Drop impact on substrates with heterogeneous stiffness

Previous studies of drop impact mainly focus on homogeneous substrates while heterogeneous substrates remain largely unexplored. A convenient preparation strategy of stiff heterogeneous substrates is presented in this work, and the drop impact on such a stiffness-patterned substrate consisting of soft spirals surrounded by a rigid region is systematically investigated. The results show that the splash behavior of a drop on a stiffness-patterned substrate exhibits distinct characteristics from those on a homogeneous substrate. Prompt splash is more likely to occur on the substrate with the greater heterogeneity of stiffness, which is reflected in the lower critical impact velocity. Moreover, the splash velocity of emitted droplet is significantly larger on the heterogeneous substrate than that on a corresponding homogeneous substrate, especially at a higher impact velocity of the drop, indicating a stronger splash intensity on the heterogeneous substrate. The difference in drop splashing between homogeneous substrate and heterogeneous substrate is largely due to the stiffness heterogeneity, rather than the variation of overall stiffness of the substrate. The use of spiral shape provides a feasible solution for introducing stiffness heterogeneity of substrate. This study is conducive to the understanding of drop impact research beyond uniform substrates, reveals the potential of using stiffness-patterned substrates to control splash, and may find useful applications in industries related to drop impact and splash.     

分子动力学模拟Cu(010)基体对负载Co-Cu双金属团簇熔化过程的影响

纳米团簇负载到基体上的结构演化和热稳定性是其走向技术应用的关键. 本文用分子动力学结合嵌入原子方法模拟了具有二十面体初始结构的Co₂₈₁Cu₂₈₀ 混合双金属团簇在Cu(010)基体上的熔化过程, 考察了基体的Cu原子可以自由移动(自由基体)和固定(固定基体)两种条件对负载团簇熔化的影响. 发现基体条件对团簇的熔化有明显的影响. 在自由基体上团簇原子的温度-能量曲线存在明显的团簇熔化时的能量突变点, 熔点为1320 K, 低于固定基体上团簇的熔点1630 K. 在升温过程中团簇的二十面体结构会在基体表面发生外延生长. 外延团簇随着温度增加发生表面预熔, 预熔原子会逐渐向基体表面扩散形成薄层, 直至完全熔化. 自由基体上团簇原子的嵌入行为会使原子的分布状态产生不同于固定基体上的演变.     

Preparation and application of the 3C–SiC substrate to piezoelectric micro cantilever transducers

This study examines the fabrication process and mechanical properties of piezoelectric films with the substrate, which is made from silicon carbide. After depositing the PZT thick film on silicon carbide substrate and silicon substrate respectively, it was shown that silicon carbide substrate formed a stable interface with PZT thick film up to 950?°C, compared with silicon substrate. In addition, the dielectric constant of the PZT thick film sintered at 950?°C on a silicon carbide substrate was 843, and this value was about over 25 % improved value compared with that on a silicon substrate. A thick film piezoelectric micro transducer of a micro cantilever type was fabricated by using a multifunctional 3C–SiC substrate. The fabricated micro cantilever was a micro cantilever with multiple thin films on either silicon or silicon carbide substrate. The piezoelectric thick-film micro cantilever that was fabricated by using a SiC substrate showed excellent mechanical and thermal properties. The piezoelectric micro cantilever on the SiC substrate shows an excellent sensitivity towards the change of mass compared with the piezoelectric micro cantilever on the Si substrate.     

Thermal stress reduction of GaAs epitaxial growth on V-groove patterned Si substrates

We investigate the thermal stresses for GaAs layers grown on V-groove patterned Si substrates by the finite-element method. The results show that the thermal stress distribution near the interface in a patterned substrate is nonuniform,which is far different from that in a planar substrate. Comparing with the planar substrate, the thermal stress is significantly reduced for the Ga As layer on the patterned substrate. The effects of the width of the V-groove, the thickness, and the width of the SiO₂ mask on the thermal stress are studied. It is found that the SiO₂ mask and V-groove play a crucial role in the stress of the Ga As layer on Si substrate. The results indicate that when the width of V-groove is 50 nm, the width and the thickness of the SiO₂ mask are both 100 nm, the Ga As layer is subjected to the minimum stress. Furthermore,Comparing with the planar substrate, the average stress of the Ga As epitaxial layer in the growth window region of the patterned substrate is reduced by 90%. These findings are useful in the optimal designing of growing high-quality Ga As films on patterned Si substrates.     

半导体纳米粒子SERS基底对大肠杆菌的无损检测研究

很多致命的疾病都与细菌感染密切相关,快速、准确地检测和鉴定细菌及微生物,一直是微生物学家及有关科研工作者追求的目标,拉曼光谱可以提供丰富的谱图信息,而表面增强拉曼光谱(SERS)有很高的检测灵敏度,然而一些贵金属SERS基底却容易使蛋白质变性,影响检测结果。以大肠杆菌(E.Coli)作为目标检测细菌,首先检测到大肠杆菌的拉曼光谱,之后采用两种不同的SERS基底(ZnO,Ag溶胶)进行检测。结果表明Ag溶胶基底有很强且较丰富的SERS信号,但是相对于E.Coli的本体拉曼谱峰有较大位移,说明与银溶胶相互作用的细菌存在一定的蛋白质变性过程;而ZnO纳米粒子与细菌作用的SERS信号虽然较弱,但是与E.Coli的本体拉曼信号较为相似,说明ZnO纳米粒子对E.Coli本体基本无损,这将有利于SERS在生物体系的无损检测。该结果可以为利用生物相容性好的半导体SERS基底进行细菌的检测提供有益的参考。     

Ultrawide frequency linewidth of the permeability spectra of FeCoN thin film sputtered on the flexible substrate

Analysis shows that it is possible to make use of dispersed magnetic ripple fields to obtain a wide frequency linewidth of permeability spectra of soft magnetic thin films. As-sputtered FeCoN thin film sputtered on flexible Kapton substrate is studied as an example. It has ultrawide frequency linewidths of its resonance peaks in the permeability spectra, compared to its counterpart deposited on Si substrate. The frequency linewidth of FeCoN on Kapton substrate decreases with external magnetic field, showing a different field dependence from that of FeCoN on Si substrate. The ultrawide frequency linewidth and its decrease with external magnetic field are ascribed to the dispersed magnetic ripple fields caused by the flexible substrate. This work shows that the flexible substrate is effective in obtaining a wide frequency linewidth of the permeability spectra of soft magnetic thin films.     

Modelling of the plasma-substrate interaction and prediction of substrate temperature during the plasma heating

Temperature of the substrate during plasma heating and spraying plays an important role on quality of the substrate and coating. In this study a three dimensional numerical model is developed to simulate the Ar-N₂ plasma jet and conjugate heat transfer between plasma and substrate. The influencing of operating parameters on thermal flux from the plasma to the substrate and substrate temperature are discussed. Transient simulations are carried out to predict the substrate temperature with heating time. The arc current, gas flow rate, stand-off distance, substrate material and environment around the substrate significantly affect the thermal flux to the substrate. Heat flux to the substrate cannot be neglected in the coating built-up models. Present model is validated by comparing the results of present model with previous predictions and measurements.     

Modelling self-ordering behaviour on Ag covered Pt vicinal surfaces

We use computer simulation to explore the formation process of a monolayer of Ag on a stepped Pt(111) substrate and the formation of 3D Pt nanostructures on an Ag covered (111) and (100) Pt substrate. We show that broken lines of Pt nanostructures are preferred at the step edges on the (111) substrate while continuous lines of Pt nanowires are preferred at the step edge on the (100) substrate. This different behaviour is due to the exposed front facet of the nanostructures running along the step, specifically for the (100) stepped substrate a nanowire grown on the step edge has a stable (111) exposed front facet, whereas a nanowire grown on the (111) substrate would have an unstable (100) front facet (depending on the direction of the step). For the Pt nanowires grown on the (100) substrate we show how arriving Pt dimers (and monomers) preferentially move up off the Ag substrate onto the nanowire's (111) facet where they undergo fast diffusion. We also show that these Pt dimers (and monomers) move up and down the nanowire's facet until a vacancy or defect is encountered.     

Adsorption on amorphous semiconductors: A modified Haldane-Anderson model

The Haldane-Anderson model previously used for describing the adsorption on a crystalline substrate is generalized to the case of an amorphous substrate. It is demonstrated that the main difference between the occupation numbers of the adatom is observed in the case where the atomic level overlaps with the band gap (for a crystalline semiconductor) and the mobility gap (for an amorphous semiconductor). The adatom charge on the amorphous substrate is smaller than that on the crystalline substrate.     

Temperature dependence of low loss polymeric AWG

We investigate on the variation of loss and temperature dependence of a polymeric arrayed waveguide grating (AWG) depending on its substrate, by fabricating 16-channel polymeric AWGs with various substrate conditions. Insertion loss for a polymeric AWG on a silicon substrate is measured as low as 3.1 dB. The temperature-dependent wavelength shift for a polymeric AWG detached from the substrate is maintained within 0.1 nm from 20 to 80 °C. But we observe a degradation of insertion loss and a little instability in wavelength characteristics both for the detached polymeric AWG and for a polymeric AWG on a polymer substrate. We investigate on those optical properties of the polymeric AWGs based on measured thermal expansion properties of the polymers.     

基于Wenzel模型的粗糙界面异质形核分析

异质形核是形核发生的主要形式. 经典形核理论对基底界面作了理想化平面假设,然而实际异质形核体系中理想平直的固体界面是不存在的,这导致了异质形核描述与实际情况的偏差. 考察了固相晶胚在非平整界面上的异质形核过程,基于Wenzel润湿模型,分析了非理想界面的粗糙度因子对固相晶胚形核功的影响规律. 结果表明:当基底与晶核之间的本征润湿角小于90°时,基底界面越粗糙越有利于形核;本征润湿角大于90°时,基底界面越粗糙越不利于形核. 同时,游离晶胚在基底上润湿是球冠晶胚形成的重要途径,粗糙界面润湿过程中界面自由能的 关键词： 异质形核 粗糙界面 Wenzel模型 润湿过程     

Physical analysis of normally-off ALD Al2O3/GaN MOSFET with different substrates using self-terminating thermal oxidation-assisted wet etching technique

Based on the self-terminating thermal oxidation-assisted wet etching technique, two kinds of enhancement mode Al$_{2}$O$_{3}$/GaN MOSFETs (metal-oxide-semiconductor field-effect transistors) separately with sapphire substrate and Si substrate are prepared. It is found that the performance of sapphire substrate device is better than that of silicon substrate. Comparing these two devices, the maximum drain current of sapphire substrate device (401 mA/mm) is 1.76 times that of silicon substrate device (228 mA/mm), and the field-effect mobility ($\mu_{\rm FEmax}$) of sapphire substrate device (176 cm$^{2}$/V$\cdot$s) is 1.83 times that of silicon substrate device (96 cm$^{2}$/V$\cdot$s). The conductive resistance of silicon substrate device is 21.2 $\Omega {\cdot }$mm, while that of sapphire substrate device is only 15.2 $\Omega {\cdot }$mm, which is 61% that of silicon substrate device. The significant difference in performance between sapphire substrate and Si substrate is related to the differences in interface and border trap near Al$_{2}$O$_{3}$/GaN interface. Experimental studies show that (i) interface/border trap density in the sapphire substrate device is one order of magnitude lower than in the Si substrate device, (ii) Both the border traps in Al$_{2}$O$_{3}$ dielectric near Al$_{2}$O$_{3}$/GaN and the interface traps in Al$_{2}$O$_{3}$/GaN interface have a significantly effect on device channel mobility, and (iii) the properties of gallium nitride materials on different substrates are different due to wet etching. The research results in this work provide a reference for further optimizing the performances of silicon substrate devices.     

Thin liquid films on a slightly inclined heated plate

The behavior of a thin liquid film on a uniformly heated substrate is considered. When the substrate is horizontal and the Marangoni number sufficiently large the film breaks up into a periodic array of drops. When the substrate is slightly inclined this drop-like state slides down the substrate. The relation between these states is discussed and their stability properties with respect to longitudinal perturbations are determined. The results shed light on the multiplicity of states accessible to systems of this type and on the possible transitions among them.     

Wetting and coalescence of the liquid metal on the metal substrate

Molecular dynamics(MD) simulations are performed to investigate the wettability of liquid metal on the metal substrate. Results show that there exists different wettability on the different metal substrates, which is mainly determined by the interaction between the liquid and the substrate. The liquid metal is more likely to wet the same kind of metal substrate,which attracts the liquid metal to one side on the hybrid substrate. Exchanging the liquid metal and substrate metal has no effect on the wettability between these two metals. Moreover, the study of metal drop coalescing indicates that the metal substrate can significantly affect the coalescence behavior, in which the changeable wettability of liquid metal plays a predominant role. These studies demonstrate that the wetting behavior of liquid metal can be controlled by choosing the suitable metal substrate.     

GaAs(001)表面外延生长Mn薄膜的XPS研究

利用x射线光电子能谱的深度剖面技术,对不同衬底温度下分子束外延生长的Mn薄膜及其与GaAs(001)衬底间的界面进行了元素组分和化学结合状态随深度变化的研究。实验发现衬底温度等于400K时制备的fcc-Mn/GaAs(001)体系中,fcc-Mn层与GaAs衬底之间存在一层较厚的Mn-Ga-As的缓冲层;衬底温度等于300K(室温)时制备的a-Mn/GaAs(001)体系中也存在类似的缓冲层,但它的厚度与fcc-Mn的情形相比要小得多;而当衬底温度等于450K时制备的体系在GaAs衬底之上全部是Mn-Ga     

Large area laser surface micro/nanopatterning by contact microsphere lens arrays

Laser surface micro/nanopatterning by particle lens arrays is a well-known technique. Enhanced optical fields can be achieved on a substrate when a laser beam passes through a self-assembled monolayer of silica microspheres placed on the substrate. This enhanced optical field is responsible for ablative material removal from the substrate resulting in a patterned surface. Because of the laser ablation, the microspheres are often ejected from the substrate during laser irradiation. This is a major issue impeding this technique to be used for large area texturing. We explored the possibility to retain the spheres on the substrate surface during laser irradiation. A picosecond laser system (wavelength of 515 nm, pulse duration 6.7 ps, repetition rate 400 kHz) was employed to write patterns through the lens array on a silicon substrate. In this experimental study, the pulse energy was found to be a key factor to realize surface patterning and retain the spheres during the process. When the laser pulse energy is set within the process window, the microspheres stay on the substrate during and after laser irradiation. Periodic patterns of nanoholes can be textured on the substrate surface. The spacing between the nanoholes is determined by the diameter of the microspheres. The depth of the nanoholes varies, depending on the number of laser pulses applied and pulse energy. Large area texturing can be made using overlapping pulses obtained through laser beam scanning.     

Effect of the nanostructuring of a Cu substrate on the fracture of heat-resistant Si-Al-N coatings during uniaxial tension

The effect of the nanostructuring of the surface layers in a Cu substrate on the microstructure, mechanical properties, and fracture mechanisms of heat-resistant Si-Al-N coatings during uniaxial tension is studied. The nanostructuring of a substrate is performed by the following two methods: bombardment by Zr⁺ ion beams and ultrasonic impact treatment. Depending on the state of the substrate, different spallation mechanisms are found to operate in the Si-Al-N coatings during mechanical loading. The maximum shear strength of the coating/substrate interface is shown to be achieved due to ion bombardment of the substrate.     

Resonant properties of the planar plasmonic crystal on a membrane substrate

The theory of the plasmon resonance excitation in the plasmonic-crystal structure on a dielectric substrate is presented. The effect of the plasmon resonance intensity oscillation as a function of the substrate thickness is predicted. It is shown that the enhancement of the plasmon resonance intensity occurs in a broad terahertz frequency range in the structure on a membrane substrate.     

基底表面纳米织构对非晶四面体碳膜结构和摩擦特性的影响研究

本文利用离子束表面改性技术对基底表面进行不同时间的轰击, 形成不同规则的纳米织构, 对不同织构的变化规律进行了研究, 同时, 利用磁过滤真空阴极电弧技术, 在具有不同纳米织构的各基底上沉积相同时间的四面体非晶碳薄膜. 采用原子力显微镜对各基底的织构进行形貌分析, 结果表明, 高能粒子束的轰击对基底表面形貌有较大的影响, 根据离子束轰击时间的不同, 可以在基底表面形成各种不同规则的纳米织构, 轰击15 min后发现基底表面形成点阵纳米织构, 之后随着时间的增加, 基本维持点阵结构. 通过X射线光电子能谱仪和摩擦磨损试验仪对沉积在具有不同织构的基底上的ta-C薄膜进行测试, 研究表明, 基底表面纳米织构的非晶层结构引起薄膜内部sp³键的含量降低, 释放了薄膜的内应力, 同时发现基底表面纳米织构将ta-C薄膜磨损时间从不足10 min提高到约70 min, 有效提高了薄膜的耐磨性.     

Imaging method of single layer graphene on metal substrate based on imaging ellipsometer with large field of view

Single layer lattice graphene deposited on the metal substrate can hardly be imaged by the optical microscope. In this Letter, a large field-of-view imaging ellipsometer is introduced to image single layer graphene which is deposited on a metal substrate. By adjusting the polarizer and the analyzer of imaging ellipsometer, the light reflected from surfaces of either single layer graphene or a Au film substrate can be extinguished, respectively.Thus, single layer graphene can be imaged correspondingly under brightfield or darkfield imaging modes. The method can be applied to imaging large-area graphene on a metal substrate.