Micro, Volume 3, Issue 4 (December 2023) – 11 articles

The structure and phenomena arising from charge transfer in cold field emission mode in a single closed carbon nanotube (CNT) under cold field emission conditions are studied. Inhomogeneities of the structure of CNT in the form of two types of superlattices are found by studying microphotographs obtained by AFM, SEM, and TEM. The features of charge transfer in a quasi-one-dimensional carbon nanotube emitter with a small gap between the anode and cathode are studied under conditions of low-voltage field emission. It is established that the $\mathrm{I}\text{-}\mathrm{V}$ characteristics reveal voltage thresholds and resonant peaks, which are associated with the opening of conduction channels in the region of van Hove singularities. In the region of peaks in the $\mathrm{I}\text{-}\mathrm{V}$ characteristics, the emission current exceeds the one calculated using the Fowler–Nordheim ($\mathrm{F}\text{-}\mathrm{N}$) function by one to three orders of magnitude. The $\mathrm{I}\text{-}\mathrm{V}$ characteristic is not that the curve straightens in F-N coordinates. It is found that the peaks in the $\mathrm{I}\text{-}\mathrm{V}$ characteristics have distinct regions of negative differential conductivity. Full article

The functionalization of copolyfluorenes containing dicyanophenanthrene units by closo-decaborate anion is described. Target copolyfluorenes were analyzed using SEM, UV-vis, luminescence, NMR, and Fourier-transform infrared (FTIR) spectroscopy. The effect of complexation with the closo-decaborate anion on the photophysical properties was studied both experimentally and theoretically. The PL data indicate an efficient charge transfer from fluorene to the dicyanophenanthrene units coordinated to the closo-decaborate. The coordination of closo-decaborate clusters to the nitrile groups of copolyfluorenes provides an important route to new materials for sensors and light-emitting devices while, at the same time, serving as a platform for further study of the nature of boron clusters. Full article

In this research article we report the potentials of chitin-based silver nanoparticles (chitin AgNPs) derived from Indian mimic goatfish (Mulloidichthys ayliffe) scales as an effective food preservation agent. The study comprehensively presents the multifaceted attributes of chitin AgNPs, including their synthesis, characterization, and antimicrobial properties. Chitin yield from M. ayliffe scales and three-spot swimming crab (P. sanguinolentus) exoskeleton was determined, with the insoluble content quantified. FTIR analysis unveiled distinct absorption peaks for chitin, and scanning electron microscopy revealed the ultrastructure of chitin from both the sources. Using UV–visible spectroscopy, the biosynthesis of AgNPs was accomplished and characterized, with the color shift of the solution serving as proof of a successful synthesis. UV–vis spectra provided insights into nanoparticle size and shape. SEM micrographs exhibited spherical particle morphology, while FTIR spectra indicated amino group interactions contributing to AgNP stabilization. The antimicrobial potential of chitin AgNPs was assessed against the food pathogen, Vibrio spp. Chitin films displayed significant antimicrobial activity, particularly AgNP-synthesized chitin from M. ayliffe scales, demonstrated the highest Vibrio spp. inhibition activity. Furthermore, chitin AgNPs were incorporated into the common chili, Capsicum annuum and the tomato, Solanum lycopersicum to extend their shelf life at room temperature. This study reveals the efficacy of chitin AgNPs from M. ayliffe scales as potent agents for food preservation, offering insights into their physical, mechanical, and antimicrobial attributes. The application of chitin AgNPs to perishable food items highlights their potential in enhancing shelf life and quality, opening innovative avenues for sustainable food preservation. Full article

The present study focuses on the synthesis of the natural product 4-methyl-umbelliferone (4-MU, hymecromone), the preparation, characterization, and biological activity evaluation of 4-MU inclusion complexes with β-cyclodextrin (β-CD), as well as their incorporation into pharmaceutical tablets. The inclusion complexes (ICs) were characterized using DLS, SEM, TGA as well as FT-IR, UV-vis, and NMR spectroscopies. The release profile of 4-MU from the β-CD-4-MU ICs was studied in three different pH: 1.2 (aqueous hydrochloric acid), 7.4, and 6.8 (phosphate-buffered solutions), to simulate the stomach, physiological, and intestine pH, respectively. The ICs were incorporated in pharmaceutical tablets which were prepared by direct compression and were characterized for their mechanical properties. The optimal composition of 4-MU as the active pharmaceutical ingredient (API) and excipients was determined using design of experiment (DoE), and the dissolution studies were performed at pH 1.2 at 37 ± 0.5 °C. The sustained release profile of the pharmaceutical tablets showed a delayed burst release effect at 20 min (20% drug release) compared to that of the ICs at the same time interval (70%). The results indicated that the kinetic model describing the release profile of 4-MU from the ICs and tablets is the Higuchi model, while the release mechanism is swelling and diffusion, as was indicated by the Korsmeyer–Peppas kinetic model. The optimization analysis revealed that the optimum composition contains x₁ = 150.95 mg of β-CD-4-MU ICs, x₂ = 82.65 mg of microcrystalline cellulose, and x₃ = 12.40 mg of calcium phosphate. Full article

In this work, we aimed to analyze the impact of extracts prepared from dried Lavandula angustifolia (lavender) flowers and leaves on the synthesis of silver nanoparticles (AgNPs) (wherein the shape and size of AgNPs and the efficiency of the process were analyzed) and to prove the possibility of transferring the AgNPs’ properties into a polymer matrix. An ex situ method was used to incorporate AgNPs and prepare polymer matrix composite (PVP-AgNPs) films (via casting) and fibers (via electrospinning). We used UV-vis absorption spectrophotometry, Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM) to analyze and characterize the AgNPs and prepared composites. The results of FTIR analysis confirmed the presence of phytochemicals that can reduce silver ions from Ag⁺ to Ag⁰ in both extracts. The presence of spherical nanoparticles was confirmed via TEM regardless of the type of extract used. However, leaf extract caused the formation of AgNPs with a narrower size interval (an average size of 20 nm), and with higher efficiency, compared to the nanoparticles prepared using the flower extract. The nanoparticles prepared using the leaf extract were then incorporated into the polymer matrix, and thin polymer composite films and fibers were successfully prepared. The anti-biofilm activity of AgNPs colloids and prepared polymer nanocomposites against green algae Chlorella kessleri was studied. The anti-biofilm properties of the AgNPs were proved, along with the efficient transfer of their toxic properties into nontoxic polymer. Full article

This research article provides a comprehensive investigation into the optoelectronic characteristics of three distinct types of cadmium sulfide (CdS) thin films, namely: (a) conventionally prepared CdS thin films using chemical bath deposition (CBD-CdS), (b) CdS thin films produced via chemical bath deposition with the inclusion of zinc (CBD-Cd_(1−x)Zn_xS, x = 0.3), and (c) CdS thin films synthesized using a seed-assisted approach, treated with ethylenediaminetetraacetic acid (EDTA), and incorporating zinc (ED/CBD + EDTA-Cd_(1−x)Zn_xS). The investigation reveals that the crystallite size of these thin films decreases upon the addition of EDTA to the reaction solution, leading to an increase in the inter-planar spacing and dislocation density. Furthermore, a blue shift in the transmittance edge of the ED/CBD + EDTA-Cd_(1−x)Zn_xS samples compared to CBD-CdS implies modifications in the band gaps of the deposited films. The incorporation of Zn²⁺ into the reaction solution results in an increased band gap value of up to 2.42 eV. This suggests that Cd_(1−x)Zn_xS thin films permit more efficient photon transmission compared to conventional CdS. Among the three types of films studied, ED/CBD + EDTA-Cd_(1−x)Zn_xS exhibits the highest optical band gap of 2.50 eV. This increase in the optical band gap is attributed to the smaller crystallite size and the splitting of the tail levels from the band structure. Additionally, the increment in the optical band gap leads to reduced light absorption at longer wavelengths, thereby enhancing the electrical properties. Notably, ED/CBD + EDTA-Cd_(1−x)Zn_xS thin films demonstrate improved photovoltaic performance in a photoelectrochemical (PEC) cell, characterized by enhanced open-circuit voltage (363 mV, V_OC), short-circuit current (35.35 μA, I_SC), and flat-band voltage (−692 mV, V_fb). These improvements are attributed to the better adhesion of CdS to the fluorine-doped tin oxide (FTO) substrate and improved inter-particle connectivity. Full article

In recent years, the field of drug delivery has seen a significant shift towards the exploration and utilization of nanoparticles (NPs) as versatile carriers for therapeutic agents. With its ability to provide exact control over NPs’ characteristics, microfluidics has emerged as a potent platform for the efficient and controlled synthesis of NPs. Microfluidic devices designed for precise fluid manipulation at the micro-scale offer a unique platform for tailoring NP properties, enabling enhanced control over NP properties such as size, morphology, and size distribution while ensuring high batch-to-batch reproducibility. Microfluidics can be used to produce liposomes, solid lipid nanoparticles, polymer-based NPs, and lipid-polymer hybrid NPs, as well as a variety of inorganic NPs such as silica, metal, metal oxide, quantum dots, and carbon-based NPs, offering precise control over composition and surface properties. Its unique precision in tailoring NP properties holds great promise for advancing NP-based drug delivery systems in both clinical and industrial settings. Although challenges with large-scale production still remain, microfluidics offers a transformative approach to NP synthesis. In this review, starting from the historical development of microfluidic systems, the materials used to create the systems, microfabrication methods, and system components will be discussed in order to provide the reader with an overview of microfluidic systems. In the following, studies on the fabrication of nanoparticles such as lipid NPs, polymeric NPs, and inorganic NPs in microfluidic devices are included. Full article

This paper presents a new MEMS varactor that uses repulsive actuation to achieve an ultra-linear capacitance-to-voltage response. The approach proposed involves actuating the moveable electrode away from the fixed electrode, instead of the conventional closing-the-gap direction. This increasing-gap movement reduces the capacitance as the actuation voltage increases. The MEMS variable capacitor is fabricated using PolyMUMPs technology and exhibits an excellent linearity factor of 99.7% in capacitance-to-voltage response, and a capacitance tuning ratio of 11× was achieved. The proposed strategy will enable the development of high-performance MEMS-based tunable devices for various applications. Full article

This work presents a dynamic modeling approach for analyzing the behavior of a bi-material cantilever actuator structure, consisting of a strip of filter paper bonded to a strip of tape. The actuator’s response is induced by a mismatch strain generated upon wetting, leading to the bending of the cantilever. The study delves into a comprehensive exploration of the dynamic deflection characteristics of the bilayer structure. It untangles the intricate connections among the saturation, modulus, hygro-expansion strain, and deflection, while uniquely addressing the challenges stemming from fluid–structure coupling. To solve the coupled fluid–solid differential equations, a combined numerical method is employed. This involves the application of the Highly Simplified Marker and Cell (HSMAC) technique for fluid flow analysis and the Finite Difference Method (FDM) for response deflection computation. In terms of the capillary flow model, the Computational Fluid Dynamics (CFD) simulations closely align with the classical Washburn relationship, depicting the wetted front’s evolution over time. Furthermore, the numerical findings demonstrate that heightened saturation levels trigger an increase in hygro-expansion strain, consequently leading to a rapid rise in response deflection until a static equilibrium is achieved. This phenomenon underscores the pivotal interplay among saturation, hygro-expansion strain, and deflection within the system. Additionally, the actuator’s response sensitivity to material characteristics is highlighted. As the mismatch strain evolving from paper hygro-expansion diminishes, a corresponding reduction in the axial strain causes a decrease in response deflection. The dynamic parameter demonstrates that the deflection response of the bilayer actuator diminishes as dynamic pressure decreases, reaching a minimal level beyond which further changes are negligible. This intricate correlation underscores the device’s responsiveness to specific material traits, offering prospects for precise behavior tuning. The dependence of paper modulus on saturation levels is revealed to significantly influence bilayer actuator deflection. With higher saturation content, the modulus decreases, resulting in amplified deflection. Finally, strong concordance is observed among the present fluidically coupled model, the static model, and empirical data—a testament to the accuracy of the numerical formulation and results presented in this study. Full article

The high breakdown electric field, n-type doping capability, availability of high-quality substrates, and high Baliga’s figure of merit of Ga₂O₃ demonstrate its potential as a next-generation power semiconductor material. However, the thermal conductivity of Ga₂O₃ is lower than that of other wide-bandgap materials, resulting in the degradation of the electrical performance and reduced reliability of devices. The heterostructure formation on substrates with high thermal conductivity has been noted to facilitate heat dissipation in devices. In this work, Ga₂O₃ thin films with an Al₂O₃ interlayer were deposited on SiC substrates by radio frequency sputtering. Post-deposition annealing was performed at 900 °C for 1 h to crystallize the Ga₂O₃ thin films. The Auger electron spectroscopy depth profiles revealed the interdiffusion of the Ga and Al atoms at the Ga₂O₃/Al₂O₃ interface after annealing. The X-ray diffraction (XRD) results displayed improved crystallinity after annealing and adding the Al₂O₃ interlayer. The crystallite size increased from 5.72 to 8.09 nm as calculated by the Scherrer equation using the full width at half maximum (FWHM). The carrier mobility was enhanced from 5.31 to 28.39 cm² V⁻¹ s⁻¹ in the annealed Ga₂O₃ thin films on Al₂O₃/SiC. The transfer and output characteristics of the Ga₂O₃/SiC and Ga₂O₃/Al₂O₃/SiC back-gate transistors reflect the trend of the XRD and Hall measurement results. Therefore, this work demonstrated that the physical and electrical properties of the Ga₂O₃/SiC back-gate transistors can be improved by post-deposition annealing and the introduction of an Al₂O₃ interlayer. Full article

Immunoassays play a pivotal role in detecting and quantifying specific proteins within biological samples. However, its sensitivity and turnaround time are constrained by the passive diffusion of target molecules towards the sensors. ACET (Alternating Current Electrothermal) enhanced reaction emerges as a solution to overcome this limitation. The ACET-enhanced biosensor works by inducing vortices through electrothermal force, which stirs the analyte within the microchannel and promotes a reaction process. In this study, a comprehensive two-dimensional finite element study is conducted to optimize the binding efficiency and detection time of an ACET-enhanced biosensor without external pumping. Optimal geometries for interdigitated electrodes are estimated to achieve significant improvements in terms of probe utilization and enhancement factor. The study’s findings demonstrate enhancement factors of 3.21, 2.15, and 3.09 along with 71.22%, 75.80%, and 57.52% normalized binding for C-reactive protein (CRP), immunoglobulin (IgG), and SARS-CoV-2, respectively. Full article