Surface Roughness Amplitude Research Articles

Orientational Transitions in Symmetric Diblock Copolymers on Rough Surfaces

We present a model addressing the orientation transition of symmetric block copolymers such as PS/PMMA on smooth and rough surfaces. The distortion free energy of parallel and perpendicular lamellar phases in contact with a rough solid surface is calculated as function of the surface roughness amplitude and wavelength, as well as the polymer lamellar periodicity (molecular weight). We find an analytical expression for the orientation transition. This expression is compared and agrees well with recent experiments done with six different polymer molecular weights and surface preparations.

Investigation of the relationship between the white layer thickness and 3D surface texture parameters in the die sinking EDM process

It is a well known fact that the EDM process results in the formation of a hard, brittle recast layer on the component's surface. Several investigations have been carried out in order to assess the nature of the recast layer in terms of its phase structure, the microhardness, presence and the density of cracks, and other surface features. Some researchers [Barash, Delpretti] have reported mathematical relationships between the thickness of the white layer and 2D amplitude surface roughness parameters (such as Ra and Rt). But so far no investigation has been reported which correlates the thickness of the white layer with 3D surface roughness parameters, especially those related to spatial parameters. This paper presents an experimental investigation of the effect of the EDM process factors (current and pulse on-time) on the thickness of the white layer. Empirical equations relating the thickness of the white layer with 3D surface texture amplitude, spatial and volume parameters are presented and their physical basis is discussed. The results of this study show that a better correlation can be obtained between the average thickness of the white layer (AWLT) and the spatial parameter, Sds as compared to other 3D surface texture parameters. This is believed to be mainly due to the similar effect of the current and pulse on-time on both AWLT and Sds. The possible effect of surface tension between the solid and liquid phases on the thickness of the white layer during erosion is also discussed.

Analysis of adhesion under wet conditions for three-dimensional contact considering surface roughness

This paper describes a numerical model to estimate the adhesion coefficient between rail and wheel under wet conditions, by applying the partial elasto-hydrodynamic lubrication (EHL) theory at three-dimensional (3D) contact considering surface roughness. The effect of the characteristics of surface roughness on the adhesion coefficient is particularly focused on in this study. Based upon numerical solutions obtained by the 3D numerical model, the effects of rolling speed, water temperature, surface roughness amplitude (i.e., standard deviation of roughness height) and parameter of roughness orientation on asperity contact pressure, which has important influence on the adhesion coefficient, are investigated under wet conditions. Furthermore, to verify the adequacy of the 3D numerical model adapted to estimate the adhesion coefficient between rail and wheel, the numerical solutions are compared with the experimental values that were obtained by a twin-disc rolling contact machine.

Statistical correlation between cell adhesion and proliferation on biocompatible metallic materials

Our ambition for several years is to appreciate and quantify the long-term adhesion of cells on materials at times where the interface between cells and substrate becomes more complex, more closed to the cell/matrix/substrate interface existing in vivo. With this objective, we quantified the long-term adhesion and proliferation of human osteoblasts cultured from 24 h to 21 days on pure titanium, titanium alloy, and stainless-steel substrates presenting six different surface morphologies and two different roughness amplitude. Hence, we did proceed to the statistical correlation of cell adhesion and cell proliferation on 30 different substrates. Additionally, we described surface topography not only by the roughness amplitude but also by the roughness morphology using new specific parameters. By multiple analysis of variance, we demonstrated that nor material composition nor surface roughness amplitude did influence cell proliferation, whereas a very significant influence of the process used to produce the surface was observed meaning that the main influent factor on cell proliferation was the surface morphology. The long-term adhesion and proliferation capacity of cells were positively correlated on 23 types of substrates on 30, this positive correlation being statistically asserted on 13 types of substrates on 23. This study is the first demonstration of the existence of a statistical correlation between long-term adhesion and proliferation capacity of human bone cells on substrates with various chemical composition, surface chemistry, and surface topography.

Effect of Molecularly Thin Lubricant on Roughness and Adhesion of Magnetic Disks Intended for Extremely High-Density Recording

For extremely high-density recording using conventional technologies, the fly-height needs to decrease to less than ten nanometers. To allow such operation, disk and slider surfaces must become extremely smooth, down to root-mean-square (RMS) roughness values of a few angstroms. For super-smooth disks, molecularly thin lubricants are applied to improve tribological performance of head/disk interfaces. The focus of this study is to quantify the effect of lubricant thickness in terms of detailed roughness parameters and to evaluate the effect of roughness and molecularly thin lubricant on adhesion of magnetic disks intended for extremely high-density recording. Three identical ultra-low-flying disks have been fabricated from the same batch for this particular experiment. To investigate the effect of molecularly thin lubricants on disk roughness, super-smooth magnetic disks with increasing lubricant thickness have been measured and studied, using a primary roughness parameter set. It describes amplitude, spatial, hybrid, and functional aspects of surface roughness and is used to quantify the extremely smooth disk roughness as a function of lubricant thickness. It is found that in addition to simple amplitude parameters, hybrid and functional parameters also capture small features on the disk roughness and show distinct trends with increasing lubricant thickness. Subsequently, a continuum-based adhesion model that uses three parameters from the primary roughness parameter set, is used to predict how the varying thickness of molecularly thin lubricant and the resulting disk roughness affect intermolecular forces at ultra-low-flying head-disk interfaces. It is found that a thicker lubricant layer of 2 nm causes higher adhesion forces for ultra-low-flying-heights in the range of 1–3 nm

Characterization of Surface Roughness and Initial Conditions for Cylindrical Hydrodynamic and Mix Experiments

Hydrodynamic experiments in cylindrical geometry are used to study both mix (compressible, in convergent geometry) and mode coupling (impact of short wavelengths on long). For both types of experiments, knowledge of the initial conditions (the surface roughness spectrum, amplitude versus wavelength, as well as all target metrology) is very important. This paper is a discussion of the techniques and efforts to document and understand our initial conditions and their uncertainties and how well we can control them.

Measurement of fiber-cladding diameter uniformity by use of whispering-gallery modes: nanometer resolution in diameter variations along millimeter to centimeter lengths

Variations in fiber-cladding diameter on a nanometer scale were measured along millimeter to centimeter lengths by use of whispering-gallery modes (WGMs) in the elastic scattering of the fiber. The fiber was side coupled with a wavelength-tunable Gaussian beam. The scattered light was imaged approximately 1:1 onto a multichannel photodiode array detector. Based on the WGM wavelength shifts along the fiber, the taper of the fiber cladding's diameter was measured on a nanometer/millimeter scale. The fiber's surface roughness amplitude (in nanometers) and granular size ( approximately 100 microm) along centimeter-length fibers could also be revealed by use of higher- Q resonances.

Study of surface roughness effects in elastohydrodynamic lubrication of rolling line contacts using a deterministic model

A sinusoidal surface roughness model is adopted for the analysis of the effects of roughness amplitude and wavelength on pressure profile, film shape, minimum film thickness and coefficient of friction in a steady state EHL line contact. The influence coefficients used for the evaluation of surface displacements are calculated by utilizing a numerical method based on Fast Fourier Transform. Significant reduction is observed in the minimum film thickness due to surface roughness. Such reduction is quantified by roughness correction factor, C R, and a relationship between C R and non-dimensional surface roughness amplitude A is derived as: C R=1−0.7823 A 0.8213. This equation may prove to be of interest from designer's viewpoint. The friction coefficient is found to increase appreciably with increasing amplitude and decreasing wavelength of surface roughness.

Role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface

Debonding of a soft adhesive from a hard flat surface is initiated by the formation of cavities which extend in the volume of the adhesive. Often these cavities nucleate at or in the immediate vicinity of the interface. Adherent's surface properties, surface topography and chemical composition have an important influence on these associated micromechanisms. We performed flat probe tests using a model acrylic latex (pressure sensitive adhesive, PSA) against various rough stainless steel surfaces, prepared by varying their degree of polishing, and we observed a dual effect of increasing the amplitude of surface roughness on the micromechanisms: a decrease of the level of stress at which cavitation occurs at the beginning of the debonding, and a decrease in the rate of expansion of the cavities in a later stage of the test.

The relative influence of the topography and chemistry of TiAl6V4 surfaces on osteoblastic cell behaviour

Proliferation and adhesion of mouse (MC3T3-E1) osteoblastic cells and primary human osteoblastic cells were carried out on Ti6Al4V titanium alloy samples with varied surface roughnesses. Mechanically or manually polished surfaces were prepared to produce respectively non-oriented or oriented residual polishing grooves. Sand-blasted surfaces were prepared using 500 μm or 3 mm alumina particles. Surface roughness parameters showed a negative correlation in comparison to proliferation and adhesion parameters. X-ray microprobe chemical surface microanalysis showed complete disturbance of the surface element composition of the Ti6Al4V alloy following sand-blasting treatment. An AlO x -enriched layer was observed on sample surfaces. This may lead to the suspicion that the concomittant effect of surface roughness amplitude and AlO x surface concentration has an effect on osteoblastic cell proliferation and adhesion. These findings show the significance of chemical surface analysis after any surface treatment of titanium-based implants before any biological use.

Interface-controlled Si/SiGe-heterostructure growth and its device application

Si/SiGe heterostructures were grown by molecular-beam epitaxy. With atomic-hydrogen irradiation during the growth of the heterostructure, characteristics of modulation-doped field-effect transistors (MODFETs) were improved. A Hall effect measurement and a device simulation revealed that carrier density capable of being confined in the Si channel is limited in the MODFETs. Surface-channel metal–oxide–semiconductor field-effect transistors (MOSFETs) with strained-Si channel on various buffer layers were fabricated. Effective electron mobility in strained-Si MOSFETs with a SiGe compositionally graded buffer layer was 60% higher than that of an unstrained-Si MOSFET. The enhancement of mobility varied with the types of the buffer layers. This variation may be attributed to the amplitude of surface roughness of the strained-Si layer.

2226 カム・フォロワ間摩擦力の近似解析

Friction characteristics between cam and follower are numerically calculated using an approximate method. The model is based on partial EHL theory which consists of a film thickness formula[Ref.1] modified from Pan-Hamrock's formula[Ref.2]) considering surface roughness and the mean contact pressure-compliance relationship (GW model[Ref.3]). The effects of non-Newtonian behavior of lubricant and surface temperature rise are taken into account for the calculation of friction force. The result of this approximate method is compared with the previous study (Tanaka et al. [Ref.4]) which solved simultaneously Reynolds equation, elasticity equation, etc. and the experimental results obtained by a made apparatus similar to the system. The validity of approximate method is also examined, for mainly the effects of amplitude and directional properties of surface roughness.

Scattering from fluid loaded targets in proximity to a sediment interface: Numerical results

A null-field T-matrix formalism developed for plane-wave scattering from a fluid-loaded elastic spherical shell in proximity to a rough fluid elastic interface [J. Acoust. Soc. Am. 101, 767–788 (1997)] is extended to include scattering from sound-hard and -soft spherical targets and a sound-hard finite cylinder with hemispherical end caps and, for a planar interface, sound-hard, sound-soft, and fluid-saturated poroelastic sediments. A variety of numerical results are obtained that demonstrate some of the effects of target and sediment parameters on target–boundary acoustic coupling and target strength. Then, for small amplitude surface roughness, a perturbation formalism is used to indicate some of the effects of interface roughness.

Polymer adsorption between a rough surface and a flat surface for an ideal long chain

AbstractWe have studied the adsorption of an ideal long polymer chain between a rough surface and a flat surface. The two surfaces are basically parallel to each other and penetrable for the polymer chain. The rough surface is modeled as a sinusoidal grating and the chain is assumed to be long enough so at the ground state dominance is tenable. By solving the diffusion equation for a polymer chain in an external field, we have investigated the related eigenvalue problem and obtained the ground state energy (the lowest confinement energy) of the system. The monomer density distributions on the two surfaces are obtained and their relations to the four relevant characteristic lengths: the separation between the two surfaces h, the confinement thickness D, the surface roughness amplitude z0 and the grating wavelength λ, are discussed.

The Effects of Roughness on Piston Ring Lubrication—Part II: The Relationship between Cylinder Wall Surface Topography and Oil Film Thickness

In this investigation, a theoretical piston ring/cylinder wall model has been utilized to study the dependence of the oil film thickness on surface roughness shape and amplitude, as well as on engine operating conditions. For a given roughness, a plateau honed cylinder wall surface was found to produce a thinner oil film. It has also been shown that the small crosshatch angle used when honing the cylinder wall produces surfaces that enhance hydrodynamic action. Presented at the 47th Annual Meeting in Philadelphia, Pennsylvania May 4–7, 1992

An investigation of light scattering from flat periodic rough surfaces for surface roughness estimation

An investigation was made into the scattering of light from flat periodic rough surfaces where the roughness amplitude is much greater than the illumination wavelength. A special scattering geometry is adopted in which the plane of incidence was parallel to the lay and grazing angles were small. The Beckmann's scattering model was applied to calculate the scattering intensity, and numerical solutions were obtained for sinusoidal rough surface profiles. The results were used to determine the influence of the surface roughness amplitude and surface spatial wavelength on the scattering pattern. It was observed that for any given scattering order, the scattered intensity oscillated as the angle of incidence increased. The degree of oscillation was found to be directly related to the surface roughness amplitude because higher roughness amplitude results in a higher oscillation frequency. This characteristic was subsequently confirmed by the experimental results. Scattering intensity distributions were also measured and they were shown to have similar trends as predicted for the low scattering orders. By adopting the results from this investigation, a new method of surface roughness estimation can be developed that would cover the roughness range of normal machined surfaces. Because it is based on the intensity variation frequency rather than on absolute scattering intensity values, the method is independent of the surface spatial wavelength and material's optical properties.

Topographical features of rotated Auger samples sputtered with inert-gas ions

The effect of sample rotation on the ion-induced surface roughening for multilayer Auger samples is described using preliminary scanning electron microscopy. The surface roughness amplitude of Cu/Ag sandwiches bombarded with 1–3 keV Ar+ and Xe+ ions was found to be dramatically reduced by sample rotation, resulting in a significant improvement in depth resolution, especially for Ar+ -bombarded samples. The sputtered surfaces of rotated samples were characterized by planar crystals developed thereon, forming a striking contrast to the stationary sample surfaces thickly covered with conical microprojections. The mechanism of this two-dimensional crystal growth is discussed briefly, in terms of surface atom mobility enhanced by ion impact.

Two-Sided Texture Effects on Ultra-Thin Wide Wedge Gas Bearings

This work seeks to determine the effects of two-sided surface roughness amplitude on ultra-thin, compressible, isothermal, infinitely wide gas bearings. The transient Reynolds equation of lubrication is solved using a finite difference scheme that is second order accurate in space and time. Solutions of the Reynolds equation are presented for bearing numbers spanning seven orders of magnitude, including those experienced in magnetic hard disk recording. The results presented here show that introducing roughness on either bearing surface causes an increase in the load carrying capacity as compared to the smooth bearing case. However, when roughness is introduced on the stationary surface, the gas bearing generates higher loads which also exhibit a peak at finite bearing numbers. The load peaks increase quadratically with increasing stationary roughness amplitude. It is also demonstrated that at very high values of the bearing number, the load becomes dependent on the amplitude of the surface roughness and not its location. This suggests that a closer look at the possibility of roughening the head surface instead of the larger disk surface in order to cause a more rapid separation is warranted. Stiction resistance would still be achieved, but perhaps more economically, and wear to both surfaces would be minimized.

Entrance and Stationary Roughness Effects on the Load Carrying Capacity of a Wide Wedge Gas Bearing

The objective of this work is the determination of the effects of surface roughness amplitude and inlet conditions on ultra-thin, compressible, isothermal, infinitely-wide gas bearings. The method of study is numerical in nature and consists of a second-order accurate finite difference solution of the Reynolds equation of lubrication without molecular slip for a range of bearing numbers spanning six orders of magnitude. The motivation for this work comes from the magnetic disk drive industry where ever decreasing head flying heights are being sought to increase the recording density. Past studies by these authors of the infinitely-wide air bearing with stationary roughness have shown that, unlike in the case of a smooth bearing, the load peaks at a finite bearing number comparable to that at which current rigid disk drives operate. This suggests that it may be possible to arrange the roughness pattern in such a way as to cause the slider to separate from the hard disk more rapidly, minimizing wear to both surfaces. A wedge bearing with stationary sinusoidal roughness is studied for different roughness amplitudes and two phases. It is shown that for all configurations considered, the load exhibits a peak unlike in the case of the smooth bearing where the load monotonically reaches a peak at an infinite gas bearing number. Two rough sliders with flat tapers smoothly attached to their leading edge are also studied to answer questions regarding the role that the inlet condition plays in the resulting magnitude and behavior of the generated load. The leading taper allows the bearing to dynamically determine the entrained flow rate and maximum pressure as well as to self prescribe the inlet condition at the leading edge of the first roughness wave. The inlet conditions prescribed by the developing flow in the flat taper region still give rise to a peak in the load. The addition of the smooth taper, however, causes an overall decrease (increase) in the load when the roughness waves are entirely above (below) the plane of the taper compared to the results of the rough bearing with no taper. It is demonstrated that all the considered roughness patterns result in a peak load at a finite bearing number. Of special interest are two bearing configurations: one composed of a smooth taper followed by a transversely roughened slider and the other is a rough slider with a transverse roughness pattern whose slope at the inlet of the bearing is negative. Both are shown to achieve a maximum lifting force at low bearing numbers, providing rapid separation while alleviating the narrow rail manufacturing problem.

Heteronucleation onto Si Surfaces

ABSTRACTSurface structure and heteronucleation of GaAs, In(Ga)As and Ge onto Si surfaces by Molecular Beam Epitaxy are studied by transmission electron microscopy as functions of substrate orientation and cleaning. We find that Shiraki cleaning of vicinal ( 4 degree misorientation ) (100) Si surfaces can produce significant surface facetting at temperatures ∼ 900°C. Subsequent nucleation of GaAs is then influenced by the facet distribution. Nucleation of InAs onto vicinal (100) Si surfaces exhibits a highly bimodal distribution of nuclei dimensions and anomalously high surface diffusion lengths. Sputter and annealing of Si surfaces produces microroughness of an amplitude a few monolayers high on (211) and vicinal and exact (100) surfaces. Subsequent growth of Si buffer layers increases the surface roughness amplitude slightly on the exact (100) and (211) surfaces and significantly on the vicinal (100) surface. Nucleation densities and surface diffusion lengths of Ge on the Si buffer layers surfaces correlate to the surface roughness amplitude. We also describe techniques for experimental quantification of surface roughness amplitudes and periodicities from electron microscope lattice structure images.