Size engineering optoelectronic features of C, Si and CSi hybrid diamond-shaped quantum dots

Electronic properties of pristine and doped graphitic germanium carbide nanomeshes

Graphitic germanium carbide (g-GeC) is a novel material that has recently aroused much interest. Porous g-GeC can be fabricated by forming a lattice of pores in pristine g-GeC. In this work, we systematically investigate the influence of creating pores within pristine g-GeC. The pores are passivated with hydrogen, nitrogen, and oxygen, with four supercell sizes. The electronic properties are calculated using the density functional theory (DFT) formalism, which revealed that hydrogen-passivated systems have bandgaps ranging from 1.80 eV to 1.93 eV. The corresponding ranges for the nitrogen- and oxygen-passivated systems are 1.21 eV to 1.58 eV, and 1.18 eV to 1.45 eV, respectively. The bandgaps are always smaller than that of the pristine g-GeC system, and they approach the pristine value for larger supercell sizes. The studied systems have charge-trapping clusters of states located above/below the valence/conduction bands, partially localized at the pore-edge atoms. Additionally, we explore the chelation doping of the N-passivated GeC nanomesh using transition metal (Ni, Pd, Pt) three-atom clusters. Interestingly, the doped systems are dilute magnetic semiconductors. The studied systems exhibit electronic properties that may be useful for sensing and spintronics.

Insights into the optoelectronic behaviour of heteroatom doped diamond-shaped graphene quantum dots

In this study we aim to manipulate the optoelectronic and photoluminescence properties of diamond-shaped graphene quantum dots (DSGQDs) in order to make them suitable for solar cells and photovoltaic devices. Using DFT and performing many-body effects studies, we investigate the impact of N, B, O, P and S heteroatom doping on DSGQDs in three different positions, namely the zigzag edge, the armchair corner and the surface, in order to identify the most appropriate and promising configurations. All the doped GQDs are found to be chemically stable making it possible to realize them experimentally. Additionally, the obtained results show that substitution with heteroatoms has a remarkable effect on the electronic energy gap, noticeably decreasing it. Doping also has a significant effect on the optical response by shifting the absorption peaks towards the visible energy range. The excitonic behaviour has revealed that these nanostructures are potential candidates for photovoltaic devices. One can deduce that doping DSGQDs with heteroatoms is useful and promising for the targeted applications.

Carbon-Based Fluorescent Nano-Biosensors for the Detection of Cell-Free Circulating MicroRNAs

Currently, non-communicable diseases (NCDs) have emerged as potential risks for humans due to adopting a sedentary lifestyle and inaccurate diagnoses. The early detection of NCDs using point-of-care technologies significantly decreases the burden and will be poised to transform clinical intervention and healthcare provision. An imbalance in the levels of circulating cell-free microRNAs (ccf-miRNA) has manifested in NCDs, which are passively released into the bloodstream or actively produced from cells, improving the efficacy of disease screening and providing enormous sensing potential. The effective sensing of ccf-miRNA continues to be a significant technical challenge, even though sophisticated equipment is needed to analyze readouts and expression patterns. Nanomaterials have come to light as a potential solution as they provide significant advantages over other widely used diagnostic techniques to measure miRNAs. Particularly, CNDs-based fluorescence nano-biosensors are of great interest. Owing to the excellent fluorescence characteristics of CNDs, developing such sensors for ccf-microRNAs has been much more accessible. Here, we have critically examined recent advancements in fluorescence-based CNDs biosensors, including tools and techniques used for manufacturing these biosensors. Green synthesis methods for scaling up high-quality, fluorescent CNDs from a natural source are discussed. The various surface modifications that help attach biomolecules to CNDs utilizing covalent conjugation techniques for multiple applications, including self-assembly, sensing, and imaging, are analyzed. The current review will be of particular interest to researchers interested in fluorescence-based biosensors, materials chemistry, nanomedicine, and related fields, as we focus on CNDs-based nano-biosensors for ccf-miRNAs detection applications in the medical field.

Interaction of hydrogen-edged boron nitride flakes with lithium: boron nitride as a protecting layer for a lithium-ion battery and a spin-dependent photon emission device

The current rechargeable battery technologies have a failure in their performance at high pressure and temperature. In this article, we have brought theoretical insights on using boron nitride flakes as a protecting layer for a lithium-ion battery device and extended its application for a spin-dependent photon emission device. Hence, the electronic properties of pristine and lithium-doped hydrogen-edged boron nitride flakes have been studied by the first principle density functional theory calculations. In this study, we have discussed the stability, adsorption energies, bond lengths, electronic gaps, frontier molecular orbitals, the density of states, charge distributions, and dipole moments of pristine and lithium hydrogen-edged doped boron nitride flakes.

Engineering silicon-carbide quantum dots for third generation photovoltaic cells

Interested in the recent development of the building up of photovoltaic devices using graphene-like quantum dots as a novel electron acceptor; we study in this work the optoelectronic properties of edge-functionalized SiC quantum dots using the first principles density functional. For an accurate quantitative estimation of key parameters, a many-body perturbation theory within GW approximation is also performmed. We examine the ability to tailor the electronic gap and optical absorption of the new class of QDs through hydroxylation and carboxylation of seam atoms, in order to improve their photovoltaic efficiency. The HOMO-LUMO energy gap was significantly altered in terms of the type, the concentration and the position of functional groups. The spatial charge separation and charge transfer characterizing our systems seem very prominent to use as dye-sensitized solar cells. Furthermore, the optical band gap of all our compounds is in the NIR-visible energy window, and exhibits a magnitude smaller than that calculated in the pristine case, which enhances the photovoltaic efficiency. Likewise, absorption curves, exciton binding energy and singlet-triplet energy splitting have been broadly modified by functionalization confirming the great luminescent yield of SiCQDs. Depending on the size, SiC quantum dots absorb light from the visible to the near-infrared region of the solar spectrum, making them suitable for third generation solar cells.

Graphene and silicene quantum dots for nanomedical diagnostics

In the present work, the prominent effects of edge functionalization, size variation and base material on the structural, electronic and optical properties of diamond shaped graphene and silicene quantum dots are investigated. Three functional groups, namely (–CH₃, –OH and –COOH) are investigated using the first principles calculations based on the density functional, time-dependent density functional and many-body perturbation theories. Both the HOMO–LUMO energy gap, the optical absorption and the photoluminescence are clearly modulated upon functionalization compared to the H-passivated counterparts. Besides the functional group, the geometric distortion induced in some QDs also influences their optical features ranging from near ultra-violet to near infra-red. All these results indicate that edge-functionalizations provide a favorable key factor for adjusting the optoelectronic properties of quantum dots for a wide variety of nanomedical applications, including in vitro and in vivo bioimaging in medical diagnostics and therapy.

In the present work, the prominent effects of edge functionalization, size variation and base material on the structural, electronic and optical properties of diamond shaped graphene and silicene quantum dots are investigated.