Azimuthal Dipolar Rotor Arrays on Surfaces

A set of dipolar molecular rotor compounds was designed, synthesized and adsorbed as self-assembled 2D arrays on Ag(111) surfaces. The title molecules are constructed from three building blocks: (a) 4,8,12-trioxatriangulene (TOTA) platforms that are known to physisorb on metal surfaces such as Au(111) and Ag(111), (b) phenyl groups attached to the central carbon atom that function as pivot joints to reduce the barrier to rotation, (c) pyridine and pyridazine units as small dipolar units on top. Theoretical calculations and scanning tunneling microscopy (STM) investigations hint at the fact that the dipoles of neighboring rotors interact through space through pairs of energetically favorable head-to-tail arrangements.     

高稳定电化学扫描隧道显微镜研制

展示了一台自制的电化学扫描隧道显微镜. 这台电化学STM具有很高的稳定性,它在XY平面和Z方向的漂移速率分别为每分钟67和55.6 pm/min. 另外,特殊设计的扫描管部件有效地避免了在高湿度的环境中大漏电电流的产生. 详细描述了这台电化学STM的机械结构.通过在硫酸铜溶液中测量STM图像证明这套系统的优异性能,得到了大范围干净有序的Au(111)表面和高分辨的高聚石墨原子图像.     

Heavy‐Atom Tunneling in the Ring Opening of a Strained Cyclopropene at Very Low Temperatures

The highly strained 1H‐bicyclo[3.1.0]‐hexa‐3,5‐dien‐2‐one 1 is metastable, and rearranges to 4‐oxacyclohexa‐2,5‐dienylidene 2 in inert gas matrices (neon, argon, krypton, xenon, and nitrogen) at temperatures as low as 3 K. The kinetics for this rearrangement show pronounced matrix effects, but in a given matrix, the reaction rate is independent of temperature between 3 and 20 K. This temperature independence means that the activation energy is zero in this temperature range, indicating that the reaction proceeds through quantum mechanical tunneling from the lowest vibrational level of the reactant. At temperatures above 20 K, the rate increases, resulting in curved Arrhenius plots that are also indicative of thermally activated tunneling. These experimental findings are supported by calculations performed at the CASSCF and CASPT2 levels by using the small‐curvature tunneling (SCT) approximation.     

Tailoring the Structure of Two‐Dimensional Self‐Assembled Nanoarchitectures Based on NiII–Salen Building Blocks

The synthesis of a series of Ni^II–salen‐based complexes with the general formula of [Ni(H₂L)] (H₄L=R²‐N,N′‐bis[R¹‐5‐(4′‐benzoic acid)salicylidene]; H₄L1: R²=2,3‐diamino‐2,3‐dimethylbutane and R¹=H; H₄L2: R²=1,2‐diaminoethane and R¹=tert‐butyl and H₄L3: R²=1,2‐diaminobenzene and R¹=tert‐butyl) is presented. Their electronic structure and self‐assembly was studied. The organic ligands of the salen complexes are functionalized with peripheral carboxylic groups for driving molecular self‐assembly through hydrogen bonding. In addition, other substituents, that is, tert‐butyl and diamine bridges (2,3‐diamino‐2,3‐dimethylbutane, 1,2‐diaminobenzene or 1,2‐diaminoethane), were used to tune the two‐dimensional (2D) packing of these building blocks. Density functional theory (DFT) calculations reveal that the spatial distribution of the LUMOs is affected by these substituents, in contrast with the HOMOs, which remain unchanged. Scanning tunneling microscopy (STM) shows that the three complexes self‐assemble into three different 2D nanoarchitectures at the solid–liquid interface on graphite. Two structures are porous and one is close‐packed. These structures are stabilized by hydrogen bonds in one dimension, while the 2D interaction is governed by van der Waals forces and is tuned by the nature of the substituents, as confirmed by theoretical calculations. As expected, the total dipolar moment is minimized     

Single-Molecule Study of a Plasmon-Induced Reaction for a Strongly Chemisorbed Molecule

Chemical reactions induced by plasmons achieve effective solar-to-chemical energy conversion. However, the mechanism of these reactions, which generate a strong electric field, hot carriers, and heat through the excitation and decay processes, is still controversial. In addition, it is not fully understood which factor governs the mechanism. To obtain mechanistic knowledge, we investigated the plasmon-induced dissociation of a single-molecule strongly chemisorbed on a metal surface, two O₂ species chemisorbed on Ag(110) with different orientations and electronic structures, using a scanning tunneling microscope (STM) combined with light irradiation at 5 K. A combination of quantitative analysis by the STM and density functional theory calculations revealed that the hot carriers are transferred to the antibonding (π*) orbitals of O₂ strongly hybridized with the metal states and that the dominant pathway and reaction yield are determined by the electronic structures formed by the molecule–metal chemical interaction.     

Geometric and Electronic Behavior of C60 on PTCDA Hydrogen Bonded Network

Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate.However,the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear.Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA)is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111).The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS)at 5 K.Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd,merely considering the HOMO-LUMO peak separation.The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system.Moreover,we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals.     

Two-dimensional Molecular Phase Transition of Alkylated-TDPB on Au(111) and Cu(111) Surfaces

The derivatives of aromatic cores bearing alkyl chains with different lengths are of potential interest in on-surface chemistry, and thus have been widely investigated both at liquid-solid interfaces and in vacuum. Here, we report on the structural evaluation of self-assembled 1,3,5-tri(4-dodecylphenyl)benzene(TDPB) molecules with increased molecular coverages on both Au(111) and Cu(111) surfaces. As observed on Au(111), rhombic and herringbone structures emerge successively depending on surface coverage. In the case of Cu(111), the same process of phase conversion is also observed, but with two distinct structures. In comparison, the self-assembled structures on Au(111) surface are packed more densely than that on Cu(111) surface under the same preparation conditions. This may fundamentally result from the higher adsorption energy of TDPB molecules on Cu(111), restricting their adjustment to optimize a thermodynamically favorable molecular packing.     

Observations and theories of quantum effects in proton transfer electrode processes

Quantum tunneling effects play an important role in a variety of chemical reactions considerably affecting the reaction rates via opening the classically forbidden paths and emerging as highly efficient or selective processes. However, in the case of electrochemical reactions, quantum tunneling effects are less investigated due to complicated nature of chemical interactions at the electrified interfaces. In this review, we summarize the experimental/theoretical concept of electrochemical quantum proton tunneling (EQPT), which is a key element in microscopic electrode processes. First, we review the experimental observations of EQPT, and next, we discuss possible theoretical pictures of the process. This review shows that a combination of a wide spectrum of scientific efforts is required to understand microscopic mechanism of EQPT including development of the precise electrochemistry-oriented experimental techniques and methodologies, formulation of the appropriate theoretical models for specific systems, and performance of the advanced computational simulations.     

Scanning tunneling microscopy with atomic resolution on ReS2 single crystals grown by vapor phase transport

Atomic resolution images of layered transition metal-dichalcogenide ReS₂ single-crystals (n-type semiconductor) were obtained using a scanning tunneling microscope with a positive tip. In most cases only unresolved clusters of four rhenium atoms could be seen. Occasional images with higher resolution showed that these bright structures consist of four separated atoms. The symmetry of the imaged atoms is identical to that of the rhenium sublattice but not to that of the sulfur atoms. We conclude therefore that the main contribution to the tunneling current is due to the rhenium atoms, although the sulfur atoms are placed by about 0.15 nm closer to the tip. Thus for our positive bias of the tip the tunneling electrons originate from occupied rhenium states in the valence band of the semiconductor.     

Accurate correction of arbitrary spin fermion quantum tunneling from non-stationary Kerr-de Sitter black hole based on corrected Lorentz dispersion relation

According to a corrected dispersion relation proposed in the study on the string theory and quantum gravity theory, the Rarita-Schwinger equation was precisely modified, which resulted in the Rarita-Schwinger-Hamilton-Jacobi equation. Using this equation, the characteristics of arbitrary spin fermion quantum tunneling radiation from non-stationary Kerr-de Sitter black holes were determined. A number of accurately corrected physical quantities, such as surface gravity, chemical potential, tunneling probability, and Hawking temperature, which describe the properties of black holes, were derived. This research has enriched the research methods and enabled increased precision in black hole physics research.