Ultrathin ZnS Single Crystal Nanowires: Controlled Synthesis and Room-Temperature Ferromagnetism Properties

Abstract

Highly uniform single crystal ultrathin ZnS nanowires (NWs) with 2 nm diameter and up to 10 μm length were fabricated using a catalyst-free colloidal chemistry strategy. The nanowires crystallized in hexagonal phase structure with preferential growth along the direction of the (001) basal plane. The strong polarity of the (001) plane composed of Zn cations or S anions drives the oriented attachment of ZnS nanocrystals (NCs) along this direction via electrostatic (or dipole) interaction. The ultrathin ZnS nanowires show intrinsic ferromagnetism at room temperature and other unusual properties related to its unique nature, such as large anisotropic lattice expansion, large blue-shift of UV-vis absorption band of the excition, and photoluminescence spectrum of the exciton band edge. First-principles DFT computation results show that Zn vacancies can induce intrinsic ferromagnetism in these undoped ZnS NWs. The main source of the magnetic moment arises from the unpaired 3p electrons at S sites surrounding the Zn vacancies carrying the magnetic moment ranging from 0.26 to 0.66 μ(B). Calculated results indicate that the magnetic moment of the ultrathin ZnS NWs can be increased by increasing the Zn vacancy concentration without significant energy cost. The calculated magnetization value (1.96 or 0.40 emu/g for Zn vacancies on the surface of NWs or inside, respectively) by Zn(53)S(54) supercell model is larger than our experimental value (0.12 emu/g at 1.8 K and 0.05 emu/g at 300 K), but the ferromagnetic result is qualitatively in agreement.

A general method for the large-scale synthesis of uniform ultrathin metal sulphide nanocrystals

“…Increasing interest in ultrathin nanomaterials is due to their attractive properties and various potential applications [6][7][8][9] . In particular, ultrathin metal sulphide nanocrystals have drawn tremendous attention owing to their unique properties arising from their exceptionally small dimensions and the resultant quantum size effects [10][11][12][13][14][15][16] . Importantly, the easy preparation and processability of these nanostructures makes them promising building blocks for a wide range of applications.…”

Controlled synthesis of Eu2+ and Eu3+ doped ZnS quantum dots and their photovoltaic and magnetic properties

“…While the ferromagnetism in ZnS is controversial, there is consensus that either Zn or S vacancies may be responsible for the ferromagnetic order. [36][37][38][39] When the Zn/S vacancies exceed a certain concentration, there may be sufficient overlap between their moments to induce ferromagnetic order. Due to its sensitivity limitation, our EDS measurements did not provide conclusive result as to which vacancies (Zn or S) were present in the samples.…”

Experimental and theoretical studies of hydroxyl-induced magnetism in TiO nanoclusters

“…DFT calculations for ZnS nanowires show that while S vacancy does not generate magnetic moments, Zn vacancies produce signicant magnetic moments that scale with Zn vacancy concentration and arise from the 3p orbitals on neighboring S sites. 3 Similar DFT calculations for ZnO thin lms and nanowires indicate that while O vacancies do not generate any magnetic moments, Zn vacancies give rise to magnetic moments that arise from the O 2p orbitals of neighboring O. 4 Both studies showcase the complex correlation among defect creation, local structural relaxation, charge redistribution, and magnetism.…”