H. Scheel

Raman scattering on silicon nanowires : The thermal conductivity of the environment determines the optical phonon frequency

We studied the Raman spectra of silicon nanowires as a function of excitation power for various ambient gases. For a given excitation power, we find that the gas thermal conductivity determines the wire temperature, which can be detected by a change in phonon frequency. This shows that the redshift of the optical phonon in silicon nanowires compared to bulk silicon is mainly due to the lower thermal conductivity of nanowires and an increase in laser heating. The spectra of nanowires allow distinguishing gases on the basis of their thermal conductivity.

On Remote and Virtual Experiments in eLearning in Statistical Mechanics and Thermodynamics

The science of physics is based on theories and models as well as experiments: the former structure relations and simplify reality to a degree such that predictions on physical phenomena can be derived by means of mathematics. The latter allow verification or falsification of these predictions. Computer sciences allow a new access to this relationship, especially well-suited for education: new technologies provide simulations for the model, virtual instruments for running and evaluating real experiments and mathematical toolkits to solve equations derived from the theory analytically and to compare the outcome of all three methods. We will demonstrate this approach on two examples: ferromagnetism and thermodynamics

A Practical Approach for Applying Online Remote Experiments: OnPReX.

The development of Internet technologies stimulates the increase of online technology-supported education in universities. Online learning based on remote experiments is capable of diminishing the scantiness in practical courses. In this paper, we present online practical courses based on remote experiments (OnPReX). These courses consist of online experiments, interactive graphics and an online tutoring-system organised at the Berlin Institute of Technology (TUB). We developed two online practical courses, one focusing on classical and the other on modern physics, for bachelor and intermediate diploma engineering students. Our online practical courses based on remote experiments took place in two test phases during two semesters. These courses were evaluated and the results were used to improve the courses. Our online practical courses on remote experiments have successfully been integrated as electives at the TUB.

Deployment of remote experiments: The OnPReX course at the TU Berlin

The development of internet technologies leads to recent trends of online based education in universities. Remote experiments give the students the possibility to experience real physical situations and compare their experimental results with those of the physical models (simulation). Online learning based on remote experiments is capable of diminishing the scantiness in practical courses in the universities. In this work we present an online practical course based on Remote Experiments (OnPReX), interactive graphics and an online tutoring system organized at the Technische Universität Berlin. Furthermore we give background information about the development of our remote experiments. The remote experiments are real-life settings, designed and engineered at the solid-state physics department of the Technische Universität Berlin. We describe the development of two online practical courses, focusing on classical and modern physics, addressed at undergraduate engineering students. We ran the online practical course based on Remote Experiments in two test phases over two semesters and conducted an evaluation from which we improved technical and pedagogical aspects of the experiments and the course.

The Teutates-Project: Tablet-PCs in Modern Physics Education

The overall objective of the TEUTATES approach is to implement a flexible mobile learning concept for a modern physics education at universities, focusing on enhanced access to a broad variety of experiments. Within a blended learning concept, Tablet-PCs allow an extended experimental part of the education right from the beginning. Different types of experiments – remote and virtual – are introduced. Executed within web-interfaces, experiments can be implemented and accessed regardless of the location of the laboratory and the experimenter. Additionally, experiments can be performed which otherwise would not be accessible for reasons of expense, security, or availability.

Dependence of the Raman Spectrum of Silicon Nanowires on the Wire Environment

The large surface to volume ratio in nanometer sized wire structures cause a strong dependence of the optical Raman mode on the thermal conductivity of a surrounding medium. On the basis of optical measurements on silicon nanowires as a function of excitation laser power we explain the very large red-shifted Raman spectra observed already for moderate laser powers. This thermal effect is enhanced by a silicon oxide sheath, rendering a reduced thermal contact of the wires to the substrate. The intrinsic redshift due to spatial confinement in silicon nanowires is found to be smaller than 2 cm −1 .