J. Eur. Opt. Society-Rapid Publ. 22, 29( 2026) 293
Fig. 1. Surface topographies measured with a WLI.
Fig. 2. Surface topographies measured with an AFM.
although they are less distinct than those on the electrolessplated NiP surface. This reduced clarity may be attributed to the softness of the electroplated Cu, which could have caused deformation during machining. For the OFC surface shown in Figure 1a, it is likely that the large step structures make it difficult to observe the hills. Although not shown here, the hills can be observed on the OFC surface when the step height is small. From these results, it is inferred that these hills, i. e., the wavinesses, were not caused by the material properties but by the motion error of the ultraprecision turning machine.
In addition, measurements were performed at three different locations near the radial midpoint of each workpiece, and the average, maximum, and minimum RMS roughness were obtained. The average, maximum, and minimum RMS roughness were 1.65, 1.78, and 1.52 nm for OFC; 0.83, 0.87, and 0.77 nm for electroplated Cu; and 1.26, 1.30, and 1.21 nm for electroless-plated NiP, respectively. The relatively large range between the maximum and minimum values for OFC is attributed to variations in the contour and height of the crystal grain boundary steps. Thus, the relative magnitudes of the average RMS roughness