The Nature of Alkanethiol Self-Assembled Monolayer Adsorption on Sputtered Gold Substrates

Abstract

A detailed study of the self-assembly and coverage by 1-nonanethiol of sputtered Au surfaces using molecular resolution atomic force microscopy (AFM) and scanning tunneling microscopy (STM) is presented. The monolayer self-assembles on a smooth Au surface composed predominantly of {111} oriented grains. The domains of the alkanethiol monolayer are observed with sizes typically of 5−25 nm, and multiple molecular domains can exist within one Au grain. STM imaging shows that the (4 × 2) superlattice structure is observed as a (3 × 2 ) structure when imaged under noncontact AFM conditions. The 1-nonanethiol molecules reside in the threefold hollow sites of the Au{111} lattice and aligned along its [112] lattice vectors. The self-assembled monolayer (SAM) contains many nonuniformities such as pinholes, domain boundaries, and monatomic depressions which are present in the Au surface prior to SAM adsorption. The detailed observations demonstrate limitations to the application of 1-nonanethiol as a resist in atomic nanolithography experiments to feature sizes of ∼20 nm.

Low‐Dimensional, Hinged Bar‐code Metal Oxide Layers and Free‐Standing, Ordered Organic Nanostructures from Turbostratic Vanadium Oxide

“…Details on specific conditions and preparations for accurate imaging of adsorbed alkanethiolates can be found in Ref. 30. The chemical composition of the samples was determined using a SISONS model EA-1108 analyzer.…”

Writing self-assembled monolayers with Cs: Optimization of atomic nanolithography imaging using self-assembled monolayers on gold substrates

“…The 150 nm size of {111} grains on Au:1 surfaces is ≃ 3 times greater than the SAM film thickness, and suggests single-crystal epitaxial growth. Some monatomic depressions exist on the surface of each grain prior to treatment in the alkanethiol solution, but we have recently demonstrated that the alkanethiol covers the surface and depressions alike [26,31]. Thus sputtered Au films produce good quality substrates for alkanethiol-based resist adsorption for atomic nanolithography applications.…”

“…This resolution issue was addressed by Love et al [25] who reported that Pd substrates yielded better post-etch resolution than their Au counterparts when coated with alkanethiol monolayers for nanolithographic purposes. We have recently reported [26] that a resolution limit of ≃ 20 nm is found when 1-nonanethiol SAMs are adsorbed on sputtered Au substrates. The results indicated that the quality of the Au surface is paramount in realizing a low defect-density molecular monolayer.…”

“…Thus, AFM, STM and GIXRD studies of the sputtered Au:1 and evaporated Au:2 surfaces, shows that sputtered Au surfaces exhibit a much lower degree of roughness, and sputtered Au surfaces contain a higher density of {111} oriented Au grains, a distinct advantage for the adsorption of alkanethiols [26,31]. The physical properties for sputtered and evaporated Au surfaces are summarized in Table I.…”

Pressure induced anisotropy of electrical conductivity in polycrystalline molybdenum disulfide

“…Each sandwich is composed of two hexagonal planes of S atoms and an intermediate hexagonal plane of Mo atoms, trigonal prismatically coordinated to the S atoms. It is important to point out that at low bias, constant current STM images reflect the local density of states at the Fermi level projected to the position of the tip apex [10,11]. In general, the images represent a convolution of the geometric and electronic structure of the surface.…”