Nanopatterned self-assembled monolayers

We report on the fabrication of chemically nanopatterned gold surfaces by combining electron-beam lithography with gas and liquid phase thiolization. The line-edge roughness of the patterns is similar to 4 nm, corresponding to a limiting feature size in the range of 15 nm. Indications for a lower packing density of the self-assembled monolayers grown in the nanofeatures are given, and evidences for the bleeding of thiols along the grain boundaries of the gold substrate are displayed. A comparison is provided between nanopatterned thiol and silane monolayers on gold and on silicon wafers, respectively. The line-edge roughnesses are shown to be close to each other for these two systems, indicating that the limiting step is currently the lithography step, suggesting possible improvement of the resolution. The advantages and drawbacks of thiol versus silane monolayers are finally discussed with respect to the formation of chemically nanopatterned surfaces

Kinetics of Exchange of Alkanethiol Monolayers Self-Assembled on Polycrystalline Gold

We report on the exchange between a hydrophilic thiol (11-mercapto-1-undecanol) in a liquid or gas phase and a hydrophobic thiol (dodecanethiol) of similar length self-assembled on a polycrystalline gold surface for a wide range of temperatures and times. The molecular composition of the mixed monolayers is determined by the static water contact angle and X-ray photoelectron spectroscopy measurements. Atomic force microscopy in lateral forcemodeis used to characterize the molecular domains at the nanometer level. The exchange first occurs rapidly at the gold grain boundaries, with an activation energy of about 66 ( 4 kJ/mol. Then, boundaries of ordered thiol domains are progressively replaced, and the exchange is slowed because only regions of increasing perfection are left untouched. Higher temperatures lead to faster kinetics of replacement and the removal of larger amounts of the original thiol. No significant difference could be detected between exchange occurring in an ethanol solution or in the gas phase, and the initial rate of exchange was found to be similar for the displacement of dodecanethiol by 11-mercapto- 1-undecanol molecules and for the converse displacemen

Nanodecoding by dewetting

Films of a block copolymer fluid are deposited on surfaces bearing nano-stripes of different wettability (see figure). The dewetting process of the fluid decodes the underlying pattern, opening trenches as narrow as 70 nm in the film, and creating fluid nanoribbons as narrow as 300 nm. The fluid ribbons are stabilized by the internal organization of the copolymer in the confined space of the ribbon

Partial dewetting of polyethylene thin films on rough silicon dioxide surfaces.

The effect of roughness on the dewetting behavior of polyethylene thin films on silicon dioxide substrates is presented. Smooth and rough silicon dioxide substrates of 0.3 and 3.2-3.9 nm root-mean-square roughness were prepared by thermal oxidation of silicon wafers and plasma-enhanced chemical vapor deposition on silicon wafers, respectively. Polymer thin films of approximately 80 nm thickness were deposited by spin-coating on these substrates. Subsequent dewetting and crystallization of the polyethylene were observed by hot-stage optical microscopy in reflection mode. During heating, the polymer films melt and dewet on both substrates. Further observations after cooling indicate that, whereas complete dewetting occurs on the smooth substrate surface, partial dewetting occurs for the polymer film on the rough surface. The average thickness of the residual film on the rough surface was determined by ellipsometry to be a few nanometers, and the spatial distribution of the polymer in the cavities of the rough surface could be obtained by X-ray reflectometry. The residual film originates from the impregnation of the porous surface by the polymer fluid, leading to the observed partial dewetting behavior. This new type of partial dewetting should have important practical consequences, as most real surfaces exhibit significant roughness

Binary chemical nanopatterns: fabrication and use as templates for electrostatic self-assembly

A versatile method to produce sub-50 nm patterned monolayers on silicon substrates is demonstrated, by combining nanolithography with gas phase silanation. These patterns may serve to control and direct the assembly of macromolecules at the nanoscale, as demonstrated by the growth of polyelectrolyte multilayers on such binary patterned substrates.Anglai