Droplet Transport on a Nano‐ and Microstructured Surface with a Wettability Gradient in Low‐Temperature or High‐Humidity Environments

Directional driving of a droplet can be achieved on a gradient‐exhibiting, nanostructured microhump (GNMH) surface at low temperature and high humidity. The GNMH surface is fabricated using a commercial carbon fiber plate with an array of microscale hump structures; nanotechniques are used to form varying nanostructures on the microhump array, producing the micro‐ and nanostructured surface. The different nanostructures result in a wettability gradient along the surface, enabling droplet transport with the help of vibration—even at low temperature or high humidity. In contrast, simply nanostructured surfaces or microstructured surfaces that also have a wettable gradient do not enable droplet transport at low temperature or high humidty. In a range of subzero temperatures or in a range of high‐humidity conditions, the GNMH surface retains its superhydrophobicity and ability for directional droplet transport along its wettability gradient. These results may assist in the design of surfaces required for cold environments, such as microreactors, chemical analytic devices, and sensors.     

Nanosecond Laser “Pulling” Patterning of Micro–Nano Structures on Zr-Based Metallic Glass

Flexible and controllable fabrication of micro–nano structures on metallic glasses (MGs) endow them with more functional applications, but it is still challenging due to the unique mechanical, physical, and chemical properties of MGs. In this study, inspired by a new physical phenomenon observed in the nanosecond laser–MG interaction (i.e., the surface structure is transformed from the normally observed microgroove into the micro–nano bulge at a critical peak laser power intensity), a nanosecond laser “pulling” method is proposed to pattern the MG surface. The formation mechanism and evolution of the micro–nano bulge are investigated in detail, and accordingly, various micro–nano structures including the unidirectional stripe, pillar, cross-hatch patterns, “JLU”, circle, triangle, and square, are derived and created on the MG surface, which affects the surface optical diffraction. Overall, this study provides a highly flexible and controllable method to fabricate micro–nano structures on MGs.     

Programmable chemical gradient patterns by soft grayscale lithography

A method for fabricating chemical gradients on planar and nonplanar substrates using grayscale lithography is reported. Compliant grayscale amplitude masks are fabricated using a vacuum-assisted microfluidic filling protocol that employs dilutions of a carbon-black-containing polydimethylsiloxane emulsion (bPDMS) within traditional clear PDMS (cPDMS) to create planar, fully self-supporting mask elements. The mask is then placed over a surface functionalized with a hydrophobic coumarin-based photocleavable monolayer, which exposes a polar group upon irradiation. The mask serves to modulate the intensity of incident UV light, thereby controlling the density of molecules cleaved. The resulting molecular-level grayscale patterns are characterized by condensation microscopy and imaging mode time-of-flight secondary-ion mass spectrometry (ToF-SIMS). Due to the inherent flexibility of this technique, the photofuse as well as the gradient patterns can be designed for a wide range of applications; in this paper two proof-of-concept demonstrations are shown. The first utilizes the ability to control the resulting contact angle of the surface for the fabrication of a passive pressure-sensitive microfluidic gating system. The second is a model surface modification process that utilizes the functional groups deprotected during the photocleavage to pattern the deposition of moieties with complementary chemistry. The spatial layout, resolution, and concentration of these covalently linked molecules follow the gradient pattern created by the grayscale mask during exposure. The programmable chemical gradient fabrication scheme presented in this work allows explicit engineering of both surface properties that dictate nonspecific interactions (surface energy, charge, etc.) and functional chemistry necessary for covalent bonding.     

Multifunctional Superamphiphobic TiO2 Nanostructure Surfaces with Facile Wettability and Adhesion Engineering

Compared to conventional top‐down photo‐cleavage method, a facile bottom‐up ink‐combination method to in situ and rapidly achieve water wettability and adhesion transition, with a great contrast on the superamphiphobic TiO₂ nanostructured film, is described. Moreover, such combination method is suitable for various kinds of superamphiphobic substrate. Oil‐based ink covering or removing changes not only the topographical morphology but also surface chemical composition, and these resultant topographical morphology and composition engineering realize the site‐selectively switchable wettability varying from superamphiphobicity to amphiphilicity, and water adhesion between sliding superamphiphobicity and sticky superamphiphobicity in micro‐scale. Additionally, positive and negative micro‐pattern can be achieved by taking advantage of the inherent photocatalytic property of TiO₂ with the assistance of anti‐UV light ink mask. Finally, the potential applications of the site‐selectively sticky superamphiphobic surface were demonstrated. In a proof‐of‐concept study, the microdroplet manipulation (storage, moving, mixing, and transfer), specific gas sensing, wettability template for positive and negative ZnO patterning, and site‐selective cell immobilization have been demonstrated. This study will give an important input to the field of advanced functional material surfaces with special wettability.     

Combinatorial approach to the edge delamination test for thin film reliability—adaptability and variability

We have demonstrated the adaptability and variability of a newly developed combinatorial edge delamination test. This was accomplished through studying the effect of substrate surface energy on the adhesion of thin films. In this combinatorial approach, a library (a single specimen) was fabricated with a polymethyl methacrylate (PMMA) film on a silicon substrate. The film has thickness gradient in one direction and the substrate has an orthogonal surface energy gradient. The thickness gradient was produced with a flow coating technique, and the surface energy gradient was controlled by partial oxidation of an alkylsilane layer on a silicon wafer. Applying a constant temperature to the specimen, interfacial debonding events were observed and a distribution of failure was constructed. Our results demonstrate the proposed combinatorial methodology for rapidly and efficiently evaluating the adhesion of general film/substrate systems as a function of many controllable parameters. In addition, this methodology can be used to predict the reliability distributions of the adhesion for practical parameters.     

Simple model for image-plane polychromatic speckle contrast.

A simple geometrical model was developed for calculation of the contrast of a polychromatic image-plane speckle pattern from a source of light with high spatial coherence. It is based on counting the number of independent speckle patterns that contribute to a given point in the image plane. This results in a simple equation for the contrast as a function of imaging geometry; relative orientation of the projection direction, observation direction, and specimen normal; bandwidth of the light source; and surface roughness. Its validity was established by comparison with an exact solution: rms errors in the calculated contrast were only 0.033 over a wide range of parameter values likely to be encountered in practice.     

Grinding surface roughness measurement based on the co-occurrence matrix of speckle pattern texture

Surface speckle pattern intensity distribution resulting from laser light scattering from a rough surface contains various information about the surface geometrical and physical properties. A surface roughness measurement technique based on the texture analysis of surface speckle pattern texture images is put forward. In the surface roughness measurement technique, the speckle pattern texture images are taken by a simple setup configuration consisting of a laser and a CCD camera. Our experimental results show that the surface roughness contained in the surface speckle pattern texture images has a good monotonic relationship with their energy feature of the gray-level co-occurrence matrices. After the measurement system is calibrated by a standard surface roughness specimen, the surface roughness of the object surface composed of the same material and machined by the same method as the standard specimen surface can be evaluated from a single speckle pattern texture image. The robustness of the characterization of speckle pattern texture for surface roughness is also discussed. Thus the surface roughness measurement technique can be used for an in-process surface measurement.     

Preparation of titanium nitride coated powders by rotary powder bed chemical vapour deposition

Titanium nitride coated powders were prepared by rotary powder bed chemical vapour deposition (CVD) in which a powder in a rotary specimen cell was heated by infrared radiation in a reactant gas stream. Titanium powder covered with TiN or Ti₂N thin film was obtained by diffusion coating treatment of titanium particles (grain size 10 to 50 µm) at 900 to 1000°C and 0.5 to 1.0 atm for 60 min in a nitrogen stream. TiN was coated on to the surface of scaly graphite particles (grain size 30 to 100 µm or 100 to 1000 µm) as well as titanium particles by CVD in the reactant system TiCl₄-N₂-H₂ at 900° C and 1 atm for 40 min. The uniformity of the coating (composition and film thickness) and the dispersability of the coated particles were considerably promoted by rotating the powder bed at about 90 r.p.m. compared with nonrotary powder bed CVD.     

A 2D surface morphology–composition gradient panel for protein-binding assays

We designed a two-dimensional (2D) morphology–composition gradient panel, which has a gradient in surface morphology at constant chemical composition along its length and a gradient in surface chemical composition without change of surface morphology in the orthogonal direction. The panels, which exhibit a 2D gradient in surface wettability, were fabricated by thermolysis of parylene-C followed by oxygen-plasma treatment for various times. As a demonstration study, binding of three different biotinylated serum proteins (B-IgG, B-A, and B-TF) to the 2D panel was investigated. The 2D gradient panels will facilitate development of optimized binding surfaces for various biotechnological applications.     

Palladium nanoparticle seeded electroless metallization of Al/Al2O3 surfaces

A simple method for the formation of palladium nanoparticles on aluminum and aluminum oxide surface is demonstrated. In the present method, the palladium nanoparticles obtained directly on the solid surface by immersing the specimen in palladium(II)acetate solution followed by reduction to metallic palladium by using sodium hypophosphite. In the investigation, as-received, boiled, electropolished and anodized aluminum was used as substrate. Additionally, the method is combined with the electroless nickel plating, which facilitates two steps metallization technique on the respective surfaces. In these cases, specimens were first immersed in palladium(II)acetate solution followed by immersion in electroless nickel plating solution, where, palladium reduced on the specimen surface providing catalytic site for the subsequent electroless nickel deposition. Using the technique, about 6 to 8.5 µm thick Ni-P metallic layer was deposited on the specimen surface.     

Domain analysis by means of magnetotactic bacteria

Magnetotactic bacteria (MB)-cocci as well as a spirillum of type Magnetospirillum gryphiswaldense-were investigated for their applicability for nondestructive domain analysis on soft magnetic materials. Solely magnetotactic cocci which show a definite swimming direction proved to be suitable for this purpose. The intensity of the domains' magnetic stray field H of coated SiFe sheets proved to be high enough to visualize main domains even in distances of 500 μm from the specimen surface, in comparison to about 5 μm for colloid particles. Thus it was possible to develop a specific “domain viewer” which allows simple handling and reuse of bacteria for repeated analysis. Based on theoretical considerations about the cocci's motion in a magnetic field, a computer program for the simulation of spatiotemporal bacterial distributions was developed. Results show that-in contrast to colloid techniques and nonmotile bacteria-the gradient of H does not influence the contrast in an essential way. Due to Brownian motion of motile bacteria, a minimum domain width is required for effective visualizations. This was confirmed by experimental results of both secondary domains of crystalline specimens and narrow surface domains of amorphous bands. However, for small domain structures of the latter, unmotile dead bacteria proved to be applicable. Finally, influences of bacterial concentrations on the contrast as well as the contrast mechanism as a function of time are discussed     

Adhesion enhancement of sol-gel coating on polycarbonate by heated impregnation treatment

The main limitation in using coated plastics for optical components, electronic applications and display systems is the softness of the substrate surfaces, which is responsible for the low impact and abrasion resistance and weak adhesion between the coating and the substrate. In this paper, we report a new strategy for surface pre-treatment of plastics using heated vacuum equipment and sol-gel materials to provide both chemical bonds and penetrated hard layer into the plastic surface to increase the overall performance of the coated plastic components. The heated vacuum treatment process involves: (1) surface cleaning and pore opening by heating and vacuum conditions, (2) impregnation of hydrolyzed hybrid precursor into polymer substrate under pressure and elevated temperature, (3) aminolysis of diffused precursor with surface to form chemical bonds and hardened surface layer, (4) formation of chemical bonds at treated surface with sol-gel hard coating. An impregnation depth of 1.5 µm was detected. Water contact angle dropped to below 40° and roughness increased after treatment. These provided better adhesion by increased wettability and contact area. Much increased nanoindentation hardness and Young's modulus after impregnation provided a gradient in mechanical properties between soft substrate and hard sol-gel coating. The hardened substrate delays the plastic deformation in substrate during pencil scratch test, thereby preventing early gouge failure. Both the better adhesion and the delayed gouge failure contributed to the increased scratch resistance from 6B to 8H after sol-gel coating.     

An experimental and numerical investigation on micro rolling for ultra-thin strip

The demand for miniaturized parts and miniaturized semi-finished products is increasing nowadays, because microforming processes can improve production rate and minimize material waste due to less forming passes. However, traditional macro metal forming processes and modelling cannot be simply scaled down to produce miniaturized micro parts. In this study, a 2-Hi micro rolling mill has been successfully built. Experimental and numerical investigations on the micro rolling process for ultra-thin SUS 304 stainless steel strip have been conducted. The experimental results show that the micro rolling deformation of ultra-thin strip is influenced by size effect which results from the specimen size difference and this size effect is embodied in the flow stress and the friction coefficient. Analytical and finite element (FE) models in describing size effect related phenomena, such as flow stress, friction, rolling force and deformation behaviour, are proposed. The material surface constraint and the material deformation mode are critical in determination of material flow stress curve. The analysis of surface roughness evolution with rolling conditions has also been performed. The identified analysis on deformation mechanics provides a basis for further exploration of the material behaviour in plastic deformation of micro scale and the development of micro scale products via micro rolling.     

Actual versus apparent within cell wall variability of nanoindentation results from wood cell walls related to cellulose microfibril angle

Hardness and elastic modulus of spruce wood cell walls parallel to their axial direction were investigated by means of nanoindentation. In the secondary cell wall layer S2 of individual earlywood and compression wood tracheids, a systematic pattern variability was found. Several factors potentially affecting nanoindentation results were investigated, i.e. specimen orientation related to the indenter tip, cutting direction during specimen preparation, tip geometry, specimen and fibre inclination, respectively, and finally micro fibril orientation. Mechanical property measurements were correlated with structural features measured by confocal Raman spectroscopy. It was demonstrated that very high variability in the measurement of micromechanical cell wall properties can be caused by unintentional small fibre misalignment by few degrees with regard to the indentation direction caused by sub-optimal specimen preparation.     

Theory of Electron Beam Moiré

When a specimen surface carrying a high-frequency line grating is examined under a scanning electron microscope (SEM), moiré fringes are observed at several different magnifications. The fringes are characterized by their spatial frequency, orientation, and contrast. These features of the moiré pattern depend on the spatial frequency mismatch between the specimen grating and the raster scan lines, the diameter of the electron beam, and the detailed topography of the lines on the specimen.A mathematical model of e-beam moiré is developed that expresses the spatial dependence of the SEM image brightness as a product of the local intensity of the scanning beam and the local scattering function from the specimen grating. Equations are derived that give the spatial frequency of the moiré fringes as functions of the microscope settings and the spatial frequency of the specimen grating. The model also describes the contrast of several different types of moiré fringes that are observed at different magnifications. We analyze the formation of these different fringe patterns, and divide them into different categories including natural fringes, fringes of multiplication, fringes of division, and fringes of rotation.     

钢板伸长率不合格原因分析

针对钢板伸长率不合格情况,在20mm厚的钢板上随机取样,进行化学成分和低高倍分析。结果表明,伸长率不合格的试样存在较严重的气泡或含有硫化亚铁的铁素体带,这是引起钢板伸长率不合格主要原因。     

Benard–Marangoni Instability as Possible Modifier of Surface Alloy Composition

Thermophysical properties of amorphous alloys represent the features of a given material specimen, and, as such, they are dependent, in general, on their elemental composition. Some properties are measured at surfaces, and others are measured for the bulk as a whole. Complications arise when the elemental composition varies as a function of position within the material specimen, as demonstrated by simultaneous measurements of thermal diffusivity and elemental composition by time-resolved spectroscopy of laser-produced plasma (LPP) plume emissions. To further understand the source of a rather common near-surface elemental composition anomaly, the evolution of the surface composition of Wood’s alloy under the influence of thermal cycling with, and without, a temperature gradient over the specimen has been investigated. Surface composition modifications have been found to take place by accumulation of irregularly spaced gray patches of an inhomogeneous composition on the surface in the presence of a temperature gradient. Determination of elemental composition by LPP spectroscopy shows the three-dimensional structure of the patches.     

Bulk Micromachining of Si by Metal‐assisted Chemical Etching

Bulk micromachining of Si is demonstrated by the well‐known metal‐assisted chemical etching (MaCE). Si microstructures, having lateral dimension from 5 μm up to millimeters, are successfully sculpted deeply into Si substrate, as deep as >100 μm. The key ingredient of this success is found to be the optimizations of catalyst metal type and its morphology. Combining the respective advantages of Ag and Au in the MaCE as a Ag/Au bilayer configuration leads to quite stable etch reaction upon a prolonged etch duration up to >5 h. Further, the permeable nature of the optimized Ag/Au bilayer metal catalyst enables the etching of pattern features having very large lateral dimension. Problems such as the generation of micro/nanostructures and chemical attacks on the top of pattern surface are successfully overcome by process optimizations such as post‐partum sonication treatment and etchant formulation control. The method can also be successful to vertical micromachining of Si substrate having other crystal orientations than Si(100), such as Si(110) and Si(111). The simple, easy, and low‐cost nature of present approach may be a great help in bulk micromachining of Si for various applications such as microelectromechanical system (MEMS), micro total analysis system (μTAS), and so forth.     

X射线粉末衍射少量试样的试样板制作

从对参与衍射的试样体积(宽度)、入射X射线在试样表面的总光量和亮度及X射线被试样吸收三个方面在扫描过程中的变化的分析出发,讨论了在试样量少到不能以薄层填满整个试样槽时,如何制作试样板以得到衍射强度高的高质量衍射谱的方法.在固定发散狭缝宽度的条件下,为使参与衍射的试样面积大,使长度方向的试样尺寸与X射线管中线焦点的长度相...     

超大比表面积ACF和常规ACF表面结构比较

聚丙烯腈基超大比表面积ＡＣＦ（ＨＳＡＣＦ）与常规的小比表面积ＡＣＦ具有不同的表面结构,常规ＡＣＦ具有较为完善的微晶结构,含有比较丰富的杂原子官能结构,主要存在于骨架碳上的含氮官能团含量较大;而对于ＨＳＡＣＦ,超微粒子尺度减小（类石墨微晶基本不存在）,主要存在于骨架碳上的含氮官能团含量较小,杂原子官能结构的浓度和化学状态与常规ＡＣＦ大不相同,这些都使ＨＳＡＣＦ具有与常规ＡＣＦ不同的纳米孔空间表面结构