Table of contents

Electric fields play a crucial role in modulating the electronic properties of nanoscale materials. Electron emission, induced by an electric field, is a representative phenomenon. Experimental and theoretical aspects of such electron emission from graphene are briefly reviewed. The emission occurs at the edge of graphene flakes, not at the surface, because the edge highly concentrates the electric field. Emission currents are sensitive to the edge shapes and edge functionalization. This review provides guiding principles for designing high-efficiency field-emission devices by using graphene nanostructures.

Superacids are strong acids with an acidity higher than pure sulfuric acid. Recently, superacid treatment of monolayer transition metal dichalcogenide (TMDC) flakes, such as MoS₂ and WS₂, has shown a dramatic enhancement of optical properties, such as photoluminescence (PL) intensity. The superacid molecule is bis(trifluoromethane)sulfonimide (TFSI). In this review paper, we summarize and discuss the recent works and the current understanding of the TFSI treatment, and finally, we describe the outlook of the treatment on monolayer TMDCs.

This paper reports the formation of flower-like hierarchical molybdenum disulfide (MoS₂) nanoparticles following a simple one-step hydrothermal process with varying temperatures (200 °C and 220 °C). The as-synthesized particles were examined crystallographically by X-ray diffraction (XRD) method which revealed the formation of hexagonal MoS₂ (2H-MoS₂) and that the crystallite size of the particles increased with increasing hydrothermal temperature. Surface morphological characteristics of the particles were investigated by a field emission scanning electron microscope (FESEM) and interesting details were revealed such as the rounded 3D flower-like microstructure of the MoS₂ particles and the petals of the flowers were composed of platelets built up by stacked-up MoS₂ nanosheets. With the increase in hydrothermal temperature, the interlayer spacing of stacked layers of intense (002) plane is slightly decreased although the crystallinity of the material is improved. Both diameter and thickness of the nanoflowers and the nanoplatelets increased twice with increasing the temperatures. A visual crystallographic perspective was presented through simulation of 3D wireframe unit cell associated with the individual lattice planes as observed in the XRD pattern of the samples. In addition, a plausible growth mechanism is proposed for the formation of the obtained MoS₂ nanoflowers on the basis of experimental observations and analysis.

Accelerated degradation tests (ADT) are widely used in the manufacturing industry to obtain information on the reliability of components and materials, by degrading the lifespan of the product by applying an acceleration factor that damage to the material. The main objective is to obtain fast information which is modeled to estimate the characteristics of the material life under normal conditions of use and to save time and expenses. The purpose of this work is to estimate the lifespan distribution of gold nanoparticles stabilized with lipoic acid (GNPs@LA) through accelerated degradation tests applying sodium chloride (NaCl) as an acceleration factor. For this, the synthesis of GNPs@LA was carried out, a constant stress ADT (CSADT) was applied, and the non-linear Wiener process was proposed with random effects, error measures, and different covariability for the adjustment of the degradation signals. The information obtained with the test and analysis allows us to obtain the life distribution in GNPs@LA, the results make it possible to determine the guaranteed time for possible commercialization and successful application based on the stability of the material. In addition, for the evaluation and selection of the model, the Akaike and Bootstrapping criteria were used.

Various nanomaterials have been produced with the development of nanotechnology, some of which have been reported to have adverse effects on several types of cells, organs, and the environment. It has been suggested that some small nanoparticles can cross the blood-brain barrier and accumulate in the brain, which may be a potential cause of brain diseases. Neuronal cells are vulnerable to hypoxia, hypotrophy, and mechanical and oxidative stress. Therefore, it is essential to assess the toxicity of nanoparticles to neurons accurately. In this report, we describe a primary culture protocol to evaluate the toxicity of nanoparticles on neurons, a potential high-throughput method for assessing the cytotoxicity, and a method for evaluating the effect on neuronal maturation. This report assessed the toxicity of silicon dioxide, zinc oxide, and iron nanoparticles using rat hippocampal neurons, which are used frequently in pharmacological and physiological studies. Based on the methods and protocols we reported in this report, it may be possible to evaluate nanotoxicity to various neurons by using primary cultures of other brain regions (cerebral cortex, cerebellum, thalamus, etc.), spinal cord, and peripheral nerves.

In the carbon nanotubes film/graphene heterostructure decorated with catalytic Pt nanoparticles using atomic layer deposition (Pt-NPs/CNTs/Gr) H₂ sensors, the CNT film determines the effective sensing area and the signal transport to Gr channel. The former requires a large CNT aspect ratio for a higher sensing area while the latter demands high electric conductivity for efficient charge transport. Considering the CNT's aspect ratio decreases, while its conductivity increases (i.e., bandgap decreases), with the CNT diameter, it is important to understand how quantitatively these effects impact the performance of the Pt-NPs/CNTs/Gr nanohybrids sensors. Motivated by this, this work presents a systematic study of the Pt-NPs/CNTs/Gr H₂ sensor performance with the CNT films made from different constituent CNTs of diameters ranging from 1 nm for single-wall CNTs, to 2 nm for double-wall CNTs, and to 10–30 nm for multi-wall CNTs (MWCNTs). By measuring the morphology and electric conductivity of SWCNT, DWCNT and MWCNT films, this work aims to reveal the quantitative correlation between the sensor performance and relevant CNT properties. Interestingly, the best performance is obtained on Pt-NPs/MWCNTs/Gr H₂ sensors, which can be attributed to the compromise of the effective sensing area and electric conductivity on MWCNT films and illustrates the importance of optimizing sensor design.

Distributed Bragg reflectors (DBRs), comprised of periodic refractive index changes, are widely used in optoelectronic devices as resonators, filters and sensors. The heterostructures required for DBRs can be difficult to implement in nanostructures due to poor compositional control on the nanoscale. In the present paper, simulation results are presented of the reflectance spectra from DBR structures that are implemented using periodic perturbations of a nanowire (NW) diameter, rather than heterostructures. The corrugated NW structure can produce a DBR stopband with reflectance near unity. The Bragg wavelength and stopband can be tuned by adjusting the pitch of the nanowire arrays, the corrugation depth, and the period of the corrugation. The proposed DBR structure presents a new paradigm for a wide range of nanoscale device applications.

This work investigates the green synthesis of silver nanoparticles (AgNPs) utilizing the aqueous leaf extract of Ocimum sanctum L. A change in colour to dark brown from yellow and an absorption maximum at 460 nm provided evidence for the synthesis of AgNPs. Several reaction conditions namely leaf extract volume, AgNO₃ concentration and duration of incubation were optimized. Maximum synthesis of AgNPs could be achieved with 1 ml of 5% aqueous leaf extract, 1 mM AgNO₃ and 2.5 h incubation period. DPPH (2, 2—diphenyl − 1 - picrylhydrazyl) assay revealed that AgNPs are better than the leaf extract in terms of antioxidant potential. These results strongly recommend the application of green-synthesized AgNPs as effective antioxidants against oxidative stresses associated with degenerative diseases. Characterization of AgNPs were then carried out using certain methods namely as x-ray diffraction (XRD) measurement, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). XRD study confirmed the synthesis of face-centered cubic-shaped AgNPs that are of crystalline nature. The mean particle size of the synthesized AgNPs computed employing the Debye–Scherrer formula, was 22 nm. FTIR study demonstrated that the AgNPs consisted of certain functional groups of O. sanctum which might have helped in reducing AgNO₃ and capping AgNPs. SEM images showed the synthesis of AgNPs of various shapes viz. globular, cubical and flaky. The scattered AgNPs were found to have a size close to 20 nm, which roughly matches with the XRD analysis of the current study.

Surface enhanced Raman spectroscopy is today an established technique used for chemical fingerprinting. Here, we showcase an engineered hierarchical substrate, in which the plasmonically active regions, restricted to a micron scale, two dimensional hexagonal pattern are examined. Spatial variation of the enhanced Raman signal from any analyte, uniformly coating the substrate, consequently bears a high registry with the underlying pattern. This spatially contrasted enhancement allows optical imaging of the 2D pattern solely using the Raman scattered photons from the analyte. While the pattern brightness and contrast determine analyte identification and detection sensitivity, hyperspectral imaging can be exploited for increasing specificity. Proof of concept demonstration of the technique is carried out via the acquisition of Raman images with rhodamine and fluorescein dyes and then applied to detect glucose in 40 mM concentration. The large area optical imaging and the requirement of long-range uniformity in the detected patterns for positive analyte detection, is implemented using a machine learning based pattern recognition protocol which also increases the statistical confidence of detection. This simultaneous, large area signal detection sacrifices continuous spectral information at the cost of speed, reproducibility and minimising human error via automation of detection in the hyperspectral imaging technique presented here.

We present a comprehensive DFT study of size-dependent atomic and electronic properties of antimony selenide (Sb₂Se₃) nanowires in three main crystallographic directions. Our calculations show a significant enhancement in the band gap of wires oriented in [100] and [010] directions due to confinement effects, however the band gap of [001] oriented wires is reduced with respect to bulk. We attribute this anomaly in band gap reduction to the surface reconstructions in these nanostructures. These surface reconstructions are similar to the polyhedral distortions observed in bulk Sb₂Se₃ under high pressure leading to the insulator-metal transition related to the topological insulating states and then at lower temperature (8K) to superconductivity.