Abstract
Surface morphologies of the electroless plated Ni-P-W coatings were investigated by Atomic Force Microscopy (AFM). The Ni-P-W coatings exhibited nodular feature with an averaged nodule size of 2-3 μm. The roughness of the coating evaluated from the AFM image was highly dependent on the acquisition area. The surface roughness was as low as 2 nm with a scan area of 0.5×0.5 μm 2 , while 24 nm was a more reliable data under sufficient surveying area wider than 5×5 μm2. The sine profile was adopted as a model of nodular feature to simulate the roughness calculation. The scattering in roughness values was reduced significantly for acquisition region larger than one wavelength of the sine profile. The critical acquisition region of one wavelength, corresponding to twice of a nodule diameter, was then determined for a nodular surface on the electroless plating.