Initial stage growth and interface formation of Al on Si(001)2 x 1

Initial stage growth and interface formation of Al on a Si(001)2x1 surface has been studied by core-level and valence-band photoelectron spectroscopy using synchrotron radiation for the Al coverages (Θ_Al) up to ∼2 ML at room temperature (RT) and 300°C. The measured Al 2p and Si 2p spectra reveal, for the first time, the existence of interfacial reaction of Al with Si in addition to the rather well-known dimer adsorption of Al. The reaction occurs even at RT for Θ_Al;≥0.5 ML, which progresses significantly by annealing at 30°C from earlier stage of adsorption. Beyond 0.5 ML, Al 2p core levels indicate formation of Al clusters at both temperatures, which is accompanied by increase of the reacted phase. This interfacial reaction explains the 1x1 phase at 300°C found by LEED and the difference in band bending between RT and 300°C above ∼0.5 ML. The evolution of the valence-band surface electronic structures with respect to ΘAl is interpreted in a consistent way to the core-level results.