Surface Science最新文献

Based on the first principles, we have calculated the influence of the applied electric field and doped X (X = N, P, As, Sb) atoms on the optoelectronic properties and phonon dispersion of the monolayer 2D material SnSe₂. The calculation results show that intrinsic SnSe₂ is a semiconductor with a band gap value of 0.884 eV. The doping of X atoms improves the energy band tunability of the monolayer SnSe₂ system and becomes more stable. The N-doped SnSe₂ system has the most stable structure and the best doping performance. When the electric field strength of 0.3 V/Å is applied on the surface of the N-doped system, the band gap of the system increases. The energy gap gradually decreases when the electric field strength continues to increase from 0.3 V/Å to 0.9 V/Å. At an applied electric field strength of 0.9 V/Å, the system changes from semiconductor to metallic properties. As far as the optical properties are concerned, the applied electric field increases the static refractive index of the system, the imaginary part of the photoconductivity increases, the energy loss function decreases, and the light absorption performance improves. The applied electric field successfully enhanced the optical properties of the SnSe₂ system. The applied electric field strength of 0.9 V/Å doped N system has the best optical properties. This provides a new way to explore the optoelectronic devices based on the SnSe₂ doped system.

In this study, the growth of ZrO_x on Au (111) was investigated using scanning tunneling microscopy (STM) and synchrotron-based ambient pressure X-ray photoelectron spectroscopy (AP-XPS). Nanostructures of ZrO_x (x = 1,2) at the sub-monolayer (≤ 0.3 ML) level were prepared by vapor depositing Zr metal onto Au (111) followed by oxidation with O₂ or CO₂. At low coverages of the admetal (< 0.05 ML), the formed ZrO_x nanostructures were dispersed randomly on the terraces and steps of the Au(111) substrate. Strong oxide-metal interactions prevented the formation of islands of zirconia. The ZrO_x nanostructures displayed a reactivity towards CO₂ and H₂ not seen for bulk zirconia. C 1 s AP-XPS results indicated that CO₂ molecules adsorbed on Zr/ZrO_x/Au(111) surfaces could undergo partial decomposition on Zr (CO_{2, gas} → CO_gas + O_ads), or react with oxygen sites from ZrO_x to yield carbonates (Zr-CO_{3, ads}). After exposing ZrO₂/Au (111) surfaces to 1:3 mixtures of CO₂:H₂, the formation of HCOO, CO₃, and CH₃O was detected in AP-XP spectra. These chemical species decomposed at temperatures in the range of 400‒600 K, making them possible reaction intermediates for methanol synthesis.

The determination of the configuration of atomic adsorbates on clean metal surfaces has been a key issue in surface science 60 years ago and still is today. We demonstrate that despite the prevalence of combined scanning tunneling microscopy and density functional theory studies of adsorbate systems the pitfalls are plentiful calling for accurate, reliable structure analyses that can be delivered by diffraction methods. We analyze and compare the ordered phases of Te on Ir(111), Ir(100), and Au(100) demonstrating the accuracy, the in-depth information and physical insight that can nowadays be obtained by quantitative low-energy electron diffraction structural analyses.

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.

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.

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.

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.