Advancing atomic nanolithography: cold atomic Cs beam exposure of alkanethiol self-assembled monolayers

Abstract

Abstract. We report the results of a study into the quality of functionalized surfaces for nanolithographic imaging. Self-assembled monolayer (SAM) coverage, subsequent post-etch pattern definition and minimum feature size all depend on the quality of the Au substrate used in atomic nanolithographic experiments. We find sputtered Au substrates yield much smoother surfaces and a higher density of {111} oriented grains than evaporated Au surfaces. A detailed study of the self-assembly mechanism using molecular resolution AFM and STM has shown that the monolayer is composed of domains with sizes typically of 5-25 nm, and multiple molecular domains can exist within one Au grain. Exposure of the SAM to an optically-cooled atomic Cs beam traversing a two-dimensional array of submicron material masks ans also standing wave optical masks allowed determination of the minimum average Cs dose (2 Cs atoms per SAM molecule) and the realization of < 50 nm structures. The SAM monolayer contains many non-uniformities such as pin-holes, domain boundaries and monoatomic depressions which are present in the Au surface prior to SAM adsorption. These imperfections limit the use of alkanethiols as a resist in atomic nanolithography experiments. These studies have allowed us to realize an Atom Pencil suitable for deposition of precision quantities of material at the micro-and nanoscale to an active surface.

Spectroscopy on the wing: Naturally inspired SERS substrates for biochemical analysis

“…The maximum coverage of alkanethiols on thermally evaporated gold substrates has been shown to be 21%; 2.5 Â 10 14 molecules/cm 2 AE 0.1 Â 10 14 molecules [48]. Assuming 100% metal coverage, this provides a conservative estimate for the enhancement factor, since the maximum density of monolayers of alkanethiols typically take 1-2 h to form.…”

In-situ examination of the selective etching of an alkanethiol monolayer covered Au{111} surface

“…Details on the substrate preparation, growth of the SAM and conditions of AFM and STM imaging can be found elsewhere [4,5]. In-situ etching took place in an in-house-fabricated cell amenable to normal AFM operation using a water-based etching solution composed of …”

Dosage Dependent Etching Mechanism of Alkanethiol Covered Au after Exposure to a Neutral Atomic Cs Beam

“…Atom lithography has been demonstrated with cesium [6,7], and it is now known that the exposure of the SAM is a sensitive function of the Cs dose, being typically 2 Cs atoms per alkanethiol molecule, i.e. 2 monolayers.…”