Stability of alkyl monolayers on chemomechanically scribed silicon to air, water, hot acid, and X-rays

Abstract

Abstract We report the stability of alkyl monolayers on scribed silicon to air, water, boiling 0.1 M H 2 SO 4 , and X-rays. Monolayers (ML) were prepared by scribing silicon surfaces in the presence of 1-pentene, 1-octene, 1-decene, 1-hexadecene, 1-chlorooctane, 1-bromopentane, 1,4-dibromobutane, methyl iodide, 1-iodopentane, 1-iododecane, 1-butanol, and 1-octanol with a computer-controlled, diamond-tipped instrument. In all cases some initial oxidation of the silicon substrate was observed by X-ray photoelectron spectroscopy (XPS), which increased with time, first rapidly, and then more slowly. Oxidation appears to proceed more quickly for silicon scribed under 1-haloalkanes than 1-alkenes, and more quickly for silicon scribed under 1-haloalkanes that were stored in air than in water. In the case of silicon scribed under an iodoalkane, the resulting iodine to silicon XPS ratio decreased with time, but even after extended exposures to air or water some iodine remained on the surfaces. Steric hindrance and/or hydrophobic effects appear to influence the degree of surface oxidation and halogen loss. The C 1s/Si 2p XPS ratios of surfaces prepared from 1-alkenes and 1-haloalkanes remain nearly constant after all exposures to air, water, hot acid and X-rays. Water capacities of hydrophobic corrals were measured in a semi-automated fashion with a Gilson 215 Liquid Handler and showed trends similar to the XPS results. Hydrophobic corrals generally retained significant fractions of their capacities to hold water with time. Sample-to-sample variation in corral capacity was attributed to variation in the scribing procedure, including possible changes in tip shape. To within experimental error no change in the amount of C, O, or Br at the surfaces was observed by XPS after nearly 4 h of illumination with monochromatic Al Kα X-rays.