Surface potential contrasts between silicon surfaces covered and uncovered with an organosilane self-assembled monolayer

Abstract

Surface potentials of Si substrates covered with a organosilane self-assembled monolayers (SAMs) were measured with reference to the substrate uncovered with the SAM using Kelvin probe force microscopy. Based on a photolithographic technique, the reference surface was prepared in a micrometer scale on each of the samples. SAMs were prepared from n-octadecyltrimethoxysilane [ODS: CH 3(CH 2) 17Si(OCH 3) 3], 3,3,3-trifluoropropyltrimethoxysilane [FAS3: CF 3(CH 2) 2Si(OCH 3) 3], heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [FAS17: CF 3(CF 2) 7(CH 2) 2Si(OCH 3) 3] or n-(6-aminohexyl) aminopropyltrimethoxysilane [AHAPS: H 2N(CH 2) 6NH(CH 2) 3Si(OCH 3) 3) by chemical vapor deposition. Potentials of the surfaces covered with ODS-, FAS3- and FAS17-SAMs became more negative than the uncovered Si substrate, while the surface covered with AHAPS-SAM showed a more positive surface potential than the reference. The potential contrasts of these SAMs to the reference were −25, −170, −225 and +50 mV for ODS-, FAS3-, FAS17- and AHAPS-SAMs, respectively. These results almost agreed with potentials expected from the dipole moments of the corresponding precursor molecules estimated by ab initio molecular orbital calculation, except for FAS3-SAM. Despite FAS3 molecule having a larger dipole moment than FAS17 molecule, the surface potential contrast of FAS3-SAM was smaller than that of FAS17-SAM, since surface coverage of FAS3-SAM was relatively incomplete compared with the other SAMs.