Influence of the concentration of H₂–D₂ mixtures on their triple-point dewetting behavior

Triple-point dewetting of pure gases like hydrogen and deuterium on solid substrates is a well-known phenomenon. This property persists even for the mixed system of H₂ and D₂. There exists an effective triple-point temperature T₃⁽mix⁾ , between the T₃ of pure H₂ and the one of pure D₂, which depends on the species concentrations. We present new investigations for a wide range of H₂–D₂ concentrations measured under different thermodynamic conditions. This allows us to map out T₃⁽mix⁾ as function of concentration, which can be different in the melting or solidifying direction. Furthermore, it turns out that the time the system needs to reach an equilibrium state can be very long and depends on concentration. This is not observed for the pure H₂ and D₂ system. Sometimes the relaxation times are so extremely long that significant hysteresis occurs during ramping the temperature, even if this is done very slowly on a scale of hours. This behavior can be understood on the basis of mixing and demixing processes. Possible differences in the species concentrations in the gas, liquid, and especially solid phase of the system are discussed. A preliminary phase diagram of the H₂–D₂ system is established

Modifikation und Nanostrukturierung magnetischer Materialien durch Ionenbestrahlung

In this work the modification of magnetic materials by ion irradiation and the application of this method to nano-structure magnetic media were investigated. Both aspects are of relevance for magnetic recording applications where the fine tuning of the magnetic material parameters and the creation of well-defined magnetic patterns are crucial for a further increase of the areal storage density.The first part reports on magnetic pattern creation by local ion irradiation. Stripe patterns of 250 nm periodicity were created in a Co/Pd multilayer thin film by focused ion beam irradiation using Ga^+ at negligible surface recession by sputtering. The magnetic reversal behavior of the irradiated medium was investigated using magnetooptical Kerr effect magnetometry and magnetic force microscopy. Most notably, a stripe pattern of alternating magnetization direction was observed at remanence. Its nature can be understood considering a reduced magnetic anisotropy in the irradiated regions such that their magnetization can be reversed by the stray fields of the neighboring nonirradiated areas. To further support this interpretation micromagnetic simulations were performed. Using appropriate (effective) material parameters the characteristic features of the reversal behavior of the stripe pattern could be reproduced. Thus, the simulations confirm the formation of magnetostatically induced alternating magnetization patterns in a medium where the magnetic properties are altered locally. The simulations further support the formation of these patterns at even smaller scales.In the second part the modification of the magnetic properties of magnetic materials by ion irradiation was studied in detail for granular CoCrPt:SiO_2 thin films exposed to Co^+ irradiation. Irradiation simulations were performed beforehand to optimize the ion energy for a maximum impact within the magnetic layer of the samples and evaluate the induced structural damage. Their results indicate a vertical mixing of the magnetic and nonmagnetic layers as well as lateral mixing across the grain boundaries. The irradiated samples were characterized using superconducting quantum interference device magnetometry, magnetooptical Kerr effect magnetometry and magnetic force microscopy. In general, the irradiation was found to affect the perpendicular anisotropy and the intergranular exchange coupling in the medium. This is indicated by a drop in coercivity, a reduction of the switching field distribution and an increase of the typical domain width with increasing irradiation fluence. The transformation from a Stoner-Wohlfarth like to a Kondorski-like reversal behavior observed in the angular dependence of the magnetic reversal further confirms the increase of the intergranular exchange coupling. To assist the interpretation of the experimental results micromagnetic simulations of the reversal behavior of granular media were performed for an extensive range of material parameters. The evolution of the experimental results as a function of fluence could be reproduced qualitatively by reducing the uniaxial anisotropy and increasing the intergranular exchange. Hence, the simulations support the modification of these material parameters as deduced from the experimental observations.The work concludes with a brief investigation on the influence of magnetostatic interactions on the switching field distribution in arrays of magnetic nanostructures by means of micromagnetic simulations. The width of the distribution was found to be independent of the anisotropy and to depend on the geometry of the array and the saturation magnetization only. A hyperbolic dependence of the switching field distribution on the spacing of the array elements was observed. Its exponent was found to depend on the size of the single elements. The study thereby confirms experimental observations of significant contributions of magnetostatic interactions to the broadening of the switching field distribution in high density nanoparticle arrays

Temperature Dependence of Hydrogen Adsorption Isotherms

In the past it has already been shown that adsorption isotherms of liquid or solid films are not described completely by the Frenkel-Halsey-Hill theory. Substrate roughness as well as thermal fluctuations have to be taken into account in understanding the adsorption behavior. The inclusion of thermal fluctuations into the adsorption theory has already been addressed and proven to provide an explanation for the deviations found in many experiments. However, a resulting temperature dependence of such isotherms has not yet been verifed. In our investigations we have addressed this issue with a series of adsorption isotherms of hydrogen on gold in a temperature range from 11K to 19.5K (i.e., below and above the triple-point temperature of hydrogen). Our measurements are compared with existing theories and the nature of the remaining discrepancies is discussed

Hydrogen Adsorption Isotherms : Modelling of Experimental Data

Adsorption isotherm measurements have shown deviations from classical theories in the past, leading to the inclusion of more complex effects into adsorption theory. We demonstrate here that in the case of hydrogen adsorption above the triple point measured by surface plasmon spectroscopy the main deviation is related to the measurement method itself. Modelling of the experimental data shows good agreement with the classical theoretical expectations, without the need of additional contributions

Influence of the concentration of Hz-D2 mixtures on their triple-point dewetting behavior

Triple-point dewetting of pure gases llke hydrogen aird deuterium on solid substrates is a well-known phenomenon. This property persists even for the mixed system of Hz and D2. There exists an effective triple-point temperature T3(mix) between the T3 of pure H2 and the one of pure Dz,which depends on the species concentrations. We present new investigations for a wide range of H2-D2 concentrations measured under diffcrerlt thermodynamic conditions. This allows us to map out T3(mix)as function of concentration, which can be different in the melting or solidifying direction. Furthermore, it. turns out that the time the system needs to reach an equiIibriun1 state can be very long and depends on concentration. This is not observed for the pure H2 and D2 system. Sometimes the relaxation times are so extremely long that significant hysteresis occurs during ramping the temperature, even if this is done very slowly on a scale of hours. This behavior can be understood on the basis of mixing and demixing processes. Possible differences in the species concentrations in the gas, liquid, and especially solid phase of the system are discussed. A preliminary phase diagram of the H2-D2 system is established

Parasitic extraction methodology for MEMS sensors with active devices

Nowadays, the demand for a MEMS development/design kit (MDK) is even more in focus than ever before. In order to achieve a high quality and cost effectiveness in the development process for automotive and consumer applications, an advanced design flow for the MEMS (micro electro mechanical systems) element is urgently required. In this paper, such a development methodology and flow for parasitic extraction of active semiconductor devices is presented. The methodology considers geometrical extraction and links the electrically active pn junctions to SPICE standard library models and subsequently extracts the netlist. An example for a typical pressure sensor is presented and discussed. Finally, the results of the parasitic extraction are compared with fabricated devices in terms of accuracy and capability

sphinx-contrib/matlabdomain: 0.21.4rc1

A Sphinx extension for documenting Matlab cod

sphinx-contrib/matlabdomain: 0.21.4rc2

A Sphinx extension for documenting Matlab cod

sphinx-contrib/matlabdomain: 0.21.4

A Sphinx extension for documenting Matlab cod