Nickel Nanofilms Electrolessly Deposited on Organosilane Nanorings and Characterized by Contact Mode AFM Combined with Magnetic Sample Modulation

Surface structures of magnetic nanorings were made using electroless deposition of Ni onto patterned templates of an amine-functionalized organosilane. Samples were prepared by chemical approaches based on colloidal lithography employing a surface mask of size-sorted, monodisperse silica spheres. Surface changes were evaluated after key points of the reactions using imaging modes of atomic force microscopy (AFM). Nanopatterns of 3-aminopropyltriethoxysilane (APTES) were prepared on Si(111) by applying a heated vapor to a surface mask of silica spheres. After rinsing, the particle mask was removed to reveal ring-shaped nanopatterns presenting amine groups at the interface. Organosilane nanopatterns were then immersed in a solution of Pd catalyst followed by treatment in a Ni plating bath. Changes in surface morphology after each reaction step were characterized ex situ using tapping-mode AFM to follow the time course of nanofabrication. Images of the Ni nanorings acquired with AFM were compared with SEM micrographs to further elucidate the morphology of the metal coatings. The magnetic character of the nanostructures was investigated with magnetic sample modulation (MSM-AFM), which is a hybrid of contact mode AFM combined with magnetic actuation of samples. Surface maps of the vibration of diamagnetic Pd and magnetic Ni nanorings were obtained with MSM-AFM, providing insight on processes of electroless plating. Fine details of the surface corrugation and grain structure of the Ni coated areas of the sample detected with SEM were sensitively resolved with MSM-AFM that were not apparent in AFM topography frames. Chemistry-based steps with electroless deposition (ELD) of metal and colloidal lithography provide a practical route for reproducible nanofabrication of highly regular geometries with high-throughput.