Advances in Quantifying and Improving Alignment of Carbon/Boron Nitride Nanotube Composite Films Towards Applications in Quantum Photonics

Single-walled carbon nanotubes (SWCNTs) are poised to support next-generation optical and electronic devices and serve as vehicles for fundamental condensed-matter investigations. While prior studies have harnessed the strong light-matter coupling present in dense, globally aligned SWCNT films assembled by vacuum filtration, individualization of luminescent SWCNTs promises efficient emission characteristics for, e.g., single photon sources in quantum-computing architectures. We demonstrate the use of boron nitride nanotubes (BNNTs) as a robust, optically inert, and alignable host material that can controllably template SWCNT positioning and enhance their luminescent yield. Along the way, we explore the effects of BNNT purification, length sorting, and solution filtration parameters on the structural ordering of resulting thin films, establishing hydrodynamic regimes that allow global alignment. Directly probing the structural alignment of BNNTs is challenging; however, polarized extinction and resonance Raman mapping of tracer SWCNTs within an aligned BNNT matrix enables resolution of mesoscopic structural detail and assessment of global alignment. Composite films containing aligned, chirality-pure semiconducting SWCNTs exhibit order-of-magnitude increases in specific fluorescence with decreasing SWCNT loadings, indicating progress and value for realizing natively embedded, individualized single-photon emitters and other functional thin-film architectures.