Arne Albrecht

Liquid‐Crystalline Elastomer Microvalve for Microfluidics

Dr. A. Sanchez-Ferrer Food & Soft Materials Science Group Institute of Food, Nutrition & Health ETH Zurich, Schmelzbergstrasse 9, 8092 Zurich, Switzerland E-mail: antoni.sanchez@agrl.ethz.ch Dr. A. Sanchez-Ferrer , Prof. H. Finkelmann Albert Ludwigs University Institute for Macromolecular Chemistry Stefan-Meier-Str. 31, 79104 Freiburg, Germany Fischl , Dr. . T Dr. M. Stubenrauch , Dr. A. Albrecht , Prof. H. Wurmus , Prof. M. Hoffmann Ilmenau University of Technology Faculty of Mechanical Engineering Department of Micromechanical Systems Max-Planck-Ring 14, 98693 Ilmenau, Germany

Black silicon—new functionalities in microsystems

Black silicon and its application as a new assembly method for silicon wafers at room temperature is presented. Needle-like structures on the surface after deep reactive ion etching with a length of 15–25 µm and 300–500 nm in diameter interlock with each other to form a bonding interface. After compression of two wafers at room temperature they generate retention forces up to 380 N cm−2 (3.8 MPa). If low contact forces are applied with partially interlocking of the needles, it is possible to generate a reversible Velcro®-like assembly. This new bonding process can be used for applications in the area of microfluidics with catalysts, microoptical or mechanical mountings or carrier wafer bonding in microelectronics.

Understanding the fast lithium storage performance of hydrogenated TiO2 nanoparticles

Anatase TiO2 is considered as one of the promising anode materials for lithium ion batteries (LIBs) because of its nontoxicity, safety, and excellent capacity retention. However, the poor rate capability of TiO2 electrodes, caused by the low electrical conductivity and lithium diffusion coefficient, strongly hinders its practical application in high power LIBs. Herein, we report on the fast lithium storage performance of hydrogenated anatase TiO2 nanoparticles (H-TiO2) prepared by a H2 plasma treatment. The scan-rate dependence of the cyclic voltammetry (CV) analysis reveals that the improved rate capability of H-TiO2 results from the enhanced contribution of pseudocapacitive lithium storage on the particle surface. Combined with the structural properties of H-TiO2, it is suggested that the disordered surface layers and Ti3+ species of H-TiO2 play an important role in the improvement of pseudocapacitive lithium storage. The results help to understand the fast lithium storage performance of H-TiO2 and might pave the way for further studies of other hydrogenated metal oxide electrodes for high power LIBs.

Ordered arrays of nanoporous gold nanoparticles

Summary A combination of a “top-down” approach (substrate-conformal imprint lithography) and two “bottom-up” approaches (dewetting and dealloying) enables fabrication of perfectly ordered 2-dimensional arrays of nanoporous gold nanoparticles. The dewetting of Au/Ag bilayers on the periodically prepatterned substrates leads to the interdiffusion of Au and Ag and the formation of an array of Au–Ag alloy nanoparticles. The array of alloy nanoparticles is transformed into an array of nanoporous gold nanoparticles by a following dealloying step. Large areas of this new type of material arrangement can be realized with this technique. In addition, this technique allows for the control of particle size, particle spacing, and ligament size (or pore size) by varying the period of the structure, total metal layer thickness, and the thickness ratio of the as-deposited bilayers.

Ordered arrays of nanoporous silicon nanopillars and silicon nanopillars with nanoporous shells

The fabrication of ordered arrays of nanoporous Si nanopillars with and without nanoporous base and ordered arrays of Si nanopillars with nanoporous shells are presented. The fabrication route is using a combination of substrate conformal imprint lithography and metal-assisted chemical etching. The metal-assisted chemical etching is performed in solutions with different [HF]/[H2O2 + HF] ratios. Both pore formation and polishing (marked by the vertical etching of the nanopillars) are observed in highly doped and lightly doped Si during metal-assisted chemical etching. Pore formation is more active in the highly doped Si, while the transition from polishing to pore formation is more obvious in the lightly doped Si. The etching rate is clearly higher in the highly doped Si. Oxidation occurs on the sidewalls of the pillars by etching in solutions with small [HF]/[H2O2 + HF] ratios, leading to thinning, bending, and bonding of pillars.

Microforming process for embossing of LTCC tapes

Embossing of low-temperature cofired ceramics (LTCC) enables the fine patterning of these multilayer materials in the green state and thus allows the fabrication of smart ceramic microsystems even for moderate quantities or prototypes. To understand the embossing process, mechanical properties such as the viscoelastic modulus, yield strain and densification are investigated for commercially available LTCC tapes. The forming and shrinkage behaviour are compared for large cavities as well as for fine patterns. The results are discussed and a comprehensive explanation of the forming mechanism is worked out. Relevant material properties are identified and the microforming of different tapes is explained under consideration of their mechanical properties. This paper therefore gives an essential guide to understanding the main forming influences and failures for LTCC tapes.

Systematic Characterization of Embossing Processes for LTCC Tapes

Embossing of LTCC green tapes allows the defined patterning of conductor paths and fluidic channels with excellent edge molding. However, basic process settings have not systematically been investigated up to now. We present a comprehensive overview, regarding basic process variables and new manufacturing approaches. Because the molding quality depends on the viscoelastic properties of the tape, rheological measurements were carried out. The influence of the basic process parameters, that is, temperature, pressure, time, and friction, were investigated systematically under the use of design of experiments. The influence of these parameters on the forming of micropatterns down to 10 μm was investigated, as also were the stress of the tape caused by the plastic deformation, the accuracy of edge molding, and the demolding behavior of the embossed tape. Optimum parameters were derived. From the analysis of variances it is clear that friction exerts the most important influence on the molding of fine patterns....

Parameter Identification on Wafer Level of Membrane Structures

A fast identification method of membrane structure parameters is investigated for an early stage of the manufacturing process. The approach consists of performing optical measurement of the modal responses of the membrane structures. This information is used in an inverse identification algorithm based on a FE model. Device characteristics can be determined by measured modal frequencies which are fed into a model based on the FE simulations. The number of parameters to be identified is thereby generally limited only by the number of measurable modal frequencies. A quantitative evaluation of the identification results permits furthermore the detection of defects like cracks which cannot be classified within a FE model. The approach is validated by first measurements which have shown a good correlation between simulated and measured modal frequencies.