Brno University of Technology

The quantitative determination of thin film thickness using X-ray emission analysis provides an accurate, non-destructive alternative to conventional characterisation methods. This study established empirical relationships among the X-ray k-ratio, backscattering electron coefficient (η), and film thickness for two-dimensional (2D) silicon (Si) and silicon dioxide (SiO₂) films, and a silicon dioxide (SiO₂) layer on a Si substrate. Monte Carlo simulations using the McXRayLite to model the electron-solid interactions at primary beam energies of 3-10 keV and film thicknesses of 2-10 nm. The Si Kα₁ signal intensity was used to compute the k-ratios for unsupported Si and SiO₂ films, whereas both Si Kα₁ and O₂ Kα₁ intensities were used for SiO₂/Si. For the Si Kα₁ signal used, a strong linear correlation was obtained between the k-ratio and the thickness of the 2D Si and SiO₂ films, where an inverse linear relationship was observed for the SiO₂/Si sample. For the O₂ Kα₁ signal used, a strong linear correlation between the k-ratio and top-film SiO2 thickness on the Si substrate was observed. The k-ratio also exhibited a consistent dependence on the backscattering coefficient (η), confirming the influence of backscattered electrons on X-ray generation. Empirical equations were derived to predict the film thickness with uncertainties below 4%, demonstrating that the k-ratio method is a reliable and accurate tool for nanoscale thin film measurements.

• A strong correlation was found between the representative cooling rate of eutectoid phase transformation and the characteristics of the pearlite matrix in a fully pearlitic ductile cast iron. • The yield limit found to be strongly dependent on the interlamellar spacing of the pearlite matrix, following a modified Hall-Petch relationship. • In regions of higher strain, the graphite morphology is the dominant factor influencing mechanical properties under static loading. • Microstructure-informed simulation provides insights into how interlamellar spacing affects yield strength, highlighting the crucial role of pearlite fineness in yielding behavior. Microstructural features of ductile cast iron (DCI), including graphite morphology and the pearlitic matrix, are influenced by solidification and subsequent eutectoid transformation and can be effectively tailored through the cooling conditions. While the relationship between pearlite characteristics and mechanical properties is well established for pearlitic steels, the specific contribution of the pearlitic matrix to the mechanical response of DCI has received limited attention. In this study, fully pearlitic DCIs were cast under various cooling rates between 0.1 to 0.34 K/s, enabling systematic variations in microstructure to be correlated with changes in mechanical properties. The resulting interlamellar spacing (ILS) of the pearlite matrix ranged from 291 to 564 nm and was associated with an approximately 70 MPa difference in yield strength. A modified Hall-Petch-type relationship was formulated to describe the dependence of yield strength on ILS. To support predictive capability, representative volume elements were generated from optical micrographs and micromechanical simulations were conducted to isolate the effect of varying ILS on yield strength. The simulation results showed excellent agreement with the experiments, confirming that the ILS predominantly governs the onset of plastic deformation and that pearlite refinement is a key controlling factor for the yield strength of pearlitic DCI.

• Accordion like V 2 CT x MXene was synthesized by HF free molten salt synthesis route. • Spatially and temporally controlled-pulse laser irradiation was used to prepare 3D architectonic films of V 2 CT x MXene. • The restacking issue of 2D nanosheets has been resolved by a very simple and scalable low power laser irradiation route. • Laser-irradiation led films demonstrated improved gas sensing performance due to enhanced active interaction volume. • Highly porous films have shown very fast response (3.32 s) and recovery (3.36 s) of the sensors. The development of efficient gas sensing material having good sensitivity, working at room temperature, and quick response and recovery is imperative for indoor environmental monitoring, especially for detecting volatile organic compounds (VOC). There has been significant interest in 2D materials for gas sensors owing to their high surface area. However, the sensitivity of these materials is limited by the restacking of the thin layers in conventional chemical exfoliation and deposition routes. We focus here on MXene as a detection surface and investigate an efficient route to prepare 3D-architectonic films having improved sensing capabilities using spatially and temporally controlled-pulse laser irradiation. For this purpose, V 2 CT x MXene has been synthesized by an HF free synthesis route and has been applied for isopropyl alcohol detection with subsequent laser treatment. By applying a variable dose of laser power (1 mW to 10 mW), the sensing performance has been optimized. The laser treated sensor (laser power 2.5 mW) has shown a high response of ∼116% towards 500 ppm of isopropyl alcohol compared to that of as deposited V 2 CT x MXene (∼28%). This enhancement was observed due to the formation of connected three dimensional structures produced by laser irradiation. Due to the formation of hierarchical 3D architecture, the sensor has shown very fast response and recovery within 3.32 sec and 3.36 sec, respectively. This study presents valuable insights into the laser irradiation technique as a scalable, contactless, and chemical free technique to produce 3D architecture MXene films with superior gas sensing performance.

Nowadays, environmentally friendly agriculture contributed to a significant interest in the production of fertilizers based on water-soluble humic substances such as humates and lignohumate. These commercial products are dark brown powders and/or concentrated alkaline solutions, containing mixture of humic substances, lingo-humic acids, and smaller proportion of lightly hydrolyzing organic compounds. Their root and foliar application increase growth of roots and leaves, chlorophyll content, and activity of plant enzymes, etc. All of this has generated intense interest for an accurate and reliable method to quantify humic substances in caustobiolites and commercial products.The aim of this work was to determine the content of humic substances in raw caustobiolites (i.e. lignite, leonardite, and alginite) and commercial humate products. Humic substances (HA and FA) were isolated from following samples: South Moravian lignite (the northern part of the Vienna basin, Mír mine near Mikulčice in the Czech Republic); leonardite (Afşin, Kahramanmaraş, Turkey); alginite (Pinciná in the Slovakia Republic); lignohumate MAX (Amagro, Prague in Czech Republic); and HumiKey (Xi´an, TBio Crop Science Co., Ltd., China). The humic substances were extracted using a new standardized method for quantification of humic substances (Lamar et al., 2014) recommended by the International Humic Substances Society. The content of humic substances was obtained by gravimetric analysis. The wt.% HA and FA contents were corrected for moisture and ash content. Furthermore, the humic substances were used in solid powder form and characterized by thermal techniques (i.e. elemental and thermogravimetric analysis), UV/Vis spectroscopy, and FTIR spectroscopy.The determining factor influencing the yield of humic substances from raw caustobiolites and commercial products is their origin and method of extraction. The greatest content of HA (54.22 ± 1.76%) was obtained for sample isolated from Turkey leonardite. In contrast, the lowest contents were determined for HAs extracted from alginite and lignohumate MAX. It is obvious that these samples are characterized by significant content of FK and lightly hydrolyzing organic compounds. Extremely high ash content was determined for alginate. Caustobiolites (e.g. alginite) with high ash and low contents of humic substances appear to be less suitable as sources of HS for agricultural purposes.All examined HAs isolated from caustobiolites were generally characterized by the complex and heterogeneous molecular structure with high average molecular weight and high degree of aromaticity. On the other hand, FAs, especially those isolated from commercial products, were predominantly aliphatic, with a smaller content of nitrogen and low degree of aromaticity and greater amount of oxygen-containing functional groups (e.g. carboxylic and phenolic).This standardized method and studies on the physicochemical properties of HS can be helpful in predicting the behavior of such fertilizer components in the environment.ReferenceLamar, R.T., Olk, D.C., Mayhew, L., Bloom, P.R., 2014. A New Standardized Method for Quantification of Humic and Fulvic Acids in Humic Ores and Commercial Products. J. AOAC Int. 97, 721-730. https://doi.org/10.5740/jaoacint.13-393.AcknowledgementThis work was supported by The NATO Science for Peace and Security Programme, project Nr. G6296. https://land-security.org/.

The confinement of molecules within the van der Waals (vdW) gap between a two-dimensional (2D) material and a catalytic substrate offers a promising route toward the development of molecule-selective catalysts with increased reaction rates and access to chemically distinct reaction environments. However, identifying the kinetic limitations and mechanistic consequences of such confined reactions remains challenging. Here, we employ an inverted wedding cake configuration of multilayer graphene on platinum to study the dynamics of graphene etching within the vdW gap by O2, H2, and CO using in situ scanning electron microscopy. Under the experimental conditions explored (up to p = 1.4 × 10-2 Pa and T = 1000 °C), the etching reactions are supply limited for O2 and H2. The reaction-limited regime is not observed even for CO, despite its anomalously enhanced transport resulting from a pronounced lifting of the vdW gap. Reactive molecular dynamics simulations reveal that confinement within the vdW gap enables additional CO-mediated etching pathways that are absent on open Pt surfaces. Our results demonstrate that intercalation does not primarily reduce reaction barriers but instead creates a confined, high-chemical-potential nanoreactor in which new reaction pathways can be accessed at comparatively low external pressures.