title: A size-dependent structural evolution of ZnS nanoparticles.
abstract: Recently, ZnS quantum dots have attracted a lot of attention since they can be a suitable alternative for cadmium-based quantum dots, which are known to be highly carcinogenic for living systems. However, the structural stability of nanocrystalline ZnS seems to be a challenging issue since ZnS nanoparticles have the potential to undergo uncontrolled structural change at room temperature. Using the molecular dynamics technique, we have studied the structural evolution of 1 to 5 nm freestanding ZnS nanoparticles with zinc-blende and wurtzite crystal structures. Simulation results revealed that relaxed configurations of ZnS nanoparticles larger than 3 nm consist of three regions: a) a crystalline core, b) a distorted network of 4-coordinated atoms environing the crystalline core, and c) a surface structure made entirely of 3-coordinated atoms. Decreasing the size of ZnS nanoparticle to 2 nm will cause the crystalline core to disappear. Further reducing the size will cause all of the atoms to become 3-coordinated. Dipole moments of zinc-blende and wurtzite nanoparticles are in the same range when the nanoparticles are smaller than 3 nm. Increasing the size makes dipole moments converge to the bulk values. This makes zinc-blende and wurtzite nanoparticles less and more polar, respectively.
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Mohammad
authors.initials: M
authors.lastname: Khalkhali
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Qingxia
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zeng
authors.affiliation: Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Hao
authors.initials: H
authors.lastname: Zhang