Regular quantum plasmons in segments of graphene nanoribbons

TL;DR

This paper investigates plasmon excitations in small graphene nanoribbons, revealing a consistent plasmon mode in larger structures and quantum effects causing deviations in ultra-narrow segments, with implications for nanoplasmonic applications.

Contribution

First-principles calculations demonstrate the existence of regular plasmon modes in small graphene nanoribbons and analyze their scaling behavior and quantum effects.

Findings

A single low-energy plasmon mode exists in nanoribbons wider than 1.5 nm.

Classical scaling law approximately applies for widths > 1.5 nm.

Quantum effects cause deviations from classical behavior in narrower ribbons.

Abstract

Graphene plasmons have advantages over noble metal plasmons, such as high tunability and low loss. However, for graphene nanostructures smaller than 10 nm, little is known about their plasmons or whether a regular plasmonic behavior exists, despite their potential applications. Here, we present first-principles calculations of plasmon excitations in zigzag graphene nanoribbon segments. Regular plasmonic behavior is found: Only one plasmon mode exists in the low-energy regime (< 1.5 eV). The classical electrostatic scaling law still approximately holds when the width (W) is larger than about 1.5 nm but totally fails when W < 1.5 nm due to quantum effects. The scaling with different doping densities shows that the plasmon is nearly free-electron plasmon instead of Dirac plasmon.