A self-consistent model to link surface electronic band structure to the voltage dependence of hot electron induced molecular nanoprobe experiments

TL;DR

This paper presents a self-consistent model linking surface electronic band structure to voltage-dependent hot electron induced reactions on Si(111)-7x7, validated by molecular nanoprobe experiments and spectroscopy data.

Contribution

A novel model connects surface band structure to voltage-dependent hot electron reactions, validated by experiments and spectroscopy, providing insights into ultrafast charge relaxation.

Findings

Model accurately fits experimental data

Explains voltage onsets and reaction probabilities

Confirms ultrafast relaxation to surface band bottom

Abstract

Understanding the ultra-fast transport properties of hot charge carriers is of significant importance both fundamentally and technically in applications like solar cells and transistors. However, direct measurement of charge transport at the relevant nanometre length scales is challenging with only a few experimental methods demonstrated to date. Here we report on molecular nanoprobe experiments on the Si(111)-7x7 at room temperature where charge injected from the tip of a scanning tunnelling microscope (STM) travels laterally across a surface and induces single adorbate toluene molecules to react over length scales of tens of nanometres. A simple model is developed for the fraction of the tunnelling current captured into each of the surface electronic bands with input from only high-resolution scanning tunnelling spectroscopy (STS) of the clean Si(111)-7x7 surface. This model is quantitatively linked to the voltage dependence of the molecular nanoprobe experiments through a single manipulation probability (i.e. fitting parameter) per state. This model fits the measured data and gives explanation to the measured voltage onsets, exponential increase in the measured manipulation probabilities and plateau at higher voltages. It also confirms an ultrafast relaxation to the bottom of a surface band for the injected charge after injection, but before the nonlocal spread across the surface.