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Post-annealing effects on (00l) texture, Cl/Se ratio, and electrical and glass-like thermal transport in Bi₄O₄SeCl₂
(2026-04-25)
Somdock, Nuttakrit
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Theekhasuk, Nattharika
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Voraud, Athorn
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Limsuwan, Pichet
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Naemchanthara, Kittisakchai
Bi₄O₄SeCl₂ is a heteroanionic layered material with intrinsically low lattice thermal conductivity and anisotropic charge transport. In this work, the effects of post-annealing temperature on the crystallographic texture, anion chemistry, defect evolution, and transport properties of Bi₄O₄SeCl₂ were systematically investigated. Polycrystalline Bi₄O₄SeCl₂, synthesized by solid-state reaction combined with high-energy ball milling, was post-annealed at 400–700 °C. X-ray diffraction and electron microscopy revealed that post-annealing eliminated the residual BiOCl precursor phase, enhanced the (00 l) preferred orientation, and promoted grain growth up to 600 °C, followed by partial texture degradation at 700 °C due to recrystallization. Energy-dispersive spectroscopy showed progressive Se and Cl volatilization during annealing, leading to an increased Cl/Se ratio. The carrier mobility and electrical conductivity reached maximum values at 600 °C, consistent with improved texture and layered-domain connectivity. Thermal transport remained lattice-dominated and only weakly temperature-dependent. The phonon mean free path, estimated using kinetic theory, was in the sub-nanometer range (∼0.25–0.57 nm), comparable to the interatomic spacing, indicating glass-like phonon transport. Representative HRTEM observations also revealed dislocation-related lattice defects and locally distorted regions, suggesting that vacancy disorder and local strain fields may provide additional phonon scattering. These results demonstrate that post-annealing optimizes electrical transport through phase purification, texture development, and defect-mediated carrier regulation, while the lattice thermal conductivity remains fundamentally limited by intrinsic glass-like phonon transport in Bi₄O₄SeCl₂.
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Dual optimization of ZT and output power in bulk Bi2Te3 through metal-assisted chemical etching
(2026-03-01)
Theekhasuk, Nattharika
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Sakulkalavek, Aparporn
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Ono, Takahito
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Sakdanuphab, Rachsak
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Nguyen, Duc Nam
Thermoelectric materials offer a promising route for sustainable energy harvesting by directly converting waste heat into electricity, enabling compact, solid-state, and environmentally friendly energy solutions. Among them, bismuth telluride (Bi₂Te₃) stands out as the benchmark material for near-room-temperature applications due to its excellent electronic transport properties and commercial maturity. However, achieving high-performance in bulk or thick-film Bi₂Te₃ remains a formidable challenge. Conventional strategies such as doping, alloying, and nanoinclusion, while successful in thin films, often fail to translate effectively to bulk systems due to issues like pore collapse, poor uniformity, and degraded electrical connectivity. These limitations hinder the formation of efficient phonon-scattering architectures without compromising charge transport, resulting in limited improvement in the thermoelectric figure of merit (ZT). In this study, we present a novel and scalable nanoengineering strategy that applies metal-assisted chemical etching (MACE) to fabricate nanoporous surface layers on bulk Bi₂Te₃ for the first time. Unlike conventional nanostructuring techniques, MACE enables the formation of oriented nanostructures via a simple wet-chemical process, offering high tunability, low cost, and compatibility with large-area substrates. To reduce interfacial resistance, nickel was subsequently electrodeposited onto the nanostructured surface, forming a conformal contact layer that improves charge extraction and output performance. By systematically tuning the MACE duration, the optimized nanostructured Bi₂Te₃ sample exhibited a 2.3-fold improvement compared to the pristine bulk sample. Furthermore, due to the increased surface area from the nanoporous architecture, the internal resistance and output power of the nanostructured Bi₂Te₃ devices demonstrated 25-fold and 5.8-fold improvments, respectively, relative to the untreated sample. These remarkable improvements are attributed to the synergistic effect of enhanced phonon scattering within the nanoporous layer and improved charge transport enabled by the conformal nickel coating. This work not only introduces a powerful nanostructuring route for Bi₂Te₃ but also establishes a practical platform for high-performance, thick-film thermoelectric devices. The findings offer deep insight into the structure, property, and performance relationships governing thermoelectric efficiency and pave the way toward the scalable fabrication of next-generation thermoelectric modules for real-world applications such as industrial waste heat recovery and self-powered electronics.
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Estimation of Vertical Jump Height using Capacitive Sensing Method
(2023-01-01)
Kaewjumras, Yongyut
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Klongratog, Bhanupol
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Inboonma, Weerayut
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Sukprasertchai, Siwakorn
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Somdock, Nuttakrit
This paper presents a low-cost vertical jump height measuring device based on the time-of-flight technique. A capacitive mat was developed and used as a sensing element to sense the athlete's feet. The capacitive mat was made from aluminum foils that dimensions of the capacitive mat ware with a width of 50.3 cm x length of 70.6 cm. The signal conditioning circuitry that was used as an analog front-end for measuring the capacitive was also described. The time difference between when athletes jumped off and reached the ground was calculated by a microcontroller. The jump height was recorded and stored via the computer. A total of 27 athletes, weighted between 48 kg to 115 kg were used as a sample. The testing results have shown that the proposed system has a percentage difference of 18.16%.
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Personal Identification using the Distance and Triangle between the Metacarpophalangeal Joints
(2022-01-01)
Srathongkao, Siwa
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Kaewjumras, Yongyut
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Ngamsapmanee, Wanasanan
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Somdock, Nuttakrit
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Sawangjit, Nalita
Personal identification using the distance among the metacarpophalangeal joints (MCPs) was presented in this study. The system was developed to specify the dorsal hand patterns. Firstly, the dorsal hand images were taken for the subjects via an infrared camera. Secondly, the dorsal hand images were converted to grayscale and binary images using image processing techniques. After that, the distance of the MCPs was measured by various the dorsal hand images including index to middle, middle to ring, ring to little, and index to little of the dorsal hand. In addition, the triangle areas between index to middle, middle to ring, ring to little, and index to little of the dorsal hand were used to specify the dorsal hand patterns. The result of the distance and the triangle area of the MCPS can be used to identify a person because of the difference of distance and the triangle area of the MCPs of each person.
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Contactless silicon-based multi-dimensional Hall sensor with simultaneous magnetic sensing and omni-rotational angle measurement
(2019-01-01)
Kaewjumras, Yongyut
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Prabket, Jirawat
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Titiroongruang, Wisut
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Niemcharoen, Surasak
This experimental research proposes a contactless silicon-based two-dimensional (2D) Hall sensor capable of simultaneous parallel- and perpendicular-directional magnetic sensing, with a 360° angle measurement. The Hall sensor was of non-symmetrical five-ohmic contact configuration (C1 – C5). In the study, experiments were carried out in three stages. In the first-stage experiment, the current (I) and voltage (V) of the 2D Hall sensor were determined under three schemes: schemes A (C1&C2), B (C2&C5), and C (C3&C4). In the second-stage experiment, the parallel and perpendicular absolute sensitivities of the 2D sensor were examined. Considering the discrepancy between the parallel and perpendicular absolute sensitivities, signal conditioning circuitry was incorporated into the sensor system to compensate, and the rotational angles measured in the final-stage experiment. The results revealed that the I-V curves were dominantly linear, corresponding to Ohm’s law. However, the parallel and perpendicular absolute sensitivities were low and unequal. Thus, signal conditioning circuitry was incorporated into the system to address the discrepancy and improve the performance. Importantly, the 2D Hall sensor exhibited a mere ±3<sup>o</sup> discrepancy between the measured and reference rotational angles, given the magnetic flux density of 1000 G, with the hysteresis error of 2.8%. In essence, the proposed contactless silicon-based 2D Hall sensor possesses high potential for high-precision industrial applications.
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Application of Multi-Dimensional Hall Sensor for Gauss Measurement
(2017-01-01)
Kaewjumras, Yongyut
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Mano, Athirot
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Titiroongruang, Wisut
This paper reported on a two-dimensional Hall sensor enabling to measure the two spatial components of the magnetic field and applied for gauss measurement application. The device was operated through only five contacts and tested by varying the magnetic flux density from -5000 to 5000 Gauss (G) and using signal conditioning circuitry for amplifying and adjusting the both similar sensitivity. After that, the output signals were converted to digital signals by ADC for transmitting a computer using LAB-VIEW programming and comparison with the standard gauss meter (F.W.Bell5170). The result of gauss measuring application comparison with the standard gauss meter has done with a precision of 0.04-3.80% including a calibration process.

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