Polymer Brushes for Molecular Transport - Paul Braun Research ...

2.2.4 Self-assembled monolayers (SAMs) formation
Fisherbrand microscope coverslips (22 mm x 22 mm x 0.17 mm) and silicon (100) wafers
(25 mm x 25 mm x 0.5 mm) were cleaned in boiling piranha solution (3:1 v/v mixture of
concentrated H2SO4 and 30% aqueous H2O2 solution) (CAUTION: piranha solutions are
strongly oxidizing and should not be allowed to contact organic solvents.) for 3 hours. They
were subsequently rinsed with an excess of Millipore ® water (18.2 MΩ·cm) and dried with
nitrogen.
Monolayers were formed by submerging cleaned substrates in hexane solutions of OTS
or CTS (2 mM) for one hour. Samples were then sonicated in hexane to remove excess material
from the surface and subsequently rinsed in hexane, ethanol and finally deionized water before
being dried with nitrogen.
PEG layers were formed using the following procedure. 100 mg of silanated PEG 2000
was dissolved in 20 mL of ethanol and 1 mL water; hydrochloric acid was added until a drop of
the solution turns pH paper a color corresponding to a pH of 2. The substrates remained in
solution for two days at room temperature and were subsequently rinsed with ethanol and
deionized water and blown dry with nitrogen.
2.2.5 Charaterization of SAMs on silica
Ellipsometry thickness data were collected on the SAMs grafted on silicon wafers. At
632.8 nm (wavelength of incident light), the refractive index and extinction coefficient of the
substrate are 3.85 and -0.02 respectively, and those of the organic layer are assumed to be 1.46
and 0 respectively. The thickness of the native oxide was subtracted from the measured
thickness of the deposited layer.
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