Can Ballistic Electrons Probe the Electronic Spectra of Individual Buried Molecules?

TL;DR

This theoretical study predicts the detectability of individual buried organic molecules using ballistic electron emission spectroscopy, highlighting the influence of molecular structure on electron transmission.

Contribution

It introduces a theoretical model for BEES of buried molecules, emphasizing how molecular composition affects electron transmission and detection feasibility.

Findings

Alkane molecules yield weak BEES signals, making detection difficult.

Unsaturated and aromatic molecules produce strong, detectable BEES signals.

Gold defects can influence electron transmission in molecular films.

Abstract

A theoretical study is presented of the ballistic electron emission spectra (BEES) of individual insulating and conducting organic molecules chemisorbed on a silicon substrate and buried under a thin gold film. It is predicted that ballistic electrons injected into the gold film from a scanning tunneling microscope tip should be transmitted so weakly to the silicon substrate by alkane molecules of moderate length (decane, hexane) and their thiolates that individual buried molecules of this type will be difficult to detect in BEES experiments. However, resonant transmission by molecules containing unsaturated C-C bonds or aromatic rings is predicted to be strong enough for BEES spectra of individual buried molecules of these types types to be measured. Calculated BEES spectra of molecules of both types are presented and the effects of some simple interstitial and substitutional gold defects that may occur in molecular films are also briefly discussed.