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Despite the remarkable theoretical applications of silicene, its synthesis remains a complex task, with epitaxial growth being one of the main routes involving depositing evaporated Si atoms onto a suitable substrate. Additionally, the requirement for a substrate to maintain the silicene stability poses several difficulties in accurately determining the growth mechanisms and the resulting structures, leading to conflicting results in the literature. In this study, large-scale molecular dynamics simulations are performed to uncover the growth mechanisms and characteristics of epitaxially grown silicene sheets on Au(111) and Au(110) substrates, considering different temperatures and Si deposition rates. The growth process has been found to initiate with the nucleation of several independent islands homogeneously distributed on the substrate surface, which gradually merge to form a complete silicene sheet. The results consistently demonstrate the presence of a buckled silicene structure, although this characteristic is notably reduced when using an Au(111) substrate. Furthermore, the analysis also focuses on the quality and growth mode of the silicene sheets, considering the influence of temperature and deposition rate. The findings reveal a prevalence of the Frank–van der Merwe growth mode, along with diverse forms of defects throughout the sheets. [ABSTRACT FROM AUTHOR]

The nucleation and growth of single-layer molybdenum disulfide single-domain nanosheets is investigated by in situ low-energy electron microscopy. We study the growth of micrometer-sized flakes and the correlated flattening process of the gold surface for three different elevated temperatures. Furthermore, the influence of surface step edges on the molybdenum disulfide growth process is revealed. We show that both nanosheet and underlying terrace grow simultaneously by pushing the surface step in the expansion process. Our findings point to an optimized growth procedure allowing for step-free, single-domain, single-layer islands of several micrometers in size, which is likely transferable to other transition-metal dichalcogenides (TMDs), offering a very fine degree of control over the TMD nanosheet structure and thickness. [ABSTRACT FROM AUTHOR]

Light emission from the M-type enantiomer of a helicene derivative (2,13-bis(hydroxymethyl)[7]-thiaheterohelicene) adsorbed on the clean Au(111) and the C60-covered Au(111) surfaces were investigated by tunneling-current-induced light-emission technique. Plasmon-originated light emission was observed on the helicence/Au(111) surface and it was strongly suppressed on the area where the helicene molecules were adsorbed at the edges of the Au(111) terraces. To avoid luminescence quenching of excited helicene molecules and to suppress strong plasmon light emission from the Au(111) surface, C60 layers were used as decoupling buffer layers between helicene molecules and the Au(111) surface. Helicene molecules were adsorbed preferentially on the Au(111) surface rather than on the C60 buffer layers due to the small interaction of the molecules and C60 islands. This fact motivated us to deposit a multilayer of helicene molecules onto the C60 layers grown on the Au(111) surface, leading to the fact that the helicene/C60 multilayer showed strong luminescence with the molecules character. We consider that such strong light emission from the multilayer of helicene molecules has a plasmon origin strongly modulated by the molecular electronic states of (M)-[7]TH-diol molecules. [ABSTRACT FROM AUTHOR]

Template-assisted growth of ordered nanomaterials was used to prepare periodic copper phthalocyanine (CuPc) nanoparticles on the Au(111) substrate. The structures were studied by ultra-high vacuum scanning tunneling microscope (STM). At the first step, Fe atoms were deposited onto the reconstructed ( 22 × 3 ) Au(111) surface and they formed the array of triangular islands at the elbows of the herringbone reconstruction. High-purity CuPc molecules were subsequently evaporated to this prestructured surface at low coverages. CuPc molecules chose to adsorb at the edge of Fe islands and formed the flower-shaped ordered nanostructures. When the coverage reached ~ 1.0 monolayer, ordered CuPc nanoparticles situated on Fe islands with the self-assembled CuPc monolayer around. The method of template-assisted growth can be used to prepare other organic nanostructures which are stable at room temperatures. [ABSTRACT FROM AUTHOR]

Maintaining clean conditions for samples during all steps of preparation and investigation is important for scanning probe studies at the atomic or molecular level. For large or fragile organic molecules, where sublimation cannot be used, high-vacuum electrospray deposition is a good alternative. However, because this method requires the introduction into vacuum of the molecules from solution, clean conditions are more difficult to be maintained. Additionally, because the presence of solvent on the surface cannot be fully eliminated, one has to take care of its possible influence. Here, we compare the high-vacuum electrospray deposition method to thermal evaporation for the preparation of C60 on different surfaces and compare, for sub-monolayer coverages, the influence of the deposition method on the formation of molecular assemblies. Whereas the island location is the main difference for metal surfaces, we observe for alkali halide and metal oxide substrates that the high-vacuum electrospray method can yield single isolated molecules accompanied by surface modifications.

We report in this communication, through in situ STM images correlated with time, and ab initio simulations of binding energies, how potential-induced surface reconstruction is formed on Au(111) single crystal in 0.1 M H2SO4. It was found that while the electrode potential after lifting the reconstructed surface is switched back to a more negative value than the potential of zero charge, the formation process of the reconstructed surface goes through two consecutive routes. In the more kinetically favorable step, and within a few minutes, the reconstructed surface follows three different lattice directions with a high proportion of semi zig-zag structures. However, by maintaining the negative applied potential, the surface reconstruction rearranges to a straighter reconstructed pattern in the second step, which is more energetically favorable.

Electrolyte composition can have significant influences on metal deposition. In this work we employ in‐situ scanning tunneling microscope (STM), together with electrochemical methods to investigate Cu deposition on Au (111) in ethaline containing CuCl2. Cyclic voltammograms in the Cu overpotential deposition regime are dominated by a rapidly rising cathodic current, accompanied by a preceding shoulder. Instantaneous nucleation and three‐dimensional growth are discerned for the Cu deposition at larger overpotential. In‐situ STM reveals the shoulder process is associated with the formation of monoatomic‐height clusters. Meanwhile, morphology evolutions of Cu nuclei along with time and potential are followed, and layered hexagonal and hexagon fortress shaped Cu nuclei and their growth are directly observed. Furthermore, atomic‐resolution imaging elucidates an ordered incommensurate (6×√79) adsorption structure on the surface of a Cu nucleus. Our observations are helpful in gaining deeper insights into the effect of deep eutectic solvents (DES) on Cu deposition at microscopic level. [ABSTRACT FROM AUTHOR]

Magnesium-based secondary batteries have been regarded as a viable alternative to the immensely popular Li-ion systems owing to their high volumetric capacity. One of the largest challenges is the selection of Mg anode material since the insertion/extraction processes are kinetically slow because of the large ionic radius and high charge density of Mg2+ compared with Li+. In this work, we prepared very thin films of Sb by electrodeposition on a Au(111) substrate. Monolayer and multilayer deposition (up to 20 monolayers) were characterized by cyclic voltammetry (CV) and scanning tunneling microscopy (STM). Monolayer deposition results in a characteristic row structure; the monolayer is commensurate in one dimension, but not in the other. The row structure is to some extent maintained after deposition of further layers. After dissolution of the Sb multilayers the substrate is roughened on the atomic scale due to alloy formation, as demonstrated by CV and STM. Further multilayer deposition correspondingly leads to a rough deposit with protrusions of up to 3 nm. The cyclic voltammogram for Mg insertion/de-insertion from MgCl2/AlCl3/tetraglyme (MACC/TG) electrolyte into/from a Sb-modified electrode shows a positive shift (400 mV) of the onset potential of Mg deposition compared to that of a bare Au electrode. From the charge of the Mg deposition, we find that the ratio of Mg to Sb is 1:1, which is somewhat less than expected for the Mg3Sb2 alloy.

Light emission from the M-type enantiomer of a helicene derivative (2,13-bis(hydroxymethyl)[7]-thiaheterohelicene) adsorbed on the clean Au(111) and the C60-covered Au(111) surfaces were investigated by tunneling-current-induced light-emission technique. Plasmon-originated light emission was observed on the helicence/Au(111) surface and it was strongly suppressed on the area where the helicene molecules were adsorbed at the edges of the Au(111) terraces. To avoid luminescence quenching of excited helicene molecules and to suppress strong plasmon light emission from the Au(111) surface, C60 layers were used as decoupling buffer layers between helicene molecules and the Au(111) surface. Helicene molecules were adsorbed preferentially on the Au(111) surface rather than on the C60 buffer layers due to the small interaction of the molecules and C60 islands. This fact motivated us to deposit a multilayer of helicene molecules onto the C60 layers grown on the Au(111) surface, leading to the fact that the helicene/C60 multilayer showed strong luminescence with the molecules character. We consider that such strong light emission from the multilayer of helicene molecules has a plasmon origin strongly modulated by the molecular electronic states of (M)-[7]TH-diol molecules.

We investigate the possibility of functionalizing Au tips by N2O molecules deposited on a Au(111) surface and their further use for imaging with submolecular resolution. First, we characterize the adsorption of the N2O species on Au(111) by means of atomic force microscopy with CO-functionalized tips and density functional theory (DFT) simulations. Subsequently we devise a method of attaching a single N2O to a metal tip apex and benchmark its high-resolution imaging and spectroscopic capabilities using FePc molecules. Our results demonstrate the feasibility of high-resolution imaging. However, we find an inherent asymmetry of the N2O probe-particle adsorption on the tip apex, in contrast to a CO tip reference. These findings are consistent with DFT calculations of the N2O- and CO tip apexes.

In the present work, the adsorption configurations, electronic states and magnetism of Fe-Pc on Au(111) are investigated using first-principles calculations. We showed that the most favored configuration is the top site using the generalized gradient approximation method SGGA, whereas, it is the hcp position with the SGGA + U approach (in the presence of the Hubbard term U). An interesting and useful result obtained is that the magnetic moments do not change upon adsorption of the iron phthalocyanine molecule on the Au surface. The Fe-Pc/Au(111) system is an interesting and important system to realize the molecular electronic or spintronic devices. This study provides new original results and insightful discussions to update our understanding and stimulate our interests in this system as well as magnetic molecules at surfaces. [ABSTRACT FROM AUTHOR]

Self-assembled monolayers (SAMs) on metal surfaces have inspired many interesting applications, such as chemical and biological sensors, molecular electronics, magnetism and protective coatings. In this respect, SAMs having different head and tail groups have been synthesised which allow the modification of the material properties by tuning intermolecular, monolayer–metal and/or monolayer–solvent interactions. In this respect, we investigate the adsorption of thiols having aromatic, p-mercaptobenzonitrile (pPhCN) or aliphatic, 2-azidoethanthiol (N3S), tail groups on Au(111) surface by means of Density Functional Theory (DFT). Monomer and dimer adsorption configurations of both pPhCN and N3S molecules as well as the modification of the electronic structures upon adsorption are studied. Our results show that different adsorption mechanisms are observed for the molecules under consideration. While monomer and dimer structures of the pPhCN prefer to adsorb laterally on the surface, for N3S vertical arrangement of the molecules enhances the molecular immobilisation. Although, dominant contributions to the adsorption energy of the laterally adsorbed pPhCN are through S–Au chemical bond, phenyl ring–surface and cyano N–surface interactions, π–π stacking of the rings contributes to the stabilisation of the complex in addition to the S–Au chemical bond in the case of vertical attachment. For N3S, on the other hand, only S–Au chemical bond determines the adsorption strength. S–Au interactions result in broad molecular orbital redistribution of the S atoms of both molecules, due to the rehybridisation of S and Au states. Density of cyano-N and cyano-C states present in the pPhCN is affected by the orientation of the rings with respect to each other. In the case of 2N3S, instead, the distribution of the tail group molecular orbitals is not modified by the adsorption. [ABSTRACT FROM AUTHOR]

Chiral molecular self‐assemblies were usually achieved using short‐range intermolecular interactions, such as hydrogen‐, metal–organic, and covalent bonding. However, unavoidable surface defects, such as step edges, surface reconstructions, or site dislocations may limit the applicability of short‐range chirality recognition. Long‐range chirality recognition on surfaces would be an appealing but challenging strategy for chiral reservation across surface defects at long distances. Now, long‐range chirality recognition is presented between neighboring 3‐bromo‐naphthalen‐2‐ol (BNOL) stripes on an inert Au(111) surface across the herringbone reconstruction as investigated by STM and DFT calculations. The key to achieving such recognition is the herringbone reconstruction‐induced local dipole accumulation at the edges of the BNOL stripes. The neighboring stripes are then forced to adopt the same chirality to create the opposite edged dipoles and neutralize the neighbored dipole moments. [ABSTRACT FROM AUTHOR]

• Structural characterisation provides mechanistic details of on-surface reactions. • X-ray standing wave (XSW) analysis yields chemical and structural properties. • Self-metalation of a porphyrin on a gold surface is described in three steps. • Close-packed, diffuse, and metalated states are observed and characterised. [Display omitted] The study of surface-confined reactions provides a route towards characterising the mechanistic processes which underpin heterogeneous catalysis. On-surface reactions provide alternative pathways to solution phase synthesis, and can be studied by a range of techniques which can provide chemical and structural information. Importantly, these kinds of studies give us the insight required to potentially control the selectivity and efficiency of these reactions, as well as allowing for the design of molecular systems with specific functionalities. Porphyrin molecules are frequently selected as participants in these systems as they offer significant customisability, with respect to the reactivity of pendant groups and metal atoms which can be incorporated within the porphyrin macrocycle. Utilising the normal incidence X-ray standing wave (NIXSW) technique in conjunction with scanning probe methods and X-ray photoelectron spectroscopy (XPS) enables the generation of detailed models of on-surface systems, including the adsorption geometries of individual molecules. Here the NIXSW technique has been used to perform structural characterisation of three distinct phases of an on-surface reaction of tetraphenyl porphyrin (TPP) on Au(111); close-packed, diffuse and metalated. Using the chemical specificity of XPS and NIXSW we gain insight into chemical and structural changes exhibited by nitrogen atoms within the porphyrin macrocycle at several stages within the reaction process. [ABSTRACT FROM AUTHOR]

We performed a study on the fundamental adsorption characteristics of Er3N@C80 deposited on W(110) and Au(111) via room temperature scanning tunneling microscopy and spectroscopy. Adsorbed on W(110), a comparatively strong bond to the endohedral fullerenes inhibited the formation of ordered monolayer islands. In contrast, the Au(111)-surface provides a sufficiently high mobility for the molecules to arrange in monolayer islands after annealing. Interestingly, the fullerenes modify the herringbone reconstruction indicating that the molecule–substrate interaction is of considerable extent. Investigations concerning the electronic structure of Er3N@C80/Au(111) reveals spatial variations dependent on the termination of the Au(111) at the interface.

Cesium oxide (CsO x ) nanostructures grown on Au(111) behave as active centers for the CO 2 binding and hydrogenation reactions. The morphology and reactivity of these CsO x systems were investigated as a function of alkali coverage using scanning tunneling microscopy (STM), ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and density functional theory (DFT) calculations. STM results show that initially (0.05-0.10 ML) cesium oxide clusters (Cs 2 O 2 ) grow at the elbow sites of the herringbone of Au(111), subsequently transforming into two-dimensional islands with increasing cesium coverage (>0.15 ML). XPS measurements reveal the presence of suboxidic (Cs y O; y ≥ 2) species for the island structures. The higher coverages of cesium oxide nanostructures contain a lower O/Cs ratio, resulting in a stronger binding of CO 2 . Moreover, the O atoms in the Cs y O structure undergo a rearrangement upon the adsorption of CO 2 which is a reversible phenomenon. Under CO 2 hydrogenation conditions, the small Cs 2 O 2 clusters are hydroxylated, thereby preventing the adsorption of CO 2 . However, the hydroxylation of the higher coverages of Cs y O did not prevent CO 2 adsorption, and adsorbed CO 2 transformed to HCOO species that eventually yield HCOOH. DFT calculations further confirm that the dissociated H 2 attacks the C in the adsorbate to produce formate, which is both thermodynamically and kinetically favored during the CO 2 reaction with hydroxylated Cs y O. These results demonstrate that cesium oxide by itself is an excellent catalyst for CO 2 hydrogenation that could produce formate, an important intermediate for the generation of value-added species. The role of the alkali oxide nanostructures as active centers, not merely as promoters, may have broad implications, wherein the alkali oxides can be considered in the design of materials tuned for specific applications in heterogeneous catalysis.

The adsorption of methylviologen dications (MV2+) on single‐crystalline Au electrodes in both H2SO4 and HClO4 was examined. MV2+ strongly interacted with sulfate and bisulfate anions adsorbed on the Au(111) electrode surface in 0.05 M H2SO4 under a controlled potential of 1.25 V vs. the reversible hydrogen electrode (RHE). A characteristic non‐Faradaic current was observed at 1.10 V vs. RHE. When adsorption of MV2+ was carried out in 0.1 M HClO4, the electrochemical response of MV2+ was less than that obtained in H2SO4. The results show that the formation of a highly ordered sulfate/bisulfate adlayer plays an important role in the formation of condensed MV2+ layers. Examination of polycrystalline Au and Au(100) electrodes revealed a poor electrochemical response due to the surface roughness of the Au substrate, but the electrochemical detection was applicable to polycrystalline Au electrodes. A systematic investigation of the structural dependency of viologen derivatives showed that molecular size is important for electrostatic interactions with a highly ordered sulfate/bisulfate adlayer. The findings of the present study demonstrate successful detection of MV2+ at a concentration of ≤1 pM with a non‐Faradaic current. [ABSTRACT FROM AUTHOR]

• Revealing the electronic structure evolution of self-assembled DBBA on A u (111) and B i - 3 × 3 - A u (111). • Showing structural difference of DBBA on A u (111) and B i - 3 × 3 - A u (111) at molecule level. • Explaining why 7-GNRs could not be formed on B i - 3 × 3 - A u (111). Atomically precise graphene nanoribbons (GNRs) can be on-surface synthesized from halogen containing molecular precursors. Here, we investigated the electronic structure evolution of 10,10′-dibromo-9,9′-bianthracene (DBBA), a famous precursor to 7-AGNRs, on both A u (111) and B i - 3 × 3 - A u (111) as a function of film thickness and post-annealing temperature using photoemission spectroscopy, low temperature scanning tunneling microscopy and density functional theories. No obvious changes in electronic structure of DBBA in three STM-observed configurations can be detected, indicating that nonplanar π -conjugated DBBA is physisorbed on both surfaces. The energy level alignments at the DBBA-substrate interfaces are demonstrated. Bismuth(Bi) insertion layer makes molecular−substrate interaction weaker, and makes the energy levels of DBBA thin film rigidly shift by ˜0.70 eV away from Fermi level, which enlarges the hole injection barrier and results in DBBA desorption at ˜470 K before dehalogenation occuring. The surface work function reduction can be explained by the push back effect and charge transfer induced interface dipole. Our findings explain why 7-GNRs could not be formed on B i - 3 × 3 - A u (111). [ABSTRACT FROM AUTHOR]

Highlights • Dehydrogenation of n -alkane follows different pathways on Au(111) and Pt(111). • CH and CC bond rupture readily occurs on Pt(111). • Aliphatic or non-aromatic unsaturated bonds are generated on Au(111). • GQDs are obtained on Pt(111) and GNRs are formed on Au(111). Abstract Thermal dehydrogenation of long n -alkane on Au(111) and Pt(111) surfaces is investigated by near the carbon K-edge X-ray absorption fine structure spectroscopy (C K-NEXAFS) and scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV). On Au(111), dehydrogenation and formation of unsaturated bonds start at temperatures above 480 K, ending at 650 K. This is confirmed by the decrease in the 1 s → σ* CH /R resonance (σ* CH /R resonance) and the evolution of the π* CC resonance in the C K-NEXAFS spectra. The aliphatic or non-aromatic unsaturated bonds are generated at the early stage of the dehydrogenation on the Au(111), which is examined by the reaction with bromine. The dual peaks of the π* CC resonance at 284–286 eV suggest the formation of polycyclic aromatic hydrocarbons (PAHs). These PAHs exhibit a ribbon or rosary and planer shape by heating at 800 K, which is observed by the STM. In contrast, dehydrogenation begins at RT on Pt(111), and is almost completed at 480 K. π* CC resonance exhibits a main peak at 286 eV, which corresponds to a graphene skeleton, with a sub peak or a shoulder at 284.6 eV, which is attributed to a carbon atom at an edge or defect. The main peak intensity increases as the temperature is raised up to 820 K. STM images obtained after heating at 820 K show nanodots having a diameter of ca. 2–3 nm. The final products upon heating to 1000 K on Pt(111) are graphene nanoflakes with a size of tens of nanometers. The difference between the products is related to the difference between the reaction pathways on Au(111) and Pt(111) surfaces. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • Temperature programmed desorption shows that the exchange of hydrogen and deuterium occurs below 200 K on Au(111). • The exchange of hydrogen and deuterium between ethanol and water molecules occurs without the presence of a reactive surface species or reactive substrate. • Isotopic studies show that the exchange occurs between both ethanol/deuterated water and ethanol–OD/water adsorbates on Au(111). • The formation of ethanol/water hydrogen–bonded networks on Au(111) is expected to facilitate the concerted motion of hydrogen/deuterium atoms at low temperatures. Abstract Proton transfer and hydrogen-bonding networks are critical in biochemical processes including protein folding and protein–protein interactions. Surface science can simplify these complex systems by studying the exchange of hydrogen and deuterium atoms between molecules supported on surfaces. Temperature programmed desorption (TPD) was used to show that the exchange of hydrogen and deuterium between co–adsorbed isotopologues of ethanol and water occurs readily at temperatures below 200 K on Au(111). Since Au(111) is an inert substrate that does not cause dissociation of water or ethanol at any temperature, the results herein suggest that Au(111) acts as a support to facilitate H/D exchange via hydrogen-bonded networks of molecular ethanol and water at low temperatures. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • At coverage less than 1 ML, Bi atoms self-assemble into the cluster array with (5 × 5) periodicity, (37 × 37) R 25. 3 ∘ in a Kagome lattice and (p × 3) stripes, sequentially. • The (5 × 5) periodicity is a low temperature (< 100 K) phase and behavior as gas at room temperature. • The results reveal the Van der Waals interaction between Au(111) and Bi adatoms. • We have optimized the small window for a stable 2D Bi in Kagome and honeycomb lattice on Au(111). Abstract Atomically thin Bismuth (Bi) films are predicated to be candidates for high temperature quantum spin hall materials. Here, we reported the structural evolutions and the corresponding electronic properties of Bi ultrathin films on Au(111) at initial stage as a function of coverage using low-energy electron diffraction (LEED), scanning tunneling microscopy (STM) and photoemission spectroscopy (PES). The small window for a stable two dimensional (2D) Bi in Kagome and honeycomb lattice on Au(111) has been optimized. LEED and STM results show that Bi atoms self-assemble into dimered (5 × 5) superdots, (37 × 37) R 25. 3 ∘ in a Kagome lattice and (p × √3) stripes sequentially in the first monolayer regime and into bi-layered Bi (110) islands afterwards. UPS results show the disappearance of Au(111) surface states at coverage of 0.18 ML, revealing the Van der Waals interactions between Au(111) and Bi adatoms. The repulsive interactions between Bi atoms prevent the 2D Bi structure from islands forming at initial stage and benefit large domains in (37 × 37) R 25. 3 ∘ Kagome lattice. Such 2D Bi may be interesting because of its relevance in terms of novel physical properties. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • The effects of substrate temperature, the flux of Ce atoms and the annealing temperature were studied for the growth of CeO x nanostructures on Au(111). • Well-defined CeO x nanostructures with monolayer or bilayer thickness could be controlled to grow on Au(111). • Surface and sub-surface O vacancies on CeO x nanostructures were identified by element-specific STM images. Abstract The construction of well-defined CeO x /Au(111) model catalysts is key to the understanding of ceria-based catalysts or the Au–CeO x interface in catalytic reactions. Conventionally, owing to the Volmer–Weber growth of ceria on Au(111), ceria nanostructures with controlled layer thickness and well-defined structure have been difficult to grow on Au(111). We explored the influence of growth parameters, such as the substrate temperature for ceria deposition, the flux of Ce atoms and the annealing temperature in this study. We found that ceria prefers to form bilayer nanostructures, i.e. two O Ce–O layers, over a large range of growth conditions, whereas monolayer ceria nanostructures could also be obtained on Au(111) with the careful control of growth kinetics. Upon the growth of these well-defined ceria nanostructures, element-specific STM images could also be achieved on their surfaces, which allow the identification of surface and sub-surface O vacancies on ceria. The construction and atomic-scale characterization of these CeO x /Au(111) model catalysts would facilitate the subsequent studies on their surface chemistry and aid our understanding on the catalysis by ceria nanostructures. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The facets of gold nanoparticle show different affinities for adsorption of DNA bases. • The Au(110) surface has the highest absorption affinity compared to the other facets. • Adsorption geometry of the CYT and ADE depend on the kind of facet of nanoparticle. • Charge transfer between nanoparticle and bases depends on the kind of facet. Abstract In this work, the adsorption activities of different facets of a spherical gold nanoparticle (Au(111), Au(100) and Au(110)) for adenine (ADE) and cytosine (CYT) in two different environments including gas phase and in the presence of solvent (water) have been investigated, separately. It has been found that the adsorption energy (E ad) and geometry of the DNA bases depend strongly on the kind of nanoparticle facet. The Au (110) facet showed the highest adsorption affinity for the ADE and CYT in both gas phase and water compared to Au(111) and Au(100) facets. Comparison of the E ads of bases calculated in the gas phase with those obtained in the presence of water showed that the electrostatic field of solvent decreases the E ads of bases, especially, for the Au (110) facet. The adsorption geometry of the CYT showed strong dependency on the kind of nanoparticle facet compared to ADE. Also, it has been shown that the direction and amount of charge transfer (CT) between the molecule and nanoparticle strongly depends on the kind of nanoparticle facet and environment. The CT is from the Au (111) facet to the ADE while the CT direction is reversed when the ADE is adsorbed on the Au (110) and Au (100) facets in the gas phase. The CT is from the CYT to three facets in the gas phase while its direction for the ADE and CYT adsorbed on Au (100) facet is reversed. The atoms in molecules (AIM) analysis has been employed to determine the bond paths (BPs) and bond critical points (BCPs) between the bases and facets. The infrared (IR) spectra of the bases adsorbed on the selected facets were calculated and compared with each other and with the spectra of the isolated bases. It was found that the symmetric and unsymmetric stretching of the N H of NH 2 group, C–H stretching of the rings and C O stretching of bases can be used for the discrimination of the selected facets. [ABSTRACT FROM AUTHOR]

Highlights • Thermally induced on-surface reactions of 2,3-dibromoanthracene molecules result in different product distributions on Au(100) and Au(111) surfaces, respectively. • Formation of dimers and trimers on Au(111) with segregation into different molecular islands while only linear dimers are formed on Au(100). • Cycloaddition reaction mode (periselectivity) can be controlled by the choice of the substrate as the [2+2+2] cycloaddition reaction is suppressed in Au(100). • Au(100) corrugation supports parallel alignment of the precursor molecules, thereby suppressing trimer formation that require a non-parallel molecular arrangement. Abstract The on-surface reaction of 2,3-dibromoanthracene molecules is studied on two surfaces, Au(100) and Au(111) that differ in their surface reconstructions and thus atomic-scale structure. After deposition intact molecules are observed, which form highly ordered close-packed islands, with preferential adsorption along the corrugation rows of the substrate in the case of Au(100). Heating the sample at 520 K induced Br dissociation and on-surface oligomerization of the thus activated anthracene moieties. While dimers and trimers are formed on Au(111) where they segregate into different molecular islands, only dimers are generated on Au(100). Hence, the reaction mode can be controlled on Au(100) which clearly favors the [2+2]cycloaddition product whereas the [2+2+2] cycloaddition reaction is suppressed. This high selectivity for forming the linear dimer seems to be caused by the adsorption geometry on the reconstructed Au(100) surface. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • The charge state of anticancer-active gold-porphyrin molecules is switched by STM manipulation. • We have chemically reduced as-deposited molecules into two different charge configurations. • Conductance mapping reveals the different distribution of the added electron either at the center gold ion or at the porphyrin macrocycle. Graphical abstract Abstract Electron transfer in weakly coupled molecules typically occurs via a transient charging of the molecule by tunneling electrons. We report on the permanent electron injection into a single molecule in a controlled manner by employing low-temperature (LT) scanning tunneling microscopy (STM). Our model system is Au(III) 5,10,15,20-tetraphenylporphyrin (AuTPP) single molecules physisorbed on a single-crystal Au(111) surface. The results of our combined topographic STM images, tunnel conductance d I /d V spectra and two-dimensional spatial d I /d V mapping experiments support a switching of the molecular charge state of AuIIITPP on Au(111) induced by STM manipulation. We successfully realized STM tip-induced chemical reduction reactions in single AuTPP molecules, reducing AuIIITPP to AuIITPP, with the extra electron distributed either preferentially in a 5d state of the center gold ion or the aromatic (pi-conjugated) tetrapyrrole macrocycle of the porphyrin ligand. Details of the electron transfer process were identified and visualized with intra-molecular resolution by single-molecule tunneling spectroscopy and orbital mapping. [ABSTRACT FROM AUTHOR]

Highlights • Stacking of MoS 2 islands onto Au(111) lattice is unique, and, hence, its growth mode. • MoS 2 on Au(111) exhibits a state in the band gap at Γ, which does not occur on freestanding or weakly bound MoS 2. • The MoS 2 moiré electronic structure is sensitive to the local atomic stacking configuration of the MoS 2 layer on Au(111). Graphical abstract Abstract Monolayer islands of molybdenum disulfide (MoS 2) on Au(111) form a characteristic moiré structure, leading to locally different stacking sequences at the S-Mo-S-Au interface. Using low-temperature scanning tunneling microscopy (STM) and atomic force microscopy (AFM), we find that the moiré islands exhibit a unique orientation with respect to the Au crystal structure. This indicates a clear preference of MoS 2 growth in a regular stacking fashion. We further probe the influence of the local atomic structure on the electronic properties. Differential conductance spectra show pronounced features of the valence band and conduction band, some of which undergo significant shifts depending on the local atomic structure. We also determine the tunneling decay constant as a function of the bias voltage by a height-modulated spectroscopy method. This allows for an increased sensitivity of states with non-negligible parallel momentum k ∥ and the identification of the origin of the states from different areas in the Brillouin zone. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) cuprous oxide (Cu2O) nanostructures (NSs) of monolayer thickness were synthesized on Au(111) and characterized using atomic-resolution scanning tunneling microscopy, X-ray photoelectron spectroscopy, and density functional theory (DFT) calculations. The surface and edge structures of 2D Cu2O were resolved at the atomic level and found to exhibit a graphene-like lattice structure. Cu2O NSs grew preferentially at the face centered cubic (fcc) domains of Au(111). Depending on the annealing temperature, the shapes and structures of Cu2O NSs were found to vary from elongated islands with a defective hexagonal lattice (mostly topological 5-7 defects) to triangular NSs with an almost-perfect hexagonal lattice. The edge structures of Cu2O NSs also varied with the annealing temperature, from predominantly the arm-chair 56 structure at 400 K to almost exclusively the zig-zag structure at 600 K. DFT calculations suggested that the herringbone ridges of Au(111) confined the growth and structure of Cu2O NSs on Au(111). As such, the arm-chair edges of Cu2O NSs, which are less stable than the zig-zag edges, could be exposed preferentially at 400 K. Cu2O NSs developed into the thermodynamically-favored triangular form and exposed zig-zag edges at 600 K, when the Au(111) substrate became mobile. The confined growth of 2D cuprous oxide on Au(111) demonstrated the importance of metal-oxide interactions in tuning the structures of supported 2D oxide NSs. [ABSTRACT FROM AUTHOR]

Synthetic materials and heterostructures obtained by the controlled stacking of exfoliated monolayers are emerging as attractive functional materials owing to their highly tunable properties. We present a detailed scanning tunneling microscopy and spectroscopy study of single layer MoS 2 -on-gold heterostructures as a function of the twist angle. We find that their electronic properties are determined by the hybridization of the constituent layers and are modulated at the moiré period. The hybridization depends on the layer alignment, and the modulation amplitude vanishes with increasing twist angle. We explain our observations in terms of a hybridization between the nearest sulfur and gold atoms, which becomes spatially more homogeneous and weaker as the moiré periodicity decreases with increasing twist angle, unveiling the possibility of tunable hybridization of electronic states via twist angle engineering.

The adsorption of the sterically hindered β-diketonate complex Fe(dpm)3, where Hdpm = dipivaloylmethane, on Au(111) was investigated by ultraviolet photoelectron spectroscopy (UPS) and scanning tunnelling microscopy (STM). The high volatility of the molecule limited the growth of the film to a few monolayers. While UPS evidenced the presence of the β-diketonate ligands on the surface, the integrity of the molecule on the surface could not be assessed. The low temperature STM images were more informative and at submonolayer coverage they showed the presence of regular domains characterized by a flat morphology and height of ≈0.3 nm. Along with these domains, tetra-lobed features adsorbed on the kinks of the herringbone were also observed. DFT-simulated images of the pristine molecule and its possible decomposition products allowed to assess the partial fragmentation of Fe(dpm)3 upon adsorption on the Au(111) surface. Structural features with intact molecules were only observed for the saturation coverage. An ex situ prepared thick film of the complex was also investigated by X-ray magnetic circular dichroism (XMCD) and features typical of high-spin iron(III) in octahedral environment were observed.

Inspired by the recent e xperimental results that the oxygen atoms adsorbed on Au(111) surface have a great influence on the mechanism and path of the decomposition of acetate( ACS Catal , 2014, 4(9): 3281−3288), the density functional theory was performed to simulate the decomposition of acetate on Au(111) surface with and without oxygen atom. The present calculation resents show that the pre-adsorbed oxygen atoms on Au(111) surface can activate the γ -CH bond of acetate and reduce the activation energy of the reaction, then finally get the product of carbon dioxide and formaldehyde. While without adsorbed oxygen atoms, acetate on Au(111) surface breaks down into carbon dioxide and methyl through C-C bond cleavage. In addition, the decomposition of acetate on Ag(111) surface with pre-adsorbed oxygen atoms has also been simulated and that of Au(111), and it was found that the oxygen atoms on Ag(111) assist γ-CH bond activation more efficiently due to its more negatively charged. The present study highlights the importance of oxygen-assisted γ- CH bond activation for oxygen-containing molecular on Au(111) and provide a new route for the synthesis of ester. [ABSTRACT FROM AUTHOR]

By in-situ low temperature scanning tunneling microscopy, we systematically investigated the superstructure evolution at Te/Au(111) interface upon increasing Te coverage. Te atoms form one-dimensional 3 R 30 ∘ chains at ∼0.10 monolayer (ML) coverage. Two two-dimensional chiral superstructures, ( 111 × 111 ) R 4 . 7 ∘ and ( 3 21 × 3 21 ) R 10 . 9 ∘ , are selectively formed with the Te coverage below and above 1/3 ML, respectively. The two chiral superstructures can be converted to each other reversibly by adding Te atoms or moderately annealing. A honeycomb-like superstructure, decorated with adatoms that are distributed in quasi-one-dimensional chains, is observed by further increasing the Te coverage to 4/9 ML. At the Te/Au(111) interface, an interfacial state at −0.65 eV to −0.55 eV below the Fermi level is also resolved by scanning tunneling spectroscopy. The formation of these Te-induced high-order superstructures is accompanied by relaxation of gold atoms in the surface layer, indicating a strong Te–Au interaction. Our work demonstrates a reliable method to fabricate Te nanostructures on noble metals in a controlled way. [ABSTRACT FROM AUTHOR]

The sulfur adsorption on gold surface is a hot topic in catalysis, electrochemistry and chemical sensors. However, the multiple structures of adsorbed sulfur and sulfur-induced reconstruction in gold substrate topography are still open problems until now. Here we performed an extensively study on sulfur adsorption on Au(111) surface based on First-Principles calculation. Our results show that the sulfur adsorption with additional Au atoms is not favorable. Thus, the well-known lifting of the herringbone reconstruction of Au(111) after sulfur adsorption can't be attributed to the lifting gold atoms. More importantly, we proposed an extremely stable configuration of S–Au(111) surface characterized by (√3 × √3)R30° at 0.33 coverage, in which each S atom is chemisorbed in 3-fold coordinated sites and all the surface-Au atoms are terminated. Finally, the good agreement between our simulated STM and LEED images and experimental observations illuminates the truth that our proposed configuration is also favorable in experiment. This super stable S-adsorbed surface can be used as a starting point for the growth of two dimensional transition metal sulfides. An extremely stable configuration for the sulfur adsorption on Au(111) surface. [Display omitted] • The herringbone reconstruction of Au(111) is not attributed to the lifting gold atoms. • An extremely stable S-adsorbed Au(111) surface characterized by (√3 × √3)R30° is proposed. • Our proposed configuration is also favorable in experiment. [ABSTRACT FROM AUTHOR]

The formation of a binary porphyrinic self-assembled system between meso-tetrakis(4-carboxyphenyl) porphyrin (TCPP) and meso-tetrakis(4-dimethyl amino) porphyrin (TDAP) was easily designed through non-covalent interactions in solution and adsorbed on a gold substrate. It was found that non-covalent interactions and geometrical conformations between porphyrins allow their self-assembly into a well-defined arrangement, which was confirmed by UV-Vis spectroscopy, electrochemistry, atomic force microscopy and density functional theory (DFT) studies.

In-situ electrochemical SERS observation was conducted at Ru/Pt alloyed overlayers formed on Au substrates with and without surface roughness. When the overlayer was formed on an electrochemically roughened Au substrate having SERS activity, spectral features of molecular adsorbates were significantly influenced by structural and compositional inhomogeneity of the surface, resulting in low spectral reproducibility under electrochemical conditions. On the other hand, when the overlayer was formed on an atomically defined Au(111), highly reproducible SERS spectra were obtained with the assistance of SERS-active sphere-plane type nano-gap structures. Application of electrochemical potentials clearly induced spectral variations such as electrochemical Stark shift of the internal molecular vibrations or appearance of molecule-to-metal charge transfer-induced Raman bands. The use of well-defined interfaces in SERS observation enabled us to obtain information on electron-vibration coupling at metal-molecule interfaces as well as vibrational information on molecular adsorption geometry. [ABSTRACT FROM AUTHOR]

The adsorption and reactivity of cyanate at Au(111) single crystal and Au(111)-25 nm thin film electrodes is studied spectroelectrochemically in sodium perchlorate solutions and compared to those of cyanuric acid (C 3 N 3 O 3 H 3 ). From the Surface Enhanced Infrared Reflection Absorption spectra obtained under Attenuated Total Reflection conditions (ATR-SEIRAS) it can be concluded that adsorbed cyanate species predominate at the electrode surface for low cyanate concentrations. However, for cyanate concentrations above 1 mM, the similarity of the ATR-SEIRA spectra with those obtained in cyanuric acid containing solutions indicates that some species coming from cyanuric acid is formed and adsorbed at the (111) gold surface sites as the result of an electroless trimerization reaction. Taking into account the results of Density Functional Theory (DFT) calculations, the experimental voltammetric and ATR-SEIRAS results agree with the formation of adlayers of specifically adsorbed triketo-monocyanurate species that adsorb perpendicular to the electrode surface. [ABSTRACT FROM AUTHOR]

The oxidation of hydroxyurea (H 2 NCONHOH, HU) at Au(100), Au(111) and Au(111)–25 nm thin film electrodes is studied spectroelectrochemically in perchloric acid solutions. HU, which in agreement with DFT results interacts weakly with the gold surfaces, oxidizes irreversibly at gold electrodes irrespective of the surface orientation. The in situ infrared external reflection spectra prove the formation of dissolved carbon dioxide and adsorbed cyanate as products of the HU electrooxidation reaction. A band at ca. 2230 cm −1 can be related both to dissolved isocyanic acid coming from the protonation of adsorbed cyanate or to nitrous oxide coming from the oxidation of hydroxylamine, which is formed (together with adsorbed cyanate) upon the chemical decomposition of hydroxyurea. ATR-SEIRAS experiments allow the observation of other adsorbate bands that can be tentatively ascribed to reaction intermediates that conserve the NCN skeleton and are bonded to the metal by the nitrogen atoms at near on-top positions. Bonding to the surface can be either unidentate or bidentate, involving covalent-type bonds or dative bonding through the lone pairs of the N atoms. Some of the signals of the experimental spectra, in particular those appearing around 1800 cm −1 , can be assigned to the CO stretch of adsorbed intermediates having a nitrosyl group formed by oxidation of the NOH moiety (namely, adsorbed nitrosoformamide or its deprotonated form). The bands observed around 1650 cm −1 can correspond either to the NO stretching mode of the former species or to the CO stretching modes of adspecies conserving the NOH group. [ABSTRACT FROM AUTHOR]

The adsorption of cyanate anions at Au(111) and Au(100) single crystal electrodes has been studied spectroelectrochemically in neutral solutions. Potential-dependent in situ InfraRed Reflection Absorption spectra obtained below the onset of cyanate oxidation were compared with previously published data and analyzed on the basis of periodical Density Functional Theory (DFT) calculations. The calculated adsorption energies for cyanate and related species suggest that cyanic and isocyanic acid adsorb weakly at the studied gold surfaces and, thus, seems not to be at the origin of any of the adsorbate bands in the experimental infrared spectra collected in the cyanate-containing solutions. The latter features can be clearly ascribed to the asymmetric OCN stretching of N-bonded cyanate species. The observation of absorption bands in a wide spectral region, including features above 2200 cm − 1 , agrees with the coexistence of N-bonded cyanate species with different adsorption sites and tilting angles. DFT calculations have revealed that although these adspecies can have significantly different frequencies, their adsorption energies are rather close. In addition, the existence of collective in-phase vibrations at relatively high cyanate coverages also contributes to the widening of the absorption bands. [ABSTRACT FROM AUTHOR]

In this work, the adsorption of the adenine (AD) and cytosine (CY) on the Au(111) nano surface (AD@Au and CY@Au) have been examined in the framework of combined quantum mechanics/molecular mechanics (QM/MM) methodology using two-layer ONIOM method and different density functional theory (DFT) functionals in the absence of periodic boundary conditions (PBC). It was found by selecting an appropriate size for the Au surface, the results obtained using QM/MM method were in good agreement with those obtained via the periodic DFT calculations with the same functional. The calculated adsorption energies ( E ad ) using M06-2X and M06-L functional were in good agreement with those, recently, obtained using periodic DFT calculations considering PBC and employing van der Waals (vdW) DFT functionals. The correlation diagram between the molecular orbitals of isolated deformed AD (AD-D) and CY (CY-D) and their molecular orbitals in AD@Au and CY@Au systems have also been investigated in this work. [ABSTRACT FROM AUTHOR]

The oxidation of hydroxyurea (H 2 NCONHOH, HU) at Au(111) single crystal and Au(111)-25 nm thin film electrodes is studied spectroelectrochemically in HClO 4 solutions using external reflection infrared and Surface Enhanced Infrared Reflection Absorption Spectroscopy under Attenuated Total Reflection conditions (ATR-SEIRAS). The in situ external reflection spectra prove the formation of dissolved carbon dioxide and adsorbed cyanate during the electrooxidation of HU. The enhanced surface sensitivity of the ATR-SEIRAS experiments facilitates the detection of adsorbed cyanate and allows the observation of other adsorbate bands tentatively ascribed to reaction intermediates involving partial oxidation of the HU molecules, some of them corresponding to nitrosyl groups. [ABSTRACT FROM AUTHOR]

We report the formation of cyanuric acid species at Au(111) electrodes in cyanate-containing solutions, due to the electroless trimerization of isocyanic acid. Similar experimental bands in the range between 1300 and 1900 cm − 1 are observed in Surface Enhanced Infrared Reflection Spectroscopy experiments under Attenuated Total Reflection conditions (ATR-SEIRAS) with solutions containing either cyanate anions at high concentration or cyanuric acid. The experimental frequencies agree well with those obtained from Density Functional Theory (DFT) calculations for the adsorbed cyanurate anion, bonded to the metal in a tridentate configuration, with its molecular plane perpendicular to the metal surface. [ABSTRACT FROM AUTHOR]