Surfaces geometry

A clean Si(100)-2 x 1 surface is formed by thermally annealing a Si( 100) substrate to 1200°C in UHV, and on cooling the surface reconstructs to form 

The roughness of the silica surface could introduce the steric hindrance of the surface accessibility similar to the effect of the micropores. In the discussion above, we assume the ideal tubular geometry of the silica surface. The use of different probe molecules for the BET measurement of silica surface area (such as N2, Ar, Kr, benzene, etc.) leads to significant difference in the surface area values for the same silica sample. It was suggested that silica surfaces possess the property of fractals [16] this essentially means that molecules of different size will see a different surface area. 

Molecular nitrogen will see a significant surface area due to its small size comparable to the dimensions of the surface roughness, while bigger molecules such as pyrene will not be able to see all ridges and valleys and will see a significantly lower effective surface area. These factors have been studied extensively [17] for silica, and authors have found fractal factors to vary between 2 and 3, depending on the silica synthesis, treatment, and so on. 

Adsorbent surface area (S) is measured as a product of molecular area (o) of a probe substance and the number of the molecules (N) in complete adsorbed monolayer. On the fractal surface the total number of molecules in the monolayer is dependent on its roughness and could be expressed as 

On the flat surface, D is equal to 2 and only in this case the surface area is not dependent on the size of probe molecule. 

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Fauster T 1988 Surface geometry determination by large-angle ion scattering Vacuum 28 129... 

Since its initial development, SERS has been used for the surface characterization of a good iiumber of systems. One important extension to the use of SERS has been in the detemiination of surface geometries. Figure Bl.22.6 shows... 

Accuracy of Pyrometers Most of the temperature estimation methods for pyrometers assume that the objec t is either a grey body or has known emissivity values. The emissivity of the nonblack body depends on the internal state or the surface geometry of the objects. Also, the medium through which the therm radiation passes is not always transparent. These inherent uncertainties of the emissivity values make the accurate estimation of the temperature of the target objects difficult. Proper selection of the pyrometer and accurate emissivity values can provide a high level of accuracy. 

Many factors influence acid corrosion. Metallurgy, temperature, water turbulence, surface geometry, dissolved oxygen concentration, metal-ion concentration, surface fouling, corrosion-product formation, chemical treatment, and, of course, the kind of acid (oxidizing or nonoxidizing, strong or weak) may markedly alter corrosion. 

A relatively complete listing of all surface geometries determined by LEED can be found in the NIST surface structure data base [2.250]. 

A meehanical analysis of the near surface stresses in a wedge test as a function of surface geometry shows that tan a is equal to the ratio of the shear stress to the peel stresses (Fig. 4). 

The word deterministic" means that the model employs a specific surface geometry or prescribed roughness data as an input of the numerical procedure for solving the governing equations. The method was originally adopted in micro-EHL to predict local film thickness and pressure distributions over individual asperities, and it can be used to solve the mixed lubrication problems when properly combined with the solutions of asperity contacts. 

Considerable numbers of the numerical solutions of full-Hlm EHL for different surface geometries, such as the smooth surfaces, surfaces with single asperity, and sinusoidal waviness, were published over the past years. They provide good reference data for the purpose of model validation. 

Surface Geometry Amplitude (/am) Wavelength (xa) Load (N) Sliding speed (mm/s)... 

The accuracy of LDF calculations in the prediction of surface geometries not only holds for clean metal surfaces such as the W(001) surface discussed above, but is also found for adsorbates such as H (27), O (28), and S (29) on Ni(OOl) surfaces. Rather than going into detail on clean and adsorbate covered surfaces, we will now focus on the description of the C-C bond by LDF theory. To this end, we first discuss a layer of condensed benzene rings, i.e. a graphite monolayer, and then focus our attention on the ethylene molecule. 

MA Ramadan, R Tawashi. Effect of surface geometry and morphic features on the flow characteristics of microsphere suspensions. J Pharm Sci 79 929-933, 1990. 

Generally, all band theoretical calculations of momentum densities are based on the local-density approximation (LDA) [1] of density functional theory (DFT) [2], The LDA-based band theory can explain qualitatively the characteristics of overall shape and fine structures of the observed Compton profiles (CPs). However, the LDA calculation yields CPs which are higher than the experimental CPs at small momenta and lower at large momenta. Furthermore, the LDA computation always produces more pronounced fine structures which originate in the Fermi surface geometry and higher momentum components than those found in the experiments [3-5]. 

The rotating hemispherical electrode (RHSE) was originally proposed by the author in 1971 as an analytical tool for studying high-rate corrosion and dissolution reactions [13]. Since then, much work has been published in the literature. The RHSE has a uniform primary current distribution, and its surface geometry is not easily deformed by metal deposition and dissolution reactions. These features have made the RHSE a complementary tool to the rotating disk electrode (RDE). 

However, there is more information in the tunneling current than just the surface geometry (e.g., STM), barrier height and shape, or barrier thickness. If a structured barrier is considered, one in which there are discrete electronic and/or vibrational... 

According to Eq. (27), Stromme et al.125,126 developed systematically the peak-current method to determine the fractal dimension of the electrode surface by using cyclic voltammetry. It must be recalled that this method is valid when the recorded current is limited by diffusion of the electroactive species to and away from the electrode surface. Since the distribution of the reaction sites provides extensive information about the surface geometry, the fractal dimension of the reaction site distribution may agree with the fractal dimension of the electrode surface which is completely electrochemical-active. In addition, it is well known that this method is insensitive to the IR drop in the electrolyte.126... 

The calculation results indicate that a plane wave cutoff energy of 280 eV and Monkhorst-Paek k-point sampling density of 4 x 4 x 4 are sufficient for the lattice constant and total energy to converge to within 0.0005 A and lO" eV respectively. For surface relaxation, a plane wave cutoff of 280 eV and a 4 x 4 x 1 k-point mesh are sufficient to converge the surface geometry to within 0.001 A and relaxed surface energies to within 0.001 Vrc. ... 

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