Submicrometer dimple array based interference color field displays and sensors

We report a technique for producing bright color fields over extended surfaces, via optical interference, with the capability of producing arbitrary visible colors in areas as small as 100 microm2. Periodic arrays of submicrometer dimples are fabricated on reflective silicon surfaces, and diffraction-induced mutual interference of light reflected from the upper and lower levels of the dimpled surfaces generates color depending on wavelength scaled dimple depth and periodicity. Colors of the entire visible spectrum can be generated by dimple arrays with different dimple depths. The topological permeability of such an open surface readily allows infusion of liquids, with different refractive indices, for color switching and detection. These easy to fabricate, scalable, robust devices, on solid as well as flexible supports, could find a wide range of applications such as cheap high-resolution printable dye/pigment-free displays, reliable index-of-refraction sensors with color readout for liquids, and lab-on-chip liquid flow monitors.     

Microstructural and chemical surface and rim zone changes of ferrite-perlite 42CrMo4 steel after electrochemical machining

Electrochemical machining is based on the anodic dissolution of most metals and generates high quality polished surfaces. However, ferrite-perlite 42CrMo4 steel reveals local optical changes at the surface after electrochemical finishing, such as a widely variable surface finish from shiny (reflective) to rough (dark) surfaces even after one processing step. The optical different surface areas of ferrite-perlite 42CrMo4 steel (AISI 4140) are studied by different electron microscopy techniques, x-ray diffraction and x-ray photoelectron spectroscopy to gain information about the local chemistry of the reaction layers and residual stresses of the rim zone. The results show that the rim zone for the different surface areas are about 50 nm–100 nm thick and contain oxygen. Selected area diffraction reveals the formation of iron(II/III) oxide (Fe₃O₄) and x-ray photoelectron spectroscopy confirms the formation of a mixed iron oxide (Fe_3-xO₄) with a variation of the oxidation state for both near-surface rim zones. Furthermore, the reflective surfaces reveal a homogeneous dissolution of ferrite and cementite lamellae whereas the rough surfaces show a preferred dissolution of cementite and an inhomogeneous dissolution of ferrite within the rim zone. X-ray diffraction measurements do not show any introduced residual stresses in the rim zone.     

Meso-scale dislocations and friction of shape-complementary soft interfaces

The interface between two surfaces patterned with complementary shapes such as arrays of ridge–channel structures or pillars accommodates relative misorientation and lattice mismatch by spontaneous production of dislocation arrays. Here, we show that the relative sliding of such an interface is accomplished by dislocation glide on the interfacial plane. An exception is the singular case where the lattices are perfectly matched across the sample dimension, in which case sliding is accompanied by motion of edge-nucleated defects. These are meso-scale analogues of molecular sliding friction mechanisms between crystalline interfaces. The dislocations, in addition to the long-range elastic energy associated with their Burgers vectors, also cause significant out-of-plane dilation, which props open the interface locally. For this reason, the sliding friction is strongly pressure dependent; it also depends on the relative orientation of the patterns. Sliding friction can be strongly enhanced compared with a control, showing that shape-complementary interfaces can be engineered for strongly enhanced pressure- and orientation-dependent frictional properties in soft solids.     

Digital speckle pattern interferometry for deformation analysis of inner surfaces of cylindrical specimens

Deformation study of curved engineering and technical surfaces, such as pipes and pressure vessels, has gained much importance in the recent past. Speckle interferometric techniques and their electronic and digital analogs, which are whole field techniques, have been effectively applied for practical nondestructive testing applications over the years. However, little work has been done that discusses the speckle fringe formation with a fruitful theoretical formulation to study deformation analysis of curved surfaces. We propose an extended theory for speckle fringe formation on curved surfaces, which can be applied to the study of curved engineering and technical specimens under various loading conditions such as in-plane, out-of-plane, and out-of-plane shear configurations. Simulated contours are generated by use of finite element models with similar loading conditions, and the data are analyzed and compared with the obtained experimental results.     

Self-organized nanotube serpentines

Carbon nanotubes have unique mechanical, electronic, optical and thermal properties, which make them attractive building blocks in the field of nanotechnology. However, their organization into well-defined straight or curved geometries and arrays on surfaces remains a critical challenge for their integration into functional nanosystems. Here we show that combined surface- and flow-directed growth enable the controlled formation of uniquely complex and coherent geometries of single-walled carbon nanotubes, including highly oriented and periodic serpentines and coils. We propose a mechanism of non-equilibrium self-organization, in which competing dissipative forces of adhesion and aerodynamic drag induce oscillations in the nanotubes as they adsorb on the surface. Our results demonstrate the use of 'order through fluctuations' to shape nanostructures into complex geometries. The nanotube serpentines and loops are shown to be electrically conducting and could therefore find a wide range of potential applications, such as receiving and transmitting antennas, heating and cooling elements, optoelectronic devices and single-molecule dynamos.     

面向多种类型和复杂边界的曲面近似展开系统

通过对曲面近似展开系统的研究，主要解决两方面关键性的技术问题，一是如何从界面中识别公式表达式并转换成系统所能识别的变量和函数；二是如何解决复杂边界的展开问题，随着这些问题的解决，研制成功了面向多种类型和复杂边界的曲面近似展开系统。     

Reduction photolithography using microlens arrays: applications in gray scale photolithography

This paper describes the application of reduction photolithography, using arrays of microlenses and gray scale masks, to generate arrays of micropatterns having multilevel and curved features in photoresist. This technique can fabricate, in a single exposure, three-dimensional microstructures (e.g., nonspherical microlens arrays) over areas of approximately 2 x 2 cm2. The simple optical configuration consisted of transparency film (having centimeter-sized features) as gray scale photomasks, an overhead projector as the illumination source, and arrays of microlenses as the size-reducing elements. Arrays of 40- and 100-microm lenses achieved a lateral size reduction of approximately 10(3) and generated patterns of well-defined, multilevel structures; these structures may find use in applications such as diffractive optics.     

Diffraction analysis of rotationally symmetric optical systems using computer-generated aberration polynomials

A ray trace scheme for the automatic generation of optical aberration polynomials to arbitrary orders pioneered by T. B. Andersen is successfully applied to the diffraction analysis of rotationally symmetric optical systems on a desk-top computer. The diffraction-based optical transfer functions at various field positions are computed using the relatively new Winograd Fourier transform algorithm. The coding includes aspherical and reflective surfaces.     

A Langmuir-Blodgett study of the orientation of the cancer photoradiation therapy drug dihematoporphyrin ether at water-air and water-fatty-acid-air interfaces

The fluorescent molecule dihematoporphyrin ether (DHE), which is known to become sequestered in cells and which is currently being used for “photoradiation” cancer therapy in clinical trials, may organize into two-dimensional arrays at a water-membrane interface. Some of the consequences of such ordering could be as follows: (1) to create a light-gathering apparatus in the cell analogous to chlorophyll in photosynthetic units; (2) to participate in the cytotoxicity mechanism of DHE, leading to the detection of anisotropy in the absorption and/or emission of visible light which would allow coupling of (cytotoxic) optical energy to the cell membrane; (3) to enhance the DHE—singlet-oxygen cytotoxicity mechanism considered to be operative in cancer cells. We present here evidence for the existence of these arrays, based on evaluation of surface pressure vs. trough area data, polarized and unpolarized visible reflectance spectra on water, and polarized and unpolarized UV-visible spectra on glass. Preliminary conclusions are as follows.

• 1.(1) DHE forms a film at water-air and water-fatty-acid-air interfaces and probably lies with its ring planes parallel to the water in an “overlapped” configuration.
• 2.(2) A shift from one absorbing species of DHE to another may occur at the water-air interface during compression experiments.
• 3.(3) DHE orientation at an interface may be affected by fatty acid present at the interface.
• 4.(4) A preferential orientation of DHE oscillators probably exists on a solid support. We investigate the analogy between DHE and the light-gathering chlorophyll photosynthetic unit, and the anisotropic (directional) capabilities of ordered DHE in Langmuir-Blodgett films and cells.

     

Monolithic folded resonator for evanescent wave cavity ringdown spectroscopy

An optical resonator is characterized that employs both ultrahigh-reflective coated surfaces and total internal reflection to enable cavity ringdown spectroscopy of surfaces, films, and liquids. The monolithic folded design possesses a polarization-independent finesse that allows polarization-dependent phenomena, such as molecular orientation, to be probed. Although a restricted bandwidth (~15% of the design wavelength) results from use of reflective coatings, the resonator provides high sensitivity and facile operation. A minimum detectable absorption of 2.2 x 10(-6) was obtained for single laser shots by use of multimode excitation at 530 nm with an excimer-pumped, pulsed dye laser.     

Highly corrected close-packed microlens arrays and moth-eye structuring on curved surfaces

The fabrication of near-micrometer-sized close-packed coherent microlens arrays on spheric or aspheric surfaces has been accomplished by use of a compact holographic projector system that was developed for producing multimicrometer down to submicrometer grid patterning on curved surfaces. The microlens arrays, which can be utilized as moth-eye relief structures, are formed in a photoimageable bisbenzocyclobutene polymeric resin by a photolytic process involving standing-wave interference patterns from the holographic projector system. Because of absorption, each integral microlenslet of the finished arrays possesses a near-paraboloid contour. The trajectories of the meridional rays from each microlenslet can be optimized to intersect at either a single point or a locus of points.     

Interface handling for three‐dimensional higher‐order XFEM‐computations in fluid–structure interaction

Three‐dimensional higher‐order eXtended finite element method (XFEM)‐computations still pose challenging computational geometry problems especially for moving interfaces. This paper provides a method for the localization of a higher‐order interface finite element (FE) mesh in an underlying three‐dimensional higher‐order FE mesh. Additionally, it demonstrates, how a subtetrahedralization of an intersected element can be obtained, which preserves the possibly curved interface and allows therefore exact numerical integration. The proposed interface algorithm collects initially a set of possibly intersecting elements by comparing their ‘eXtended axis‐aligned bounding boxes’. The intersection method is applied to a highly reduced number of intersection candidates. The resulting linearized interface is used as input for an elementwise constrained Delaunay tetrahedralization, which computes an appropriate subdivision for each intersected element. The curved interface is recovered from the linearized interface in the last step. The output comprises triangular integration cells representing the interface and tetrahedral integration cells for each intersected element. Application of the interface algorithm currently concentrates on fluid–structure interaction problems on low‐order and higher‐order FE meshes, which may be composed of any arbitrary element types such as hexahedra, tetrahedra, wedges, etc. Nevertheless, other XFEM‐problems with explicitly given interfaces or discontinuities may be tackled in addition. Multiple structures and interfaces per intersected element can be handled without any additional difficulties. Several parallelization strategies exist depending on the desired domain decomposition approach. Numerical test cases including various geometrical exceptions demonstrate the accuracy, robustness and efficiency of the interface handling. Copyright © 2009 John Wiley & Sons, Ltd.     

Deformation of internal boundaries

A geometrical analysis of the deformation of internal boundaries is presented using the slip systems as reference co-ordinate axes to describe the orientation of the two phases adjacent to the boundary. The present analysis can be applied to any type of boundary such as a grain boundary, a twin boundary or a two-phase interface. The nature of the disturbance left by a dislocation cutting through the boundary is characterized by a boundary dislocation, the Burgers vector of which can be determined from the orientation relationship between the adjacent slip systems. Whenever the crystal dislocation, cutting through the boundary, has a Burgers vector component normal to the boundary, the disturbance also possesses a ledge character, the motion of which may cause both grain boundary sliding as well as migration. The formulae derived are applied to simple cases to determine the nature of the boundary dislocations.     

Low-cost lithographic fabrication of relief patterns in a SiO2-TiO2 hybrid Sol-Gel glass on curved surfaces

We describe a low-cost method of fabricating optical patterns in a hybrid sol-gel glass on curved surfaces by means of soft lithography. The ion etching step, which is presently difficult to realize on curved surfaces, is avoided in this process. Using the proposed soft lithography technique, it is possible to transfer high-quality patterns to a hybrid sol-gel glass on curved surfaces. This technique offers a low-cost and simple method for obtaining optical glass structures on such surfaces. The use of a sol-gel glass (replacing an epoxy) layer greatly prolongs the life of replica gratings, especially in the vacuum ultraviolet applications. The text was submitted by the authors in English.     

Geometric analysis of woven or braided reinforcement for use in composite shells

Analytical and computational means are developed for a geometric analysis of a woven fabric or braiding reinforcement in laminated composite shells. The analysis involves numerical construction of the fiber trajectories in each lamina of a doubly curved shell and is needed for assuring both the statical adequacy (strength, stiffness) and the geometric feasibility of the reinforcement. The output includes the fiber lengths in each of the two fiber arrays (determining the cutout pattern for the lamina) and the fiber intersection angle (which defines the directional lay-up at any location in the shell).

The accuracy of the developed geometric analysis and its sensitivity to initial conditions are assessed by comparing the obtained results with available exact analytical solutions for surfaces of translation. The analysis is shown to be robust and computationally efficient, so that aside from its immediate use, it can serve as a basis for addressing a more challenging problem—the geometric optimization of a laminated composite shell.     

Imaging with tilted surfaces: an efficient matrix method for the generalized Scheimpflug condition and its application to rotationally symmetric triangulation

An efficient two-dimensional matrix method is presented that facilitates the design of optical systems with tilted surfaces for which the requirement or knowledge of the orientation of the image plane is necessary, i.e., for which a generalized Scheimpflug condition is needed. In more general terms, the method results in imaging properties of second-order expansion, but the method is linear. Therefore the complexity of the design process is considerably reduced. The strength of the design method is demonstrated in detail for a novel application in which a reflective optical system of several surfaces is required for rotationally symmetric triangulation.     

Plasmonic Janus Microspheres Created from Pickering Emulsion Drops

Metal nanostructures have been created in a film format to develop unique plasmonic properties. Here, well-defined metal nanostructures are designed on the surface of microspheres to provide plasmonic microgranules. As conventional techniques are inadequate for nanofabrication on spherical surfaces, photocurable emulsion drops with a regular array of silica particles are employed at the interface to create periodic nanostructures. The silica particles, originating from the dispersed phase, fully cover the interface by forming a non-close-packed hexagonal array after drop generation, and slowly protrude to the continuous phase during aging while their interparticle separation decreases. Therefore, hexagonal arrays of spherical dimples with controlled geometry and separation are created on the surface of microspheres by photocuring the drops and removing the particles. Directional deposition of either aluminum or gold results in a continuous film with a hexagonal array of holes on the outermost surface and isolated curved disks in dimples, which renders the hemisphere of microspheres plasmonically colored. The resonant wavelength is controlled by adjusting the aging time, metal thickness, and size of silica particles, providing various plasmonic colors. This granular format of the plasmonic Janus microspheres will open a new avenue of optical applications including active color pixels, optical barcodes, and microsensors.     

Printed multilayer superstructures of aligned single-walled carbon nanotubes for electronic applications

We developed means to form multilayer superstructures of large collections of single-walled carbon nanotubes (SWNTs) configured in horizontally aligned arrays, random networks, and complex geometries of arrays and networks on a wide range of substrates. The approach involves guided growth of SWNTs on crystalline and amorphous substrates followed by sequential, multiple step transfer of the resulting collections of tubes to target substrates, such as high-k thin dielectrics on silicon wafers, transparent plates of glass, cylindrical tubes and other curved surfaces, and thin, flexible sheets of plastic. Electrical measurements on dense, bilayer superstructures, including crossbars, random networks, and aligned arrays on networks of SWNTs reveal some important characteristics of representative systems. These and other layouts of SWNTs might find applications not only in electronics but also in areas such as optoelectronics, sensors, nanomechanical systems, and microfluidics.     

任意开口薄壁截面圆弧曲梁的通用线性理论

在曲梁精确的翘曲位移基础上,根据变分原理,提出了对任意开口薄壁截面圆弧曲梁通用的线性理论,给出平衡微分方程和相应的边界条件。定义了两个新的变量H_v和H_θ,借助它们可以很方便地计算曲梁中的剪力和扭矩。最后就该理论在常见截面形式(工字形,槽形及无对称轴H形)水平曲梁中的应用进行说明,并与已有理论进行比较。     

Free and forced vibration analysis of thin, laminated, cylindrically curved panels

A comprehensive vibration study of thin, laminated, cylindrically curved shell panels (based on the shell theory of Love with a modification by Arnold and Warburton) is conducted by using the h-p version of the finite-element method (FEM). Polynomially enriched stiffness and mass matrices are derived from classical shell theory using Symbolic Computing, and then stored in algebraic form for a single, generic element. A number of such elements may then be combined to form the global stiffness and mass matrices for a more general co-axial and/or co-circumferential assembly. Any of the classical edge conditions, or point corner supports, may be accommodated in the analysis; forcing may be applied through one or more point forces acting normal to the shell surface. Excellent agreement has been found with the work of other investigators, and some new results are presented for a multiply supported curved panel made from the aluminium-glass-fibre hybrid GLARE. The h-p method is shown, by example, to offer an efficient means of conducting typical repetitive sensitivity analyses, such as varying the fibre orientation and the stacking sequences of a given panel.