Publications at the Institute of Physics

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Schütt, Timo; Geitner, Robert; Bode, Stefan; Schubert, Ulrich Sigmar;
Dialysis diffusion kinetics in polymer purification. - In: Macromolecules, ISSN 1520-5835, Bd. 54 (2021), 20, S. 9410-9417

Diffusion kinetics of a prior developed automated dialysis system are investigated via in situ NMR spectroscopy for an optimization of conventional and advanced polymer purification. Using a polymeric solution, mixed with the respective monomer, several parameters like starting concentration, solvent volume, and solvent exchange by flow or complete one-time exchange are varied, resulting in a significant decrease of purification time for the automated setup. With an increased solvent flow (from 0.9 to 5.5 mL/min), 5.4 h and 2000 mL of solvent are required to decrease the monomer concentration to the detection limit. Without solvent flow, which corresponds to conventional dialysis, only 9 h and 250 mL of solvent are required for the same result, which is a time- and solvent-saving development for common purification of polymers.
Sha, Mo; Zhao, Huaping; Lei, Yong;
Updated insights into 3D architecture electrodes for micropower sources. - In: Advanced materials, ISSN 1521-4095, Bd. 33 (2021), 45, 2103304, insges. 17 S.

Microbatteries (MBs) and microsupercapacitors (MSCs) are primary on-chip micropower sources that drive autonomous and stand-alone microelectronic devices for implementation of the Internet of Things (IoT). However, the performance of conventional MBs and MSCs is restricted by their 2D thin-film electrode design, and these devices struggle to satisfy the increasing IoT energy demands for high energy density, high power density, and long lifespan. The energy densities of MBs and MSCs can be improved significantly through adoption of a 2D thick-film electrode design; however, their power densities and lifespans deteriorate with increased electrode thickness. In contrast, 3D architecture electrodes offer remarkable opportunities to simultaneously improve MB and MSC energy density, power density, and lifespan. To date, various 3D architecture electrodes have been designed, fabricated, and investigated for MBs and MSCs. This review provides an update on the principal superiorities of 3D architecture electrodes over 2D thick-film electrodes in the context of improved MB and MSC energy density, power density, and lifespan. In addition, the most recent and representative progress in 3D architecture electrode development for MBs and MSCs is highlighted. Finally, present challenges are discussed and key perspectives for future research in this field are outlined.
Liang, Feng; Zhang, Kaiwen; Zhang, Lei; Zhang, Yingjie; Lei, Yong; Sun, Xueliang;
Recent development of electrocatalytic CO2 reduction application to energy conversion. - In: Small, ISSN 1613-6829, Bd. 17 (2021), 44, 2100323, insges. 29 S.
Im Titel ist "2" tiefgestellt

Carbon dioxide (CO2) emission has caused greenhouse gas pollution worldwide. Hence, strengthening CO2 recycling is necessary. CO2 electroreduction reaction (CRR) is recognized as a promising approach to utilize waste CO2. Electrocatalysts in the CRR process play a critical role in determining the selectivity and activity of CRR. Different types of electrocatalysts are introduced in this review: noble metals and their derived compounds, transition metals and their derived compounds, organic polymer, and carbon-based materials, as well as their major products, Faradaic efficiency, current density, and onset potential. Furthermore, this paper overviews the recent progress of the following two major applications of CRR according to the different energy conversion methods: electricity generation and formation of valuable carbonaceous products. Considering electricity generation devices, the electrochemical properties of metal-CO2 batteries, including Li-CO2, Na-CO2, Al-CO2, and Zn-CO2 batteries, are mainly summarized. Finally, different pathways of CO2 electroreduction to carbon-based fuels is presented, and their reaction mechanisms are illustrated. This review provides a clear and innovative insight into the entire reaction process of CRR, guiding the new electrocatalysts design, state-of-the-art analysis technique application, and reaction system innovation.
Calderón, Jesús A.; Rincón, Carlos; Agreda, Martin; Jiménez de Cisneros, Juan José;
Design and analysis of a mechanical ventilation system based on cams. - In: Heliyon, ISSN 2405-8440, Bd. 7 (2021), 10, e08195, insges. 16 S.

Low-cost mechanical ventilators have been developed in order to deal with the shortage of traditional ventilators whose quantity is not sufficient in an emergency context in Perú. Protofy, a company from Spain, designed one of the first low-cost mechanical ventilation systems OxyGEN which was approved by a medicine agency in its country in special context of COVID 19. Therefore, as main of this article, a redesign of this system named OxygenIP.PE was carried out according to local requirements and available technology, but maintaining its working concept based on compression mechanism by cams. Sensors were added and a control algorithm of the respiratory rate was developed. Ventilation curves monitoring over time was implemented; in this sense, a mathematical model of the whole system was developed. OxygenIP.PE was redesigned, fabricated, and tested measuring its ventilation curves over time. Results indicate that this redesign provides a sturdy equipment able to work during a longer lifetime than the original. The replicability of the ventilation curves behavior is ensured, while the mechanism dimensions are adapted for a particular airbag resuscitator. The mathematical model of the whole system can satisfactorily determine the ventilation curves over time and is used to show the air pressure, volume, and flow as a function of the compression arm's angular position and differential pressure through the breathing circuit measurement, furthermore the algorithms designed as a consequence of the mathematical model were implemented for Raspberry and ARDUINO microcontrollers. There were obtained parameters of pressure 10-65 cmH2O, airflow 50-65 l/m, volume 0-0.5 l, at two values of beat per minute (BPM) 15 and 25.
Nandy, Manali; Paszuk, Agnieszka; Feifel, Markus; Koppka, Christian; Kleinschmidt, Peter; Dimroth, Frank; Hannappel, Thomas;
A route to obtaining low-defect III-V epilayers on Si(100) utilizing MOCVD. - In: Crystal growth & design, ISSN 1528-7505, Bd. 21 (2021), 10, S. 5603-5613

Low-defect III-V multilayer structures grown on Si(100) open opportunities for a wide range of cost-effective high-performance photovoltaic and optoelectronic devices. For that, (Al)GaP epilayers prepared almost lattice-matched on Si(100) substrates can serve as high-quality virtual substrates for subsequent heteroepitaxial growth. The evolution of crystal defects, such as stacking fault pyramids or threading dislocations, needs to be impeded already during the first preparation step, the III-V-on-Si nucleation, as they tend to propagate into the subsequently grown layers and increase nonradiative electron-hole recombination rates, which finally degrade the device performance. We establish a ternary GaP/AlP pulsed nucleation process on Si(100) substrates fabricated by metalorganic chemical vapor deposition, and compare it to the defect evolution from pure GaP nucleation layers (NLs). The entire procedure was optically monitored in situ using reflection anisotropy spectroscopy. Crystal defects were investigated by electron channeling contrast imaging. GaP grown on GaP/AlP NLs exhibits drastically reduced densities of threading dislocations and stacking faults by 1 and 2 orders of magnitude, respectively, compared to buffer layers grown on binary GaP NLs. We observed that the surface morphology at the initial stage of growth of these buffer layers is significantly smoother compared to the buffer layers grown on pure GaP NLs using atomic force microscopy. The proposed nucleation procedure here is supposed to substantially improve the crystalline quality of III-V buffer layers integrated on Si(100) wafers.
Alam, Shahidul; Nádaždy, Vojtech; Váry, Tomáš; Friebe, Christian; Meitzner, Rico; Ahner, Johannes; Anand, Aman; Karuthedath, Safakath; Castro, Catherine S. P. De; Göhler, Clemens; Dietz, Stefanie; Cann, Jonathan; Kästner, Christian; Konkin, Alexander; Beenken, Wichard J. D.; Anton, Arthur Markus; Ulbricht, Christoph; Sperlich, Andreas; Hager, Martin; Ritter, Uwe; Kremer, Friedrich; Brüggemann, Oliver; Schubert, Ulrich Sigmar; Ayuk Mbi Egbe, Daniel; Welch, Gregory C.; Dyakonov, Vladimir; Deibel, Carsten; Laquai, Frédéric; Hoppe, Harald;
Uphill and downhill charge generation from charge transfer to charge separated states in organic solar cells. - In: Journal of materials chemistry, ISSN 2050-7534, Bd. 9 (2021), 40, S. 14463-14489

It is common knowledge that molecular energy level offsets of a type II heterojunction formed at the donor-acceptor interface are considered to be the driving force for photoinduced charge transfer in organic solar cells. Usually, these offsets - present between molecular energy levels of the donor and acceptor - are obtained via cyclic voltammetry (CV) measurements of organic semiconductors cast in a film or dissolved in solution. Simply transferring such determined energy levels from solution or film of single materials to blend films may be obviously limited and not be possible in full generality. Herein, we report various cases of material combinations in which novel non-fullerene acceptors did not yield successful charge transfer, although energy levels obtained by CV on constituting single materials indicate a type II heterojunction. Whilst the integer charge transfer (ICT) model provides one explanation for a relative rise of molecular energy levels of acceptors, further details and other cases have not been studied so far in great detail. By applying energy-resolved electrochemical impedance spectroscopy (ER-EIS) on several donor-acceptor combinations, a Fano-like resonance feature associated with a distinctive molecular energy level of the acceptor as well as various relative molecular energy level shifts of different kinds could be observed. By analyzing ER-EIS and absorption spectra, not only the exciton binding energy within single materials could be determined, but also the commonly unknown binding energy of the CT state with regard to the joint density of states (jDOS) of the effective semiconductor. The latter is defined by transitions between the highest occupied molecular orbitals (HOMO) of the donor and the lowest unoccupied molecular orbitals (LUMO) of the acceptor. Using this technique among others, we identified cases in which charge generation may occur either via uphill or by downhill processes between the charge transfer exciton and the electronic gap of the effective semiconductor. Exceptionally high CT-exciton binding energies and thus low charge generation yields were obtained for a case in which the donor and acceptor yielded a too intimate blend morphology, indicating π-π stacking as a potential cause for unfavorable molecular energy level alignment.
Zhang, Huanming; Zhou, Min; Zhao, Huaping; Lei, Yong;
Ordered nanostructures arrays fabricated by anodic aluminum oxide (AAO) template-directed methods for energy conversion. - In: Nanotechnology, ISSN 1361-6528, Bd. 32 (2021), 50, 502006, insges. 27 S.

Clean and efficient energy conversion systems can overcome the depletion of the fossil fuel and meet the increasing demand of the energy. Ordered nanostructures arrays convert energy more efficiently than their disordered counterparts, by virtue of their structural merits. Among various fabrication methods of these ordered nanostructures arrays, anodic aluminum oxide (AAO) template-directed fabrication have drawn increasing attention due to its low cost, high throughput, flexibility and high structural controllability. This article reviews the application of ordered nanostructures arrays fabricated by AAO template-directed methods in mechanical energy, solar energy, electrical energy and chemical energy conversions in four sections. In each section, the corresponding advantages of these ordered nanostructures arrays in the energy conversion system are analysed, and the limitation of the to-date research is evaluated. Finally, the future directions of the ordered nanostructures arrays fabricated by AAO template-directed methods (the promising method to explore new growth mechanisms of AAO, green fabrication based on reusable AAO templates, new potential energy conversion application) are discussed.
Zhao, Xingxing; Zhang, Chenglin; Yang, Guowei; Wu, Yuhan; Fu, Qun; Zhao, Huaping; Lei, Yong;
Bismuth selenide nanosheets confined in thin carbon layers as anode materials for advanced potassium-ion batteries. - In: Inorganic chemistry frontiers, ISSN 2052-1553, Bd. 8 (2021), 18, S. 4267-4275

Metal selenides as promising anode materials for potassium ion batteries (PIBs) have attracted great research attention. However, it is still a challenge to promote its practical application due to the unsatisfactory cyclability resulting from large volume variation and sluggish kinetics. Herein, we tackle this issue by focusing on a promising but undemonstrated anode, bismuth selenide for PIBs which possesses a high theoretical capacity and good electronic conductivity. Benefitting from the carbon layer coating, Bi2Se3C has the capability to inhibit self-aggregation and buffer the volume expansion, leading to outstanding potassium-ion storage capability. It exhibits a very high reversible capacity of 526 mA h g^-1 at 50 mA g^-1, as well as superior cyclability and rate capability while maintaining a high capacity of 214 mA h g^-1 at 1.0 A g^-1 after 1000 cycles. Furthermore, its fast and reversible ion storage mechanism was verified, which first involves conversion and subsequent alloying redox reactions. This work enriches the understanding and development of stable conversion/alloying-based anodes for high-performance potassium-ion batteries.
Lindt, Kevin; Gizatullin, Bulat; Mattea, Carlos; Stapf, Siegfried;
Non-exponential 1H and 2H NMR relaxation and self-diffusion in asphaltene-maltene solutions. - In: Molecules, ISSN 1420-3049, Bd. 26 (2021), 17, 5218, insges. 35 S.
Im Titel sind "1" und "2" hochgestellt

The distribution of NMR relaxation times and diffusion coefficients in crude oils results from the vast number of different chemical species. In addition, the presence of asphaltenes provides different relaxation environments for the maltenes, generated by steric hindrance in the asphaltene aggregates and possibly by the spatial distribution of radicals. Since the dynamics of the maltenes is further modified by the interactions between maltenes and asphaltenes, these interactions - either through steric hindrances or promoted by aromatic-aromatic interactions - are of particular interest. Here, we aim at investigating the interaction between individual protonic and deuterated maltene species of different molecular size and aromaticity and the asphaltene macroaggregates by comparing the maltenes NMR relaxation (T1 and T2) and translational diffusion (D) properties in the absence and presence of the asphaltene in model solutions. The ratio of the average transverse and longitudinal relaxation rates, describing the non-exponential relaxation of the maltenes in the presence of the asphaltene, and its variation with respect to the asphaltene-free solutions are discussed. The relaxation experiments reveal an apparent slowing down of the maltenes dynamics in the presence of asphaltenes, which differs between the individual maltenes. While for single-chained alkylbenzenes, a plateau of the relaxation rate ratio was found for long aliphatic chains, no impact of the maltenes aromaticity on the maltene-asphaltene interaction was unambiguously found. In contrast, the reduced diffusion coefficients of the maltenes in presence of the asphaltenes differ little and are attributed to the overall increased viscosity.
Emminger, Carola; Abadizaman, Farzin; Samarasingha, Nuwanjula S.; Menéndez, José; Espinoza, Shirly; Richter, Steffen; Rebarz, Mateusz; Herrfurth, Oliver; Zahradník, Martin; Schmidt-Grund, Rüdiger; Andreasson, Jakob; Zollner, Stefan;
Analysis of temperature-dependent and time-resolved ellipsometry spectra of Ge. - In: IEEE Xplore digital library, ISSN 2473-2001, (2021), insges. 2 S.