The Journal of Physical Chemistry C最新文献

Research on sustainable energy has intensified to reduce greenhouse gas emissions, especially CO₂. One promising strategy is the catalytic reduction of CO₂ to methanol, and indium oxide (In₂O₃) has emerged as a highly efficient catalyst, with high turnover rates and selectivity. This work investigates methanol, the end product of CO₂ reduction, and its interaction with the In₂O₃(111) surface. Utilizing an ultrahigh vacuum (UHV) environment, this study combines temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), noncontact atomic force microscopy (nc-AFM), scanning tunneling microscopy (STM), and density functional theory (DFT) calculations. The coverages investigated range from 1 to 12 methanol molecules per unit cell. The results are compared to water adsorption on In₂O₃(111), as the chemical behavior of both molecules is similar in many respects. At low coverage, the adsorption patterns and interactions with the In₂O₃(111) surface mirror those seen with water, including dissociative and molecular adsorption. The first three methanol molecules dissociate at specific sites within the surface unit cell, while molecular adsorption becomes favored for subsequent molecules at temperatures below 300 K. At the highest coverage (before multilayer adsorption) methanol and water exhibit distinct structures due to their differing hydrogen bonding capabilities.

Low interfacial thermal conductance often emerges as a primary barrier to effective heat management in advanced nanodevices. This study examines how topological defects affect the interfacial thermal conductance of graphene/SiC lateral heterostructure, utilizing nonequilibrium molecular dynamics simulations. The significant lattice mismatch between graphene and SiC results in a pristine interface that experiences severe strain and structural distortion, ultimately reducing the level of phonon transmission. By introduction of 5|8|5 topological defects, the interfacial deformation is effectively alleviated, thereby improving phonon coupling across the boundary. The results reveal an unconventional increase in interfacial thermal conductance, with the maximal value achieved when three defects are incorporated, representing a 61% improvement compared with the pristine interface. However, an excessive number of defects can lead to a reduction in the thermal conductivity. These findings demonstrate that controlled defect engineering offers a tunable pathway to optimize interfacial heat transport in 2D heterostructures, providing valuable insights for thermal management in nanoscale devices.

Mayer bond order (MBO) allows partitioning of total charge in a given system into overlap population components which can be interpreted as charges shared among atoms and retained by them through atomic orbitals. In this work, we formulate a spatial distribution of these partitioned components, rendering a breakup of the total charge density into individual densities of charges shared between all the available pairs of atoms, as well as charges exclusively retained by each of the atoms themselves. The spatial density of the interatomic MBOs in particular facilitates an unbiased physical description of electrons shared between two atoms, thus essentially constituting a plottable representation of a covalent bond, obtained without inducing any explicit localization of electrons between atoms, which otherwise is an inherent source of bias. We demonstrate the proposed formulation in the basis of Wannierized atomic orbitals constructed from first principles, in a few representative varieties of systems with varying degrees of interatomic hybridization, including scenarios of multicentered bonds in molecules, to metavalent bonding in periodic systems introduced and debated in the past few years. Pertinently, in GeTe, we find two electrons (2e) contributed by collinear p orbitals in each of the three Ge–Te–Ge(Te–Ge–Te) segments passing through Te(Ge), constituting a compact distribution of 2e over the 3 atom segments (3c), along with the relatively inert s electrons maintaining a spherical shape, to facilitate near completion of subshell filling of both the atoms, thus supporting the prevalence of 3c-2e metavalent bonding in the class of narrow band gap rock-salt structures.

MXenes have shown great potential in electronic and optoelectronic applications. However, the optical properties of these highly conductive two-dimensional materials are not fully understood. The broad near-infrared (IR) optical extinction (∼1.5 eV) in Ti₃C₂T_x with mixed terminations (T_x: ═O, −OH, −F, −Cl) has been widely attributed to a localized surface plasmon resonance (LSPR). However, previous simulations suggest this peak may be due to an interband transition (IBT). Here, we show that the real component of the dielectric constant of Ti₃C₂T_x at this peak is positive (ε₁ > 0), as measured by spectroscopic ellipsometry (SE), ruling out the possibility of LSPR. Moreover, this band nearly vanishes for experimentally synthesized chlorine-terminated Ti₃C₂Cl₂. Density functional theory (DFT) calculations confirm an IBT origin for this band, specifically due to the oxygen terminations (Ti₃C₂O₂). Metallic behavior is only experimentally observed below 1 eV (ε₁ < 0), and DFT calculations predict surface plasmon polaritons (SPPs) in the mid-IR (∼0.5 eV, outside the optical domain) and only for Ti₃C₂O₂, but not for Ti₃C₂Cl₂ or other terminations. Additionally, we demonstrate that making thicker Ti₃C₂T_x MXene films and/or removing the intercalated water can induce a blue shift in this IBT due to the influence of water in facilitating the out-of-plane conductivity. The IBT assignment is critical because its light-matter interaction is fundamentally different from that of an LSPR, providing a new foundation for designing innovative MXene-based optoelectronic materials, which can be tailored through their termination states, while an LSPR would be insensitive to such synthetic variations.

Edge-functionalized transition metal dichalcogenide nanoribbons of the zigzag type (zTMDCNRs) are explored in terms of their spin transmission properties. Specifically, systems of the type 5-zWXYNR+nad (X, Y = S, Se; n = 0 1, 2; ad = H, B, C, N, and O), involving five rows of a zWXY unit, are investigated as transmission elements between semi-infinite electrodes to identify atomic adsorbates and adsorption conditions for maximizing the spin polarization of current traversing the ribbons. Janus counterparts of these units, asymmetric structures comprising a transition metal layer sandwiched by two different chalcogen layers, are included in this study. In all cases considered, density functional theory modeling, involving the hybrid Heyd–Scuseria–Ernzerhof exchange–correlation functional, is combined with the nonequilibrium Green’s function approach to determine both spin and charge transport properties. The effect of selected atomic absorbates on the geometric, electronic, and magnetic properties of 5-zWXYNR (X, Y = S, Se) is evaluated. A protocol is formulated to assess the spin-filtering capacity of 5-zWXYNR+nad as a function of the nature and the density of atomic adsorbates, in terms of electrode band structure analysis. Spin gaps emerging close to the Fermi energy of the electrode are shown to provide an effective predictor of the degree of current spin polarization achieved by any of the transmission systems studied here. For any adsorbate configuration considered, ferromagnetic and antiferromagnetic ordering is examined and the impact of the magnetic phase on the spin-transport properties is discussed. A spin-selective negative differential resistance effect is identified in the pristine nanoribbon systems.

We investigated the mechanisms underlying strong metal-support interactions in CO oxidation using model systems where noble metal crystals support reducible, monolayer-thick CoO_x films. The effect of the Co oxidation state, film thickness, and substrate identity were studied in varying reaction conditions using ambient pressure X-ray photoelectron spectroscopy. At low O₂ pressures, the same oxide phase forms on both Pt(111) and Au(111) surfaces. But when heated at higher O₂ pressures, the oxide phase depends on the substrate. We found that CoO_x/Pt is more active for the CO oxidation reaction than CoO_x/Au, even when both surfaces stabilize the same oxide phase. DFT calculations on these and related noble-metal-supported CoO_x films reveal an SMSI-induced reactivity enhancement that strongly depends on the oxide film thickness and which is mediated by charge transfer between the metal and oxide. Charge transfer is also found to correlate with the reaction energy and activation barrier for CO oxidation. This effect was found to be greatest for oxide films on Pt, decreasing on other noble metal supports in the order Pt > Pd > Au > Ag, in agreement with the experiments. The role of charge transfer in the activation barriers and reaction energies provides insight into the nature of SMSI-induced catalytic activity, and suggests that the noble metal work function can serve as an indicator for the strength of SMSI effects.

In this work, we aim to describe the energetics associated with the formation of ammonia from N₂ interacting with doped hydroxylated rutile TiO₂(110) surfaces with the vacant O_2c site, following the reaction N₂ + 3H₂O → 2NH₃ + 3/2O₂. The water molecules interact with the surface, creating exposed Ti–OH groups that can transfer hydrogen to the adsorbed N₂ molecule. Two metal dopants are evaluated: Mo and Ta. For both metals, calculations show a dramatic decrease in the energy of most intermediates during the entire mechanism, leading to more favorable reaction mechanisms. Nonetheless, it is worth noting that when the Ti_6c site of the vacant site is doped with either Mo or Ta, there is a stronger effect on the energetics than doping on the exposed Ti_5c sites. The effect of increasing the concentration of metal dopants on the vacant site was also investigated. In this case, calculations indicate that a higher percentage of the dopant on the surface results in a more substantial decrease in the energy of most intermediates, suggesting that increasing the dopant content could be beneficial for the catalytic process.

Dry reforming of ethane (DRE) with carbon dioxide, a key reaction for converting shale gas into value-added products, offers an efficient route for carbon resource utilization. This process proceeds through two competing pathways: C–C bond cleavage leading to syngas formation and oxidative dehydrogenation yielding ethylene. Achieving precise control over product selectivity while maintaining catalyst stability through catalyst design remains a major challenge. In this study, we combine density functional theory (DFT) calculations with microkinetic modeling to elucidate the structure-performance relationship of DRE on Ni(111) and Ni(211) surfaces. A comprehensive reaction network comprising 52 intermediates, 139 transition states, and 141 elementary steps is constructed for the DRE reaction. The Ni(111) terraces promote sequential dehydrogenation to CH₂CH₂*, resulting in approximately 60% ethylene selectivity with minimal coke formation. In contrast, the Ni(211) step edges exhibit superior C–C bond activation and enhanced syngas selectivity but also strongly adsorb carbonaceous intermediates (C*, CC*, CCH*), leading to significant carbon accumulation and catalyst deactivation. Kinetic analyses reveal that the coverage-dependent balance between forward and reverse reaction rates is the primary factor governing selectivity. These findings establish a fundamental reactivity-stability trade-off in Ni-catalyzed DRE, and possible strategies to optimize catalytic activity, selectivity, and coke resistance are proposed.

Machine-learning-accelerated discovery of monoclinic BeA₂X₄ (A = Al, Ga, In; X = Se, Te) yields six infrared-absorbing chalcogenides with thickness-tunable absorptance. A 3814-compound prototype library was stability- and gap-screened to 1268 candidates; XGBoost (R² = 0.939, MAE = 0.241 eV) nominated BeAl₂Se₄, BeGa₂Se₄, BeIn₂Se₄, BeAl₂Te₄, BeGa₂Te₄, and BeIn₂Te₄. Hybrid-DFT (HSE06) and 10,000 fs ab initio molecular dynamics (AIMD) simulations at 300 K confirm the monoclinic Pm structure with thermal robustness. BeGa₂Se₄ exhibits the highest Vickers hardness (1.59 GPa), and BeAl₂Te₄ exhibits the largest Poisson ratio (0.44). The strong anisotropic absorption spans 0.5–1.6 eV, peaking at 1.21 × 10⁵ cm^–1 (BeIn₂Se₄) and 1.16 × 10⁵ cm^–1 (BeAl₂Te₄, 0.5–1 eV). Absorptance scales linearly with thickness: 0.747 (500 nm BeAl₂Se₄), 0.726 (450 nm BeGa₂Se₄), and 0.650 (300 nm BeIn₂Se₄), defining a 300–500 nm design window that balances absorption gain against carrier transport loss. Direct band gaps eliminate phonon bottlenecks, while their systematic narrowing with A/X cation radii enables continuous spectral tuning across the near- to mid-infrared. The quantitative structure–absorption map provides experimentally accessible guidelines for next-generation infrared absorption coatings and photodetector absorber layers.

Hydroxide catalysis bonding (HCB), also known as silicate bonding, is widely employed to join oxide materials in precision optical instruments due to its ability to form strong, thin bonds under mild conditions. The chemical reactions underlying HCB, including hydration, polymerization, and dehydration, have been relatively well understood, yet the atomic-scale chemical structure of the bonded interface after water removal remains unexplored, limiting a complete mechanistic understanding of HCB. In this study, sodium silicate (mSiO₂:Na₂O) was employed as the HCB layer, with sapphire chosen as a model substrate to resolve the interfacial bonding mechanism. We combined ab initio molecular dynamics (AIMD) simulations and experimental validation to elucidate the interfacial chemistry. AIMD simulations revealed atomic-level processes including interfacial Al–O partial amorphization, Na migration, and formation of Al–O–Si and Al–O–Na linkages. The simulations predicted that the optimal bonding strength appears at a SiO₂/Na₂O molar ratio (m) of approximately 2, a result validated by bonding tests and corroborated by ATR-IR spectroscopy showing Al–O–Si bond formation at the interface. These results establish a direct relationship between SiO₂/Na₂O molar ratio, interfacial atomic structure, and mechanical strength, providing valuable guidance for designing robust HCB technologies.