Surface topography and light scattering were measured on 15 samples ranging from those having smooth surfaces to others with ground surfaces. The measurement techniques included an atomic force microscope, mechanical and optical profilers, confocal laser scanning microscope, angle-resolved scattering, and total scattering. The samples included polished and ground fused silica, silicon carbide, sapphire, electroplated gold, and diamond-turned brass. The measurement instruments and techniques had different surface spatial wavelength band limits, so the measured roughnesses were not directly comparable. Two-dimensional power spectral density ͑PSD͒ functions were calculated from the digitized measurement data, and we obtained rms roughnesses by integrating areas under the PSD curves between fixed upper and lower band limits. In this way, roughnesses measured with different instruments and techniques could be directly compared. Although smaller differences between measurement techniques remained in the calculated roughnesses, these could be explained mostly by surface topographical features such as isolated particles that affected the instruments in different ways.
We have studied the growth of the silver sulfide tarnish film which forms on silver deposited on smooth, amorphous substrates and rough and smooth polycrystalline substrates. Both ellipsometric and electron-microscope techniques were used to measure the average thickness of the tarnish films. The growth rate was found to be variable depending on the concentration of the sulfurous gases. In normal laboratory air (measured concentrations of H2S and SO2 less than 0.2 parts per billion) a 1-Å-thick tarnish film can be expected to form in 1 h, 3–6 Å in 1 day, 15–30 Å in 1 week, and 60 Å or more in 1 month. The tarnish growth can be completely stopped by placing the silver in a dry-nitrogen atmosphere. Conversely, in a humid atmosphere containing about 10% H2S, growth rates of as much as 100 Å/h can be obtained. The silver sulfide formed as small, randomly spaced, approximately round clumps having a site density about one hundred times larger than the patch density reported for thermally etched silver surfaces. All clumps nucleated on initial exposure, the clump density remained constant with time, and the clumps grew much slower than the tarnish patches on thermally etched silver. Coalescence toward a continuous film was slow; even after 41 days, only 53% of one silver surface was covered with tarnish.
The power spectral density (PSD), in its two-dimensional form, has been designated as the preferred quantity for specifying surface roughness on a draft international drawing standard for surface texture. The correct calculation of the one-dimensional PSD from discrete surface profile data is given, and problems in using fast Fourier-transform routines that are given in some of the standard reference books are flagged. The method given here contains the correct normalizing factors. Two ways to reduce the variance of the PSD estimate are suggested. Examples are shown of the variance reduction possible in the PSD's.
The author presents an overview of evaluation techniques that are appropriate for characterizing the surface roughness of optical thin films and surfaces. These include microscopes ranging from low power optical microscopes to scanning probe microscopes that can measure the topography of individual atoms or groups of atoms, optical non-contact and mechanical contact profilers, some of which can give topographic maps of surface areas, and total integrated scattering and angle-resolved scattering that yield statistical properties of surfaces. Theories are needed to relate scattering to surface roughness; these are valid only for certain types of roughness. Examples are given showing how various surface evaluation techniques can be used for characterizing selected surfaces.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.