Tunable Optical Properties of Thin Films Controlled by the Interface Twist Angle

Control of materials properties has been the driving force of modern technologies. So far, materials properties have been modulated by their composition, structure, and size. Here, by using cathodoluminescence in a scanning transmission electron microscope, we show that the optical properties of stacked, >100 nm thick hexagonal boron nitride (hBN) films can be continuously tuned by their relative twist angles. Due to the formation of a moire superlattice between the two interface layers of the twisted films, a new moire ' sub-band gap is formed with continuously decreasing magnitude as a function of the twist angle, resulting in tunable luminescence wavelength and intensity increase of >40x. Our results demonstrate that moire ' phenomena extend beyond monolayer-based systems and can be preserved in a technologically relevant, bulklike material at room temperature, dominating optical properties of hBN films for applications in medicine, environmental, or information technologies.

Automated summary

The optical properties of stacked hexagonal boron nitride films can be continuously tuned by their relative twist angles, leading to the formation of a moire superlattice and a new moire ' sub-band gap with decreasing magnitude as the twist angle changes. This results in tunable luminescence wavelength and intensity increase of over 40 times, demonstrating the potential for dominating optical properties in hBN films for various technological applications.