Picosecond laser structuration under high pressures: observation of boron nitride nanorods

TL;DR

This study demonstrates that picosecond UV-laser processing of hexagonal boron nitride at high pressures induces the formation of boron nitride nanorods through a process influenced by laser pulse duration, ambient gas, and pressure conditions.

Contribution

It reveals a novel laser-induced nanorod nucleation mechanism in hBN under high-pressure conditions, highlighting the role of non-linear photon absorption and structural defect dynamics.

Findings

Nanorods form under 5 ps and 0.45 ps pulses in nitrogen at high pressure.

High pressure enhances ablation confinement and backscattering effects.

Longer 150-ps pulses produce amorphous boron suboxide contaminated structures.

Abstract

We report on picosecond UV-laser processing of hexagonal boron nitride (hBN) at moderately high pressures above 500 bar. The main effect is specific to the ambient gas and laser pulse duration in the ablation regime: when samples are irradiated by 5 ps or 0.45 ps laser pulses in nitrogen gas environment, multiple nucleation of a new crystalline product - BN nanorods - takes place. This process is triggered on structural defects, which number density strongly decreases upon recrystallization. Non-linear photon absorption by adsorbed nitrogen molecules is suggested to mediate the nucleation-growth. High pressure is responsible for the confinement and strong backscattering of ablation products. A strong surface structuring also appears at longer 150-ps laser irradiation in similar experimental conditions. However, the transformed product in this case is amorphous strongly contaminated by boron suboxides BxOy.