  The surface topography of diamond coatings strongly affects surface
properties such as adhesion, friction, wear, and biocompatibility. However, the
understanding of multi-scale topography, and its effect on properties, has been
hindered by conventional measurement methods, which capture only a single
length scale. Here, four different polycrystalline diamond coatings are
characterized using transmission electron microscopy to assess the roughness
down to the sub-nanometer scale. Then these measurements are combined, using
the power spectral density (PSD), with conventional methods (stylus
profilometry and atomic force microscopy) to characterize all scales of
topography. The results demonstrate the critical importance of measuring
topography across all length scales, especially because their PSDs cross over
one another, such that a surface that is rougher at a larger scale may be
smoother at a smaller scale and vice versa. Furthermore, these measurements
reveal the connection between multi-scale topography and grain size, with
characteristic scaling behavior at and slightly below the mean grain size, and
self-affine fractal-like roughness at other length scales. At small (subgrain)
scales, unpolished surfaces exhibit a common form of residual roughness that is
self-affine in nature but difficult to detect with conventional methods. This
approach of capturing topography from the atomic- to the macro-scale is termed
comprehensive topography characterization, and all of the topography data from
these surfaces has been made available for further analysis by experimentalists
and theoreticians. Scientifically, this investigation has identified four
characteristic regions of topography scaling in polycrystalline diamond
materials.
