Nickel LEED patterns

Fig. 26. (a) A (1 x 2) LEED pattern produced by adsorption of Hg on Ni(l 10) at 25°C. Normal incidence, 147 eV. Half order beams, of which 1 J and 1 J are marked by arrows show that the periodicity has been doubled along the [001] direction of the surface, (b) Model proposed for a nickel (110) surface after exposure to hydrogen. The reconstructed surface is believed to be stabilized by mobile adsorbed H atoms present on the inclined surfaces of embryonic 111 planes. Locations of H atoms are not specified for this model. [Adapted by permission from lyid. Eng. Chem. 57, July (1965), 19-39, page 26. Copyright 1965 by the American Chemical Society.]... 

Most investigations of catalytic interest concerning the H2 -j- O2 reaction have been on nickel substrates. Farnsworth et al. (226) report that on Ni(lOO) a C(2 x 2)-0 LEED pattern shows no alteration of positions of half-order beams upon exposure to H2 at 25°C. However O2 reacted readily with preadsorbed H2 to produce a hexagonal layer of Ni(OH)2 at room temperature, with the (0001) basal plane of the hydroxide parallel to the Ni(lOO) surface. It is of interest that on Ni(lOO), adsorption of HgO at 25°C produces a C(2 x 2) pattern similar to the C(2 X 2)-0 pattern. No further changes occur, however, and suppression of formation of NiO, which develops by O2 exposure to clean nickel at room temperature, is attributed to the H atoms present in the H2O molecule. Since, by the principle of microscopic reversibility, the cata-... 

Figure 1.19 The structure of oxygen adsorbed on a close-packed nickel surface together with the corresponding LEED pattern...

That the thermal annealing of a nickel single crystal surface, for example Ni(llO) at temperatures between 1400-1700°K, does produce a change in the LEED diffraction pattern has been well documented 155,156). This additional pattern could not be removed even when the sample was heated to a temperature where there was appreciable... 

Four decades ago, Davisson and Germer (19-22) diffracted a beam of slow electrons from a (111) face of a nickel single crystal and at once revealed the great power of LEED for the study of surfaces. In their experiment the Ni(lll) diffraction pattern was altered when CO gas molecules were adsorbed into a structure having lateral periodicity... 

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