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Monolayer transition metal dichalcogenide VTe2exhibits multiple charge density wave (CDW) phases, mainly (4 × 4) and (4 × 1). Here we report facile dynamic and tens-of-nanometer scale switching between these CDW phases with gentle bias pulses in scanning tunneling microscopy. Bias pulses purposely stimulate a reversible random CDW symmetry change between the isotropic (4 × 4) and anisotropic (4 × 1) CDWs, as well as CDW phase slips and rotation. The switching threshold of ∼1.0 V is independent of bias polarity, and the switching rate varies linearly with the tunneling current. Density functional theory calculations indicate that a coherent CDW phase switching incurs an energy barrier of ∼2.0–3.0 eV per (4 × 4) unit cell. While there is a challenge in understanding the observed large-area CDW random fluttering, we provide some possible explanations. The ability to manipulate electronic CDW phases sheds new light on tailoring CDW properties on demand.

In this study, we found that the local density of states and ionization energy spectrum of the valence electrons of methylnitrene (NCH3) adsorbed on Cu(110) can be calculated from molecular orbital calculations of a simple artificial isolated NCH3–Cu2molecular cluster in which the two Cu atoms form bonds to the N atom. Such a NCH3–Cu2cluster represents the basic structural unit of a NCH3molecule adsorbing on a Cu double-added-row structure. This finite NCH3–Cu2cluster structure is not optimized as a single system but is extracted directly from an optimized surface structure obtained by density functional theory with periodic boundary conditions. With this approach, we obtained excellent agreement between the measured ultraviolet photoemission spectra (UPS) and the theoretical calculation results. To further examine this minimal cluster concept, we analyzed methoxy (OCH3) adsorption on Cu(110) and found a OCH3–Cu3cluster structure. On the basis of this structure, we calculated UPS and also obtained substantial agreement with the experimental UPS. These results may indicate that, when substrate adatoms bridge the adsorption of a molecule and a surface, a small cluster consisting of the adsorbate and the neighboring bonding substrate adatoms suffices to describe the electronic structure of the valence electrons of the adsorbates.

In this study, we used scanning tunneling microscopy (STM) and density functional theory (DFT) to examine the bonding structure of CH3N adsorbed on the Cu(110) surface. A previous study [Chin. J. Phys.2005, 43, 212–218] shows the adsorbed CH3N aggregate to form a zigzag structure with a p(2 × 3) unit cell, without considering the possibility of adsorbate-induced surface reconstruction. Here, we propose a revised adsorption structure, with the key feature of bonding each CH3N with two Cu adatoms in a tetrahedral manner. Three structure models (double-row, dimer, and alternative-dimer) are examined by ab initio calculations. We find that the most energetically favorable model is the double-row model with CH3N bonding alternatingly along either side of double added rows from Cu adatoms.

We present the density functional calculations for the adsorption of a single platinum (Pt) atom on the 2-fold bridged-oxygen (Ob) covered graphene (graphene oxide, GO). We found the incoming Pt at low kinetic energies prefers to interact with only one Oband the reaction weakens the coupling of the Obwith the underlying two carbon atoms to give rise to an upward tilted Pt–Oaconfiguration with the Oasingly connected to one of the underlying carbon (C1L) and leaving a semifilled and lone-paired orbital on the other carbon (C*). The highly reactive and long-lived C* plays an important role determining the energy barriers and branching nature of the subsequent reaction pathways. By being long-lived, reactions of the C* spilt into the early- and late-C* pathways depending when the long-lived C* is participated in the reaction. The early-C* pathways involve direct reactions of the C* with either the Pt or the neighboring carbons with low energy barriers (Ea< 0.3 eV) and give rise to stable local minimum states. In contrast, the C* in the late-C* pathways remains a radical such that the product states are less stable and the reactions that follows can again split into the early- and late-C* manifolds. This bifurcation stops when the C* quenches. To our surprise, we found the C*, via a rehybridization from sp3to sp2with Ea= 0.23 eV, can attack the C1Lthat is singly connected to the Pt–Oaon the Oaend to give rise to the ejection of the Pt–O molecule from the GO surface. This self-cleaning mechanism indicates that a molecule chemisorbed on the carbon-based surface can be removed with an Eaapproximately equal to that for the sp3-to-sp2rehybridization of the carbon lattice.

The clean-off reaction of AgO added rows by CO on Ag(110) and Au/Ag(110) bimetallic surfaces was studied by scanning tunneling microscopy (STM) and compared with density functional theory (DFT). This combined study of a model system illustrated the complexity of catalytic enhancement in bimetallic systems. By analyzing in situ time-lapsed STM image series, we found that CO oxidation on a Au-enriched Ag(110) surface leads to an exponential depletion of oxygen with time and a reaction rate that is synergistically enhanced by the presence of Au. First principles calculations indicate that the local atomic configuration around the active reaction sites at the chain ends and the preference of Au atom substitution into the subsurface second Ag layer are of critical importance. By calculating CO adsorption energies and reaction barriers for plausible reaction pathways, a detailed description of the CO oxidation reaction emerges. For the optimal reaction pathway, a large (∼0.09 eV) barrier reduction and a small barrier of ∼0.01 eV were found for the Eley−Rideal (ER) mechanism. In contrast, a small (∼0.03 eV) barrier reduction and a moderate barrier of ∼0.23 eV were obtained for the Langmuir−Hinshelwood (LH) mechanism. The ER transitional state was also found to be lower in energy. We conclude that, irrespective of whether the ER mechanism is actually rate dominating, it is definitively enhanced.

We present a novel approach for room-temperature molecular manipulation which exploits the reduced thermal mobility of chemisorbed molecular radicals, with cyclopentadienyl, C5H5, on Ag(100) as an example. Several novel manipulation modes are demonstrated, all achieved at room temperature. Most notably, the dynamics of the radicals can be directly visualized during manipulation, revealing their preferred direction of motion to be perpendicular to the tip displacement. Additionally, individual radicals can be selectively desorbed intact. These findings point to the feasibility of controlling surface chemistry and molecular engineering down to the fundamental ligand level.