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
Fullerene C60 films on dental implants: durability study after in vitro short-term exposure. - In: Diamond and related materials, ISSN 0925-9635, Bd. 135 (2023), 109886
The carbon fullerene C60 is an anti-inflammatory substance that reduces cellular stress levels. In this study, C60 fullerenes were deposited on complex dental implants to improve cell attachment and vitality. For the first time, fullerene C60 films were deposited via high-vacuum sublimation on complex-shaped Ti-6Al-4V dental implants with a threaded-screw design. The “as-deposited” fullerene C60 films were compared with fullerene C60 films on dental Ti-6Al-4V implants using a threaded-screw design after three weeks of incubation in Hank's balanced salt solution (HBSS). It was proven by Raman spectroscopy that the incubation in potassium and alkali-ion rich HBSS at 37 ˚C resulted in a reduction of monomeric fullerene C60 fraction and an increase in dimer, linear chain and polymerized C60 molecules. Furthermore, the structure of the C60 films differed depending on the measurement position on dental implants with a threaded-screw design. The fraction of monomeric fullerene C60 was highest on top of the trapezoidal thread, which had a micropatterned topography. Nano-indentations were performed at this position with a maximum load of 1000 μN. The fullerene C60 films showed a nano-hardness of 0.3 ± 0.1 GPa and a Young's modulus of 7.6 ± 3.6 GPa at this position, which is typical for monomeric fullerene C60 with weak interatomic interaction in the face-centred-cubic crystal structure. The murine embryonal calvarial stem-cell line MC3T3-E1 (ECACC, UK), which is driven toward osteogenic differentiation, spread out extremely well on the fullerene C60 film, with improved cell morphology compared to uncoated Ti-6Al-4V. Cell nuclei density were determined to be 237.5 cell nuclei per mm2 for the Ti-6Al-4V dental implants with a threaded-screw design with fullerene C60 coating in “as-deposited” condition. This was approximately 40 % better than that of uncoated Ti-6Al-4V dental implants with a threaded-screw design.
https://doi.org/10.1016/j.diamond.2023.109886
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
Perturbations of periodic Sturm-Liouville operators. - In: Advances in mathematics, ISSN 1090-2082, Bd. 422 (2023), 109022, S. 1-22
https://doi.org/10.1016/j.aim.2023.109022
State and parameter estimation for retinal laser treatment. - In: IEEE transactions on control systems technology, ISSN 1558-0865, Bd. 31 (2023), 3, S. 1366-1378
Adequate therapeutic retinal laser irradiation needs to be adapted to local absorption. This leads to time-consuming treatments as the laser power needs to be successively adjusted to avoid undertreatment and overtreatment caused by too low or too high temperatures. Closed-loop control can overcome this burden by means of temperature measurements. To allow for model predictive control schemes, the current state and the spot-dependent absorption need to be estimated. In this article, we thoroughly compare moving horizon estimator (MHE) and extended Kalman filter (EKF) designs for joint state and parameter estimation. We consider two different scenarios, the estimation of one or two unknown absorption coefficients. For one unknown parameter, both estimators perform very similarly. For two unknown parameters, we found that the MHE benefits from active parameter constraints at the beginning of the estimation, whereas after a settling time, both estimators perform again very similarly as long as the parameters are inside the considered parameter bounds.
https://doi.org/10.1109/TCST.2022.3228442
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
Facile microwave plasma driven 3D-WSe2 2H-1T phase modulation for improving NO2 gas sensing performance. - In: Sensors and actuators, ISSN 0925-4005, Bd. 387 (2023), 133822
In recent years, transition metal dichalcogenides (TMDs) have been widely used for gas sensors. Here, three-dimensional (3D) WSe2 nanosheet arrays were surface treated by microwave plasma. Based on the original 3D structure, a 1T/2H hybrid phase structure was constructed by phase modulation, and Se vacancies were introduced to effectively improve its gas sensing performance. After only 60 s of treatment, the response (52.24 %), response/recovery time of the sample for 1 ppm NO2 were significantly improved with excellent stability and selectivity at room temperature. The intrinsic mechanism of its performance enhancement was elicited through various characterizations and molecular model construction. It is demonstrated that microwave plasma is a promising treatment method to improve the gas-sensitive performance of TMDs.
https://doi.org/10.1016/j.snb.2023.133822
Archaeal and extremophilic bacteria from different archaeological excavation sites. - In: International journal of molecular sciences, ISSN 1422-0067, Bd. 24 (2023), 6, 5519, S. 1-18
Beside natural factors, human activities are important for the development of microbiomes. Thus, local soil bacterial communities are affected by recent activities such as agriculture, mining and industry. In addition, ancient human impacts dating back centuries or millennia have changed soils and can emboss the recent bacterial communities up to now, representing a certain long-term "memory of soil". Soil samples from five different archaeological excavation places were investigated for the presence of Archaea with a Next Generation Sequencing (NGS) analysis of the DNA coding for 16S r-RNA sequences. It was found that the abundance of Archaea differs strongly between less than one and more than 40 percent of bacteria. A Principal Component Analysis (PCA) of all samples shows that the archaeological excavation places can be distinguished from each other by the archaeal component of soil bacterial communities, which presents a typical pattern for each place. Most samples are marked by the dominance of Crenarchaeota, which are presented mainly by ammonia-related types. High contents of Nanoarchaeaota have been observed in one ash deposit of a historical saline and all samples of a historical tannery area. These samples are also marked by a significant presence of Dadabacteria. The specific abundancies of special Archaea - among them ammonia-oxidizing and sulphur-related types - are due obviously to former human activities and support the concept of the "ecological memory of soil".
https://doi.org/10.3390/ijms24065519
An in-depth understanding of photophysics in organic photocatalysts. - In: Journal of semiconductors, ISSN 2058-6140, Bd. 44 (2023), 3, 030401, S. 1-4
https://doi.org/10.1088/1674-4926/44/3/030401