van der Waals SWCNT@BN Heterostructures Synthesized from Solution-Processed Chirality-Pure Single-Wall Carbon Nanotubes

Evaluating the Efficiency of Boron Nitride Coating in Single-Walled Carbon-Nanotube-Based 1D Heterostructure Films by Optical Spectroscopy

Single-walled carbon nanotube (SWCNT) films exhibit exceptional optical and electrical properties, making them highly promising for scalable integrated devices. Previously, we employed SWCNT films as templates for the chemical vapor deposition (CVD) synthesis of one-dimensional heterostructure films where boron nitride nanotubes (BNNTs) and molybdenum disulfide nanotubes (MoS2NTs) were coaxially nested over the SWCNT networks. In this work, we have further refined the synthesis method to achieve precise control over the BNNT coating in SWCNT@BNNT heterostructure films. The resulting structure of the SWCNT@BNNT films was thoroughly characterized using a combination of electron microscopy, UV-vis-NIR spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and Raman spectroscopy. Specifically, we investigated the pressure effect induced by BNNT wrapping on the SWCNTs in the SWCNT@BNNT heterostructure film and demonstrated that the shifts of the SWCNT's G and 2D (G') modes in Raman spectra can be used as a probe of the efficiency of BNNT coating. In addition, we studied the impact of vacuum annealing on the removal of the initial doping in SWCNTs, arising from exposure to ambient atmosphere, and examined the effect of MoO3 doping in SWCNT films by using UV-vis-NIR spectroscopy and Raman spectroscopy. We show that through correlation analysis of the G and 2D (G') modes in Raman spectra, it is possible to discern distinct types of doping effects as well as the influence of applied pressure on the SWCNTs within SWCNT@BNNT heterostructure films. This work contributes to a deeper understanding of the strain and doping effect in both SWCNTs and SWCNT@BNNTs, thereby providing valuable insights for future applications of carbon-nanotube-based one-dimensional heterostructures.

Boosting the Faraday Efficiency of Electrochemical Ammonia Synthesis via the Strain Effect Induced by Interfacial Hybrid Formation between BN and Carbon Nanotubes

The electrochemical nitrogen reduction reaction (eNRR) is a highly promising alternative to the Haber-Bosch (H-B) process, but its commercial development is limited by the high bond energy of N2 molecules and the presence of the competitive hydrogen evolution reaction (HER). Here, a metal-free composite electrocatalyst of boron nitride (h-BNNs) and carbon nanotubes (CNTs) was explored through the interfacial hybridization of h-BNNs and CNTs, which showed a highly improved eNRR Faraday efficiency (FE) of 63.9% and an NH3 yield rate of 36.5 μg h-1 mgcat.-1 at -0.691 V (vs RHE). New chemical bonds of C-B and C-N were observed, indicating a strong interaction between CNTs and h-BNNs. According to the Raman spectra and the optimized model of h-BNNs/CNTs, an obvious strain effect between h-BNNs and CNTs was supposed to play a significant role in the highly improved FE, compared with the FE of h-BNNs alone (4.7%). Density functional theory (DFT) calculations further showed that h-BNNs/CNTs had lower energy barriers in eNRR, giving them higher N2 to NH3 selectivity, while h-BNNs have lower energy barriers in the HER. This work shows the important role of the strain effect in boosting the selectivity in the eNRR process.

Patterned growth of two-dimensional atomic layer semiconductors

Transition metal dichalcogenides (TMDCs), which are representative of two-dimensional (2D) semiconductors, have attracted tremendous attention over the last two decades. TMDCs are regarded as potential candidates in modern nano- and optoelectronic applications due to their unique crystal structures and outstanding electronic and optoelectronic properties. For practical use, 2D semiconductors need to be fabricated with diverse morphologies for integration into electronic devices and to perform different functionalities. Controlled patterning synthesis with programmable geometries is therefore highly desired. We review state-of-the-art strategies for the patterned growth of atomic layer TMDCs and their heterostructures, including additive manufacturing and subtractive manufacturing for patterning single TMDC materials and the introduction of other low-dimensional nanomaterials as growth templates or hetero-atoms for element conversion in patterning TMDC heterostructures. The optoelectronic and electronic applications of the as-grown monolayer TMDC patterns are introduced. Future challenges and the prospects for the patterned growth of 2D semiconductors are discussed based on present achievements.

Ion and Hydrodynamic Translucency in 1D van der Waals Heterostructured Boron-Nitride Single-Walled Carbon Nanotubes

An unresolved challenge in nanofluidics is tuning ion selectivity and hydrodynamic transport in pores, particularly for those with diameters larger than a nanometer. In contrast to conventional strategies that focus on changing surface functionalization or confinement degree by varying the radial dimension of the pores, we explore a unique approach for manipulating ion selectivity and hydrodynamic flow enhancement by externally coating single-walled carbon nanotubes (SWCNTs) with a few layers of hexagonal boron nitride (h-BN). For van der Waals heterostructured BN-SWCNTs, we observed a 9-fold increase in cation selectivity for K+ versus Cl- compared to pristine SWCNTs of the same 2.2 nm diameter, while hydrodynamic slip lengths decreased by more than an order of magnitude. These results suggest that the single-layer graphene inner surface may be translucent to charge-regulation and hydrodynamic-slip effects arising from h-BN on the outside of the SWCNT. Such 1D heterostructures could serve as synthetic platforms with tunable properties for exploring distinct nanofluidic phenomena and their potential applications.

Subnanometer-Wide Indium Selenide Nanoribbons

Indium selenides (In_xSe_y) have been shown to retain several desirable properties, such as ferroelectricity, tunable photoluminescence through temperature-controlled phase changes, and high electron mobility when confined to two dimensions (2D). In this work we synthesize single-layer, ultrathin, subnanometer-wide In_xSe_y by templated growth inside single-walled carbon nanotubes (SWCNTs). Despite the complex polymorphism of In_xSe_y we show that the phase of the encapsulated material can be identified through comparison of experimental aberration-corrected transmission electron microscopy (AC-TEM) images and AC-TEM simulations of known structures of In_xSe_y. We show that, by altering synthesis conditions, one of two different stoichiometries of sub-nm In_xSe_y, namely InSe or β-In₂Se₃, can be prepared. Additionally, in situ AC-TEM heating experiments reveal that encapsulated β-In₂Se₃ undergoes a phase change to γ-In₂Se₃ above 400 °C. Further analysis of the encapsulated species is performed using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), energy dispersive X-ray analysis (EDX), and Raman spectroscopy, corroborating the identities of the encapsulated species. These materials could provide a platform for ultrathin, subnanometer-wide phase-change nanoribbons with applications as nanoelectronic components.