Increasing active surface area to fabricate ultra-hydrophobic surface by using "Black silicon" with bosch etching process

Needle-shaped pillars so-called "Black silicon" (B-Si) were fabricated by etching cleaned silicon wafer with fluorine-based deep reactive ion etching plasma. The B-Si pillar with the pillar size (a) and spacing (b) of 250 nm, and height (h) of 6.47 microm, coated with SiOxFy film had water contact angle (WCA) and ethylene glycol contact angle (ECA) of 159.8 degrees and 135.5 degrees, respectively. After coating the pillar with trichloro(1H,1H, 2H,2H-perfluorooctyl)silane (TPFS), the WCA and ECA increased to 166.2 degrees and 161.8 degrees, respectively. At the optimum etching condition, the B-Si pillar with the size a = 376 nm, b = 576 nm, h = 6.47microm, and the aspect ratio of 14.80 showed the WCA and ECA of 4.25 degrees and 14.77 degrees, respectively. After coating with the TPFS, liquid droplets ran across the sample's surface rapidly and the WCA and ECA could not be measured. Moreover, when the pillar height was increased twice, the WCA and ECA of the B-Si with and without the TPFS coating were greater than 170 degrees, indicating excellent water-and-oil repellency and can be applied for Micro-Electro-Mechanical Systems (MEMS).     

Pillar-assisted epitaxial assembly of toric focal conic domains of smectic-a liquid crystals

SU-8 pillar-assisted epitaxial assembly of toric focal conic domains (TFCDs) arrays of smectic-A liquid crystals is studied. The 3D nature of the pillar array is crucial to confine and direct the formation of TFCDs on the top of each pillar and between neighboring pillars, leading to highly ordered square and hexagonal array TFCDs. Excellent agreement between the experimentally obtained critical pillar diameter and elasticity calculation is found.     

通过粒子辅助水滴模板法制备超疏水材料

利用水滴模板法成功制备出孔径可控的具有结构规则的聚合物多孔膜,并以所制备多孔膜为模板利用反向复刻法复制孔洞阵列结构,得到具有微米级突起阵列结构的聚二甲基硅氧烷(PDMS)膜片,然后将事先排布好的二氧化硅微球阵列通过热压印法转移到具有微米级突起结构的PDMS膜片上,然后成功制备出具有微纳米复合突起结构的膜片。通过对具有不同突起结构组合的PDMS膜片进行接触角测试发现,膜片的接触角随着其表面粗糙程度的增大而增大,即具有微纳复合结构膜片接触角((150.7±3.2)°)最大,达到了超疏水的效果;无突起结构膜片的接触角((108.9±3.1)°)最小;而仅具有微米级结构膜片的接触角((134.6±1.0)°)居中,这符合目前已知的物质表面浸润性与其表面粗糙度的关系。另外,经测试,具有微纳复合结构的膜片接触角最大达到155°,同时具有非常大的滚动角,使得这种膜片材料具备了粘性超疏水的性能,而这种特殊浸润表面性质可以在液体无损传输、生化分离等领域拥有巨大的应用前景。     

Wafer-scale patterning of sub-40 nm diameter and high aspect ratio (>50:1) silicon pillar arrays by nanoimprint and etching

We demonstrate wide-area fabrication of sub-40?nm diameter, 1.5?μm tall, high aspect ratio silicon pillar arrays with straight sidewalls by combining nanoimprint lithography (NIL) and deep reactive ion etching (DRIE). Imprint molds were used to pre-pattern nanopillar positions precisely on a 200?nm square lattice with long range order. The conventional DRIE etching process was modified and optimized with reduced cycle times and gas flows to achieve vertical sidewalls; with such techniques the pillar sidewall roughness can be reduced below 8?nm (peak-to-peak). In some cases, sub-50?nm diameter pillars, 3?μm tall, were fabricated to achieve aspect ratios greater than 60:1.     

Research on Contact Behavior of Single Asperity on Work Roll Surface in Mixed Lubrication

The present paper focuses on asperity contact during cold rolling at a microscopic level. As analyses of such a contact are not practical with experimental facilities, a three-dimensional finite element method (FEM) is adopted to simulate the indentation and furrow behaviors of a single asperity on work roll surface in mixed lubrication. The effects of the tensile stress, the hydrodynamic pressure and the plastic deformation of steel strip are considered comprehensively. Most calculations are done for parabolic asperities, but for comparison purposes, some results are presented for sinusoidal and elliptical asperities. The indentation behaviors including uplift height of edges and plastic deformations of strip steel are calculated and analyzed. The friction during furrow behaviors is also considered. It reveals that the reduction and lubrication condition has a significant effect on the uplift height of strip steel edges around the asperity. Furthermore, long-term repeated effects of mixed lubrication contact are liable to spark asperity wear and decrease the roughness of rolls and even cause the failure of rolls in strip rolling mills.     

基于分形的三维粗糙表面弹塑性接触力学模型与试验验证

基于分形几何理论,利用双变量的Weierstrass-Mandelbrot函数模拟三维分形粗糙表面,建立了三维分形粗糙表面弹塑性接触模型。推导出各等级微凸体发生弹性、弹塑性以及完全塑性变形的存在条件。确定了粗糙表面上各等级微凸体的面积分布密度函数,获得了总接触载荷和真实接触面积之间的关系式。计算结果表明:单个微凸体的临界接触面积与其尺寸相关,随着微凸体等级的增大,微凸体的高度和峰顶曲率半径减小。微凸体的变形顺序为弹性变形、弹塑性变形和完全塑性变形,与经典的赫兹模型保持一致。粗糙表面的力学性能仅与最小等级及后续的6个等级微凸体相关,其余微凸体基本上对整个粗糙表面的力学性能影响很小。最后对粗糙表面的接触力学性能进行了试验测试,验证了该模型的合理性与正确性。     

Microtubule gliding and cross-linked microtubule networks on micropillar interfaces

We combined biochemical and topographical patterning to achieve motor-driven microtubule gliding on top of microfabricated pillar arrays with limited and controllable surface interactions of gliding microtubules. Kinesins immobilized on pillar heads pushed microtubules from the top of one micropillar to the next bridging up to 20 mum deep gaps filled with buffer solution. Distances of more than 10 mum were by-passed, and microtubule buckling was occasionally observed. The velocity distributions of microtubules gliding on poly(dimethylsiloxane) (PDMS) pillars, on flat PDMS, and on glass were found to be different, most likely due to topological and/or chemical differences between the substrates. We also used pillar arrays to suspend cross-linked microtubule networks, whose structural characteristics were governed by the topographical characteristics of the pillar pattern. These experiments open new possibilities to study the dynamics and the self-organization of motor/microtubule networks in defined topologically structured environments.     

Fabrication of sub-25 nm diameter pillar nanoimprint molds with smooth sidewalls using self-perfection by liquefaction and reactive ion etching

Self-perfection by liquefaction (SPEL) was used to fabricate nanoimprint molds with an array of sub-25?nm diameter pillars (200?nm period), resulting in nearly perfect cylindrical shape and smooth sidewalls. SPEL turned an array of irregularly shaped Cr polygons into an array of nearly perfect circular dots with small diameter. The Cr dot arrays were then transferred to SiO(2) or Si pillar arrays by means of reactive ion etching to produce imprint molds. High-fidelity nanoimprint lithography using the pillar molds was also demonstrated.     

On the temperature in the wheel–rail rolling contact*

The flash temperature in an asperity of the rail due the wheel–rail rolling contact is investigated. First the contact configuration and the total heat produced are explained. Then approaches to heat partitioning between the two contacting bodies are discussed. A new heat partitioning factor is derived for the case of frictional heating and heating due to plastic deformation, thereby taking into account the roughness of the contacting surfaces by a contact intensity factor distribution as well as the local pressure intensification by individual asperities. Several roughness distributions are studied. Finally, an explicit calculation is outlined of the asperity flash temperature at the end of the contact, expressed by two temperatures and two factors contributing to the partitioning of heat between the contacting bodies.     

Toughening mechanisms in bioinspired multilayered materials

Outstanding mechanical properties of biological multilayered materials are strongly influenced by nanoscale features in their structure. In this study, mechanical behaviour and toughening mechanisms of abalone nacre-inspired multilayered materials are explored. In nacre''s structure, the organic matrix, pillars and the roughness of the aragonite platelets play important roles in its overall mechanical performance. A micromechanical model for multilayered biological materials is proposed to simulate their mechanical deformation and toughening mechanisms. The fundamental hypothesis of the model is the inclusion of nanoscale pillars with near theoretical strength (σ_th ~ E/30). It is also assumed that pillars and asperities confine the organic matrix to the proximity of the platelets, and, hence, increase their stiffness, since it has been previously shown that the organic matrix behaves more stiffly in the proximity of mineral platelets. The modelling results are in excellent agreement with the available experimental data for abalone nacre. The results demonstrate that the aragonite platelets, pillars and organic matrix synergistically affect the stiffness of nacre, and the pillars significantly contribute to the mechanical performance of nacre. It is also shown that the roughness induced interactions between the organic matrix and aragonite platelet, represented in the model by asperity elements, play a key role in strength and toughness of abalone nacre. The highly nonlinear behaviour of the proposed multilayered material is the result of distributed deformation in the nacre-like structure due to the existence of nano-asperities and nanopillars with near theoretical strength. Finally, tensile toughness is studied as a function of the components in the microstructure of nacre.     

The role of debris-induced cantilever effects in cyclic fatigue of micron-scale silicon films

The presence of debris, surface roughness, or other asperities on crack faces creates a geometry that is reminiscent of a lever (the crack face) on a fulcrum (the debris or surface asperity). This ‘cantilever effect’ is intuitive and is routinely forwarded as a mechanism for crack advance when compressive loads are applied. Recently this cantilever effect has also been linked to fatigue of micron‐scale silicon films. Finite‐element modelling was used in this study to evaluate different wedging configurations that would be likely to occur within micromachined silicon thin films. The results of the model clearly show that wedges or other asperities in the wake of a crack do not increase the magnitude of the stress intensity factor during compression.     

Template-assisted large-scale ordered arrays of ZnO pillars for optical and piezoelectric applications

Spatially separated ZnO pillars, typically 300 nm in diameter and 2 microm in height, are fabricated via a template-directed approach that leads to long-range hexagonal order. The templates of Au nanodisk arrays are obtained by using metal membranes as a lithography mask. The growth of ZnO pillars is performed in a double-tube system through vapor diffusion-deposition. The growth mechanism of the pillars is studied in detail and is proposed to be a combination of vapor-liquid-solid and vapor-solid models. The piezoelectric and optical properties of single pillars are characterized using piezoresponse force microscopy and micro-photoluminescence spectroscopy, respectively. The pillars show strong excitonic emissions up to room temperature, which indicate a relatively low defect density and good crystalline quality. The obtained piezoelectric coefficient d(33) is (7.5+/-0.6) pm V(-1), which is to our knowledge the first reported value for a single nanopillar.     

Experimental and mathematical modeling for fracture of rock joint with regular asperities

This paper is aimed at developing a mathematical model for the deformation behavior of a rock joint that explicitly accounts for the effects of joint surface topography. The present work is focused on rock joints with triangle-shaped regular asperities. Specimens of artificial rock joint with triangle-shaped asperities were made of simulated rock material and tested in the laboratory. Experimental results are examined to identify three mechanisms that influence the deformation of a rock joint: sliding, separation of asperity contact-faces, and shear fracture of asperities. A modeling methodology is then described and the behaviors of an asperity contact-face, including separation, sliding and shear fracture are discussed. The stress-deformation relationship of a rock joint is subsequently derived and the model performance is evaluated by comparing the predicted results from the derived model and the measured results from experiments.     

Controlled growth and field-emission properties of NbSe2 micro/nanostructured films

Single-crystalline NbSe2 nanobelt, nanorod (containing nanotube), and microplate films were grown on Nb substrates by a surface-assisted chemical-vapor-transport (CVT), respectively. The nanobelts have a rectangular section of 50 x 250 to 300 x 4500 nm2, and a length up to 330 microm. The nanorods have a hexagonal section with a diameter of about 0.1-0.5 microm, and a length up to 15 microm. The nanotubes have rectangular, pentagonal or round sections with a diameter of about 0.4-0.5 microm, a tube-wall thickness of about 45 nm, and a length up to several microns. The microplates have a hexagonal section with a diameter of about 0.05-10 microm and a thickness of about 100 to 600 nm. Field-emission experiments using the films as cold electron cathodes showed that they had notable emission currents and low turn-on fields, suggesting their potential applications in field emission devices.     

High-aspect-ratio, silicon oxide-enclosed pillar structures in microfluidic liquid chromatography

The present paper discusses the ability to separate chemical species using high-aspect-ratio, silicon oxide-enclosed pillar arrays. These miniaturized chromatographic systems require smaller sample volumes, experience less flow resistance, and generate superior separation efficiency over traditional packed bed liquid chromatographic columns, improvements controlled by the increased order and decreased pore size of the systems. In our distinctive fabrication sequence, plasma-enhanced chemical vapor deposition (PECVD) of silicon oxide is used to alter the surface and structural properties of the pillars for facile surface modification while improving the pillar mechanical stability and increasing surface area. The separation behavior of model compounds within our pillar systems indicated an unexpected hydrophobic-like separation mechanism. The effects of organic modifier, ionic concentration, and pressure-driven flow rate were studied. A decrease in the organic content of the mobile phase increased peak resolution while detrimentally effecting peak shape. A resolution of 4.7 (RSD = 3.7%) was obtained for nearly perfect Gaussian shaped peaks, exhibiting plate heights as low as 1.1 and 1.8 μm for fluorescein and sulforhodamine B, respectively. Contact angle measurements and DART mass spectrometry analysis indicate that our employed elastomeric soft bonding technique modifies pillar properties, creating a fortuitous stationary phase. This discovery provides evidence supporting the ability to easily functionalize PECVD oxide surfaces by gas-phase reactions.     

Superhydrophobic films on glass surface derived from trimethylsilanized silica gel nanoparticles

The paper deals with the fabrication of sol-gel-derived superhydrophobic films on glass based on the macroscopic silica network with surface modification. The fabricated transparent films were composed of a hybrid -Si(CH(3))(3)-functionalized SiO(2) nanospheres exhibiting the desired micro/nanostructure, water repellency, and antireflection (AR) property. The wavelength selective AR property can be tuned by controlling the physical thickness of the films. Small-angle X-ray scattering (SAXS) studies revealed the existence of SiO(2) nanoparticles of average size ～9.4 nm in the sols. TEM studies showed presence of interconnected SiO(2) NPs of ～10 nm in size. The films were formed with uniformly packed SiO(2) aggregates as observed by FESEM of film surface. FTIR of the films confirmed presence of glasslike Si-O-Si bonding and methyl functionalization. The hydrophobicity of the surface was depended on the thickness of the deposited films. A critical film thickness (>115 nm) was necessary to obtain the air push effect for superhydrophobicity. Trimethylsilyl functionalization of SiO(2) and the surface roughness (rms ≈30 nm as observed by AFM) of the films were also contributed toward the high water contact angle (WCA). The coated glass surface showed WCA value of the droplet as high as 168 ± 3° with 6 μL of water. These superhydrophobic films were found to be stable up to about 230-240 °C as confirmed by TG/DTA studies, and WCA measurements of the films with respect to the heat-treatment temperatures. These high water repellant films can be deposited on relatively large glass surfaces to remove water droplets immediately without any mechanical assistance.     

多尺度模拟研究纳米凸体几何形貌对初始塑性的影响

研究金属表面微凸体的力学行为对深入理解摩擦、磨损和设计微纳米机电器件有很大帮助.采用准连续方法探索了纳米压痕作用在薄膜(001)表面的纳米微凸体几何形貌对铝和铜薄膜初始塑性的影响规律.结果显示,相较于平坦表面,微凸体的存在显著地降低了薄膜的屈服应力.矩形微凸体横纵比对屈服应力的影响不大.随着底角α的增大,梯形微凸体的屈服应力呈现降低的趋势,尤其是α＞54.7°.同时,在纳米尺度限制全位错形成的条件下,铝中可能容易形成挛晶结构.     

Fabrication of Hierarchical Pillar Arrays from Thermoplastic and Photosensitive SU‐8

By exploiting the thermoplastic and photosensitive nature of SU‐8 photoresists, different types of hierarchical pillar arrays with variable aspect ratios are fabricated through capillary force lithography (CFL), followed by photopatterning. The thermoplastic nature of SU‐8 enables the imprinting of micropillar arrays with variable aspect ratios by CFL using a single poly(dimethylsiloxane) mold, simply by tuning the initial film thickness of SU‐8 on a substrate. The pillar array is subsequently photopatterned through a photomask, followed by post‐exposure baking above the glass transition temperature (T_g) of SU‐8. The pillars in the exposed region become highly crosslinked and, therefore, neither soluble nor able to reflow above T_g, whereas the pillars in the unexposed regions can reflow and flatten out. Two developing strategies are investigated after UV exposure of the SU‐8 pillar arrays including i) solvent development and drying and ii) thermal reflow to create bilevel hierarchical structures with short pillars and single‐level, dual‐scaled, high‐aspect‐ratio (up to 7.7) pillars in a microdot array, respectively.     

Micro and macro contact mechanics for interacting asperities

Contact of rough surfaces at micro and macro scales is studied in this paper. The asperities at micro scale are characterised by small radius of curvature whereas the waviness is characterised by large radius of curvature. When two rough surfaces come in contact, on the micro scale, of asperities contacts in a very small area leave large gaps between the surfaces; whereas on the macro scale the surfaces conform to each other under the application of load without gaps. Contact at micro scale is modelled by superposition of Hertzian stress fields of individual asperity contacts and the waviness at macro scale is modelled as a mixed boundary problem of rough punch indentation where displacements of uneven profile are prescribed along the region of contact. In both the cases for simplification the roughness is assigned to one surface making the other surface perfectly flat an assumption often made in contact mechanics of rough bodies. The motivation for modelling the asperities at micro scales comes from the preliminary results obtained from photoelastic experiments. Numerical results are presented based on the analytical results available for Hertzian contacts. The motivation for modelling the asperities at macro scales comes from the results available in literature for flat contacts from solving mixed boundary elasticity problems. A condition of full stick is assumed along the contact which is a common assumption made for rough contacts. The numerical results are presented for both the cases of rough contact at micro and macro scales.     

Optical observations of “junction growth” in asperities of copper,aluminium, PTFE and nylon under combined normal and tangential stresses

An experimental investigation is described in which the phenomenon of junction growth in model conical and spherical asperities of copper, aluminium, PTFE and nylon has been examined optically. The test asperity was first normally pressed against a smooth flat surface of soda-lime glass and the contact observed through the glass surface. In the presence of the normal load the asperity deformed plastically. When a tangential force was applied, the size of the real area of contact between the two solids, as measured in situ, was found to increase for all the asperities used. Depending upon the geometry and material of the test asperity, the increase in the size of the contact area was up to 40%. The behaviour was compared with an analytical expression for junction growth in the case of a right circular cylindrical asperity. The closest agreement between the measurements and the theory was found for the 60° conical asperities of work-hardened copper and for nylon spheres. The sliding of the asperity on the glass plate caused transfer of the material of the former to the latter. This occurred for all the asperities used. Moreover, the sliding of the metallic asperities resulted in up to 5 m deep grooves on them as well as on the glass plate. These observations have also been briefly discussed.