Strong room-temperature ferromagnetism of pure ZnO nanostructure arrays via colloidal template

Abstract

Room temperature ferromagnetism in pure ZnO is a very interesting phenomenon, but the reported intensity is usually as weak as 10 À2 to 10 À3 emu g À1 and the mechanism is still in debate. Here, we report room-temperature ferromagnetism as strong as 6.1 emu g À1 from un-doped ZnO ordered arrays fabricated by a colloidal template method, and show a remarkable dependence of such ferromagnetism on grain size for the first time. Interestingly, the M S of samples could be tuned over a large scale, from 0.1 to 6.1 emu g À1 by adjusting the annealing time. Further study shows that grain size and oxygen are dominant factors for such magnetism. When the grain size, in vacuum, increases from 3 to 15 nm, the M S decreases from 5.7 to 0.25 emu g À1 . For 3 nm grain size, ageing in the presence of oxygen, such as in air, for 1 week causes the M S to decrease to one-tenth of the original value. However, the M S of samples aged in vacuum does not change distinctly. Based on the observation and analysis of the above phenomena, we propose that oxygen vacancies at the surface of nanoparticles contribute to the ferromagnetism. This study could provide very simple and cheap semiconductor nanostructures with strong room temperature ferromagnetism for future spintronic applications and will deepen our understanding of the defect-related origin of such magnetism in ZnO.

Synthesis and photoluminescence properties of ZnS nanobowl arrays via colloidal monolayer template

“…In recent years, monolayer colloidal crystal template (MCCT) has proved to be an effective approach for fabricating ordered nanoarrays due to their low cost, flexibility, and various morphologies [ 22 , 23 ]. Moreover, MCCT exhibits excellent compatibility with traditional fabrication technologies, such as sol-gel [ 24 , 25 ], pulse laser deposition [ 26 ], vapor deposition [ 27 ], and electrochemical deposition [ 28 - 30 ]. It is worth noting that the nanosphere lithography at the solution surface (NSLSS) had been developed by Qi's group [ 8 , 31 , 32 ], which provides a practical route for fabricating high-quality 2D nanoarrays with special morphologies.…”

Hierarchically structured nanowires on and nanosticks in ZnO microtubes

“…Micro/nanowire materials are fascinating systems for the investigation of electrical transport, optical, magnetic, and mechanical properties 5 6 , whereas semiconducting and ferromagnetic combined functionalities are important for technological application in spintronic devices. For example, ZnO nanostructured materials are suggested to exhibit ferromagnetic-like properties, which have been attributed to the presence of intrinsic defect/strain 7 8 . Taking advantage of magnetic and electric properties, such as spin dependent electron transport and phase transition from insulator to metallic behavior 9 10 , these materials may be converted in sophisticated and miniaturized devices 11 12 .…”

Hemi‐Shell Arrays Harvesting Ultra‐Broadband Light

“…All chemicals were used as received without further purification. Glass and silicon substrates were cleaned according to previously published procedures . A large area (about 80 cm 2 ) of colloidal monolayer was synthesized via self‐assembly at the air–water interface, as shown in Figure S15, Supporting Information.…”