Surface potential microscopy for organized molecular systems

Surface potentials of organosilane self-assembled monolayers (SAMs) formed on silicon substrates were measured using Kelvin-probe force microscopy (KFM) employing a SAM formed from n-octadecyltrimethoxysilane [ODS: CH3(CH2))(17-)Si(OCH3)(3)] as a reference. The reference ODS surface was prepared in a micrometer scale on each of the samples based on a photolithographic technique using vacuum ultra-violet light at 172 nm. Another SAM was prepared on the same sample surface from heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane (fluoroalkylsilane with 17 fluorine atoms, FAS17), 3,3,3-trifluoropropyltrimethoxysilane (fluoroalkylsilane with three fluorine atoms, FAS3), n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) or (chloromethyl)phenyltrimethoxysilane (CMPS). Potentials of the surfaces covered with FAS17-SAM, FAS3-SAM and CMPS-SAM became more negative than ODS-SAM, while the surface covered with AHAPS-SAM showed a more positive surface potential than the reference. The acquired potential contrasts of the regions covered with FAS17, FAS3, AHAPS and CMPS with reference to ODS were - 180, -150, +50 and -30 mV, respectively. These results almost agreed with potentials expected from the dipole moments of the corresponding precursor molecules estimated by ab initio molecular orbital calculation. (C) 2002 Elsevier Science B.V. All rights reserved.