Surface coverage profiles

Fig. 9. Comparison of the analytical SCF model [56] with the full numerical SCF calculation [53] for the segment density profile in flat, grafted layers at various surface densities (o is the fraction of the maximum possible surface coverage of grafted ends). The analytical profile is parabolic to its tip, while the numerical calculation shows that the density at the periphery of the layer drops off exponentially...

Figure 8.13 In situ electrochemical SXS characterization of PtsNi) 11) and Pt(l 11) surfaces (a)XRV measurements forPtsNitlll) at the (0, 0, 2.7) (filled squares) andPt(lll)at (1, 0, 3.6) (open triangles) (b) surface coverage by underpotentially deposited hydrogen (Hupd) and hydroxyl species (OHad) calculated from the cyclic voltammograms (c) segregation profile ascertained from the SXS measurements. (Reprinted with permission from Stamenkovic et al. [2007a]. Copyright 2007. American Association for the Advancement in Science.)...

Figure 16.5. CV profiles for the Pt(lll) electrode in 0.05 M HCIO4 (main graph) and evolution of the CeHe surface coverage (inset) as a function of C6H<5 concentration electrode cycling in the 0.05-0.42 V range . s =50 mV s T= 298 K.

Figure 14. Simple model demonstrating how adsorption and surface diffusion can co-Urnit overall reaction kinetics, as explained in the text, (a) A semi-infinite surface establishes a uniform surface coverage Cao of adsorbate A via equilibrium of surface diffusion and adsorption/desorption of A from/to the surrounding gas. (b) Concentration profile of adsorbed species following a step (drop) in surface coverage at the origin, (c) Surface flux of species at the origin (A 4i(t)) as a function of time. Points marked with a solid circle ( ) correspond to the concentration profiles in b. (d) Surface flux of species at the origin (A 4i(ft>)) resulting from a steady periodic sinusoidal oscillation at frequency 0) of the concentration at the origin.

Leermakers, F.A.M., Atkinson, P.J., Dickinson, E., Horne, D.S. (1996). Self-consistent-field modeling of adsorbed P-casein effects of pH and ionic strength on surface coverage and density profile. Journal of Colloid and Interface Science, 178, 681-693. 

The significance of the type designations, A, A, B, and B, are discussed in the text (also see Sheppard (4) for a visual display of the spectra). b (bcc), body-centered cubic (fee), face-centered cubic (hep), hexagonal close packed. Exhibits a soft rCH mode. d Two closely related species. Somewhat different spectra were reported in Dinardo et al. (16) JThe term 8 denotes surface coverage. e When ethyne is coadsorbed with CO, this spectrum has a type A profile. 

However, the surface coverage is the same for both copolymers when weakly adsorbed to the surface. Surface density profiles were also compared. Finally, scaling relationships for triblock copolymer adsorption under weak adsorption conditions were derived (Haliloglu et al. 1997). In a related paper (Nguyen-Misra et al. 1996), adsorption and bridging of triblock copolymers in an athermal solvent and confined between two parallel flat surfaces were studied, and the dynamic response of the system to sinusoidal and step shear was examined. 

Neutron reflectometry studies on mixed DPPC/oleic acid monolayers have been conducted using the CRISP reflectometer at RAL. First, the stmcture of DPPC monolayers was determined by measuring reflectivity profiles from three different isotopic forms of the DPPC monolayer system. This was achieved using hydrogenated (h-DPPC) and chain perdeuterated (d-DPPC) phospholipids and two different subphases of D2O and ACMW. The monolayers were studied at three surface coverages of approximately 50, 60, and 70 A /molecule. Examination of the surface pressure-area isotherm reveals that the main LE/LC phase transition for DPPC monolayers occurs over this range of molecular area (Lewis and Hadgraft, 1990). 

A comparison between pulsed flow and conventional pulsed static calorimetry techniques for characterizing surface acidity using base probe molecule adsorption has been performed by Brown and coworkers [20, 21]. In a flow experiment, both reversible and irreversible probe adsorption occurring for each dose can be measured, and the composition of the gas flow gas can be easily modified. The AHads versus coverage profiles obtained from the two techniques were found to be comparable. The results were interpreted in terms of the extent to which NH3 adsorption on the catalyst surface is under thermodynamic control in the two methods. 

Dynamic radiometry results on a Pt/Ru electrode are shown in Fig. 26. There is a clear similarity between the data shown in Figs. 25 and 26, highlighting hysteresis on both the HE and TIE profiles. However, the drop in CO surface coverage and the maximum current on the positive-going scan on Pt/Ru occur at a potential c.a. 0.2 V less positive than on Pt, and the maximum CO coverage at the Pt/Ru electrode is about half of that at the Pt electrode. 

Figure 3.22. Segment density profiles for amphiphiles in monolayers , Q mean field A. O, Monte Carlo. The normalized density distribution normal to the surface is givenas a function of distance, characterized by the layer number, at two Indicated values of the surface coverage, T= 300 14 chain elements, (Redrawn from Wang ind Rice, loc. cit.)...

Fig. 3.4 Characterization of Pt Niilll) surface red curves) compared to Pt(lll) blue curves) (a) In situ SXS profiles (confirmed existence of (lll)-skin structure as weU as improved stability over Pt(l 11) in designated potential range) (a ) Segregation profile (between 0.05 and 1.0 V first atomic layer 100 at.%, second 48 at.%, third 82 at.% and fourth 75 at.% of Pt) (b) Cyclic voltammograms and (c) surface coverage by hydrogenated species and oxide species. Reprinted with permission from [23], copyright 2007 by American Association for the Advancement of Science...

Near-field scanning microwave microscopy (NSMM) is another system that has been used for label-free detection of both DNA and RNA molecules (42). NSMM monitors the microwave reflectance, a factor that depends on the dielectric permittivity profile across the microarray surface (42). This parameter is, in turn, dependent on the length and surface coverage of the strands, as well as on the hybridization state of the molecules (e.g., unhybridized single-stranded probe vs. hybridized duplex). NSMM technique demonstrated an acceptable resolution (potentially less than 50 pm) and comparable sensitivity to the fluorescent detection (42). 

Numerous experimental studies have dealt with the problem of the conformation of N-mer brush layers immersed in P-mer melts (P>N1/2), and created by diblock copolymers [240,241,261] or other end-functioned polymers [242-245, 249,262,264,265]. The volume fraction vs depth profiles ( >(z) of end-segregating polymers (as in Figs. 36), obtained in the course of these studies, yield the surface coverage o. o is related to the surface excess z as... 

Two relatively similar brushes - PI-dPS(N=893) at the free surface of the PS matrix (P=88-3173) and (COOH)dPS (N=929) grafted onto silicon substrate in the PS matrix (P=6442) - were studied by NRA [241] and SIMS [249],respectively. The NRA data were fitted with a simple top hat brush profile (Figs. 33 and 36) and its width was taken as a measure of the brush height L. In the other study, the mean brush height L was approximated by the half-width of the brush layer as measured by SIMS. The variation of L with the surface coverage o is shown in... 

It was proposed by Andricacos et al This mechanism considers one-additive system. It is noted in Ref. 47 (Ch. 10, Sections 10.4 and 10.5) that in general, adsorption of additives (inhibitor) at the cathode affects the kinetics and growth mechanism of electrodeposition. The surface coverage of the additive (inhibitor), 0, is a function of the diffusion controlled rates of the adsorption-desorption processes. In the differential-inhibition mechanism it is assumed that a very wide range of additive fluxes over the micro-profile (vias and trenches) exists, that is, extremely low flux in deep interior comers, low flux at the bottom center, moderate flux at the sidewalls, and high flux at shoulders. 

The steady-state surface coverage by the carbon monoxide residue can be studied by anodic stripping voltammetry. By this technique, it is possible to separate the adsorption residue contribution from the bulk electrooxidation process. The micro-flux cell is adapted with a big flask containing the supporting electrolyte, which is used to wash the cell until there is no trace of methanol in solution. The current vs. potential profile mn from the adsorption potential upward is the tripping profile for the oxidation of the adsorbed residue. An example is presented in Figure 2.4. 

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