First-principles calculations were conducted to investigate the structural,electronic,and magnetic properties of single Fe atoms and Fe dimers on Cu_(2)N/Cu(100).Upon adsorption of an Fe atom onto Cu_(2)N/Cu(100),robust Fe-N bonds form,resulting in the incorporation of both single Fe atoms and Fe dimers within the surface Cu_(2)N layer.The partial occupancy of Fe-3d orbitals lead to large spin moments on the Fe atoms.Interestingly,both single Fe atoms and Fe dimers exhibit in-plane magnetic anisotropy,with the magnetic anisotropy energy(MAE)of an Fe dimer exceeding twice that of a single Fe atom.This magnetic anisotropy can be attributed to the predominant contribution of the component along the x direction of the spin-orbital coupling Hamiltonian.Additionally,the formation of Fe-Cu dimers may further boost the magnetic anisotropy,as the energy levels of the Fe-3d orbitals are remarkably influenced by the presence of Cu atoms.Our study manifests the significance of uncovering the origin of magnetic anisotropy in engineering the magnetic properties of magnetic nanostructures.
Lattice parameters are a basic quantity in material characterization,and a slight alteration in lattice parameters directly affects the properties of materials.However,there are still considerable controversies as to whether lattice expansion or contraction occurs in metallic nanomaterials with size reduction.Here,the size dependences of the lattice parameter and surface free energy of clean Cu(100)films are investigated via simulations.Lattice parameters of the exposed surfaces contract,whereas lattice expansion occurs along the direction perpendicular to the surfaces with decreasing film thicknesses.This is striking since the metallic bonds usually lack strong directionality,and it is always regarded that the lattice variations in all directions are consistent.The contraction parallel to the surface is more severe than the expansion perpendicular to the surface in films.The lattices change from cubic to tetragonal with decreasing film thickness.Consequently,common contractions and occasional expansions of the lattice parameters of Cu nanoparticles have been observed in previous experiments.Increasing free energy and surface free energy with decreasing thicknesses is the thermodynamic origin of the lattice variations.Our study therefore provides a comprehensive physical basis for the surface effects on the lattice variations.
Six-dimensional quantum dynamics calculations for the state-to-state scattering of H_(2)/D_(2) on the rigid Cu(100)surface have been carried out using a time-dependent wave packet approach,based on an accurate neural network potential energy surface fit for thousands of density functional theory data computed with the opt PBE-vd W density functional.The present results are compared with previous theoretical and experimental ones regarding to the rovibrationally(in)elastic scattering of H_(2) and D_(2) from Cu(100).In particular,we test the validity of the site-averaging approximation in this system by which the six-dimensional(in)elastic scattering probabilities are compared with the weighted average of four-dimensional results over fifteen fixed sites.Specifically,the site-averaging model reproduces vibrationally elastic scattering probabilities quite well,though less well for vibrationally inelastic results at high energies.These results support the use of the site-averaging model to reduce computational costs in future investigations on the state-to-state scattering dynamics of heavy diatomic or polyatomic molecules from metal surfaces,where full-dimensional calculations are too expensive.
The kinetics of Al-Ni and Cu-Ni nanodroplets spreading over a Cu substrate in the presence of a temperature difference between them is studied via molecular dynamics simulations.The simulations show that significant dissolution reactions occur for the two systems and there is no precursor film generated during spreading.The spreading rate significantly increases when nanodroplets contain less Ni atoms in the Al-Ni/Cu wetting systems.However,a different trend is observed in the Cu-Ni/Cu wetting systems.The spreading rate remains unchanged regardless of the ratio of Cu to Ni atoms owing to the fact that Cu and Ni have almost the same lattice constants.The simulations also demonstrate that,because of the temperature gradient between the nanodroplet and substrate,local solidification takes place in the later spreading stage,which significantly hinders spreading.Due to the mismatch of lattice constants between Al and the Cu atoms in the Al-Ni/Cu wetting systems,hexagonal closest packed(hcp),body centered cubic(bcc),and face centered cubic(fcc)arrangements of atoms are observed when the Al-Ni nanodroplets solidify completely,whereas there is only a fcc arrangement in the Cu-Ni/Cu wetting systems.
WANG ShaoyuWANG ZijieWANG ShuolinYANG YanruHUANG CongliangWANG Xiaodong
The interaction between a probing tip and an adsorbed molecule can significantly impact the molecular chemical structure and even induce its motion on the surface.In this study,the tip-induced bond weakening,tilting,and hopping processes of a single molecule were investigated by sub-nanometre resolved tip-enhanced Raman spectroscopy(TERS).We used single carbon monoxide(CO)molecules adsorbed on the Cu(100)surface as a model system for the investigation.The vibrational frequency of the C−O stretching mode is always redshifted as the tip approaches,revealing the weakening of the C−O bond owing to tip−molecule interactions.Further analyses of both the vibrational Stark effect and TERS imaging patterns suggest a delicate tilting phenomenon of the adsorbed CO molecule on Cu(100),which eventually leads to lateral hopping of the molecule.While a tilting orientation is found toward the hollow site along the[110]direction of the Cu(100)surface,the hopping event is more likely to proceed via the bridge site to the nearest Cu neighbour along the[100]or[010]direction.Our results provide deep insights into the microscopic mechanisms of tip−molecule interactions and tip-induced molecular motions on surfaces at the single-bond level.
We carry out ab initio density functional theory calculations to study manipulation of electronic structures of selfassembled molecular nanostructures on metal surfaces by investigating the geometric and electronic properties of glycine molecules on Cu(100).It is shown that a glycine monolayer on Cu(100)forms a two-dimensional hydrogen-bonding network between the carboxyl and amino groups of glycine using a first principles atomistic calculation on the basis of a recently found structure.This network includes at least two hydrogen-bonding chains oriented roughly perpendicular to each other.Through molecule–metal electronic hybridization,these two chains selectively hybridized with the two isotropic degenerate Cu(100)surface states,leading to two anisotropic quasi-one-dimensional surface states.Electrons occupying these two states can near-freely move from a molecule to its adjacent molecules directly through the intermolecular hydrogen bonds,rather than mediated by the substrate.This results in the experimentally observed anisotropic free-electron-like behavior.Our results suggest that hydrogen-bonding chains are likely candidates for charge conductors.
Linwei ZhouChen-Guang WangZhixin HuXianghua KongZhong-Yi LuHong GuoWei Ji
