Surface reconstructions play a crucial role in surface science because of their influence on the adsorption and arrangement of molecules or nanoparticles. On the Au(111) surface, the herringbone reconstruction presents favorable anchoring at the elbow sites, where the highest reactivity is found. In this work, we deposited large organic perchlorinated molecules on a Au(111) surface via high-vacuum electrospray deposition. With noncontact atomic force microscopy measurements at room temperature, we studied the molecular structures formed on the surface before and after annealing at different temperatures. We found that a supramolecular layer is formed and that a hexagonal reconstruction of the Au(111) surface is induced. After high-temperature annealing, the molecules are removed, but the hexagonal Au(111) surface reconstruction is preserved. With the hexagonal Au(111) surface reconstruction, a periodic lattice of anchoring sites is formed.

van der Waals MnPS compound belonging to the class of Néel-type antiferromagnets (AFM) has recently emerged as a promising two-dimensional material for spintronic applications. In this study, we report on the electron spin resonance (ESR) study of an MnPS single crystal across the Néel transition temperature ( = 78 K) for the magnetic field applied in the directions parallel and perpendicular to the crystallographic axis. Furthermore, the ESR angular dependence at a temperature near has been investigated. We observed multiple resonance modes with antiferromagnetic, ferromagnetic, and paramagnetic characters. In addition, we revealed the occurrence of complex spin-spin correlations and a magnetic-topological Berezinskii-Kosterlitz-Thouless (BKT) phase transition (i.e., bound vortex-antivortex pairs) at with / typically found in two-dimensional magnets.

Oxidation-reduction cycles (ORCs) on Au(111) in 0.1 M sulfuric acid solution change the electrode morphology due to the formation of many new nanosized islands. With increasing the cycle number, the roughness of the surface increases due to the formation of multiatomic-step adatom islands and pits. The final roughness value is a function of the applied potential window, number of ORCs, scan rate, electrolyte concentration, and any applied delay time. In a first experiment, the roughening was tracked by recording the STM images in 11 steps during 200 ORCs. The results show the formation of pyramidal islands and a linear correlation between the roughness amplitude and the cycle number. In a second experiment, the 200 cycles were studied in 38 steps, while after each step, two images were recorded with a 3 min delay by holding the potential in the double-layer window. This leads to a lower roughness increase due to the high surface mobility of the Au surface atoms, which smoothens the surface during the delay time. Finally, the oxidation-reduction charge density per cycle shows an inverse correlation with surface roughness due to the (111) terrace showing a higher surface oxidation charge than the other sites and facets. Each delay causes a strong increase in the oxidation charge which is a consequence of surface smoothening during the delays leading to an enhancement of the (111) related oxidation charge.

Atomic defects associated with vacancies in two-dimensional transition metal dichalcogenide monolayers efficiently trap charged carriers and strongly localize excitons. Defects in semiconducting monolayers are seldomly utilized for enhancing optical phenomena, although they may provide resonant intermediate states within the energy band gap for applications with multiphoton excitations, like highly efficient and thermally robust photon upconversion. In an MoS monolayer encapsulated by hBN with high defect and resident electron densities, we observe an upconversion of localized exciton (X) emission with a huge energy gain of up to 290 meV. The upconverted X emission is robust up to temperatures of about 120 K and exhibits a sublinear or a nearly linear laser power dependence for the energy gain of about 100 meV and above 200 meV, respectively. The upconversion mechanism is explained by a cooperative energy transfer process between the photocreated and resident electrons, in which hybridized pairs of single sulfur vacancies likely act as real intermediate states. Additionally, we find a weak upconversion of the neutral exciton photoluminescence with an energy gain of about 350 meV for quasi-resonant excitation of the X exciton. It is attributed to a two-step, two-photon absorption.

The growth and structure of two-dimensional iron silicate and iron germanate films on Ru(0001) are studied. We investigate in detail the temperature-dependent film formation of ultrathin layers of iron silicate and iron germanate. These two-dimensional films can be seen as model systems for more complex catalytically active structures, such as zeolites, which can be used as selective catalysts or molecular sieves. The experimental methods of XPS, LEED, LEEM, LEEM-IV, and XPEEM are applied for correlated chemical and physical characterization in situ and in real time, and DFT is applied for theoretical consideration. We show that both systems can be considered as two-layered systems, with a monolayer of iron oxide at the Ru interface and a monolayer of silica or germania on top, respectively. The Fe-Fe distance in the iron oxide layer is influenced by the Si-O-Si or Ge-O-Ge bond length, in agreement with those of unstrained silicates or germanates. Moreover, iron silicate can be prepared using different preparation methods. The actual loading of Fe atoms is three per unit cell for FeGeO and only two for FeSiO.

We have investigated charge generation pathways in efficient organic photovoltaic blends of the polymer donor D18 and the small-molecule acceptor Y6 using transient absorption and time-resolved fluorescence spectroscopies. We find that energy transfer from D18 to Y6 outcompetes electron transfer and is followed by exciton diffusion from regions of the disordered Y6 phase to Y6 aggregates before hole transfer to D18. Aggregation of Y6 molecules increases their ionization energy by ∼0.3 eV and provides a driving force for hole transfer from Y6 excitons and spontaneously generated charge pairs to D18. We observed ultrafast depolarization of the Y6 ground-state bleaching in <200 fs, which indicates delocalization of primary excitons in Y6 aggregates. This delocalization can explain the spontaneous generation of charge pairs in neat Y6 films and Y6-rich blends. Our results show that subtle aggregation control of the low-energy absorber can be used for balancing photocurrent generation with low voltage loss in photovoltaic blends.

Personalized medicine and drug discovery are different, yet overlapping, fields, and information from each field is exchanged to improve the other. The current methods used for devising personalized therapeutic plans and developing drug discovery applications are costly, time-consuming, and complex; thus, their applicability is limited in both fields. However, surface-enhanced Raman spectroscopy (SERS) offers potential solutions to current challenges. This Mini-Review explores the utility of SERS in drug discovery and personalized medicine. The Mini-Review starts with a brief overview of these fields, including the main challenges and current methods, and then explores examples where SERS has been used to overcome some of the main challenges in both fields. It ends with brief conclusions, perspectives, and current challenges limiting the practical application of SERS.

In this work, we theoretically investigate the impact of kinetic and thermodynamic properties on the performance of photocatalytic cells operating in an unassisted tandem configuration, including electron affinity and ionization energies, recombination rates, and reaction rates. To this end, we present general rules and metrics for identifying and isolating the origin of an observed shift in the onset potential at either the photoanode or the photocathode of these devices. The correlation between kinetic and thermodynamic shifts in the onset potential is demonstrated through the use of band diagrams and key comparable features within readily accessible characterization tools: current-voltage plots are taken both under illumination and in the dark and further coupled with Mott-Schottky plots. To illustrate this conceptual framework, a model system comprised of a p-type doped BiVO photocathode and an n-type doped BiVO photoanode is employed. By varying each of the aforementioned kinetic and thermodynamic parameters in isolation, the manner in which these various mechanisms shift the onset potential is demonstrated. This work intends to showcase how kinetic and thermodynamic effects are distinctly manifested in these commonly used characterization tools and further proposes thermodynamic band-edge engineering as a potentially useful and largely unexplored avenue for possibly improving tandem cell performance, in addition to the conventional approach of optimizing kinetics.

The enhancement of the molecular Raman signal in plasmon-assisted surface-enhanced Raman scattering (SERS) results from electromagnetic and chemical mechanisms, the latter determined to a large extent by the chemical interaction between the molecules and the hosting plasmonic nanoparticles. A precise quantification of the chemical mechanism in SERS based on quantum chemistry calculations is often challenging due to the interplay between the chemical and electromagnetic effects. Based on an atomistic description of the SERS signal, which includes the effect of strong field inhomogeneities, we introduce a comprehensive approach to evaluate the chemical enhancement in SERS, which conveniently removes the electromagnetic contribution inherent to any quantum calculation of the Raman polarization. Our approach uses density functional theory (DFT) and time-dependent DFT to compute the total SERS signal, together with the electromagnetic and chemical enhancement factors. We apply this framework to study the chemical enhancement of biphenyl-4,4'-dithiol embedded between two gold clusters. Although we find that for small clusters the total SERS enhancement is mainly determined by the chemical mechanism, our procedure enables removal of the electromagnetic contribution and isolation of the contribution of the bare chemical effect. This approach can be applied to reproduce and understand Raman line activation and strength in practical and challenging SERS configurations such as in plasmonic nano- and pico-cavities.

Noble metals such as gold and silver have been used extensively for a range of plasmonic applications, including enhancing the fluorescence rate of a dye molecule, as evidenced by numerous experiments over the past two decades. Recently, a variety of doped semiconductors have been proposed as alternative plasmonic materials, exhibiting plasmonic resonances from ultraviolet to far-infrared. In this work, we investigate the suitability of these alternative materials for enhancing the fluorescence of a molecule. Considering nanosized spheres, we study their response under plane wave illumination and the resulting enhancement factors when coupled to a quantum emitter. Comparisons with standard plasmonic metals reveal that semiconductor materials lead to a significantly reduced, and often strongly quenched, emission of light caused by their dominant absorption, which hinders fluorescence enhancement. However, we show that enhancement may be obtained when considering poor emitting dyes and high refractive index environments. Our findings demonstrate that these alternative materials result in weaker fluorescence enhancement compared to their plasmonic counterparts. Nonetheless, there are means to compensate for this, and a reasonable enhancement can be achieved for dyes in the infrared spectrum.

Co nanoparticles (NPs) dispersed on ceria have been widely studied as active catalytic materials for many industrially relevant reactions. The detailed nature of such particles and the factors affecting their interaction with ceria remain to be better understood. In this study, a very low coverage (∼0.02 ML) of Co is deposited on a model CeO(111) thin-film surface and is examined using scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). The Co NPs that nucleate on terrace sites grow with coverage in this range to a maximum size of ca. 40 Co atoms, with an average diameter and height of 16.1 and 1.1 Å, respectively. Global minimization of the structures of Co NPs consisting of up to 23 Co atoms on CeO(111) is performed based on the minima hopping algorithm and density functional theory (DFT) calculations, and the energetic and chemical properties of the resulting NPs are analyzed. While the theoretical findings are consistent with the STM observations on the strong Co-ceria interactions and the prevalence of oxidic Co species, some notable discrepancies are identified, including inconsistent aspect ratios and the existence of a low oxidation state Co species. The combined experimental and theoretical findings provide new insights into Co NPs formed on ceria and identify areas requiring further investigation.

The dynamic environment within lithium-ion batteries induces significant changes in local thermodynamic functions, hampering the accurate prediction of the stability of the cathodes during cycling. While delithiation primarily affects the surface properties of the cathode structure, there is a lack of fundamental understanding concerning the evolution of interfacial energies with varying stoichiometry. Here, we used microcalorimetry to quantify the thermodynamic changes between the stoichiometric and partially delithiated nano-LiCoO states for the first time. A mild delithiation from LiCoO to LiCoO caused a surface energy reduction, negatively affecting the adhesion between adjacent grains by ∼0.4J/m. The introduction of lanthanum at 1.0 atom % reduced the surface energy of the stoichiometric LiCoO while forcing a constant surface energy state during delithiation down to LiCoO. This reduced the thermodynamic stress between grains during lithium cycling, mitigating degradation mechanisms. The lanthanum-induced surface stabilization also inhibited the coarsening and dissolution of the cathode particles. We used electron microscopy to propose an atomistic mechanism by which the lanthanum doping pins surface dissolution for improved cathode stability.

Hydrogen is a crucial element in the green energy transition. However, its tendency to react with and diffuse into surrounding materials poses a significant challenge. Therefore, developing coatings to protect system components in hydrogen environments (molecular, radicals (H*), and plasma) is essential. In this work, we report group IV-V transition metal carbide (TMC) thin films as potential candidates for protective coatings in H* environments at elevated temperatures. We expose TiC, ZrC, HfC, VC, NbC, TaC, and CoC thin films, with native surface oxycarbides/oxides (TMO C /TMO ), to H* at elevated temperatures. Based on X-ray photoelectron spectroscopy performed on the samples before and after H*-exposure, we identify three classes of TMCs. HfC, ZrC, TiC, TaC, NbC, and VC (class A) are found to have a stable carbidic-C (TM-C) content, with a further subdivision into partial (class A1: HfC, ZrC, and TiC) and strong (class A2: TaC, NbC, and VC) surface deoxidation. In contrast to class A, a strong carbide reduction is observed in CoC (class B), along with a strong surface deoxidation. The H* interaction with TMC/TMO C /TMO is hypothesized to entail three processes: (i) hydrogenation of surface C/O atoms, (ii) formation of CH /OH species, and (iii) subsurface C/O atom diffusion to the surface vacancies. The number of adsorbed H atoms required to form CH /OH species (i) and the corresponding thermodynamic energy barriers (ii) are estimated based on the change in the Gibbs free energy (Δ) for the reduction reactions of TMCs and TMO . Hydrogenation of surface carbidic-C atoms is proposed to limit the reduction of TMCs, whereas the deoxidation of TMC surfaces is governed by the thermodynamic energy barrier for forming HO.

We present unprecedented results on the damage thresholds and pathways for boron nitride nanotubes (BNNT) under the influence of energetic electrons in an oxidative gas environment, using an environmental aberration-corrected electron microscope over a range of oxygen pressures. We observe a damage cascade process that resists damage until a higher electron dose, compared with carbon nanotubes, initiating at defect-free BNNT sidewalls and proceeding through the conversion from crystalline nanotubes to amorphous boron nitride (BN), resisting oxidation throughout. We compare with prior results on the oxidation of carbon nanotubes and present a model that attributes the onset of damage in both cases to a physisorbed oxygen layer that reduces the threshold for damage onset. Surprisingly, increased temperatures offer protection against damage, as do electron dose rates that significantly exceed the oxygen dose rates, and our model attributes both effects to a physisorbed oxygen population.

A novel approach to selectively modify narrow subareas of metallic nanostructures adjacent to plasmonic hotspots, where strong electromagnetic field amplification occurs upon localized surface plasmon (LSP) excitation, is reported. In contrast to surface plasmon-triggered polymerization, it relies on plasmonically enhanced multiphoton crosslinking (MPC) of polymer chains carrying photoactive moieties. When they are contacted with metallic nanostructures and irradiated with a femtosecond near-infrared beam resonantly coupled with LSPs, the enhanced field intensity locally exceeds the threshold and initiates MPC only at plasmonic hotspots. This concept is demonstrated by using gold nanoparticle arrays coated with two specifically designed polymers. Local MPC of a poly(,-dimethylacrylamide)-based copolymer with an anthraquinone crosslinker is shown via atomic force microscopy. Additionally, MPC is tested with a thermoresponsive poly(-isopropylacrylamide)-based terpolymer. The reversible thermally induced collapse and swelling of the MPC-formed hydrogel at specific nanoparticle locations are confirmed by polarization-resolved localized surface plasmon resonance (LSPR) spectroscopy. These hybrid metallic/hydrogel materials can be further postmodified, offering attractive characteristics for future spectroscopic/bioanalytical applications.

Nanocrystalline ceria exhibits significant redox activity and oxygen storage capacity. Any factor affecting its morphology can tune such activities. Strain is a promising method for controlling particle morphology, whether as core@shell structures, supported nanoparticles, or nanograins in nanocrystalline ceria. A key challenge is to define routes of controlling strain to enhance the expression of more active morphologies and to maintain their shape during the lifespan of the particle. Here, we demonstrate a computational route to gain insights into the strain effects on particle morphology. We use density functional theory to predict surface composition and particle morphology of strained ceria surfaces, as a function of environmental conditions of temperature and partial pressure of water. We find that adsorbed molecular water is not sufficient to shift stability and as such under all compressive and tensile strains studied, the most stable particle is of octahedral shape, similarly to the unstrained case. When dissociative water is involved at the surfaces of the particle, then the most stable particle morphology changes under high water coverage and tensile strain to cuboidal or truncated cuboidal shapes. This shift in shape is due to strain effects that affect the strength of water adsorption.

In this work, we present a method for direct, site-selective growth of tellurium nanowires by electrochemical deposition. The Te nanowires were grown laterally between two specially designed nanoband electrodes across a gap, and over a dielectric material, forming a lateral device structure directly. The resulting wires are crystalline and phase pure, as evidenced by Raman spectroscopy, EDS (energy dispersive X-ray spectroscopy), and ADF-STEM (annular dark field scanning transmission electron microscopy). The precise conditions for lateral growth of the nanowires were investigated and the fabrication of an electronic device from the as-deposited material, without the need for any transfer process or further contact fabrication, is demonstrated.

Accurate and complete microkinetic models (MKMs) are powerful for anticipating the behavior of complex chemical systems at different operating conditions. In heterogeneous catalysis, they can be further used for the rapid development and screening of new catalysts. Density functional theory (DFT) is often used to calculate the parameters used in MKMs with relatively high fidelity. However, given the high cost of DFT calculations for adsorbates in heterogeneous catalysis, linear scaling relations (LSRs) and machine learning (ML) models were developed to give rapid estimates of the parameters in MKM. Regardless of the method, few studies have attempted to quantify the uncertainty in catalytic MKMs, as the uncertainties are often orders of magnitude larger than those for gas phase models. This study explores uncertainty quantification and Bayesian Parameter Estimation for thermodynamic parameters calculated by DFT, LSRs, and GemNet-OC, a ML model developed under the Open Catalyst Project. A model for catalytic partial oxidation of methane (CPOX) on Rhodium was chosen as a case study, in which the model's thermodynamic parameters and their associated uncertainties were determined using DFT, LSR, and GemNet-OC. Markov Chain Monte Carlo coupled with Ensemble Slice Sampling was used to sample the highest probability density (HPD) region of the posterior and determine the maximum of the a posteriori (MAP) for each thermodynamic parameter included. The optimized microkinetic models for each of the three estimation methods had quite similar mechanisms and agreed well with the experimental data for gas phase mole fractions. Exploration of the HPD region of the posterior further revealed that adsorbed hydroxide and oxygen likely bind on facets other than Rhodium 111. The demonstrated workflow addresses the issue of inaccuracies arising from the integration of data from multiple sources by considering both experimental and computational uncertainties, and further reveals information about the active site that would not have been discovered without considering the posterior.

Nucleation particles, solid phases dispersed throughout a medium to decrease the energy barrier for solidification or other reversible phase transitions, are generally selected on the basis of structural or interfacial energy considerations between the host phase and the solid phase that is crystallizing. However, the existence of chemical reactions between the nucleation particles and the host phase can obscure these underlying relationships, thereby complicating the process of selection of active nucleation particle phases. Here, we reveal the origin of nucleation activity of barium-based nucleation particles in the salt hydrate calcium chloride hexahydrate (CCH), a candidate for near room temperature thermal energy storage. We demonstrate that these compounds undergo a series of cation exchange and secondary precipitation reactions, resulting in an assemblage of solid precipitates with some degree of limited solid solution, which collectively dramatically reduce undercooling in CCH, but which obscure the identification of a single crystalline phase primarily responsible for the nucleation of crystalline CCH from the liquid. Importantly, this result illustrates a pathway to harness in situ chemical reactions to generate stable active nucleation particles in reactive phase change materials, which may not be readily synthesized by alternative methods, or which may not be active or remain stable when added in isolation.

Computation has long proven useful in understanding heterogeneous catalysts and rationalizing experimental findings. However, computational design with experimental validation requires somewhat different approaches and has proven more difficult. In recent years, there have been increasing successes in such computational design with experimental validation. In this Perspective, we discuss some of these recent successes and the methodologies used. We also discuss various design strategies more broadly, as well as approximations to consider and pitfalls to try to avoid when designing for experiment. Overall, computation can be a powerful and efficient tool in guiding catalyst design but must be combined with a strong fundamental understanding of catalysis science to be most effective in terms of both choosing the design methodology and choosing which materials to pursue experimentally.

A combination of analytical ultracentrifugation (AUC) and fluorescence spectroscopy are utilized to orthogonally probe compositions of adsorbed surfactant layers on the surface of (7,5) species single-wall carbon nanotubes (SWCNTs) under conditions known to achieve differential partitioning in aqueous two-phase extraction (ATPE) separations. Fluorescence emission intensity and AUC anhydrous particle density measurements independently probe and can discriminate between adsorbed surfactant layers on a (7,5) nanotube comprised of either of two common nanotube dispersants, the anionic surfactants sodium deoxycholate and sodium dodecyl sulfate. Measurements on dispersions containing mixtures of both surfactants indicate near total direct exchange of the dominant surfactant species adsorbed to the carbon nanotube at a critical concentration ratio consistent with the ratio leading to partitioning change in the ATPE separation. By conducting these orthogonal measurements in a complex environment reflective of an ATPE separation, including multiple surfactant and polymer solution components, the results provide direct evidence for the hypothesis that it is the nature of the adsorbed surfactant layer that primarily controls partitioning behavior in selective ATPE separations of SWCNTs.