Stability and reactivity of (5×20) and (1×1) Pt(100) surfaces

Pt(100)–(5×20) adsorbs hydrogen to significant coverages only below T∠260 K. At ∠190 K the coverage is sufficient to produce a LEED pattern with very strong integral order beam but some weak fractional order beams are visible. For the present purposes this pattern is designated (1×1). The most strongly adsorbed hydrogen species do not desorb from the (1×1) surface below ∠380–390 K. The difference in behavior between the (5×20) and (1×1) surfaces is attributed to a ∠30% decrease in the heat of adsorption of hydrogen on the (5×20) compared to the (1×1) surface. At 120 K both surfaces exhibit similar initial sticking coefficients. The absolute coverages of adsorbed D at 195 K were measured by nuclear microanalysis. Argon-ion-induced damage increases the temperature at which the (1×1) surface reconstructs such that at doses exceeding 3×1015 Ar+ cm−2 (5 keV), the surface does not reconstruct below 770 K. This appears to be the temperature at which the random step structure, indicated by the LEED data, anneals out. In the presence of adsorbed H, a dose of only 2×1014 Ar+ cm−2 (5 keV) increases the phase (1×1)→(5×20) transition temperature to ≳ 390 K (from ∠350 K for an undamaged surface), so that it is possible to desorb the hydrogen leaving a clean (1×1) surface. A sputtered surface (∠5×1014 Ar+ cm−2; 5 keV) was examined by Rutherford backscattering and less than 2×1014 Pt cm−2 were displaced from their bulk lattice positions.

Stability and reactivity of (5×20) and (1×1) Pt(100) surfaces Journal Articles