Zeitschriftenaufsätze und Buchbeiträge

The fabrication of cupric oxide (CuO) nanowires from Cu particles via thermal oxidation provides a simple and scalable method to produce hierarchical structures. A stress-induced growth mechanism is believed to account for the nanowire formation while a slow oxidation rate is favored to sustain the driving force. Here, CuO whiskers are grown from Au-Cu nanoparticles because the formation of Au-Cu phases decreases the Cu diffusion rate and in turn slows down the oxidation rate. The driving force for the whisker growth is attributed to the compressive stress imposed by the CuO shell on the Au-Cu core, which is induced by the significantdifference in their linear thermal expansion coefficients. The contribution of the compressive stress is proved by the calculation. Moreover, preferred oxidation is observed and it is related to the crystalline structures of different facets existing on the surface of Au-Cu nanoparticles. The more compact the plane, the slower the diffusion rate through the plane, resulting in the formation of thinner CuO on the relevant facet. The results open a cost-effect way to fabricate hybrid nanostructures consisting of Cu-based core-shell nanoparticles attached with CuO whiskers and bring new insights into the oxidation behaviors of Cu on different crystal planes.

Time-resolved photoluminescence (TRPL) measurements and the extraction of meaningful parameters involve four key ingredients: a suitable sample such as a semiconductor double heterostructure, a state-of-the-art measurement setup, a kinetic model appropriate for the description of the sample behavior, and a general analysis method to extract the model parameters of interest from the measured TRPL transients. Until now, the last ingredient is limited to single curve fits, which are mostly based on simple models and least-squares fits. These are often insufficient for the parameter extraction in real-world applications. The goal of this article is to give the community a universal method for the analysis of TRPL measurements, which accounts for the Poisson distribution of photon counting events. The method can be used to fit multiple TRPL transients simultaneously using general kinematic models, but should also be used for single transient fits. To demonstrate this approach, multiple TRPL transients of a GaAs/AlGaAs heterostructure are fitted simultaneously using coupled rate equations. It is shown that the simultaneous fits of several TRPL traces supplemented by systematic error estimations allow for a more meaningful and more robust parameter determination. The statistical methods also quantify the quality of the description by the underlying physical model.

Electrodeposition is a versatile instrumental technique, already applied in many industrial fields. However, the deposition of silicon and other reactive elements is still challenging and requires further research and improvement. Accomplishing an efficient electrodeposition of silicon at room temperature is very attractive due to the high number of manufacturing technologies that would benefit from this approach. This work provides an overview of the electrochemical approaches for silicon deposition performed in organic electrolytes. The main factors that impact this process are individually discussed and exemplified with appropriately updated literature sources. Furthermore, the previously available research on characterization of electrodeposited silicon containing layers is provided. These studies are presented in the context of better understanding the structure, composition, and functional properties of the deposited silicon material, which may attract the attention of young academic scientists and process engineers.

The input of combustion heat in engines has a major impact on the piston friction and the resulting wear of the piston skirt. The new methodology presented here enables the simulation of combustion heat input during motored operation, and thus a detailed investigation of the piston friction under realistic piston temperature profiles of real engine operation is possible. For this purpose a standardized engine test bench for motored friction evaluations was expanded to include, among other things, a movable high-power diode laser with special defocusing optics. The setup of the test engine is based on the FEV teardown step methodology [1] and has open access to the engine piston from above due to a cylinder head dummy. Thus, the heat input by means of a high-power diode laser into the piston crown can be made. The reduced engine structure also enables a precise and highly accurate evaluation of the piston friction. A previously conducted validation process of the methodology ensures the most accurate possible replication of fired piston temperature profiles. The comparison between the piston temperatures measured in fired operation and those simulated in motored operation for a partial load operating point shows a maximum variance deviation of only 15˚C depending on the measuring point. The new methodology is also used in particular for the evaluation and detection of critical piston friction conditions. Experiments in this context are presented and discussed exemplary by using three measurement series at different operating temperatures and engine speeds. There is a gradual increase in the laser power for each series of measurements and thus in the heat input into the piston. The increase in heat input leads to a significant increase in friction at all operating points due to thermal expansion and the associated decrease reduction in piston clearance. Depending on the operating temperature and the engine speed, a critical piston friction condition is achieved and detected by the level of friction increase. The additional use of ultrasonic sensors and the knock sensor installed as standard makes a simultaneous measurement of the structure-borne sound signals possible. The increase in the acceleration levels of all sensors correlates here with the increase in piston friction. An evaluation of the noise, vibration, and harshness (NVH) measurement in both the frequency range and the crank angle (CA) range shows conspicuous high-frequency excitation levels that occur in the top dead center area. This correlation can be proven for all three measurement series. The results obtained here may open a path to an improved piston cooling strategy in the future.

There is an apparent mismatch between electron paramagnetic resonance and Mössbauer spectroscopy results on the charge and spin states of dilute Fe impurities in NaCl; Mössbauer spectroscopy data have been interpreted in terms of high-spin Fe2+, while electron paramagnetic resonance studies suggest low-spin Fe1+. In the present study, the charge and spin states of dilute substitutional Fe impurities in NaCl and LiF have been investigated with 57Mn&flech;57Fe emission Mössbauer spectroscopy. A scheme is proposed which takes into account the effects of nearest-neighbor distances and electronegativity difference of the host atoms on the Mössbauer isomer shift and allows for the unequivocal differentiation between high-spin Fe2+ and high/low-spin Fe1+ in Mössbauer spectroscopy. From these considerations, the Mössbauer results are found to be consistent with dilute Fe impurities in NaCl and LiF in a low-spin Fe1+ state. These conclusions are supported by theoretical calculations of isomer shifts and formation energies based on the density-functional theory. The experimental results furthermore suggest that charge compensation of dilute Mn2+ dopants in NaCl and LiF is achieved by Na vacancies and F− interstitials, respectively.