Probing Adsorption Configurations of Small Molecules on Surfaces by Single-Molecule Tip-Enhanced Raman Spectroscopy

Determining the adsorption configurations of organic molecules on surfaces, especially for relatively small molecules, is a key issue for understanding the microscopic physical and chemical processes in surface science. In this work, we have applied low-temperature ultrahigh-vacuum tip-enhanced Raman scattering (TERS) technique to distinguish the configurations of small 4,4′-bipyridine (44BPY) molecules adsorbed on the Ag(111) surface. The observed Raman spectra exhibit notable differences in the spectral features which can be assigned to three different molecular orientations, each featuring a specific fingerprint pattern based on the TERS selection rule that determines the distribution of the relative intensities of different vibrational peaks. Furthermore, such a small molecule can in turn act as a local probe to provide information on the local electric field distribution at the tip apex. Our work showcases the capability of TERS technique for obtaining information on adsorption configurations of small molecules on surfaces down to the single-molecule level, which is of fundamental importance for many applications in the fields of molecular science and surface chemistry.     

单原子作为保护基团实现石墨双炔纳米线的表面合成

由于在贵金属表面的双炔单元具有高反应活性,表面合成半导体性质的石墨双炔纳米线通常会受到副反应的严重影响,难以分立的纳米线的高质量制备.本文利用化学气相沉积1,4-bis(4-bromophenyl)-1,3-butadiyne分子到表面发生Ullmann偶联反应,可实现无支链的石墨双炔纳米线[-C≡C-Ph_2-C≡C-]_n (PYP)的高产率合成.进一步的单化学键分辨的非接触原子力显微镜表征揭示了单个金增原子与双炔键之间形成了π-ligand键,有效地充当了反应过程中双炔单元的保护基团,避免了偶联过程中的副反应,从而实现了分立的超长石墨双炔纳米线的合成.这项研究将启发对在表面反应中各类表面增原子所起保护作用的更深入研究.     

二维α-In2Se2的铁电性与器件应用

铁电体具有可控的非易失电极化，在现代电子学中有着广泛的应用，例如大容量电容器、新型二极管、铁电场效应晶体管、铁电隧道结等．伴随着电子元器件的不断微型化，传统铁电体面临着极大的挑战，即在器件减薄过程中受限于临界尺寸效应，铁电性很难稳定存在于纳米乃至单原子层二维极限厚度下．鉴于二维范德华材料具有界面饱和、层间相互作用弱、易于实现二维极限厚度等特性，因此，在二维材料家族中寻找室温二维铁电性将是解决传统铁电体瓶颈的有效方法．本文将首先回顾近年来二维铁电物性研究的相关背景，并针对其中在技术应用上较为重要的α-In２Se３ 面外铁电性作详细介绍，最后总结基于二维α-In２Se３ 的铁电器件应用进展。     

Ground state cooling of an optomechanical resonator with double quantum interference processes

We present a cooling scheme with a tripod configuration atomic ensemble trapped in an optomechanical cavity.With the employment of two different quantum interference processes,our scheme illustrates that it is possible to cool a resonator to its ground state in the strong cavity-atom coupling regime.Moreover,with the assistance of one additional energy level,our scheme takes a larger cooling rate to realize the ground state cooling.In addition,this scheme is a feasible candidate for experimental applications.     

High-resolution three-dimensional atomic microscopy via double electromagnetically induced transparency

We aim to present a new scheme for high-dimensional atomic microscopy via double electromagnetically induced transparency in a four-level tripod system. For atom–field interaction, we construct a spatially dependent field by superimposing three standing-wave fields(SWFs) in 3 D-atom localization. We achieve a high precision and high spatial resolution of an atom localization by appropriately adjusting the system variables such as field intensities and phase shifts. We also see the impact of Doppler shift and show that it dramatically deteriorates the precision of spatial information on 3 D-atom localization. We believe that our suggested scheme opens up a fascinating way to improve the atom localization that supplies some practical applications in atom nanolithography, and Bose–Einstein condensation.     

Layer Dependence of Graphene for Oxidation Resistance of Cu Surface

We studied the oxidation resistance of graphene-coated Cu surface and its layer dependence by directly growing monolayer graphene with different multilayer structures coexisted, di-minishing the influence induced by residue and transfer technology. It is found that the Cu surface coated with the monolayer graphene demonstrate tremendous difference in oxidation pattern and oxidation rate, compared to that coated with the bilayer graphene, which is considered to be originated from the strain-induced linear oxidation channel in monolayer graphene and the intersection of easily-oxidized directions in each layer of bilayer graphene, respectively. We reveal that the defects on the graphene basal plane but not the boundaries are the main oxidation channel for Cu surface under graphene protection. Our finding indi-cates that compared to putting forth efforts to improve the quality of monolayer graphene by reducing defects, depositing multilayer graphene directly on metal is a simple and effective way to enhance the oxidation resistance of graphene-coated metals.     

Dearomative Ring-Fused Azafulleroids and Carbazole-Derived Metallofullerenes: Reactivity Dictated by Encapsulation in a Fullerene Cage

Herein, we report divergent additions of 2,2′-diazidobiphenyls to C₆₀ and Sc₃N@I_h-C₈₀. In stark contrast to that of the previously reported bis-azide additions, the unexpected cascade reaction leads to the dearomative formation of azafulleroids 2 fused with a 7-6-5-membered ring system in the case of C₆₀. In contrast, the corresponding reaction with Sc₃N@I_h-C₈₀ switches to the C−H insertion pathway, thereby resulting in multiple isomers, including a carbazole-derived [6,6]-azametallofulleroid 3 and a [5,6]-azametallofulleroid 4 and an unusual 1,2,3,6-tetrahydropyrrolo[3,2-c]carbazole-derived metallofullerene 5 , whose molecular structures have been unambiguously determined by single-crystal X-ray diffraction analyses. Among them, the addition type of 5 is observed for the first time in all reported additions of azides to fullerenes. Furthermore, unexpected isomerizations from 3 to 5 and from 4 to 5 have been discovered, providing the first examples of the isomerization of an azafulleroid to a carbazole-derived fullerene rather than an aziridinofullerene. In particular, the isomerism of the [5,6]-isomer 4 to the [5,6]-isomer 5 is unprecedented in fullerene chemistry, contradicting the present understanding that isomerization generally occurs between [5,6]- and [6,6]-isomers. Control experiments have been carried out to rationalize the reaction mechanism. Furthermore, representative azafulleroids have been applied in organic solar cells, thereby resulting in improved power conversion efficiencies.     

Correlation between Interfacial Structures and Device Performance: The Double-Edged Sword Effect of Lead Iodide in Perovskite Solar Cells

The interfacial electronic structure of perovskite layers and transport layers is critical for the performance and stability of perovskite solar cells (PSCs). The device performance of PSCs can generally be improved by adding a slight excess of lead iodide (PbI₂) to the precursor solution. However, its underlying working mechanism is controversial. Here, we performed a comprehensive study of the electronic structures at the interface between CH₃NH₃PbI₃ and C₆₀ with and without the modification of PbI₂ using in situ photoemission spectroscopy measurements. The correlation between the interfacial structures and the device performance was explored based on performance and stability tests. We found that there is an interfacial dipole reversal, and the downward band bending is larger at the CH₃NH₃PbI₃/C₆₀ interface with the modification of PbI₂ as compared to that without PbI₂. Therefore, PSCs with PbI₂ modification exhibit faster charge carrier transport and slower carrier recombination. Nevertheless, the modification of PbI₂ undermines the device stability due to aggravated iodide migration. Our findings provide a fundamental understanding of the CH₃NH₃PbI₃/C₆₀ interfacial structure from the perspective of the atomic layer and insight into the double-edged sword effect of PbI₂ as an additive.     

Influence of Atomistic Protrusion on the Substrate on Molecular Luminescence in Tunnel Junctions

Scanning tunneling microscope (STM) induced luminescence can be used to study various optoelectronic phenomena of single molecules and to understand the fundamental photophysical mechanisms involved. To clearly observe the molecule-specific luminescence, it is important to improve the quantum efficiency of molecules in the metallic nanocavity. In this work, we investigate theoretically the influence of an atomic-scale protrusion on the substrate on the emission properties of a point dipole oriented parallel to the substrate in a silver plasmonic nanocavity by electromagnetic simulations. We find that an atomic-scale protrusion on the substrate can strongly enhance the quantum efficiency of a horizontal dipole emitter, similar to the situation with a protrusion at the tip apex. We also consider a double-protrusion junction geometry in which there is an atomic-scale protrusion on both the tip and the substrate, and find that this geometry does provide significantly enhanced emission compared with the protrusion-free situation, but does not appear to improve the quantum efficiency compared to the mono-protrusion situation either at the tip apex or on the substrate. These results are believed to be instructive for future STM induced electroluminescence and photoluminescence studies on single molecules.     

Efficient error estimation in quantum key distribution

In a quantum key distribution(QKD)system,the error rate needs to be estimated for determining the joint probability distribution between legitimate parties,and for improving the performance of key reconciliation.We propose an efficient error estimation scheme for QKD,which is called parity comparison method(PCM).In the proposed method,the parity of a group of sifted keys is practically analysed to estimate the quantum bit error rate instead of using the traditional key sampling.From the simulation results,the proposed method evidently improves the accuracy and decreases revealed information in most realistic application situations.