Adsorption and thermal reaction of short-chain iodoalkanes on Ge(100)

The adsorption and thermal decomposition of iodoalkanes CH₃I, C₂H₅I, and C₄H₉I on Ge(100) were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectra (XPS) using synchrotron radiation. At 105 K, the iodoalkanes adsorb both molecularly and dissociatively on Ge(100); the shorterchain iodoalkane dissociates to form a surface alkyl and an I adatom to a greater extent. The chemisorbed iodoalkane gradually dissociates to form a surface alkyl and an I adatom in a temperature range 200-370 K. At 720 K, most surface CH₃ desorbs directly from the surface, and other surface CH₃ radicals undergo disproportionation to desorb as CH₄. Surface C ₂H₅ and C₄H₉ mostly undergo β-hydride elimination to desorb as C₂H₄ and C ₄H₈ at ̃550 K, respectively. The temperature for C₄H₉ to react is slightly lower than that for C ₂H₅ because the C₄H₉ chain exhibits a stronger interaction with the surface than C₂H₅. The I adatom can react with a H atom liberated during decomposition of a surface alkyl and subsequently desorbs as molecular HI in two temperature regimes, ̃650 and ̃720 K. Some I adatoms are removed from the surface via direct desorption in atomic form at 720 K. On annealing to 770 K, the Ge surface becomes free of I adatom but retains a deposit of residual C as adatoms. According to our data, the temperature of fabrication and operation of a Ge-based device with the alkyl monolayer is suggested to be not higher than 530 K.