Investigation Of Doping And Compositing Effect On Structure, Optical And Magnetic Properties Of CuO Nanomaterials

CuO is a kind of multifunctional material,which has a wide range of applications in solar cells,capacitors,sensors,and photocatalysts and so on.At present,a large number of scientific researches are still confined to the photoelectric properties of CuO nanomaterials.The research on its magnetic property is very scarce,which limits the multi-functionalization of materials.Therefore,the methods of doping modification and compositing modification have been put forward in the hope of improving the physical properties of CuO-based materials by adjusting the electronic band structure.In view of the current situation,this paper experimently verifies the feasibility of introducing spin properties into CuO system and explains the origin of magnetism.Three sections were carried out.?1?Cr-doped CuO nanostructures have been synthesized via a one-step hydrothermal approach.SEM results exhibit that the morphology evolves from the sheet-like to rod-like structures with increasing Cr doping.The bandgap of CuO reduces slightly due to the presence of intra-gap defect states.The analyses of PL and Raman spectra prove that the structure defects exist in the synthesized samples.The oxygen vacancies decrease and copper vacancies(V_Cu)increase obviously after Cr doping or being annealed.The room temperature ferromagnetism?RTFM?was discovered in this system and V_Cu as the origin of FM introduce a moment on metal ions,mediating the FM between chromium and copper spins.This literature firstly studies the FM of Cr-doped CuO system and reasonably reveals the desired FM originating from the V_Cu.?2?CuO/ZnO nanocomposites have been successfully synthesized by a one-step hydrothermal method with different phase ratios.SEM and TEM results show that the obtained products of nanosheets are composed of small primary particles with an average size of about 20 nm.With the increasing proportion of CuO phase,nanosheets have significant collapse and the amount of small sheets increases obviously.The abnormal room temperature ferromagnetism was discovered at the interface between diamagnetic ZnO and antiferromagnetic CuO,which can be tuned by changing the phase ratios.Optical spectra indicate that the interaction between ZnO and CuO modifies the electronic structure of nanocomposites.XPS results verify the valence change of Cu ions and the presence of oxygen vacancies,which are ultimately responsible for the observed ferromagnetism.The indirect double-exchange model was employed to explain the origin of magnetism.?3?Nanostructured CuO/ZnO heterojunctions were fabricated via a template-free hydrothermal reaction.The prepared CuO/ZnO nanocomposites are composed of one dimensional?1D?hexagonal ZnO nanorods and two-dimensional?2D?monoclinic CuO nanosheets.The single crystal nature of both ZnO and CuO was confirmed.Optical spectra show the widened absorption range from UV to visible light,which suggests the potential of the obtained CuO/ZnO composites for visible-light-driven photocatalyst.The point defects at the interface play the leading role in triggering ferromagnetism of CuO/ZnO composites.Fundamentally,the ferromagnetism can be understood by the charge-transfer mechanism according to Stoner theory.The point defects and charge transfer would raise the density of states at E_F to a narrow peak.When the Stoner criterion is satisfied spontaneous ferromagnetism occurs.