Search

Reversible transformations between fractals and periodic structures are of fundamental importance for understanding the formation mechanism of fractals. Currently, it is still a challenge to controllably achieve such a transformation. We investigate the effect of CO and CO2 molecules on Sierpiński triangles (STs) assembled from Fe atoms and 4,4″-dicyano-1,1′:3′,1″-terphenyl (C3PC) molecules on Au surfaces. Using scanning tunneling microscopy, we discover that the gas molecules induce a transition from STs into 1D chains. Based on density functional theory modeling, we propose that the atomistic mechanism involves the transformation of a stable 3-fold coordination Fe(C3PC)3 motif to Fe(C3PC)4 with an axially bonded CO molecule. CO2 causes the structural transformation through a molecular catassembly process. [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]

The study of lanthanide (Ln)-transition-metal (TM) heterometallic clusters which play key roles in various high-tech applications is a rapid growing field of research. Despite the achievement of numerous Ln-TM cluster compounds comprising one Ln atom, the synthesis of Ln-TM clusters containing multiple Ln atoms remains challenging. Here, we present the preparation and self-assembly of a series of Au-bridged heterometallic clusters containing multiple cerium (Ce) atoms via on-surface coordination. By employing different pyridine and nitrile ligands, the ordered coordination assemblies of clusters containing 2, 3 and 4 Ce atoms bridged by Au adatoms are achieved on Au(111) and Au(100), as revealed by scanning tunneling microscopy. Density functional theory calculations uncover the indispensable role of the bridging Au adatoms in constructing the multi-Ce-containing clusters by connecting the Ce atoms via unsupported Ce-Au bonds. These findings demonstrate on-surface coordination as an efficient strategy for preparation and organization of the multi-Ln-containing heterometallic clusters. The preparation of lanthanide-transition metal clusters containing multiple lanthanide atoms remains challenging. Here, the authors present the controlled on-surface formation of ligand-stabilized heterometallic Ce/Au clusters containing two, three and four Ce atoms bridged by Au adatoms. [ABSTRACT FROM AUTHOR]

Metal-organic structures are controllably prepared by tuning molecular size, supported substrates, and different kinds of metals. They are characterized by ultra-high vacuum low-temperature scanning tunnelling microscopy and Density functional theory calculations. The relatively larger size of all-trans-retinoic acid (ReA) compared to (2E,4E)-3-methyl-5-(2,6,6-trimethylcyclohex-1-enyl)penta-2,4-dienoic acid (DiA) leads to a bigger gap between neighboring ReA in a tetramer and allows for insertion of molecules, forming high density patterns. ReA forms various structures with different ratios (4:0, 3:1, 2:2) of the two chiral enantiomers on the less reactive Au(111) other than Ag(111). Unlike transition metals, electrostatic attraction between molecules and alkali metals is the origin of the formation of large quartet islands. [ABSTRACT FROM AUTHOR]

Controllable molecular self-assembly is vital for nanostructure construction. Here, three different self-assembling networks are realized by varying the chemical composition of the molecular building blocks of the same architecture. This is the first time that S⋯N electrostatic attraction has been employed to regulate surface self-assembly. All molecular structures are characterized using low-temperature scanning tunnelling microscopy. The density functional theory calculations elaborate the structure formation mechanism. [ABSTRACT FROM AUTHOR]

Defining the axis of a molecular rotation is vital for the bottom-up design of molecular rotors. The rotation of tin-phthalocyanine molecules on the Ag(111) surface is studied by scanning tunneling microscopy and atomic/molecular manipulation at 4 K. Tin-phthalocyanine acts as a molecular rotor that binds to Ag adatoms and the substrate. Four different rotation axes are constructed at positions from the center to the periphery of the molecule. Furthermore, using the asymmetric appearance of the modified molecule, the rotation direction of the molecules is identified. This work provides a new approach for designing molecular rotors or motors with definable rotation radii and functions. [ABSTRACT FROM AUTHOR]

The adsorption of phthalocyanines (Pc) to various surfaces has recently been reported to lead to a lowering of symmetry from C4 to C2 in scanning tunneling microscope (STM) images. Possible origins of the reduced symmetry involve the electronic structure or geometric deformation of the molecules. Here, the origin of the reduction is clarified from a comprehensive theoretical study of CoPc adsorbed on the Cu(111) surface along with the experimental STM data. Total energy calculations using different schemes for the exchange-correlation energy and STM simulations are compared against experimental data. We find that the symmetry reduction is only reproduced when van der Waals corrections are included into the formalism. It is caused by a deformation along the two perpendicular molecular axes, one of them coming closer to the surface by around 0.2 Å. An electronic structure analysis reveals (i) the relevance of the CoPc interaction with the Cu(111) surface state and (ii) that intramolecular features in dI/dV maps clearly discriminate a Co-derived state from the rest of the Pc states. [ABSTRACT FROM AUTHOR]

A new type of two-dimensional crystal comprising supramolecular pentamers on Au(111) is studied using an ultra-high vacuum low-temperature scanning tunnelling microscope. (2E,4E)-3-Methyl-5-(2,6,6-trimethylcyclohex-1-enyl)penta-2,4-dienoic acid molecules form pentamers through five-fold O…H–O hydrogen bonds. In ordered arrays, pentamers interact with each other via van der Waals interactions. The impacts of different annealing temperatures and substrates on the formation of pentamer patterns are systemically investigated. [ABSTRACT FROM AUTHOR]

Atomic-scale mechanochemistry is realized from force exerted by a C60-functionalized scanning tunneling microscope tip. Two conformers of tin phthalocyanine can be prepared on coinage-metal surfaces. A transition between these conformers is induced on Cu(111) and Ag(100). Density-functional calculations reveal details of this reaction. Because of the large energy barrier of the reaction and the strong interaction of SnPc with Cu(111), the process cannot be achieved by electrical means. [ABSTRACT FROM AUTHOR]

Crystalline structures with Sierpiński triangles as building blocks were constructed via a templating method in an ultra-high vacuum and studied by low-temperature scanning tunneling microscopy. Cobalt atoms and 4,4′′-dicyano-1,1′:3′,1′′-terphenyl molecules were used to build the Sierpiński triangles. The Au(100)-(hex), Au(111)-22 ×UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/, and stepped Au(111) surfaces were used as templates to guide the packing of Sierpiński triangles. One-dimensional double chains and two-dimensional small domains of Sierpiński triangles were successfully prepared using the method in experiments. [ABSTRACT FROM AUTHOR]

Kinetically controlled hierarchical self-assemblies of all-trans-retinoic acid on Au(111) were investigated via low-temperature scanning tunneling microscopy in ultra-high vacuum. The dominant molecular hierarchical superstructure could be selectively controlled to dimer, tetramer, or pentamer patterns, which were stabilized by hydrogen bonds and van der Waals interactions. [ABSTRACT FROM AUTHOR]

Ordered two-dimensional arrays of silver adatoms with tunable metal atom density stabilized by 1,4-diethynyl-2,5-dimethylbenzene, a terminal alkyne, were prepared on Ag(111) and scrutinized by scanning tunneling microscopy and density functional theory calculations. Stabilization of the adatom arrays was attributed to the substrate-mediated electron localizations of the Ag adatom and terminal alkynyl in the molecule. [ABSTRACT FROM AUTHOR]

Abstract: Scanning tunneling microscopy (STM) was used to study the surface structures of dry-prepared and di-chloroethane-treated HOPG samples. Both triangular and honeycomb structures were simultaneously observed with the same tip at room temperature around a strand (grain boundary) on the HOPG surface. This observation did not support the tip effect in STM imaging explanation for HOPG in literature. A general layer-sliding model was utilized to explain the experimental results: sliding of the HOPG topmost layer was used to explain the origins of the triangular and honeycomb structures, and molecule intercalation into inter-layer spacing between the first and second layers of HOPG induced inhomogeneous deformation of the HOPG topmost layer that accordingly generated the Moiré patterns of the HOPG sample in di-chloroethane. [Copyright &y& Elsevier]

The adsorbed magnetic molecules with tunable spin states have drawn wide attention for their immense potential in the emerging fields of molecular spintronics and quantum computing. One of the key issues toward their application is the efficient controlling of their spin state. This review briefly summarizes the recent progress in the field of molecular spin state manipulation on surfaces. We focus on the molecular spins originated from the unpaired electrons of which the Kondo effect and spin excitation can be detected by scanning tunneling microscopy and spectroscopy (STM and STS). Studies of the molecular spin-carriers in three categories are overviewed, i.e., the ones solely composed of main group elements, the ones comprising 3d-metals, and the ones comprising 4f-metals. Several frequently used strategies for tuning molecular spin state are exemplified, including chemical reactions, reversible atomic/molecular chemisorption, and STM-tip manipulations. The summary of the successful case studies of molecular spin state manipulation may not only facilitate the fundamental understanding of molecular magnetism and spintronics but also inspire the design of the molecule-based spintronic devices and materials. [ABSTRACT FROM AUTHOR]