Synchronous Differential Hot-charge Emission Spectroscopy: The Principle

TL;DR

The paper introduces synchronous differential Hot-charge Emission Spectroscopy (sd-HotES), a novel method that isolates molecular energy-level alignment at buried interfaces by removing tunneling background noise, thus enhancing detection sensitivity.

Contribution

It develops and validates sd-HotES, a new technique that directly reconstructs molecular charge transmission, enabling threshold-free, bias-insensitive interface analysis.

Findings

sd-HotES effectively isolates molecular ELA signals.

The method enhances detection of weak spectral features.

Simulations confirm robustness against noise.

Abstract

Energy-level alignment (ELA) at buried interfaces between electrode and molecular materials sets charge injection barriers, carrier selectivity, and ultimately device efficiency, yet it is challenging to quantify under operating conditions. Hot-charge emission spectroscopy (HotES) probes ELA by injecting ballistic carriers across a tunneling oxide. Yet, the technique inherently convolutes the molecular response with a strong, energy-dependent tunneling background, complicating the isolation of the true ELA. We introduce synchronous differential HotES (sd-HotES), defined as the ratio of the differential conductance of the hot-charge and tunneling channels of the HotES. Physical modeling and numerical simulations validate that this ratio directly reconstructs the intrinsic molecular charge transmission, enabling the threshold-free and probe-bias-insensitive extraction of ELA. By effectively eliminating the masking tunneling background, sd-HotES substantially boosts detection sensitivity; weak spectral features previously hidden in conventional HotES become clearly resolvable, as demonstrated in lock-in simulations including realistic noise. This study establishes the fundamental operating principles of sd-HotES and highlights it as a powerful, broadly applicable strategy for accessing buried interface properties for the study of molecular and hybrid devices.