Cryogenic etching for pattern transfer into silicon of Mix-and-Match structured resist layers. - In: Microelectronic engineering, Bd. 227 (2020), 111325, insges. 5 S.
A Mix-and-Match lithography method for a high-resolution, high-precision and cost effective lithography tool using DLW and FE-SPL was developed and successfully realized. The pattern transfer from the photoresist to the silicon substrate is done by so-called "cryogenic etching". It means that the substrate is cooled down to cryogenic temperatures. In contrast to etching processes at standard room temperature, the cryogenic temperatures (below -100 ˚C) enable a highly anisotropic etching process. The difference between etching at room temperature compared to cryogenic etching is carried out in this work. The advantages of the etching process are highlighted for the pattern transfer from Mix-and-Match-structured samples. Therefore, the used photoresist mr-P 1201LIL (microresist technologies GmbH) has been examined concerning its silicon-to-resist selectivity which could be determined to be 6:1 for the applied etching recipe. Using cryogenic etching, we are now able to transfer the Mix-and-Match-structured patterns into silicon with appreciable high selectivities. This opens a novel pathway for the manufacturing of quantum devices on large wafers. The paper discusses current research results based on the TU Ilmenau Nanopositioning and Nanomeasuring Machines (NPMM) including the novel application of nanofabrication. First, the basic setup and the resulting benefits of the NPMMs for measuring and fabrication in a working volume of up to 200 mm × 200 mm × 25 mm while abiding nanometer accuracy is described. This is in contradiction to state-of-the-art AFM scanners, which have a limited working range of appr. 100 [my]m × 100 [my]m. Next, the principle and the results of different nanofabrication technologies are shown. These include Scanning Probe Lithography (SPL), Direct Laser Writing (DLW) and UV-nanoimprint lithography (NIL). Last, efforts for further improving the feature placement accuracy of the NPMMs as well as attempts to combine several fabrication technologies to improve their throughput are touched on.
https://doi.org/10.1016/j.mee.2020.111325
Effect of polyalcohols on the anticorrosive behaviour of alkyd coatings prepared with drying oils. - In: Progress in organic coatings, Bd. 145 (2020), 105671
https://doi.org/10.1016/j.porgcoat.2020.105671
Optical measurements on thermal convection processes inside thermal energy storages during stand-by periods. - In: Optics, ISSN 2673-3269, Bd. 1 (2020), 1, S. 155-172
Thermal energy storages (TES) are increasingly important for storing energy from renewable energy sources. TES that work with liquid storage materials are used in their most efficient way by stratifying the storage fluid by its thermal density gradient. Mixing of the stratification layers during stand-by periods decreases the thermal efficiency of the TES. Tank sidewalls, unlike the often poorly heat-conducting storage fluids, promote a heat flux from the hot to the cold layer and lead to thermal convection. In this experimental study planar particle image velocimetry (PIV) measurements and background-oriented schlieren (BOS) temperature measurements are performed in a model experiment of a TES to characterise the influence of the thermal convection on the stratification and thus the storage efficiency. The PIV results show two vertical, counter-directed wall jets that approach in the thermocline between the stratification layers. The wall jet in the hot part of the thermal stratification shows compared to the wall jet in the cold region strong fluctuations in the vertical velocity, that promote mixing of the two layers. The BOS measurements have proven that the technique is capable of measuring temperature fields in thermally stratified storage tanks. The density gradient field as an intermediate result during the evaluation of the temperature field can be used to indicate convective structures that are in good agreement to the measured velocity fields.
https://doi.org/10.3390/opt1010011
Challenges of temperature measurement during the friction stir welding process. - In: Measuring Equipment and Metrology, ISSN 2617-846X, Bd. 81 (2020), 1, insges. 8 S.
The exact determination of the process zone temperature can be considered as an increasingly important role in the control and monitoring of the friction stir welding process (FSW). At present, temperature measurement is carried out with the aid of a temperature sensor integrated into the tool (usually thermocouples). Since these cannot be attached directly to the joining area, heat dissipation within the tool and to the environment cause measurement deviations as well as a time delay in the temperature measurement. The article describes a process and the challenges that arise in this process, how a direct temperature measurement during the process can be achieved by exploiting the thermoelectric effect between tool and workpiece, without changing the tool by introducing additional temperature sensors.
https://doi.org/10.23939/istcmtm2020.01.034
Crystallinity, thermal diffusivity, and electrical conductivity of carbon black filled polyamide 46. - In: Journal of applied polymer science, ISSN 1097-4628, Bd. 137 (2020), 29, 48882, S. 1-10
https://doi.org/10.1002/app.48882
Combination of MRI and SEM to assess changes in the chemical properties and permeability of porous media due to barite precipitation. - In: Minerals, ISSN 2075-163X, Bd. 10 (2020), 3, 226, insges. 20 S.
The understanding of the dissolution and precipitation of minerals and its impact on the transport of fluids in porous media is essential for various subsurface applications, including shale gas production using hydraulic fracturing ("fracking"), CO2 sequestration, or geothermal energy extraction. In this work, we conducted a flow through column experiment to investigate the effect of barite precipitation following the dissolution of celestine and consequential permeability changes. These processes were assessed by a combination of 3D non-invasive magnetic resonance imaging, scanning electron microscopy, and conventional permeability measurements. The formation of barite overgrowths on the surface of celestine manifested in a reduced transverse relaxation time due to its higher magnetic susceptibility compared to the original celestine. Two empirical nuclear magnetic resonance (NMR) porosity-permeability relations could successfully predict the observed changes in permeability by the change in the transverse relaxation times and porosity. Based on the observation that the advancement of the reaction front follows the square root of time, and micro-continuum reactive transport modelling of the solid/fluid interface, it can be inferred that the mineral overgrowth is porous and allows the diffusion of solutes, thus affecting the mineral reactivity in the system. Our current investigation indicates that the porosity of the newly formed precipitate and consequently its diffusion properties depend on the supersaturation in solution that prevails during precipitation.
https://doi.org/10.3390/min10030226
An experimental study on lap joining of multiple sheets of aluminium alloy (AA 5754) using friction stir spot welding. - In: The international journal of advanced manufacturing technology, ISSN 1433-3015, Bd. 107 (2020), 7/8, S. 3093-3107
Friction stir spot welding (FSSW) process is widely used in the automotive industry for a range of applications such as battery components, standard wire connectors and terminals. This manuscript addresses two grand challenges in the arena of FSSW, hitherto, unaddressed in the extant literature: (i) lap joining of thin sheets (0.3 mm thickness) of AA 5754 alloy and (ii) lap joining of more than two sheets using FSSW. To accomplish this task, a novel pinless convex-shaped tool was designed to alter the stress state while gradually advancing the tool which led to achieving stress state necessary for obtaining defect-free lap joints. The weld joints were inspected by optical microscopy, SEM imaging and analysed by nanoindentation tests and Vickers microindentation tests for assessment of the quality of the weld interface (WI). Process parameters of FSSW such as torque on the tool and axially applied load were used to analytically obtain the average local measure of peak normal and axial stresses as well as the coefficient of friction in the contact zone. In samples welded at low rotational speeds, the strain-hardening mechanism was seen dominating in contrast to samples welded at higher rotational speeds, which showed thermal softening. As a direct consequence of this, the samples welded at low rotational speeds showed much higher hardness at the weld surface than the samples welded at higher speeds. A strong transition of strain hardening to thermal softening was noticeable beyond an applied strain rate of 400 s^-1.
https://doi.org/10.1007/s00170-020-05214-z
Numerical analysis of temperature distribution during laser deep welding of duplex stainless steel using a two-beam method. - In: Welding in the world, ISSN 1878-6669, Bd. 64 (2020), 5, S. 623-632
https://doi.org/10.1007/s40194-020-00857-8
Development of a highly productive GMAW hot wire process using a two-dimensional arc deflection. - In: Welding in the world, ISSN 1878-6669, Bd. 64 (2020), 5, S. 873-883
Gas metal arc welding (GMAW) processes are used in a wide range of applications due to their high productivity and flexibility. Nevertheless, the supplied melting wire electrode leads to a coupling of material and heat input. Therefore, an increase of the melting rate correlates with an increase of the heat input by the arc at the same time. A possibility to separate material and heat input is to use an additional wire, which reduces penetration and worsens the wetting behaviour. Consequently, bead irregularities such as bonding defects or insufficient root weldings can occur. In the context of this article, a controlling system for a two-dimensional magnetic arc deflection is presented, which allows to influence arc position as well as material transfer. The analysed GMAW hot wire process is characterised by high melting rates while also realising a sufficient penetration depth and wetting behaviour.
https://doi.org/10.1007/s40194-020-00880-9
Effect of local gas flow in full penetration laser beam welding with high welding speeds. - In: Applied Sciences, ISSN 2076-3417, Bd. 10 (2020), 5, 1867, S. 1-19
Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.
https://doi.org/10.3390/app10051867