Regulation of the surface potential of silicon substrates in micrometer scale with organosilane self-assembled monolayers

Microstructures composed of two types of organosilane self-assembled monolayers (SAMs) terminated with different functional groups have been constructed on silicon substrates covered with native oxide. Surface potential images of these microstructures were acquired by Kelvin-probe force microscopy (KFM). By chemical vapor deposition (CVD), the SAMs were fabricated from n-octadecyltrimethoxysilane (ODS) [H3C(CH2)(17)Si(OCH3)(3)], fluoroalkylsilane (FAS), that is, heptadecafluoro-1,1,2,2-tetrahydro-decyl-1-trimethoxysilane [F(3)QCF(2))(7)(CH2)(2)Si(OCH3)(3)], and n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) [H2N(CH2)(6)NH(CH2)(3)Si(OCH3)(3)]. Through a photolithographic technique, binary microstructures consisting of ODS/FAS and ODS/AHAPS were constructed. A surface potential contrast of the two SAMs in each of the binary microstructures was clearly detected by KFM. The surface potential of the FAS-terminated region was ca. 180 mV lower than that of the ODS-terminated region, while the potential of the AHAPS-terminated region was ca. 50 mV higher. These results agree with surface potentials of the SAMs predicted from dipole moments of the corresponding precursor organosilane molecules as estimated by ab initio molecular orbital (MO) calculations. Moreover, by applying the surface potential contrasts experimentally acquired by KFM to surface potential contrast occupied area with single molecule curves theoretically derived by MO calculations, packing densities of the SAMs prepared by CVD were confirmed to be, smaller than those of Langmuir-Blodgett monolayers.