二维有序碳氮材料选择性生长的衬底调控机制

Two-dimensional(2D)ordered carbon–nitrogen binary compounds(C_(x)N_(y))show great potential in many fields owing to their diverse structures and outstanding properties.However,the scalable and selective synthesis of 2D C_(x)N_(y)compounds remain a challenge due to the variable C/N stoichiometry induced coexistence of graphitic,pyridinic,and pyrrolic N species and the competitive growth of graphene.Here,this work systematically explored the mechanism of selective growth of a series of 2D ordered C_(x)N_(y)compounds,namely,the g-C_(3)N_(4),C_(2)N,C_(3)N,and C_(5)N,on various epitaxial substrates via first-principles calculations.By establishing the thermodynamic phase diagram,it is revealed that the individualized surface interaction and symmetry match between 2D C_(x)N_(y)compounds and substrates together enable the selective epitaxial growth of single crystal 2D C_(x)N_(y)compounds within distinct chemical potential windows of feedstock.The kinetics behaviors of the diffusion and attachment of the decomposed feedstock C/N atoms to the growing C_(x)N_(y)clusters further confirmed the feasibility of the substrate mediated selective growth of 2D C_(x)N_(y)compounds.Moreover,the optimal experimental conditions,including the temperature and partial pressure of feedstock,are suggested for the selective growth of targeted 2D C_(x)N_(y)compound on individual epitaxial substrates by carefully considering the chemical potential of carbon/nitrogen as the functional of experimental parameters based on the standard thermochemical tables.This work provides an insightful understanding on the mechanism of selective epitaxial growth of 2D ordered C_(x)N_(y)compounds for guiding the future experimental design.

Electron doping induced stable ferromagnetism in two-dimensional GdI_(3)monolayer

As a two-dimensional material with a hollow hexatomic ring structure,Néel-type anti-ferromagnetic(AFM)GdI_(3)can be used as a theoretical model to study the effect of electron doping.Based on first-principles calculations,we find that the Fermi surface nesting occurs when more than 1/3 electron per Gd is doped,resulting in the failure to obtain a stable ferromagnetic(FM)state.More interestingly,GdI_(3)with appropriate Mg/Ca doping(1/6 Mg/Ca per Gd)turns to be half-metallic FM state.This AFM–FM transition results from the transfer of doped electrons to the spatially expanded Gd-5d orbital,which leads to the FM coupling of local half-full Gd-4f electrons through 5d–4f hybridization.Moreover,the shortened Gd–Gd length is the key to the formation of the stable ferromagnetic coupling.Our method provides new insights into obtaining stable FM materials from AFM materials.