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)S H) on Ni(lll) in ultrahigh vacuum was studied using angle-dependent X- ray photoelectron spectroscopy (ADXPS) and temperature-programmed deso rption(TPD). We present evidence which shows that 11-mercaptoundecanoi c 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 atten uation in ADXPS, was comparable to ellipsometric measurements of relat ed n-alkanethiols on Au(lll). The interaction of polar (CH3OH) and non polar (n-C6H14) probe molecules with this acid-terminated surface show ed that the former interact more strongly than the latter as studied b y 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 des orption 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).