  Aminosilanes are routinely employed for charge reversal or to create coupling
layers on oxide surfaces. We present a chemical vapor deposition method to
pattern mica surfaces with regions of high-quality aminosilane
(3-aminopropyltriethoxysilane, APTES) monolayers. The approach relies on the
vapor deposition of an aminosilane through a patterned array of through-holes
in a PDMS (poly(dimethylsiloxane)) membrane that acts as a mask. In aqueous
solutions the surfaces have regular patterns of charge heterogeneities with
minimal topographical variations over large areas. This versatile dry lift-off
deposition method alleviates issues with multilayer formation and can be used
to create charge patterns on curved surfaces. We identify the necessary steps
to achieve high quality monolayers and charge reversal of the underlying mica
surface: 1) hexane extraction to remove unreacted PDMS oligomers from the
membrane that would otherwise deposit on and contaminate the substrate, 2)
oxygen plasma treatment of the top of the membrane surfaces to generate a
barrier layer that blocks APTES transport through the PDMS, and 3) decrease of
the vapor pressure of APTES during deposition to minimize APTES condensation at
the mica-membrane-vapor contact lines and to prevent multilayer formation.
Under these conditions, AFM imaging shows that the monolayers have a height of
0.9nm with an increase in height up to 3nm at the mica-membrane-vapor contact
lines. Fluorescence imaging demonstrates pattern fidelity on both flat and
curved surfaces, for feature sizes that vary between 6.5-40 um. We verify
charge reversal by measuring the double layer forces between a homogeneous
APTES monolayers and a mica surface in aqueous solution and we characterize the
surface potential of APTES monolayers by measuring the double layer forces
between identical APTES surfaces. We obtain a surface potential of 110mV at pH
4.0.
