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The type of passivating ligands and the ligand exchange method influence the quality of lead sulfide quantum dot films. This imssssparts on the efficiency of optoelectronic devices. To get a compact arrangement of the nanocrystals in a thin film (⁓100 nm) via self-assembling, we used organic-inorganic perovskites with mixed halides for the solid-state exchange of oleic acid ligands on PbS QDs (⁓ 4 nm). Formamidinium lead halides FAPbIxBr3-x (x = 3,2,1,0) were used. X-ray spectroscopy shows that successful replacement of oleic acid with FA happens by short immersion of the films (2 min) in the solution. Transmission electron microscopy shows that nano-scale cracks, short-range ordering, and fusion of the nanocrystals happen during the exchange with FAPbI3. Gradual substitution of I− with Br− ions improves the film homogeneity with fewer defects (nano-scale holes and cracks). Uniform cubic assembly of the nanocrystals without defects and high coverage density is obtained with FAPbBr3. The findings are applied to the fabrication of field effect phototransistors on Si/SiO2/graphene wafers. Photoresponse of the devices indicates that the stability of the films in humidified air (26°C and 51% humidity) is improved from less than 14 days for iodine to more than 60 days for bromine. The ILIGHT/IDARK ratio, responsivity, and specific detectivity increase by 64%, 55%, and 60%, respectively, with FAPbBr3. Prevention of lead sulfide nanocrystal aggregation and the formation of large-scale self-assemblies with perovskite ligands is of technical importance for next-generation optoelectronic applications.

Promising properties of boron nitride nanomaterials such as their chemical, thermal, and mechanical stability have made them suitable materials in a various range of applications. However, their low electrical conductivity and wide bandgap, particularly in the case of boron nitride quantum dots (BNQDs), have given rise to severe limitations. Efforts on bandgap engineering through doping and surface functionalization have gained little success due to their high thermodynamic stability and inertness. Herein, we present a novel approach to functionalize BNQDs by hydroxyl, methyl, and amine functional groups aiming to adjust the electronic structure. The successful exfoliation is demonstrated by transmission electron microscopy, and surface functionalization is elaborated by FTIR and XPS. Modifications of the electronic and optical properties are shown by UV–Vis and PL measurements. The formation of two absorption edges in bandgaps of BNQDs due to the delocalizing of the Px and Pz orbitals as result of edge/surface passivating groups is demonstrated. Splitting of the main transition bandgap of bulk BN from 5.9 eV to two absorption edges for hydroxyl (2.3-3.6 eV), methyl (3.2-4.2 eV), and amine (3.1-4 eV) is shown. These findings offer a bandgap engineering approach for BNQDs, which can boost their applications in quantum emitters (nanophotonics) and photovoltaic devices.

Moving from two-dimensional hexagonal boron nitride (2D h-BN) flatlands towards their quantum sized zero-dimensional (0D) islands, as the newest member of the h-BN family, has recently opened up novel research areas due to the emergence of unique optical and physicochemical properties, excellent thermal and chemical stability, and desirable biocompatibility. This review elaborates on the fundamental properties of 2D and 0D h-BN nanomaterials and covers the latest progress in the fabrication and applications of BN nanosheets (BNNSs) and quantum dots (BNQDs). Initially, the transformation of properties in h-BN nanomaterials is discussed when moving from the 2D realm towards the 0D quantum zone. Then, top-down and bottom-up synthesis methods of 2D h-BN are reviewed, analyzing each method’s advantages and shortcomings. The review will continue explaining the fabrication methods of BNQDs and the impact of synthesis technique on their physiochemical characteristics. Special attention is given to surface chemistry of BNQD nanocrystals that can alter their electronic band structure and optoelectronic properties. Thereafter, detailed discussion on the implementation of BNNSs and BNQDs in various applications, e.g., catalysts, sensors, bioimaging probes, proton exchange membranes, and photocatalytic activators, is provided. At last, an overview of the ongoing challenges and future directions for BNQD research is presented.

Ever-increasing significance of composite materials with high thermal conductivity, low thermal expansion coefficient and high optical bandgap over the last decade, have proved their indispensable roles in a wide range of applications. Hexagonal boron nitride (h-BN), a layered material having a high thermal conductivity along the planes and the band gap of 5.9 eV, has always been a promising candidate to provide superior heat transfer with minimal phonon scattering through the system. Hence, extensive researches have been devoted to improving the thermal conductivity of different matrices by using h-BN fillers. Apart from that, lubrication property of h-BN has also been extensively researched, demonstrating the effectivity of this layered structure in reduction of friction coefficient, increasing wear resistance and cost-effectivity of the process. Herein, an in-depth discussion of thermal and tribological properties of the reinforced composite by h-BN will be provided, focusing on the recent progress and future trends.