Surface depletion effects

Calahorra, Y. Ritter, D., Surface depletion effects in semiconducting nanowires having a non-uniform radial doping profile. J. Appl. Phys. 2013,114,124310. 

For a fluid at a hard wall this implies p(r) = constant. As expected, because the theory leaves out the entropic effects of confinement, namely chain connectivity, it is in qualitative error for the depletion effects" for a polymer at a surface [118-120]. 

According to the macropore formation mechanisms, as discussed in Section 9.1, the pore wall thickness of PS films formed on p-type substrates is always less than twice the SCR width. The conductivity of such a macroporous silicon film is therefore sensitive to the width of the surface depletion layer, which itself depends on the type and density of the surface charges present. For n-type substrates the pore spacing may become much more than twice the SCR width. In the latter case and for macro PS films that have been heavily doped after electrochemical formation, the effect of the surface depletion layer becomes negligible and the conductivity is determined by the geometry of the sample only. The conductivity parallel to the pores is then the bulk conductivity of the substrate times 1 -p, where p is the porosity. 

At moderate to high polymer concentrations, the free polymer chains in the solution may begin to exercise an influence. One such effect is the so-called depletion flocculation caused by the exclusion of polymer chains in the region between two particles when the latter are very close to each other (i.e., at surface-to-surface distances less than or equal to approximately the radius of gyration of the polymer chains). The depletion effect is an osmotic effect and is discussed further in Section 13.6. 

Figure 16. Examples of deposition shapes in pyrolytic-laser-assisted CVD (a) first-order surface reaction, no mass-transfer effects (b) first-order surface reaction, depletion effects and (c) Langmuir-Hinshelwood surface kinetics, no mass transfer effects. The ratio r/w is the radial position relative to the beam...

Interfacial processes can only be studied in the flat interface stirred cell in cases when there is no depletion within the diffusion film, and when there are no complicating surface adsorption effects. 

Electrolytic etching has been used to reveal p-n junctions (43) as well as to remove n- or p-type material preferentially from diodes and transistors (28). These processes make use of the rectifying barrier of p-n junctions as well as the hole depletion effect at the surface of n-type germanium and silicon. 

Even when the reaction rate at the surface is effectively infinite, chemical kinetics in the gas can influence the carbon-burning rate. Equation (28) requires that residence times in the gas are short enough to prevent chemical depletion of O2 from occurring before oxygen reaches the solid surface. At sufficiently high temperatures—for example, above about 3500K—a substantial amount of dissociation of O2 may occur [39] O atoms are appreciably more reactive than O2 molecules on carbon surfaces... 

Negative adsorption is in most cases very small compared to positive adsorption and therefore not easily detected directly. A sophisticated optical technique (evanescent-wave-induced fluorescence, EWIF) has been used to prove the reduction in segment concentration close to a non-adsorbing surface Depletion also has an effect on the flux of polymer solutions through pores since the viscosity of the liquid near the non-adsorbing surface is lower than that of the polymer solution, the flux is then higher than would be expected on the basis of the bulk viscosity. Negative adsorption at a liquid-air interface leads to a measurable increase In surface tenslon ... 

A second consequence of the surface valence charge depletion relates to surface stress. It seems to now be rather well-established that clean unreconstructed elemental metal surfaces are in a state of tensile stress [60]. This means that the surface atoms would prefer to have a shorter interatomic spacing parallel to the surface. In some cases (such as Au(lll) and Au(lOO) surfaces) this effect can lead to a reconstruction of the surface layer to a (more) close-packed overlayer (e.g. [61]). However, in most metals the surface atoms that are under tensile stress are locked in the periodic potential of the underlying bulk. Substituting some fraction of the atoms in such a surface by... 

At least three of the studied blends [16,145] h86 (N86=1520)/d75 (N75=1625, deuteration extent e=0.4),d75/h66 (N66=2030) and h66/d52 (N52=1510 as well as e=0.34) may be described by a rather small Afs driving surface segregation. In an extreme case of the lowest Afs magnitude the enrichment-depletion effect is expected, as observed for the h66/d52 blend (see the next section). Here we characterize this class of mixtures with the results obtained for the h86/d75 blend. Surface excess z has been determined [145] as a function of bulk concentration at two different temperatures the corresponding (f) values are denoted as open circles (O) in the h86/d75 phase diagram (see inset to Fig. 21a). Surface segregation of the h86 component with a local concentration ( >(z) has been stud-... 

These conditions will ensure that snfficient flnx is maintained into deep narrow volnmes, that shadowing and depletion effects dnring deposition are minimised and that a continnons conformal coverage is obtained. There are now several solution-phase deposition techniques available that show excellent surface coverage and a few gas-phase techniques that seem similarly suitable. 

Kraemer et al. (2002) demonstrated that DFOB had a strongly depleting effect on Eu(III) sorption by goethite and boehmite above pH 5. The dramatic reduction in sorbed Eu(III) was attributed to the formation of a strong cationic complex tliat was repelled from the positively charged surface of either goethite and boehmite. 

Surface-dependent effects. It is an underappreciated fact that 384- and 1,536-well formats have a proportionately higher contacted surface area versus contained assay volume see Table 2), so any surface-dependent phenomena is amplified with both positive (e.g., plate coating or ELISA assays) and deleterious (e.g., limiting enzyme depletion by absorption) effects. 

In either case, an important study would be to address the depletion effect of the slurries being used for CMP planarization. This would answer the question of how far into the pad surface effective material removal is... 

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