Mechanical characterization and cleaning of CVD single-layer h-BN resonators

Abstract

Hexagonal boron nitride is a 2D material whose single-layer allotrope has not been intensively studied despite being the substrate for graphene electronics. Its transparency and stronger interlayer adhesion with respect to graphene makes it difficult to work with, and few applications have been proposed. We have developed a transfer technique for this extra-adhesive material that does not require its visual localization, and fabricated mechanical resonators made out of chemical vapor-deposited single-layer hexagonal boron nitride. The suspended material was initially contaminated with polymer residues from the transfer, and the devices showed an unexpected tensioning when cooling them to 3 K. After cleaning in harsh environments with air at 450 °C and ozone, the temperature dependence changed with f₀Q products reaching 2 × 10¹⁰ Hz at room temperature. This work paves the way to the realization of highly sensitive mechanical systems based on hexagonal boron nitride, which could be used as an alternative material to SiN for optomechanics experiments at room temperature.

Nanofabrication: optimized transfer enables hexagonal boron nitride mechanical resonators

An improved transfer method allows easy placement of highly transparent and strongly adhesive hexagonal boron nitride on target substrates. A team led by Santiago J. Cartamil-Bueno at Delft University of Technology developed a technique that enables the transfer of large-area, single-layer hexagonal boron nitride films grown by chemical vapor deposition onto a substrate of choice, whilst not requiring optical visualization. Following an additional cleaning step, the atomically thin membranes were transferred onto circular microcavities patterned on a silicon oxide substrate, resulting in the formation of suspended drums. Cleaning in harsh environments using a mixture of air and ozone is instrumental to a substantial improvement in the quality factor of the drums, indicating that undesired contamination causes damping of the mechanical motion. These results show promise for the development of sensitive hexagonal boron nitride resonators.