Large scale and high density regular array of magnetic quantum dots by nanosphere lithography

Magnetic quantum dots are single domain magnetic particles which have attracted intense study recently for their fundamental and technological properties. Large scale preparation of monodiapersed and similar shaped magnetic quantum dots remains a challenge at high area density. X-ray lithography is expansive to set up and have limited lateral resolution for nanometer sized magnetic quantum dots. Electron beam lithography technique is also high cost and inefficient tool. This has prompted a number of alternative methods based on self-organized structure such as self-assembled diblock copolymer (Science, Vol. 290, 2000). In this paper, we report the preparation of high density patterned magnetic dots of varying size and shape by nanosphere lithography. Although nanosphere lithography has been widely used to produce mesoscopic scale dot arrays, we find that one can not directly scale them down without modification because of the conformal deformation of polystyrene spheres we have employed. We have used ion beam modification technique to controllably reopen the pore structure, alloying size and shape selective deposition of regular array of magnetic nanoparticles between 20-50 nm in size. The magnetic and electrical characterization of the large scale array has been carried out by SQUID, VSM and magnetic force microscopy and the result will be reported as a function of structural, material and processing parameters.