Atomically thin hexagonal boron nitride (h‐BN) is an emerging star of 2D materials. It is taken as an optimal substrate for other 2D‐material‐based devices owing to its atomical flatness, absence of dangling bonds, and excellent stability. Specifically, h‐BN is found to be a natural hyperbolic material in the mid‐infrared range, as well as a piezoelectric material. All the unique properties are beneficial for novel applications in optoelectronics and electronics. Currently, most of these applications are merely based on exfoliated h‐BN flakes at their proof‐of‐concept stages. Chemical vapor deposition (CVD) is considered as the most promising approach for producing large‐scale, high‐quality, atomically thin h‐BN films and heterostructures. Herein, CVD synthesis of atomically thin h‐BN is the focus. Also, the growth kinetics are systematically investigated to point out general strategies for controllable and scalable preparation of single‐crystal h‐BN film. Meanwhile, epitaxial growth of 2D materials onto h‐BN and at its edge to construct heterostructures is summarized, emphasizing that the specific orientation of constituent parts in heterostructures can introduce novel properties. Finally, recent applications of atomically thin h‐BN and its heterostructures in optoelectronics and electronics are summarized.

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The Fe 3 O 4 @LaF 3 :Ce 3+ -Tb 3+ bifunctional composite nanoparticles were fabricated with a facile layer-bylayer technology. To get these bifunctional nanocomposites, the as-prepared magnetic (Fe 3 O 4 ) and luminescent (LaF 3 :Ce 3+ -Tb 3+ ) nanoparticles were modified with polyelectrolyte to get positively charged and negatively charged surfaces, respectively. The nanocomposites were then obtained by absorbing the negatively charged LaF 3 :Ce 3+ -Tb 3+ @(PAH/PSS) 2 luminescent nanoparticles onto the positively charged Fe 3 O 4 @(PAH/PSS) 2 / PAH magnetic nanocrystal surface through electrostatic interaction. The nanocomposites were characterized with transmission electron microscope (TEM), powder X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, Fourier transform infrared (FTIR), and fluorescence technologies. Results indicate that these nanocomposites possess both high magnetization and strong fluorescence, which allows them great potential for bioapplications such as magnetic bioseparation, magnetic resonance imaging (MRI), and drug/gene delivery, simultaneously coupled with fluorescence immunoassays/imaging.

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