An improved micromechanical method for investigating the mechanical properties of poly-silicon membranes

Freestanding poly-silicon membranes are of increasing importance for designing MEMS devices such as pressure sensors, microphones and gyroscopes. It is crucial to accurately determine the mechanical properties of such membranes not only to access parameters for designing new devices but also for assuring proper performance and quality in service. Classically, microscopic tensile tests [1-3] or bulge tests [4] were conducted to obtain Young’s modulus and strength of the membrane material. These methods however are prone to artifacts due to crack initiation at edge defects (e.g. predefined notches in tensile specimens [3] or slits in bulge test samples [4]). In search of a method more sensitive to the membrane surface rather than specimen geometries, a novel approach has been introduced more recently. By loading the center region of a circumferentially clamped membrane with a spherical probe, the membrane is stretched all the way up to rupture while precisely recording the load-deflection data. Complementary FEA simulations allow for determining the failure stresses of individual membranes, based on the mechanical test data. In a subsequent step the tests are analyzed via a two-parameter Weibull approach to statistically evaluate the characteristic fracture strength. The membranes tested in the given project had a thickness of only 330 nm over a diameter of 1 mm. The necessity to apply minute forces while testing the compliant membranes at quite large deflections with high precision proves to be challenging. Additionally the need for statistical verification requires conducting multiple tests in a reasonable time frame. In the presented work a commercial nanoindenter has been used to match the aforementioned requirements. Lately some methodological improvements have been implemented to maximize throughput by automation and improve accuracy by refining the data analysis to capture the experimental conditions most realistically. Some of these approaches will be illustrated by recent data and explained in detail

Numerical Analysis of Ca2+ Depletion in the Transverse Tubular System of Mammalian Muscle

AbstractCalcium currents were recorded in contracting and actively shortening mammalian muscle fibers. In order to characterize the influence of extracellular calcium concentration changes in the small unstirred lumina of the transverse tubular system (TTS) on the time course of the slow L-type calcium current (ICa), we have combined experimental measurements of ICa with quantitative numerical simulations of Ca2+ depletion. ICa was recorded both in calcium-buffered and unbuffered external solutions using the two-microelectrode voltage clamp technique (2-MVC) on short murine toe muscle fibers. A simulation program based on a distributed TTS model was used to calculate the effect of ion depletion in the TTS. The experimental data obtained in a solution where ion depletion is suppressed by a high amount of a calcium buffering agent were used as input data for the simulation. The simulation output was then compared with experimental data from the same fiber obtained in unbuffered solution. Taking this approach, we could quantitatively show that the calculated Ca2+ depletion in the transverse tubular system of contracting mammalian muscle fibers significantly affects the time-dependent decline of Ca2+ currents. From our findings, we conclude that ion depletion in the tubular system may be one of the major effects for the ICa decline measured in isotonic physiological solution under voltage clamp conditions

Zur Biodiversität von Pflanzenarten in unserer Ernährung: Eine vierwöchige Studie mit Biologiestudierenden der Hochschule Bremen

In einer vierwöchigen Studie wurde an der Hochschule Bremen mit Studierenden und Betreuen-den des Internationalen Studiengangs Technische und Angewandte Biologie B. Sc. (ISTAB) eine Erfassung der in diesem Zeitraum von ihnen verzehrten Pflanzenarten durchgeführt. Die ver-zehrten Pflanzenarten wurden von jedem der 37 teilnehmenden Probanden erfasst, ohne den Verzehr zu quantifizieren. Unter den 37 Probanden befanden sich 20 Männer (3 Vegetarier, 17 Omivore) und 17 Frauen (2 Veganer, 9 Vegetarier, 6 Omnivore). Das Alter der Probanden erstreckte sich von 19 bis zu 56 Jahren mit einem Median von 22 Jahren. In der Summe wurden 280 verschiedene Pflanzenarten aus 95 Pflanzenfamilien notiert. Davon wurden neun Arten – Mais (Zea mays), Reis (Oryza sativa), Kartoffel (Solanum tuberosum), Tomate (Lycopersicon esculentum), Zwiebel (Allium cepa), Apfel (Malus domestica), Zitrone (Citrus limon), Pfeffer (Piper nigrum) und Petersilie (Petroselinum crispum) – von allen 37 Probanden verzehrt. Eine sehr hohe Anzahl von 64 Pflanzenarten wurde von nur jeweils einer Person genannt. Die geringste Anzahl verzehrter Pflanzenarten wies ein omnivorer Mann mit 49 Arten auf, die maximale An-zahl wurde von einer veganen Frau mit 172 Pflanzenarten erreicht. In Bezug auf die Artenvielfalt an Pflanzen ernährte sich die Gruppe der Männer signifikant artenärmer als diejenige der Frauen. Vegetarier (inkl. Veganer) ernährten sich bezüglich der Pflanzenartenvielfalt insgesamt sehr signi-fikant artenreicher als Omnivore. Betrachtet man die Ähnlichkeit in Bezug auf verzehrte Pflan-zenarten einzelner Probanden zueinander, gibt es jedoch keine eindeutige erkennbare Abhängig-keit von Geschlecht oder Ernährungsweise. Die Studie, die im Kontext der Lehrveranstaltung „Angewandte Botanik“ als begleitende Übung durchgeführt wurde, machte deutlich, dass der Zugang zur Botanik über die eigene Ernährung erkennbar die Motivation und das Engagement von Studierenden fördern kann, sich mit den Inhalten der Lehrveranstaltung auseinanderzusetzen. Dies beinhaltete auch das Erkennen der hohen Bedeutung der pflanzlichen Biodiversität als Natur- aber auch als Kulturgut, deren Erhalt essentiell ist.We carried out a four-week term study about how many plant species were consumed by the students and lecturers of the course “Applied Botany” at the International Study Program Indus-trial and Environmental Biology of the Bremen University of Applied Sciences. Each participant documented every plant species that was consumed without quantifying the amount. 37 people participated in the study, 20 males (3 vegetarians, 17 omnivores) and 17 females (2 vegans, 9 vegetarians, 6 omnivores). The age of the participants ranged from 19 years up to 56 years with a median of 22 years. In total, 280 different plant species from 95 different plant families were consumed. Nine of which – maize (Zea mays), rice (Oryza sativa), potato (Solanum tuberosum), tomato (Lycopersicon esculen-tum), onion (Allium cepa), apple (Malus domestica), lemon (Citrus limon), pepper (Piper nigrum) and parsley (Petroselinum crispum) – were eaten by every participant. 64 plant species were consumed by only one participant each. The lowest number of plant species with 49 was consumed by an om-nivorous male, the highest number with 172 species was eaten by a vegan female. Female partici-pants showed a significantly higher diversity of plant species in their nutrition than male partici-pants. The group of vegetarian and vegan participants consumed significantly more plant species than the group of omnivorous participants. However, we found no clear groups of diets or sex considering the similarity of participants regarding the consumed plant species. Integrating this study about food plants in the course Applied Botany clearly increased the moti-vation and interest of the students in dealing with the subject of botany. Particularly the identifi-cation of different plant species, that were part of their personal diet, supported a deeper under-standing about the importance of biodiversity in (food) plant species

Residual Stress Measurement on a MEMS Structure With High-Spatial Resolution

A new approach to the local measurement of residual stress in microstructures is described in this paper. The presented technique takes advantage of the combined milling-imaging features of a focused ion beam (FIB) equipment to scale down the widely known hole drilling method. This method consists of drilling a small hole in a solid with inherent residual stresses and measuring the strains/displacements caused by the local stress release, that takes place around the hole. In the presented case, the displacements caused by the milling are determined by applying digital image correlation (DIC) techniques to high resolution micrographs taken before and after the milling process. The residual stress value is then obtained by fitting the measured displacements to the analytical solution of the displacement fields. The feasibility of this approach has been demonstrated on a micromachined silicon nitride membrane showing that this method has high potential for applications in the field of mechanical characterization of micro/nanoelectromechanical systems

Combination of PIP and LSI processes for SiC/SiC ceramic matrix composites

Silicon carbide fiber-reinforced silicon carbide matrix composites (SiC/SiC CMCs) are promising candidates for hot gas components in jet engines. Three common manufacturing routes are chemical vapor infiltration, reactive melt infiltration (RMI) and polymer infiltration and pyrolysis (PIP). A combination of the processes seems attractive: the remaining porosity after PIP process can be closed by subsequent siliconization, resulting in a dense material. This work describes a new approach of a combined PIP and RMI process. SiC/SiC CMCs were manufactured by PIP process using Hi-Nicalon Type S fibers. An additional RMI was carried out after a reduced number of PIP cycles. Microstructure was examined via microCT, SEM and EDS. Bending strength was determined to 433 ​MPa; strain to failure was 0.60%. The overall processing time was reduced by 55% compared to standard PIP route. The hybrid material contained 70% less unreacted carbon than material produced by LSI process alone