the lattice scaling, a transparent band as long as the layer thickness is in the subwavelength ranging. It illustrates the transparent band is controlled by mechanisms beyond the Bragg scattering: the shorter-wavelength band edge comes from the intensive resonant absorption behavior of the metals, while the longer-wavelength band edge is determined by zero (volume) averaged permittivity εeff=0. Moreover, a Lorentz-Drude model for the permittivity of a ε-negative (ENG) metamaterial is used to show that a transparent band may be obtained in a subwavelength structure consisting of ENG multilayers with total length less than both the center wavelength and the half width of the band. 相似文献
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垂直腔面发射激光器中顶层相位对模式特性的影响 总被引:4,自引:1,他引:3
研究了垂直腔面发射激光器中不同的顶层厚度对激光器模式特性的影响。结果表明空气界面反射与分布布拉格反射器(DBR)的反射率反相时,将导致阈值增益增加几倍,而且模式光场强度在出射端面有反常的增强,但对光场进入分布布拉格反射器的等效厚度影响不大。精确腐蚀顶层厚度可供替调节分布布拉格反射器周期数,以改善器件特性。 相似文献
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J.H. Yang N.N. Yang Y.M. Zhang Y. Liu M.B. Wei Y.T. Yang R. Wang S.Y. Yang 《Solid State Communications》2011,151(20):1428-1432
[Co/Pt]n multilayers with different Co thickness have been deposited on a silicon (Si) substrate to obtain better perpendicular anisotropy. The 0.5 nm thickness of the Co layer was chosen as the optimized thickness of the multilayer. Magnetic nanostructures with cap configuration were fabricated based on the template of polystyrene (PS) colloid sphere arrays with various curvature radius. Compared to the flat multilayer, the cap multilayer showed an oblique average anisotropy axis. When the curvature radius of the colloidal sphere increased, the shape of the multilayers changed from ellipsoidal to spherical, which led to a different dependence of magnetic properties on the field angles. The varying shape anisotropy, the dipole-dipole interaction between small magnetic caps, and the special nucleation mechanism on the spheres larger than 400 nm caused the Mr/Ms ratio and the coercivity to first increase and then decrease with varying curvature radius of the PS spheres. 相似文献
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Diffuse reflectance or optical scattering in thin films and multilayers can pose serious limiting factors to their desired or ultimate performances. Besides, such studies provide valuable information related to the buried microstructures and interfaces. Synchrotron radiation is the most appropriate source to record wavelength dependent polarized light scattering in thin films and multilayers. In the present experiment several gadolinia, silica thin films and multilayers were studied for their light scattering using the white light synchrotron beam. Various thin film layer geometries were selected to probe the results due to different types and combinations of interfaces. Due to phase coherent delay in certain optical non-wedged component used in the experimental setup very interesting spectral interference were noticed as the modulations in the diffuse reflectance signal. Appropriate modeling approach utilizing Gaussian function de-convolution technique is used to compute the pulse delay between the back reflected and forward propagating scattering signals that lead to such spectral interference. Alternatively inverse fast Fourier transform (IFFT) and analytical techniques were adopted to determine the group delays. The diffuse reflectance spectra were finally compared with their specular counter part and a shift both in the wavelength and phase were noticed. This may be explained on the basis of thin film roughness factors, different polarizations and incident geometries used in the measurements. However, all most all the spectral scattering signals exhibited the features resembling their specular reflection characteristic. 相似文献
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Saibal Basu 《Pramana》2008,71(4):777-784
A polarized neutron reflectometer for vertical samples is available at Dhruva reactor guide hall, Trombay. The reflectometer
has been designed for horizontal scattering vector. It uses a position-sensitive detector for obtaining the reflectivity pattern.
This arrangement allows one to obtain diffuse or off-specular intensity around any specular peak at one go. We have used this
instrument for studying the structure of various metal-metal and metal-semiconductor multilayers by specular reflectometry.
We have also been successful in understanding interface morphology of several films through diffuse neutron reflectometry
(DNR) on this reflectometer. Some of the recent results are presented in this paper to demonstrate the strength of these two
techniques.
相似文献
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《Current Applied Physics》2009,9(4):852-855
A new approach to obtain a spread-out Bragg peak (SOBP) using the MINUIT fit is presented. The SOBP has been adopted in proton therapy in order to irradiate a proton beam equally over the tumor along the beam direction. In principle, an SOBP can be easily obtained by using several Bragg peaks from different beam energies, since the position of the peak varies with the energy. However, this is not practical in real medical situations, because the beam energy is fixed by the accelerator. Thus, a modulation method has been employed to obtain an SOBP, where the position of Bragg peak is controlled by a modulator with varying thickness. In this study, we use the GEANT4 package to simulate a generic proton therapy apparatus. A modulator with thickness control is assumed in the proton therapy setup and a set of Bragg peaks is obtained from the GEANT4 simulation. Assuming that the position and the size of the tumor are known, we first determine which Bragg peaks should be used in the fit. Then a MINUIT fit is applied to calculate the weights of each Bragg peak in order to maximize the flatness of the SOBP while minimizing the dose in the normal tissue area, thus maximizing the dose in the tumor. The fit has turned out to be very robust and converges quickly. Since the MINUIT is a small size library and the proposed SOBP fit shows stable behavior, this method can be readily applied to the real therapy. 相似文献
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Grazing X-ray reflectometry is used in order to characterize thin layer stacks, in particular periodic multilayers. The specular reflectivity depends on the thickness, the complex refractive index of each layer and on the roughness of the interfaces. By a trial and error method, the experimental reflectivity curve can be fitted with a theoretical one, and so, the parameters of the stack can be obtained. This numerical method needs usually initial guess of the kind of results.Fourier transform method allows to obtain directly the values of distances between interfaces, with a good approximation depending on the maximum angular scan of the measure. It can also reveal some particularity of the multilayer, i.e. periodic multilayered structures with more than two layers per period. As an illustration of this characterization method, some examples in XUV optical domain will be shown. This method can also be used for the characterization of many kinds of multilayer stacks, in particular semi-conductor heterostructures ones, under the condition that adjacent layers have sufficient contrast index at the wavelength of the X-ray source. 相似文献
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Development of design guides to estimate the difference in speech interference level due to road traffic noise between a reference position and balcony position or façade position is explored. A previously established and validated theoretical model incorporating direct, specular and diffuse reflection paths is used to create a database of results across a large number of scenarios. Nine balcony types with variable acoustic treatments are assessed to provide acoustic design guidance on optimised selection of balcony acoustic treatments based on location and street type. In total, the results database contains 9720 scenarios on which multivariate linear regression is conducted in order to derive an appropriate design guide equation. The best fit regression derived is a multivariable linear equation including modified exponential equations on each of nine deciding variables, (1) diffraction path difference, (2) ratio of total specular energy to direct energy, (3) distance loss between reference position and receiver position, (4) distance from source to balcony façade, (5) height of balcony floor above street, (6) balcony depth, (7) height of opposite buildings, (8) diffusion coefficient of buildings and (9) balcony average absorption. Overall, the regression correlation coefficient, R2, is 0.89 with 95% confidence standard error of ±3.4 dB. 相似文献
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《Superlattices and Microstructures》1994,15(4):483-487
Optical properties of periodic amorphous semicondctor multilayers can be understood by the effective medium treatment. Once the randomness is introduced to amorphous semiconductor multilayers, two effects of the randomness on the optical spectra are observed. One is a distortion of the interference patterns in transmittance and reflectance spectra. The other is the appearance of a randomness-related anomalous peak in the reflectance spectrum whose height increases with the randomness in the thickness of the well or the barrier layers. These effects are studied experimentally and by the simulation, and explained by the classical localization of the light propagation. The prospects for the application of the random multilayers studied in this work are discussed briefly. 相似文献
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运用遗传算法优化设计了Mo/B4C多层膜结构。入射光入射角度取10°时,设计的理想多层膜膜对数为150,周期为3.59 nm,Gamma值(Mo膜厚与周期的比值)为0.41,峰值反射率为33.29%。采用恒功率模式直流磁控溅射方法制作Mo/B4C多层膜。通过在Mo/B4C多层膜与基底之间增加15 nm厚的Cr粘附层,提高多层膜与基底的粘附力。另外,还采用调整多层膜Gamma值的方法减小其内应力,调整后多层膜结构周期为3.59 nm, Mo膜厚1.97 nm, B4C膜厚1.62 nm,峰值反射率26.34%。制备了膜对数为150的Mo/B4C膜并测量了其反射率,在波长7.03 nm处,Mo/B4C多层膜的近正入射反射率为21.0%。最后对测量结果进行了拟合,拟合得到Mo/B4C多层膜的周期为3.60 nm,Gamma值0.60,界面粗糙度为0.30 nm。 相似文献
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Time-resolved X-ray scattering was employed to in-situ monitor the epitaxial growth process of the thin films and multilayers of EuTiO3 and SrTiO3 during pulsed laser deposition. The temporal intensity oscillations of the reflected X-rays at auti-Bragg position and the transient processes following the flux pulses were observed. The temporal intensity oscillations were used to control the film thickness, and the reflectivity along the crystal truncation rod was used to measure both the film thickness and the surface/interface roughness. The primary features of the X-ray intensity oscillations were reproduced via simulating the experimental data using diffusive rate equation model. Several mechanisms of determining the X-ray intensity features were discerned. 相似文献
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Constantin D Ollinger C Vogel M Salditt T 《The European physical journal. E, Soft matter》2005,18(3):273-278
We studied by X-ray reflectivity the behaviour of fully hydrated solid-supported lipid
multilayers under the influence of a transverse electric field, under conditions routinely used in the
electroformation process. The kinetics of sample loss (unbinding) was measured as a function of the
amplitude and frequency of the applied field by monitoring the integrated intensity of the Bragg peaks. We
also performed a time-resolved analysis of the intensity of the first Bragg peak and characterized the
final state of the sample. 相似文献