Debye temperature of the pentagonal surface of the quasicrystal Al–Pd–Mn

The temperature dependence of the specular-beam intensity in low-energy electron diffraction is determined at the fivefold-symmetry surface of the icosahedral quasicrystal Al–Pd–Mn. The logarithm of the relative intensity is linear in temperature up to 570 K, suggesting the applicability of the standard Debye theory also to quasicrystalline surfaces. First, the temperature dependence of the Bragg-peak energy is measured by recording I–V spectra at different temperatures. The resulting shift to lower energies is accounted for mainly by the lattice expansion perpendicular to the surface. A value of about 0.8 eV is found in the temperature range considered here and included in the analysis. As a result of several measurements, a Debye temperature of 298±7 K is found at 43 eV beam energy. This quantity is a measure for the atomic mean-square vibrational amplitude 〈u2〉 normal to the surface. The value associated with the pentagonal surface is very close to the bulk value of 312 K, determined in X-ray diffraction.