Ultrasmooth hexagonal boron nitride (h-BN) can dramatically enhance the carrier/phonon transport in interfaced transition metal dichalcogenides (TMDs), and amplify the effect of quantum capacitance in field-effect gating. All of the current processes to realize h-BN-based heterostructures involve transfer or exfoliation. Rational chemistries and process techniques are still required to produce large-area, transfer-free, directly grown TMDs/BN heterostructures. Here, we demonstrate a novel boron-oxygen chemistry route for oxide-assisted nucleation and growth of large-area, uniform, and ultrathin h-BN directly on oxidized substrates (B/N atomic ratio = 1:1.16 ± 0.03 and optical band gap = 5.51 eV). These intimately interfaced, van der Waals heterostructures of MoS2/h-BN and WS2/h-BN benefit from 6.27-fold reduced roughness of h-BN in comparison to SiO2. This leads to reduction in scattering from roughness and charged impurities, and enhanced carrier mobility verified by an increase in electrical conductivity (5 times for MoS2/h-BN and 2 times for WS2/h-BN). Further, the heterostructures are devoid of wrinkles and adsorbates, which is critical for 2D nanoelectronics. The versatile process can potentially be extrapolated to realize a variety of heterostructures with complex sandwiched 2D electronic circuitry.

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Hexagonal boron nitride (h-BN) is an ideal platform for interfacing with two-dimensional (2D) nanomaterials to reduce carrier scattering for high-quality 2D electronics. However, scalable, transfer-free growth of hexagonal boron nitride (h-BN) remains a challenge. Currently, h-BN-based 2D heterostructures require exfoliation or chemical transfer of h-BN grown on metals resulting in small areas or significant interfacial impurities. Here, we demonstrate a surface-chemistry-influenced transfer-free growth of large-area, uniform, and smooth h-BN directly on silicon (Si)-based substrates, including Si, silicon nitride (SiN), and silicon dioxide (SiO), via low-pressure chemical vapor deposition. The growth rates increase with substrate electronegativity, Si < SiN < SiO, consistent with the adsorption rates calculated for the precursor molecules via atomistic molecular dynamics simulations. Under graphene with high grain density, this h-BN film acts as a polymer-free, planar-dielectric interface increasing carrier mobility by 3.5-fold attributed to reduced surface roughness and charged impurities. This single-step, chemical interaction guided, metal-free growth mechanism of h-BN for graphene heterostructures establishes a potential pathway for the design of complex and integrated 2D-heterostructured circuitry.

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Hexagonal boron nitride (h-BN) sheets possess an exclusive set of properties, including wide energy band gap, high optical transparency, high dielectric breakdown strength, high thermal conductivity, UV cathodoluminescence, and pronounced thermochemical stability. However, functionalization of large h-BN layers has remained a challenge due to their chemical resistance and unavailable molecular-binding sites. Here we report on the protonation of h-BN via treatment with chlorosulfonic acid that not only exfoliates "large" h-BNs (up to 10 000 μm) at high yields (∼23%) but also results in their covalent functionalization by introducing four forms of aminated nitrogen (N) sites within the h-BN lattice: sp-delocalized and sp-quaternary protonation on internal N sites (>N═ and >NH-) and pyridinic-like protonation on the edge N sites (═NH- and -NH-). The presence of these groups transforms the chemically passive h-BN sheets to their chemically active form, which as demonstrated here can be used as scaffolds for forming composites with plasmonic gold nanoparticles and organic dye molecules. The dispersion of h-BNs exhibits an optical energy band gap of 5.74 eV and a zeta potential of ζ = +36.25 mV at pH = 6.1 (ζ = +150 mV), confirming high dispersion stability. We envision that these two-dimensional nanomaterials with an atomically packed honeycomb lattice and high-energy band gap will evolve next-generation applications in controlled-UV emission, atomic-tunneling-barrier devices, ultrathin controlled-permeability membranes, and thermochemically resistive transparent coatings.

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Recent studies of the high energy‐conversion efficiency of the nanofluidic platform have revealed the enormous potential for efficient exploitation of electrokinetic phenomena in nanoporous membranes for clean‐energy harvesting from salinity gradients. Here, nanofluidic reverse electrodialysis (NF‐RED) consisting of vertically aligned boron‐nitride‐nanopore (VA‐BNNP) membranes is presented, which can efficiently harness osmotic power. The power density of the VA‐BNNP reaches up to 105 W m−2, which is several orders of magnitude higher than in other nanopores with similar pore sizes, leading to 165 mW m−2 of net power density (i.e., power per membrane area). Low‐pressure chemical vapor deposition technology is employed to uniformly deposit a thin BN layer within 1D anodized alumina pores to prepare a macroscopic VA‐BNNP membrane with a high nanopore density, ≈108 pores cm−2. These membranes can resolve fundamental questions regarding the ion mobility, liquid transport, and power generation in highly charged nanopores. It is shown that the transference number in the VA‐BNNP is almost constant over the entire salt concentration range, which is different from other nanopore systems. Moreover, it is also demonstrated that the BN deposition on the nanopore channels can significantly enhance the diffusio‐osmosis velocity by two orders of magnitude at a high salinity gradient, resulting in a huge increase in power density.

Binding graphene with auxiliary nanoparticles for plasmonics, photovoltaics, and/or optoelectronics, while retaining the trigonal-planar bonding of sp hybridized carbons to maintain its carrier-mobility, has remained a challenge. The conventional nanoparticle-incorporation route for graphene is to create nucleation/attachment sites via "carbon-centered" covalent functionalization, which changes the local hybridization of carbon atoms from trigonal-planar sp to tetrahedral sp. This disrupts the lattice planarity of graphene, thus dramatically deteriorating its mobility and innate superior properties. Here, we show large-area, vapor-phase, "ring-centered" hexahapto (η) functionalization of graphene to create nucleation-sites for silver nanoparticles (AgNPs) without disrupting its sp character. This is achieved by the grafting of chromium tricarbonyl [Cr(CO)] with all six carbon atoms (sigma-bonding) in the benzenoid ring on graphene to form an (η-graphene)Cr(CO) complex. This nondestructive functionalization preserves the lattice continuum with a retention in charge carrier mobility (9% increase at 10 K); with AgNPs attached on graphene/n-Si solar cells, we report an ∼11-fold plasmonic-enhancement in the power conversion efficiency (1.24%).