The Chemisorbed State Geometric Aspects

We have seen that the kind of metal used and the atomic structure of its surface both affect the ease with which the hydrogen molecule becomes dissociatively 

Thus far we have been concerned almost exclusively with low index surfaces of single crystals of pure metals, for good reason. In the older work on metal powders and films, their polycrystalline nature forbade the drawing of conclusions about surface geometry, and their doubtful cleanliness was a continual worry. Only the work on FEM and FIM produced results of comparable importance, although these techniques are now rarely used. There have however been a number of studies of stepped surfaces. The behaviour of chemisorbed hydrogen on Ni(997), which is a stepped version of Ni(l 11), is dominated by the plane areas, but the order-disorder transition from the (2 x 2)2H phase to the randomly located lattice gas was raised by about 40 K by the presence of the steps, which stabilise the ordered structure. 

---