Piezoresistive cantilevers with an integrated bimorph actuator

Scanning Probe Microscopy (SPM) has become of fundamental importance for research in area of micro and nano-technology. The continuous progress in these fields requires ultra sensitive measurements at high speed. The imaging speed limitation of the conventional Tapping Mode SPM is due to the actuation time constant of piezotube feedback loop that keeps the tapping amplitude constant. In order to avoid this limit a deflection sensor and an actuator have to be integrated into the cantilever. In this work has been demonstrated the possibility of realisation of piezoresistive cantilever with an embedded actuator. Piezoresistive detection provides a good alternative to the usual optical laser beam deflection technique. In frames of this thesis has been investigated and modelled the piezoresistive effect in bulk silicon (3D case) for both n- and p-type silicon. Moving towards ultra-sensitive measurements it is necessary to realize ultra-thin piezoresistors, which are well localized to the surface, where the stress magnitude is maximal. New physical effects such as quantum confinement which arise due to the scaling of the piezoresistor thickness was taken into account in order to model the piezoresistive effect and its modification in case of ultra-thin piezoresistor (2D case). The two-dimension character of the electron gas in n-type piezoresistors lead up to decreasing of the piezoresistive coefficients with increasing the degree of electron localisation. Moreover for p-type piezoresistors the predicted values of the piezoresistive coefficients are higher in case of localised holes. Additionally, to the integration of the piezoresistive sensor, actuator integrated into the cantilever is considered as fundamental for realisation of fast SPM imaging. Actuation of the beam is achieved thermally by relying on differences in the coefficients of thermal expansion between aluminum and silicon. In addition the aluminum layer forms the heating micro-resistor, which is able to accept heating impulses with frequency up to one megahertz. Such direct oscillating thermally driven bimorph actuator was studied also with respect to the bimorph actuator efficiency. Higher eigenmodes of the cantilever are used in order to increase the operating frequencies. As a result the scanning speed has been increased due to the decreasing of the actuation time constant. The fundamental limits to force sensitivity that are imposed by piezoresistive deflection sensing technique have been discussed. For imaging in ambient conditions the force sensitivity is limited by the thermo-mechanical cantilever noise. Additional noise sources, connected with the piezoresistive detection are negligible.

Determination of yield and quality parameters of energy crops applying laboratory and field spectroscopy

A real-time analysis of renewable energy sources, such as arable crops, is of great importance with regard to an optimised process management, since aspects of ecology and biodiversity are considered in crop production in order to provide a sustainable energy supply by biomass. This study was undertaken to explore the potential of spectroscopic measurement procedures for the prediction of potassium (K), chloride (Cl), and phosphate (P), of dry matter (DM) yield, metabolisable energy (ME), ash and crude fibre contents (ash, CF), crude lipid (EE), nitrate free extracts (NfE) as well as of crude protein (CP) and nitrogen (N), respectively in pretreated samples and undisturbed crops. Three experiments were conducted, one in a laboratory using near infrared reflectance spectroscopy (NIRS) and two field spectroscopic experiments. Laboratory NIRS measurements were conducted to evaluate to what extent a prediction of quality parameters is possible examining press cakes characterised by a wide heterogeneity of their parent material. 210 samples were analysed subsequent to a mechanical dehydration using a screw press. Press cakes serve as solid fuel for thermal conversion. Field spectroscopic measurements were carried out with regard to further technical development using different field grown crops. A one year lasting experiment over a binary mixture of grass and red clover examined the impact of different degrees of sky cover on prediction accuracies of distinct plant parameters. Furthermore, an artificial light source was used in order to evaluate to what extent such a light source is able to minimise cloud effects on prediction accuracies. A three years lasting experiment with maize was conducted in order to evaluate the potential of off-nadir measurements inside a canopy to predict different quality parameters in total biomass and DM yield using one sensor for a potential on-the-go application. This approach implements a measurement of the plants in 50 cm segments, since a sensor adjusted sideways is not able to record the entire plant height. Calibration results obtained by nadir top-of-canopy reflectance measurements were compared to calibration results obtained by off-nadir measurements. Results of all experiments approve the applicability of spectroscopic measurements for the prediction of distinct biophysical and biochemical parameters in the laboratory and under field conditions, respectively. The estimation of parameters could be conducted to a great extent with high accuracy. An enhanced basis of calibration for the laboratory study and the first field experiment (grass/clover-mixture) yields in improved robustness of calibration models and allows for an extended application of spectroscopic measurement techniques, even under varying conditions. Furthermore, off-nadir measurements inside a canopy yield in higher prediction accuracies, particularly for crops characterised by distinct height increment as observed for maize.

Organische Düngung und reduzierte Bodenbearbeitung als Steuerungsfaktoren für die C-, N-, P- und S-Speicherung von Mikroorganismen

In dieser Arbeit wurden zum einen die Auswirkungen mineralischer und organischer Düngung und zum anderen der Einfluss reduzierter Bodenbearbeitung (Kreiselegge) im Vergleich zum Einsatz des Wendepfluges auf die Nährstoffspeicherung der mikrobiellen Biomasse untersucht. Dabei wurde deutlich, dass sowohl organische Düngung als auch die reduzierte Bodenbearbeitung zu einer Erhöhung des organischen Kohlenstoffs (Corg), des Stickstoff-Gesamtgehalts (N) und des mikrobiellen Biomasse Kohlenstoffs (Cmik) und Stickstoffs (Nmik) führten. Der Einsatz organischer Dünger wies darüber hinaus höhere Gehalte an Schwefel (S) auf, während der Einsatz der Kreiselegge auch den mikrobiellen Biomasse Phosphor (Pmik) gegenüber der Pflugvariante erhöhte. Des Weiteren zeigten die Untersuchungen des pilzlichen Biomarkers Ergosterol einen signifikant höheren Gehalt mit mineralischer Düngung plus Strohrückführung und beim Einsatz des Wendepfluges im Vergleich zu organischer Düngung und reduzierter Bodenbearbeitung. Dies führte sowohl bei mineralischer Düngung als auch bei dem Einsatz des Wendepfluges zu einem signifikant höheren Ergosterol/Cmik-Quotienten, der bei hohen Werten auf einen höheren Anteil saprotropher Pilze an der gesamten mikrobiellen Gemeinschaft schließen lässt. Im Zusammenhang mit der Möglichkeit saprotropher Pilze, ihre Schwefelinkorporation um 130% zu steigern, zeigten sich höhere Gehalte des mikrobiellen Schwefels unter mineralischer Düngung und des Einsatzes des Wendepflugs, bei denen der Anteil saprotropher Pilze erhöht war. Dies führte zu einem geringeren C/Smik-Quotienten, der somit als Maß für eine Veränderung der mikrobiellen Gemeinschaft herangezogen werden kann. Des Weiteren ließ sich feststellen, dass trotz eines erhöhten Pilzanteils an der mikrobiellen Gemeinschaft unter Pflugbearbeitung und mineralischer Düngung die Substratnutzungseffizienz, die durch Pilze gewöhnlich erhöht wird, hier nicht gesteigert wurde. Somit lässt sich festhalten, dass sowohl organische Düngung als auch der Einsatz der Kreiselegge mit reduzierter Bodenbearbeitung zu einer Erhöhung Bodenfruchtbarkeit erhaltender Messgrößen, wie Corg, N, Cmik und Nmik führten. Das Bodenmaterial beider Langzeitversuche wurde nach den Laboruntersuchungen mit flüssigem Stickstoff schockgefroren und anschließend gefriergetrocknet, um mittels Nahinfrarot Spektroskopie (NIRS) und unterschiedlichen Berechnungsverfahren die Bodeneigenschaften vorherzusagen. Die Messgrößen des pH-Werts, Corg, N, P, S, K, Mg, Mn, Fe, Al wurden mit NIRS in einer exzellenten Vorhersagegüte bestimmt, während die Vorhersage von Cmik, Nmik und dem Ergosterol/Cmik-Quotienten nur zu einer annähernd quantitativen Bestimmung führte. Die unterschiedlichen Berechnungen mittels Kreuzvalidierung und separater Kalibrierung/Validierung zeigten zwar, dass die Kreuzvalidierung zu einer höheren Anzahl erfolgreich vorhergesagter Parameter führte, diese jedoch nicht zur Erstellung einer Kalibrationsdatenbank herangezogen werden kann, da hier nur eine geschlossene Population betrachtet wird. Die unterschiedlichen Selektionsverfahren zeigten nur einen geringen Einfluss auf die Vorhersagegenauigkeit. Während die Aufteilung des Datensatzes in einen kleineren, homogeneren Datensatz der einzelnen Standorte zu keiner besseren Vorhersagegüte im Vergleich zum Gesamtdatensatz führte. Daher bleibt festzuhalten, dass NIRS vor allem für die Vorhersage der Grundmessgrößen wie Corg, den Gesamtgehalten und Cmik und Nmik Einsatz finden kann, während für die erfolgreiche Vorhersage für weitere mikrobielle Biomasse-Parameter noch Forschungsbedarf besteht, wie z.B. zur Probenvorbereitung.

Biomass, quality traits and methane production of extensive grassland: biodiversity effects and sensor approaches

Energy policies around the world are mandating for a progressive increase in renewable energy production. Extensive grassland areas with low productivity and land use limitations have become target areas for sustainable energy production to avoid competition with food production on the limited available arable land resources and minimize further conversion of grassland into intensively managed energy cropping systems or abandonment. However, the high spatio-temporal variability in botanical composition and biochemical parameters is detrimental to reliable assessment of biomass yield and quality regarding anaerobic digestion. In an approach to assess the performance for predicting biomass using a multi-sensor combination including NIRS, ultra-sonic distance measurements and LAI-2000, biweekly sensor measurements were taken on a pure stand of reed canary grass (Phalaris aruninacea), a legume grass mixture and a diversity mixture with thirty-six species in an experimental extensive two cut management system. Different combinations of the sensor response values were used in multiple regression analysis to improve biomass predictions compared to exclusive sensors. Wavelength bands for sensor specific NDVI-type vegetation indices were selected from the hyperspectral data and evaluated for the biomass prediction as exclusive indices and in combination with LAI and ultra-sonic distance measurements. Ultrasonic sward height was the best to predict biomass in single sensor approaches (R² 0.73 – 0.76). The addition of LAI-2000 improved the prediction performance by up to 30% while NIRS barely improved the prediction performance. In an approach to evaluate broad based prediction of biochemical parameters relevant for anaerobic digestion using hyperspectral NIRS, spectroscopic measurements were taken on biomass from the Jena-Experiment plots in 2008 and 2009. Measurements were conducted on different conditions of the biomass including standing sward, hay and silage and different spectroscopic devices to simulate different preparation and measurement conditions along the process chain for biogas production. Best prediction results were acquired for all constituents at laboratory measurement conditions with dried and ground samples on a bench-top NIRS system (RPD > 3) with a coefficient of determination R2 < 0.9. The same biomass was further used in batch fermentation to analyse the impact of species richness and functional group composition on methane yields using whole crop digestion and pressfluid derived by the Integrated generation of solid Fuel and Biogas from Biomass (IFBB) procedure. Although species richness and functional group composition were largely insignificant, the presence of grasses and legumes in the mixtures were most determining factors influencing methane yields in whole crop digestion. High lignocellulose content and a high C/N ratio in grasses may have reduced the digestibility in the first cut material, excess nitrogen may have inhibited methane production in second cut legumes, while batch experiments proved superior specific methane yields of IFBB press fluids and showed that detrimental effects of the parent material were reduced by the technical treatment