Other metastable phenomena

Several other sources of external excitation result in metastable defect or dopant creation in a-Si H. Most have the characteristic property that a shift in the Fermi (or quasi-Fermi) energy causes a slow increase in the density of states and that annealing to 150-200 °C reverses the effect. The phenomena are therefore similar in origin to the optically-induced states and fall within the same general description of departures from the thermal equilibrium state induced by excess carriers. 

A point to note is that the defect creation at the interface is quite strongly thermally activated, unlike the Staebler-Wronski effect which is almost athermal. The likely explanation is that the light excitation provides all the energy needed to overcome the barrier, whereas the interface bias reduces the barrier by the shift of E., but a thermal activation energy is still needed. These different situations are illustrated in Fig. 6.25. 

---

A comparison of the dry-salt diagrams of the metastable phase equilibrium at 308.15 K and the stable phase equilibrium at 298.15 K for the same system is shown in Figure 8. The metastable crystallization regions of borax and potassium chloride are both enlarged while the crystallized area of other minerals existed is decreased. When compared with the stable system, the solubility of borax in water in the metastable system is increased from 3.13 % to 5.70 %. The metastable phenomenon of borax is obvious in this reciprocal quaternary system. 

The phenomenon of metastability depends upon a slow or negligible rate for a particular reaction of a phase or species. The same substance may, however, participate in other reactions which attain equilibrium—e.g.,... 

Although very often one can conclude that the MC method allows to obtain exact solutions, nevertheless it does not eliminate incorrect results, either. Thus an additional peak has been observed between two main peaks in the ordering region on the TDS curve with the use of this method [300], which is absent if the equations reported in other work [301] are used. The peak is attributed to the absence of an equilibrium distribution of the adspecies within the adlayer (the phenomenon of metastability). The absence of such a peak has been confirmed by computations using the transition matrix technique [302]. 

The phenomenon of hysteresis is widespread in nature. Behavior of many systems in physics [1], chemistry [2], biology [3], social science [4, 5], and interdisciplinary sciences [6] exhibit hysteresis. The most general reason for existing of these phenomena is as follows if we reverse the path in the control variables space, we do not necessarily reverse the path in state variables space. Physically it means that there are two or more different local minima and only one corresponds to the thermodynamic equilibrium state, the others must be metastable. These persisting metastable states are responsible for the origin of hysteresis. Among these systems adsorption hysteresis stands out because of its direct and close connection with a number of other complicate phenomena and relevant... 

---