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Characterization of Bi-doped FAPbI3 perovskite films investigated by X-ray absorption spectroscopy
(2025-12-01)
Wechprasit, Tirapat
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Bootchanont, Atipong
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Infahsaeng, Yingyot
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Wongjom, Poramed
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Wannapaiboon, Suttipong
A thorough investigation of perovskite structures formed through doping is essential for advancing the efficiency and stability of perovskite solar cells. In this study, Bi-doped FAPbI<inf>3</inf> perovskite films with varying Bi concentrations (0.5–2%) were fabricated using a spin-coating technique on ITO glass substrates. Then the films’ phase structure, local structure, and optical characteristics were analyzed. X-ray diffraction (XRD) analysis revealed that the pristine FAPbI<inf>3</inf> film exhibited both hexagonal and cubic phases, indicating structural instability. In contrast, Bi-doped FAPbI<inf>3</inf> films predominantly displayed a cubic perovskite structure, with a notable reduction in the XRD peak intensity corresponding to the hexagonal phase. UV–Vis spectroscopy showed that the undoped FAPbI<inf>3</inf> film had an absorption edge in the visible-near infrared range, while Bi-doping caused a redshift, indicating a reduction in the optical band gap. The calculated results show that optical band gaps decrease with increasing Bi, from a value of 1.49 (pure) to 1.43 (2% Bi) eV. X-ray absorption near edge structure (XANES) analysis confirmed the oxidation states of Pb2+ and Bi3+ ions across all samples, with Bi ions replacing Pb in the local structure. Photoluminescence (PL) measurements revealed an increased PL intensity with 1% Bi doping (7 105) compared with pristine FAPbI<inf>3</inf> (4.7 105), suggesting a reduction in carrier recombination. These findings demonstrate the potential of Bi-doping to stabilize perovskite structures with improved optoelectronic properties.
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The influence of palladium doping on the structural, morphological, optical and electronic properties of formamidinium lead iodide perovskite films
(2025-12-01)
Wechprasit, Tirapat
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Bootchanont, Atipong
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Infahsaeng, Yingyot
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Wongjom, Poramed
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Wannapaiboon, Suttipong
In this study, we investigated the effects of palladium (Pd) doping on the properties of formamidinium lead iodide (FAPbI<inf>3</inf>) perovskite films. Pd was doped at concentrations ranging from 0.5 to 2 % and coated onto indium tin oxide (ITO) glass substrates using a spin-coating technique. The crystal structure of the films was characterized using X-ray diffraction (XRD), revealing that Pd-doping reduces the hexagonal phase while increasing the cubic phase in the FAPbI<inf>3</inf> lattice. The optical properties were evaluated using ultraviolet–visible spectrophotometry (UV–Vis), showing changes in light absorption and a reduction in the energy gap with Pd incorporation. Scanning electron microscopy (SEM) was employed to examine the morphological properties of the films, indicating significant surface alterations and formation of larger grain sizes due to Pd incorporation. The electronic structure of perovskite films was thoroughly investigated using X-ray photoelectron spectroscopy (XPS). These findings demonstrate that Pd-doping significantly affects the structural, optical, and electronic properties of FAPbI<inf>3</inf> perovskite films, with potential implications for enhancing the performance of perovskite-based devices.
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Design and Implementation of a High-Field NdFeB Magnet System for Investigating the Spin Seebeck Effect
(2025-01-01)
Nachaithong, Theeranuch
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Wongjom, Chalothon
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Samransuksamer, Benjarong
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Phumying, Santi
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Pongophas, Ekkarat
The generation of pure spin current through thermal gradients, known as the spin Seebeck effect (SSE), has garnered significant interest in spintronics. In this study, we design and construct a permanent magnetic instrument setup to generate a variable external magnetic field using NdFeB permanent magnets to observe the SSE. The experimental setup is composed of three crucial components: the magnetic field, the temperature gradient, and electronic control systems. Si/yttrium iron garnet (YIG)/platinum (Pt) and Si/nickel (Ni) samples, prepared via sputtering techniques, were utilized for standard calibration purposes. The results show that the external magnetic field produced by NdFeB varies with the gap distance between the two magnetic poles, following an exponential decrease in field strength with increasing gap distance. The magnetic field at the center can be adjusted from ±20 to ±5000 Oe. The temperature gradient stabilizes after approximately 10 min, with a temperature difference ( ΔT ) between the heated and cooled sides ranging from 0 to 30 K. For instrument testing, we performed magnetic field and angle-dependent measurements on Si/YIG/Pt and Si/Ni samples. The results indicate that the magnetic field dependence of the permanent magnet instrument (PMI) does not exhibit the voltage loop switching seen with an alternative magnetic coil (AMC) but shows analogous behavior at high magnetic fields. Moreover, the angle dependence of both PMI and AMC yielded comparable results. In conclusion, our PMI setup procedures effectively facilitate the observation of the SSE.
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Spin Seebeck effect and large spin conversion in amorphous Fe2TiSb/polycrystalline Y3Fe5O12 thin films
(2024-05-30)
Wongjom, Poramed
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Wongjom, Chalothon
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Pongophas, Ekkarat
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Infahsaeng, Yingyot
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Maiaugree, Wasan
This study investigates spin current generation in a Fe<inf>2</inf>TiSb/Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf> multi-layer thin film as prepared via the magnetron sputtering method. Comprehensive characterization techniques are employed to assess film properties, including X-ray diffraction, energy-dispersive X-ray spectroscopy, Scanning electron microscopy, and Vibrating sample magnetometer. The Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf> material exhibits a polycrystalline ferromagnetic insulator behavior, while the 20 nm-thick Fe<inf>2</inf>TiSb film displays small ferromagnetic metal properties with an amorphous structure. Spin current analysis utilizes the longitudinal spin Seebeck effect configuration, considering magnetic field and temperature dependencies and the results show that spin conversion within the Fe<inf>2</inf>TiSb/Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf> structure is influenced by both the spin Seebeck effect and the anomalous Nernst effect, resulting in an overall spin signal enhancement. The spin Seebeck coefficient of Fe<inf>2</inf>TiSb/Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf> was approximately 0.103 μV/K within a magnetic field of 300 mT.
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Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect
(2024-03-01)
Phumying, Santi
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Wongjom, Chalothon
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Pongophas, Ekkarat
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Infahsaeng, Yingyot
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Maiaugree, Wasan
The generation of spin voltage by heat, known as the spin Seebeck effect (SSE), involves the injection of spin current from a ferromagnetic to a normal metal. In this study, the shunting effect in SSE is investigated within a hybrid structure consisting of iron (Fe) and cobalt (Co) films deposited on a Si-wafer substrate using thermal evaporation [Si/Fe(500 nm)/Co(10 nm)]. Spin voltage measurements performed in the in-plane configuration revealed a voltage reversal in the Co film and Fe film. However, in the hybrid structure (Si/Fe/Co), the voltage signal exhibited consistent directionality. This intriguing observation hints at a potential shunting effect, wherein the voltage influence from the Fe layer contributes to the Co film. Consequently, it is deduced that a significant shunting effect occurs when the resistivity of Fe is approximately three orders of magnitude lower than that of the Co film. This insight sheds light on the intricate dynamics of spin thermoelectric applications, emphasizing the role of material properties in optimizing performance.
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The Spin Voltage Enhancement in Si/YIG/Co, Fe Spin Hall Thermopiles
(2024-01-01)
Kumpor, Wimutti
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Kuptapol, Perawas
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Wongjom, Chalothon
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Pongophas, Ekkarat
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Infahsaeng, Yingyot
Spin-Hall thermopiles have been previously proposed as a means to enhance the spin Seebeck effect (SSE). However, the use of platinum (Pt) for spin detection drives costs high and proves an impediment for scalability. In this work, a cost-effective spin-Hall thermopile constructed from opposite spin-Hall angle ferromagnets, cobalt (Co) and iron (Fe), is reported. The devices are fabricated using a standard sputter-coated yttrium iron garnet (YIG) substrate that serves as the spin injector, and thermally evaporated Co and Fe strips that enable spin detection. When serially connected to form a (YIG/Co, Fe) thermopile structure, measurements indicate a significant enhancement of the spin voltage that results from the additive spin contributions of the opposite spin-Hall angle ferromagnets and the anomalous Nernst effect (ANE) that they exhibit. The YIG/Co, Fe thermopile reported here offers a cost-effective alternative to Pt-based thermopiles and the possibility of large-scale implementation to realize future thermoelectric generators.
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Low-Cost Instrument for the Versatile Measurement of Spin Caloritronic Phenomena: Spin Seebeck Effect, Anisotropic Magnetoresistance, Anomalous Hall Effect, and Anomalous Nernst Effect
(2023-01-01)
Pongophas, Ekkarat
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Infahsaeng, Yingyot
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Maiaugree, Wasan
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Phumying, Santi
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Pattanakul, Rungrueang
In this article, we report on a low-cost instrument for the versatile measurement of spin caloritronics phenomena such as the spin Seebeck effect (SSE), anomalous Nernst effect (ANE) anisotropic magnetoresistance (AMR), and anomalous Hall effect (AHE). Solenoid coils provide a uniform variable magnetic field while the sample was sandwiched between thermal baths and measured in a vacuum chamber. Our results show excellent magnetic field uniformity (±0.37 mT) within the magnet gap and high stability of the generated temperature difference (±0.07 K). For verifying the effectiveness of our instrument, Yttrium Iron garnet (YIG)/Co structure was used to measure the SSE, AMR, and AHE, while a SiO2/Co structure was used for measuring the ANE. Our SSE measurements of the YIG/Co structure were found to be comparable with that of a commercially available instrument. We can therefore conclude that our low-cost and versatile instrument can be used to effectively observe spin Caloritronics phenomena.
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Characterization and electrochemical properties of CuO–Cu2O@rGO nanocomposite synthesized by a seed-mediated growth process
(2022-04-01)
Wongjom, Poramed
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Tuichai, Wattana
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Karaphun, Attaphol
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Phrompet, Chaiwat
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Daengsakul, Sujittra
A CuO–Cu<inf>2</inf>O@rGO nanocomposite (CuO–Cu<inf>2</inf>O@rGO NCP) has been successfully prepared through a seed-mediated growth process. X-ray diffraction (XRD) analysis results indicated a monoclinic phase of CuO–Cu<inf>2</inf>O@rGO NCP with space group C2/c. Transmission electron microscopy (TEM) revealed agglomeration of the CuO and Cu<inf>2</inf>O nanoparticles in the rGO sheet matrix. The interaction of CuO–Cu<inf>2</inf>O@rGO NPC resulted from the aggregation and overlapping of CuO and Cu<inf>2</inf>O nanoparticles owing to the influence of a seed-mediated growth process. The electrochemical properties of the CuO–Cu<inf>2</inf>O@rGO NPC electrode indicate the storage of energy at the surface through a pseudo-capacitive mechanism. The specific capacitance at a current density of 0.5 A g−1 and the average percentage capacity retention after 1000 cycles of a CuO–Cu<inf>2</inf>O@rGO electrode at a current density of 10 A g−1 were evaluated as 125.54 F g−1 and 89.87 ± 3.30%, respectively. In the CuO–Cu<inf>2</inf>O@rGO electrode, the incorporated rGO affects the electrical conductivity and the synergistic interactions in charge–discharge processes. Interestingly, these results showed that the material was synthesized through a seed-mediated growth process and reveal the key factors that determine the combination and volume expansion of the reversible redox transition between Cu+ and Cu2+ during charge–discharge processes.
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The Observation of Spin Seebeck Effect of Hybrid Structure in Bulk Sintering Polycrystalline of Yttrium Iron Oxide (Y3Fe5O12)/Pt
(2022-01-01)
Wongjom, Poramed
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Phatthanakun, Rungrueang
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Ruttanapun, Chesta
In this article, we report the observation of spin Seebeck effect (SSE) of hybrid structure in bulk sintering polycrystalline of yttrium iron oxide (Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf>, YIG)/Pt. The bulk YIG polycrystalline is prepared by solid press mechanic and then coated with Pt 10 nm thickness. The voltage of inverse spin Hall effect (V<inf>ISHE</inf>) in Pt/YIG polycrystalline is detected by in plane magnetization configuration (IM) and then filter out the anomalous Nernst effect (ANE) by perpendicular magnetization configuration (PM). The results show that the V<inf>ISHE</inf> signal can be observed in bulk YIG polycrystalline. In addition, the efficiency of spin injection from YIG to Pt is compared between Pt/YIG single crystal and bulk polycrystalline of hybrid structure. The V<inf>ISHE</inf> signal of Pt/YIG single crystal and bulk polycrystalline are 197.61 nV/K and 23.22 nV/K, respectively. The V<inf>ISHE</inf> voltage of YIG single crystal is higher than bulk polycrystalline about 9 times. Whereas, the porous size in bulk YIG polycrystalline of solid press is determined around 214 ± 81 nm but it cannot detect in YIG single crystal. Thus, the porous size and surface roughness between YIG and Pt might be the major role of the spin current (J<inf>s</inf>) transfer.
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The observation of spin Seebeck effect in opposite spin Hall angle materials of polycrystalline bulk-Fe3O4/(Co/Fe) systems
(2022-01-01)
Bavontaweepanya, Ruchipas
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Infahsaeng, Yingyot
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Pongophas, Ekkarat
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Maiaugree, Wasan
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Piyasin, Piyawat
In this study, we report on the observation of spin current in opposite spin Hall angle materials of polycrystalline bulk-Fe3O4/Co and polycrystalline bulk-Fe3O4/Fe spin Seebeck effect (SSE) devices. In contrast to prior works, a facile and low-cost hot-pressing powder metallurgy process was employed to manufacture the polycrystalline bulk-Fe3O4 samples. The crystal structure, magnetization properties, and electrical resistivity characterizations of the fabricated bulk-Fe3O4, which were performed using x-ray diffraction, vibration sample microscope, and four-point probe, respectively, revealed excellent agreement with those of conventional Fe3O4. By taking advantage of the fact that the SSE signal in our devices is typically contaminated with the anomalous Nernst effect (ANE), we show that the total thermo-voltage obtained from our devices can be enhanced by the significant ANE signals exhibited by the Co and Fe spin detectors. Importantly, the ANE contributions could be filtered out from the main signal by independent measurements of the ANE voltage in SiO2/Co and SiO2/Fe systems, thereby allowing the approximate extraction of the SSE voltage. Our experiments reveal that the polarity of the measured ANE (and pure SSE voltages) are opposite to each other in the bulk-Fe3O4/Co and bulk-Fe3O4/Fe structures, thus proving the opposite spin-hall angles character of these materials. The findings of this work provide a pathway for further exploration of methods through which the thermo-voltage output in future spin-Hall thermopile devices may be improved using materials manufactured via a facile, low-cost, and easily scalable process.

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