Sticking coefficient of hydrogen

Fig. 18. Variation of the initial sticking coefficient of hydrogen on polycrystalline nickel as a function of sulfur coverage (adapted from Ref. 163).

In the plasma experiments, the sticking coefficient of hydrogen on niobium must be equal to one if the membrane is to be classified as truly superpermeable. For highly energetic and ionized plasma species, including H2+, H3+, D2+ and D3+,... 

The sticking coefficient of H2 on a metal has been determined through an adsorption experiment. The metal surface is assumed to have No = 1.5 x 10 sites m and each adsorption site is assumed to be occupied by one hydrogen atom when the surface is saturated. The experiment was performed by exposing the surface to a known pressure of hydrogen over a well-defined period of time (dosis) and then sequentially determining how much was adsorbed by, for example, TPD. All adsorption experiments where performed at such low temperatures that desorption could be neglected. 

Fig. 1.28. The change in sticking coefficient of atoms of hydrogen during doping of film of ZnO by atoms of Ag (/), Zn (2) and applying the transverse electric field to the film O) [198, 199]...

The activation energy for adsorption of hydrogen on copper was set at 30 kJ mol-1, in agreement with the literature (80). A sticking coefficient of unity was assumed for this step. Furthermore, the entropy of the adsorbed surface hydrogen was adjusted in the analysis. 

It is a well-studied system [2, 61], but still it is discussed very controversially, as far as experiment [62-67] as well as theory is concerned [14, 36, 37, 68-73], This debate was fueled by the so-called barrier puzle While the sticking coefficient of molecular hydrogen on Si surfaces is very small [67, 74]... 

Another set of experiments was carried out in an IJHV-based system working with well-defined, quantified particle beams. This system was employed to measure the sticking coefficient of methyl radicals (CH3), the simultaneous interaction of CH3 radicals and atomic hydrogen or low energy ions leading to chemical sputtering and ion-induced deposition, respectively, and the simultaneous interaction of all tree species (CH3, H, and ions). 

The sticking coefficient of methyl radicals on a hydrocarbon surface at 340 K is of the order of 10-5 to 10 4. The temperature dependence of this process was determined in the range from 340 to 800 K. Simultaneous exposure of the surface to atomic hydrogen and CH3 leads to an increase of the sticking coefficient up to 1(P2 depending on the H flux. Simultaneous interaction of CH3 and low-energy ions (E < 1 keV) also causes an enhancement of CH3 sticking to about HP2. 

A pronounced effect of atomic hydrogen on the deposition rate was found in experiments using quantified radical-beam sources [94]. The sticking coefficient of methyl radicals can be enhanced by about two orders of magnitude if the surface is activated by a sufficiently high flux of atomic hydrogen (of the order of 1019 H/m2 s). 

One of the major results is shown in Figure 4.23, which is reproduced from the elegant work of Hayden et al. [197]. Here the sticking coefficient of pure molecular hydrogen is measured on Cu(llO) as a function of translational energy using a... 

Fig. 4.23 Sticking coefficient of molecular hydrogen on Cu(llO) as a function of translational energy (open symbols). By measuring the sticking coefficient for a fixed nozzle temperature at HOOK and reducing the translational energy by back-seeding, it...

Figure 7.3. Uptake curves of hydrogen on Cu(lOO). Here the dosage has been converted into the equivalent number of monolayers (ML). Note that the sticking coefficient is very low and that 1.8 bar of H2 was required. The insert shows Arrhenius plots ofthe extracted...

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