Well-defined nanostructures for electrochemical energy conversion and storage. - In: Advanced energy materials, ISSN 1614-6840, Bd. 11 (2021), 15, 2001537, insges. 53 S.
Electrochemical energy conversion and storage play crucial roles in meeting the increasing demand for renewable, portable, and affordable power supplies for society. The rapid development of nanostructured materials provides an alternative route by virtue of their unique and promising effects emerging at nanoscale. In addition to finding advanced materials, structure design and engineering of electrodes improves the electrochemical performance and the resultant commercial competitivity. Regarding the structural engineering, controlling the geometrical parameters (i.e., size, shape, hetero-architecture, and spatial arrangement) of nanostructures and thus forming well-defined nanostructure (WDN) electrodes have been the central aspects of investigations and practical applications. This review discusses the fundamental aspects and concept of WDNs for energy conversion and storage, with a strong emphasis on illuminating the relationship between the structural characteristics and the resultant electrochemical superiorities. Key strategies for actualizing well-defined features in nanostructures are summarized. Electrocatalysis and photoelectrocatalysis (for energy conversion) as well as metal-ion batteries and supercapacitors (for energy storage) are selected to illustrate the superiorities of WDNs in electrochemical reactions and charge carrier transportation. Finally, conclusions and perspectives regarding future research, development, and applications of WDNs are discussed.
https://doi.org/10.1002/aenm.202001537
Deformed microcavities with very high Q-factors and directional farfield emission. - In: EOS Annual Meeting (EOSAM 2020), (2020), 01006, S. 1-2
We report the design and optimized fabrication of deformed whispering gallery mode resonators in silica with solely ICP-RIE. This allows us to control the morphology of the resonators more freely and results in low surface roughness. The light was coupled into the resonator using a state of the art tapered fiber approach and we determined the Q-factor in the range of 10^5
https://doi.org/10.1051/epjconf/202023801006
Ag-nanoparticles-decorated Ge-nanowhisker grafted on carbon fiber cloth as flexible and effective SERS substrates. - In: ChemistrySelect, ISSN 2365-6549, Bd. 5 (2020), 27, S. 8338-8343
Three-dimensional (3D) flexible surface enhanced Raman scattering (SERS) substrates of silver nanoparticles (Ag-NPs) decorated Germanium nanowhiskers (Ge-NWHKs) grafted on carbon fiber cloth (CFC) (denoted as Ag-NPsGe-NWHKs@CFC) are constructed via chemical vapor deposition growth of high-density Ge-NWHKs on CFC and then assembly of Ag-NPs on the Ge-NWHKs by galvanic displacement. Ordered 3D framework of Ge-NWHKs grafted flexible CFC impels the formation of large amounts of Ag-NPs with homogenous distribution via spontaneous reduction of Ag+ ions. Thus, the Ag-NPs@Ge-NWHKs@CFC SERS substrates present ultra-high sensitivity, good reproducibility, and high flexibility. This SERS sensor has achieved a detection limit of 1 pM for Rhodamine 6G and 0.1 nM for thiram respectively. The as-fabricated SERS substrates show promising potential for applications in rapid detection of trace organic pollutants in the aquatic environment.
https://doi.org/10.1002/slct.202001290
Electrochemical nucleation of silicon in ionic liquid-based electrolytes. - In: Meeting abstracts, ISSN 2151-2043, Bd. MA2020-01 (2020), 19, 1181
https://doi.org/10.1149/MA2020-01191181mtgabs
Electrodeposition of cuprous oxide on a free-standing porous Cu framework for photoelectrochemical water splitting. - In: Meeting abstracts, ISSN 2151-2043, Bd. MA2020-02 (2020), 15, 1425
https://doi.org/10.1149/MA2020-02151425mtgabs
Impact of defects on magnetic properties of spinel zinc ferrite thin films. - In: Physica status solidi, ISSN 1521-3951, Bd. 257 (2020), 7, 1900630, insges. 11 S.
The recent developments in the study of magnetic properties in the spinel zinc ferrite system are explored. Engineering of ionic valence and site distribution allows tailoring of magnetic interactions. Recent literature is reviewed, and own investigations are presented for a conclusive understanding of the mechanisms responsible for the magnetic behavior in this material system. By varying the Zn-to-Fe ratio, the deposition, as well as thermal annealing conditions, ZnFe2O4 thin films with a wide range of crystalline quality are produced. In particular, the focus is on the magnetic structure in relation to spectroscopic properties of disordered ZnFe2O4 thin films. Comparing the cation distribution in film bulk (optical transitions in the dielectric function) and near-surface region (X-ray absorption), it is found that an inhomogeneous cation distribution leads to a weaker magnetic response in films of inverse configuration, whereas defects in the normal spinel are likely to be found at the film surface. The results show that it is possible to engineer the defect distribution in the magnetic spinel ferrite film structure and tailor their magnetic properties on demand. It is demonstrated that these properties can be read out optically, which allows controlled growth of the material and applications in future magneto-optical devices.
https://doi.org/10.1002/pssb.201900630
Atomic surface structure of MOVPE-prepared GaP(111)B. - In: Applied surface science, Bd. 534 (2020), 147346
Controlling the surface formation of the group-V face of (111)-oriented III-V semiconductors is crucial for subsequent successful growth of III-V nanowires for electronic and optoelectronic applications. With a view to preparing GaP/Si(111) virtual substrates, we investigate the atomic structure of the MOVPE (metalorganic vapor phase epitaxy)-prepared GaP(111)B surface (phosphorus face). We find that upon high-temperature annealing in the H2-based MOVPE process ambience, the surface is phosphorus-depleted, as evidenced by X-ray photoemission spectroscopy (XPS). However, a combination of density functional theory calculations and scanning tunneling microscopy (STM) suggests the formation of a partially H-terminated phosphorus surface, where the STM contrast is due to electrons tunneling from non-terminated dangling bonds of the phosphorus face. Atomic force microscopy (AFM) reveals that a high proportion of the surface is covered by islands, which are confirmed as Ga-rich by Auger electron spectroscopy (AES). We conclude that the STM images of the samples after high-temperature annealing only reflect the flat regions of the partially H-terminated phosphorus face, whereas an increasing coverage with Ga-rich islands, as detected by AFM and AES, forms upon annealing and underlies the higher proportion of Ga in the XPS measurements.
https://doi.org/10.1016/j.apsusc.2020.147346
Control of magnetic properties in spinel ZnFe2O4 thin films through intrinsic defect manipulation. - In: Journal of applied physics, ISSN 1089-7550, Bd. 128 (2020), 16, 165702, insges. 7 S.
Im Titel sind "2" und "4" tiefgestellt
We present a systematic study of the magnetic properties of ZnFe2O4 thin films fabricated by pulsed laser deposition at low and high oxygen partial pressure and annealed in oxygen and argon atmosphere, respectively. The as-grown films show strong magnetization, closely related to a non-equilibrium distribution of defects, namely, Fe cations among tetrahedral and octahedral lattice sites. While the concentration of tetrahedral Fe cations declines after argon treatment at 250 ˚C, the magnetic response is enhanced by the formation of oxygen vacancies, evident by the increase in near-infrared absorption due to the Fe2+-Fe3+ exchange. After annealing at temperatures above 300 ˚C, the weakened magnetic response is related to a decline in disorder with a partial recrystallization toward a less defective spinel configuration.
https://doi.org/10.1063/5.0019712
Advances in epitaxial GaInP/GaAs/Si triple junction solar cells. - In: 2020 47th IEEE Photovoltaic Specialists Conference (PVSC), (2020), S. 0194-0196
https://doi.org/10.1109/PVSC45281.2020.9300594
Electrogravimetry and structural properties of thin silicon layers deposited in sulfolane and ionic liquid electrolytes. - In: ACS applied materials & interfaces, ISSN 1944-8252, Bd. 12 (2020), 51, S. 57526-57538
Potentiostatic deposition of silicon is performed in sulfolane (SL) and ionic liquid (IL) electrolytes. Electrochemical quartz crystal microbalance with damping monitoring (EQCM-D) is used as main analytical tool for the characterization of the reduction process. The apparent molar mass (Mapp) is applied for in situ estimation of the layer contamination. By means of this approach, appropriate electrolyte composition and substrate type are selected to optimize the structural properties of the layers. The application of SL electrolyte results in silicon deposition with higher efficiency compared to the IL 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP][TFSI]. This has been associated with the instability of the IL in the presence of silicon tetrachloride and the enhanced incorporation of IL decomposition products into the growing silicon deposit. X-ray photoelectron spectroscopy (XPS) analysis supports the results about the layer composition, as suggested from the microgravimetric experiments. Attention has been given to the impact of practically relevant substrates (i.e., Cu, Ni, and vitreous carbon) on the reduction process. An effective deposition can be carried out on the metal electrodes in both electrolytes due to accelerated reaction kinetics for these types of substrates. However, on vitreous carbon (VC), a successful reduction of SiCl4 can only be accomplished in the IL, while the electroreduction process in SL is dominated by the decomposition of the electrolyte. For short deposition times, the scanning electron microscopy (SEM) images display rough morphologies in the nanometer range, which evolve further to structures with increased length scale of the surface roughness. The development of a rough interface during deposition, resulting in QCM damping at advanced stages of the process, is interpreted by a model accounting for the resistive force caused by the interaction of the liquid with a nonuniform layer interface. By using this approach, the individual contributions of the surface roughness and viscoelastic effects to the measured damping values are estimated.
https://doi.org/10.1021/acsami.0c14694