Microstructural characterization of nanocrystalline hexagonal boron nitride thin films deposited by ion-beam assisted pulsed laser deposition

Abstract

In recent years, hexagonal boron nitride (hBN) thin films have garnered considerable attention across various fields, including electronics, anti-corrosion coatings, tribology, and optoelectronics. Boron nitride films produced via physical vapor deposition typically result in amorphous microstructure and suffer from issues such as cracking and delamination. The synthesis of crystalline hBN thin films typically demands higher processing temperatures, toxic gas precursors, and catalytic metal substrates. Hence, this research aims to produce crystalline hBN films at relatively lower temperatures without toxic gas precursors. hBN thin films were deposited on silicon (100) substrates at 600 °C using an ion beam-assisted pulsed laser deposition. The study explores the microstructural evolution and surface morphology of deposited films under different Ar:N2 gas mixtures (ranging from 0% to 100% N2) and varying ion beam energies (from 0 to 400 eV). Microstructural analysis showed the hBN nanocrystallite formation in films deposited with N2 content of 50% and higher and an ion beam energy equal to or exceeding 200 eV, and the crystallite size was measured to be ∼24±8 nm. Raman spectra, grazing incidence X-ray diffraction, and transmission electron microscopy confirm the presence of hBN phase in as-deposited films. Films deposited with an N2 content of ≥50% and ion beam energy of ≥200 eV showed improved crystallinity, increased island size, and density of hBN nanocrystallites. The addition of ion bombardment comparatively made films rougher due to grain growth and formation of larger hBN nanoislands, and surface roughness increased with an increase in N2 content and ion beam energy. The results indicate that the ion beam bombardment facilitates nanograin formation and improves the crystallinity of hBN films even at lower deposition temperatures, offering the promise of advancing their use into practical applications across various fields.