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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]

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]

Potassium (K) cations are spontaneously formed upon thermal deposition of low‐coverage K onto an ultrathin CuO monolayer grown on Cu(110) and they were explored by low‐temperature scanning tunneling microscopy (STM) and X‐ray photoemission spectroscopy. The formed K cations are highly immobile and thermally stable. The local work function around an individual K cation decreases by 1.5±0.3 eV, and a charging zone underneath it is established within about 1.0 nm. The cationic and neutral states of the K atom are switchable upon application of an STM bias voltage pulse, which is simultaneously accompanied by an adsorption site relocation. [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]

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]

Ullmann coupling of 4-bromobiphenyl thermally catalyzed on Ag(111), Cu(111), and Cu(100) surfaces was scrutinized by scanning tunneling microscopy as well as theoretical calculations. Detailed experimental evidence showed that initial formation of organometallic intermediates on the surface, as self-assembled structures or sparsely dispersed species, is determined by the subsequent reaction pathway. Specifically, the assembled organometallic intermediates at full coverage underwent a single-barrier process to directly convert into the final coupling products, while the sparsely dispersed intermediates at low coverage went through a double-barrier process via newly identified clover-shaped intermediates prior to formation of the final coupling products. These findings demonstrate that a self-assembly strategy can efficiently steer surface reaction pathways and dynamics. [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]