Sub 10 nm Nanochannels Enable Directional Quasi Ballistic Exciton Transport over 5 {\mu}m at Room Temperature

TL;DR

This paper introduces a femtosecond laser technique to create sub 10 nm dielectric nanochannels on hBN, enabling directional, quasi ballistic exciton transport over 5 micrometers in MoSe2, surpassing previous diffusion limits.

Contribution

It develops a resist-free, scalable laser writing method to fabricate ultra-narrow dielectric nanochannels that control exciton pathways in 2D materials.

Findings

Achieved sub 10 nm nanochannels with smooth boundaries on hBN.

Extended exciton transport distance to over 5 micrometers.

Demonstrated programmable, directional exciton transport pathways.

Abstract

Nanoscale potential wells provide a powerful means to engineer energy landscapes in low dimensional materials, enabling control over quantum states, carrier dynamics, and optoelectronic responses. Such confinement governs phenomena including charge localization, transport anisotropy, band structure modulation, and light matter interaction strength. However, realizing clean and well defined nanostructures remains technically challenging, as fabrication techniques such as focused ion beam (FIB) milling and electron beam lithography frequently introduce structural disorder, residual contamination, or detrimental interactions with the underlying substrate. Here, we develop a femtosecond laser direct writing technique to create sub 10 nm wide dielectric nanochannels with smooth, continuous boundaries on hexagonal boron nitride (hBN) substrates, without using resists or chemical etchants. As a demonstration, these nanochannels are employed to define programmable dielectric landscapes in monolayer molybdenum diselenide (MoSe2), forming excitonic energy funnels that suppress scattering and significantly extend the exciton transport distance. Transport is reshaped from isotropic diffusion with submicron range to directional super diffusion exhibiting quasi ballistic transport exceeding 5 um, more than 20 times longer than in unpatterned systems. The smooth dielectric boundaries further enable precise control over exciton trajectories, allowing for programmable transport pathways. This dry, scalable, and substrate compatible approach offers a robust platform for exciton engineering and integrated quantum photonic devices.