Gating of a molecular transistor: Electrostatic and Conformational

TL;DR

This paper develops a framework to compare electrostatic and conformational gating mechanisms in molecular transistors, revealing conditions under which conformational effects can enhance transconductance.

Contribution

It provides a general analytical approach to evaluate and compare gating mechanisms in molecular transistors, highlighting the importance of molecular dipole moments.

Findings

Electrostatic gating reaches the thermal limit without tunneling.

Conformational gating can outperform electrostatic gating if the molecular dipole is large.

The advantage of conformational gating is independent of mode softness or geometry.

Abstract

We derive a general result that can be used to evaluate and compare the transconductance of different field-effect mechanisms in molecular transistors, both electrostatic and conformational. The electrostatic component leads to the well-known thermal limit in the absence of tunneling. We show that in a standard three-terminal geometry and in the absence of strong electron-phonon coupling, the conformational component can lead to significant advantages only if the molecular dipole moment \mu is comparable to et_ox, t_ox being the thickness of the oxide. Surprisingly this conclusion is independent of the ``softness'' of the conformational modes involved, or other geometrical factors. Detailed numerical results for specific examples are presented in support of the analytical results.