Molecular Tools for Non-Planar Surface Chemistry

TL;DR

This paper introduces silicon-specific molecular tools that enable out-of-plane reactions on silicon surfaces, expanding the scope of surface chemistry and molecular engineering on silicon beyond traditional in-plane reactions.

Contribution

The study develops a general framework for designing molecular tools that facilitate out-of-plane reactions on silicon surfaces, validated with experimental and theoretical methods.

Findings

Successful creation of silicon-specific molecular tools validated by SPM and XPS

Demonstration of out-of-plane radical reactivity on Si(100) surfaces

Potential for diverse applications in silicon surface engineering

Abstract

Scanning probe microscopy (SPM) investigations of on-surface chemistry on passivated silicon have only shown in-plane chemical reactions, and studies on bare silicon are limited in facilitating additional reactions post-molecular-attachment. Here, we enable subsequent reactions on Si(100) through selectively adsorbing 3D, silicon-specific "molecular tools". Following an activation step, the molecules present an out-of-plane radical that can function both to donate or accept molecular fragments, thereby enabling applications across multiple scales, e.g., macroscale customizable silicon-carbon coatings or nanoscale tip-mediated mechanosynthesis. Creation of many such molecular tools is enabled by broad molecular design criteria that facilitate reproducibility, surface specificity, and experimental verifiability. These criteria are demonstrated using a model molecular tool tetrakis(iodomethyl)germane ($Ge(CH_{2}I)_{4}$; TIMe-Ge), with experimental validation by SPM and X-ray photoelectron spectroscopy (XPS), and theoretical support by density functional theory (DFT) investigations. With this framework, a broad and diverse range of new molecular engineering capabilities are enabled on silicon.