Effects Of Surface Geometry Research Articles

The influences of roughness on film thickness measurements by Mueller matrix ellipsometry

The accuracy of measurement of the thickness of uniform thin films on solid substrates by null ellipsometry is severely limited when the substrate is rough. It is impossible to separate these two effects experimentally with the null ellipsometer, and there is no theoretical basis or generally used model available to separate these effects. Thus, a dual rotating-compensator Mueller matrix ellipsometer has been constructed to carry out film thickness measurements on rough substrates. Measurements were made on a set of specially prepared specimens of 8630 steel, roughened by grit blasting with aluminum oxide. Grit sizes and blasting pressures were varied to produce 11 different roughness values ranging from 0.01 to 1.295 μm Ra, as measured with a stylus tracer device. Upon each of the 11 roughness groups, films of magnesium fluoride were overlaid to thicknesses of 89, 180, 254, and 315 nm. One set of specimens was left uncoated. Experimental results for film thickness measurements on rough surfaces matched the ideal (for smooth surfaces) form well for roughnesses up to 0.13 μm Ra, at most angles of incidence. For rougher specimens, significant deviations in results were observed for all but the largest angles of incidence. The nonideal data were attributed to the cross-polarization effects of surface geometry, and apparent depolarization. The resolution of thickness measurements was 1 nm for polished specimens, and decreased continuously to 10 nm for the roughest specimens examined.

Diffusion-limited processes on fractal surfaces generated as a set of scaled Walsh functions

The Monte Carlo technique was used for modelling mass transport to fractal electrode surfaces under conditions of a potentiostatic pulse and linear scan voltammetry. Fractal surfaces of different fractal dimension D were constructed using the Walsh-Hadamard transform. The effects of surface geometry on the form of the current response and long-time cut-off are discussed with respect to the validity of diagnostic procedures used for the electrode kinetics on smooth electrodes.

Effect of surface geometry on polymer adsorption. 3. Competitive adsorption at the .theta. point

Adsorption isotherms of binary mixtures of polystyrenes (PS) with narrow molecular weight distributions and a polydisperse PS on porous and nonporous silica surfaces have been measured in cyclohexane. For the adsorption of the binary mixture on the porous silica, when both PS chains can penetrate into the pores without significant deformation, a complete preferential adsorption of the large PS chain over the small one is observed at the plateau in the adsorption isotherm and the adsorption isotherm has a rounded shape. By contrast, when the large PS component in the mixture adsorbs more than the small PS component at the plateau, i.e. incomplete preferential adsorption, the total amount adsorbed at the plateau is larger than that for the complete preferential adsorption

Reactions at the gas-phase-porous-solid interface: Mechanisms and effects of surface geometry around room temperature

The luminescence quenching of Ru(bpy) 2+ 3 by molecular oxygen on a porous silica and controlled porous glass was studied at the 253–353 K temperature range. The reaction was observed to take place by a mixture of an Eley-Rideal (ER) and a Langmuir-Hinshelwood mechanism. The relative contribution of the two mechanisms was calculated and the ER component was found to dominate at higher temperatures. The lack of effect of the average pore diameter (apd) on the rate of the quenching reaction supports our contention that the Knudsen diffusion controlled reaction theory developed elsewhere is incorrect. In addition we show that, for porous solids, diffusion controlled reaction theory is not applicable in principle below the Knudsen regime.

Evaluation of particle effects in bremsstrahlung and in quantitative energy-dispersive x-ray microanalysis

The magnitude and the spectral form of bremsstrahlung signal contains much information about the target and is significantly influenced by the surface irregularities. By computer modelling, it is possible to extract the information to perform more accurate quantitative x-ray microanalysis for specimens with special geometries. In this research, bremsstrahlung spectra obtained from electron beams striking at selected locations of spherical particles were investigated by Monte Carlo simulations and experimental observations. The effects of surface geometries and the x-ray path lengths in the specimens on the variation of bremsstrahlung spectra and peak-to-background ratios were studied.The Monte Carlo electron trajectory calculations were determined with a screened Rutherford cross-section and a plural scattering model. The continuum x-ray depth profile is computed using Kramer's bremmstrahlung cross-section. The cross-section for inner shell ionization proposed by Green and Cosslett were employed for calculating characteristic x-rays. Bethe stopping power was determined by using the Luo-Joy modification at low energies. The mass absorption coefficient was calculated using Heinrich expression. The detector efficiency was determined experimentally.

A study of the activity of chemical groups on carbonaceous and model surfaces by infinite dilution chromatography

Surface properties of activated carbons and carbon fibers subjected to oxidation processes are investigated by means of inverse gas chromatography (IGC). A general correlation between surface density of acidic groups and the empirical parameter eπ related to electron acceptor interactions is established. Model adsorbents based on benzene derivatives with known numbers of functional groups are also studied by IGC to examine the effect of surface geometry in relationship to the eπ results from the carbons.

Effect of surface geometry on polymer adsorption. 2. Individual adsorption and competitive adsorption

Kinetics and isotherms of individual and binary mixture of various monodisperse polystyrenes on three porous silica surfaces were investigated in cyclohexane and CCl 4 as a function of the ratio of the pore size to twice the radius of gyration of a PS chain in a bulk solution

Fractal analysis of surface geometry effects on catalytic reactions

Abstract We study the effects of the surface morphology of catalysts on their performance. The surface geometry parameter is varied by taking surfaces of different fractal dimensions. The reaction mechanisms studied are the Eley-Rideal process (diffusion controled) and some modifications of it (chemically controled and side-reaction of the reactant). Theory predicts B(t) = Kt3−D/2 were B(t) is the amount reacted after time t, D is the surface fractal dimension, and K is a collection of constants. In a detailed simulation study we verified the theoretical prediction and were able to retrieve not only D, but, for the first time also K. Conditions under which an increase in surface roughness can either enhance or quench the efficiency of the catalytic reaction are identified and explained.

Fractal analysis of surface geometry effects on catalytic reactions

We study the effects of the surface morphology of catalysts on their performance. The surface geometry parameter is varied by taking surfaces of different fractal dimensions. The reaction mechanisms studied are the Eley-Rideal process (diffusion controled) and some modifications of it (chemically controled and side-reaction of the reactant). Theory predicts B( t) = K t 3− D/2 were B( t) is the amount reacted after time t, D is the surface fractal dimension, and K is a collection of constants. In a detailed simulation study we verified the theoretical prediction and were able to retrieve not only D, but, for the first time also K. Conditions under which an increase in surface roughness can either enhance or quench the efficiency of the catalytic reaction are identified and explained.

Diffusion-limited reactions at solid-liquid interfaces: effects of surface geometry

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDiffusion-limited reactions at solid-liquid interfaces: effects of surface geometryJoshua Samuel, Michael Ottolenghi, and David AvnirCite this: J. Phys. Chem. 1991, 95, 5, 1890–1895Publication Date (Print):March 1, 1991Publication History Published online1 May 2002Published inissue 1 March 1991https://doi.org/10.1021/j100158a004RIGHTS & PERMISSIONSArticle Views337Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (743 KB) Get e-Alerts

Effect of surface geometry on adsorption and desorption of polymer chains

Adsorption and desorption of polystyrenes (PS) at three different porous silica surfaces in cyclohexane is investigated as a function of the size ratio of the average pore diameter to twice the radius gyration of a PS chain. The adsorption isotherms for the porous silica surfaces are almost the same as for the nonporous silica in their shape. However, the plateau adsorbed amount increases with an increase in the size ratio. A similar surface geometry effect is also observed for the desorption of polystyrenes by dioxane. These phenomena can be interpreted in the terms of the surface fractal when the whole polymer chain is regarded as the yardsticks

Atomistic Study of the Clean and Hydroxylated TiO2 Surface

ABSTRACTThe coverage of an oxidized Ti-surface by amphoteric OH groups seems to be the driving mechanism for the attachement of bone material to Ti-implants. To contribute to the quantitative and fundamental understanding of this phenomenon, an ab-inito surface method was applied to calculate the electronic structure and energetics of the clean and hydroxylated (110) TiO2 rutile surface. Some of the most important relaxation and reconstruction effects of surface geometries were derived from total energy minimization.

Effect of Surface Geometry and Morphic Features on the Flow Characteristics of Microsphere Suspensions

In this paper we present a study on the effect of surface ruggedness of microspheres on the rheological behavior of their suspensions. For this purpose, different types of ragweed pollen grains were selected as models of natural microspheres. A computer‐image processing system based on Fourier and fractal analysis of the contour was used to quantitate the micromorphology and surface roughness. The viscosity of suspensions, prepared by the dispersion of the different types of microspheres in heavy liquid paraffin, was determined. It was found that an increase in surface roughness causes an increase in the viscosity of the suspension. Additional resistance to flow could be attributed to internal friction within the suspension due to an increase in the area of contact (during collision or aggregation) among the microspheres, and between microspheres and liquid environment. These findings suggest that the surface geometry of solid particles (e.g., microcapsules, beads, and microspheres) could have a significant effect on the performance of these microparticles in suspension.

Effect of surface geometry and orientation on laminar natural convection heat transfer from a vertical flat plate with transverse roughness elements

An interferometric technique was used to determine local heat transfer coefficients for surfaces with repeated ribs and steps. The effects of parameters such as protuberance height-to-spacing ratio, conductivity of ribs, and angle of inclination were studied. It was found that heat transfer enhancement, relative to a plain vertical surface of equal projected area, was possible in laminar natural convection using transverse roughness elements of proper size and shape. In general, the stepped surfaces helped improve the heat transfer. The maximum increase in average heat transfer coefficient was 23.2% with a step pitchto-height ratio of 16. The study indicated the presence of an optimum step pitch-to-height ratio. All of the ribbed surfaces resulted in degraded heat transfer performance.

Experimental study of the enhancement of condensation heat transfer on downward-facing horizontal surfaces.

Experiments were performed to study the effects of surface geometry and porous drainage strip on the condensation heat transfer performance of downward-facing submerged and vapor space condensers to be used for the immersion cooling modules. A smooth surface and two finned surfaces with and without the porous drainage strip were tested for condensation of R-113 and methanol. For the submerged condensers, formation of vapor space under the condensing surface was observed in the low-heat.flux regime, whereas the surface was covered with rising bubbles in the high-heat-flux regime. For both the submerged and vapor space condensers, significant heat transfer enhancement over the smooth surface value was provided by the finned surfaces. For the vapor space condensers, further heat transfer enhancement was provided by use of the porous drainage strip.

The effects of the fractal geometry of surfaces on the adsorption conformation of polymers at monolayer coverage part I. The case of polystyrene

Surface geometry effects on the adsorption conformations of polymers under plateau conditions are found and analyzed by using fractal geometry considerations. The re-analysis of many adsorption studies, with special emphasize on polystyrene, shows that while on a flat surface a dense packing is formed, distorting the solution conformation into a prolate shape, on highly porous objects the solution conformation changes only slightly upon adsorption. These general trends show a surprisingly low sensitivity to the chemical nature of the polymer—solvent—surface system, emphasizing the crucial role of environmental geometry in determining adsorption conformations.

Helical repeat and linking number of surface-wrapped DNA.

The geometric properties of duplex DNA are systematically altered when the DNA is wrapped on a protein surface. The linking number of surface-wrapped closed circular DNA is the sum of two integers: the winding number, phi, a function of the helical repeat; and the surface linking number, SLk, a newly defined geometric constant that accounts for the effects of surface geometry on the twist and writhe of DNA. Changes in the helical repeat, h, and in the winding number can be deduced solely from surface geometry and superhelix density, sigma. This treatment relates the theoretically important properties twist and writhe to the more experimentally accessible quantities phi, h, SLk, and sigma. The analysis is applied to three biologically important cases: interwinding of DNA in a plectonemic superhelix, catenated DNA, and minichromosomes.

High-speed photography of surface geometry effects in liquid/solid impact

Recent theoretical studies of liquid/solid impact, in particular the geometric wave theory of Lesser and Field, have emphasized the importance of the detailed geometry in the contact area. In parallel with the theoretical work, we have developed a two-dimensional technique using gels for impact and shock studies. A combination of high-speed photography and schlieren optics allows the shocks in the liquid and solid, if it is transparent, to be visualized, as well as important processes, such as jetting, to be recorded. This paper describes the gel technique and gives results for a range of surface geometries for collision velocities of a few hundred meters per second. The relevance to damage initiation in liquid/solid impact problems, such as rain erosion, steam turbine blade erosion, and cavitation, are discussed.

Surface-enhanced Raman scattering as a probe of surface geometry effects on the polymerization of a acrylic acid on silver

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSurface-enhanced Raman scattering as a probe of surface geometry effects on the polymerization of a acrylic acid on silverJ. S. Suh and K. H. MichaelianCite this: J. Phys. Chem. 1987, 91, 3, 598–600Publication Date (Print):January 1, 1987Publication History Published online1 May 2002Published inissue 1 January 1987https://doi.org/10.1021/j100287a022RIGHTS & PERMISSIONSArticle Views166Altmetric-Citations31LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (394 KB) Get e-Alerts

Hydrogenolysis of n-butane over the (111) and (110)-(1.times.2) surfaces of iridium: a direct correlation between catalytic selectivity and surface structure

Since the use of oriented single crystals as catalysts allows a unambiguous assessment of the effects of surface geometry, the authors have investigated the hydrogenolysis of n-C/sub 4/H/sub 10/ over the close-packed (111) and the corrugated (110)-(1 x 2) surfaces of Ir. The selectivity for C/sub 2/H/sub 6/ production from the hydrogenolysis of n-C/sub 4/H/sub 10/ over Ir catalysts scales with the concentration of low-coordination-number metal surface atoms.