Atomically Precise Electron Beam Sculpting of Bilayer h-BN: The Role of Crystallographic Orientation and Milling Strategy

TL;DR

This paper demonstrates atomically precise sculpting of bilayer h-BN using focused electron beams, emphasizing the importance of crystallographic orientation and milling strategy for achieving smooth, narrow nanoribbons.

Contribution

It introduces a predictive framework based on moiré lattice analysis and compares sequential versus parallel milling, showing sequential milling yields superior atomic-scale precision.

Findings

Sequential milling reduces unwanted exposure and improves edge quality.

Armchair direction cuts produce smoother edges than zigzag.

Moiré pattern analysis guides optimal milling orientations.

Abstract

Achieving atomic precision in top-down manufacturing remains a fundamental challenge nanofabrication technology. Here, the focused electron beam of a scanning transmission electron microscope is used to demonstrate atomically precise sculpting of hexagonal boron nitride (h-BN) bilayers, achieving nanoribbons as narrow as 6 {\AA} with atomically smooth edges. The key to this precision lies in understanding how the underlying atomic structure, particularly in twisted bilayer systems, influences the milling process. High-angle annular dark-field imaging combined with multislice simulations reveals distinct intensity signatures that allow identification of different stacking arrangements within moir\'e patterns. Mathematical analysis of moir\'e lattices provides a predictive framework for determining optimal cutting directions, with cuts along armchair directions yielding superior edge quality compared to zigzag orientations. Surprisingly, a sequential milling approach, where a small electron beam subscan area is translated during the process, produces significantly better results than parallel milling of the entire target region. To understand these differences we implemented a stochastic milling model that reveals that sequential milling minimizes unwanted exposure to surrounding material through beam tail effects. These findings establish a framework for achieving atomic precision in electron beam sculpting of two-dimensional materials and provide fundamental insights applicable to the broader challenge of top-down nanofabrication.