Showing papers on "Surface roughness published in 2000"

Effects of the Surface Roughness on Sliding Angles of Water Droplets on Superhydrophobic Surfaces

Abstract: Various superhydrophobic films having different surface roughnesses were prepared, and the relationships between the sliding angle, the contact angle, and the surface structure were investigated. In the highly hydrophobic region, the sliding angles of water droplets decreased with increasing contact angles. Microstructural observation revealed that surface structures that can trap air are important for the preparation of low-sliding-angle surfaces. We have also derived an equation that describes the relationship between sliding angles and contact angles on superhydrophobic surfaces with roughness. The results calculated on the basis of this equation agreed well with the experimental ones. Moreover, we have successfully prepared a transparent superhydrophobic film whose sliding angle is ∼1° for a 7 mg water droplet. On this film, there was almost no resistance to the sliding of water droplets. The film obtained satisfies the requirements of superhydrophobicity, transparency, and a low water sliding angle.

Roughness-induced non-wetting

Abstract: It is shown that a certain class of self-affine profiles of surface roughness may render any substrate with a non-zero microscopic contact angle non-wet, i.e., give it a macroscopic contact angle close to 180 degrees. This is in some contrast to previous work and not only of potential applicational interest, but may also contribute to the amazing water repellency of some plant leaves.

Direct experimental evidence of slip in hexadecane: solid interfaces

Abstract: The boundary condition for the flow velocity of a Newtonian fluid near a solid wall has been probed experimentally with a novel setup using total internal reflection-fluorescence recovery after photobleaching leading to a resolution from the wall of the order of 80 nm. For hexadecane flowing on a hydrocarbon/lyophobic smooth surface, we give what we think to be the first direct experimental evidence of noticeable slip at the wall. We show that the surface roughness and the strength of the fluid-surface interactions both act on wall slip, in antagonist ways.

Effect of size and roughness on light transmission in a Si/SiO2 waveguide: Experiments and model

Abstract: In this letter, we experimentally evaluate the effect of miniaturization and surface roughness on transmission losses within a Si/SiO2 waveguide system, and explain the results using a theoretical model. Micrometer/nanometer-sized waveguides are imperative for its potential use in dense integrated optics and optical interconnection for silicon integrated circuits. A theoretical model was employed to predict the relationship between the transmission losses of the dielectric silicon waveguide and its width. This model accurately predicts that loss increases as waveguide width decreases. Furthermore, we show that a major source of loss comes from sidewall roughness. We have constructed a complete contour map showing the interdependence of sidewall roughness and transmission loss, to assist users in their design of an optimal waveguide fabrication process that minimizes loss. Additionally, users can find an effective path to reduce the scattering loss from sidewall roughness. Using this map, we confirm that n...

Qualitative and quantitative study of human osteoblast adhesion on materials with various surface roughnesses.

Abstract: We quantitatively evaluated the adhesion of human osteoblasts on orthopedic metallic substrates (Ti6Al4V alloy) with various surface roughnesses at several times after inoculation and studied its correlation with qualitative changes in the expression of adhesion proteins and with parameters extensively describing the surface topographies. Cells were orientated in a parallel order on polished surfaces. This orientation was not affected by residual grooves after polishing. On sandblasted surfaces the cells never attained confluence and had a stellate shape, and the cell layer had no particular organization. Extracellular matrix (fibronectin, type I collagen, osteopontin) and cytoskeletal protein (actin, vinculin) orientation reflected the cell layer organization. In our experiment human osteoblasts expressed α3β1 integrin but not α2β1 integrin. In addition to currently analyzed roughness magnitude parameters, we calculated roughness organization parameters (fractal dimension parameters) of the substrates. We observed lower adhesion and proliferation on less organized surfaces (i.e., sandblasted ones). The significant statistical correlation observed between fractal dimension parameters (describing surface roughness organization) and cell parameters adds a new concept to the studies of substratum roughness influence on cell behavior. An attempt at modelization of the cell–surface interaction was made that includes the influence of fractal dimensions parameters.

Suggested guidelines for the topographic evaluation of implant surfaces.

Abstract: The bone anchorage components of commercially available oral implant systems differ in surface roughness by at least sixfold. Correct reporting of the surface roughness of implant systems is important, since one cannot exclude the possibility that surface roughness will influence clinical results. However, many confusing statements are found in the literature when the surface topography of implants is described. Different measuring instruments and techniques strongly influence the outcome of a topographic characterization. Furthermore, a screw-type design introduces problems for most measuring instruments. Without a standard procedure, it is generally impossible to compare values from one study with another. The aim of the present study was to suggest standards for topographic evaluation of oral implants in terms of measuring equipment, filtering process, and selection of parameters. It is suggested that the measuring instrument be able to measure all parts of a threaded implant if the investigation relates to such a design. Preferably, 3-dimensional measurements should be performed. On screw-type implants, tops, valleys, and flanks should be evaluated. At least 3 samples in a batch should be evaluated, filter size must be specified, and at least one of each height, spatial, and hybrid parameter should be presented.

Kilometer‐scale roughness of Mars: Results from MOLA data analysis

Abstract: The Mars Orbiter Laser Altimeter (MOLA) data are used to characterize the kilometer-scale surface roughness of Mars. The median absolute value of the differential slope at a given baseline is proposed as a data-derived measure of the surface roughness at this scale. Study of the scale dependence of roughness for the smoothest terrains gives an independent estimate of 20 cm for MOLA ranging accuracy. The baseline lengths from 0.6 to ∼20 km are used, and kilometer-scale roughness is mapped for the entire surface. The maps show that different geological units have distinctive roughness characteristics. Scale dependence of roughness for a number of geological units is presented and discussed. The southern polar cap is rougher than the northern at kilometer and subkilometer scale, which suggests differences in the sublimation/condensation balance. The Vastitas Borealis Formation has a distinctive 3-km-scale background surface topography, which suggests a nonvolcanic origin for its upper layer. Young volcanic plains in Amazonis Planitia and the eastern part of Elysium Planitia are very similar to each other in their roughness characteristics and differ from other volcanic plains on Mars, which suggests a distinctive eruption style. There are systematic latitudinal variations of roughness in both the southern highlands and the northern lowlands: terrains at high latitude are smoother at short baselines; the characteristic vertical scale related to this difference is several meters. Processes that could be responsible for formation of this trend include creep of ice-rich near-surface material at high latitudes, treatment of the surface with repetitive deposition and sublimation of seasonal frost, climate-controlled deposition and/or cementation of dust at high latitudes, and repetitive sublimation and accumulation of subsurface ice at low latitudes with climate variations. All mechanisms of origin could operate more effectively under different climate conditions. Relevant morphological observations favor mechanisms involving deposition of smooth blankets at high latitudes.

Roughness evolution of ion sputtered rotating InP surfaces: pattern formation and scaling laws.

Abstract: The topography evolution of simultaneously rotated and Ar (+) ion sputtered InP surfaces was studied using scanning force microscopy. For certain sputter conditions, the formation of a highly regular hexagonal pattern of close-packed mounds was observed with a characteristic spatial wavelength which increases with sputter time t according to lambda approximately t(gamma) with gamma approximately 0.26. Based on the analysis of the dynamic scaling behavior of the surface roughness, the evolution of the surface topography will be discussed within the limits of existing models for surface erosion by ion sputtering.

On the characterization of agricultural soil roughness for radar remote sensing studies

Abstract: The surface roughness parameters commonly used as inputs to electromagnetic surface scattering models (SPM, PO, GO, and IEM) are the root mean square (RMS) height s, and autocorrelation length l. However, soil moisture retrieval studies based on these models have yielded inconsistent results, not so much because of the failure of the models themselves, but because of the complexity of natural surfaces and the difficulty in estimating appropriate input roughness parameters. In this paper, the authors address the issue of soil roughness characterization in the case of agricultural fields having different tillage (roughness) states by making use of an extensive multisite database of surface profiles collected using a novel laser profiler capable of recording profiles up to 25 m long. Using this dataset, the range of RMS height and correlation values associated with each agricultural roughness state is estimated, and the dependence of these estimates on profile length is investigated. The results show that at spatial scales equivalent to those of the SAR resolution cell, agricultural surface roughness characteristics are well described by the superposition of a single scale process related to the tillage state with a multiscale random fractal process related to field topography.

Electrochemical pretreatment of polycrystalline gold electrodes to produce a reproducible surface roughness for self-assembly: a study in phosphate buffer pH 7.4

Abstract: It has been emphasized in several studies that the state of the surface, including the surface roughness, is very important for the reproducible formation of high-quality self-assembled monolayers on gold. The pulsed-potential pretreatment procedure described in this paper can, in a reproducible way, reduce the surface roughness of mechanically polished polycrystalline gold electrodes by a factor 2. The developed procedure, in which the gold is alternately oxidized and reduced, has been optimized for use in a flow system (100 mM phosphate buffer pH 7.4). The influence of the pretreatment procedure on the surface roughness of the electrodes has been studied by in-situ oxygen adsorption measurements using cyclic voltammetry. The most effective pulse regime in producing a gold surface with a reproducible and relatively low surface roughness is a triple-potential pulse waveform, with potentials of +1.6, 0.0, and −0.8 V vs SCE and pulse widths of 100 ms for each potential. Prolonged pulsing for 2000−5000 s wit...

Assessment of effective-medium theories in the analysis of nucleation and microscopic surface roughness evolution for semiconductor thin films

Abstract: Real-time spectroscopic ellipsometry (SE) data collected during the nucleation and growth of hydrogenated amorphous silicon (a-Si:H) thin films have been analyzed by applying one and two layer optical models incorporating different effective medium theories (EMT's). The purpose of the EMT's is to simulate the dielectric functions of the microscopically inhomogeneous nucleating and surface roughness layers used in the models. Five one-parameter EMT's have been considered in this study for the characterization of three classes of microscopically inhomogeneous layers, including (i) 5\char21{}20 \AA{}-thick nucleating layers consisting of isolated a-Si:H clusters on the underlying substrate, (ii) 10\char21{}15 \AA{}-thick nucleation-induced surface roughness layers on very thin (200 \AA{}) a-Si:H films, and (iii) 40\char21{}80 \AA{}-thick substrate-induced surface roughness layers on thicker (g2500 \AA{}) a-Si:H films. In all three applications, the Bruggeman effective medium approximation (EMA) provides the best overall fits to the time evolution of the SE data, and complexities beyond the simple one-parameter EMA cannot be justified in view of existing experimental limitations. Furthermore, many of the general features of nucleation, coalescence, and bulk layer growth deduced in the SE analysis and used in previous studies to understand and optimize materials and device fabrication, are found to be essentially independent of the EMT used in the analysis.

Microstructural study of the theta-alpha transformation in alumina scales formed on nickel-aluminides

Abstract: Luminescence spectroscopy and scanning electron microscopy have been used to study the transformation from theta-Al2O3 to alpha-Al2O3 on the surface of platinum-modified nickel aluminide, (Ni,Pt)Al, bond coats on superalloys during initial stages of oxidation at 1,000-1,200°C. The transformation can proceed in a number of ways, depending on the surface roughness, leading to different microstructures of the stable alpha-alumina scale. The use of the luminescence method makes it possible to correlate microstructural features of the oxide with the local stress through piezospectroscopic shifts of both alpha- and theta-alumina optical spectra.

Adhesion Forces Measured by Atomic Force Microscopy in Humid Air

Abstract: Adhesive forces measured with an atomic force microscope under ambient conditions are generally regarded to be dominated by non-surface-specific capillary force. In this study, the nature of the “pull-off” force on a variety of surfaces was investigated as a function of relative humidity. The results indicate that even under the condition where capillary condensation occurs there is chemical specificity in the measured pull-off force. Issues such as tip−surface contact time and surface roughness were ruled out as possible artifacts. A mathematical model of pull-off force as a function of relative humidity is proposed in which the chemical specificity is explained.

Parametric process optimization to improve the accuracy of rapid prototyped stereolithography parts

Abstract: The functional requirements of a rapid prototyping system are speed and accuracy, and they are both functions of vendor defaulted and user selected manufacturing parameters. Accuracy is evaluated by dimensional errors, form errors and surface roughness of manufactured parts. A specially designed specimen with 20 dimensional, geometrical, and surface roughness features has been used in the inspection of RP manufacturing processes. In terms of Taguchi experimental design techniques, an orthogonal array of experiments has been developed which has the least number of experimental runs and desired process parameter settings. Using a 3-D coordinate measuring machine and surface profilometer, a series of measurements in evaluating the SLA parts quality has been conducted to find the functional relationships between the output part quality and input manufacturing process parameters. Two analysis tools, response surface methodology and Analysis of Variance (ANOVA), have been used to evaluate the SLA RP process and to perform the product optimization. The optimal setups of SLA manufacturing parameters for both individual features and a general part with various features have been concluded from this study.

Rubber Friction on Self-Affine Road Tracks

Abstract: A basic theoretical concept of rubber friction on rough surfaces is presented that relates the frictional force to the dissipated energy of the rubber during sliding stochastic excitations on a broad frequency scale. It is shown that this is of high relevance for tire traction and allows for a prediction of the likely level of friction of tread compounds on the basis of viscoelastic data. The impact of both, the frequency dependent loss- and storage modulus on the frictional force during sliding of tires on rough tracks, is demonstrated quantitatively for different sliding velocities. The effect of the surface roughness of road tracks is described by three characteristic surface descriptors, i.e., the fractal dimension and the correlation lengths parallel and normal to the surface. These descriptors can be obtained from a fractal analysis of the road texture via stylus- or laser measurements. In particular, it is shown that the applied model of rubber friction is in agreement with the classical f...

Theoretical investigation of the distance dependence of capillary and van der Waals forces in scanning force microscopy

Abstract: The capillary and van der Waals forces between a tip and a plane in a scanning force microscope (SFM) are calculated. The forces are calculated for a fixed distance of tip and sample, as well as during retracting of the tip from the sample surface. The exact geometric shape of the meniscus is considered, with the boundary condition of fixed liquid volume during retraction. The starting volume is given by the operating and environmental conditions (surface tension, humidity, and tip geometry) at the point of lowest distance between tip and surface. The influence of the different parameters, namely, humidity, tip geometry, tip-sample starting distance, surface tension, and contact angles are studied. For each force curve also the geometric shape of the meniscus is calculated. The capillary forces are compared with van der Waals forces to understand their relative importance in various operating conditions. In addition to application in SFM, this analysis is useful in the design of surface roughness in microdevices for low adhesion in operating environments.

An Investigation into Roller Burnishing

Abstract: Burnishing, a plastic deformation process, is becoming more popular as a finishing process: thus, how to select the burnishing parameters to reduce the surface roughness and to increase the surface microhardness is especially crucial This paper reports the results of an experimental program to study the influence of different burnishing conditions on both surface microhardness and roughness: namely, burnishing speed, force, feed, and number of passes Also, it reports the relationship between residual stress and both burnishing speed and force The residual stress distribution in the surface region that is orthogonally burnished is determined using a deflection etching technique Mathematical models are presented for predicting the surface microhardness and roughness of St-37 caused by roller burnishing under lubricated conditions Variance analysis is conducted to determine the prominent parameters and the adequacy of the models From an initial roughness of about Ra 45 μm, the specimen could be finished to a roughness of 05 μm It is shown that the spindle speed, burnishing force, burnishing feed and number of passes have the most significant effect on both surface microhardness and surface roughness and there are many interactions between these parameters The maximum residual stress changes from tensile to compressive with an increase in burnishing force from 5 to 25 kgf With a further increase in burnishing force from 25 to 45 kgf, the maximum residual stress increases in compression

Effect of surface roughness of porcelain on adhesion of bacteria and their synthesizing glucans

Abstract: Statement of Problem: In some instances of porcelain restoration, refinishing is inevitable. In terms of plaque accumulation on porcelain, refinishing could be a substitute method for glazing. Purpose: This study compared the amount of adhesion of plaque components (bacterial cells and glucans) on porcelain disks with various degrees of surface roughness to assess the effects of surface roughness on the amount of plaque accumulation. Material and Methods: Radiolabeled cell suspensions were incubated with porcelain disks for 3, 8, and 24 hours at 37°C, and the amounts of adhered cells and glucans were measured by using a liquid scintillation method. Results: The amount of cells and glucans adhered on porcelain increased with incubation time. The surface roughness value and the amount of plaque adhesion decreased with the increase in polishing level. However, the greatest amount of plaque was adhered on glazed surfaces, although their surfaces were smoother than the surfaces polished with 120- or 600-grit abrasive papers. Conclusion: With the exception of glazed surfaces, a positive correlation between surface roughness and the amount of plaque accumulation was observed. Repolishing with a diamond paste would not induce problems of plaque accumulation, compared with an intact glazed surface. (J Prosthet Dent 2000;83:664-7)

Adhesion at a granular surface

Abstract: The adhesion of an ultrathin carbon nitride (CN) coating to the surface of a two-phase CoPt–SiO2 granular film heterogeneous at the 10 nm scale has been studied using nanoscratch techniques. The nanoscratch resistance was found to depend sensitively on the volume fraction of the two phases. Both nanoscratch experiments and complementary electron microscopy observations indicate that CN adheres much more strongly to the SiO2 matrix than to the CoPt granules resulting in enhanced tribological performance in SiO2-rich films. The relative weakness of the CN/CoPt interface is correlated to the absence of interfacial metal nitride formation. The adhesion of the CN coating to the granular surface, the intrinsic mechanical properties of the underlying granular film (nanoindentation hardness and modulus), and the vertical rms surface roughness of the granular layer are all fundamentally changed as the CoPt content reaches the percolation threshold.

Stress and deformation along wavy frictional faults

Abstract: Locally inhomogeneous stress states are expected along faults owing to slip on geometrically irregular fault surfaces. We use an analytical model of elastic deformation along a wavy frictional fault to evaluate the variation in local stress state as a function of surface roughness, elastic modulus, slip, coefficient of friction, and far-field stress. The total stress state along the fault may be described by the sum of a basic stress component resulting from frictional slip on a planar fault surface and a perturbed stress component resulting from the presence of roughness. Roughness produces a variation in normal stress across the fault surface, and assuming roughness and modulus appropriate to crustal faults, the normal stress should be reduced to a near-zero magnitude locally, such that separation of fault walls is likely. The large variation in normal stress along the fault surface resulting from fault roughness may be responsible, in part, for complexity in moment release during large earthquakes and for lateral variation in seismic coupling along faults. The variation in principal stress orientations and magnitudes along a fault increases with a decrease in the coefficient of friction of the fault. The location and size of regions with a high likelihood for brittle failure depend on the orientation of the far-field principal stress and fault friction. The average orientation of the principal stresses in the region of likely failure is not the same as the far-field principal stress orientation. Although inversion of earthquake and fabric data for stress orientation along a fault may be possible, the model results suggest that inversion results are insufficient to determine far-field stress states and fault friction without additional independent data.