An influence of pretreatment conditions on surface structure and reactivity of Pt(100) towards CO oxidation reaction

We present a combined electrochemical and in situ STM study of the surface structure of Pt(100) single crystal electrodes in dependence on the cooling atmosphere after flame annealing. The following cooling conditions were applied: Ar/H2 and Ar/CO mixtures (reductive atmosphere), argon (inert gas) and air (oxidative atmosphere). Surface characterization by in-situ STM allows deriving direct correlations between surface structure and macroscopic electrochemical behavior of the respective platinum electrodes. We investigated the influence of defect type and density as well as long range surface order on the kinetics of the CO electro-oxidation reaction. The defect-rich Pt(100) electrodes as cooled in air or Ar, and followed by immersion in the hydrogen adsorption region display higher activities as compared to the rather smooth Pt(100)-(1 × 1) electrode cooled in an Ar/H2-atmospher

Halide electroadsorption on single crystal surfaces

The structure and phase behavior of halides have been investigated on single crystals of Ag and Au using synchrotron x-ray scattering techniques. The adlayer coverages are potential dependent. For all halides studied the authors found that with increasing potential, at a critical potential, a disordered adlayer transforms into an ordered structure. Often these ordered phases are incommensurate and exhibit potential-dependent lateral separations (electrocompression). The authors have analyzed the electrocompression in terms of a model which includes lateral interactions and partial charge. A continuous compression is not observed for Br on Ag(100). Rather, they find that the adsorption is site-specific (lattice gas) in both the ordered and disordered phases. The coverage increases with increasing potential and at a critical potential the disordered phase transforms to a well-ordered commensurate structure

Ab-initio study of the thermopower of biphenyl-based single-molecule junctions

Employing ab-initio electronic structure calculations combined with the non-equilibrium Green's function technique, we study the dependence of the thermopower Q on the conformation in biphenyl-based single-molecule junctions. For the series of experimentally available biphenyl molecules, alkyl side chains allow us to gradually adjust the torsion angle \phi\ between the two phenyl rings from 0 to 90{\deg} and to control in this way the degree of \pi-electron conjugation. Studying different anchoring groups and binding positions, our theory predicts that the absolute values of the thermopower decrease slightly towards larger torsion angles, following an a+b*cos^{2}\phi\ dependence. The anchoring group determines the sign of Q and a,b, simultaneously. Sulfur and amine groups give rise to Q,a,b>0, while for cyano Q,a,b<0. The different binding positions can lead to substantial variations of the thermopower mostly due to changes in the alignment of the frontier molecular orbital levels and the Fermi energy. We explain our ab-initio results in terms of a \pi-orbital tight-binding model and a minimal two-level model, which describes the pair of hybridizing frontier orbital states on the two phenyl rings. The variations of the thermopower with \phi\ seem to be within experimental resolution.Comment: 8 pages, 4 figues, 3 table

Цифровой двойник стенда физического подобия, имитирующий процесс переработки нефти

Цель работы – разработка и реализация полной математической модели стенда физического подобия по изучению алгоритмов автоматического управления в гидродинамических системах. В процессе исследования проводились исследования по получению математической модели стенда физического подобия, обработка экспериментальных данных, уточнение модели, синтез простейших алгоритмов автоматического управления одноконтурных систем. В результате исследования была получена математическая модель, адекватно описывающая происходящие процессы в системе. В будущем планируетсяулучшить модель, реализовать когнитивного помощника, обеспечить всестороннее цифровое планирование.The purpose of the work is the development and implementation of a complete mathematical model of the physical similarity stand for the study of automatic control algorithms in hydrodynamic systems. In the course of the research, research was carried out to obtain a mathematical model of the physical similarity stand, processing of experimental data, refinement of the model, synthesis of the simplest algorithms for automatic control of single-loop systems. As a result of the research, a mathematical model was obtained that adequately describes the processes occurring in the system. It is planned to improve the model, implement a cognitive assistant, and provide digital planning

Ab initio calculations for bromine adlayers on the Ag(100) and Au(100) surfaces: the c(2x2) structure

Ab initio total-energy density-functional methods with supercell models have been employed to calculate the c(2x2) structure of the Br-adsorbed Ag(100) and Au(100) surfaces. The atomic geometries of the surfaces and the preferred bonding sites of the bromine have been determined. The bonding character of bromine with the substrates has also been studied by analyzing the electronic density of states and the charge transfer. The calculations show that while the four-fold hollow-site configuration is more stable than the two-fold bridge-site topology on the Ag(100) surface, bromine prefers the bridge site on the Au(100) surface. The one-fold on-top configuration is the least stable configuration on both surfaces. It is also observed that the second layer of the Ag substrate undergoes a small buckling as a consequence of the adsorption of Br. Our results provide a theoretical explanation for the experimental observations that the adsorption of bromine on the Ag(100) and Au(100) surfaces results in different bonding configurations.Comment: 10 pages, 4 figure, 5 tables, Phys. Rev. B, in pres

Single-molecule detection of dihydroazulene photo-thermal reaction using break junction technique

基于隧穿机制的电输运是物质世界的基本过程之一。在单分子尺度，分子结构的细微变化足以导致电学性质的显著区别，这也使通过单分子电学检测方法研究化学反应过程成为可能。在这一研究工作中，课题组将通常用于单分子电学测量的裂结技术用于单分子尺度反应动力学的表征。这一工作也为未来的合成化学和化学工程研究提供了一种新思路，即通过纳米技术构造反应微环境，可以实现化学反应速率、产物和产率的优化。 该研究工作是在洪文晶教授和丹麦哥本哈根大学Mogens B. Nielsen教授的共同指导下，通过跨学科的国际合作所完成的。其中洪文晶教授课题组负责该研究工作的实验表征和统计分析，丹麦哥本哈根大学Mogens B. Nielsen教授课题组负责分子体系的合成，Kurt V. Mikkelsen教授和Gemma C. Solomon教授课题组分别负责了该研究工作的反应动力学和电输运理论计算，这也是洪文晶教授课题组与上述研究团队的首次科研合作。我校萨本栋微纳研究院的杨扬助理教授也参与了数据分析和机理讨论的部分工作。 洪文晶教授课题组长期致力于单分子尺度下的化学反应、分子组装、分子器件电输运等方面的相关研究，开发了一系列能够在单分子尺度实现精密控制和精确测量的科学仪器。以此为基础，课题组与国内外材料化学和理论研究团队密切合作，在单分子尺度电输运的量子干涉效应、电化学调控和化学反应表征等领域进行了一系列探索。【Abstract】Charge transport by tunnelling is one of the most ubiquitous elementary processes in nature. Small structural changes in a molecular junction can lead to significant difference in the single-molecule electronic properties, offering a tremendous opportunity to examine a reaction on the single-molecule scale by monitoring the conductance changes. Here, we explore the potential of the single-molecule break junction technique in the detection of photo-thermal reaction processes of a photochromic dihydroazulene/vinylheptafulvene system. Statistical analysis of the break junction experiments provides a quantitative approach for probing the reaction kinetics and reversibility, including the occurrence of isomerization during the reaction. The product ratios observed when switching the system in the junction does not follow those observed in solution studies (both experiment and theory), suggesting that the junction environment was perturbing the process significantly. This study opens the possibility of using nano-structured environments like molecular junctions to tailor product ratios in chemical reactions.This work was generously supported by the University of Copenhagen, the Danish e-Infrastructure Cooperation, the European Union Seventh Framework Programme (FP7/2007-2013) under the ERC grant agreement no.258806, the Danish Council for Independent Research—Natural Sciences, the Carlsberg foundation, NSFC (21673195,21503179), EC FP7 ITNs ‘MOLESCO’ project numbers 606728, and the Young Thousand Talent Project of China. 研究工作得到了国家自然科学基金（21673195，21503179）、固体表面物理化学国家重点实验室、能源材料化学协同创新中心（2011-iChEM）的大力资助与支持