Sapphire (112¯0) surface: Structure and laser-induced desorption of aluminum

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Abstract
The laser-induced desorption of particles from a well-characterized sapphire (112¯0) surface at laser wavelengths of 1064 nm (1.17 eV) and 355 nm (3.51 eV) was investigated by time-of-flight mass spectrometry. Below the laser ablation threshold, only aluminum ions were observed to desorb with average kinetic energies of 7.0±0.7 eV at both photon energies. The high kinetic energies of the desorbing aluminum ions indicate that the desorption mechanism is electronic. The surface atomic and electronic structure was studied with low-energy electron diffraction (LEED), reflection electron-energy-loss spectroscopy, and Auger electron spectroscopy. After heating the surface to over 1500 K, a reconstructed surface exhbiting a (12×4) LEED pattern was established. The electron-energy-loss spectrum from the (12×4) surface revealed the presence of surface electronic states in the bulk band gap of sapphire as evidenced by a broad (∼2 eV full width at half maximum) energy-loss feature centered at 3.6 eV. The surface electronic states are believed to participate in the photon-absorption process.