Journal of Nano Research Vol. 91

Abstract: Hexagonal boron nitride nanosheets (BNNSs), are among the most prominent layered two-dimensional (2D) nanomaterials due to their superior thermal, electrical, and dielectric properties. However, their strong interlayer bonding limits efficient exfoliation into few-layer structures. In this study, a mixed-solvent strategy based on 1-cyclohexyl-2-pyrrolidone (CHP) and deionized water was developed for rapid and scalable production of BNNSs via sonication-assisted liquid-phase exfoliation (LPE). A CHP/water ratio of 1:20 enabled stable dispersion of exfoliated hBN at a concentration of 1.05 mg/mL, with 56% of the starting material delaminated. Atomic force microscopy (AFM) analysis revealed that 16.8% of the exfoliated product consisted of nanosheets thinner than five layersafter a fast exfoliation. In contrast, exfoliation using IPA/water (3:7) under identical conditions yielded predominantly thick, stacked hBN structures. Spectroscopic and microscopic analyses, including UV–Vis, FTIR, XRD, and Raman, confirmed effective delamination and structural preservation of CHP-exfoliated BNNSs. These results highlight the critical role of solvent composition and demonstrate the superior performance of CHP-based systems as a co-solvent for time-efficient exfoliation. This scalable and safer approach can be adapted for other layered materials and holds strong potential for expanding the use of BNNSs in advanced technological applications.

Abstract: Control of the orientation and length of silicon nanowire (SiNW) arrays has been achieved in large-scale single-crystalline SiNW arrays fabricated by a metal-assisted chemical etching technique. Well-aligned vertical and slanted SiNW arrays with ultra-high aspect ratios have been successfully fabricated, yielding nanowires with lengths of approximately 110 µm and diameters ranging from 100 to 200 nm after 75 minutes of etching. This formation is attributed to the selective etching of the silicon surface directly in contact with Ag particles via a microscale electrochemical cell consisting of a metal catalyst, Si substrate, and etchant solution. Moreover, the effects of etching parameters (AgNO₃ concentration, etching time, and H₂O₂ concentration) and substrate properties (crystal orientation) on the as-prepared SiNWs have been systematically investigated. The results indicate that the morphology of the fabricated silicon nanostructures depends remarkably on AgNO₃ concentration. The length of SiNWs shows a linear dependence on the etching time (0-1 h). Fast SiNW formation with a rate of 1.7 µm min^-1 is achieved under optimized process conditions. However, the etching rate decreases slowly for long etching times (>1 h). Substrate properties have a direct relation to the SiNW orientation. By variation of the H₂O₂ concentration, inclined or vertical etching can be achieved on Si(111) substrates. SiNWs can be understood on the basis of the self-assembled localized microscopic electrochemical cell model. Finally, the optical properties of SiNWs etched in solutions with different concentrations of H₂O₂ have also been discussed.

Abstract: CuO/TiO₂ nanocomposites were synthesized using an economical drop-casting method and subsequently irradiated with high-energy C⁺ ions at fluence levels of 1 × 10¹⁴, 1 × 10¹⁵, 1 × 10¹⁶, and 1 × 10¹⁷ ions cm⁻². While ion irradiation of metal oxide materials is well established, the systematic investigation of C⁺ ion effects on the structural and optical properties of CuO/TiO₂ nanocomposites under these specific fluence conditions has been limited. This study therefore contributes new insight into how controlled C⁺ irradiation can tailor the behavior of this composite. These un-irradiated and irradiated nanocomposites were characterized using various techniques such as Energy Dispersive X-Ray Spectroscopy (EDX), Raman Spectroscopy, Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Photoluminescence (PL) Spectroscopy and Diffuse Reflectance Spectroscopy (DRS) to analyze structural, morphological and optical properties of these nanocomposites. The Raman and EDX analysis confirmed the formation of pure CuO/TiO₂ nanocomposites. The SEM results represent the spherical morphology of these nanocomposites in aggregated form. PL spectra’s depicted the pure and C⁺ ions irradiated nanocomposites were the same before and after C⁺ irradiation in the Photoluminescence emission. DRS results indicated that band gap energy was decreased as the fluence rate of C⁺ ions increased up to 1 × 10¹⁷ ions cm^-2.

Abstract: Formaldehyde is an indoor pollutant that poses a risk to human health, and prolonged exposure may lead to various diseases. Therefore, highly sensitive and selective detection technologies are needed to accurately monitor formaldehyde concentrations. In₂O₃ is a commonly-used semiconductor material in gas sensing. However, the gas sensing performance of pure In₂O₃ sensors falls far from expectation and the construction of heterojunctions is an effective strategy to resolve such issue. In this study, indium oxide-based composites (Co₃O₄/In₂O₃) with a typical p-n heterojunction were synthesized via a simple template-free hydrothermal method for high-performance formaldehyde sensing. XRD, SEM, TEM, and XPS confirmed the p-n heterojunction formation and its positive impact on enhancing surface reactivity. Gas-sensing tests demonstrated that the 3 wt% Co₃O₄/In₂O₃ sensor exhibited optimal performance. The 3 wt% Co₃O₄/In₂O₃ sensor exhibited a response value of 11.1 to 100 ppm formaldehyde at 300°C that was threefold higher than that of pure In₂O₃ (3.77); its recovery time was 41 seconds quicker than that of In₂O₃ (73 s vs. 114 s). The sensor also showed excellent selectivity, reproducibility, and stability. This research presents a scalable, heterojunction-driven design concept for the next generation of gas sensors.

Abstract: Semiconductor quantum dots (QDs) exhibit significant potential for laser applications, where a thorough understanding of their optical gain properties and excitonic dynamics is crucial for performance optimization. In this study, state-resolved pump-probe transient spectroscopy was employed to investigate the optical gain and exciton dynamics in CdSe QDs. The results reveal that the gain threshold increases with pumping photon energy, attributed to the competition between surface trapping and intraband relaxation, as well as to the increased biexciton binding energy associated with higher-energy excitonic charge distributions. Notably, the biexciton binding energy reverses from negative to positive values with increasing pump energy, a transition that underpins the observed rise in gain threshold. Additionally, time-resolved decay curves demonstrate accelerated excitonic recombination at higher pump fluences, indicating a greater proportion of biexcitons relative to single excitons. These findings provide valuable insights for tailoring optical gain in quantized nanostructures and optimizing QD-based laser devices.

Abstract: Doping CZTS (copper-zinc-tin-sulfide) by replacing zinc with cadmium atoms is a crucial process for improving its electrical and optical properties. The primary goal is to modify the bandgap and increase the electrical conductivity of the material to enhance its efficiency in solar cell applications. This substitution induces a phase transition in the crystal structure from kesterite (favorable for zinc) to stannite (stable for cadmium). Experimental results showed that the pure sample (x = 0) was unstable, with a large dispersion in the conductivity measurements. Adding cadmium at a low ratio (x = 0.01225) improved the stability of the measurements while the conductivity decreased to ~10 S/m due to distortion stress in the crystal lattice. Increasing the ratio to x = 0.0269 resulted in a dramatic jump in the conductivity (~56 S/m) which is an indication of the onset of the phase transition. A computer code based on the K-Means algorithm was used to analyze the dispersion of measurements and isolated the most statistically reliable group.

Abstract: In this study, zinc telluride (ZnTe) thin films were deposited using radio frequency (RF) sputtering at various powers ranging from 100 to 250 W for 60 minutes. Structural and optical properties were investigated as a function of RF power. X-ray diffraction (XRD) analysis revealed that increasing the RF power led to a growth in the crystallite size from 3 to 9.4 nm, while dislocation density and microstrain decreased. The ZnTe films exhibited a cubic crystal structure with a lattice parameter of 6.08 Å. Scanning Electron Microscopy (SEM) showed that the film surfaces are uniform and free of cracks. Optical measurements using UV-Vis-NIR spectrophotometry indicated that both transmittance and optical band gap increased from 1.82 to 1.94 eV with increasing RF power. The modulation of the optical and structural properties of ZnTe thin films by RF power, as demonstrated in this study, opens perspectives for optimizing these materials in real device architectures, particularly for more efficient solar cells or high-performance sensors.

Abstract: Ag@TiO₂ core-shell nanoparticles (NPs) were synthesized through an environmentally benign, two-step method utilizing Aloe vera extract as a natural reducing and capping agent. Structural and morphological characterization via X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM) confirmed the successful formation of spherical core-shell structures with a size range of 10-40 nm. Optical analysis revealed a wide bandgap of 4.8 eV, indicative of quantum confinement effects. While electrokinetic measurements suggested moderate colloidal stability (zeta potential near 0 mV), the nanoparticles exhibited potent, strain-dependent antimicrobial activity. Notably, they demonstrated superior efficacy against Gram-positive Staphylococcus epidermidis (32 mm inhibition zone) compared to Gram-negative Escherichia coli (21 mm inhibition zone). This green synthesis route presents a sustainable strategy for producing antibacterial nanoparticles with enhanced activity against Gram-positive pathogens.

Abstract: Pure and silver-doped zinc oxide (ZnO) nanoparticles were synthesized via phyto-mediation using Stachytarpheta jamaicensis leaf extract to develop an eco-friendly method for synthesizing nanoparticles with enhanced properties. Zinc nitrate and silver nitrate were employed as precursors for ZnO and Ag-doped ZnO nanoparticles, respectively. The synthesized nanoparticles were characterized using Ultraviolet-Visible (UV-Vis) spectroscopy, Fourier Transform Infrared (FTIR) spectroscopy and Scanning Electron Microscopy - Energy Dispersive X-ray Spectroscopy (SEM-EDS) to investigate their optical and morphological properties. Results revealed that the absorption peaks of the synthesized nanoparticles confirmed the formation of nanoparticles, with Ag doping causing a red shift in the absorption spectrum. SEM images indicated a spherical morphology, with slight agglomeration in the doped samples. Doping with silver enhanced the optical properties, which could have potential applications in catalysis, sensing, and biomedical fields. Furthermore, the nanoparticle extracts were subjected to antimicrobial test against two bacterial strains (Escherichia coli and Staphylococcus aureus) using a modified disk diffusion method and compared with the antibacterial effect with the standard antibacterial drug, Ampicillin. Ampicillin only showed antibacterial activity against S. aureus and had no antibacterial effect on E. Coli. Result of this study showed that the 5% and 10% Ag-doped ZnO NPs showed strong antibacterial activity against both gram-positive (S. aureus) and gram-negative (E. coli) bacterial strains.

Abstract: An axial-flux motor using sintered iron (Fe) nano-polycrystalline body has been developed at the first time. In this study, its mechanical properties such as rotational speed, torque, and output power properties were compared with those of axial-flux motors using soft iron cores. Experimental results showed that the maximum rotational speed of the axial-flux motor using sintered Fe nano-polycrystalline was 8000 rpm with load, double that of the axial-flux motors using a soft iron core. The torques of both types of motors were around 0.01Nm with a little difference, and the axial-flux motor using sintered Fe nano-polycrystalline had double the output power while keeping torque the same. Sintered Fe nano-polycrystalline has significantly higher magnetic permeability than common iron materials. The material has lower magnetic saturation flux density. Fe nanoparticles were produced from iron oxide particles by using high-repetition laser pulse in liquid. Core inductors with this material were fabricated. Measurements of the core inductor magnetization clarified that the specific permeability of the sintered Fe nano-polycrystalline was 1 million, much higher than the 1000-2000 of soft iron.