Highly-rough surface carbon nanofibers film as an effective interlayer for lithium-sulfur batteries. - In: Journal of semiconductors, ISSN 2058-6140, Bd. 41 (2020), 9, 092701, S. 1-6
Lithium-sulfur (Li-S) battery with a new configuration is demonstrated by inserting a flexible nitrogen-doping carbon nanofiber (N-CNFs) interlayer between the sulfur cathode and the separator. The N-CNFs film with high surface roughness and surface area is fabricated by electrospinning and a subsequent calcination process. The N-CNFs film interlayer not only effectively traps the shuttling migration of polysulfides but also gives the whole battery reliable electronic conductivity, which can effectively enhance the electrochemical performance of Li-S batteries. Finally, Li-S batteries with long cycling stability of 785 mAh/g after 200 cycles and good rate capability of 573 mAh/g at 5 C are achieved.
https://doi.org/10.1088/1674-4926/41/9/092701
Scanning probe lithography on calixarene towards single-digit nanometer fabrication. - In: International journal of extreme manufacturing, ISSN 2631-7990, Volume 2 (2020), number 3, 032005, Seite 1-21
Cost effective patterning based on scanning probe nanolithography (SPL) has the potential for electronic and optical nano-device manufacturing and other nanotechnological applications. One of the fundamental advantages of SPL is its capability for patterning and imaging employing the same probe. This is achieved with self-sensing and self-actuating cantilevers, also known as 'active' cantilevers. Here we used active cantilevers to demonstrate a novel path towards single digit nanoscale patterning by employing a low energy (<100 eV) electron exposure to thin films of molecular resist. By tuning the electron energies to the lithographically relevant chemical resist transformations, the interaction volumes can be highly localized. This method allows for greater control over spatially confined lithography and enhances sensitivity. We found that at low electron energies, the exposure in ambient conditions required approximately 10 electrons per single calixarene molecule to induce a crosslinking event. The sensitivity was 80-times greater than a classical electron beam exposure at 30 keV. By operating the electro-exposure process in ambient conditions a novel lithographic reaction scheme based on a direct ablation of resist material (positive tone) is presented.
https://doi.org/10.1088/2631-7990/aba2d8
OPM magnetorelaxometry in the presence of a DC bias field. - In: EPJ Quantum Technology, ISSN 2196-0763, Bd. 7 (2020), 12, insges. 14 S.
Spatial quantitative information about magnetic nanoparticle (MNP) distributions is a prerequisite for biomedical applications like magnetic hyperthermia and magnetic drug targeting. This information can be gathered by means of magnetorelaxometry (MRX) imaging, where the relaxation of previously aligned MNP's magnetic moments is measured by sensitive magnetometers and an inverse problem is solved. To remove or minimize the magnetic shielding in which MRX imaging is carried out today, the knowledge of the influence of background magnetic fields on the MNP's relaxation is a prerequisite. We show MRX measurements using an intensity-modulated optically pumped magnetometer (OPM) in background magnetic fields of up to 100 [my]T. We show that the relaxation parameters alter or may be intentionally altered significantly by applying static fields parallel or antiparallel to the MNPs alignment direction. Further, not only the relaxation process of the MNP's magnetic moments could be measured with OPM, but also their alignment due to the MRX excitation field.
https://doi.org/10.1140/epjqt/s40507-020-00087-3
Compensation of motion-induced phase errors and enhancement of Doppler unambiguity in TDM-MIMO systems by model-based estimation. - In: IEEE sensors letters, ISSN 2475-1472, Volume 4 (2020), issue 10, 7003504, 4 Seiten
Utilization of multiple input multiple output (MIMO) systems in radar and channel sounding has gained increased attention in recent years. Quite often, time-division multiplexing (TDM) is employed to realize orthogonal waveforms at the transmitter. Apart from its advantages, TDM has two severe drawbacks. First, motion-induced phase variations become indistinguishable from phase migration due to the signal's arrival direction. This is termed angle-Doppler coupling, which causes ambiguities in angle, and Doppler estimation. Second, the unambiguously resolvable Doppler, i.e., the Doppler bandwidth, is reduced. In this letter, a model-based estimation approach will be proposed, which compensates for angle-Doppler coupling, and restores the Doppler bandwidth. A data model for the MIMO observations is derived, which is exploited by a maximum likelihood estimator to infer angle, delay, and Doppler from the observations. The performance of the proposed approach will be testified by simulations.
https://doi.org/10.1109/LSENS.2020.3020700
Realization of moisture-resistive perovskite films for highly efficient solar cells using molecule incorporation. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 12 (2020), 35, S. 39063-39073
The development of highly crystalline perovskite films with large crystal grains and few surface defects is attractive to obtain high-performance perovskite solar cells (PSCs) with good device stability. Herein, we simultaneously improve the power conversion efficiency (PCE) and humid stability of the CH3NH3PbI3 (CH3NH3 = MA) device by incorporating small organic molecule IT-4F into the perovskite film and using a buffer layer of PFN-Br. The presence of IT-4F in the perovskite film can successfully improve crystallinity and enhance the grain size, leading to reduced trap states and longer lifetime of the charge carrier, and make the perovskite film hydrophobic. Meanwhile, as a buffer layer, PFN-Br can accelerate the separation of excitons and promote the transfer process of electrons from the active layer to the cathode. As a consequence, the PSCs exhibit a remarkably improved PCE of 20.55% with reduced device hysteresis. Moreover, the moisture-resistive film-based devices retain about 80% of their initial efficiency after 30 days of storage in relative humidity of 10-30% without encapsulation.
https://doi.org/10.1021/acsami.0c09046
Ultrafast dynamics of hot charge carriers in an oxide semiconductor probed by femtosecond spectroscopic ellipsometry. - In: New journal of physics, ISSN 1367-2630, Bd. 22 (2020), 083066, insges. 14 S.
https://doi.org/10.1088/1367-2630/aba7f3
Age-related differences of motor cortex plasticity in adults: a transcranial direct current stimulation study. - In: Brain stimulation, ISSN 1876-4754, Bd. 13 (2020), 6, S. 1588-1599
Background - Cognitive, and motor performance are reduced in aging, especially with respect to acquisition of new knowledge, which is associated with a neural plasticity decline. Animal models show a reduction of long-term potentiation, but not long-term depression, in higher age. Findings in humans are more heterogeneous, with some studies showing respective deficits, but others not, or mixed results, for plasticity induced by non-invasive brain stimulation. One reason for these heterogeneous results might be the inclusion of different age ranges in these studies. In addition, a systematic detailed comparison of the age-dependency of neural plasticity in humans is lacking so far. - Objective - We aimed to explore age-dependent plasticity alterations in adults systematically by discerning between younger and older participants in our study. - Methods - We recruited three different age groups (Young: 18-30, Pre-Elderly: 50-65, and Elderly: 66-80 years). Anodal, cathodal, or sham transcranial direct current stimulation (tDCS) was applied over the primary motor cortex with 1 mA for 15 min to induce neuroplasticity. Cortical excitability was monitored by single-pulse transcranial magnetic stimulation as an index of plasticity. - Results - For anodal tDCS, the results show a significant excitability enhancement, as compared to sham stimulation, for both, Young and the Pre-Elderly groups, while no LTP-like plasticity was obtained in the Elderly group by the applied stimulation protocol. Cathodal tDCS induced significant excitability-diminishing plasticity in all age groups. - Conclusion - Our study provides further insight in age-related differences of plasticity in healthy humans, which are similar to those obtained in animal models. The decline of LTP-like plasticity in higher age could contribute to cognitive deficits observed in aging.
https://doi.org/10.1016/j.brs.2020.09.004
Investigation of magnetically driven passage of magnetic nanoparticles through eye tissues for magnetic drug targeting. - In: Nanotechnology, ISSN 1361-6528, Bd. 31 (2020), 49, 495101, S. 1-12
This paper elucidates the feasibility of magnetic drug targeting to the eye by using magnetic nanoparticles (MNPs) to which pharmaceutical drugs can be linked. Numerical simulations revealed that a magnetic field gradient of 20 T m^-1 seems to be promising for dragging magnetic multicore nanoparticles of about 50 nm into the eye. Thus, a targeting magnet system made of superconducting magnets with a magnetic field gradient at the eye of about 20 T m^-1 was simulated. For the proof-of-concept tissue experiments presented here the required magnetic field gradient of 20 T m^-1 was realized by a permanent magnet array. MNPs with an optimized multicore structure were selected for this application by evaluating their stability against agglomeration of MNPs with different coatings in water for injections, physiological sodium chloride solution and biological media such as artificial tear fluid. From these investigations, starch turned out to be the most promising coating material because of its stability in saline fluids due to its steric stabilization mechanism. To evaluate the passage of MNPs through the sclera and cornea of the eye tissues of domestic pigs (Sus scrofa domesticus), a three-dimensionally printed setup consisting of two chambers (reservoir and target chamber) separated by the eye tissue was developed. With the permanent magnet array emulating the magnetic field gradient of the superconducting setup, experiments on magnetically driven transport of the MNPs from the reservoir chamber into the target chamber via the tissue were performed. The resulting concentration of MNPs in the target chamber was determined by means of quantitative magnetic particle spectroscopy. It was found that none of the tested particles passed the cornea, but starch-coated particles could pass the sclera at a rate of about 5 ng mm^-2 within 24 h. These results open the door for future magnetic drug targeting to the eye.
https://doi.org/10.1088/1361-6528/abb0b4
Liquid-based battery temperature control of electric buses. - In: Energies, ISSN 1996-1073, Bd. 13 (2020), 19, 4990, S. 1-20
Previous research identified that battery temperature control is critical to the safety, lifetime, and performance of electric vehicles. In this paper, the liquid-based battery temperature control of electric buses is investigated subject to heat transfer behavior and control strategy. Therefore, a new transient calculation method is proposed to simulate the thermal behavior of a coolant-cooled battery system. The method is based on the system identification technique and combines the advantage of low computational effort and high accuracy. In detail, four transfer functions are extracted by a thermo-hydraulic 3D simulation model comprising 12 prismatic lithium nickel manganese cobalt oxide (NMC) cells, housing, arrestors, and a cooling plate. The transfer functions describe the relationship between heat generation, cell temperature, and coolant temperature. A vehicle model calculates the power consumption of an electric bus and thus provides the input for the transient calculation. Furthermore, a cell temperature control strategy is developed with respect to the constraints of a refrigerant-based battery cooling unit. The data obtained from the simulation demonstrate the high thermal inertia of the system and suggest sufficient control of the battery temperature using a quasi-stationary cooling strategy. Thereby, the study reveals a crucial design input for battery cooling systems in terms of heat transfer behavior and control strategy.
https://doi.org/10.3390/en13194990
Application of hydrosilane-free atmospheric pressure chemical vapor deposition of SiOx films in the manufacture of crystalline silicon solar cells. - In: Thin solid films, ISSN 1879-2731, Bd. 713 (2020), 138338
In this work we present SiOx films deposited in cost-effective laboratory scale three-dimensional printed atmospheric pressure chemical vapor deposition setup. As SiOx films are deposited at room temperature without complex vacuum systems, they can be a good candidate for the use in commercial c-Si solar cell production lines. The quality of the deposited films was investigated as to their integrity, conformity with various surfaces, and post-treatment resilience such as stability against etchants and annealing. Several applications of the SiOx film prepared with the atmospheric pressure chemical vapor deposition (APCVD) were discussed. In one application, the APCVD SiOx was utilized to effectively promote single-side texturing of Float Zone and Czochralski Si wafers by coating only one side with SiOx and subsequently annealing prior to texturing in an alkaline aqueous solution. Another application was to exploit the APCVD SiOx as a plating mask for silicon heterojunction solar cells. Two processing options prior to the oxide-film deposition were investigated: i) application of an Ag seed-layer, which promotes subsequent electroplating, and ii) printing of an organic grid, which, after stripping, creates openings in the SiOx that facilitate electroplating of the solar cell's electrode on the underlying transparent conducting oxide. In a different application, the APCVD SiOx films acted as protection against parasitic plating on the front side of passivated emitter and rear solar cells. The deposited films were characterized by ellipsometry, hemispherical reflectance measurements, scanning electron microscopy, energy dispersive X-ray spectroscopy and optical microscopy.
https://doi.org/10.1016/j.tsf.2020.138338