Surface Science最新文献

Understanding the structure of catalyst surfaces with adsorbed molecules is key to improving catalyst design. Scanning tunneling microscopy (STM) allows the observation of adsorption states and sites and provides insights into diffusion and desorption processes; however, the presence of multiple types of molecules on the surface presents challenges such as the identification of species and verification of reaction progress, particularly at room temperature or higher. In this study, we develop a protocol for the height classification analysis of STM images using the Watershed algorithm. This method is applied to a system involving the co-adsorption of H₂O and CO on the Fe₃O₄(111) surface, which represents the beginning of the water-gas shift reaction. Water molecules and dissociated OH species were identified in STM images of the Fe₃O₄(111) surface following the adsorption of water. Furthermore, gradual changes in the types of surface species were observed upon exposure of the surface to CO, indicating reaction progression. Our observations suggest that CO may react with molecular water rather than with dissociated OH on Fe sites. Despite its simplicity, the height classification analysis effectively identifies changes in the adsorbates on the catalyst surface. This method can be extended to other catalyst surfaces with adsorbed gasses.

As a nanofabrication technology, atomic layer deposition (ALD) has been widely used in the fields of displays, microelectronics, nanotechnology, catalysis, energy and coatings. It demonstrates excellent conformality, large-area uniformity and precise control of the sub-monolayer film. Al₂O₃ ALD using trimethylaluminum (TMA) and water (H₂O) as precursors is the most ideal ALD model system. In this work, the reactions of TMA and H₂O with the surface have been investigated using density functional theory (DFT) calculations in order to obtain more information on the reaction mechanism of the complicated H₂O-based ALD of Al₂O₃. In the TMA reaction, the methyl ligands can be eliminated and new Al-O bonds can be formed via ligand exchange reactions. In the H₂O reaction, the methyl ligand on the surface can be further eliminated and new AlO bonds can be formed. Meanwhile, the coupling reactions between the surface methyl and hydroxyl groups can further form new AlO bonds and release CH₄ or H₂O to densify the Al₂O₃ film. These complicated reaction mechanisms of Al₂O₃ H₂O-based ALD can provide theoretical guidance for the precursor design and ALD growth of other oxides and aluminum-based compounds.

The atomic structure of MoO_x films formed upon a gradual thermal reduction of an ordered MoO₃ monolayer on the Pd(100) substrate was explored via surface science characterization techniques and density functional theory (DFT) calculations. Two main reduction stages were identified. First, the initial oxygen excess was gradually eliminated by altering the domain boundary length, orientation, and atomic structure. The films nevertheless remained O-rich, with numerous terminal oxygen atoms (formation of MoO groups), and an elevated work function. Second, multiple ordered O-lean phases were formed, characterized by either very few or no terminal oxygen atoms, and a much smaller surface work function. According to calculations, the positive charging of the Pd substrate stabilizes the oxygen excess during the first stage, but during the second reduction stage, the substrate becomes negatively charged, stabilizing enhanced cation oxidation states. On their basis, the mechanisms underlying the oxygen release from the initial c(2 × 2) domains were disclosed. The experiments showed that the film reduction is perfectly reversible, which highlights the very promising properties of the MoO₃/Pd system for heterogeneous catalysis.

Based on the first-principles ab initio calculation method of density functional theory (DFT), the adsorption models of Cl₂ molecules on both the TiC_0.89O_0.11(001) intact surface and the carbon vacancy surface were established, followed by calculations and analysis of the adsorption structures, adsorption energy, differential charge density, and density of states (DOS). The results demonstrate that the adsorption process of Cl₂ molecules on the TiC_0.89O_0.11(001) surface involves chemical adsorption, with a higher likelihood of dissociation into Cl atoms during adsorption. These dissociated Cl atoms can potentially interact with surface Ti and/or C atoms to form Ti-Cl bonds, C-Cl bonds, Ti-Cl-C bonds, and Ti-Cl-Ti bonds. Simultaneously, the stability of the adsorbed structure is influenced by both the bonding conditions between Cl atoms and surface atoms and the position of Cl atom adsorption (e.g., whether it is located above the vacancy C). Following adsorption, there is a weakening in the bonding strength of Ti-C or Ti-O bonds on the TiC_0.89O_0.11(001) surface. During the adsorption process, Cl atoms can either act as electron donors or acceptors. When the Ti-Cl bond structure is formed, Cl atoms function as electron acceptors; however, when the C-Cl bond structure is established, Cl atoms predominantly act as electron donors. Surface Ti atoms act as electron donors while surface C and O atoms function as electron acceptors. Additionally, the presence of surface carbon vacancy enhances the interaction between Cl and Ti atoms, weakens the interaction between Cl and C atoms, and attenuates the interaction between C, O, and Ti atoms in the structure. And it can augment the electron acquisition by Cl₂ molecules upon adsorption, reduce the adsorption energy, and promote greater stability in the adsorption structure. All the effects contribute to facilitating TiCl₄ formation.

This study explores the potential of nitrobenzene as an anolyte material for nonaqueous redox flow batteries (RFBs) by theoretically examining its low-coverage adsorption behavior on neutral and charged Ag(111) model electrode surfaces. At the low coverage limit, DFT calculations show a preference for nitrobenzene to adsorb parallel to the surface, with the benzene ring and nitro group centered over HCP sites. Interactions between nitrobenzene and the surface were analyzed using induced charge density analysis, Bader charge analysis, and projected density of states (PDOS). It was found that nitrobenzene adsorbs primarily through van der Waals interactions with the surface. As nitrobenzene accumulates negative charge, the strength of adsorption diminishes. Understanding the electrode-electrolyte interface is crucial for enhancing RFB electrochemical performance, and this study sheds light on nitrobenzene's interaction with a model Ag electrode.

Non periodic density functional theory calculations are used to investigate the role of cobalt atoms in the adsorption of thiophene on small Mo and MoCo clusters. Metallic aggregates play the role of those active sites found in the true catalysts. Two interaction modes between thiophene and metallic sites are considered, namely, the S-mode, in which the organosulfur molecule interacts through the S atom, and the R-mode, in which the interaction takes place through the thiophene ring. A large number of sites, in which thiophene effectively adsorbs, was found, both in the monometallic case and in the bimetallic one. Considerably larger adsorption energies were found when thiophene interacts via the R-mode than when adsorption occurs through the S-mode. The activation of C-S bonds is also more important for R-mode cases than for S-mode ones. Further analysis made on some selected systems and based on density of states and molecular orbital overlap population-projected density of states reveals that thiophene and metallic clusters interact in an energy range around −6.0 eV with respect to the Fermi energy. Bands observed at energies below −6.0 eV correspond to thiophene states that become shifted with respect to the values obtained for isolated thiophene depending on the strength of the interaction. Bands above -6.0 eV describe how C and S atoms interact with Co and Mo ones, providing both bonding and antibonding patterns that helps to understand the overall interaction. Most important is the finding that cobalt atoms seem to play no relevant role during the adsorption of thiophene on metallic sites. Thus, present results obtained using non periodic GGA density functional theory seem to point to cobalt taking part in another step of the overall HDS process, hydrogen adsorption or hydrogen attack to C-S bonds, for instance.

The primary cause of global warming is the emission of greenhouse gases such as CO₂. So reducing CO₂ emissions is vital. This paper investigates the impact of the atom K as a promoter of MgO on the CO₂ adsorption properties using the DFT theoretical computational method. By analyzing the adsorption energy, bader charge as well as the density of states and COHP, it was found that K-promoting the MgO (100) surface resulted in a redistribution of charge on the MgO surface and enhanced CO₂ adsorption compared to the pure MgO surface. The presence of K atoms causes orbital hybridization among O (CO₂) and Mg atoms, O (CO₂) atoms and K atoms, and the surface O atoms and K atoms. These interactions lead to the formation of (MgO)Mg-O(CO₂) and (CO₂)O−K−O(MgO) chemical bonds. The adsorption energy of CO₂ on the K-promoted MgO surface increased from -0.32 eV to -1.01 eV compared to the pure surface, enhancing the adsorption of CO₂.

Nitrogen oxides play a significant role in various biomedical conditions, including respiratory disorders, asthma, and cardiovascular problems, underscoring the urgent need for sensitive and selective devices in biomedical applications. This study offers a comprehensive analysis of the sensitivity of β-tellurene doped with 2.22 % tungsten to nitrogen oxides (NO, NO₂, and N₂O). Site-specific doping of tellurene with tungsten reduces the band gap and introduces magnetization in β-tellurene. The strong adsorption energies observed for NO, NO₂, and N₂O at site A (-2.45 eV, -2.39 eV, and -2.80 eV, respectively) suggest that W-doped β-Te monolayers are promising candidates for gas storage for these compounds. Conversely, weaker adsorption energies for the same gases at site B (-0.74 eV, -1.74 eV, and -0.09 eV) highlights the importance of doping location. The adsorption energy values at site B indicate that W-doped β-Te monolayers have potential as sensing materials for NO and as adsorbents for NO₂ gas. Conversely, the weak adsorption energy for N₂O at the B site demonstrates its non-interacting behaviour with the W-doped β-Te monolayer. Additionally, the negligible change in electronic properties and minimal charge transfer suggest that this configuration is unsuitable for N₂O storage and sensing. The spin-resolved current-voltage characteristics of doped tellurene reveal distinct behaviors influenced by gas molecule adsorption. Overall, these findings underscore the potential of W-doped tellurene as a site-specific material for the adsorption and sensing of targeted gases.

Surface science studies of electrochemical interfaces and processes have gained increasing popularity in the last decades, owning to the increasing importance of electrochemistry for key technologies of the 21th century, especially in electric energy storage and conversion. In situ and operando surface-sensitive methods, such as scanning probe microscopy and surface X-ray diffraction, as well as complementary ab initio theory can provide atomic-scale information on solid electrode surface in contact with liquid electrolytes, including structural changes under reaction conditions. The level of detail obtainable by these approaches is illustrated in this short review for selected examples. These include the adsorption of sulfate and other oxyanions, where a crucial role of coadsorbed water is found, the restructuring of Cu electrode surfaces under hydrogen evolution and CO₂ reduction conditions, and the mechanisms of electrochemical Pt oxidation and its correlation with Pt dissolution.