Adsorption and Thermal Reaction of Short-Chain Iodoalkanes on Ge(100)

Abstract

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 shorter-chain 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 C2H5 and C4H9 mostly undergo β-hydride elimination to desorb as C2H4 and C4H8 at ∼550 K, respectively. The temperature for C4H9 to react is slightly lower than that for C2H5 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.