Surface Roughness Factor Research Articles

Atomic force microscopy study of morphology and dislocation structure of InAs and GaSb grown on highly mismatched substrates

We have studied the surface morphology and dislocation structure of InAs grown on GaAs or InP substrates and of GaSb grown on GaAs substrates by metalorganic chemical vapour deposition (MOCVD). Atomic force microscopy (AFM) has been used to determine quantitative threading dislocation densities by observing singularities in the atomic terrace structure. All layers were grown using a thin ∼ 100 nm low temperature buffer layer grown at 400°C, which was found to greatly improve surface morphology for all materials combinations studied. The lowest dislocation densities were found for thick GaSb layers on GaAs, with around 1 × 10 6 cm −2 for a 5 μm layer. While somewhat higher levels were observed for InAs (5 × 10 6 cm −2 ), the surface roughness for these films was significantly lower. In all samples the limiting factor for surface roughness is observed to be the formation of hillocks consisting of growth spirals centred on dislocations. We suggest ways in which these data may be used to calculate some fundamental MOCVD crystal growth parameters such as the critical radius for nucleation.

Contact length in grinding: Part 2: Evaluation of contact length models

A non-linear curve fit method was used to identify model parameters for the prediction of contact length in grinding. The evaluation shows that the model based on a surface roughness factor demonstrates a high degree of correlation with experimental trends and behaviour. It was found that the roughness parameter R r is insensitive to depth of cut, speed ratio and material hardness, but is sensitive to the wheel-workpiece material combinations and whether grinding is conducted with or without coolant.

Effect of Mechanical Pretreatment on Gas Nitriding Behavior of Austenitic Stainless Steels

In order to develop a method of gas nitriding of austenitic stainless steels without chemical treatment such as pickling, three types of steels, SUS304, SUS316 and SUS310, were pretreated under various mechanical processes (as-cut with resinoid blade, polishing with emery papers, grinding with CBN wheel, and shot peening), followed by nitriding in NH3 gas with a flow rate of 2.8 m 3 /h at 843 K for 20 h. The influence of the mechanical pretreatment on nitriding behavior was examined in connection with two factors of surface roughness and strain-induced martensite. Nitriding reaction depends primarily on surface roughness in SUS310 and SUS316. This nitriding reaction is markedly enhanced with increasing surface roughness when its value exceeds 6 and 1 μm for SUS310 and SUS316, respectively, while no reaction is recognized for the surface roughness less than these values. In SUS304, martensitic transformation is readily induced by the mechanical pretreatment, and not only the surface roughness but also the strain-induced martensite contribute to nitriding behavior. It is confirmed from the present results that mechanical pretreatment enables the gas nitriding of austenitic stainless steels without pickling, when the surface roughness and the amount of strain-induced martensite are controlled properly.

Influence of Surface Defect Structure on the Underpotential Deposition of Pb Monolayers at Ag(111)

The underpotential deposition (upd) of Pb monolayers at Ag(111) thin-film electrodes in perchlorate solutions have been investigated as a function of the substrate defect structure. Ag(111) films were grown epitaxially on muscovite mica by thermal evaporation and annealed at 300 °C at 10-6 Torr for periods between 0 and 12 h. X-ray diffraction and electrochemical scanning tunneling microscopy indicate that thermal annealing significantly increases the degree of film crystallinity and smoothness. A more ideal voltammetric response for the upd of Pb was obtained using Ag thin-film electrodes that were annealed for periods longer than 6 h. Specifically, the width of the upd voltammetric wave, as well as the splitting between the cathodic and anodic peaks, was found to decrease with an increase in annealing time. Surface roughness factors (defined as the ratio of the electrochemically-active area relative to the geometric area) for the Ag(111) films decreased from 1.15 for unannealed films to 0.99 ± 0.03 for films after 12 h of annealing. The results indicate that previously reported voltammetric features observed for the upd of Pb monolayers in perchlorate solutions are associated with Pb deposition at Ag(111) surface defect sites.

Characterization by a.c. impedance spectroscopy of highly oriented pyrolytic graphite surfaces modified by argon plasma etching

The a.c. impedance technique has been used to characterize the surface of a highly oriented pyrolytic graphite (HOPG) basal plane after exposure to an argon plasma. HOPG surfaces show considerable roughening for plasma etching times of up to 60 min as evidenced by scanning electron microscopy. Later, a.c. impedance measurements were carried out in alkaline aqueous solutions to characterize the hydrogen-evolution reaction and the data were analysed using the constant-phase element model for etching times of up to 1 h. They showed that the surface roughness factor increases almost linearly with the etching time.

Theoretical submonolayer adsorption isotherms for hydrogen on a heterogeneous surface

The results of theoretical calculations of physical adsorption isotherms for hydrogen on a heterogeneous surface over a pressure range 10 exp–16<P (Torr)<104 and at temperatures of 3.0, 4.2, 6.0, 10, 15, 20, 25, 30, and 40 K are presented. The values of the relative coverage, Θ, span the range 10−11 up to unity. The form of the isotherm used was the Dubinin–Radushkevich equation: ln Θ=−B[RT ln(P/P0)]2 with B−1/2=528 cal/mol, R=1.9865 cal/mol deg, and P0=vapor pressure of hydrogen at the chosen temperature. In regions where this isotherm is not applicable the results have been rounded off to give the correct limiting values, i.e., Θ=kP (Henry’s law with k constant) for parts of the isotherms at T=30 and 40 K, and P=P0 for Θ≫1. Although the calculations predict only relative coverage, they provide a useful way of evaluating the surface roughness factor for hydrogen of an experimental surface. For a porous adsorbent the theory indicates how to convert the experimental data to relative coverage. Once this is done, experimental results can be compared directly with these calculations.

The dissolution of naturally weathered feldspar and quartz

Surface area measurements and dissolution experiments were performed on subsamples from a naturally weathered mineral assemblage (100–1000 μm) consisting of feldspar and quartz. The subsamples were obtained by splitting the assemblage into four different ranges of grain density, each of which was sieved to three different size fractions. BET-krypton and geometric surface areas, combined with mineralogical data and average grain diameters, showed that (1) surface roughness factors of the subsamples are generally much higher than those of freshly created surfaces by grinding and (2) for individual density ranges (i.e., at constant mineralogical composition), the surface roughness factor decreases linearly with decreasing grain diameter. Scanning electron microscopy and X-Ray diffraction showed that contributions to the surface roughness factors from secondary mineral coatings, macropores (diameters >50 nm) and etch pits are insignificant. In contrast, krypton adsorption data indicated that by far most surface roughness is due to the presence of micropores and mesopores (diameters <50 nm). These findings strongly suggest that, during natural weathering, micropores/mesopores develop at sites whose density (cm −2 of geometric surface area) is approximately proportional to grain diameter. Multivariate linear regression showed that, at similar grain diameters, the micropore/mesopore density increases in the order: quartz < microcline < albite < oligoclase/andesine. This sequence is similar to the well-known sequence of relative weatherability of these minerals, suggesting a relationship between weatherability and micropore/mesopore density. At pH 3 HCl and ambient temperature, dissolution rates of Na, K, Ca, Al and Si from the subsamples normalized to the BET-krypton surface area, were essentially independent of the grain diameter. Due to effects from surface roughness, dissolution rates normalized to the geometric surface area were essentially proportional to grain diameter. Comparison with micropore/mesopore and etch pit densities showed that the dissolution rates are determined by the pores, rather than by the etch pits. Furthermore, theoretical arguments indicate that the pore area perpendicular to the mineral surface (i.e., the pore “walls”) is essentially nonreactive and that the dissolution rates are largely determined by the pore area parallel to the mineral surface (the pore “bottoms”). The pore area parallel to the mineral surface is equivalent to (1) the leached layer/fresh mineral interface, if the micropores/mesopores develop in leached layers or (2) the dislocation outcrops where strained mineral material is in contact with the solution, if the micropores/mesopores develop at crystal defects. Tentative calculations suggest that (1) as in the laboratory dissolution during the previous natural weathering of the sample occurred from the micropore “bottoms“ rather than from the etch pits and (2) dissolution from the etch pits becomes more important with increasing exposure time to weathering conditions.

Pt/HClO 4 interface CPE: influence of surface roughness and electrolyte concentration

The double-layer region impedance of polycrystalline Pt/perchloric acid solutions interfaces was measured to determine the influence of electrode surface roughness and solution electrolyte concentration on the fractional power n of the constant phase element cpe associated to frequency dispersion in the impedance behaviour of this system. The surface roughness factor was obtained through the adsorption charge of hydrogen from cyclic voltammograms. The solution electrolyte concentration was found to have a significant effect on the cpe only when smaller than 0.5 moll −1. On the other hand, the frequency dispersion was found to depend directly on the surface roughness. An empirical linear relationship was found between the exponent n and the inverse if the roughness factor, leading to a minimum value of 76° for the phase angle; this value contrasts to the theoretically predicted value of 45°. From a general logarithmic relationship between roughness factor δ and the fractal dimension d of the electrode surface, derived from known equations, and the linear relationship between n and 1/δ, an empirical logarithmic relationship between n and d is obtained. This empirical relationship contrasts with linear relationships previously derived by other authors.

Study of Electrodeposited Nickel‐Molybdenum, Nickel‐Tungsten, Cobalt‐Molybdenum, and Cobalt‐Tungsten as Hydrogen Electrodes in Alkaline Water Electrolysis

Electrodeposited nickel‐molybdenum, nickel‐tungsten, cobalt‐molybdenum, and cobalt‐tungsten were characterized for the hydrogen evolution reaction (HER) in the electrolysis of 30 w/o KOH alkaline water at 25°C. The rate‐determining step (rds) of the HER was suggested based on the Tafel slope of polarization and the capacitance of electrode‐solution interface determined by ac impedance measurement. The HER on the nickel‐ and cobalt‐based codeposits was enhanced significantly compared with that on the electrolytic nickel and cobalt with comparable deposit loadings. The decrease in the HER overpotential was more pronounced on the molybdenum‐containing codeposits, particularly on cobalt‐molybdenum which also showed a high stability. The enhancement of the HER was attributed to both the synergetic composition and the increased active surface of the codeposits. The real electrocatalytic activity of the electrodes and the effect of their surface increase were distinguished quantitatively. The linear relations between HER overpotential and surface roughness factor of the electrodes on a Y‐log(X) plot were obtained experimentally and interpreted based on the Tafel law.

The effect of natural weathering on dissolution rates

Surface area measurements and dissolution experiments were performed on a naturally weathered mineral assemblage rich in quartz and feldspar. The surface areas of unfractured (612 μm) and ground samples were measured at different levels of surface detail, using a dissecting microscope, SEM, and the BET-krypton method. Roughness factors of the freshly created surfaces by grinding were 2.1 (SEM at 10,000× magnification) and 4.8 (BET), respectively. Roughness factors of the naturally weathered surfaces were 2.8 (SEM at 10,000×, including effects from etch pitting) and 34 (BET), respectively. These data indicate that (1) a large amount of BET surface area was created during natural weathering, and (2) etch pits did not contribute significantly to the BET surface area created during natural weathering. Comparison with data from the literature further suggests that the surface roughness factor of naturally weathered feldspar grains decreases with decreasing grain diameter. Also, most BET surface area additionally created during natural weathering appeared to be nonreactive. At pH 3 and pH 5 HCl, steady-state dissolution rates of Na, K, Ca, Al, and Si (mol·cm −2 of BET surface·s −1) were determined for the unfractured sample and for four ground samples of increasingly smaller average grain diameter. The data from the ground samples were used to extrapolate the dissolution rate of hypothetical fresh-surface grains to the average diameter of the unfractured, naturally weathered sample material. The results showed that, at 612 μm, freshly created BET surfaces would dissolve approximately one order of magnitude faster than their naturally weathered counterparts. Comparison with literature data suggests that this discrepancy in dissolution rate, at equal diameters of freshly created and naturally weathered grains, increases with increasing grain diameter. Dissolution rates of freshly created feldspar surfaces in the laboratory are frequently up to several orders of magnitude higher than those of naturally weathered feldspar surfaces in actual field situations. The findings from this research partly explain such discrepancies. However, other factors (such as imperfect contact between solution and solids, the presence of organic ligands, etc.) should also be considered in explaining the discrepancies.

Review of nondestructive techniques designed to evaluate elevated temperature toughness degradation

This paper represents a brief review of a selection of semi-nondestructive, nondestructive techniques designed to assess a materials in-service toughness degradation in the elevated temperature regime. Such an assessment in one prerequisite in arriving at realistic life evaluations of high temperature components. Both the auger electron spectroscopy (AES) and analytical electron microscopy (AEM) have shown some potential, but, to-date, AEM is not really a practical method, for measuring, from both a quantitative and reproducible viewpoint, monolayer type elemental segregation. The Electrochemical Polarisation Kinetic Reactivation (EPR) test and the chemical etching techniques have been continuously developed over the past decade and represent attractive, totally nondestructive, toughness degradation assessment techniques. Discussed are some of the limitations of the EPR test. Chemical etching techniques have demonstrated unique relationships between FATT; the shift in FATT, and such parameters as grain boundary groove width, M, replica surface roughness, R max , and grain boundary ratio factor D o /D a where D o is austenite grain size revealed by a nital etch and D a is grain size revealed by a picric acid etch. They exhibited excellent potential in the field of the practical nondestructive assessment of grain boundary embrittlement whether as a result of phosphorus (Ferritic steels) or carbide or sigma phase precipitation (Stainless steels). Finally, it has been shown that the recent development of a miniature sample sampling technique now makes the small punch test an attractive technique for assessing the material toughness of critical plant locations. Indeed, the small punch test exhibited the least data scatter in the prediction of FATT than do other indirect methods utilising composition and grain boundary evaluations.

The dependence of the surface diffusion coefficients of gold atoms on the potential: its influence on reconstruction of metal lattices

By using a method based on the time dependence of the surface roughness factor of electrodispersed gold electrodes it was possible to estimate values of the surface diffusion coefficients (Ds) of gold atoms in contact with an 1M HClO4 electrolytic solution at room temperature and as a function of the potential. The exponential growth of Ds with E at potentials positive with respect to the zero charge potential (Ez), is interpreted as a consequence of the increase in the surface mobility of gold atoms, associated with their growing interactions with species in the electrolyte (water molecules), and the consequent decrease of their interactions with bulk gold atoms, i.e. with the loss in metallic character inherent in the use of individual orbitais in the formation of covalent bonds with hydroxyls arising from water molecules.

Surface roughness of minerals and implications for dissolution studies

Large, naturally weathered mineral fragments are often ground and sieved to obtain samples for dissolution studies. If the fragments are ground to much smaller dimensions, the samples are normally assumed to contain one type of (fresh) surface only. A model has been developed to test the validity of this assumption. The model describes the surface roughness factor of ground mineral material as a function of grain size and can be used to: 1. (1) estimate the roughness factors of the freshly created and the naturally weathered surfaces; 2. (2) estimate the ratio of fresh to total surface area for the ground samples, both for geometric and for actual surfaces; and 3. (3) check the internal consistency of surface area measurements. Literature data were evaluated for intensively ground size fractions of nine different naturally weathered feldspars. Roughness factors of freshly created surfaces ranged from 2.5–11. Roughness factors of naturally weathered surfaces ranged from 130–2600, which is much higher than is generally recognized for feldspars. Comparison with surface roughness estimates from Scanning Electron Microscopy strongly suggests that etch pit formation plays a minor role in the increase in actual surface area during natural weathering. Instead, virtually all increase in surface area must be attributed to the formation of internal surface structures like micropores. The model also showed that for these ground samples, the assumption of one type of (fresh) surface is approximately correct for the geometric surfaces. For the actual (BET) surfaces, ratios of fresh to total surface area varied over almost the entire range from 0 to 1. This demonstrates that, even after intensive grinding, samples from large, naturally weathered mineral fragments can still contain substantial proportions of weathered BET surface area. Thus, previous dissolution studies in terms of fresh BET surface only may have been misinterpreted.

Fractal characterisation of electrodispersed gold electrodes

The fractal dimension of the surface, D s, of thin columnar gold electrodeposits (surface roughness factor 50–100) grown on gold wire cathodes by electroreducing hydrous gold oxide layers has been determined by measuring the diffusion controlled current of the Fe(CN) 4− 6/Fe(CN) 3− 6 reaction. The diffusion current ( I) vs. time ( t) relationships obeyed a Iα t −α dependence with D s = 2α + 1. The initial D s, value is 2.5 ± 0.1, and decreases to 2.3 ± 0.1 by keeping the deposit in contact with the electrolyte solution at 298 K due to the smoothing of the rough metal surface by surface diffusion.

Glassy carbon surface effects on the electroreduction of aromatic carbonyl compounds. II Benzophenone

Results of the voltammetric study of benzophenone reduction in dimethylformamide and aqueous media on GCE are presented together with the comparative discussion of the data for mercury and other electrodes available in the literature. The formation and stability of anion radicals and dianions and their reactivity with protonating agents on GCE are similar to those on mercury electrodes. A new surface prewave noticed in aprotic and neutral aqueous solutions on GCE has not so far been reported on any other electrode. All experimental evidences support the view that this prewave is due to the surface protonation by the acidic functional groups on GCE. The surface protonation is found to be a slow time-dependent process requiring 3-4 minutes for completion. The surface concentration evaluated from the faradaic response of the surface process is found to be around 30% or even less if the surface roughness factor is considered,. The importance of this finding to the general concept of surface acidity effects on electrocatalysis is also emphasised.

Ｍｏスパッタ膜の微視的形態に及ぼす電力密度の影響 表面粗さ測定による評価

Ｍｏスパッタ膜の微視的形態に及ぼす電力密度の影響 表面粗さ測定による評価

The Evaluation of Surface Diffusion Coefficients of Gold and Platinum Atoms at Electrochemical Interfaces from Combined STM‐SEM Imaging and Electrochemical Techniques

A simple method is presented for measuring the surface diffusion coefficients of Au and Pt atoms at electrodispersed electrodes of the same metals in contact with . The technique is based upon the time dependence of the surface roughness factor of electrodispersed metal overlayers. The method requires a model for the surface roughness of the metal structure. The model is deduced from microscopic measurements by a STM integrated into a conventional SEM microscope. This allows the relationship between the roughness factor and the area of the surface structure to be obtained. For Au and Pt in contact with an electrolyte solution, the values of our diffusion coefficients are higher than those reported in vacuum at the same temperature.

The surface diffusion of gold atoms on gold electrodes in acid solution and its dependence on the presence of foreign adsorbates

The surface diffusion coefficient ( D s) of Au atoms in 0.5 M H 2SO 4 at 298 K has been determined from the time dependence of the surface roughness factor of electrodispersed Au electrodes in 0.5 M H 2SO 4. The value of D s for 0.5 M H 2SO 4 is 5 × 10 −14 cm 2 s −1, a figure which depends considerably on the presence of adsorbable species in solution. Thus, the adsorption of pyridine produces a remarkable decrease of D s, Whereas the adsorption of Cl − ion results in the opposite effect. The corresponding values of D s are 1.2 × 10 −14 cm 2 s −1 for 0.5 M H 2SO 4 + 0.1 M pyridine, and 2.5 × 10 −13 cm 2 s −1 for 0.5 M H 2SO 4 + 5 × 10 −4 M KCl. These results are interpreted through the influence of the adsorbate on the Au surface atom diffusion mechanism.

等方性黒鉛の気孔構造のモデリング ＩＩ

Important parameters in the modeling of the pore structure of graphite are average diameter and number density of distributed capillary tubes in the bulk. However, in order to describe theoretically pore structure elements such as pore volume and gas permeability, average square diameter and average cubic diameter are newly defined. Then formulations for surface roughness factor, integral pore volume and gas permeability are made. As pore parameters of graphite pore size and integral pore volume are reported by manufacturers. Values of surface roughness factors and gas permeabilities are calculated by putting these parameter values into the formulas and compared with available experimental data for the two elements. As a conclusion pore size takes generally lager value by factor of about 3 than average diameter defined in this modeling.

ChemInform Abstract: Electrochemical and FTIR Spectroscopic Characterization of Ferrocyanide‐Modified TiO2 Electrodes Designed for Efficient Photosensitization

Abstractshow that surface roughness factors of ∼ 100‐200 are necessary for efficient dye sensitization.