A New Method of Preparing Monolayers on Silicon and Patterning Silicon Surfaces by Scribing in the Presence of Reactive Species

Here we describe a new and simple method for preparing alkyl monolayers on silicon, which consists
of mechanically scribing oxide-coated silicon while it is wet with 1-alkenes or 1-alkynes (neat or in inert
solvents) under ambient conditions. X-ray photoelectron spectroscopy, time-of-flight secondary ion mass
spectrometry, wetting data, and stability tests suggest covalent bonding of unsaturated species to exposed
silicon surfaces. Enclosures (hydrophobic corrals) made by scribing silicon that is wet with unsaturated
hydrophobic species hold droplets of water and liquids with substantially lower surface tensions. Wetting
tests suggest that 1-alkynes make better hydrophobic corrals than 1-alkenes, and theoretical results
suggest it should be more difficult for alkyl chains of chemisorbed 1-alkenes to pack than those of 1-alkynes.
Underivatized interior regions of hydrophobic corrals are functionalized with polyelectrolyte multilayers.
Theoretical energies for water and methanol droplets (gravitational and surface) in hydrophobic corrals
are calculated, and a model of failure of liquid droplets in hydrophobic corrals is presented.