Multilayers surfaces

Delplancke-Ogletree, M. P. and Monteiro, O. R., Wear Behavior of Diamond-Like Carbon/Metal Carbide Multilayers," Surface and Coatings Technology, Vol. 108-109, 1998, pp. 484-488. 

Dekempeneer, E., Van Acker, K., Vercammen, K., Meneve, J., Neerinck, D., Eufinger, S., Pappaert, W., Sercu, M., and Smeets, J., Abrasion Resistant Low Friction Diamond-Like Multilayers," Surface and Coatings Technology, Vol. 142-144,2001,pp. 669-673. 

Type II This is the most common type where multilayer surface adsorption is observed. 

Fig. 3.1. Monolayer and multilayer surface phases of the n-paraffins C3—Cj on Pt(l 11), and the temperatures at which they are observed at 10" Torr...

Adsorption of block copolymers onto a surface is another pathway for surface functionalization. Block copolymers in solution of selective solvent afford the possibility to both self-assemble and adsorb onto a surface. The adsorption behavior is governed mostly by the interaction between the polymers and the solvent, but also by the size and the conformation of the polymer chains and by the interfacial contact energy of the polymer chains with the substrate [115-119], Indeed, in a selective solvent, one of the blocks is in a good solvent it swells and does not adsorb to the surface while the other block, which is in a poor solvent, will adsorb strongly to the surface to minimize its contact with the solvent. There have been a considerable number of studies dedicated to the adsorption of block copolymers to flat or curved surfaces, including adsorption of poly(/cr/-butylstyrcnc)-ft/od -sodium poly(styrenesulfonate) onto silica surfaces [120], polystyrene-Woc -poly(acrylic acid) onto weak polyelectrolyte multilayer surfaces [121], polyethylene-Wocfc-poly(ethylene oxide) on alkanethiol-patterned gold surfaces [122], or poly(ethylene oxide)-Woc -poly(lactide) onto colloidal polystyrene particles [123],... 

Figure 2 A schematic view of formation of multilayer surface films by secondary reactions of native films with solution species.

Figure 3 A schematic view of formation of multilayer surface films on active metals exposed fresh to solution phase. Stage I Fresh surface-nonselective reactions Stage II Initial layer is formed, more selective surface film formation continues Stage III Formation of multilayer surface films Stage IV Highly selective surface reactions at specific points partial dissolution of surface species Stage V Further reduction of the surface species close to the active metal, deposition-dissolution of surface species at steady state the surface film is comprised of a multilayer inner compact part and an outer porous part.

These processes lead to a complicated morphology of the active metal surface and the formation of multilayer surface films whose outer solution side is porous and nonuniform (as confirmed by SEM studies [446]). Discharge curves of Ca-TC prototype cells, which are very flat [445], prove that the basic mechanism of transport through the surface film during discharge is the first one suggested above i.e., the Cl- migrates from the outer side of the surface films to... 

Surface molecules with their polar groups buried are called endotropic , this is the normal stable position. Such surfaces have little reactivity or adsorptive power. Multilayer surfaces may be conditioned , the top... 

From combined theoretical and experimental insights, nanostructured Pt core-shell electrocatalyst architectures have recently emerged as promising, cost-effective cathode fuel cell catalysts. Pt-enriched multilayer surface shells surround Pt-poor cores that modify the reactivity of the surface Pt layer. 

Gupta BD, Sharma AK (2005) Sensitivity evaluation of a multilayered surface plasmon resonance-based fiber optical sensor a theoretical study. Sensors Actuators B Chem 107 40-46... 

Electrode surfaces modified with a multilayered surface architecture prepared by a layer-by-layer repeated deposition of several enzyme mono-layers show a modulated increase of surface-bound protein with a subsequent increase in output current, which is directly correlated with the number of deposited protein layers. The versatility of this approach allows alternate layers of different proteins for the manufacture of electrode surfaces, which are the basis for multianalyte sensing devices with multiple substrate specificities. The surface chemistry used for the manufacture of multilayered electrode surfaces is similar to that previously described for the preparation of affinity sensors, and is based on the stabilization of self-assembled multilayer assemblies by specific affinity interactions, electrostatic attraction, or covalent binding between adjacent monolayers. 

The term surface alloy is somewhat generic and may refer to a variety of different systems. Here, we apply it to those systems where ultra-thin metal layers (i.e. a few atomic layers thick) are deposited on a bulk metal surface and where the system is subsequently annealed in vacuum in order to obtain alloying in a surface region a few atoms thick. In these conditions it is possible to obtain single atomic layer binary phases, or multilayer surface alloy phases (also termed epitaxial alloys (for a general discussion of these surface alloys, see [5]. Relatively to the subject of the present paper, two Pt-Sn systems have been studied Sn-Pt(l 11) and Sn-Pt(lOO). The behavior and the structural properties of these systems will be discussed in detail in the following. 

The formation of multilayer surface alloys has also been investigated in the Sn-Pt(l 11) system, where Galeotti et al. [37] reported the formation of ordered, epitaxial alloyed Pt-Sn phases. The deposition of amounts of Sn up to 5 mono-layers (ML) at room temperature led to disordered or anyway non-epitaxial tin films. Annealing the deposited films led to interdiffusion and to the formation of various alloy phases (Fig. 17). Alloying was detectable in XPS from the... 

The Al(l 11)—(2 X 2)—Na phase, as described in Sec. 3.1, is a complicated multilayer surface alloy. We regard the successful prediction [58, 86] of the structure of this phase by DFT calculations, as evidenced by the detailed, quantitative agreement with experimental results shown in Table 6, as marking a major advance in the application of DFT theory to surfaces. 

A general description of the multilayer surface binary alloys formed by Na, and the multilayer surface ternary alloys formed by coadsorption of Na with K,... 

Single-layer surface alloys Multilayer surface alloys... 

Rb, or Cs, is only possible in part. They can be described in terms of adsorption on a substrate whose first layer contains some fraction of a monolayer of vacancies, just as in the case of the single-layer surface alloys. These vacancies are occupied with a first layer of Na. A second layer of Na (or K, Rb, or Cs in the case of the ternary alloys) is then adsorbed on the A1 vacancy layer. However, in the case of the Al(lll)—(2 x 2) multilayer surface alloys, this second layer of Na is adsorbed in fee sites on the A1 vacancy layer, and the A1 atoms ejected from the vacancy layer are readsorbed in hep sites on the vacancy layer. By contrast, in the Al(l 10)—(4 x 1)—3Na multilayer surface alloy, the second Na layer is adsorbed in sites of low symmetry on the vacancy layer, and the A1 atoms ejected from the vacancy layer do not form a part of the structure, but presumably diffuse to surface steps where they are readsorbed. 

The multilayer surface alloy formed by Li adsorption on Al(lOO) is exceptional in that substitution of 1/2 ML A1 by Li occurs in both the first and third A1 layers. An unexpected feature of this structure is that the registry of Li atoms in the first and third layers is such that they are staggered along the surface normal direction, as in the Al3Ti-type bulk alloy structure, rather than collinear, as in the expected CusAu-type bulk alloy structure known to be adopted by the metastable, AlsLi bulk alloy. DPT calculations for this system lead to the novel prediction that the AlaLi bulk alloy has a stacking fault at the surface, such that it can be described as an AlaTi-type surface on a CuaAu-type bulk. 

Kapoor and Yang [54,55] modified Eq. 5.54 to account for siuface heterogeneity. Multilayer surface adsorption was considered by Chen and Yang [56], Chen et al. [57], and Sikavitsas and Yang [58] who derived an important extension of... 

In this model also the decrease of the pore radius due to the formation of an adsorbed layer is incorporated. Flow 1 in Fig. 9.9 is the case of combined Knudsen molecular diffusion in the gas phase and multilayer (surface) flow in the adsorbed phase. In case 2, capillary condensation takes place at the upstream end of the pore (high pressure Pi) but not at the downstream end (P2), and in case 3 the entire capillary is filled with condensate. The crucial point in cases 3 and 4 is that the liquid meniscus with a curved surface not only reduces the vapour pressure (Kelvin equation) but also causes a hydrostatic pressure difference across the meniscus and so causes a capillary suction pressure Pc equal to... 

The case of Sn-Pt(lll) helps to understand the phenomena that occur in the interplay of the single-layer and the multilayer alloy formation. Other known cases are Au-Cu(lOO) [52] and Al-Ni(lOO) [54]. In other cases, such as Co-Pt(lll) [55], only the multilayer surface alloys have taken known to form. 

The scope of the present paper is to emphasize the role of wetting and spreading in the aging by sintering, and in the redispersion of supported metal catalysts. In the next section, some experimental results regarding the behavior of iron supported on alumina are presented to demonstrate that surface phenomena do play a major role. This is followed by stability considerations which are employed to explain the coexistence of multilayer surface films with crystallites in an oxygen atmosphere and the rupture of thin films into crystallites in a hydrogen atmosphere. 

Figure 3.8 Multilayer surface adsorption model for the BET isotherm.

So we have a bare surface sq and a surface that is occupied with a monomolecular layer s. This means also that multilayer surfaces are not present, i.e., si = 0, S3 = 0,Si =0. If the total area is A, then this area is A = so + ... 

Ning, L., Kommireddy, D.S., Lvov, Y., Liebenberg, W., Tiedt, L.R., De Villiers, M.M. Nanoparticle multilayers Surface modification of photosensitive drug microparticles for increased stability and in vitro bioavailability. J. Nanosci. Nanotechol. 2006, 6 (9-10), 3252-3260. 

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