Polarization relaxation energy substrate

The difference in measured values of a for xenon in the gas phase and on the surface is equal to twice the polarization relaxation energy of the substrate, e . The details of this argument can be found in reference (13). 

The physical origin of this structural flexibility of the FeO overlayer is still unclear, the more so since no clear trend is observable in the sequence of lattice parameters of the coincidence structures. The FeO(l 11) phase forming up to coverages of 2-3 ML is clearly stabilized by the interactions with the Pt substrate since FeO is thermodynamically metastable with respect to the higher iron oxides [106,114], FeO has the rock salt structure and the (111) plane yields a polar surface with a high surface energy [115], which requires stabilization by internal reconstruction or external compensation. The structural relaxation observed in the form of the reduced Fe—O... 

A further disadvantage is the rapid strain relaxation occurring in GaN films on SiC(liOO). The residual strain present even in thin GaN layers is negligibly small in comparison to that in GaN films on y-LiAlO2(100). As we will see in the subsequent chapter by Grahn, the comparatively large strain in the latter films is crucial for applications of these films for polarization-sensitive devices. Finally, for these applications, it is often desirable that the substrate is transparent at the energy of the GaN band gap, a property that 6H-SiC does not possess. 

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