Surface Science最新文献

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.

Graphene-supported Co clusters were investigated by high-resolution XPS, TPD and IRRAS using CO as a probe molecule. CO adsorption was observed at edge, on-top and bridge/hollow sites on the as-prepared clusters. Temperature-programmed XPS showed CO dissociation at T > 300 K. The CO desorption temperatures were determined by TPD measurements to be 260, 320 and 400 K for CO^{bridge/hollow}, CO^edge and CO^top, respectively. The CO dissociation products were used to investigate the adsorption of CO on carbon and oxygen precovered Co clusters. Site blocking by these adatoms was found resulting in the absence of CO^edge (XPS and TPD) and a decrease of the CO adsorption capacity (XPS, TPD and IRRAS). Additionally, no CO dissociation was found on the precovered clusters concluding a blocking of the catalytically active sites which are the edge sites of the clusters.

The surface chemistry of Ru atomic layer deposition (ALD) processes based on the use of tris(2,2,6,6-tetramethyl-3,5-heptanedionato)ruthenium(III) (Ru(tmhd)₃) and either molecular oxygen or atomic hydrogen on aluminum oxide films was characterized by a combination of surface-sensitive techniques. The thermal decomposition of the Ru metalorganic precursor was determined, by using a combination of reflection-absorption infrared spectroscopy (RAIRS), temperature programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS), to start below 400 K and to take place in a stepwise fashion over a wide range of temperatures. Gas-phase products from this chemistry include 2,2,6,6-tetramethyl-3,5-heptanedione (the protonated ligand, Htmhd; in a TPD peak at 520 K), isobutene (540 K; indicating the fragmentation of the organic ligands), and other products from isomerization and/or aldol condensation (650 and 730 K). This chemistry is accompanied by the reduction of the Ru³⁺ ions in two stages, involving the loss of some of their ligands and their direct bonding to the substrate first (between 500 and 600 K) and a full reduction to a metallic state later on (600–700 K). ALD cycles using either molecular oxygen or atomic hydrogen resulted in the slow build-up of Ru on the surface, but the co-deposition of carbon could not be avoided, at least in the initial cycles, while the alumina surface was still exposed. With O₂, the Ru atoms alternate between partially-oxidized (after the O₂ exposures) and zero-valent (after the Ru(tmhd)₃ doses) states, and some Ru loss in the form of the volatile RuO₄ oxide was seen after the second half of the ALD cycles; neither the Ru oxidation state alternation nor the elimination of some Ru from the surface were observed when using H·. The deposited Ru was determined, by combining results from angle-resolved XPS (ARXPS) and low-energy ion scattering (LEIS) experiments, to grow as 3D nanoparticles rather than as a layer-by-layer 2D film, presumably because the Ru precursor preferentially adsorbs (and decomposes more cleanly) on the metal surface. A discussion is provided of the implications of these results for the design of ALD processes.

Dicarboxylic acids, including tartaric acid, have played a crucial role alongside amino acids in the study of chiral recognition on metal surfaces. Over the past two decades, significant insights into surface stereochemistry have emerged, particularly on Cu(110). This review examines various phenomena observed during the interaction of 1,4-dicarboxylic acids with the Cu(110) surface. We explore diverse aspects such as chiral surface reconstructions, intermolecular chiral recognition, stereoselective autocatalytic decomposition, and chiral symmetry breaking through doping.

The substrate-modulation effect permeates throughout the realm of surface chemistry, particularly in the field of on-surface reactions. A comprehensive understanding of the interactions between molecules and substrates is crucial for the selective synthesis of designed graphene-based materials. In this review, we examine the substrate-modulation effect of surface-assisted reactions, focusing on the reaction mechanisms. We begin by elucidating how the substrates influence various process of the surface-assisted reaction, including adsorption, migration, and reaction of molecules. Additionally, substrates act as charge donors and acceptors to facilitate charge transfer between substrates and molecules, thereby tuning the electronic structure of the molecules.

Relativistic DFT calculations performed for Bi layers adsorbed on the Mo(112) surface have shown that Bi atoms tend to occupy adsorption sites in furrows and, at a half-monolayer coverage, form a rectangular p(2 × 1) structure. For a complete Bi monolayer, the most preferred structure is the centered c(2 × 1) structure, with one half of Bi adatoms in on-row sites. No Bi-induced surface states have been indicated along Γ – X, corresponding to the direction along furrows, which can explain only minor changes in the band structure and density of states in vicinity of E_F with increasing Bi coverage. On the contrary, changes in the band structure along Γ – Y turn out to be very significant. Specifically, the SOC-splitting band, associated with surface states generated by the Bi adlayer, moves upward and twice crosses E_F thus becoming a valence band. This feature may be important in the search for new layered structures for nano and spin-electronics.