Carbon nanotube field-effect sensors for single-molecule detection

This thesis describes a detection system for single molecules based on individual single-walled carbon nanotube field-effect sensors. The sensitivity, spatial confinement and transducer gain of the sensor is derived from a conductance controlled electrochemically created defect, which is also chemically reactive. An automated microfluidic system is designed to enable long and stable measurements of the carbon nanotube device in aqueous environment with temperature control of ±0.1°C. A probe DNA can be covalently attached to the defect through an amide bond and the conductance is modulated when a target DNA binds to the probe. As a result, the conductance shows a traditional random telegraph signal and fluctuates between a hybridized and melted state. By monitoring the conductance as a function of temperature, the kinetics and thermodynamics can be extracted, which are comparable to previous fluorescent correlation spectroscopy studies using optical fluorescent resonant energy transfer. By studying the fluctuation amplitude as a function of charge proximity, buffer concentration and solution potential, it is shown that the sensor is based on a field-effect. The sensor has a temporal resolution of 200 μs and a signal to noise ratio of 3-8 when continuously measuring for 30 seconds. By further reducing the parasitics, the sensor has the capabilities to detect biomolecule kinetics down to microsecond resolution, which could make it an attractive tool for single-molecule experiments with fast kinetics

Kernel Flow:a high channel count scalable time-domain functional near-infrared spectroscopy system

Significance: Time-domain functional near-infrared spectroscopy (TD-fNIRS) has been considered as the gold standard of noninvasive optical brain imaging devices. However, due to the high cost, complexity, and large form factor, it has not been as widely adopted as continuous wave NIRS systems. Aim: Kernel Flow is a TD-fNIRS system that has been designed to break through these limitations by maintaining the performance of a research grade TD-fNIRS system while integrating all of the components into a small modular device. Approach: The Kernel Flow modules are built around miniaturized laser drivers, custom integrated circuits, and specialized detectors. The modules can be assembled into a system with dense channel coverage over the entire head. Results: We show performance similar to benchtop systems with our miniaturized device as characterized by standardized tissue and optical phantom protocols for TD-fNIRS and human neuroscience results. Conclusions: The miniaturized design of the Kernel Flow system allows for broader applications of TD-fNIRS.</p

Investigation of Facetted Growth in Heavily Doped Silicon Crystals Grown in Mirror Furnaces

Herein, facets and related phenomena are studied for silicon crystals grown in the and directions, using the Zone Melting and Floating Zone techniques. Investigating the central facets of dislocation-free crystals as a baseline allowed for the determination of the local temperature gradients. When comparing these results to dislocated crystals, the presence of dislocations caused a clear reduction in the facet size, correlated with a reduction in the required local supercooling to estimated maximum values of around 0.6 K. Furthermore, for crystals grown on the rough {100} interface, attempts to provoke a morphological instability of the local phase boundary succeeded for crystallization velocities in the range of 10–16 mm/min, in good agreement with theory. Contrary to this observation, crystals grown in the direction remained morphologically stable even at higher crystallization velocities due to the stabilizing effect of the atomically smooth interface. Additionally, crystals grown in the direction with an oxygen skin by the Zone Melting technique reproducibly showed a non-periodic fluctuation of the central facet diameter at a certain translation velocity

Versatile soft X-ray-optical cross-correlator for ultrafast applications

We present an X-ray-optical cross-correlator for the soft ( > 150   eV) up to the hard X-ray regime based on a molybdenum-silicon superlattice. The cross-correlation is done by probing intensity and position changes of superlattice Bragg peaks caused by photoexcitation of coherent phonons. This approach is applicable for a wide range of X-ray photon energies as well as for a broad range of excitation wavelengths and requires no external fields or changes of temperature. Moreover, the cross-correlator can be employed on a 10 ps or 100 fs time scale featuring up to 50% total X-ray reflectivity and transient signal changes of more than 20%

Open Educational Resources an der Hochschule Hannover

Das Konzept soll eine Grundlage zur Bereitstellung von Open Educational Resources (OER) für Studierende der Hochschule Hannover sein. Entstanden ist dieses auf Grundlage eines Studierendenprojektes (Bereitstellung von OER auf einer geeigneten Plattform) des Studiengangs "Informationsmanagement – berufsbegleitend". Aufgrund der kurzen Projektzeit, Schwierigkeiten bei der Auswahl einer geeigneten Plattform und einer problematischen Inhaltsrecherche konnte keine langfristige Lösung zur Bereitstellung von OER gefunden werden. Dieses Konzept soll die Erfahrungen der Projektgruppe zusammenfassen und an die Bibliothek der Hochschule Hannover sowie das E-Learning-Center weitergegeben werden. Ergänzt wird das Konzept durch allgemeine Informationen zu OER, Vorschläge für die Bereitstellung und Ideen für das weitere Vorgehen

Time-resolved soft X-ray absorption spectroscopy in transmission mode on liquids at MHz repetition rates

We present a setup combining a liquid flatjet sample delivery and a MHz laser system for time-resolved soft X-ray absorption measurements of liquid samples at the high brilliance undulator beamline UE52-SGM at Bessy II yielding unprecedented statistics in this spectral range. We demonstrate that the efficient detection of transient absorption changes in transmission mode enables the identification of photoexcited species in dilute samples. With iron(II)-trisbipyridine in aqueous solution as a benchmark system, we present absorption measurements at various edges in the soft X-ray regime. In combination with the wavelength tunability of the laser system, the set-up opens up opportunities to study the photochemistry of many systems at low concentrations, relevant to materials sciences, chemistry, and biology

Kernel Flow:A high channel count scalable TD-fNIRS system

Time-Domain Near-Infrared Spectroscopy (TD-NIRS) has been considered as the gold standard of non-invasive optical brain imaging devices. However, due to the high cost, complexity, and large form-factor, it has not been as widely adopted as Continuous Wave (CW) NIRS systems. Kernel Flow is a TD-NIRS system that has been designed to break through these limitations by maintaining the performance of a research grade TD-NIRS system while integrating all of the components into a small modular device. The Kernel Flow modules are built around miniaturized laser drivers, custom integrated circuits, and specialized detectors. The modules can be assembled into a system with dense channel coverage over the entire head. We show performance similar to benchtop systems with our miniaturized device.</p