Optimization of micro and nanoimprint de-embossing by elastic fracture modelling

A semi-analytical model is presented for the de-embossing phase of the nanoimprint patterning process. The model is based on established principles of elastic fracture mechanics as developed for fibre-bridged cracking in composites. De-embossing is idealized as a steady-state fracture process, which enables the energy change to be considered by reference to a unit cell of a cylindrical polymer post, de-embossing from an axisymmetric stamp. The model provides predictions of the achievable limits for de-embossing as a function of key geometrical variables such as feature size, area ratio and aspect ratio and material properties such as interfacial adhesion, shear strength, polymer yield strength and the ratio of the elastic moduli of the polymer and the stamp. Process 'maps' have been created showing de-embossing limits. A strong dependence of the achievable aspect ratio on the pattern area ratio and the interfacial shear stress is seen. For polymer yield stresses similar to that of PMMA, the critical interfacial strain energy release rate has little effect on de-embossing. Large area and aspect ratios are predicted to be achievable by keeping the ratio of polymer and stamp Young's moduli between 0.015 and 2.5. The model provides key insights into the physical origins of previously observed limits on the achievable aspect ratios and area ratios achieved by imprint patternin

Sub-μ\mu structured Lotus Surfaces Manufacturing

Sub-micro structured surfaces allow modifying the behavior of polymer films or components. Especially in micro fluidics a lotus-like characteristic is requested for many applications. Structure details with a high aspect ratio are necessary to decouple the bottom and the top of the functional layer. Unlike to stochastic methods, patterning with a LIGA-mold insert it is possible to structure surfaces very uniformly or even with controlled variations (e.g. with gradients). In this paper we present the process chain to realize polymer sub-micro structures with minimum lateral feature size of 400 nm and up to 4 micrometers high.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/handle/2042/16838

First-principles calculation of the intersublattice exchange interactions and Curie temperatures of full Heusler alloys Ni2MnX (X=Ga, In, Sn, Sb)

The interatomic exchange interactions and Curie temperatures in Ni-based full Heusler alloys Ni2MnX with X=Ga, In, Sn and Sb are studied within the framework of the density-functional theory. The calculation of the exchange parameters is based on the frozen-magnon approach. Despite closeness of the experimental Curie temperatures for all four systems their magnetism appeared to differ strongly. This difference involves both the Mn-Mn and Mn-Ni exchange interactions. The Curie temperatures, Tc, are calculated within the mean-field approximation by solving a matrix equation for a multi-sublattice system. Good agreement with experiment for all four systems is obtained. The role of different exchange interactions in the formation of Tc of the systems is discussed.Comment: 6 pages, 4 figure

Shape-memory polymers as flexible resonator substrates for continuously tunable organic DFB lasers

We introduce shape-memory polymers (SMP) as substrate material for active optical devices. As an exemplary application we build a tunable organic semiconductor distributed feedback (DFB) laser. Hence, we transfer a second order Bragg grating with a period of 400 nm into SMP foils by hot embossing. The composite organic gain medium Alq3:DCM evaporated on the SMP substrate serves as laser active material. Mechanical stretching of the substrate increases the grating period temporarily and triggering the shape-memory effect afterwards reduces the period on demand. In this way, we can adjust the grating period to achieve a broad continuously tuning of the laser emission wavelength by 30 nm

Modeling of large area hot embossing

Today, hot embossing and injection molding belong to the established plastic molding processes in microengineering. Based on experimental findings, a variety of microstructures have been replicated so far using the processes. However, with increasing requirements regarding the embossing surface and the simultaneous decrease of the structure size down into the nanorange, increasing know-how is needed to adapt hot embossing to industrial standards. To reach this objective, a German-Canadian cooperation project has been launched to study hot embossing theoretically by a process simulation and experimentally. The present publication shall report about the first results of the simulation - the modeling and simulation of large area replication based on an eight inch microstructured mold.Comment: Submitted on behalf of EDA Publishing Association (http://irevues.inist.fr/EDA-Publishing

Fabrication and evaluation of a nickel shim for large-area hot embossing of plant surface structures

Petal textures exhibit outstanding broadband and omnidirectional light harvesting properties on solar cells [1,2] + by choice of low surface energy materials their self-cleaning properties can be harnessed [3]. A hot embossing routine via robust nickel embossing tools has been developed for a large area fabrication of such textures

Snake‐Inspired, Nano‐Stepped Surface with Tunable Frictional Anisotropy Made from a Shape‐Memory Polymer for Unidirectional Transport of Microparticles

The ventral scales of many snake species are decorated with oriented micro‐fibril structures featuring nano‐steps to achieve anisotropic friction for efficient locomotion. Here, a nano‐stepped surface with tunable frictional anisotropy inspired by this natural structure is presented. It is fabricated by replicating the micro‐fibril structure of the ventral scales of the Chinese cobra (Naja atra) into a thermo‐responsive shape‐memory polymer via hot embossing. The resulting smart surface transfers from a flat topography to a predefined structure of nano‐steps upon heating. During this recovery process, the nano‐steps grow out of the surfaces resulting in a surface with frictional anisotropy, which is characterized in situ by an atomic force microscopy. The desired frictional anisotropy can be customized by stopping the heating process before full recovery. The nano‐stepped surface is employed for the unidirectional transport of microscale particles through small random vibrations. Due to the frictional anisotropy, the microspheres drift unidirectionally (down the nano‐steps). Finally, dry self‐cleaning is demonstrated by the transportation of a pile of microparticles

Bio-inspired, large scale, highly-scattering films for nanoparticle-alternative white surfaces

Inspired by the white beetle of the genus Cyphochilus, we fabricate ultra-thin, porous PMMA films by foaming with CO_2 saturation. Optimising pore diameter and fraction in terms of broad-band reflectance results in very thin films with exceptional whiteness. Already films with 60 µm-thick scattering layer feature a whiteness with a reflectance of 90%. Even 9 µm thin scattering layers appear white with a reflectance above 57%. The transport mean free path in the artificial films is between 3.5 µm and 4 µm being close to the evolutionary optimised natural prototype. The bio-inspired white films do not lose their whiteness during further shaping, allowing for various applications

Smart structures

Treball desenvolupat dins el marc del programa 'European Project Semester'.Since a few years, the civil engineering world can see a changing about how to preserve and monitor the structures. Thanks to the system of Smart Structures we can notice the early damages on the structure and anticipate the future. This science is already applied on bridges and now different researches work on buildings, such as the company Neàpolis in Vilanova i la Geltrú. As participators of European Project Semester at the Universitat Politècnica de Catalunya a feasibility study and cost analysis for the implementation of Smart Structure systems had to be done. This has been an assignment of the innovation agency Neàpolis, which was founded in 2007 by the city council of Vilanova I la Geltrú. The outcome of this project should be a cost-benefit-analysis, which compares the costs to the savings and recommendations for the implementation of sensors in the Sant Antoni church and the Neàpolis building. The research has been done in order to give Neàpolis an indication whether Smart Structures are feasible to put into buildings by lowering maintenance cost and improving the life span of buildings. There is not a known study that is similar to this project, in our knowledge this is the first feasibility study on Smart Structure Systems that has been performed. This is why the research is of importance to the company. Because it has been not possible to gain a great deal of useful information from the internet, the assistance of the supervisors Félix Ruiz Gorrindo and Pau Martí and third parties has been necessary. In this report you can read on the one hand about the way research has been done. First there are pointed out the most important advantages of Smart Structures. Then there are information about the research of sensors and pathologies that could occur in buildings and how they are related to the project. Our supervisors have been given us lectures about civil engineering to explain the different ways of how a building can be constructed. On the other hand you can find information about the planning of the implementation of the Smart Structures in the Neàpolis building and the Parroquia Arciprestal Sant Antoni Abat (Sant Antoni church). The buildings are both located in Vilanova i la Geltrú, Spain. After the inspection of both buildings and the transfer of the blueprints we were looking for the best positions for the sensors in the buildings. Therefrom we deduced different concepts for the implementation based on different states of intensities. Relation to these results formulas has been created to show from which point the implementation of Smart Structure systems in buildings is feasible. There are proposed formulas for the feasibility in time as well as formulas for the break-even-point. Also the different parameters are explained in this report. In the end an example of the Neàpolis building was realised, to prove that the proposed formulas are meaningful. With the gathering of all the information a conclusion has been drawn on which recommendations have been given