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We perform azimuth time tracking of multiple thunderstorm centers on the globe, which are sources of extremely low frequency (ELF) electromagnetic waves propagating in the spherical Earth‐ionosphere cavity. For observations made in September 2023 we identify azimuths of numerous global emission centers using our data sampled at 3 kHz at the Hylaty station in Poland. We confirm significant and relatively regular thunderstorm azimuth variation during the solar terminator passage over the observation site. The magnitude and duration of the azimuth deviations depend on the observed azimuths but are also varying between successive days and changing detailed thunderstorm activity patterns. The measured maximum positive (preferentially at the sunrise time) and negative (preferentially at the sunset time) azimuth deviations reach even above 20°$\mathit{{}^{\circ}}$for waves propagating close to the terminator. We discovered also particular composite deviation structures, with the negative azimuth deviation directly preceding a larger positive one, sometimes occurring near the morning terminator passage 100 km above the surface. It is possibly the first detection of the ELF equivalent of the “greyline” transmission known in the HF radio propagation. At azimuths distant from the terminator one can observe decreasing of the regular deviation magnitude and occasionally lower magnitude deviations with opposite sign. The variations between successive days are expected to result from varying thunderstorm activity on Earth as well variability of ionospheric parameters, in particular of ionization gradients and nonuniformities occurring along the terminator. We postulate that the observed deviations result from a signal refraction at the varying ionospheric gradients. Extremely low frequency (ELF; below 1 kHz) electromagnetic waves are generated by thunderstorm lightning discharges in the atmosphere. Such waves can propagate several times around the Earth within the spherical Earth‐ionosphere resonance cavity. Our study of directions of arriving ELF signals shows regular azimuth refraction effects at the ionosphere day‐night (a solar terminator) gradients as well as varying azimuth perturbations due to local non‐uniformities. The effects are well visible at the period of terminator transition above our Hylaty measuring station, with ∼1–2 hr characteristic time scales. For the first time we also identify the low damped ELF equivalent of the “greyline” transmission known in the HF radio wave propagation along the terminator. The azimuth deviations can reach even above 20° for the waves propagating close to the terminator and decrease for larger angles, or even can change sign for large angles. Comparing the azimuth deviation pattern changing in following days proves a significant role of (local) fluctuations of the ionosphere ionization structure. This study proves efficiency of our proposed approach for the ELF wave azimuth derivation for the described studies of the terminator influence and varying daily azimuth structures, as compared to studies of individual high‐amplitude impulses. We present observations of ELF electromagnetic waves refracted on the ionospheric gradients at the day/night terminatorPositive and negative azimuth variations can reach above 20°, with an occasional negative to positive variation at the sunriseSignificant variations are observed in daily azimuth distributions resulting from varying ionosphere irregularities along the terminator We present observations of ELF electromagnetic waves refracted on the ionospheric gradients at the day/night terminator Positive and negative azimuth variations can reach above 20°, with an occasional negative to positive variation at the sunrise Significant variations are observed in daily azimuth distributions resulting from varying ionosphere irregularities along the terminator

Solar flares have profound impacts on the lower ionosphere and long‐distance radio propagation. Extremely low frequency (ELF: 3–3,000 Hz) waves are challenging to observe and experience unique interactions with the lower ionosphere. The primary natural sources of ELF waves are thunderstorm lightnings across the globe. Using a newly developed azimuth determination technique and improved observation hardware we show that ELF attenuation in the Earth‐Ionosphere spherical cavity decreases and propagation velocity increases under the influence of an M‐class solar flare. Using a two‐parameter model of the lower ionosphere, the observations are shown to be consistent with increased electron density and sharper gradients in the D‐region resulting from X‐ray radiation. The sharper electron density gradient is primarily responsible for the propagation velocity increase, suggesting a unique capability that ELF observations can bring to global remote sensing of the lower ionosphere under space weather perturbations. Solar flares are large emissions of energy from the Sun that hit the Earth with X‐rays and ultraviolet emissions. A solar flare has significant effects on the upper atmosphere of the Earth, known as the ionosphere. The solar flare X‐ray radiation leads to an increase in free electron density in the lower ionosphere by ionizing more of the neutral atmosphere. This increase in electron density can in turn have profound effects on long range radio wave propagation. In this study we focus on observations of Extremely Low Frequency (ELF: 3–3,000 Hz) waves and how they are affected by a solar flare. ELF waves are challenging to observe and generate. The primary source of ELF radiation on Earth is thunderstorm lighting. We use a new analysis technique and improved observation hardware to show that ELF waves propagate more effectively and faster under the influence of a solar flare. The unique response of ELF waves to solar flares can be leveraged in global monitoring of the lower ionosphere which is important for a wide range of communication technologies. Applying new data analysis, we show solar flare effects on the extremely low frequency emissions from global lightningAn M‐class solar flare causes decreased attenuation and increased group velocity in ELF bandThe measured propagation parameters agree with theoretical modeling and suggest global remote sensing capabilities using ELF observations Applying new data analysis, we show solar flare effects on the extremely low frequency emissions from global lightning An M‐class solar flare causes decreased attenuation and increased group velocity in ELF band The measured propagation parameters agree with theoretical modeling and suggest global remote sensing capabilities using ELF observations

Molecular self-assembly based on the spontaneous arrangement of simple, functional molecules on atomically flat surfaces has been recognized, in the past decades, as an extremely useful tool for the rational fabrication of one-atom-thick nanomaterials, with potential application in heterogeneous catalysis, selective adsorption, and sensing. The physicochemical properties of such supramolecular constructs are determined mainly by the proper choice of chemical interactions cementing their components. Particularly suitable for this purpose are directional, reversible ligand → metal coordinate bonds. In this contribution, we present the results of coarse-grained Monte Carlo (MC) computer simulations performed on the family of isomeric, star-shaped molecular building blocks, coadsorbed with low-coordinated metal atoms on the triangular lattice. We have found that depending on the position of active centers (functional groups) attached to the terminal segments of investigated molecules, the bottom-up fabrication of complex metal-organic overlayers, like nanoporous networks, nonregular tessellations, and ladder-like chains, is possible. The obtained patterns are described and classified according to their geometrical properties. The herein presented theoretical predictions can be especially helpful for scanning tunneling microscopy (STM) experimentalists interested in the rational designing of novel surface-supported metal-organic architectures with an unusual morphology and tunable physicochemical properties.

In this paper, we check how the molecular architecture influences the self-assembly process of tetrapod molecules. These particles were built of the linear core and four attached arms. For this purpose, we employ molecular dynamics simulation together with the lattice Monte Carlo method to investigate the formation of supramolecular networks. To characterize them, we evaluated structure parameters such as distribution of the core–core angle, average degree of association, and theoretical diffractograms. Moreover, we conclude that for the latter parameter, the influence of the rotation of differently oriented domains may lead to wrong interpretation of results.

Surface-confined self-assembly of organic building blocks is a versatile method of creation of low dimensional structures with potential applications in nanotechnology and material engineering. A key factor which often determines morphology of such 2D supramolecular assemblies is the geometry and functionality of a molecular tecton at play. In this contribution we use theoretical modeling to predict the structure of adsorbed systems in which tripod molecules with reduced symmetry interact via a short-range anisotropic pair potential. To that end the self-assembly of a tripod molecule with one shortened/elongated arm, adsorbed on a triangular lattice is modeled using the Monte Carlo simulation method. The probe asymmetric molecule consist of a few interconnected segments and it is equipped with terminal interaction centers (active segments) with differently assigned interaction directions. Our study focuses on the effect of directionality of intermolecular interactions on the morphology of the resulting supramolecular 2D assemblies. It is demonstrated that a suitable encoding of the interaction directions allows for the creation of largely diversified adsorbed structures including aperiodic porous networks, molecular ladders, strings, ribbons and dispersed aggregates. Main differences and similarities between the findings reported for the asymmetric molecules and their C3-symmetric counterparts are also discussed. The obtained results can be helpful in designing new molecular tectons for controlled on-surface self-assembly and coupling reactions, as they provide useful information on the molecule-superstructure relation. This preliminary information can, for example, facilitate screening of molecular libraries to select an optimal molecule able to create low-dimensional structures with predefined properties.

The self-assembly behavior of a V-shaped bispyridine, 1,3-bi(4-pyridyl)benzene (BPyB), was studied by scanning tunneling microscopy on the (111) surfaces of Cu, Ag, and Au. BPyB molecules coordinately bonded with active Cu adatoms on Cu(111) in the form of complete polygonal rings at low coverages. On Ag(111), BPyB molecules aggregated into two-dimensional islands by relatively weak intermolecular hydrogen bonds. The coexistence of hydrogen bonds and coordination interaction was observed on the BPyB-covered Au(111) substrate. Density functional theory calculations of the metal–molecule binding energy and Monte Carlo simulations were performed to help understand the forming mechanism of molecular superstructures on the surfaces. In particular, the comprehensive orbital composition analysis interprets the observed metal–organic complexes and reveals the importance of relativistic effects for the extraordinary activity of gold adatoms. The relativistic effects cause the energy stability of the Au 6s atomic orbital and decrease the energy separation between the Au 6s and 5d orbitals. The enhanced sd hybridization strengthens the N–Au–N bond in BPyB–Au–BPyB complexes.

Self-assembly of 1,3,5-tris(4-mercaptophenyl)benzene (TMB), a 3-fold symmetric, thiol-functionalized aromatic molecule, was studied on Au(111) with the aim of realizing extended Au–thiolate-linked molecular architectures. The focus lay on resolving thermally activated structural and chemical changes by a combination of microscopy and spectroscopy. Thus, scanning tunneling microscopy (STM) provided submolecularly resolved structural information, while the chemical state of sulfur was assessed by X-ray photoelectron spectroscopy (XPS). Directly after room-temperature deposition, only less well ordered structures were observed. Mild annealing promoted the first structural transition into ordered molecular chains, partly organized in homochiral molecular braids. Further annealing led to self-similar Sierpiński triangles, while annealing at even higher temperatures again resulted in mostly disordered structures. Both the irregular aggregates observed at room temperature and the chains were identified as metal–organic assemblies, whereby two out of the three intermolecular binding motifs are energetically equivalent according to density functional theory (DFT) simulations. The emergence of Sierpiński triangles is driven by a chemical transformation, i.e., the conversion of coordinative Au–thiolate to covalent thioether linkages, and can be further understood by Monte Carlo simulations. The great structural variance of TMB on Au(111) can on one hand be explained by the energetic equivalence of two binding motifs. On the other hand, the unexpected chemical transition even enhances the structural variance and results in thiol-derived covalent molecular architectures.

Directing the self-assembly of organic molecules toward low-dimensional superstructures has been an attractive method of fabrication of functional materials with programmable architecture. In this contribution, using theoretical modeling, we demonstrate how fine-tuning of directional intermolecular interactions which are encoded in a simple organic building block allows for the creation of surface-confined assemblies with largely diversified morphology. To that end, the self-assembly of a model tripod-shaped molecule adsorbed on a triangular lattice was simulated using the canonical ensemble Monte Carlo method. The simulations were performed for flat, rigid building blocks built of four discrete segments (core plus three arm segments) and equipped with adjustable peripheral interaction centers providing directional intermolecular bonds. The simulated results revealed that changes in the directionality of interactions imposed on the centers are responsible for the emergence of different molecular structures including ordered porous networks, chain and ladder structures, and chiral patterns. The obtained assemblies were analyzed and classified with respect to their structural and energetic properties. Our theoretical investigations showed that small changes in the position of the outer interaction centers in a tripod functional molecule can have dramatic effect on the morphology of the resulting 2D structures. On the other hand, these findings can be helpful in predicting the self-assembly of organic tripod molecules with the different interaction patterns discussed in this study. This information can be relevant, for example, to synthetic chemists seeking for an optimal building block able to self-assembly into a 2D superstructure with predefined properties.

Recent studies demonstrate that simple functional molecules, which usually form two-dimensional (2D) crystal structures when adsorbed on solid substrates, are also able to self-assemble into ordered openwork fractal aggregates. To direct and control the growth of such fractal supramolecules, it is necessary to explore the conditions under which both fractal and crystalline patterns develop and coexist. In this contribution, we study the coexistence of Sierpiński triangle (ST) fractals and 2D molecular crystals that were formed by 4,4″-dihydroxy-1,1′:3′,1″-terphenyl molecules on Au(111) in ultrahigh vacuum. Growth competition between the STs and 2D crystals was realized by tuning substrate and molecular surface coverage and changing the functional groups of the molecular building block. Density functional theory calculations and Monte Carlo simulations are used to characterize the process. Both experimental and theoretical results demonstrate the possibility of steering the surface self-assembly to generate fractal and nonfractal structures made up of the same molecular building block.

Self-similar fractals are of importance in both science and engineering. Such fractals are constructed in this study by using 120° V-shaped 4,4″-dicyano-1,1′:3′,1″-terphenyl molecules and Fe atoms on Au(111), and studied in detail by low-temperature scanning tunneling microscopy.

In a culture that is increasingly colonized by commercial dynamics, it is important to observe how pervasive commercialization has become, particularly with respect to institutions intended to eschew such effects. This study is a longitudinal content analysis of National Public Radio (NPR) news stories over the last decade that examines the content of the stories on its flagship programs Morning Edition and All Things Considered to assess whether the network has changed, presenting a more commercial rationality. Research has demonstrated that a more market-driven quest for revenue has impacted programming, rendering it more formatted and homogeneous. Amid a decline in government funding, NPR has further embraced a programming model reflecting a more commercial tone in its news content. The data from the content analysis reveal mixed and tempered results, indicating some movement toward more commercially driven content in certain areas, particularly with a decrease in the amount of stories featuring diversity content and an increase in the frequency of promotional content on All Things Considered in 2010. The implications of these findings speak to the larger issue advanced by Critical Theory concerning the preservation of the marketplace of ideas in the United States.

On-surface Ullmann coupling is a versatile and appropriate approach for the bottom-up fabrication of covalent organic nanostructures. In two-dimensional networks, however, the kinetically controlled and irreversible coupling leads to high defect densities and a lack of long-range order. To derive general guidelines for optimizing reaction parameters, the structural quality of 2D porous covalent networks was evaluated for different preparation protocols. For this purpose, polymerization of an iodine- and bromine-functionalized precursor was studied on Au(111) by scanning tunneling microscopy under ultrahigh vacuum conditions. By taking advantage of the vastly different temperature thresholds for C–Br and C–I cleavage, two different polymerization routes were compared – hierarchical and direct polymerization. The structural quality of the covalent networks was evaluated for different reaction parameters, such as surface temperatures, heating rates, and deposition rates by statistical analysis of STM data. Experimental results are compared to Monte Carlo simulations.

Creation of two-dimensional superstructures using coordination chemistry principles is a promising method to fabricate new nanomaterials with predefined architecture and functionality. In this work we use a simple lattice Monte Carlo (MC) model to study the mixed self-assembly of a family of ditopic linkers and metal atoms adsorbed on a triangular lattice. In particular, we focus on the role of directional short-range metal–linker interactions in the formation of local coordination motifs responsible for the development of periodic and random molecular patterns. To that end canonical ensemble MC simulations were performed in which both components of the adsorbed mixture were assumed to consist of discrete segments, each of which occupies one lattice site. Accordingly, the metal atoms were modeled as single segments while the linker was represented by a rigid linear chain whose terminal segments are able to form directional bonds with a neighboring metal atom. The simulated results demonstrated that depending on the assumed directionality of the metal–linker interaction and composition of the adsorbed phase, the self-assembly can lead to the formation of largely diversified planar structures including random strings, nanorings, chiral and achiral porous networks, and fractal-like aggregates. The insights from our theoretical investigations can be helpful in designing 2D metal–organic molecular architectures comprising simple functional building blocks.

The Mn—Mn bonds in the two independent mol­ecules of the unsolvated title compound, [Mn2(C25H22P2)(CO)8], (I), are 2.9714 (7) and 2.9746 (7) Å. This bond is distinctly shortened in the toluene hemisolvate, [Mn2­(C25­H22P2)(CO)8]·­0.5C7H8, (II), to 2.9338 (14) Å and this shortening is accompanied by an increase in magnitude of the P—Mn—Mn—P torsion angle [26.93 (3) and 28.44 (3)° in (I), and 33.25 (7)° in (II)], while the P⋯P `bite' is much less affected [3.092 (2) and 3.099 (2) Å in (I), and 3.091 (3) Å in (II)]. The toluene solvate mol­ecule in (II) lies on a twofold axis.

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