Adsorption of 11-mercaptoundecanoic acid on Ni(111) and its interaction with probe molecules

The gas-phase adsorption of 11-mercaptoundecanoic acid (HOOC(CH2)(10)SH) on Ni(lll) in ultrahigh vacuum was studied using angle-dependent X-ray photoelectron spectroscopy (ADXPS) and temperature-programmed desorption(TPD). We present evidence which shows that 11-mercaptoundecanoic acid is adsorbed to Ni(lll) via the sulfur atom with the carboxylic acid group disposed away from the surface. The monolayer thickness of this molecule, 10.4 +/- 1.7 Angstrom, estimated by photoelectron attenuation in ADXPS, was comparable to ellipsometric measurements of related n-alkanethiols on Au(lll). The interaction of polar (CH3OH) and nonpolar (n-C6H14) probe molecules with this acid-terminated surface showed that the former interact more strongly than the latter as studied by TPD. A Redhead analysis was used to analyze the TPD spectra of CH3OH and n-C6H14 desorbing from this thiol-covered, acid-terminated Ni(111) surface. The calculated low-coverage desorption energy for CH3OH desorption from HOOC(CH2)(10)SH/Ni(111) was 41 kJ mol(-1). The calculated low-coverage desorption energy for n-C6H14 desorption from HOOC(CH2)(10)SH/Ni(lll) was 37 kJ mol(-1).