Hydrogen motion

As described above, there is a striking correlation between the creation and annealing kinetics of metastable defects in a-Si H and the motion of bonded hydrogen. There are essentially two classes of models proposed to both account for this agreement and to explain the microscopic mechanisms for hydrogen diffusion. One type of model assumes that the hydrogen is intrinsically mobile and moves from one bonded position to another 

DIFFUSION COEFFICIENT ACTIVATION ENERGY AND PREEXPONENTIAL FACTOR FOR UNDOPED AMORPHOUS SILICON 

Reference Growth process Hydrogen content (at. %) Deposition temperature (°C) ED(eV) D0(cm2/sec) Measurement technique 

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Hydrogen motion, H+, H or H, is often involved in the rate-limiting step of many enzyme catalysed reactions. Here, QM tunnelling can be important and is reflected in the values of the measured kinetic isotope effects (KIEs) [75], Enzyme motion... 

Fig. 15. Minimal energy path for hydrogen motion in the A2A (3s) electronic state of C2H5. (From Zyubin et al.123)...

To determine the kinetics of the hydrogen motion from BC to BC site adjacent to the B, the decay of the stress-induced dichroism was measured at several temperatures. A [110] stress was applied at an elevated temperature (77 K) to align the B—H centers. The samples were cooled to the measurement temperature with the stress maintained. The stress was removed and a and a// were measured as a function of time at fixed temperature. 

Since A B is found from bias annealing experiments to be a function of nBT (Street and Kakalios, 1986 Kakalios and Street, 1987), then rcreat or rann (or both) will similarly depend on nBX. r is the rate of defect creation or removal and therefore is related to hydrogen motion it follows that >H will also be a function of nBx. 

Does the above model for hydrogen motion apply to other amorphous semiconductors, such as a-Si H, a-Ge H, a-SixGe x-. H, a-SixCi-x Experimental determinations of whether the conclusions for a-Si H apply to these other amorphous alloys would greatly advance our understanding of these materials and would likely improve their technological usefulness. 

G. Majer, E. Stanik, S. Orimo, NMR studies of hydrogen motion in nanostructured hydrogen-graphite systems. J. Alloys Compd., 356-357 (2003) 617-621. 

Though the BS experiments have been very useful for gaining insight into the hydrogen motions taking place during a-relaxation, they are affected by a number of shortcomings ... 

As a first approximation to the influence of structure on the vibrational frequencies, we shall concentrate on the M-H-M tri-atomic array. For a linear M-H-M unit, the normal modes are very simple. There is a Raman-active symmetric M-H-M stretch (Structure 9) that only involves motion of the massive metal and therefore occurs at much lower frequencies than the B-B and M-B stretching modes discussed in a previous section. In an intermediate frequency region, a doubly degenerate M-H deformation mode occurs that involves hydrogen motion (Structure 10), and at high frequencies, an asymmetric ir-active stretching vibration (Structure 11) should be observed. 

INS 4000-200 ca. 10 Moderate Finely divided Yes Hydrogenic motions Limited ... 

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