Kabeer Jasuja

Aqueous dispersions of few-layer-thick chemically modified magnesium diboride nanosheets by ultrasonication assisted exfoliation

The discovery of graphene has led to a rising interest in seeking quasi two-dimensional allotropes of several elements and inorganic compounds. Boron, carbon’s neighbour in the periodic table, presents a curious case in its ability to be structured as graphene. Although it cannot independently constitute a honeycomb planar structure, it forms a graphenic arrangement in association with electron-donor elements. This is exemplified in magnesium diboride (MgB2): an inorganic layered compound comprising boron honeycomb planes alternated by Mg atoms. Till date, MgB2 has been primarily researched for its superconducting properties; it hasn’t been explored for the possibility of its exfoliation. Here we show that ultrasonication of MgB2 in water results in its exfoliation to yield few-layer-thick Mg-deficient hydroxyl-functionalized nanosheets. The hydroxyl groups enable an electrostatically stabilized aqueous dispersion and create a heterogeneity leading to an excitation wavelength dependent photoluminescence. These chemically modified MgB2 nanosheets exhibit an extremely small absorption coefficient of 2.9 ml mg−1 cm−1 compared to graphene and its analogs. This ability to exfoliate MgB2 to yield nanosheets with a chemically modified lattice and properties distinct from the parent material presents a fundamentally new perspective to the science of MgB2 and forms a first foundational step towards exfoliating metal borides.

Reversibly Compressible and Stretchable “Springlike” Polymeric Nanojunctions Between Metal Nanoparticles

The ability to control the electronic properties and manipulate the surface chemistries of zero(0D), one(1D), and twodimensional (2D) nanostructures has led to the development of novel nanoscale constructs with a wide range of applications. Over the last decade, molecules with actuating mechanics and unique structural properties have been incorporated between electrode junctions to develop memory switches, shuttles, and rectifiers. In addition, 0D nanoparticles have been used for plasmonic devices, gas detection, and biodevices, 1D nanowires for nanogenerators and biosensors, and 2D graphene nanostructures in solar cells and gas sensors. Furthermore, the mobility of nanocomponents has recently brought a new degree of freedom in nanodevice operations using novel nanoelectromechanical systems, such as carbon-nanotube switches, biodevices, gas detectors, touch sensors, elastic membranes, and mechanical gauges. Integrating such mobility of nanoparticles with the elasticity of polymers can produce next-generation springlike electromechanical nanodevices and molecular machines. Herein, we present a study of the electromechanics of an array of gold nanoparticles (GNPs) with springlike nanoscale polymeric junctions incorporated between them. Integration of the elasticity of polymeric junctions into a device construct requires 1) sustained forces applied to the junction from opposite directions, 2) a structurally wellintegrated polymeric junction, and 3) a nonrigid system with reasonable mobility to achieve unrestrained motion. Herein, we consider a device with crosslinked poly(allylamine hydrochloride) (cPAH) molecules sandwiched between 30-nm GNPs (Figure 1). Metal nanoparticles, with their low mass and electronic properties that are sensitively dependent on organic capping and interparticle distance, are great candidates for both applying confined forces and measuring molecular deformation, while the cPAH provides the elastic polymeric junction. The GNP–cPAH structure is fabricated by a diffusional electrostatic assembly process, in which the thickness of the internanoparticle polymeric nanojunctions

Chelation assisted exfoliation of layered borides towards synthesizing boron based nanosheets

The ability to exfoliate tightly bound layered ionic solids has vastly expanded the realm of 2D materials beyond graphene. A crucial step in such exfoliation strategies involves extraction of the inter-planar atoms holding the layers together. Here we present a chelation assisted selective extraction strategy for exfoliating layered metal borides, a family of layered ionic solids that are isostructural to intercalated graphite, with metal atoms sandwiched between graphenic planes of boron. We present evidence for the exfoliation of two metal borides, namely magnesium diboride and aluminium diboride, into aqueous dispersions of few-layer-thick boron based nanosheets, by employing chelation assisted targeted extraction of the inter gallery metal atoms. Chemical analysis of the nanosheets reveals a substantial loss of metal atoms and the presence of boron-planes decorated with hydride, hydroxyl, and oxy-functional groups that are likely derived from the aqueous milieu. The nanosheets exhibit a distinct crumpled morphology with micron-scale lateral dimensions and few layer thickness. These functionalized nanosheets derived from metal borides present promising platforms to leverage the potential of nanoscaled boron. The soft chemical exfoliation approach demonstrated here achieves delamination in a single step under ambient conditions without any additional aides like sonication and holds immense prospects for exfoliating a host of 3D precursors.

Ionic Liquid Assisted Exfoliation of Layered Magnesium Diboride

The discovery of graphene showcased anability to isolate atomic thin sheet from layered graphite, and presented a precedent to the scientific community for exploring a similar possibility in other layered materials. Magnesium diboride (MgB2), which has metal atoms sandwiched in between boron honeycomb planes, represents an ionic layered material isostructural to intercalated graphite. We show that ultrasonication of MgB2 in ionic liquid (1-butyl-3-methyl imidazolium tetrafluoroborate)results in a stable dispersion of few-layer-thick boron based nanosheets. Furthermore, these nanosheets (~3-6 µm wide, ~2 nm thick) are found to exhibit an optical band-gap of ~3.3eV alongwith excitation wavelength dependent photoluminescence.