Roughness measurement using a shearing interference microscope

A shearing interference microscope has high image stability even under vibration. This paper proposes a method of rms roughness measurement of smooth surfaces using shearing interference microscope images which include interference fringes. It makes use of the fact that, when the shearing length is extended in comparison with the autocorrelation length of the rough surface, the shearing interference image has a close relationship with the rms roughness of the measured surface. Principle and theory are discussed as well as the result of measurements of precision-finish surfaces 20-100-A rms.     

Carbon buffer layers for smoothing superpolished glass surfaces as substrates for molybdenum /silicon multilayer soft-x-ray mirrors

Zerodur and BK7 glass substrates (developed by Fa. Glaswerke Schott, D-55014 Mainz, Germany) from Carl Zeiss Oberkochen polished to a standard surface roughness of varsigma = 0.8 nm rms were coated with a C layer by electron-beam evaporation in the UHV. The roughness of the C-layer surfaces is reduced to 0.6 nm rms. A normal-incidence reflectance of 50% at a wavelength of 13 nm was measured for a Mo/Si multilayer soft-x-ray mirror with 30 double layers (N = 30) deposited onto the BK7/C substrate, whereas a similar Mo/Si multilayer (N = 30) evaporated directly onto the bare BK7 surface turned out to show a reflectance of only 42%.     

Wavefront aberrations of rotationally symmetric CGHs fabricated by a polar coordinate laser plotter

Computer-generated holograms (CGHs) were fabricated by a polar coordinate laser plotter. The wavefront aberrations of these CGHs caused by fabrication inaccuracies were measured interferometrically. We tested Fresnel zone plates as typical examples of CGHs with focal ratios of ?/10 and ?/5 with a Fizeau interferometer. The tests comprised both binary phase holograms and binary amplitude holograms. The wavefront aberrations of the CGHs had an rms variation of about λ /50. Two types of aberrations were identified and could be referred to certain writing errors. Their size was deduced from the interferograms.     

Effect of interface structure correlation on magnetoresistance of Fe/Cr multilayers

Effect of interfacial roughness on giant magnetoresistance (GMR) in Fe/Cr multilayers has been studied. A set of samples is prepared by simultaneously depositing on a set of float-glass (FG) substrates with varying rms surface roughness. This causes the correlated part of the rms roughness to vary from sample to sample. Another set of specimen is irradiated with 200 MeV Ag ions in order to induce uncorrelated roughness at the interfaces. In both the cases morphological and other microstructural features of different multilayers remained similar, thus allowing one to separate the effect of interface roughness from that of morphological changes. GMR measurements on these multilayers show that increasing interfacial roughness causes GMR to decrease nonlinearly. It is found that the effect of uncorrelated part of the roughness is much stronger than that of the correlated part.     

Surface morphologies of sputter-deposited aluminum films studied using a high-resolution phase-measuring laser interferometric microscope

Sputter-deposited aluminum (Al) film surface morphologies were studied with a new nondestructive method that incorporates a high-resolution phase-measuring laser interferometric microscope. Good correlation is obtained between rms roughness and reflectivity for various conditions of temperature and argon gas pressure. It should be noted that the rms roughness is much more sensitive than reflectivity when reflectivity exceeds 90%. A drastic change is observed in the temperature dependence of the rms roughness and the skewness at 200 °C. As a result there are changes in Al grain sizes and surface morphologies based on concomitant scanning electron microscope observations. We found that the rms roughness value depends on the resolution of the objective especially when the Al grain sizes are comparable to the resolution.     

Microscopic surface structure of C/SiC composite mirrors for space cryogenic telescopes

We report on the microscopic surface structure of carbon-fiber-reinforced silicon carbide (C/SiC) composite mirrors that have been improved for the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and other cooled telescopes. The C/SiC composite consists of carbon fiber, silicon carbide, and residual silicon. Specific microscopic structures are found on the surface of the bare C/SiC mirrors after polishing. These structures are considered to be caused by the different hardness of those materials. The roughness obtained for the bare mirrors is 20 nm rms for flat surfaces and 100 nm rms for curved surfaces. It was confirmed that a SiSiC slurry coating is effective in reducing the roughness to 2 nm rms. The scattering properties of the mirrors were measured at room temperature and also at 95 K. No significant change was found in the scattering properties through cooling, which suggests that the microscopic surface structure is stable with changes in temperature down to cryogenic values. The C/SiC mirror with the SiSiC slurry coating is a promising candidate for the SPICA telescope.     

Modeling and measurements of atomic surface roughness

We present a geometrical model of atomic topography with which to obtain a quantitative assessment of surface roughness. A series of two- and three-dimensional atomic surface roughness equations with sufficiently realistic parameters is developed to permit quantitative comparison with scanning-tunneling microscope and atomic-force microscope (AFM) experimental results. The model is sufficiently simple that one can easily use it to interpret experimental data. Tables are provided with estimated values for two- and three-dimensional rms atomic surface roughness in pure metal crystals and ionic crystals based on the atomic surface roughness equations. We use these roughness equations to determine the roughness of cleaved muscovite mica [essentially, KAl(2)(OH)(2)Si(3)AlO(10)]; the calculated values for both two- and three-dimensional roughness are consistent with those obtained in our AFM measurements. In addition, we demonstrate both theoretically and experimentally that atomic surface roughness is never zero.     

Magnetic and insulating properties of electrical steel with a new insulating coating

New inorganic-organic coatings for nonoriented electrical sheets have been developed. Smooth and dull sheets having surface roughnesses of 0.18 μm. H root mean square (rms) and 0.75 μm. H rms, respectively, were coated with different weights of a bichromate-emulsion resin solution. Another sheet having a surface roughness of 0.18 μm. H rms was treated with a bichromate-emulsion resin solution containing a dispersed polyethylene resin powder to provide surface roughness. Results indicated that this third sheet exhibits a higher lamination factor and surface resistivity than the coated sheet whose surface roughness is provided by the dullness of the sheet itself. Moreover, it has a lower core loss and requires less ac exciting current when used in welded motor cores at given thicknesses. When weldability is not a factor, then the smooth sheet having a surface roughness of 0.18 μm. H rms and treated with the inorganic-organic coating is the most suitable: it has the highest lamination factor, the least amount of core loss, and requires the least amount of ac exciting current.     

Topographic measurements of precision-ground optical glasses

We studied the surfaces of six precision-ground optical glass samples of fused silica, BK-7, BaCD16, LaC14, NbF1, and LHG8 glass, using a mechanical profiler, a photon tunneling microscope, and a scanning force microscope. The measured roughnesses of the scanning force microscope varied from 3.5 A rms for BK-7 glass to 30 A rms for LHG8 laser glass. Good agreement was obtained among the roughness values measured with all three instruments.     

Effects of substrate and deposition method onto the mirror scattering

The effect of surface roughness onto the mirror scattering has been studied. Five kinds of substrates with different surface roughness were fabricated. On those substrates, dielectric multilayer coating for high reflectivity was deposited by ion-beam sputtering (IBS) and by electron-beam (EB) evaporation. Total integrated scattering (TIS) measurement setup was built for the evaluation of deposited samples. Most of the IBS mirrors showed lower scattering than the EB mirrors, which were deposited on the similar substrates in surface roughness. The ratio of substrate TIS to mirror TIS was defined for evaluation. It increased abruptly at approximately 2A in surface roughness, which indicated that to make low-loss mirrors, the substrate roughness should be less than 2A in rms.     

Fluid jet polishing of optical surfaces

We present a new finishing process that is capable of locally shaping and polishing optical surfaces of complex shapes. A fluid jet system is used to guide a premixed slurry at pressures less than 6 bars to the optical surface. We used a slurry comprising water and 10% #800 SiC abrasives (21.8 mum) to reduce the surface roughness of a BK7 sample from 350 to 25 nm rms and to vary the shape of a polished sample BK7, maintaining its surface roughness of 1.6 nm rms, thereby proving both the shaping and polishing possibilities of the presented method.     

Surface finish requirements for soft x-ray mirrors

We have examined the correlations between direct surface-finish metrology techniques and normalincidence, soft x-ray reflectance measurements of highly polished x-ray multilayer mirrors. We find that, to maintain high reflectance, the rms surface roughness of these mirrors must be less than ~ 1 ? over the range of spatial frequencies extending approximately from 1 to 100 μm(-1)1 (i.e., spatial wavelengths from 1 μm to 10 nm). This range of spatial frequencies is accessible directly only through scanning-probe metrology. Because the surface-finish Fourier spectrum of such highly polished mirrors is described approximately by an inverse power law (unlike a conventional surface), bandwidth-limited rms roughness values measured with instruments that are sensitive to only lower spatial frequencies (i.e., optical or stylus profileres) are generally uncorrelated with the soft x-ray reflectance and can lead to erroneous conclusions regarding the expected performance of substrates for x-ray mirrors.     

Effect of Initial Surface Quality on Final Roughness and Texture of Annealed Ni-5at.%W Tapes Coated with a Gd2Zr2O7 Buffer Layer

Surface roughness of Ni-5at.%W tapes in cold-rolled and annealed conditions after subsequent deposition of a Gd₂Zr₂O₇ buffer layer has been studied as a function of the polishing grade, taking grain boundary grooving into account. It is found that annealing decreases the initial mean surface roughness achieved by mechanical polishing of the cold-rolled material, except after very fine polishing. Furthermore, compared to the surface of the tape annealed after fine polishing, the mean roughness slightly increases after the deposition of the buffer layer. Grain boundary grooving was found to impose a lower limit for the mean surface roughness. In the annealed tapes, the fraction of orientations within 5^○ from the ideal cube orientation was observed to be very sensitive to the surface roughness before annealing.     

Roughness and recording properties of particulate tapes: A quantitative study

Recording properties such as modulation noise and output are known to be strongly influenced by the surface roughness of the magnetic coating. On the basis of a simple two-dimensional model for the contact between magnetic head and coating we are able to account for the roughness effects quantitatively. The head-tape distance is used as an intermediate parameter. Our model was successfully tested by experiments on 8 mm metal powder tapes and 1/2-inch video tapes.     

Investigation of the properties of an ion-etched plane laminar holographic grating

We have measured the efficiency over the range 125-225 A of a bare ion-etched plane laminar holographic grating made of fused silica and with 1000 grooves/mm. The measured efficiency of each order oscillates with wavelength because of constructive and destructive interference between radiation diffracted from the lands and the grooves. We measured the grating groove profile with an atomic force microscope, and the resulting groove depth of 434 ? 6 A agrees well with the values determined independently from the oscillatory behavior of the efficiency measurements. Grating efficiency in the +1 order peaked at values of 0.027%, 0.011%, and 0.005% at wavelengths of 191, 157, and 132 A, respectively; and the derived groove efficiencies are 27%, 25%, and 27%. The irregular shape at the land-groove edges dominates the large grating roughness of 23-45-A rms, but even regions far from the edges have a roughness of 10-18-A rms. The average groove profile was used to model the grating efficiency, and the resulting wavelengths predicted for different order maxima and minima agree well with measured wavelengths, although the calculated efficiencies are greater than the measured results by 10-20%.     

Effects of interface roughness on the spectral properties of thin films and multilayers

We introduce two parameters, large-scale and small-scale rms roughness, to take into account the interface properties of thin films and multilayers in the calculation of their specular reflectance and transmittance. A theoretical motivation for the introduction of these two parameters instead of a standard single rms roughness is provided. Experimental power spectral density functions of several samples are used to illustrate ways in which the parameters introduced can be evaluated.     

High density recording with perpendicular Co-Cr-Nb media and ring heads

Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI).     

Optical profilometry of poly(methylmethacrylate) surfaces after reshaping with a scanning photorefractive keratectomy (SPRK) system

A prototype frequency-quintupled Nd:YAG laser was used with a scanning system to create, on poly(methylmethacrylate) (PMMA) blocks, ablations corresponding to a correction of 6 diopters of myopia by photorefractive keratectomy. The topography of the ablated samples was measured with an optical profilometer to evaluate the smoothness and accuracy of the ablations. The ablation depth was larger than expected. With a 50% to 70% spot overlap, large valleylike variations with a maximum peak-to-peak amplitude of 20 μm were observed. With an 80% spot overlap, the rms surface roughness was 1.3 μm, and the central flattening was 7 diopters. This study shows that optical profilometry can be used to determine precisely the ablation per pulse and the smoothness and accuracy of surface ablations. Knowing the exact ablation per pulse is necessary to produce a smooth and accurate corneal surface by scanning photorefractive keratectomy.     

Experimental determination of the surface roughness parameter in metal films

New approximate equations for the conductivity of metal films are derived from the theoretical predictions of the surface roughness model previously proposed to describe the effect of the rms surface roughness on the film conductivity. Comparison between exact and approximate values of the film conductivity shows good agreement in well defined thickness and roughness parameters ranges. It is found that these approximate equations are convenient tools for a systematic study of the influence of annealing temperature or condensation conditions on the film surface properties. On the basis of the present model previously published data are reinterpreted giving experimental values for the fractional change in the surface roughness due to the nucleation of a metal overlayer.     

Analysis of the surface roughness and dimensional accuracy capability of fused deposition modelling processes

Building up materials in layers poses significant challenges from the viewpoint of material science, heat transfer and applied mechanics. However, numerous aspects of the use of these technologies have yet to be studied. One of these aspects is the characterization of the surface roughness and dimensional precision obtainable in layered manufacturing processes. In this paper, a study of roughness parameters obtained through the use of these manufacturing processes was made. Prototype parts were manufactured using FDM techniques and an experimental analysis of the resulting roughness average ( R a ) and rms roughness ( R q ) obtained through the use of these manufacturing processes was carried out. Dimensional parameters were also studied in order to determine the capability of the Fused Deposition Modelling process for manufacturing parts.