The surface structure of GaAs(001) has been studied by using angle resolved photoemission fine structure (ARPEFS)

which confirms the ‘Ga bi-layer’ model proposed by Biegelsen. The results show that two adjacent outmost Ga atoms (dimmer) move close together along [110] direction to form an 8.3% deviation from the bulk site. And the outmost Ga dimmers relax inward 2.1%. The surface structure of S-passivated GaAs(001) has also been investigated with the method of X-ray photoelectron diffraction (XPD). The results demonstrate that the passivated S atoms are located on the bridge of the first layer Ga atoms and bind them with the bond length of 3.62? and the bond angle of 61.2°. The surface polarity of GaN(0001) grown on the substrate of Al2O3 is also studied by using energy dependence photoelectron diffraction as well as the calculation of multiple scattering cluster models

which confirms that its polarity is Ga termination.