Data-driven forecasting of nonequilibrium solid-state dynamics. - In: Physical review, ISSN 2469-9969, Bd. 107 (2023), 18, 184306, S. 184306-1-184306-18
We present a data-driven approach to efficiently approximate nonlinear transient dynamics in solid-state systems. Our proposed machine-learning model combines a dimensionality reduction stage with a nonlinear vector autoregression scheme. We report an outstanding time-series forecasting performance combined with an easy-to-deploy model and an inexpensive training routine. Our results are of great relevance as they have the potential to massively accelerate multiphysics simulation software and thereby guide the future development of solid-state-based technologies.
https://doi.org/10.1103/PhysRevB.107.184306
Recent progress and future prospect of novel multi-ion storage devices. - In: Journal of semiconductors, ISSN 2058-6140, Bd. 44 (2023), 4, 040201, S. 1-5
https://doi.org/10.1088/1674-4926/44/4/040201
From a wide band gap to the superconducting proximity effect: Fe on Pb(111). - In: New journal of physics, ISSN 1367-2630, Bd. 25 (2023), 3, 033036, insges. 1-15 S.
Epitaxially grown Fe nanostructures on Pb(111) were studied by low-temperature scanning tunneling microscopy and spectroscopy. The deposited Fe assemblies are classified into two groups according to their electronic behavior close to the Fermi energy. One group exhibits a wide energy gap of 0.7 eV that is independent of the temperature ranging from 5 K to room temperature. These Fe islands indicate the absence of the superconductivity proximity effect in their interior. The other group shows a metallic behavior at the Fermi level. The substrate superconducting phase locally enters into these islands, which is evidenced by a sharp resonance at the Fermi energy presumably signaling Andreev reflection at the magnet-superconductor interface.
https://doi.org/10.1088/1367-2630/acc607
Three-dimensional MoS2 nanosheet structures: CVD synthesis, characterization, and electrical properties. - In: Crystals, ISSN 2073-4352, Bd. 13 (2023), 3, 448, S. 1-14
The proposed study demonstrates a single-step CVD method for synthesizing three-dimensional vertical MoS2 nanosheets. The postulated synthesizing approach employs a temperature ramp with a continuous N2 gas flow during the deposition process. The distinctive signals of MoS2 were revealed via Raman spectroscopy study, and the substantial frequency difference in the characteristic signals supported the bulk nature of the synthesized material. Additionally, XRD measurements sustained the material’s crystallinity and its 2H-MoS2 nature. The FIB cross-sectional analysis provided information on the origin and evolution of the vertical MoS2 structures and their growth mechanisms. The strain energy produced by the compression between MoS2 islands is assumed to primarily drive the formation of vertical MoS2 nanosheets. In addition, vertical MoS2 structures that emerge from micro fissures (cracks) on individual MoS2 islands were observed and examined. For the evaluation of electrical properties, field-effect transistor structures were fabricated on the synthesized material employing standard semiconductor technology. The lateral back-gated field-effect transistors fabricated on the synthesized material showed an n-type behavior with field-effect mobility of 1.46 cm2 V^-1 s^-1 and an estimated carrier concentration of 4.5 × 10^12 cm^-2. Furthermore, the effects of a back-gate voltage bias and channel dimensions on the hysteresis effect of FET devices were investigated and quantified.
https://doi.org/10.3390/cryst13030448
Tetrachromatic vision-inspired neuromorphic sensors with ultraweak ultraviolet detection. - In: Nature Communications, ISSN 2041-1723, Bd. 14 (2023), 1, 2281, S. 1-9
Sensing and recognizing invisible ultraviolet (UV) light is vital for exploiting advanced artificial visual perception system. However, due to the uncertainty of the natural environment, the UV signal is very hard to be detected and perceived. Here, inspired by the tetrachromatic visual system, we report a controllable UV-ultrasensitive neuromorphic vision sensor (NeuVS) that uses organic phototransistors (OPTs) as the working unit to integrate sensing, memory and processing functions. Benefiting from asymmetric molecular structure and unique UV absorption of the active layer, the as fabricated UV-ultrasensitive NeuVS can detect 370 nm UV-light with the illumination intensity as low as 31 nW cm^-2, exhibiting one of the best optical figures of merit in UV-sensitive neuromorphic vision sensors. Furthermore, the NeuVS array exbibits good image sensing and memorization capability due to its ultrasensitive optical detection and large density of charge trapping states. In addition, the wavelength-selective response and multi-level optical memory properties are utilized to construct an artificial neural network for extract and identify the invisible UV information. The NeuVS array can perform static and dynamic image recognition from the original color image by filtering red, green and blue noise, and significantly improve the recognition accuracy from 46 to 90%.
https://doi.org/10.1038/s41467-023-37973-0
Orbital and skeletal structure of a single molecule on a metal surface unveiled by scanning tunneling microscopy. - In: The journal of physical chemistry letters, ISSN 1948-7185, Bd. 14 (2023), 16, S. 3946-3952
Atomic-scale spatial characteristics of a phthalocyanine orbital and skeleton are obtained on a metal surface with a scanning tunneling microscope and a CO-functionalized tip. Intriguingly, the high spatial resolution of the intramolecular electronic patterns is achieved without resonant tunneling into the orbital and despite the hybridization of the molecule with the reactive Cu substrate. The resolution can be fine-tuned by the tip-molecule distance, which controls the p-wave and s-wave contribution of the molecular probe to the imaging process. The detailed structure is deployed to minutely track the translation of the molecule in a reversible interconversion of rotational variants and to quantify relaxations of the adsorption geometry. Entering into the Pauli repulsion imaging mode, the intramolecular contrast loses its orbital character and reflects the molecular skeleton instead. The assignment of pyrrolic-hydrogen sites becomes possible, which in the orbital patterns remains elusive.
https://doi.org/10.1021/acs.jpclett.3c00460
Enhancement of graphene phonon excitation by a chemically engineered molecular resonance. - In: Physical review letters, ISSN 1079-7114, Bd. 130 (2023), 11, S. 116201-1-116201-6
The abstraction of pyrrolic hydrogen from a single phthalocyanine on graphene turns the molecule into a sensitive probe for graphene phonons. The inelastic electron transport measured with a scanning tunneling microscope across the molecular adsorbate and graphene becomes strongly enhanced for a graphene out-of-plane acoustic phonon mode. Supporting density functional and transport calculations elucidate the underlying physical mechanism. A molecular orbital resonance close to the Fermi energy controls the inelastic current while specific phonon modes of graphene are magnified due to their coupling to symmetry-equivalent vibrational quanta of the molecule.
https://doi.org/10.1103/PhysRevLett.130.116201
Quantitative stray-field T1 relaxometry with the matrix pencil method. - In: Journal of magnetic resonance, ISSN 1096-0856, Bd. 351 (2023), 107435
The matrix pencil method (MPM) is tested as an approach to quantitatively process multiexponential low-field nuclear magnetic resonance T1 relaxometry data. The data is obtained by measuring T1 saturation recovery curves in the highly inhomogeneous magnetic field of a stray-field sensor. 0.9% brine solutions, doped with different concentrations of a Gd3+ containing contrast agent, serve as test liquids. Relaxation-times as a function of contrast-agent concentration along with the T1 relaxation curves for combinations of multiple different test liquids are measured, and the results from processing using MPM as well as inverse Laplace transformation as a benchmark are compared. The relaxation-time resolution limits of both procedures are probed by gradually reducing the difference between the relaxation-times of two liquids measured simultaneously. The sensitivity to quantify the relative contribution of each component to the magnetization build-up curve is explored by changing their volume ratio. Furthermore, the potential to resolve systems with more than two components is tested. For the systems under test, MPM shows superior performance in separating two or three relaxation components, respectively and effectively quantifying the time constants.
https://doi.org/10.1016/j.jmr.2023.107435
Dangling bond defects on Si surfaces and their consequences on energy band diagrams: from a photoelectrochemical perspective. - In: Solar RRL, ISSN 2367-198X, Bd. 7 (2023), 9, 2201063, S. 1-10
Using silicon in multijunction photocells leads to promising device structures for direct photoelectrochemical water splitting. In this regard, photoelectron spectra of silicon surfaces are used to investigate the energetic condition of contact formation. It is shown that the Fermi-level position at the surface differs from the values expected from their bulk doping concentrations, indicating significant surface band bending which may limit the overall device efficiency. In this study, the influence of different surface preparation procedures for p- and n-doped Si wafers on surface band bending is investigated. With the help of photoemission and X-ray absorption spectroscopy, Si dangling bonds are identified as dominating defect centers at Si surfaces. These defects lead to an occupied defect band in the lower half and an unoccupied defect band in the upper half of the Si bandgap. However, partial oxidation of the defect centers causes a shift of defect bands, with only donor states remaining in the Si bandgap. Source-induced photovoltages at cryogenic temperatures indicate that partial surface oxidation also decreases the recombination activity of these defect centers. It is shown that defect distribution, defect concentration, and source-induced photovoltages need to be considered when analyzing Fermi-level pinning at Si surfaces.
https://doi.org/10.1002/solr.202201063
CO2 conversion toward real-world applications: electrocatalysis versus CO2 batteries. - In: Advanced functional materials, ISSN 1616-3028, Bd. 33 (2023), 32, 2300926, S. 1-38
Electrochemical carbon dioxide (CO2) conversion technologies have become new favorites for addressing environmental and energy issues, especially with direct electrocatalytic reduction of CO2 (ECO2RR) and alkali metal-CO2 (M-CO2) batteries as representatives. They are poised to create new economic drivers while also paving the way for a cleaner and more sustainable future for humanity. Although still far from practical application, ECO2RR has been intensively investigated over the last few years, with some achievements. In stark contrast, M-CO2 batteries, especially aqueous and hybrid M-CO2 batteries, offer the potential to combine energy storage and ECO2RR into an integrated system, but their research is still in the early stages. This article gives an insightful review, comparison, and analysis of recent advances in ECO2RR and M-CO2 batteries, illustrating their similarities and differences, aiming to advance their development and innovation. Considering the crucial role of well-designed functional materials in facilitating ECO2RR and M-CO2 batteries, special attention is paid to the development of rational design strategies for functional materials and components, such as electrodes/catalysts, electrolytes, and membranes/separators, at the industrial level and their impact on CO2 conversion. Moreover, future perspectives and research suggestions for ECO2RR and M-CO2 batteries are presented to facilitate practical applications.
https://doi.org/10.1002/adfm.202300926