In Situ Dynamic Spectroscopic Ellipsometry Characterization of Cu-Ligated Mercaptoalkanoic Acid “Molecular” Ruler Multilayers

TL;DR

Researchers used spectroscopic ellipsometry to study how molecular layers and copper ions assemble into precise nanoscale structures.

Contribution

The study introduces in situ dynamic spectroscopic ellipsometry to monitor and optimize molecular-ruler nanogap fabrication in real time.

Findings

In situ ellipsometry measurements match ex situ methods for chemical film thickness.

Real-time monitoring allows optimization of Cu-ligated MHDA multilayer assembly.

The technique preserves film quality while reducing deposition time.

Abstract

Hybrid strategies that combine conventional top-down lithography with bottom-up molecular assembly are of interest for a range of applications including nanolithography and sensors. Interest in these strategies stems from the ability to create complex architectures over large areas with molecular-scale control and precision. The molecular-ruler process typifies this approach where the sequential layer-by-layer assembly of mercaptoalkanoic acid molecules and metal ions are combined with conventional top-down lithography to create precise, registered nanogaps. However, the quality of the metal-ligated mercaptoalkanoic acid multilayer is a critical characteristic in generating reproducible and robust nanoscale structures via the molecular-ruler process. Therefore, we explore the assembly of alkanethiolate monolayers, mercaptohexadecanoic acid (MHDA) monolayers, and Cu-ligated MHDA multilayers on Au{111} substrates using atomic force microscopy and in situ dynamic spectroscopic ellipsometry. The chemical film thicknesses in situ dynamic spectroscopic ellipsometry agree with previous ex situ surface analytical methods. Moreover, in situ dynamic spectroscopic ellipsometry provides insight into the assembly process without interrupting the assembly process and potentially altering the characteristics of the resulting chemical film. By following the real-time dynamics of each deposition step, the assembly of the Cu-ligated MHDA multilayers can be optimized to minimize deposition time while having minimal impact to the quality of the chemical film.

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