Quasicrystal surfaces: Potential as templates for molecular adsorption

We report on investigations of the potential for using quasicrystal surfaces as templates for molecular adsorption. The quasicrystalline surfaces of the i-Al-Pd-Mn and the d-Al-Ni-Co quasicrystals have been dosed with various molecules and the surface reactivity characterised by Fourier transform infrared spectroscopy (FTIR). The reflected signal intensities obtained are much weaker than those obtained from other crystals such as metals. Although both quasicrystals are Al-based their surface reactivities are seen to differ. For the Al-Pd-Mn surface, NO and HCOOH both dissociate at the surface and CO does not adsorb. CD₄O adsorption leads to multilayers as in other crystals. C₆H₆ molecules stick at low coverages and at low temperatures whilst not affecting the LEED pattern. For the Al-Ni-Co surface, CO molecules stick via activated adsorption to atop sites with vibrational frequencies very similar to CO adsorption on Ni. HCOOH forms multilayers at low temperatures which is reduced to a monolayer upon heating to 173 K; changes in the symmetry of the bonding are observed, which is also seen for HCOOH on Ni surfaces. NO and CD₄O showed no characteristic spectra, which may be due to dissociation or a very low sticking probability. We summarise these observations and draw some conclusions as to the most favourable route for molecular overlayer formation.