Substrate tuned reconstructed polymerization of naphthalocyanine on Ag(110)

The linkage structures between monomers make great influence on the properties of polymers.The synthesis of some special linkage structures can be challenging,which is often overcome by employing special reaction conditions.Here,we build dihydropentalene linkage in poly-naphthalocyanine on Ag(110)surface.Scanning tunneling microscopy(STM)and non-contact atomic force microscopy(nc-AFM)measurements confirm the dihydropentalene linkage structure and a possible formation path with reconstruction steps is proposed.The controlled experiment on Ag(100)surface shows no dihydropentalene structures formed,which indicates the grooved substrate is necessary for the reconstruction.This work provides insights into the surface restricted reactions that can yield special structures in organic polymers.     

1,4-丁二硫醇分子器件电输运性质的力敏特性研究

基于杂化密度泛函理论,研究了1,4-丁二硫醇分子体系的结构随电极作用力的变化及拉断过程;并利用弹性散射格林函数方法进一步计算了不同电极作用力下分子体系的电输运特性.结果显示,界面结构不同,拉断分子体系所用的拉力也不同:分子末端硫原子处于Au(111)面的空位上方时,拉断分子体系需约1.75 nN的拉力;若金电极表面存在孤立金原子与1,4-丁二硫醇分子末端的硫原子相连,拉断分子体系只需约1.0 nN的力,且伴有孤立金原子被拉出.两种情况分别与不同实验测量相符合.分子在压缩过程中发生扭曲并引起表面金原子滑移,然而压缩扭曲过程与拉伸回复过程不可逆.电极拉力约为0.7—0.8 nN时,分子体系在不同界面构型下以及在不同扭转状态下,电导都出现极小值,这与实验结论一致.分子的末端原子与电极间耦合强度随电极作用力的变化是引起分子体系电导变化的主要因素.实验在0.8 nN附近同时测得较小概率的高电导值与双分子导电有关.     

Structural and thermal stabilities of Au@Ag core-shell nanoparticles and their arrays:A molecular dynamics simulation

Thermal stability of core-shell nanoparticles(CSNPs)is crucial to their fabrication processes,chemical and physical properties,and applications.Here we systematically investigate the structural and thermal stabilities of single Au@Ag CSNPs with different sizes and their arrays by means of all-atom molecular dynamics simulations.The formation energies of all Au@Ag CSNPs we reported are all negative,indicating that Au@Ag CSNPs are energetically favorable to be formed.For Au@Ag CSNPs with the same core size,their melting points increase with increasing shell thickness.If we keep the shell thickness unchanged,the melting points increase as the core sizes increase except for the CSNP with the smallest core size and a bilayer Ag shell.The melting points of Au@Ag CSNPs show a feature of non-monotonicity with increasing core size at a fixed NP size.Further simulations on the Au@Ag CSNP arrays with 923 atoms reveal that their melting points decrease dramatically compared with single Au@Ag CSNPs.We find that the premelting processes start from the surface region for both the single NPs and their arrays.