High-resolution electron-energy-loss spectroscopy (HREELS) has been used to study the vibrational spectra of chemisorbed atomic H on the GaAs(100)c(2×8), (4×6), (4×1), and c(8×2) surface structures. Our results show that both As–H and Ga–H species are present on the GaAs(100)c(2×8) surfaces even at very low exposures. This result is notable because it indicates that the c(2×8) structure is terminated with less than a full monolayer of As atoms. Furthermore, HREELS results indicate that a wide range of surface stoichiometries exists for this surface with the Ga–H mode actually slightly stronger than the As–H mode at the higher annealing temperatures. On the c(8×2) structure the HREELS data show almost exclusively Ga–H with little or no As–H. Strong similarities are observed between the (4×1) and the c(8×2) surfaces, particularly after sufficient annealing, which minimizes the presence of the more As-rich (1×6) domains that often accompanies the (4×1) structure. Several model structures incorporating dimer vacancies are discussed in relation to the HREELS data.
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Frankel et al. (1987) studied this question.