Frozen capillary waves on glass surfaces: an AFM study

Using atomic force microscopy on silica and float glass surfaces, we give evidence that the roughness of melted glass surfaces can be quantitatively accounted for by frozen capillary waves. In this framework the height spatial correlations are shown to obey a logarithmic scaling law; the identification of this behaviour allows to estimate the ratio kT_F/πγ where k is the Boltzmann constant, γ the interface tension and T_F the temperature corresponding to the “freezing” of the capillary waves. Variations of interface tension and (to a lesser extent) temperatures of annealing treatments are shown to be directly measurable from a statistical analysis of the roughness spectrum of the glass surfaces.     

气体团簇离子束两步能量修形法的平坦化效应

本文提出采用气体团簇离子束的两步能量修形法来改善4H-SiC(1000)晶片表面形貌.先用15 keV的高能Ar团簇离子进行整体修形,再用5 keV的低能团簇离子优化表面.结果表明,在相同的团簇离子剂量下,与单一15 keV的高能团簇处理相比,两步法修形后的表面具有更低的均方根粗糙度,两者分别为1.05 nm和0.78 nm.本文还以原子级平坦表面为研究对象,揭示了载能团簇引起的半球形离子损伤(弧坑)与团簇能量的关系,及两步能量修形法在弧坑修复中的优势.在原子力显微镜表征的基础上,引入了二维功率谱密度函数,以直观全面地给出材料的表面形貌特征及其随波长(频率)的分布.结果表明,经任何能量的团簇离子轰击的表面,在0.05—0.20μm波长范围内,团簇轰击都能有效地降低粗糙度,而在0.02—0.05μm范围内,则出现了粗化效应,这是由于形成了半球形离子损伤,但第二步更低能量的团簇离子处理可以削弱这种粗化效应.     

SIMS depth profiling of ‘frozen’ samples: in search of ultimate depth resolution regime

We have performed secondary ion mass spectrometry depth profiling analysis of III–V based hetero‐structures at different target temperatures and found that both the surface segregation and surface roughness caused by ion sputtering can be radically reduced if the sample temperature is lowered to ?150 °C. The depth profiling of ‘frozen’ samples can be a good alternative to sample rotation and oxygen flooding used for ultra‐low‐energy depth profiling of compound semiconductors. Copyright © 2016 John Wiley & Sons, Ltd.     

Effect of surface morphology on measurement and interpretation of boundary slip on superhydrophobic surfaces

Highly liquid repellent surfaces have been obtained by the combination of roughness and hydrophobicity. Studies have reported that the flow over such surfaces exhibits larger boundary slip as compared to the smooth hydrophobic surfaces. However, the surface roughness can also lead to apparent slip. Thus, the effect of the two factors, that is, wettability and roughness, needs to be segregated. In this study, we have measured the slippage of water on rough hydrophilic and hydrophobic surfaces using colloidal probe atomic force microscopy technique (CP‐AFM). Results showed that the effect of surface roughness on the measured slip is dominant over that of wettability. It was also found that slip on surfaces with sparsely distributed asperities is highly local and measurements on various locations give dissimilar results. The results suggested that the main reason of the larger slip, on rough hydrophobic surfaces, is likely to be the roughness and not the hydrophobicity. Moreover, it was also found that the slip does not vary considerably with the increase or decrease in the shear rate. Most likely, this kind of slip phenomena is caused by the apparent decrease of the drag force, because the nanoasperities on the surface restrict the probe from reaching the surface properly. Copyright © 2016 John Wiley & Sons, Ltd.     

点、线接触真实粗糙表面的弹流润滑研究

本文给出了点、线接触的真实粗糙表面的微弹流数值解。在给定随机粗糙表面样本后,求解大小不同的载荷和粗糙的弹流问题。从计算结果可以看出,由于Reynolds方程中速度项的作用,在表面对应粗糙的位置处引起了压力变化,从而因其产生的弹性变形使粗糙变得平滑。对此光滑表面解可以看出,因粗糙引起的压力和膜厚的变化在光滑解附近波动。载荷较大时,压力分节接近固体接触情况。     

Fractals — An overview of potential applications to transport in porous media

We present an overview of the potential applicability of fractal concepts to various aspects of transport phenomena in heterogeneous porous media. Three examples of phenomena where a fractal approach should prove illuminating are presented. In the first example we consider pore level heterogeneities as typified by pore surface roughness. We suggest that roughness may be usefully modelled by fractal curves and surfaces and also cite experimental evidence for regarding pores as fractals. In the second example we consider a fractal network approach to modelling large-scale heterogeneities. The presence of features on all length scales in simple fractal models should capture the essential role played by the presence of heterogeneities on many scales in natural reservoirs. Studies of transport phenomena in such models may yield valuable insights into the problems of macroscopic dispersion. The final example concerns dispersion in multiphase flow. Here the fractal character is attributed to the distribution of the fluid phases rather than the porous medium itself. Again studies of transport phenomena in simple fractal models should help to clarify various problems associated with the corresponding phenomena in real reservoirs.     

非牛顿流体有限长粗糙轴承分析

本文采用H.Christense力提出的随机粗糙模型,推导了幂律型流体纵向粗糙型和横向粗糙型润滑雷诺方程和相应的承载力、流量系数和摩擦系数的计算公式.对有限长动载径向轴承纵向粗糙型雷诺方程,用差分方法进行数值求解,得到了粗糙度和幂律指数对轴承的压力分布、承载力、流量系数和摩擦系数影响曲线,并有表面粗糙度和润滑油的非牛顿特性独立地影响轴承油膜力学特性的结论.     

Micro fabrication of microlens arrays by micro dispensing

In this study, master of the microlens arrays is fabricated using micro dispensing technology, and then electroforming technology is employed to replicate the Ni mold insert of the microlens arrays. Finally, micro hot embossing is performed to replicate the molded microlens arrays from the Ni mold insert. The resin material is used as the dispensing material, which is dropped on a glass substrate. The resin is exposed to a 380 W halogen light. It becomes convex under surface tension on the glass substrate. A master for the microlens arrays is then obtained. A 150‐nm‐thick copper layer is sputtered on the master as an electrically conducting layer. The electroforming method replicates the Ni mold insert from the master of the microlens arrays. Finally, micro hot embossing is adopted to replicate the molded microlens arrays. The micro hot embossing experiment employs optical films of polymethylmethacrylate (PMMA) and polycarbonate (PC). The processing parameters of micro hot embossing are processing temperature, embossing pressure, embossing time, and de‐molding temperature. Taguchi's method is applied to optimize the processing parameters of micro hot embossing for molded microlens arrays. An optical microscope and a surface profiler are utilized to measure the surface profile of the master, the Ni mold insert and the molded microlens arrays. AFM is employed to measure the surface roughness of the master, the Ni mold insert and the molded microlens arrays. The sag height and focal length are determined to elucidate the optical characteristics of the molded microlens arrays. Copyright © 2009 John & Sons, Ltd.     

反射式光纤位移传感器应用设计实验

基于光的反射原理并结合光纤传感器的特点,设计了反射式光纤位移传感器应用设计性实验.利用反射式光纤传感器测量微小位移的原理,通过测量输出电压与位移的关系确定工作点,测得表面柤糙程度不同的真假钞的输出信号,从而实现对纸币的真假识别.     

Experimental investigation of a modified Beckmann-Kirchhoff scattering theory for the in-process optical measurement of surface quality

An experimental investigation of a modified Beckmann-Kirchhoff scattering theory applied in an in-process optical measurement of surface quality is described. The proposed theory describes the scattered light intensity distribution from a surface with the additional layers, and can be employed to analyze the surface characteristics in in-process measurement. Based on light scattering principle and machine vision method, the surface roughness is extracted to testify the correction of the modified Beckmann-Kirchhoff scattering theory. The experimental apparatus consists of a collimated laser diode, a beam splitter, a screen, a measuring lens and a camera. Test specimens with different surface roughness are studied. The results obtained demonstrate the feasibility of in-process optical measurement of surface quality using the modified model.