Materials Science Forum Vol. 1055

Abstract: Heat transfer simulation in Bi₂Te₃, Ca₂FeMoO₆, and SrTiO₃ solid module single-leg had been investigated using COMSOL Multiphysics package. The software COMSOL Multiphysics was used to investigate the temperature distribution, electrical potential distribution, power output, and current vs temperature throughout the length of the sample for Bi₂Te₃, Ca₂FeMoO₆, and SrTiO₃ which one of these three materials was showing potential as TE materials. The simulation showed that the perovskite material Ca₂FeMoO₆ and SrTiO₃ had shown a net temperature difference across lengths of +191.943°C and +7.54°C while Bi₂Te₃ showed a net temperature difference of -60°C. Next, in electrical potential distribution across the length, Ca₂FeMoO₆ and SrTiO₃ produced a higher voltage of 170mV and 160mV, while Bi₂Te₃ produced 49mV. The values of the power output for the three materials were calculated with 0.7A input current. It was found that Ca₂FeMoO₆, SrTiO₃, and Bi₂Te₃ generated 119mW, 113mW, and 34mW in the simulation. The simulation results revealed that the Bi₂Te₃ is a p-type thermoelectric element and has the potential use in cooling due to Peltier cooling effect. However, Ca₂FeMoO₆ and SrTiO₃ are n-type thermoelectric elements with a heating effect. The simulation and investigation of TE material using COMSOL Multiphysics showed more potentials and helped to explore, predicted and evaluated the conditions for other new TE materials.

Abstract: — Synthesized single-walled carbon nanotubes (SWCNTs) consist of a mixture of chiralities and therefore a post-synthesis separation is essential to separate them based on electronic type i.e., metallic (m-SWCNT) or semiconducting (s-SWCNT) for device applications. A key parameter to measure the effectiveness of separation process is the enrichment composition percentage between m-SWCNT and s-SWCNT, which can be estimated via several methods based on optical characterizations. In this paper, we compare the composition percentage estimations from 3 different methods based on Raman spectroscopy and UV-Vis optical absorption spectroscopy. The estimation methods are radial breathing mode (RBM) peak analysis, optical absorption area under curve (OUA) and first derivative amplitude of the optical absorption curve (FDA). Four different SWCNT sources were used in this study, which were subjected to post-synthesis separation process via agarose gel chromatography. Raman and UV-Vis spectroscopy measurements were carried out on all samples, before and after separation. From the estimations, we observed firstly that there are some variations on the estimated enrichment compositions between different methods, although the values are comparable. Secondly, for some SWCNTs samples, only a certain estimation method showed reliable composition percentage. The results presented in this work may provide viable options for characterizations of SWCNTs as there is no direct method to quantify the absolute composition percentage of SWCNTs based on electronic type. Keywords— single-walled carbon nanotube, separation, electronic type, optical characterization, purity percentage.

Abstract: This paper studies how the various calcination temperatures affect the structural properties of Barium Titanate (BaTiO₃) and (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9) (BCZT) using solid-state reaction methods. BaTiO₃ and BCZT powders are calcined at various temperatures ranging from 1100°C–1300°C. Using X-ray diffraction, the phase formation, crystal structure and crystallite size of BaTiO₃ and BCZT powders were determined. The cubic crystal structure has been formed for BaTiO₃ and BCZT. At 1200°C, the reaction between BaCO₃ and TiO₂ was complete to produce BaTiO₃ composition. For BCZT composition were not fully react based on the phase structure in XRD due to impurity peak. Next, the crystallite size of BaTiO₃ powder becomes larger with increasing calcination temperature. Meanwhile, BCZT crystallite size becomes smaller when the calcination temperature is increased has discussed at the end of this paper.

Abstract: Chemical fertilizers are used in large quantities to boost the plant's development. Approximately 90 % of the fertilizer used is lost due to runoff and other processes, resulting in surface and groundwater contamination downstream. Nanofertilizers are believed to be more ecologically friendly and effective when used in small quantities. The use of nanomaterials in agriculture is not always successful. Nanoparticles may readily be discharged into water or the air, where they are ingested by living creatures, causing toxicity in humans, animals, and aquatic life. The aquatic environment has been contaminated with fertilizer runoff, which has been found to have fatal and sublethal impacts on aquatic species. In this work, the harmful effects of NPK-nanofertilizers were determined using the zebrafish embryo toxicity test (ZFET). To summarize, all nanofertilizers were dissolved in deionized water and diluted into concentration ranges in embryo medium. The toxicity of the fertilizer sample was next assessed on the early development of zebrafish embryos from 24 hours post-exposure (hpe) to 120 hpe. The survival rate, LC₅₀, hatching rate, heart rate, and teratogenicity were all assessed. Toxicity of nanofertilizers T1, T2, and T3 to zebrafish embryos was moderate, with LC₅₀ values of 45.7, 38.56, and 19.52 mM, respectively. While no teratogenic defect was seen in embryos treated with the respective samples from 0 hpe to 120 hpe, there was no teratogenic defect observed in the embryos treated with the respective samples from 0 hpe to 120 hpe. The larval heartbeat and hatching rate are unaffected by the nanofertilizer samples. As a result, the current study lays the groundwork for understanding the developmental toxicity of nanofertilizers in zebrafish embryos. Because little is known about the harmful effects of nanofertilizers on aquatic vertebrate species, this knowledge is essential for future research evaluating aquatic risk from nanofertilizers.

Abstract: Nanotechnology permits broad advances in agricultural research, such as disease prevention and treatment in plants using various approaches including nano-fungicide. Nano-fungicide has been able to draw much attention due to its higher efficacy even at very low doses because nano-sized particles could be more chemically reactive and bioactive than larger particles. Nano-fungicide is defined as a nanomaterial containing an active ingredient (essential oil etc.) with fungicide action and is incorporated into nano-emulsion. Nano-emulsion is obtained when the size of an emulsion droplet reaches approximately 20-500 nm. The physicochemical properties of nano-emulsions are interesting for practical applications especially in agriculture because of their small droplet size and long-term stability. Previously, a nano-fungicide formulation was developed using the nano-emulsion composition of the detergent Span 80 and Tween 80 and the essential oil extracted from the plant leaves of Cinnamomum zeylanicum (cinnamon) was successful to control the growth of Aspergillus flavus in storage grain corn. In this study, we investigated the effect of temperature at 4°C, 30°C and 60°C on the size and polydispersity index (PDI) of the nano-emulsion droplet at day 1, 30 and 60 of storage. The results of the nano-emulsion droplet size were significantly increased at 60°C after 30 and 60 days of storage and stable from 4 to 30°C even at 60 days of storage. This study provides a strategy to evaluates the effect of environmental factors on the quality of the formulated product, which is utilized for the prediction of its shelf life and determine proper storage conditions. Therefore, the optimized nano-emulsion formulation was characterized by droplet size and PDI for 2 months.

Abstract: Few-layer graphene sheets were synthesis using LPE with ultrasonic-assisted. The pristine graphite is directly exfoliated in deionized water with small addition of NH₃ solution. In this study, we will investigate the relationship between concentration of NH₃ solution corresponds to the graphene yield. The concentration of the NH₃ solution varies from 18% to 26%. NH₃ solution plays an important role as a medium to peel of graphite in the exfoliation process to form few-layer graphene sheets. The structural properties of the few-layer graphene sheets were examined using XRD, Raman Analysis, Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscope (SEM) followed by UV-Vis Spectroscopy for its optical properties. The finest of few-layer graphene sheets was produced at 26% of NH₃ concentration. This optimization results in a few layers of graphene sheets that may be used in the fields of nanoelectronics and optoelectronics.

Abstract: The research on transparent heater (Thf) films rapidly increases due to their unique photoelectric properties, leading to new generation of optoelectronic device. Here, we report a simple method to fabricate transparent heater based on Al-doped SnO₂ (ASO) thin films. ASO films with 5 wt% Al as dopant were synthesized with various deposition times, namely, 5, 10 and 15 minutes using ultrasonic spray pyrolysis method. The correlation of deposition time on their structural characteristic, optical, electrical and thermal properties has been investigated. X-ray diffraction studies found that all samples exhibit tetragonal structure with preferred orientation along (110) plane. Meanwhile, the UV-Vis transmittance indicated that the sample having good optical transparency in visible light spectrum with the average transmittance up to 89.7%. The sheet resistance of ASO thin films was found to decrease as the deposition time increases to 10 minutes. Furthermore, Al-doped SnO₂ based transparent heater prepared with 10 minutes deposition time presents the excellent thermal temperature up to 76.3 °C at the applied voltage of 20 volt. The above findings reveal that Al-doped SnO₂ can be used as an alternative compound to substitute higher cost indium tin oxide as transparent heater. Keywords: aluminium, composite, spray pyrolysis, SnO₂, transparent heater

Abstract: Microelectrode arrays (MEAs) are gaining interest in electroanalysis owing to its distinctive voltammetry properties compared to its macro counterparts. Among the MEAs widely fabricated and studied are microdisc array and microband array. We report here the microfabrication of 10 μm microband array (number of band in an array, N=17) and its application in labelless impedimetric sensing of T-2/HT-2 toxin. The microband array has recess depth (i.e. Si₃N₄ passivation thickness) of 200 nm. Upon fabrication, the device was first characterized via visual inspection and electrochemical analysis. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies were performed in 1 mM ferrocenecarboxylic acid (FCA) in 0.01 M PBS, pH 7.4. At scan rate of 100 mv s^-1, cyclic voltammogram for the microband array exhibited a slight peak-shaped CV; and was found to be scan-rate dependent. Experimental limiting current of the microband array (529±7 nA) was slightly lower compared to the calculated theoretical current (632 nA) indicating mixed diffusion profile of the microband array. The device was then employed in immunosensor construction for T-2/HT-2 toxins detection. T-2 mycotoxin and its metabolite (HT-2), are target of concern in the biosensing application due to its lethal toxicity and prominent presence in EU grains industry. Surface functionalization for anti-T-2 monoclonal antibody (mAb) immobilization was first achieved via surface hydroxylation with plasma cleaning and piranha solution treatment, followed by (3-Aminopropyl) triethoxysilane (APTES) silanization and 15 minutes pre-incubation with various concentrations of anti-T-2 toxin mAb in EDC/NHS mixture. The optimal concentrations for anti-T-2 toxin mAb immobilization on the microband array surface was determined at 0.75 mg mL^-1. Based on the calibration curve developed in buffer solution system, the functionalized microband array was proven sensitive as it was able to detect T-2/HT-2 toxin at low dynamic working range (0-25 ppb) and limit of quantitation (LOQ) achieved at 4.89 ppb.

Abstract: Zinc oxide-titanium dioxide (ZnO-TiO₂) have been successfully synthesized by hydrothermal method. ZnO-TiO₂ nanocomposite were prepared at different molar ratio 100:0, 100:0, 30:70, 50:50 and 70:30. The objective of this research is to determine the effect of molar ratios on the structural and optical properties of ZnO-TiO₂ nanocomposite. The samples were analyzed using X-ray diffraction (XRD) analysis, Field-emission scanning electron microscopy (FESEM) and UV-Vis spectroscopy. Based on the XRD results, it is revealed that ZnO-TiO₂ nanocomposite consists of hexagonal wurtzite structure of ZnO and mixed of anatase/ rutile phase of TiO₂. FESEM images showed ZnO in rod-like structure while TiO₂ is formed in nanoparticle. ZnO-TiO₂ composite is formed combination of rod-like and nanoparticles. UV-Vis spectra showed that all samples exhibited good absorption towards UV region. The calculated energy band gaps of ZnO-TiO₂ composite are 2.92 eV which is slightly smaller compared to bulk ZnO and TiO₂. The tuning energy band gaps of ZnO-TiO₂ composite samples is a good indicator for use in catalytic activities.

Abstract: Advanced power electronic application normally requires high-speed semiconductor switches in a compact design that are capable to transform electrical energy between the sources and the loads with high efficiency. In electronics, inefficiency is a waste that also translated into unnecessarily high costs and limits the device performance. As the number of connected devices increases in modern applications, more efficient power conversion is necessary especially for advanced power electronic systems. Therefore, in this research, on-chip thermal management is designed to improve the power conversion efficiency of Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT). Since the inefficiency in the electronic component is always referred to as losses in the form of heat, proper thermal management is needed to improve the device performance. As nanotechnology promise to be the foundation of the next industrial revolution, the research towards nanoenhanced semiconductor devices has aroused widespread attention from researchers, scientists and engineers. In this research, two-dimensional nanomaterials (2DNMs) are used as heat spreaders to reduce the localized hot spot temperature in GaN HEMT for higher device efficiency. The fabrication process flow, process issues, process characterization, material characterization and thermal performance of the nanomaterial heat spreader are the main topics to be discussed in this paper. Based on the experiment the monolayer graphene can improve the thermal resistance by at least 0.5 K/W. This may help to improve the GaN HEMT device efficiency especially when the device is operated under high power density.