Publications at the Department of Mathematics and Natural Sciences from 2019

Results: 873
Created on: Wed, 27 Mar 2024 23:21:20 +0100 in 0.0762 sec


Koch, Juliane; Liborius, Lisa; Kleinschmidt, Peter; Prost, Werner; Weimann, Nils; Hannappel, Thomas
Impact of the tip-to-semiconductor contact in the electrical characterization of nanowires. - In: ACS omega, ISSN 2470-1343, Bd. 9 (2024), 5, S. 5788-5797

Well-defined semiconductor heterostructures are a basic requirement for the development of high-performance optoelectronic devices. In order to achieve the desired properties, a thorough study of the electrical behavior with a suitable spatial resolution is essential. For this, various sophisticated tip-based methods can be employed, such as conductive atomic force microscopy or multitip scanning tunneling microscopy (MT-STM). We demonstrate that in any tip-based measurement method, the tip-to-semiconductor contact is decisive for reliable and precise measurements and in interpreting the properties of the sample. For that, we used our ultrahigh-vacuum-based MT-STM coupled in vacuo to a reactor for the preparation of nanowires (NWs) with metal organic vapor phase epitaxy, and operated our MT-STM as a four-point nanoprober on III-V semiconductor NW heterostructures. We investigated a variety of upright, free-standing NWs with axial as well as coaxial heterostructures on the growth substrates. Our investigation reveals charging currents at the interface between the measuring tip and the semiconductor via native insulating oxide layers, which act as a metal-insulator-semiconductor capacitor with charging and discharging conditions in the operating voltage range. We analyze in detail the observed I-V characteristics and propose a strategy to achieve an optimized tip-to-semiconductor junction, which includes the influence of the native oxide layer on the overall electrical measurements. Our advanced experimental procedure enables a direct relation between the tip-to-NW junction and the electronic properties of as-grown (co)axial NWs providing precise guidance for all future tip-based investigations.



https://doi.org/10.1021/acsomega.3c08729
Horak, Iryna; Skaterna, Tetiana; Lugovskyi, Serhii; Krysiuk, Iryna; Tykhomyrov, Artem; Prylutska, Svitlana; Tverdokhleb, Nina; Senenko, Anton; Cherepanov, Vsevolod; Drobot, Liudmyla; Matyshevska, Olga; Ritter, Uwe; Prylutskyy, Yuriy
Antimetastatic lung cancer therapy using alkaloid Piperlongumine noncovalently bound to С60 fullerene. - In: Journal of drug delivery science and technology, Bd. 92 (2024), 105275, S. 1-10

A novel nanoformulation, C60 fullerene loaded with a plant alkaloid Piperlongumine (PL) molecules (C60-PL nanocomplex), as a potential drug for the treatment of highly metastatic lung cancer was created and characterized by using ultrasonic technology, computer simulation, atomic force and scanning tunneling microscopy. The aim of the study was to evaluate the antimetastatic potential of PL alone and the C60-PL nanocomplex using Lewis lung carcinoma (LLC) cell line as a model. Evidence has been obtained that the 2:1C60-PL nanocomplex is a potent agent capable of effectively reducing the survival, migration and invasion of LLC cells in vitro, as well as tumor growth and metastasis in vivo compared to free PL. These effects in cell behavior were shown to be associated with an increased Bax expression and high level of cleaved PARP confirming the proapototic potential of C60-PL nanocomplex as well as down-regulation of the mRNA of epithelial-mesenchymal transition regulator Twist1 and cancer stem cell marker CD44, a reduced level of phosphorylated mTOR and adaptor protein Ruk/CIN85. Histological analysis of the lung tissue of LLC-bearing mice showed that in animals that received the C60-PL nanocomplex, the regression of metastases prevailed over their growth. The obtained results allow to conclude that the proposed C60-PL nanocomplex represents a promising drug for the treatment of metastatic lung cancer.



https://doi.org/10.1016/j.jddst.2023.105275
Duan, Yu; Sun, Deen; Zhang, Sam; Wang, Shengyi; Qiu, Jiajia; Feng, Shuanglong
Multi-strategy coordination enables WSe2 to achieve high-performance real-world detection of NO2. - In: Sensors and actuators, ISSN 0925-4005, Bd. 403 (2024), 135183, S. 1-10

In recent years, WSe2 has become an ideal material for room-temperature NO2 gas sensing, but its low response and long response time limit its application. In this study, we combined multiple strategies of constructing a three-dimensional structure, introducing Se vacancies, Au nanoparticle sensitization, and 1 T/2 H-phase modulation. The synergistic effect was utilized to effectively enhance the gas adsorption, charge transfer degree, and carrier transport capacity of WSe2 and achieve high-performance NO2 detection. The prepared V-WAAP achieved high response (78.32%) with a short response time (33 s), and outstanding stability and selectivity for low concentration (1 ppm) NO2. The intrinsic factors of sensing performance improvement were comprehensively analyzed by combining the results of compositional and structural characterization. In addition, we verified its potential for practical applications by assembling a V-WAAP-based NO2 gas sensing equipment.



https://doi.org/10.1016/j.snb.2023.135183
Ran, Yan; Xu, Changfan; Ji, Deyang; Zhao, Huaping; Li, Liqiang; Lei, Yong
Research progress of transition metal compounds as bifunctional catalysts for zinc-air batteries. - In: Nano research energy, ISSN 2790-8119, Bd. 3 (2024), 1, e9120092, S. 1-23

Zinc-air batteries (ZABs) are widely studied because of their high theoretical energy density, high battery voltage, environmental protection, and low price. However, the slow kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the air electrode limits the further application of ZABs, so that how to develop a cheap, efficient, and stable catalyst with bifunctional catalytic activity is the key to solving the development of ZABs. Transition metal compounds are widely used as cathode materials for ZABs due to their low cost, high electrocatalytic activity, and stable structure. This review summarizes the research progress of transition metal compounds as bifunctional catalysts for ZABs. The development history, operation principle, and mechanism of ORR and OER reactions are introduced first. The application and development of transition metal compounds as bifunctional catalysts for ZABs in recent years are systematically introduced, including transition metal oxides (TMOs), transition metal nitrides (TMNs), transition metal sulfides (TMSs), transition metal carbides (TMCs), transition metal phosphates (TMPs), and others. In addition, the shortcomings of transition metal compounds as bifunctional catalysts for ZABs were summarized and reasonable design strategies and improvement measures were put forward, aiming at providing a reference for the design and construction of high-performance ZABs cathode materials. Finally, the challenges and future in this field are discussed and prospected.



https://doi.org/10.26599/NRE.2023.9120092
Li, Qicong; Yue, Shizhong; Huang, Zhitao; Li, Chao; Sun, Jiaqian; Dong, Keqian; Wang, Zhijie; Liu, Kong; Qu, Shengchun; Lei, Yong
Dissociation of singlet excitons dominates photocurrent improvement in high-efficiency non-fullerene organic solar cells. - In: Nano research energy, ISSN 2790-8119, Bd. 3 (2024), 1, e9120099, S. 1-8

In organic solar cells, the singlet and triplet excitons dissociate into free charge carriers with different mechanisms due to their opposite spin state. Therefore, the ratio of the singlet and triplet excitons directly affects the photocurrent. Many methods were used to optimize the performance of the low-efficiency solar cell by improving the ratio of triplet excitons, which shows a long diffusion length. Here we observed that in high-efficiency systems, the proportion of singlet excitons under linearly polarized light excitation is higher than that of circularly polarized light. Since the singlet charge transfer state has lower binding energy than the triplet state, it makes a significant contribution to the charge carrier generation and enhancement of the photocurrent. Further, the positive magnetic field effect reflects that singlet excitons dissociation plays a major role in the photocurrent, which is opposite to the case of low-efficiency devices where triplet excitons dominate the photocurrent.



https://doi.org/10.26599/NRE.2023.9120099
Heri, Sebastian; Lieb, Julia; Rosenthal, Joachim
Self-dual convolutional codes. - In: IEEE transactions on information theory, Bd. 70 (2024), 2, S. 950-963

This paper investigates the concept of self-dual convolutional codes. We derive the basic properties of this interesting class of codes and we show how some of the techniques to construct self-dual linear block codes generalize to self-dual convolutional codes. As for self-dual linear block codes we are able to give a complete classification for some small parameters.



https://doi.org/10.1109/TIT.2023.3343108
Eichfelder, Gabriele; Quintana, Ernest
Set-based robust optimization of uncertain multiobjective problems via epigraphical reformulations. - In: European journal of operational research, ISSN 0377-2217, Bd. 313 (2024), 3, S. 871-882

In this paper, we study a method for finding robust solutions to multiobjective optimization problems under uncertainty. We follow the set-based minmax approach for handling the uncertainties which leads to a certain set optimization problem with the strict upper type set relation. We introduce, under some assumptions, a reformulation using instead the strict lower type set relation without sacrificing the compactness property of the image sets. This allows to apply vectorization results to characterize the optimal solutions of these set optimization problems as optimal solutions of a multiobjective optimization problem. We end up with multiobjective semi-infinite problems which can then be studied with classical techniques from the literature.



https://www.sciencedirect.com/science/article/pii/S0377221723007208/pdfft?md5=f5272f8643b0ce953294091001149d0f&pid=1-s2.0-S0377221723007208-main.pdf
Zheng, Yingshuang; Li, Huchao; Jiang, Ting; Jiao, Fei; Li, Jie; Lei, Yong; Tian, Guofeng; Bi, Jinshun; Xuan, Yundong; Li, Liqiang; Ji, Deyang; Hu, Wenping
Interfacial molecular screening of polyimide dielectric towards high-performance organic field-effect transistors. - In: Chinese chemical letters, ISSN 1878-5964, Bd. 35 (2024), 2, 108796

The compatibility of the gate dielectrics with semiconductors is vital for constructing efficient conducting channel for high charge transport. However, it is still a highly challenging mission to clearly clarify the relationship between the dielectric layers and the chemical structure of semiconductors, especially vacuum-deposited small molecules. Here, interfacial molecular screening of polyimide (Kapton) dielectric in organic field-effect transistors (OFETs) is comprehensively studied. It is found that the semiconducting small molecules with alkyl side chains prefer to form a high-quality charge transport layer on polyimide (PI) dielectrics compared with the molecules without alkyl side chains. On this basis, the fabricated transistors could reach the mobility of 1.2 cm2 V−1 s−1 the molecule with alkyl side chains on bare PI dielectric. What is more, the compatible semiconductor and dielectric would further produce a low activation energy (EA) of 3.01 meV towards efficient charge transport even at low temperature (e.g., 100K, 0.9 cm2 V−1 s−1). Our research provides a guiding scheme for the construction of high-performance thin-film field-effect transistors based on PI dielectric layer at room and low temperatures.



https://doi.org/10.1016/j.cclet.2023.108796
Kröger, Jörg; Uchihashi, Takashi
Electron spin finds a fresh excitation. - In: Nature physics, ISSN 1745-2481, Bd. 20 (2024), 1, S. 4-5

The Kondo effect - the screening of an impurity spin by conduction electrons - is a fundamental many-body effect. However, recent experiments combined with simulations have caused a long-standing model system for the single-atom Kondo effect to fail.



https://doi.org/10.1038/s41567-023-02265-3
Böhme, Thomas; Harant, Jochen; Kriesell, Matthias; Mohr, Samuel; Schmidt, Jens M.
Rooted minors and locally spanning subgraphs. - In: Journal of graph theory, ISSN 1097-0118, Bd. 105 (2024), 2, S. 209-229

Results on the existence of various types of spanning subgraphs of graphs are milestones in structural graph theory and have been diversified in several directions. In the present paper, we consider “local” versions of such statements. In 1966, for instance, D. W. Barnette proved that a 3-connected planar graph contains a spanning tree of maximum degree at most 3. A local translation of this statement is that if G is a planar graph, X is a subset of specified vertices of G such that X cannot be separated in G by removing two or fewer vertices of G, then G has a tree of maximum degree at most 3 containing all vertices of X. Our results constitute a general machinery for strengthening statements about k-connected graphs (for 1 ≤ k ≤ 4) to locally spanning versions, that is, subgraphs containing a set X ⊆ V (G) of a (not necessarily planar) graph G in which only X has high connectedness. Given a graph G and X ⊆ V (G), we say M is a minor of G rooted at X, if M is a minor of G such that each bag of M contains at most one vertex of X and X is a subset of the union of all bags. We show that G has a highly connected minor rooted at X if X ⊆ V (G) cannot be separated in G by removing a few vertices of G. Combining these investigations and the theory of Tutte paths in the planar case yields locally spanning versions of six well-known results about degree-bounded trees, Hamiltonian paths and cycles, and 2-connected subgraphs of graphs.



https://doi.org/10.1002/jgt.23012