Influence of lens fluorescence on fluorescence lifetime imaging ophthalmoscopy (FLIO) fundus imaging and strategies for its compensation. - In: Translational Vision Science & Technology, ISSN 2164-2591, Bd. 9 (2020), 8, 13, S. 1-10
https://doi.org/10.1167/tvst.9.8.13
Influence of thermal treatment on the magnetic properties and morphology of electrodeposited Fe-Co films. - In: Journal of magnetism and magnetic materials, ISSN 1873-4766, Bd. 513 (2020), 167204
Fe-Co films were prepared by electrodeposition from an electrolyte containing citric acid and annealed afterwards at different temperatures up to 700 ˚C. The grain sizes of the deposits increased from 11 nm to 30 nm with increasing annealing temperature, which lead to changes in magnetic properties of deposits. SQUID measurements indicate that there is a difference between the coercive force, Hc, of the as deposited samples (17 Oe) and the heat-treated samples (25-40 Oe) with a measurement error of 1-2 Oe. The remnant magnetization, Mr, decreased from 190 ± 12 emu/cm^3 for the as deposited to 75 ± 5 emu/cm^3 for the annealed samples, respectively. The saturation magnetization, Ms, seems not to be influenced strongly by the thermal treatment, with the only exception for the samples annealed at 500 ˚C. Thus, Ms has a slightly decreasing tendency from 1880 ± 90 emu/cm^3 for the as-deposited samples to 1780 ± 85 emu/cm^3 for samples annealed at 700 ˚C. The biggest value for Ms (2100 ± 105 emu/cm^3) was obtained if the samples were annealed at 500 ˚C. The thermal treatment generated cracks in the deposits. Interestingly, these cracks had a regular rectangular shape only if the deposits were annealed at 600 ˚C. The coercivity of the layers annealed at 600 ˚C was lower compared to layers annealed at the other temperatures. Magnetic force microscopy measurements indicated the magnetic domain distribution and the topography of the annealed deposits. The deposits showed the best soft magnetic properties if annealed between 500 and 600 ˚C.
https://doi.org/10.1016/j.jmmm.2020.167204
NiCo2O4Ni2P nanorods grown on nickel nanorod arrays as a bifunctional catalyst for efficient overall water splitting. - In: Materials today, ISSN 2468-6069, Bd. 17 (2020), 100490
The development of efficient and durable non-noble metal catalysts remains a challenge in electrocatalytic water splitting applications. To address this, a bifunctional catalyst involving hierarchical NiCo2O4Ni2P nanorods grown on nickel nanorod arrays (NiCo2O4@Ni2P/NAs) was designed and fabricated in this study for overall water splitting that provided high activity and acceptable stability. And if used as the cathode and anode in alkaline media, the NiCo2O4@Ni2P/NAs only required 1.58 V to achieve a current density of 10 mA cm^-2, which is superior to most reported catalysts and can be attributed to a unique core-shell structure and coexisting crystalline/amorphous Ni2P phases.
https://doi.org/10.1016/j.mtener.2020.100490
Molten iodide salt electrolyte for low-temperature low-cost sodium-based liquid metal battery. - In: Journal of power sources, ISSN 1873-2755, Bd. 475 (2020), 228674
Using low-melting-point electrolytes could overcome various key challenges of low-cost sodium-based liquid metal batteries (Na-LMBs), e.g. high rates of self-discharge and degradation of structural materials, by lowering their operating temperatures. Molten halide salts are considered promising electrolyte candidates for Na-LMBs due to their high stability and electrical conductivity. In this work, thermodynamic simulation via FactSageTM and thermal analysis via e.g. Differential Scanning Calorimeter (DSC) were carried out to explore the NaI-LiI-KI system, since it could be a promising electrolyte for Na-LMBs due to its low melting point and Na solubility. The results show that the eutectic NaI-LiI-KI performs as a pseudo-binary salt with a melting point of ˜290 ˚C. In this pseudo-binary salt, the solubility of NaI in the eutectic LiI-KI is ˜7 mol%. Using the eutectic NaI-LiI-KI electrolyte, Na-LMBs could be operated at < 350 ˚C. Moreover, the Na solubility and Na+ conductivity of the eutectic NaI-LiI-KI electrolyte, which are vital to the battery performance, were estimated by calculation based on the literature data. Additionally, its applicability and economy were also discussed based on cost pre-analysis of salt materials, salt treatment and structural materials regarding salt corrosivity.
https://doi.org/10.1016/j.jpowsour.2020.228674
Cation exchange behavior during the redox switching of poly (3,4-ethylenedioxythiophene) films. - In: Journal of solid state electrochemistry, ISSN 1433-0768, Bd. 24 (2020), 11/12, S. 3231-3244
Poly (3,4-ethylenedioxythiophene), PEDOT, films were synthesized at room temperature by potentiodynamic and potentiostatic step deposition in aqueous solutions containing EDOT monomer and LiClO4. In some solutions, the effect of small amounts of sodium dodecylsulfate, SDS, on the polymerization rate of EDOT and on the stiffness of the obtained PEDOT film was studied. The obtained PEDOT films were transferred in aqueous solutions containing cations with different molar mass, such as H+, Li+, Na+, K+, and Cs+. The apparent molar masses of the exchanged species during potentiodynamic experiments were determined by in situ microgravimetry. These measurements underlined the importance of the electrolyte chosen for electropolymerization process. It is known that SDS anions can be trapped inside the polymer layer during electropolymerization, providing them with a cation exchange behavior. However, even if the PEDOT films were deposited from an electrolyte without SDS, they still acted as cation exchangers.
https://doi.org/10.1007/s10008-020-04809-6
Electrocodeposition of titanium and gallium from 1-butyl-1-methylpyrrolidiniumtrifluoromethanesulfonate. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Volume 167 (2020), number 12, 122512
Electrochemical co-deposition of gallium and titanium on copper and gold substrates from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate was investigated in the temperature range from 25 ˚C to 140 ˚C. Crystalline gallium-titanium alloys were obtained by annealing the deposits at 800 ˚C for 16 h. X-ray diffraction performed on the annealed specimens confirmed the formation of crystalline phases. In situ quartz crystal microbalance experiments gave further insight into the initial stages of gallium-titanium co-deposition. One can tune the composition of the films by changing the deposition potential or the deposition technique. Gallium rich films with more than 60 wt% were obtained by potentiostatic depositions at 140 ˚C. We could show that no elemental titanium can be electrodeposited from bis(cyclopentadienyl)titanium(IV) bis(trifluoromethanesulfonate) in 1-butyl-1-methyl- pyrrolidinium trifluoromethanesulfonate. The addition of GaCl 3 to the electrolyte facilitated the reduction of Ti(IV) species.
https://doi.org/10.1149/1945-7111/abb27f
Numerical simulation of copper deposition in the Hull cell based on Butler-Volmer kinetics. - In: Journal of the Electrochemical Society, ISSN 1945-7111, Volume 167 (2020), number 12, 122506
In industry plating baths are often characterized by visual evaluation of a Hull cell deposition. In an academic approach, kinetic parameters are determined with cyclic voltammetry to obtain a deeper understanding of reaction mechanisms. In this paper we combine both approaches and show how via numerical simulations based on the boundary element method kinetic parameters can be extracted from Hull cell experiments. This combined method enables a better understanding of industrial electroplating processes without losing important information about coating and visual appearance. The validation is done in an acidic copper system using the kinetic parameters obtained from cyclic voltammetry for simulating the current density distribution and the cell voltage of a Hull cell deposition, followed by a comparison with experimental data. As an additional insight obtained from this study, the presence of O2 lowers the anodic transfer coefficient, while Cl- ions in the electrolyte increase the exchange current density.
https://doi.org/10.1149/1945-7111/abb1d5
Taguchi method in experimental procedures focused on corrosion process of positive current collector in lithium-ion batteries. - In: Electrochimica acta, ISSN 1873-3859, Bd. 360 (2020), 137011
Planning the design and discussing the results are routine tasks carried out daily by researchers all over the world. This study is focused on making these stages of research time- and cost-efficient without affecting the reliability of the data. Following the principles of the Taguchi method brings such a result. This approach ensures the quality of research by optimisation of the experimental procedure. In the presented work, the Taguchi method solves an exemplary research problem of the corrosion process of aluminium current collector in lithium-ion batteries. Operating factors selected for the optimisation include temperature (25, 35, 45˚C), the volume ratio of ethylene carbonate to diethyl carbonate in the solvent (1:1, 1:2, 1:4), and type of lithium salt (LiPF6, LiTFSI, LiBOB). Using three operating factors with three levels of variability requires data assembly in an orthogonal array L9 with nine experimental runs in total. In this study, the Taguchi approach is validated by performing a full-factorial procedure of twenty-seven individual experiments. The response of tested systems is analysed by cyclic voltammetry and electrochemical impedance spectroscopy, which enables the evaluation of corrosion parameters in each experimental run. The assessed parameters indicate the intensity of the aluminium corrosion depending on the operating conditions. These conditions cause unwanted variance, which accelerates corrosion and lowers the life expectancy of lithium-ion batteries. The Taguchi signal-to-noise-ratio analysis reveals that the most significant variation is caused by the lithium salt in the electrolyte (S/N LiBOB ≥ LiPF6 > LiTFSI). Temperature and alkyl carbonates play a secondary role. The Taguchi prediction method is also consistent with the full-factorial approach, which warrants reliability.
https://doi.org/10.1016/j.electacta.2020.137011
Quantification of the As/P content in GaAsP during MOVPE growth. - In: Applied physics letters, ISSN 1077-3118, Bd. 117 (2020), 6, S. 061601-1-061601-5
Epitaxial integration of direct-bandgap III-V compound semiconductors with silicon requires overcoming a significant lattice mismatch. To this end, GaAsP step-graded buffer layers are commonly applied. The thickness and composition of the individual layers are decisive for the envisaged strain relaxation. We study GaAsP growth by metalorganic vapor phase epitaxy in situ with reflection anisotropy spectroscopy. We find that the growth surface exhibits optical fingerprints of atomically well-ordered surfaces. These allow for tuning the interface preparation between adjacent layers. The spectral position of the characteristic peaks in the RA spectra, which are related to surface-modified bulk transitions, behaves similarly upon an increased As content as does the E1 interband transition of GaAsP at the growth temperature. The impact of strain on this shift is negligible. We thus monitor a bulk property via the surface reconstruction. An empiric model enables quantification of the As content of individual layers directly in situ without growth interruptions and for various surface reconstructions. Our findings are suitable for a simplified optimization of the GaAsP buffer growth for high-efficiency devices.
https://doi.org/10.1063/5.0012948
Augmentation of absorption channels induced by wave-chaos effects in free-standing nanowire arrays. - In: Optics express, ISSN 1094-4087, Bd. 28 (2020), 16, S. 23569-23583
Plenty of issues on quantal features in chaotic systems have been raised since chaos was accepted as one of the intrinsic properties of nature. Through intensive studies, it was revealed that resonance spectra in chaotic systems exhibit complicated structures, which is deeply concerned with sophisticated resonance dynamics. Motivated by these phenomena, we investigate light absorption characteristics of chaotic nanowires in an array. According to our results, a chaotic cross-section of a nanowire induces a remarkable augmentation of absorption channels, that is, an increasing number of absorption modes leads to substantial light absorption enhancement, as the deformation of cross-section increases. We experimentally demonstrate the light absorption enhancement with free-standing Si-nanowire polydimethylsiloxane (PDMS) composites. Our results are applicable not only to transparent solar cells but also to complementary metal-oxide-semiconductor (CMOS) image sensors to maximize absorption efficiency.
https://doi.org/10.1364/OE.398687