Fluorination of Single-Wall Carbon Nanotubes: Toward “Diamond Nanoribbons”

The paper was published in J. Phys. Chem. C.

In a presented paper, we have identified a new type of one-dimensional nanomaterial called bilayer diamond-like nanoribbons. These nanoribbons can be synthesized by fluorinating single-wall carbon nanotubes, a process that involves attaching fluorine atoms to the nanotube structure. When zigzag or armchair nanotubes are functionalized with fluorine atoms, the carbon atoms change from sp2 to sp3 hybridization, causing the nanotube to collapse and form interlayer C-C bonding in a specific pattern. This process ultimately results in the formation of bilayer diamond nanoribbons, a new class of diamond-like ribbon and nanofiber structures.

Left: The process of collapsing a carbon nanotube into a bilayer diamond ribbon when exposed to fluorine. Right: unusual dependence of the band gap of a nanoribbon depending on its width and structure

The band gap of these nanoribbons is almost constant regardless of their width and depends on their morphology. However, nanoribbons containing an 8-membered ring exhibit special behavior, with electrons from the ring creating an additional band at the edge of the conduction band, which significantly reduces the band gap of the structure. This unique electronic property could make these nanoribbons useful in the development of advanced electronic devices and energy storage systems.

The mechanical stiffness of these nanoribbons is also high and comparable to that of graphene and carbon nanotubes. This robustness makes them ideal candidates for use in composites, where they could serve as a stiff and strong filler material. The high stiffness and unique electronic properties of bilayer diamond-like nanoribbons could also make them suitable for applications in nanomechanics and energy storage, such as in NEMS (Nanoelectromechanical Systems).

These findings could inspire further experimental and theoretical research into the formation of diamond-like nanoribbons from chiral carbon nanotubes. The discovery of bilayer diamond-like nanoribbons opens up a new world of possibilities for the development of advanced materials with unique electronic, mechanical, and optical properties. As researchers continue to explore and understand these novel nanomaterials, we can expect to see new and exciting applications in various fields, from electronics and energy storage to composites and nanomechanics.

Resistive Switching in Bigraphene/Diamane

The paper was published in Nanomaterials.

In this study, we investigated the resistive switching behavior of a lateral 2D composite structure consisting of bilayer graphene and diamane (2D diamond). We observed the local diamondization of bilayer graphene on a La3Ga5SiO14 substrate under focused electron beam irradiation. Raman spectroscopy analysis revealed an elevated density of sp3-hybridized carbon in the irradiated regions. The current-voltage characteristics of the bilayer graphene before and after the electron beam-induced transition demonstrated a significant increase in resistance upon the formation of the diamane structure.

Furthermore, the resistive switching behavior of a nanostructure consisting of bilayer graphene, diamane, and bilayer graphene was investigated. A voltage sweeps from 0 V to -1 V and then to 1 V and back to 0 V resulted in resistive switching from a high resistance state to a low resistance state and back. This switching behavior was attributed to the migration of hydrogen ions and/or oxygen-related groups, leading to the reduction of sp2 carbon bonds in the bilayer graphene.

In our theoretical investigation, we focused on understanding the influence of an electric field on the bonding of functional groups to the surface and the overall stability of a diamond film. To achieve this, we designed a graphene/diamane heterostructure, where the diamond layer is stabilized by oxygen atoms in the form of peroxide groups from the langasite substrate on one side and hydrogen atoms released from the PMMA coating on the other side. This model represents a diamond nanoribbon embedded within a graphene bilayer. The stability of the diamond film is closely tied to the strength of the C-O and C-H bonds. The presence of functional groups on the film surface contributes to its stability, and their desorption can lead to the cleavage of the film. Our simulations demonstrate that when a sufficiently strong electric field is applied to a lateral bigraphene/diamane/bigraphene nanostructure, it can induce the migration of oxygen-related groups. This migration process results in the breaking of interlayer sp3 carbon bonds and the disruption of the diamane structure. The alteration of the carbon bonding configuration and the disruption of the diamane structure play a crucial role in this process, enabling the system to exhibit distinct electrical properties and undergo reversible transitions between resistive and conductive states.

The results of this study highlight the potential of using bilayer graphene and diamane structures for resistive switching applications. The ability to control the conductive properties through electric voltage opens up possibilities for the development of novel memristor devices with improved performance. Further research can explore the optimization of the fabrication process and the integration of these structures into practical devices for various applications, including power-efficient implementation of artificial intelligence and advanced computing systems.

Riboflavin Adsorption on h-BN for Drug Delivery Applications

The paper was published in International Journal of Molecular Sciences.

The presented study employed density functional theory (DFT) simulations to comprehensively investigate the adsorption behavior of riboflavin (Rf) on both defect-free and vacancy-containing hexagonal boron nitride systems. The findings reveal that the Rf molecule undergoes physical adsorption on the surface of the carrier, exhibiting minimal alteration in its chemical structure.

The most stable configuration observed involves the parallel alignment of the riboflavin molecule with the h-BN surface, forming π-π stacking interactions. This is corroborated by the adsorption energies obtained at various positions of the drug molecule. The molecular orbitals of riboflavin's isosurfaces provides a comprehensive understanding of the binding nature between riboflavin and h-BN based on the HOMO and LUMO location on the isoalloxazine site.

Remarkably, the presence of nitrogen vacancies significantly impacts the binding characteristics, as the carriers interact with the vacant riboflavin orbitals. Consequently, riboflavin transforms into an electron acceptor in the BN(Nv)@Rf system, attracting electron density by approximately 0.5 e-. This behavior starkly contrasts with the interactions observed in defect-free h-BN and h-BN with boron vacancies (BN(Bv)), see the Figure.

Distribution of spatial charge density difference in (a) BN@Rf, (b) BN(Bv)@Rf and (c) BN(Nv)@Rf structures and corresponding freestanding parts, side and top view. The loss and gain of charge are denoted by blue and yellow clouds, respectively. The boron, nitrogen, carbon, oxygen, and hydrogen atoms are marked by green, blue, black, red and cyan colors, respectively

These results validate the potential of h-BN as a promising carrier for riboflavin molecules, as the π-π bond formed between the drug and the carrier exhibits substantial strength, providing a solid foundation for drug delivery systems. However, it is crucial to exercise control over the structural perfection of h-BN, as the presence of vacancies can induce charging on riboflavin.

In summary, our study provides valuable insights into the stability and interactions of vitamin B2 with hexagonal boron nitride. The comprehensive understanding gained regarding their binding characteristics and the influence of defects enhances our ability to design and optimize drug delivery systems based on h-BN.