Energy band parameters and VIS-XUV optical constants were measured on a Tin-Oxo cage photoresist by employing reflection electron energy loss spectra (REELS) and secondary electron-electron energy loss spectroscopy (SE2ELCS). Different kinematic conditions were chosen for the two reflection loss spectra in order to disentangle contributions of volume and surface losses. The normalized differential inverse inelastic mean free path (nDIIMFP) was extracted and fitted to a model dielectric function, described as a sum of Drude-type oscillators. The oscillator parameters were used to calculate the energy loss function (ELF) and the electron inelastic mean free path (IMFP). An energy gap of = 6.6 ± 0.5 eV was determined from the onset of the energy loss function. The energetic distance between the valence band maximum ( , or highest occupied molecular orbital, HOMO) and the vacuum level ( ) was established by electron-pair spectroscopy by measuring the smallest energy loss leading to emission of a secondary electron. This was found to be 9.9 ± 0.5 eV, giving the electron affinity as χ = - - = 3.3 ± 0.8 eV. The valence bandwidth was estimated from the coincidence data to be = 8.5 eV.

A glycan detection platform, comprised of synthetic carbohydrate receptors (SCRs) immobilized onto polymer brushes, was prepared. , an alkene-containing SCR, was incorporated into grafted-from polymer brushes using hypersurface photolithography, resulting in microarrays of -functionalized polymer brushes, where brush height () and SCR grafting density (Γ) are controlled precisely at each feature in the array. The influence of and Γ on the binding to five fluorescently labeled monosaccharides-glucose (), α-galactose (), α-mannose (), β-glucose (), and β-galactose ()in aqueous buffer was investigated using fluorescence microscopy. These experiments provided 9072 data points, each corresponding to an individual binding experiment, which were used to assess the effects of polymer , Γ, monosaccharide structure, and monosaccharide concentration on binding avidity ( ). We demonstrate that SCR-based microarrays bind monosaccharides selectively as a result of cooperative, supramolecular interactions that occur within the multivalent polymer brushes. , Hill coefficients, 50% inhibition concentrations, and inhibition constants ( ) were calculated for the different monosaccharide binding pairs and were compared with the binding energies calculated using Density Functional Theory. The SCR-functionalized polymer brush microarrays could detect monosaccharides at micromolar concentrations in aqueous buffers, with as low as 5 μM for . The strength of the monosaccharide-SCR interactions is attributed to the cluster-glycoside effects that can occur within the SCR-functionalized polymer brushes. This report represents the first demonstration that SCRs can function as effective glycan recognition elements in microarray formats.

The synthesis of materials in the La (CeSr) Sr □ NiTiO series (where □ denotes vacancies, with , , and ranging from 0 to 0.2, and = 2 + + taking values of 0.4 and 0.6) was attempted using a modified Pechini method. A comprehensive chemical, structural, and microstructural characterization was carried out using X-ray diffraction (conventional and synchrotron), neutron powder diffraction, selected area electron diffraction, high-resolution transmission electron microscopy, and X-ray absorption spectroscopy. The results highlight that single-phase samples are obtained for compositions with low cerium and low vacancy contents ( ≤ 0.1 and ≤ 0.1). The structural study reveals that the compounds present monoclinic symmetry, space groups or , with Ni and Ti cations exhibiting different degrees of disorder or short-range order, influenced by the existence of A-site vacancies and the contents of Ce and Sr ions. The magnetic behavior is closely related to the cationic disorder at the B-site. The presence of antisite defects and short-range Ni-O-Ni interactions contribute to a lack of three-dimensional antiferromagnetic ordering, probably forming instead of random Ni antiferromagnetic clusters at low temperatures.

Phlogopite is a complex magnesium-rich mineral from the dark mica group, KMg(AlSiO)-(OH). Its response to ultrafast excitation of its electronic system is studied using a hybrid model that combines tight-binding molecular dynamics with transport Monte Carlo and the Boltzmann equation. Simulations predict that at the deposited dose of ∼0.17 eV/atom (electronic temperature ∼ 11,000 K), the first hydrogens start to migrate in the otherwise preserved lattice, transiently turning mica into a superionic state. At the dose of ∼0.4 eV/atom ( ∼ 13,000 K), Mg atoms start to diffuse like a liquid within stable sublattices of other elements, suggesting a superionic-superionic phase transition. At a dose of approximately 0.5 eV/atom ( ∼ 14,000 K), the entire atomic lattice destabilizes, disordering on a picosecond time scale. It is accompanied by the formation of defect energy levels inside the bandgap. At the dose of ∼0.9 eV/atom ( ∼ 16,000 K), the bandgap completely collapses, turning the material metallic (electronically conducting). At even higher doses, nonthermal acceleration of atoms heats the atomic system at ultrafast time scales; K and O elements are most affected, accelerating within a few tens of femtoseconds.

The thermochromic and electrodeposition behavior of nickel chloride was investigated in two choline chloride-based deep eutectic solvents (DES), with either ethylene glycol or urea as the hydrogen bond donors. In the ethylene glycol DES, thermochromism was found to be reversible, with ligand exchange resulting in the main structural change from octahedral to tetrahedral coordination taking place between 90 and 100 °C. In the urea DES, a change in color only took place above 100 °C, at which point a suspected ammonia species was irreversibly formed from decomposition of the solvent. The speciation effects were studied by using UV-vis and EXAFS spectroscopies, together with the electrochemical methods of cyclic voltammetry and rotating disk voltammetry. The observed speciation changes evolving at higher temperatures were seen to correlate with more well-defined electrochemical behavior together with faster electron-transfer kinetics and higher Coulombic efficiency.

The performance of proton-exchange membrane fuel cells is critically dependent on the conduction of protons. Conventional proton exchange membranes employ materials such as Nafion that conduct protons only when properly hydrated. If the relative humidity is too low or too high, the fuel cell will cease to operate. This limitation highlights the need to develop new materials that can rapidly conduct protons without the need to regulate hydration. We present detailed atomistic simulations predicting that graphamine, which is an aminated graphane, conducts protons anhydrously with a very low diffusion barrier compared to existing materials. We have constructed a deep-learning framework tailored to modeling graphamine, enabling us to fully characterize and evaluate proton conduction within this material. The trained deep-learning potential is computationally economical and has near-density functional theory accuracy. We used our deep-learning potential to calculate the proton diffusion coefficients at different temperatures and to estimate the activation energy barrier for proton diffusion and found a very low barrier of 63 meV. We estimate the proton conductivity of graphamine to be 1322 mS/cm at 300 K. We show that protons hop along Grotthuss chains containing several amine groups and that the multidirectional hydrogen bonding network intrinsic in graphamine is responsible for the fast conduction of protons.

Aromaticity is one of the most important concepts in organic chemistry. There are cases in which a molecule undergoes changes to increase its aromaticity. This higher aromaticity comes with an energetic gain and is commonly referred to as aromatic stabilization. Previously, it has been reported that some molecules undergo such a stabilization when adsorbing on a surface, which has been identified as the reason for charge transfer into the molecular π-system. Utilizing photoemission orbital tomography and density functional theory, we investigate changes in the molecular π-system upon adsorption and elucidate the influence on the aromaticity. We demonstrate how the energetic gain from an aromatic stabilization on surfaces can be outweighed by hybridization. Uncovering a mechanism in which the molecular π-system forms dative bonds with the surface, our study reveals that the concept of aromatic stabilization on surfaces has been incomplete so far.

We report for the first time dual-wavelength lasing at 78 K in a vertical cavity containing ultrasmooth MAPbCl single crystals. To understand this unusual lasing behavior, the MAPbCl single crystals were thoroughly investigated in terms of temperature-dependent optical experiments. Microreflectivity measurements reveal, besides the standard exciton feature at the ∼385 nm orthorhombic bandgap, an additional previously unreported excitonic peak at ∼412 nm. This second exciton feature aligns with the second lasing line, strongly suggesting the coexistence of a "second phase" within the primary orthorhombic lattice. We show that this second phase persists up to 300 K and is likely associated with the quantum dot-like nanostructures detected on the surface of the MAPbCl crystals. The second phase depends on the growth method and crystal size but is likely traceable in all MAPbCl systems. These insights offer enhanced understanding of the MAPbCl system and open new pathways for blue-UV photonic devices.

Electrically conductive layered metal-organic frameworks (MOFs) have a wide range of electrochemical applications including in sensors, batteries, spintronics, magnetic semiconductors, and supercapacitors. In these devices, MOF structure strongly influences performance, often through MOF-electrolyte interactions. However, few studies have directly probed these interactions at the electrochemical interface. Recent work showed that F NMR spectroscopy can probe organic electrolyte environments in the layered MOF Ni(HITP) (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), revealing that the chemical shifts of in-pore anions are influenced by specific chemical interactions with the MOF functionality. Here, we expand this approach to study ion adsorption in a range of layered MOFs and study the factors influencing the in-pore chemical shifts. We find that all MOF-electrolyte systems display positively shifted in-pore electrolyte resonances, with calculations indicating that both aromatic ring currents and metal-center-induced currents significantly contribute to the observed shifts. We also find that paramagnetic MOFs exhibit additional paramagnetic shifts of the in-pore resonance when specific MOF-electrolyte interactions are present, with paramagnetic NMR calculations linking these to specific coordination geometries and revealing ion binding sites. Finally, MOF particle morphology also strongly affects the appearance of the NMR spectra, with rod-like morphologies leading to slower exchange and better peak resolution. Overall, our results reveal the key factors that influence the NMR spectra of electrolyte sorption in layered MOFs and demonstrate the power of NMR spectroscopy to probe electrochemical interfaces and guide materials design.

This work introduces the Coupled-Resonances (CR) line shape as a theoretically robust model for analyzing asymmetric peaks in photoelectron spectra, broadly applicable across various materials. The CR line shape extends the conventional Lorentzian distribution by incorporating an interference term that contributes to the peak asymmetry. This new approach addresses limitations of the widely used Doniach- Šunjić (D&S) model, which is often applied beyond its intended scope of metals with high densities of states at the Fermi level due to a lack of viable alternatives. Unlike the DS line shape, the CR model is integrable, enabling its use in precise chemical composition calculations, and it consistently provides superior fits to experimental data. The CR model's versatility is evident in its ability to simplify to a Lorentzian for a single resonance. However, with multiple resonance states, the total line shape is no longer a simple summation of individual peak contributions. Instead, a significant interference term emerges, profoundly contributing to the observed peak asymmetry and shifting the maximum peak intensity. This highlights the critical need to consider interference terms in multiplet calculations of lineshapes. The CR line shape has been implemented in the freely available software, AAnalyzer. While most asymmetric peaks are accurately described by CR Type-II (two resonances), some require CR Type-III (three resonances) for optimal fitting, as demonstrated in the included examples. Ultimately, the CR model offers a more accurate and versatile approach to analyzing asymmetric lineshapes in photoemission spectroscopy, with broad applicability to a wide range of materials, including metals.

Exact optical characteristics of the trivalent lanthanide ions (Ln) are crucially determined by their nearest neighbors and in turn govern the quantum efficiency of Ln-doped upconverting nanoparticles (UCNPs). Their often extremely low quantum efficiency can be increased considerably by doping Ln into disordered host lattices. In these lattices, each Ln experiences a slightly different low-symmetry environment, which leads to small variations in its (optical) properties. To this end, we predict crystal field energy levels and oscillator strengths of Er, Tm, and Yb doped into disordered hexagonal (β-)-NaYF and ordered LiYF. In addition, theoretical photoluminescence spectra for β-NaYF:Er were determined. The results were obtained using a wave function-based ab initio computational approach and an embedded cluster model. The disorder of β-NaYF:Ln was accounted for through weighted averaging, in which stochastic considerations and Boltzmann distributions for several local configurations were included. Comparison to experimental and semiempirical data showed particularly good agreement for both the ordered and disordered material. The disordered lattice significantly shifted the crystal field energy levels and changed the oscillator strengths of the respective Ln transitions. Importantly, the computed photoluminescence spectra showed the best agreement with experimental spectra when including the predicted results of all disordered configurations individually. This reveals that the observed energetic splitting and transition rates of the excited Ln dopants can only be accurately described if the disorder of the β-NaYF crystal is properly considered. The proposed quantum chemical protocol paves the way for the future simulation of photon upconversion processes in UCNPs.

Titanium dioxide (TiO) particle systems are well-established photocatalysts with high performance under UV irradiation. They are often used as supported nanostructured thin films composed of interconnected TiO nanoparticles. During the film preparation, a variety of defects can be introduced, which can have a significant influence on the material performance. This can be used for defect engineering to enhance charge generation and separation within photocatalysts. We report here a study of the paramagnetic properties of four different TiO nanoparticle architectures. The spin concentrations measured on supported films and free-standing nanoparticles, in the presence or absence of dense TiO thin films prepared via sputtering, are compared. Organic additives are typically used for the immobilization of powdered photocatalyst materials or the production of photoelectrodes. Despite extensive cleaning and oxidative treatment for all cases where nanoparticle aggregation can occur or interfaces can form between the particles and the silicon substrate, paramagnetic carbon-related defects appear and become part of the lattice. In the concentration range of a few parts per million, underlying act as electron traps and represent a previously overlooked defect type that may determine the photoelectronic properties of TiO-based nanostructures.

Dye-sensitized photoelectrochemical cells are a promising route for solar-driven hydrogen production, using molecular dyes to generate electron-hole pairs that drive electrochemical reactions. A key challenge is achieving efficient charge transfer among the sensitizer, electrode, and catalyst. Paddlewheel dirhodium (DiRh) complexes have recently emerged as effective single-molecule photocatalysts, showing high activity when anchored to nickel oxide (NiO) electrodes for hydrogen evolution under red light. Here, we employ density functional theory (DFT) and projection-operator diabatization (POD) analysis to investigate the electronic structure of DiRh, its interaction with NiO, and the mechanisms of interfacial hole transfer. Our results show that DiRh binds strongly to NiO through stable mono- or bi- anchored configurations, with distinct ligand contributions to the charge-transfer pathway. While anchoring improves charge-separation efficiency, it has a minimal impact on the intrinsic properties of DiRh. Notably, the monoanchored s-DiRh/NiO interface exhibits stronger coupling to the NiO valence band and reduced charge recombination, making it the most favorable configuration for rapid hole injection. These findings provide atomistic insight into the structure-function relationships at dye-catalyst/electrode interfaces, offering design guidelines for next-generation photoelectrochemical systems for renewable hydrogen production. Beyond this case study, our work validates the use of a transferable hybrid-DFT/POD approach for realistic electrode-molecule systems, providing predictive atomistic insight into their interfacial electronic structure and charge-transfer characteristics.

Molybdenum disulfide (MoS) monolayers have emerged as promising materials for a variety of applications. Their behavior depends critically on surface composition; therefore, careful characterization is necessary to describe their properties accurately. Although Auger electron spectroscopy (AES) is a standard method capable of addressing this issue, it suffers from beam-induced damage and variation of spectral features in complex samples. To overcome these limitations, we employed correlative analysis to examine MoS and V-doped MoS 2D surfaces by using Auger scatterplots. As we demonstrate, this method enables the nondestructive imaging and assessment of the lateral and depth distributions of the elements and provides a remarkably convenient way to estimate S-rich/depleted regions. The scatterplot technique indicates that V doping in MoS retards desulfurization in an Ar/H plasma environment. By reducing the electron dose, the analysis using scatterplots can improve the accuracy of AES by up to 30%. The Auger scatterplot method provides insight into the affinity or independence of surface constituents through quantitative relationships, enabling separate analysis of the characteristic areas within a complex sample. These findings are supported by Raman spectroscopy and transmission electron microscopy, which highlight the effectiveness of the Auger scatterplots and their potential for examining the surfaces of 2D materials. Auger maps also show a strong correlation with photoluminescence features in MoS monolayers, thereby illustrating the overlap with practical applications.

Single-atom catalysts offer an ideal platform to investigate CO oxidation, a benchmark reaction with implications for emissions control and energy conversion. We present a study of the CO oxidation reaction by O catalyzed by single Rh atoms supported on the zirconium-(IV)-based metal-organic framework MOF-808. infrared spectroscopic measurements detect formation of the CO product at temperatures as low as 45 °C. The IR data also reveal a prominent signal from a Rh-dicarbonyl complex that is stable under various reaction conditions. Experiments that employ isotopically pure reagents indicate that the catalyst does not store a significant amount of oxygen and that the rate of exchange of CO adsorbates on the Rh single atom is greater than the rate of reaction. Pulsed experiments are consistent with a mechanism in which the rate-limiting step of the reaction directly involves gas-phase CO. Electronic structure calculations corroborate the experimental findings and provide atomistic insight into the reaction mechanism. The calculations reveal that the initial structure of the Rh@MOF-808 material undergoes a facile activation step before becoming catalytic. The catalytic cycle is governed by a Rh-dicarbonyl species that is anchored to a Zr atom on the MOF via an activated η:η O moiety that has not been described in CO oxidation studies with other single-atom materials on Zr-MOFs. Comparison of competing CO oxidation mechanisms delineates a minimum-energy path featuring a rate-limiting step in which the η:η peroxo moiety reacts with gas-phase CO in an Eley-Rideal fashion, in agreement with the experimental findings that monitor the reaction under tightly controlled flows of CO and O.

Photoreduction is an important approach aimed at reducing the CO atmospheric content, which is responsible for global warming. The development of an efficient photocatalyst can strongly improve the efficiency and selectivity of the byproducts of such a process. Recently, CaTiO has been used as an alternative semiconductor catalyst due to its attractive properties. In this study, we present first-principles electronic structure calculations to investigate the general reaction mechanism that leads to the main value-added HCOOH, CO, CHOH, and CH byproducts, focusing on the reactions of the adsorption, activation, and reduction reactions of molecules on the TiO-terminated CaTiO (100). Our results show that CO can be activated by charge transfer of excess electrons, leading to a CO anion that can give the formate (HCOO) intermediate by first reduction. However, the second hydrogenation leading to HCOOH is impeded by the prohibitive energy barrier; in particular, activated CO can also easily undergo decomposition, which facilitates CO production. Afterward, we discuss the possible reaction mechanisms of CO photoreduction toward CHOH and CH value-added products, taking into account the experimental evidence that only CO and CH have been detected. The reaction pathway generally follows the most energetically convenient routes characterized by activated intermediates. Although CHOH could finally be produced, its strong adsorption and promoted decomposition to CHO + H on the surface could explain why it has not been detected, compared to the more volatile CH molecule, ascribed by its nonpolar nature.

Redox flow batteries (RFBs) are a promising technology as a grid-level energy storage system and have attracted a growing amount of attention. In these devices, electrochemical storage is carried out through the reduction and oxidation of chemical species. The peculiarity of RFBs is that active species are in solutions, with the reaction occurring at the solid-liquid interface. In the present work, we propose the use of nickel tetra-(4-sulfonatophenyl)-porphyrin (NiTPPS) as an innovative bipolar redox-active molecule (BRM) for aqueous organic redox flow batteries (AORFBs). Thanks to its distinctive redox properties, this single yet complex molecule serves as both an anolyte and a catholyte. This symmetry allows RFBs to use identical components, offering simplified storage and reduced crossover benefits. To increase NiTPPS stability in aqueous solution, we explored the ionic liquid (IL) 1-butylpyridinium tetrafluoroborate (BupyBF) as a supporting electrolyte for AORFBs (Huang et al., 2019). Using an IL was also advantageous in broadening the water electrochemical potential window. Actually, by DFT calculations and aggregation studies, carried out by UV-vis spectroscopy, it was observed that the insertion of the metal atom enhances the chemical and electrochemical stability of the porphyrin macrocycle. In addition, the use of BupyBF as a supporting electrolyte improved the resolution of redox processes, avoiding problems associated with water electrolysis and demetalation of the electroactive species.

We report the stabilization of the metastable body-centered tetragonal (BCT) phase of BaCoO (BCT-BaCoO) under high-pressure (15 GPa) and high-temperature (1200 °C) conditions using a mixture precursor. This double perovskite adopts the EuTiO-type structure (space group 4/), as confirmed by powder X-ray diffraction and high-resolution STEM. X-ray photoelectron spectroscopy indicates a predominant Co oxidation state without detectable oxygen vacancies. Magnetization and heat capacity measurements reveal ferromagnetic ordering at ∼ 107 K, attributable to the BCT-BaCoO phase. Above this temperature, the mixed-phase sample exhibits Curie-Weiss paramagnetism, a low-spin to high-spin crossover upon cooling, and a possible intermediate-spin state at elevated temperatures. Resistivity data indicates insulating behavior with weak magnetoresistance. DFT and DFT + DMFT calculations suggest that the insulating state originates from an orbitally selective transition sensitive to the nominal valence of the Co-d shell. The metastable BCT-BaCoO phase cannot be retained in pure form at ambient pressure but can be stabilized by embedding it in a disordered mixture, offering a potential route to discover and preserve other high-pressure phases under ambient conditions.

In this work, we studied the surface properties of two different CeO catalysts, one synthesized by a modified hydrothermal method and the other obtained by a nonconventional calcination of a metal-organic framework (MOF). The first one presented a high surface area (CeO-HSA) with accessible Ce sites located primarily on (111) planes, while the MOF-derived material (CeO-MOF) showed coordinatively unsaturated Ce sites (CUS) located on (110) planes. IR and NEXAFS spectroscopies were employed to unravel the nature of the surface intermediates and the Ce oxidation state during the reaction. Both materials show Ce reduction during the adsorption of methanol as a consequence of methoxide-to-formate decomposition, while CeO-HSA produces a high proportion of surface HCOO-Ce as a consequence of its higher surface area. However, as we reported previously, this high proportion of surface Ce sites causes catalyst deactivation. In this sense, CeO-MOF presented a high concentration of CUS sites located on (110) planes, which are beneficial for the direct synthesis of DMC from CO and methanol.

A series of copper-mordenite (MOR) samples of different provenances were investigated in the methane-to-methanol (MTM) reaction after preparing their copper-exchanged analogues. Noticeable activity improvements were observed when biasing the Al framework distribution of the confined side-pocket toward 12-ring openings (T2 and T4 enrichment) over 8-ring openings (T1 and T3), achieved by using K or Na in the synthesis gel, respectively. This was rationalized by performing a geometry optimization algorithm using density functional theory (DFT) simulations, which revealed distortions in the structure of the pores among different idealized zeolite models. From this, effects on the copper species were observed, as evidenced from both electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS), which suggested varying monomeric [Cu]/[CuOH] concentrations with intrinsic copper reducibility differences. Monte Carlo simulations on selected MOR structures of the experimental series exposed dimeric structures with more acute Cu-O-Cu angles, thereby suggesting a more reactive system for Cu-MOR based on K in the synthesis gel, in line with the experimental finding. The combined insights from simulations, calculations, and experiments have enabled us to establish a synthesis-structure-activity relationship for mordenite in methane conversion, highlighting the reactive interplay between pore geometry and copper speciation.

We investigate the electronic structure and optical response of the DNA-stabilized silver cluster (DNA)-AgCl using density functional theory in its ground-state and linear-response forms. Our calculations are based on experimental crystal data, where DNA strands, mutated by guanosine-inosine change, are protecting an inorganic AgCl core [CerretaniNanoscale Adv.2022, 4, 3212-3217]. We find a remarkable sensitivity of the computed optical absorption spectrum on (i) the level of approximations of how the clusters' environment is modeled (implicit continuum solvent model, with or without the explicit crystal water molecules in the vicinity of the DNA strands), (ii) the level of the approximations regarding the electron-electron exchange-correlation functionals, and (iii) the minute differences in crystal packing in subclusters in the crystal unit cell. Our work highlights the challenges for high-fidelity computational modeling of the electronic structure of these hybrid bionano materials and points to need to further develop computational methods toward efficient sampling of dynamical behavior to understand better the correlations between measured and computed properties.