Rapid and controllable synthesis of nanocrystallized nickel-cobalt boride electrode materials via a mircoimpinging stream reaction for high performance supercapacitors. - In: Small, ISSN 1613-6829, Bd. 16 (2020), 39, 2003342, insges. 13 S.
Nickel-cobalt borides (denoted as NCBs) have been considered as a promising candidate for aqueous supercapacitors due to their high capacitive performances. However, most reported NCBs are amorphous that results in slow electron transfer and even structure collapse during cycling. In this work, a nanocrystallized NCBs-based supercapacitor is successfully designed via a facile and practical microimpinging stream reactor (MISR) technique, composed of a nanocrystallized NCB core to facilitate the charge transfer, and a tightly contacted Ni-Co borates/metaborates (NCBi) shell which is helpful for OH^- adsorption. These merits endow NCBNCBi a large specific capacity of 966 C g^-1 (capacitance of 2415 F g^-1) at 1 A g^-1 and good rate capability (633.2 C g^-1 at 30 A g^-1), as well as a very high energy density of 74.3 Wh kg^-1 in an asymmetric supercapacitor device. More interestingly, it is found that a gradual in situ conversion of core NCBs to nanocrystallized Ni-Co (oxy)-hydroxides inwardly takes place during the cycles, which continuously offers large specific capacity due to more electron transfer in the redox reaction processes. Meanwhile, the electron deficient state of boron in metal-borates shells can make it easier to accept electrons and thus promote ionic conduction.
https://doi.org/10.1002/smll.202003342
Investigation of epitaxial graphene via Raman spectroscopy: origins of phonon mode asymmetries and line width deviations. - In: Carbon, ISSN 1873-3891, Bd. 170 (2020), S. 666-676
In this work a comprehensive study is presented for the analysis of epitaxial graphene layers using Raman spectroscopy. A wide range of graphene types is covered, from defective/polycrystalline single layer graphene to multilayer graphene with low defect density. On this basis the influence of strain type, Fermi level and number of layers on the Raman spectrum of graphene is investigated. A detailed view on the 2D/G dispersion and the respective slopes of uniaxially and biaxially strained graphene is given and its implications on the asymmetry of the G peak analyzed. A linear dependency of the phonon mode asymmetry on uniaxial strain is presented in addition to the known Fermi level dependence. Additional impacts on the asymmetry are found to be arising from the defect density and transfer doping of adsorbates. The discovered transfer doping mechanism is contrary to pure phonon excitation through excitons and exhibits increasing asymmetry with increasing Fermi level. A new characteristic correlation between the 2D mode line width and the inverse I(D)/I(G) ratio is introduced that allows the determination of the strain type and layer number and explains the difference between Raman line widths of monolayer graphene on different substrates.
https://doi.org/10.1016/j.carbon.2020.07.016
A close step towards industrialized application of solar water splitting. - In: Journal of semiconductors, ISSN 2058-6140, Bd. 41 (2020), 9, 090401, S. 1-3
https://doi.org/10.1088/1674-4926/41/9/090401
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
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
Hybrid GA-gradient method for thin films ellipsometric data evaluation. - In: Journal of computational science, ISSN 1877-7503, Bd. 47 (2020), 101201
A global-search method which applies the concept of genetic algorithm (GA) with gradient-based optimizer is proposed for the problem of experimental data analysis from spectroscopic ellipsometry on thin films. The method is applied to evaluate the data obtained for samples with different structure complexity, starting with transparent monolayers (SiO2, HfO2) on a substrate, through absorbing film (diamond-like carbon) and multilayer structures. We demonstrate that by using this method we are able to find material parameters even for limited a priori knowledge about the sample properties, where classical methods fail.
https://doi.org/10.1016/j.jocs.2020.101201
First-principles study of the structural and electronic properties of the GaAsxP1-x surface. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 6.9
Impact of the upcoming "Nationale Forschungsdaten Infrastruktur NFDI" on the SKM Community. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), PSV III
Atomic-Layer-Deposited TiO2 protection layers for InP photocathodes. - In: DPG-Frühjahrstagung (DPG Spring Meeting) of the Condensed Matter Section (SKM) together with the DPG Division Environmental Physics and the Working Groups Accelerator Physics; Equal Opportunities; Energy; Industry and Business; Physics, Modern IT and Artificial Intelligence, Young DPG, (2020), HL 24.5