Laser-induced ripple structures on Ni–P substrates

Abstract

The ripple structures induced in Ni–P disks by 248 nm excimer laser pulses are experimentally investigated by varying laser fluence (175–270 mJ/cm 2 for 150 pulses) and pulse number (400–1000 pulses for 118 mJ/cm 2). A quantity [ R a/( Λ/2)] is proposed to characterize the real contact area at the head–disk interface. This quantity is defined as the ratio of roughness height R a to half ripple period ( Λ/2). The maximum shear stress and the plasticity index have been derived to analyze the ability for ripple structures to withstand stress and the head–ripple contact mode, respectively. Increasing fluence and pulse number may lead to an increase in ripple periodicity, and on the contrary, decreases in corresponding maximum shear stress, real contact area [ R a/( Λ/2)] and plasticity index. The laser parameters (fluence and pulse number) represent effective approaches to improve the tribology of the head–disk interface by controlling the laser-induced ripple pattern such as periodicity and roughness height. The laser irradiation with lower fluence and fewer pulses is helpful in producing the required ripple structure for laser texturing in magnetic media. This structure can meet the requirements of elastic contacts between head and disk, and less deformation under stress, although with a slight sacrifice in contact-area reduction.