Effect of the amorphous thin layer on the surface growth of amorphous/crystalline binary multilayer films

The effect of the amorphous thin layer on the surface growth of amorphous/crystalline binary multilayer films has been studied by using a continuum model. It is shown that both the surface roughness and the growth exponent of amorphous/crystalline binary multilayer films decrease with increasing thickness ratio between amorphous and crystalline layers. Our simulations have also revealed, in contrast to the monotonous rise in surface roughness observed in single-layer films grown on flat substrates, the surface growth of a multilayer film consists of two processes: interface smoothing and roughening, namely the film roughness decreases during the growth of amorphous thin layers but increases monotonously during the growth of crystalline thin layers. The observed interface smoothing and roughening can be obviously influenced by the change in the thickness ratio between amorphous and crystalline layers. The rise in thickness ratio between amorphous and crystalline layers enhances the interface smoothing effect but lowers the interface roughening effect and consequently shows a marked smoothing effect on the surface roughness.     

On the role of scattering by surface roughness in silicon inversion layers

Experimental results are presented, which strongly suggest that scattering of carriers by surface roughness may be important in the silicon inversion layer of metal-oxide-semiconductor structures. Low temperature data for p-type channels on identical orientation at high surface field show that mobility results in this region are dependent only on the mode of sample preparation and are independent of surface charges. The most reasonable explanation for these observations is offered by a scattering mechanism which is closely associated with the surface condition of the SiSiO₂ interface, namely, scattering by surface roughness. This scattering is a direct result of the fluctuating potential caused by the imperfect interface which is only a small distance from the inversion carriers. A calculation of the effect of surface roughness on surface carrier mobility is also given and found to be in satisfactory agreement with the experimental results. The application of the theory to the observed results permits an estimate to be made of the physical dimensions of the surface roughness of the Si-SiO₂ interface.     

Interface roughness, surface roughness and soft X-ray reflectivity of Mo/Si multilayers with different layer number

A series of Mo/Si multilayers with the same periodic length and different periodic number were prepared by magnetron sputtering, whose top layers were respectively Mo layer and Si layer. Periodic length and interface roughness of Mo/Si multilayers were determined by small angle X-ray diffraction (SAXRD).Surface roughness change curve of Mo/Si multilayer with increasing layer number was studied by atomic force microscope (AFM). Soft X-ray reflectivity of Mo/Si multilayers was measured in National Synchrotron Radiation Laboratory (NSRL). Theoretical and experimental results show that the soft X-ray reflectivity of Mo/Si multilayer is mainly determined by periodic number and interface roughness, surface roughness has little effect on reflectivity.     

The influence of surface roughness in X-ray resonant magnetic reflectivity experiments

We present simulations of X-ray resonant magnetic reflectivity (XRMR) spectra of the surface magnetic dead layer in La_1−x Sr _x MnO₃ (LSMO) films that take in account the effect of different forms of roughness that can be encountered experimentally. The results demonstrate a method to distinguish between surface (morphological) roughness, and two generic kinds of magnetic roughness at the buried interface between the surface dead layer and the fully magnetic bulk part of the film. We show that the XRMR technique can distinguish between different types of magnetic roughness at the dead layer/bulk interface only if the sample surface is nearly atomically flat (the morphological roughness is one unit cell or less). Furthermore, to distinguish between the two types of magnetic roughness, the simulations show that fitting of XRMR spectra out to very high incidence angles must be performed. In the specific case of LSMO films with a dead layer with average thickness of 4 unit cells, this corresponds to an incidence angle > 50^∘.     

表面粗糙度对固体内部超声背散射的影响

超声背散射法可通过多晶体金属内部的空间方差信号,实现微观结构参数的无损评价,但表面粗糙度对评价模型的精度及实用性存在显著影响.基于高斯声束理论推导垂直入射粗糙界面的纵波声场,以此研究声能的Wigner分布规律;在超声的波长远大于粗糙度的前提下,构造表面粗糙度修正系数,并建立粗糙界面的单次散射响应模型,揭示粗糙度对超声波背向散射的影响规律.用304不锈钢制备轮廓均方根值为0.159μm的光滑试块和25.722μm的粗糙试块开展超声背散射实验,结果表明模型在粗糙度修正前后均可实现光滑试块的晶粒尺寸有效评价,但未经修正的传统模型对粗糙试块的晶粒尺寸评价结果与金相法结果的相对误差高达-21.35%,而本模型的评价结果与金相法结果符合得很好,相对误差仅为1.35%.可见,本模型能有效补偿粗糙度引起的超声背散射信号衰减,从而提高晶粒尺寸无损评价的精度.     

离子束作用下的光学表面粗糙度演变研究

 为了获得超光滑光学表面,介绍了离子束作用下改善表面粗糙度的抛光方法,并通过相关的实验进行了验证。光学材料是典型的硬脆材料,在加工过程中的表面粗糙度要经历复杂的演变过程。离子束加工作为光学镜面加工中的最后一道工序,如果在修正面形的同时,能够有效地改善表面粗糙度,那么离子束加工的性能就可以得到更好的延伸。分析了离子束作用下的粗糙度演变机理,在此基础上提出了倾斜入射抛光和牺牲层抛光技术2种改善表面粗糙度的方法,并使用原子力显微镜进行了测量。实验结果表明：以45°倾斜入射抛光熔石英样件,其粗糙度由初始的0.67nm RMS减小到0.38nm RMS;涂上牺牲层的材料表面粗糙度由0.81nm RMS减小到0.28nm RMS,倾斜入射抛光和牺牲层抛光技术能够有效地改善表面粗糙度。     

相移干涉法测量ICF微球内表面粗糙度

 通过分析光线通过微球壳层后各界面的相位分布,讨论了相移干涉法测量微球内表面粗糙度的基本原理,研究了微球上部壳层对内表面粗糙度测量的影响,得到了聚苯乙烯,聚a甲基苯乙烯微球的内表面形貌特征图像,测量数据与原子力显微镜测量数据在同一量级。以微球壳层对超光滑碳化硅及单晶硅片表面形貌的调制作用为研究对象,讨论了微球的外表面粗糙度以及微球壁厚对内表面粗糙度测量结果的影响,确定了相移干涉法测量微球内表面粗糙度的不确定度,实验结果表明：对于表面粗糙度小于30 nm、厚度小于9 mm的微球,测量不确定度小于0.4 nm。     

The role of surface roughness in total internal reflection ellipsometry of hybrid systems

Total internal reflection ellipsometry (TIRE) technique was used to investigate the role of surface roughness in the hybrid system composed of octadecanethiole layer on Au thin film. The samples with Au films of different microstructure were explored. The experimental results were interpreted in the model, which took into account the surface roughness of Au film in the hybrid system. It was shown that optical parameters of octadecanethiole were in correspondence for samples of different microstructure in the case of adequate models used for interpretation of TIRE data.     

Reflectometry of absorbing uniaxial multilayer media

A novel reflection technique for index determination of isotropic or uniaxial absorbing multilayer on a lower refractive index substrate is presented. Above the angle of total reflection at the layer-substrate interface characteristic minima occur in the reflectivity which are suitable for high accuracy fitting of the layer parameters. The 4 × 4 transfer matrices of uniaxial multilayer are given for computer evaluation. Refraction index determination of a poled polymeric layer on an indium-tin-oxide coated glass is demonstrated. Advantages of the new method are outlined.     

金刚石薄膜红外椭圆偏振参量的计算与拟合

用红外椭圆偏振仪对热丝化学气相沉积法制备的金刚石薄膜的光学参量进行了测量。由于表面状态和界面特性的差异，分别对镜面抛光硅片和粗糙氧化铝基片上的金刚石薄膜建立了不同的模型，并在此基础上进行了测试结果的计算拟合。为了综合反应诸如表面粗糙度等表面界面因素对测试结果的影响，根据衬底特性将表面层和界面层分离出来，并采用Bruggeman有效介质方法对它们的影响进行了近似处理。结果表明，硅衬底上金刚石薄膜的椭偏数据在模型引入了厚度为879nm的表面粗糙层之后能得到很好的拟合。而对于氧化铝衬底上的金刚石薄膜而言，除了在薄膜表面引入了粗糙层之外，还必须在衬底和金刚石界面处加入一层由体积分数为0．641的氧化铝、体积分数为0．2334的金刚石和体积分数为0．1253的空隙组成的复合过渡层(厚度995nm)，才能使计算值与实验参量很好地吻合。     

Investigation in the interface roughness of DC-sputtered Mo/B4C multilayer mirrors with variable layer pairs for 7-nm soft X-ray polarizers

The surface and interface roughness of Mo/B₄C multilayer mirrors for 7-nm soft X-ray polarizer with variable layer pairs (N = 50, 70, 90 and 110), fabricated by DC sputtering technique is investigated by atomic force microscopy and X-ray scattering and reflecting. The experimental results present that the surface and interface roughness of Mo/B₄C multilayer mirrors increase layer by layer from its substrate as its Mo layer thickness greater than 2 nm, and the roughness grown tendency could be characterized by a quadratic function.     

Interface models and processing technologies for surface passivation and interface control in III-V semiconductor nanoelectronics

Interface models and processing technologies are reviewed for successful establishment of surface passivation, interface control and MIS gate stack formation in III-V nanoelectronics. First, basic considerations on successful surface passivation and interface control are given, including review of interface models for the band alignment at interfaces, and effects of interface states in nanoscale devices. Then, a brief review is given on currently available surface passivation technologies for III-V materials, including the Si interface control layer (ICL)-based passivation scheme by the authors’ group. The Si-ICL technique has been successfully applied to surface passivation of nanowires and to formation of a HfO₂ high-k dielectric/GaAs interfaces with low values of the interface state density.     

Single layer homogeneous model for surface roughness by polarized light scattering

In this paper a homogeneous single layer model for surface roughness by polarized light has been developed. It has been shown that the reflectance change in non-absorbing layer is directly proportional to the refractive index of the ambient and substrate media for s polarization but inversely proportional to the p polarization and it is directly proportional to the square of the thickness of the layer for both the polarization. In an absorbing layer, it has been shown that the thickness of the layer is equal to the twice of surface roughness of the single layer identical system for s polarization but it is ratio of twice of surface roughness to the square of refractive index of thin film for p polarization. The extinction coefficient of the layer is directly proportional to the thickness of that layer for both the polarization. The consequence of the scattered light on the specular reflectance and transmittance for oblique incidence shows that there is reduction in reflectance (in both non-absorbing and absorbing cases) and transmittance (in the absorbing case for p polarization only), due to roughness on the surface under the Drude effective-medium approximation. Thus such an absorbing layer provides a valid model for the effect of scatter on the transmittance for p polarization only.     

Effect of surface roughness on leakage current and corrosion resistance of oxide layer on AZ91 Mg alloy prepared by plasma electrolytic oxidation

The influence of the surface roughness of Mg alloys on the electrical properties and corrosion resistance of oxide layers obtained by plasma electrolytic oxidation (PEO) were studied. The leakage current in the insulating oxide layer was enhanced by increasing the surface roughness, which is a favorable characteristic for the material when applied to hand-held electronic devices. The variation of corrosion resistance with surface roughness was also investigated. The corrosion resistance was degraded by the increasing surface roughness, which was confirmed with DC polarization and impedance spectroscopy. Pitting corrosion on the passive oxide layer was also analyzed with a salt spray test, which showed that the number of pits was not affected by the surface roughness when the spray time reached 96 h.     

Investigation of interface roughness cross-correlation properties of optical thin films from total scattering losses

The interface roughness and interface roughness cross-correlation properties affect the scattering losses of high-quality optical thin films. In this paper, the theoretical models of light scattering induced by surface and interface roughness of optical thin films are concisely presented. Furthermore, influence of interface roughness cross-correlation properties to light scattering is analyzed by total scattering losses. Moreover, single-layer TiO₂ thin film thickness, substrate roughness of K9 glass and ion beam assisted deposition (IBAD) technique effect on interface roughness cross-correlation properties are studied by experiments, respectively. A 17-layer dielectric quarter-wave high reflection multilayer is analyzed by total scattering losses. The results show that the interface roughness cross-correlation properties depend on TiO₂ thin film thickness, substrate roughness and deposition technique. The interface roughness cross-correlation properties decrease with the increase of film thickness or the decrease of substrates roughness. Furthermore, ion beam assisted deposition technique can increase the interface roughness cross-correlation properties of optical thin films. The measured total scattering losses of 17-layer dielectric quarter-wave high reflection multilayer deposited with IBAD indicate that completely correlated interface model can be observed, when substrate roughness is about 2.84 nm.     

Solid-gas interface thermal conductance for the thermal barrier coating with surface roughness: The confinement effect

The yttria-stabilized zirconia (YSZ) is a famous thermal barrier coating material to protect hot-end components of an engine. As a characteristic feature of the YSZ, the surface roughness shall play an important role in the interface thermal conductance between the YSZ and gas, considering that the gas is typically at an extremely high temperature. We investigate the effect of the surface roughness on the thermal conductance of the YSZ-gas interface with surface roughness described by nanoscale pores on the surface of the YSZ. We reveal two competitive mechanisms related to the microstructure of the pore, i.e., the actual contact area effect and the confinement effect. The increase of the pore depth will enlarge the actual contact area between the YSZ and gas, leading to enhancement of the solid-gas interface thermal conductance. In contrast to the positive actual contact area effect, the geometry-induced confinement effect greatly reduces the interface thermal conductance. These findings shall offer some fundamental understandings for the microscopic mechanisms of the YSZ-gas interface thermal conductance.     

Surface‐sensitive reflection‐mode EXAFS from layered sample systems: the influence of surface and interface roughness

The calculation of reflection‐mode grazing‐incidence X‐ray absorption spectra from single surfaces and (multi‐)layered systems is studied here. In particular, the influence of the surface and interface roughness was investigated in detail. Simulations of grazing‐incidence reflection‐mode EXAFS spectra using a simple Fresnel theory neglecting any effect of roughness are compared with the Névot–Croce model and the elaborated distorted‐wave Born approximation which both include surface and interface roughness. Data are presented for clean gold surfaces, where the strong influence of the surface roughness on the resulting spectra is demonstrated. Furthermore, in the case of layered systems, the influence of both the outer (air or vacuum side) surface roughness and the inner interface roughness on the reflection‐mode EXAFS spectra is evaluated. The practical consequences of the observed correlations are discussed, and a quantitative data analysis of a copper sample that was oxidized in ambient air for several months is shown, including the evaluation of specular reflectivity profiles at fixed energy.     

The low-temperature mobility of two-dimensional electron gas in AlGaN/GaN heterostructures

To reveal the internal physics of the low-temperature mobility of two-dimensional electron gas （2DEG） in Al- GaN/GaN heterostructures, we present a theoretical study of the strong dependence of 2DEG mobility on Al content and thickness of AlGaN barrier layer. The theoretical results are compared with one of the highest measured of 2DEG mobility reported for AlGaN/GaN heterostructures. The 2DEG mobility is modelled as a combined effect of the scat- tering mechanisms including acoustic deformation-potential, piezoelectric, ionized background donor, surface donor, dislocation, alloy disorder and interface roughness scattering. The analyses of the individual scattering processes show that the dominant scattering mechanisms are the alloy disorder scattering and the interface roughness scattering at low temperatures. The variation of 2DEG mobility with the barrier layer parameters results mainly from the change of 2DEG density and distribution. It is suggested that in AlGaN/GaN samples with a high Al content or a thick AlGaN layer, the interface roughness scattering may restrict the 2DEG mobility significantly, for the AlGaN/GaN interface roughness increases due to the stress accumulation in AlGaN layer.     

Effects of surface mechanical attrition treatment (SMAT) on a rough surface of AISI 316L stainless steel

Surface mechanical attrition treatment (SMAT) improves mechanical properties of metallic materials through the formation of nanocrystallites at their surface layer. It also modifies the morphology and roughness of the work surface. Surface roughening by the SMAT has been reported previously in a smooth specimen, however in this study the starting point was a rough surface and a smoothening phenomenon is observed. In this paper, the mechanisms involved in the surface smoothening of AISI 316L stainless steel during the SMAT are elucidated. The SMAT was conducted on a specimen with a roughness of R_a = 3.98 μm for 0–20 min. The size of milling balls used in the SMAT was varied from 3.18 mm to 6.35 mm. The modification of subsurface microhardness, surface morphology, roughness and mass reduction of the specimen due to the SMAT were studied. The result shows the increasing microhardness of the surface and subsurface of the steel due to the SMAT. The impacts of milling balls deform the surface and produce a flat-like structure at this layer. Surface roughness decreases until its saturation is achieved in the SMAT. The mass reduction of the specimens is also detected and may indicate material removal or surface erosion by the SMAT. The size of milling ball is found to be the important feature determining the pattern of roughness evolution and material removal during the SMAT. From this study, two principal mechanisms in the evolution of surface morphology and roughness during the SMAT are proposed, i.e. indentation and surface erosion by the multiple impacts of milling balls. A comparative study with the results of the previous experiment indicates that the initial surface roughness has no influence in the work hardening by the SMAT but it does slightly on the saturated roughness value obtained by this treatment.