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## Creator

[Masahiro Goto](https://orcid.org/0000-0002-1003-2781), [Michiko Sasaki](https://orcid.org/0000-0002-2336-5788)

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[MgSiSn/Mg2Sn amorphous–crystalline nanocomposites with enhanced figure-of-merit performance for efficient thermoelectric conversion](https://mdr.nims.go.jp/datasets/51366987-0306-4753-bfa4-e8e9cfa6b611)

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Template for Electronic Submission to ACS Journals 1 MgSiSn/Mg2Sn Amorphous–Crystalline Nanocomposites with Enhanced Figure-of-Merit Performance for Efficient Thermoelectric Conversion Masahiro Goto* and Michiko Sasaki * Thermal Energy Materials Group, Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan Correspondence and requests for materials should be addressed to M.G. (email: goto.masahiro@nims.go.jp) or M.S. (email: sasaki.michiko@nims.go.jp) ABSTRACT:   Thermoelectric conversion is emerging as an efficient method for transforming waste heat into electricity. Approximately 60% of unrecovered waste heat is below 500 K, necessitating suitable materials. Bi2Te3-based compounds, widely commercialized for this purpose, exhibit a figure of merit (zT) of one near room temperature but are expensive and highly toxic. While less toxic and more abundant materials including Mg2Sn and Mg2Si are explored as alternatives, their zT values remain considerably low. For zT enhancement, Mg2SixSny nanocomposite thin films were fabricated using a combinatorial sputter coating system. Through interfacial engineering and nanocrystallization, this system produced multilayered (ML) Mg2Si and Sn structures that overcame the trade-off relationship among  2 Seebeck coefficient, electrical conductivity, and thermal conductivity, achieving zT values of 0.021 and 0.083 at room temperature and 520 K, respectively. ML samples were fabricated on flexible substrates for potential wearable thermoelectric applications. This zT-enhancement strategy can yield high-performance, ecofriendly thermoelectric thin films. KEYWORDS: Thermoelectric conversion, Sputter coating, Thin film, Coating, Combinatorial technology, Magnesium silicide, Flexible thermoelectric device  1. Introduction Thermoelectric energy conversion has garnered increasing attention as an efficient method for converting waste heat into electricity, making it a promising technology for energy harvesting across various applications. Approximately 60% of unrecovered waste heat exists at temperatures below 500 K, making low-temperature thermoelectric materials crucial for effective energy harvesting[1]. Among commercially available thermoelectric materials, Bi2Te3-based compounds, which exhibit a figure of merit (zT) of approximately one, are preferred for near-room-temperature applications[2]. However, their widespread adoption is hindered by high cost and toxicity concerns. To address these limitations, researchers have explored alternative thermoelectric materials such as Mg2Sn- and Mg2Si-based compounds, which are more abundant and less toxic[3]. However, their relatively low zT values prevent them from serving as effective replacements for Bi2Te3-based materials, making improvements in zT performance a critical research focus. Simultaneously, the rising demand for lightweight, flexible thermoelectric devices particularly for wearable electronics and curved surfaces along with the need for reduced material usage, has spurred interest in the development of thin-film thermoelectric materials. However, these thin-film materials generally exhibit poorer performance than their bulk  3 counterparts. Recent advancements in deposition and evaluation techniques have enabled the optimization of the composition and introduction of doping elements into Mg2Sn- and Mg2Si-based thin films, improving their zT values[4-34]. Although Mg2Si and Mg2Sn have long been researched as thermoelectric materials, their low electrical conductivity and high thermal conductivity result in a relatively low zT value. To improve the zT values of these materials, researchers have added doping elements that enhance electrical conductivity; alternatively, they have partially substituted the Si sites with doping elements having a larger atomic radius than Si to reduce thermal conductivity. The efficiency of thermoelectric materials is evaluated using zT, a dimensionless parameter defined as zT = (S2 σ/κ)T, where S denotes the Seebeck coefficient (SC, S = DV/DT), σ denotes electrical conductivity (EC), κ represents thermal conductivity (TC), and T signifies absolute temperature. TC (κ) comprises two components: electronic TC (κel) and lattice TC (κlat). Among these, κel is related to EC (σ) through the Wiedemann–Franz law: κel = LσT, where L denotes the Lorentz number. Consequently, optimizing one parameter to enhance zT often leads to compensatory changes in another, leading to a trade-off. One approach to improving zT performance involves utilizing nanocomposite thin films with low-dimensional structures, which enhance zT performance by leveraging the quantum and classical size effects of electrons and phonons[35-37]. In such structures, the SC is expected to increase owing to the steepening of the density of states (DOS) slope near the Fermi level with decreasing dimensionality. Under these conditions, TC is also expected to decrease owing to enhanced phonon scattering caused by an increase in interfacial density. If Mg2Si- and Mg2Sn-based thermoelectric materials can exhibit high zT values using this approach, then thermoelectric devices can be fabricated from environmentally friendly, inexpensive materials.  4 The development of novel thermoelectric materials requires a film-coating system that can efficiently and reproducibly generate various materials with controlled nanostructures. We have developed a combinatorial sputter coating system (COSCOS), which can precisely control the film-coating parameters and automatically fabricate multiple samples with different crystal, nanostructures, and compositions; additionally, we have used it to develop novel materials for thermoelectricity[38, 39], thermal management[40-50], tribology[51-57], and other applications. The objective of this study is not to identify materials with the highest zT values but to verify whether nanostructure control can overcome the trade-off relationship among the three parameters governing thermoelectric performance, thereby enabling the application of the proposed approach to thermoelectric materials with high zT values or to develop new thermoelectric materials. For this purpose, we fabricate nanocomposite thin films composed solely of Mg, Sn, and Si— widely available elements—and simplify material structures using COSCOS. Notably, this technique offered high control over material nanostructures, enabling improvements in zT through low-dimensional and interfacial effects. 2. Experimental procedure 2.1 Sample fabrication apparatus Nanocomposite thin films composed of Mg, Sn, and Si were fabricated using a combinatorial sputter coating system (COSCOS), as depicted in Fig. 1. Notably, the COSCOS is a system widely used for material development across various fields. It enables a streamlined research and development process, from material discovery to device fabrication, facilitating the rapid identification of high-performance materials and their integration into industrial applications. The sputtering method offers control over numerous experimental parameters, including working pressure, gas composition, partial pressure of mixed gases, radio frequency (RF) power, substrate temperature, substrate–target distance, and bias voltage. By modifying these parameters, thin  5 films with varying properties can be produced. Furthermore, even when desirable material properties are achieved, ensuring reproducibility in thin-film fabrication is crucial for conducting fundamental research and advancing practical applications. However, the need to control multiple experimental parameters and the lack of reproducibility in thin-film fabrication have been identified as major challenges in the sputtering process. To address these issues and enable high-throughput material discovery, we introduced the basic concept of the COSCOS, which applies combinatorial technology to sputter coating. Unlike conventional combinatorial techniques, the COSCOS was designed to streamline the entire process, from rapid material discovery to industrial-scale applications, including device fabrication.   The COSCOS primarily consists of a vacuum chamber, multiple sample holders, sputter cathodes, a vacuum pumping system, and an automated valve control system. A large front hatch in the vacuum chamber allows for efficient sample loading and unloading. The chamber is evacuated using a high-capacity turbomolecular pump (Shimadzu Model TMP-803LM(0), 800 L/s), achieving a vacuum of up to 2 × 10−6 Pa without the need for chamber baking. Fig. 1. Schematic illustration of the COSCOS.  6 Generally, during chamber baking, contamination from the chamber walls affects the substrate surface, making it difficult to achieve reproducible sample fabrication. To address this, various commercially available and custom-developed magnetron sputter cathodes are used to supply material elements, in combination with RF and direct current (DC) power supplies as needed. This setup allows for the deposition of a wide range of materials, including metals, ceramics, semiconductors, and polymers. To enhance the reproducibility of sputter-coated films, the vacuum chamber pressure is monitored using a capacitance manometer (CM) during sputtering. This system is integrated with a gate valve controller for feedback control, ensuring a stable sputtering gas pressure. The CM is specifically used owing to its ability to withstand 100% oxygen environments, as filament-based vacuum gauges cannot operate under high oxygen concentrations due to filament burnout. Additionally, the multi-sample holder (Fig. 1(a)) enables the simultaneous preparation of multiple samples, with up to 14 samples typically processed in a single vacuum evacuation. Fig. 1(b) presents a photograph of the vacuum chamber interior with its front door open. Here, discharge occurs from the three magnetron sputter cathodes positioned at the bottom of the chamber. The sample exchange mechanism is located at the top, while the sputter cathodes are at the bottom. A mask plate is placed at the bottom of the sample exchange mechanism, ensuring that only one sample is coated at a time. Once the coating process is completed, the multi-sample holder rotates, positioning the next sample for deposition. Heat transfer between individual sample fixtures and the multi-sample holder is minimized using alumina spacers, allowing only the sample at the coating position to be heated to approximately 1273 K. During this heating process, the remaining 13 samples are continuously water-cooled, maintaining the temperature rise for non-coated samples within 80 K. A thermocouple, in contact with both the sample holder and the heater, performs feedback control to maintain a constant set temperature. Additionally, a DC bias voltage of up to 1200 V can be applied to the sample. The substrate–target distance is adjustable using a motor-driven linear positioning mechanism. Coating parameters, including sputter gas pressure, gas composition, partial pressure, sputter power, substrate temperature, substrate–target distance, and bias voltage, can be configured and remotely controlled via an external control system. The control system allows manual implementation of individual system functions and real-time monitoring of system status. Once the predefined process recipe is initiated, the coating procedure runs fully automatically. Real-time monitoring of film thickness, temperature, and gas pressure during coating is possible, with  7 all data recorded in a log file. These data, along with the results of sample property evaluations, are stored in a database and integrated with materials informatics technology to facilitate the discovery of new materials. Overall, this automated fabrication process offers several advantages. First, the system is capable of producing thin films with a relatively large area, facilitating their use in various applications. Automation also reduces the workload on researchers, allowing them to focus on other tasks while experiments are underway. Additionally, reproducibility is improved by eliminating human variability in the process. In summary, this approach dramatically improves the efficiency of materials development, enabling systematic exploration of thin-film materials with novel properties and facilitating performance optimization—tasks that previously required considerable time and effort. Although not attempted in this study, the fabricated thin-film thermoelectric materials can be integrated with electrodes to produce thermoelectric devices using the device fabrication mode of the COSCOS. This capability highlights the COSCOS as an efficient system for rapid thermoelectric material exploration and device fabrication.  2.2 Fabrication of nanomaterials Nanocomposite Mg, Sn, and Si thin films were fabricated using the COSCOS with two sputter cathodes. The films were deposited at room temperature onto microelectromechanical system (MEMS) sample tips (Fig. 2) for thermoelectric property measurements, with a floating potential applied during the coating process. For sputter coating, Mg2Si (diameter: 50 mm, thickness: 6 mm, 99% purity, Kojundo Chemical Lab. Co., Ltd.) and Sn (diameter: 50 mm, thickness: 6 mm, 99.999% purity, Kojundo Chemical Lab. Co., Ltd.) sputter targets were used with high-purity argon gas (99.999%) at a working pressure of 0.4 Pa. The RF power was set to 60 W for the Mg2Si target and 100 W for the Sn target during ML sample preparation. The target–sample distance was fixed at 190 mm, and pre-sputtering was performed for 15 min. ML thin films were fabricated by alternating layers of Mg2Si and Sn in three different configurations: 18 nm/2 nm, repeated 143 times (18/2 × 143; hereafter 18/2); 18 nm/4 nm, repeated 136 times (18/4 × 136; hereafter 18/4); and 18 nm/8 nm, repeated 63 times (18/8 × 63; hereafter 18/8). The total thicknesses of these samples were 2860, 2992, and 1638 nm, respectively. These films were then coated onto microelectromechanical system sample tips for thermoelectric measurements.  8 Film thickness was initially monitored using a conventional quartz crystal thickness monitor and later precisely determined by transmission electron microscopy (TEM). A non-ML thin film with the same elemental composition as the 18/2 ×143 sample was also prepared by fixing the RF power for the Sn target at 100 W while varying the RF power for the Mg2Si target. Additionally, to assess the applicability of the 18/2 ×143 nanostructured sample for flexible thermoelectric devices, a thin film was deposited on a polyimide substrate.  2.3 Characterization The crystal structure, multilayer arrangement, material composition, and elemental distribution of the thin films were analyzed using TEM (JEOL JEM-ARM200F) with energy-dispersive X-ray spectroscopy and electron diffraction. The in-plane thermoelectric properties of the samples, including the Seebeck coefficient, electrical conductivity, and thermal conductivity, Fig. 2. Fabrication and thermoelectric property assessment of Mg2Si/Sn nanocomposite thin films using the COSCOS.   9 were assessed using a thin-film analyzer (TFA) (LINSEIS TFA). Measurements of additional thermoelectric parameters such as carrier density, mobility, Hall coefficient, and heat capacity were obtained from the same sample to ensure consistency and improve measurement reliability. The thermoelectric samples were deposited on a designated area of the MEMS sample tips using a metal mask in the COSCOS (Fig. 2). After removing the mask, the sample tip was inserted into the TFA system. Fourteen test probes were then connected to the electrodes of the MEMS sample, allowing automated thermoelectric property analysis. Further details on the analysis method are available in previous reports[58]. Details regarding the thermoelectric measurement apparatus are provided in Fig. 2. During thermoelectric property measurements under heating, the initial sample nanostructures underwent modifications, leading to corresponding changes in thermoelectric performance. We investigated the relationship between these structural transformations and thermoelectric property variations to acquire insights for improving zT values. For comparison, a reference sample with the same elemental composition as the 18/4 sample but without an ML structure was also prepared.  3. Results and discussion Subsequently, the thermoelectric properties of the nanostructured samples (18/2, 18/4, and 18/8) and the non-nanostructured reference sample (labeled Normal in the figure) were analyzed, as depicted in Fig. 3. The corresponding results, displayed in Fig. 3a, reveal that the 18/4 and 18/8 samples exhibited higher SC values than the Normal and 18/2 samples. After annealing, the SC of the 18/4 sample reached its maximum of 167 µV/K, approximately 13 times higher than that of the annealed Normal sample (13 µV/K). The SC values of all samples except 18/2 increased after annealing, with the most pronounced increase observed in the 18/4 sample. This suggests that the initial ML structure underwent changes during annealing, as will be discussed  10 later. In contrast, the SC of the 18/2 sample was lower than that of the Normal sample. Similarly, the EC values of all ML samples (18/2, 18/4, and 18/8) were also lower than those of the Normal sample across the entire temperature range, as illustrated in (Fig. 3). Additionally, annealing decreased the EC of the 18/4 sample but increased the EC of the 18/2 and 18/8 samples.  The EC of the Normal sample, remained nearly unchanged. As illustrated in Fig. 3c, the TC values of all ML samples were substantially lower than that of the Normal sample. Specifically, for the 18/4 sample, TC increased slightly after annealing but remained around 1 W/mK. In contrast, the TC values of the 18/2 and 18/8 samples decreased after annealing, with the lowest value of 0.3 W/mK observed for the 18/2 sample at 373 K, which was remarkably low compared Fig. 3. Temperature dependence of the thermoelectric properties of Mg2Si/Sn nanocomposite thin-film samples (18/2, 18/4, and 18/8) and the non-nanostructured reference sample (denoted as "Normal" in the figure): (a) Seebeck coefficient (S), (b) electrical conductivity, (c) thermal conductivity, and (d) figure of merit (zT).   11 to the typical values observed for conventional Mg2Si-based materials. Fig. 3d presents the temperature dependence of zT values. Notably, the zT values of the 18/4 and 18/8 samples were higher than those of the Normal and 18/2 samples. Further, annealing increased the zT value of the 18/4 sample by approximately 2.3. Compared to the Normal sample, this zT represented an increase of nearly tenfold. These results demonstrated that the ML samples achieved substantial improvements in thermoelectric performance. To simplify the graph, only data obtained during the heating phases before and after the annealing of each sample were shown. The actual data were more complex; for example, the data of sample 18/4 were collected during 10 cycles of the heating and cooling phases (Fig. 4). At the start of evaluation, temperature was limited to approximately 400 K or lower to avoid sudden changes in the nanostructure and to investigate Fig. 4. Ten repeated cycles of the temperature dependence of the figure of merit (zT) of a Mg2Si/Sn nanocomposite thin-film sample (18/4).  12 the detailed correlation between nanostructure differences and thermoelectric properties. The samples could be evaluated even after 10 repeated cycles, confirming their stability. The temperature dependence of the zT value for an 18/2 × 143 nanostructured sample was measured via 10 cycles of heating and cooling. To avoid complicating their display, only data obtained during the temperature rise are shown. In addition, data acquisition failed during the seventh cycle. The thermoelectric characteristics improved through repeated measurements. The sample remained suitable for evaluation even after 10 measurements, confirming its sufficient stability. To suppress rapid changes in the nanostructure caused by high-temperature heating, the initial maximum temperature was set low (368 K during the 1st cycle, 383 K during the 2nd cycle, 388 K during the 3rd cycle, and similarly up to the 10th cycle). Gradual nanostructure variations caused by sample heating during multiple thermal–electric property evaluations clearly changed the zT value. As shown in the graph, the zT value improved through consecutive measurements. To investigate the reasons underlying the observed zT increase for the 18/4 sample, transmission electron microscopy (TEM) and electron diffraction (ED) analyses were performed, as depicted in Fig. 5 and Fig. 6. A well-ordered ML structure was observed near the substrate of the 18/4 sample, as illustrated in Fig. 5a. However, toward the surface, the structure became scaly and disordered, as illustrated in Fig. 5b. This transformation is attributed to the effect of increasing temperature within the film during sputter deposition and the stress induced by lattice mismatch. After annealing, the overall film structure became more uniform, as depicted in Fig. 5c. In contrast, the periodic structure of the interface became less distinct, and tiny crystal grains, ranging from several nanometers to approximately 20 nm in diameter, formed (Fig. 5d). Fig. 7 presents elemental mapping images of the samples obtained using energy-dispersive X-ray  13 spectroscopy (EDX). As illustrated in Fig. 7a, in the as-deposited state, despite the alternating deposition of Mg2Si and Sn, Mg was uniformly distributed throughout the film, whereas Si and Sn formed a distinct periodic structure. After annealing, as illustrated in Fig. 7b, Mg species Fig. 5. Transmission electron microscopy images of an Mg2Si/Sn nanocomposite thin-film sample (18/4). (a) A superlattice-like structure is observed in the region near the substrate in the as-deposited sample. (b) The superlattice interfaces are clearly visible, exhibiting a well-defined periodic structure, though the layers become curved near the surface. (c) In the annealed sample, the interfaces appear faint and show signs of disruption. (d) Nanocrystalline domains are dispersed across the entire region, with some areas exhibiting torn interfaces.  14 Fig. 7. Elemental mapping images obtained via energy-dispersive X-ray spectroscopy. (a) In the as-deposited sample, despite the alternating deposition of Mg2Si and Sn, Mg was uniformly distributed throughout the film, while Si and Sn formed a distinct periodic structure. (b) After annealing, Mg migrated toward the Sn regions, becoming more separated from the Si regions. Consequently, the periodic structure was largely preserved, although some interfaces were disrupted. Fig. 6. Electron diffraction analysis of the Mg2Si/Sn nanocomposite thin film labeled as 18/4. (a) The as-deposited multilayer film consisted of Mg9Sn5 nanocrystals embedded in an amorphous matrix. (b) After annealing, the Mg9Sn5 nanocrystals transformed into Mg2Sn nanocrystals with diameters ranging from a few nanometers to approximately 20 nm.  15 increasingly migrated toward Sn, separating from Si. Consequently, the periodic structure of the sample was largely retained, although some interfaces were disrupted. The crystal structure of the 18/4 sample, analyzed using ED, is presented in Fig. 6. In the as-deposited state, tiny Mg9Sn5 nanocrystals were embedded in the amorphous layers of the ML 18/4 sample (Fig. 6a). Upon annealing, these Mg9Sn5 nanocrystals transformed into Mg2Sn nanocrystals. Additionally, annealing led to grain growth, as evidenced by the appearance of crystal sizes ranging from a few nanometers to approximately 20 nm. The following discussion focuses on factors contributing to the increase in the zT value of the 18/4 sample. Initially, the 18/4 sample had an ML structure composed of 18-nm-thick Mg2Si layers and 4-nm-thick Sn layers. Subsequent annealing led to the formation of a nanocomposite thin film, where numerous Mg2Sn microcrystals were dispersed within an amorphous MgSiSn matrix. Fig. 8a illustrates the temperature-dependent carrier density of the 18/4 sample before and after annealing. Notably, the as-deposited sample reached its maximum carrier density of 1.8 × 1026 m−3 at 338 K. However, after annealing, the carrier density increased with temperature across the entire measurement range, rising from 0.3 × 1026 m−3 at 308 K to 0.94 × 1026 m−3 at 518 K. Despite this temperature-dependent increase, the overall carrier density in the annealed sample was lower than that in the as-deposited sample. Fig. 8b presents the temperature-dependent Hall coefficient of the 18/4 sample. The as-deposited 18/4 sample exhibited a low Hall coefficient of 4 × 10−8 m3/C, whereas the annealed sample exhibited a higher value of 2.1 × 10−7 m3/C at 308 K, which decreased with increasing temperature, reaching 6.6 m3/C at 518 K. Further, the temperature-dependent carrier mobility of the 18/4 sample is presented in Fig. 8c. For the as-deposited sample, mobility increased from 3.1 cm2/Vs at 308 K to 4.2 cm2/Vs at 368 K. However, for the annealed sample, mobility remained nearly constant at approximately 3.7  16 cm2/Vs. Finally, Fig. 8d illustrates the temperature-dependent heat capacity of the 18/4 sample, which increases linearly with temperature. Specifically, before annealing, heat capacity rose from 1.85 J/gK at 308 K to 2.00 J/gK at 368 K, whereas after annealing, it increased from 1.77 J/gK at 308 K to 2.13 J/gK at 518 K. Fig. 9 illustrates the changes in electronic TC (κel) and lattice TC (κlat) for the ML 18/4 sample and Normal (non-multilayered) sample. The results indicated that multilayering reduced κel and κlat. In the as-deposited state, the κlat values of the ML sample were notably low, measuring 0.74 W/mK at 308 K and 0.84 W/mK at 368 K. Annealing led to an increase in these κlat values; however, they remained low, measuring 1.0 W/mK at 308 K and 1.26 W/mK at 518 K. Further, the κel values of the as-deposited 18/4 sample ranged from 0.05 W/mK at 308 K to 0.08 W/mK at 368 K and further decreased after annealing, Fig. 8. Temperature dependence of the carrier properties and heat capacity of the Mg2Si/Sn nanocomposite thin-film sample 18/4: (a) carrier density, (b) Hall coefficient, (c) mobility, and (d) heat capacity.  17 reaching as low as 0.02 W/mK at 308 K and 0.07 W/mK at 518 K. In contrast, κel and κlat were higher for the Normal sample, ranging from 1.5 to 4.2 W/mK. Overall, the increase observed in κel for the annealed sample was attributed to progressive crystallization. These results demonstrated that multilayering was highly effective in suppressing TC.  Collectively, the results discussed so far indicated that the thickness of the ML film, optimization of the interfacial structure between layers through annealing, and controlled dispersion of Mg2Sn microcrystals within the amorphous matrix were key factors contributing to Fig. 9. Electronic thermal conductivity (κel) and lattice thermal conductivity (κlat) of the Mg2Si/Sn nanocomposite thin-film sample 18/4 and the non-nanostructured reference sample ("Normal"). (a) κel and κlat for the 18/4 sample. (b) κel and κlat for the reference sample. Multilayering effectively reduced both κel and κlat.  18 the improvement in zT. As illustrated in Fig. 3b, TC decreases considerably with annealing, likely owing to phonon scattering induced by the introduction of interfaces and the formation of amorphous–crystalline hybrid structures[59-69]. If the ML structure were entirely regular and ordered, phonon scattering would be limited to its narrow interfaces. However, in reality, interface scattering and the mixed amorphous‒microcrystalline state of constituent materials in the ML structure contributed to the reduction in TC.  Phonon scattering is known to be effective at the interfaces between amorphous and crystalline materials. In terms of charge carrier properties, our results reveal that the optimized ML structure of the 18/4 sample substantially improves its SC while minimizing the reduction in its EC (Fig. 3a and 3b). This enhancement is attributed to nanostructuring-induced modifications in the DOS, which improve the SC[70-75]. Additionally, the energy filtering effect may have facilitated selective transport of carriers with specific energy levels[76-104]. In summary, optimizing the thickness of the ML film, its interfacial states, and its nanocrystalline–amorphous structure enables effective tuning of both carrier and phonon scattering, ultimately leading to an improvement in zT performance. In addition to the Mg, Sn, and Si nanocomposite thin films, ML samples were also fabricated on flexible polyimide polymer substrates for potential Fig. 10. Photograph of the Mg2Si/Sn nanocomposite thin-film sample deposited on a flexible polyimide substrate for potential application in flexible thermoelectric devices. The film demonstrated strong adhesion and mechanical stability, remaining intact without peeling even when the substrate was bent.   19 applications in thin-film thermoelectric devices. As depicted in Fig. 10, the ML samples on polyimide remained intact even when the substrate was bent, demonstrating sufficient adhesion strength and film rigidity for flexible device applications. Table 1 lists the zT or power factor (PF) values reported for Mg2SixSny thermoelectric materials. The zT values of bulk Mg2Si and Mg2Sn were 0.0016 at 323 K and 0.013 near room temperature. By optimizing the Si:Sn composition ratio, the zT value of bulk Mg2Si0.4Sn0.6 was increased to 0.03 at 323 K and 0.28 at 300 K. Thermoelectric thin films, which generally exhibit lower crystallinity than bulk materials, tended to have considerably lower zT values. However, in 2019 and 2021, Safavi et al. obtained zT values of 0.1 and 0.0007 for nondoped Mg/Sn = 1.78 and Mg2Si0.35Sn0.65 thin films at 300 K through composition optimization. Additionally, Byeon et al. reported a zT of 0.0124 for an Mg1.9(Si,Sn) thin film. Notably, the abovementioned studies evaluated the SC, EC, and TC data of identical thin-film samples under consistent environmental conditions for zT determination. One of the primary reasons for the lack of reports on the zT performance of thermoelectric thin films is the difficulty in measuring TC under consistent conditions. In this study, zT and PF values of 0.021 and 7.1 × 10−5 W/mK2 at 323 K and 0.083 and 2.1 × 10−4 W/mK2 at 520 K, respectively, were achieved for an MgSiSn-based amorphous thin film containing Mg2Sn nanocrystals. These zT values are approximately 30 times higher than those of non-nanostructured Mg2Si0.35Sn0.65 thin films and approximately 10 times higher than those of thin films with the same composition as the Normal sample in this study. These results demonstrate that the controlled fabrication of nanostructures is an effective approach for enhancing zT.   20 Table 1. Comparison of zT values between Mg2SixSny materials reported in previous studies and this study. Year Compound Type zT @ 300K zT max PF (W/mK2) Author 2006 Mg2Si (Bulk) n 0.0016 (323K) 0.13  (653K)  Aizawa et al.4 2006 Mg2Sn (Bulk) p 0.013 (323K) 0.013 (323K)  Aizawa et al.4 2006 Mg2Si0.4Sn0.6 (Bulk) p 0.03           (323K) 0.13  (653K)  Aizawa et al.4 2006 Mg2Si0.4Sn0.6 (Bulk) p 0.28 1.1      (800K)  Zaitsev et al.5 2015 Mg2Si n --- --- 7 × 10−7 (323 K) 3.5 × 10−5 (723 K) Tani et al. 10 2018 Mg2Si n --- --- 7.6 × 10−6 (300 K) Yazdi et al.12 2019 Mg2Sn p --- --- 8.5 × 10−4 (519 K) Tani et al.15 2019 Mg/Sn = 1.78 p 0.1 0.26       (473 K) --- Safavi et al.14 2021 Mg2Si0.35Sn0.65 p 0.0007 0.0042   (473 K) --- Safavi et al.19 2023 Mg1.9(Si,Sn) p 0.0124 0.0143 (360K) --- Byeon et al.24 2025 a-MgSiSn /nc-Mg2Sn p 0.021 0.083     (520 K) 7.1 × 10−5 (300 K) 2.1 × 10−4 (520 K) This Study 2025 Mg2SiSn0.04 p 0.0022 0.0061 (430 K) 4.0 × 10−5 (300 K) 7.7 × 10−5 (520 K) This Study  4. Conclusions  21 This study aimed to improve the performance of thermoelectric materials in converting waste heat below 500 K into usable energy—a regime where existing commercial alternatives, such as Bi2Te3, encounter limitations owing to high cost and toxicity. To this end, the study examined Mg2Si-based materials composed of abundant, low-toxicity elements that could serve as viable alternatives. The objective was to improve zT by leveraging the low-dimensional and interfacial effects of nanocomposite thin films. The SC reached its maximum in specific multilayer configurations, attaining considerably higher values than the standard composition after annealing. EC generally decreased in ML samples but was slightly enhanced by annealing. In contrast, TC was substantially reduced through multilayering, demonstrating the effectiveness of this approach in suppressing heat flow. The enhancement in zT was primarily attributed to the formation of Mg2Sn nanocrystals within the amorphous MgSiSn matrix following annealing. TEM and EDX analyses revealed notable annealing-induced structural changes, including elemental redistribution and grain growth, which played a crucial role in improving thermoelectric properties. Additionally, flexible thermoelectric devices were successfully fabricated and tested, confirming that these materials can be incorporated into wearable electronics without performance degradation. Ultimately, this study demonstrates the feasibility of achieving near-bulk performance in thin-film MgSiSn thermoelectric materials. As such, nanostructure control can dramatically improve the zTs of thermoelectric materials with ubiquitous elemental systems, in which zT is low for practical applications. In the future, the possibility of creating nanostructures that can improve zT in bulk materials through doping and composite material processes should be investigated. This will lead to the applications of these nanostructures in wearable devices and other thermoelectric power-generation devices. Overall,  22 the present findings suggest that the proposed approach can contribute to the development of high-performance thermoelectric materials with improvements in zT.  Acknowledgements This research was supported by Japan Science and Technology Agency (JST) CREST under the projects “Exploring Innovative Materials in Unknown Search Space” (JPMJCR21O2), CREST and “Scientific Innovation for Energy Harvesting Technology” (JPMJCR16Q5). A part of this work was also supported by Grant-in-Aid for Scientific Research (C) 24K07349 and 25K08337 from the Japan Society for the Promotion of Science (JSPS).  References [1] P. Baskaran, M. Rajasekar, Recent trends and future perspectives of thermoelectric materials and their applications, Rsc Adv, 14 (2024) 21706-21744. [2] Z. Soleimani, S. Zoras, B. Ceranic, S. Shahzad, Y.L. Cui, A review on recent developments of thermoelectric materials for room-temperature applications, Sustain Energy Techn, 37 (2020). [3] R. Santos, S.A. Yamini, S.X. Dou, Recent progress in magnesium-based thermoelectric materials, Journal of Materials Chemistry A, 6 (2018) 3328-3341. [4] T. Aizawa, R. Song, A. Yamamoto, Solid state synthesis of ternary thermoelectric magnesium alloy, MgSiSn, Mater Trans, 47 (2006) 1058-1065. [5] V.K. Zaitsev, M.I. Fedorov, E.A. Gurieva, I.S. Eremin, P.P. Konstantinov, A.Y. Samunin, M.V. Vedernikov, Highly effective MgSiSn thermoelectrics, Phys Rev B, 74 (2006). [6] L. Chuang, N. Savvides, T.T. Tan, S. Li, Thermoelectric Properties of Ag-doped MgGe Thin Films Prepared by Magnetron Sputtering, J Electron Mater, 39 (2010) 1971-1974. [7] H. Le-Quoc, A. Lacoste, E.K. Hlil, A. Bè, T.T. Vinh, D. Fruchart, N. Skryabina, Thin films of thermoelectric compound MgSn deposited by co-sputtering assisted by multi-dipolar microwave plasma, J Alloy Compd, 509 (2011) 9906-9911. [8] W. Liu, X.J. Tan, K. Yin, H.J. Liu, X.F. Tang, J. Shi, Q.J. Zhang, C. Uher, Convergence of Conduction Bands as a Means of Enhancing Thermoelectric Performance of  -Type MgSiSn Solid Solutions, Physical Review Letters, 108 (2012).  23 [9] G.Y. Jiang, J. He, T.J. Zhu, C.G. Fu, X.H. Liu, L.P. Hu, X.B. Zhao, High Performance Mg2(Si,Sn) Solid Solutions: a Point Defect Chemistry Approach to Enhancing Thermoelectric Properties, Advanced Functional Materials, 24 (2014) 3776-3781. [10] J. Tani, H. Kido, Electrical properties of MgSi thin films on flexible polyimide substrates fabricated by radio-frequency magnetron sputtering, J Ceram Soc Jpn, 123 (2015) 298-301. [11] C. Prahoveanu, A. Lacoste, C. de Vaulx, K. Azzouz, M. Salaun, Y.Q. Liu, D. Tainoff, O. Bourgeois, L. Laversenne, Effect of texture on the structural and transport properties of Sb-doped MgSi thin films, J Alloy Compd, 688 (2016) 195-201. [12] M.A.P. Yazdi, N. Martin, C. Petitot, K. Neffaa, F. Palmino, F. Cherioux, A. Billard, Influence of Sputtering Parameters on Structural, Electrical and Thermoelectric Properties of Mg-Si Coatings, Coatings, 8 (2018). [13] H. Kamila, P. Sahu, A. Sankhla, M. Yasseri, H.N. Pham, T. Dasgupta, E. Mueller, J. de Boor, Analyzing transport properties of p-type MgSi-MgSn solid solutions: optimization of thermoelectric performance and insight into the electronic band structure, Journal of Materials Chemistry A, 7 (2019) 1045-1054. [14] M. Safavi, N. Martin, V. Linseis, F. Palmino, F. Cherioux, A. Billard, M.A.P. Yazdi, Thermoelectric properties improvement in MgSn thin films by structural modification, J Alloy Compd, 797 (2019) 1078-1085. [15] J. Tani, H. Ishikawa, Thermoelectric properties of MgSn thin films fabricated using radio frequency magnetron sputtering, Thin Solid Films, 692 (2019). [16] Z.C. Huang, K. Hayashi, W. Saito, Y. Miyazaki, Realizing p-type MgSn Thermoelectrics via Ga-Doping and Point Defect Engineering, Acs Appl Energ Mater, 4 (2021) 13044-13050. [17] B. Ryu, E.A. Choi, S. Park, J. Chung, J. de Boor, P. Ziolkowski, E. Müller, S. Park, Native point defects and low p-doping efficiency in Mg(Si,Sn) solid solutions: A hybrid-density functional study, J Alloy Compd, 853 (2021). [18] M. Safavi, N. Martin, E. Aubry, V. Linseis, A. Billard, M.A.P. Yazdi, Thermoelectric Performance of Ge-Doped MgSiSn Thin Films, J Mater Eng Perform, 30 (2021) 4045-4052. [19] M. Safavi, N. Martin, E. Aubry, V. Linseis, A. Billard, M.A.P. Yazdi, Impacts of Cu-Doping and Mg-Deficiency on MgSn Thin Films Thermoelectric Properties, J Electron Mater, 50 (2021) 2738-2749. [20] W. Saito, K. Hayashi, Z.C. Huang, K. Sugimoto, K. Ohoyama, N. Happo, M. Harada, K. Oikawa, Y. Inamura, K. Hayashi, T. Miyazaki, Y. Miyazaki, Chemical-Pressure-Induced Point Defects Enable Low Thermal Conductivity for MgSn and MgSi Single Crystals, Acs Appl Energ Mater, 4 (2021) 5123-5131. [21] J. Ju, K. Yin, M.F. Fang, H. Cai, H. Liu, Effect of Bi doping on the thermoelectric properties of MgSiGe4Sn compound, J Mater Res Technol, 18 (2022) 3520-3525. [22] D. Shiojiri, T. Iida, H. Kakio, M. Yamaguchi, N. Hirayama, Y. Imai, Enhancement of thermoelectric performance of MgSi via co-doping Sb and C by simultaneous tuning of electronic and thermal transport properties, J Alloy Compd, 891 (2022). [23] I. Assahsahi, B. Popescu, R. El Bouayadi, D. Zejli, M. Enculescu, A. Galatanu, Thermoelectric properties of p-type Mg2Si0.3Sn0.7 doped with silver and gallium, J Alloy Compd, 944 (2023). [24] S. Byeon, B. Wiendlocha, J. de Boor, K. Nielsch, H. Jin, Effect of Mg deficiency on the thermoelectric properties of Mg2(Si, Sn) solid solutions, J Alloy Compd, 954 (2023).  24 [25] Z.C. Huang, K. Hayashi, W. Saito, J. Pei, J.F. Li, Y. Miyazaki, Enhanced thermoelectric performance of p-type MgSn single crystals  multi-scale defect engineering, Journal of Materials Chemistry A, 11 (2023) 2652-2660. [26] B.I. Rabiu, B. Huang, W.A. Shah, X. Luo, Y. Yang, Thermoelectric performance of Mg2.2(Ge0.9Sn0.1) ternary solid solution doped with Ag, Bi, Ni and Sb, Chem Phys Lett, 823 (2023). [27] D.D. Degefa, N.B. Mereke, M.Z. Biweta, Z.A. Rabba, M.A. Mekonnen, Investigation of structural, electrical, dynamical, optical, and thermoelectric properties of Sr-doped MgSi systems using first-principles calculations, J Mater Res, 39 (2024) 2531-2541. [28] W.Y. Guo, J.H. Li, H.X. Pan, Y.Z. Deng, B. Chen, R. Jing, P.F. Chui, Improving n-type thermoelectric performance of MgSiSn compounds via high pressure and Sb-doping, J Alloy Compd, 1002 (2024). [29] P. Mangelis, A. Sousanis, G. Mesaritis, P.S. Ioannou, A.K. Soiland, Y.J. Xu, T. Kyratsi, High Thermoelectric Performance of Bi-Doped MgSiSn and MgSiSn based on Recyclable Si Kerf Derived from PV Manufacturing, Acs Appl Electron Ma, 6 (2024) 2988-2998. [30] M. Cahana, Y. Gelbstein, Mechanical and transport properties of thermoelectric Bi-doped Mg2SixGeySn1-x-y alloys, J Alloy Compd, 1021 (2025). [31] X.Y. Dong, R.Y. Zhai, B.W. Zheng, H.X. Guo, X. Chen, X.B. Liu, H.R. Sun, M.C. Guo, Y.S. Zhang, Achieving a High in n-Type Sb-Doped MgSiSn via High-Pressure-Modulated Microstructures, Acs Appl Mater Inter, 17 (2025) 21431-21439. [32] S. Karunakaran, V. Vijay, S. Harish, M. Navaneethan, J. Archana, Synergistic effect of mass and strain field phonon scattering in Bi and Sb co-doped MgSi for thermoelectric applications, Mat Sci Semicon Proc, 192 (2025). [33] P. Mangelis, P.S. Ioannou, A.K. Soiland, T. Kyratsi, Mechanical Alloying: An Advantageous Method for the Development of MgSiSn and MgSi Thermoelectrics Using Commercial and Recyclable Silicon, Acs Appl Energ Mater, 8 (2025) 1783-1795. [34] P.K. Sharma, C. Kachhara, N. Laihnuna, S. Kedia, Elastic mechanical thermodynamic and thermoelectric properties of pristine and titanium doped MgSi: a density functional theory study, J Phys-Condens Mat, 37 (2025). [35] L.D. Hicks, M.S. Dresselhaus, Effect of Quantum-Well Structures on the Thermoelectric Figure of Merit, Phys Rev B, 47 (1993) 12727-12731. [36] L.D. Hicks, M.S. Dresselhaus, Thermoelectric Figure of Merit of a One-Dimensional Conductor, Phys Rev B, 47 (1993) 16631-16634. [37] L.D. Hicks, T.C. Harman, X. Sun, M.S. Dresselhaus, Experimental study of the effect of quantum-well structures on the thermoelectric figure of merit, Phys Rev B, 53 (1996) 10493-10496. [38] M. Goto, M. Sasaki, Y.B. Xu, T.Z. Zhan, Y. Isoda, Y. Shinohara, Control of p-type and n-type thermoelectric properties of bismuth telluride thin films by combinatorial sputter coating technology, Appl Surf Sci, 407 (2017) 405-411. [39] M. Sasaki, S.H. Ju, Y.B. Xu, J. Shiomi, M. Goto, Identifying Optimal Strain in Bismuth Telluride Thermoelectric Film by Combinatorial Gradient Thermal Annealing and Machine Learning, Acs Comb Sci, 22 (2020) 782-790. [40] Y.B. Xu, R. Kato, M. Goto, Effect of microstructure on Au/sapphire interfacial thermal resistance, J Appl Phys, 108 (2010). [41] Y.B. Xu, M. Goto, R. Kato, Y. Tanaka, Y. Kagawa, Thermal conductivity of ZnO thin film produced by reactive sputtering, J Appl Phys, 111 (2012).  25 [42] T.Z. Zhan, Y.B. Xu, M. Goto, Y. Tanaka, R. Kato, M. Sasaki, Y. Kagawa, Thermal conductivity of sputtered amorphous Ge films, Aip Adv, 4 (2014). [43] T.Z. Zhan, Y.B. Xu, M. Goto, Y. Tanaka, R. Kato, M. Sasaki, Y. Kagawa, Phonons with long mean free paths in a-Si and a-Ge, Appl Phys Lett, 104 (2014). [44] T. Zhan, Y. Xu, M. Goto, Y. Tanaka, R. Kato, M. Sasaki, Thermal boundary resistance at Au/Ge/Ge and Au/Si/Ge interfaces, Rsc Adv, 5 (2015) 49703-49707. [45] T.Z. Zhan, M. Goto, Y.B. Xu, Y. Kinoshita, M. Ishikiriyama, C. Nishimura, Modification of thermal conductivity and thermal boundary resistance of amorphous Si thin films by Al doping, Rsc Adv, 7 (2017) 7901-7905. [46] M. Goto, Y.B. Xu, T.Z. Zhan, M. Sasaki, C. Nishimura, Y. Kinoshita, M. Ishikiriyama, Ultra-low thermal conductivity of high-interface density Si/Ge amorphous multilayers, Applied Physics Express, 11 (2018). [47] K. Uchida, M. Sasaki, Y. Sakuraba, R. Iguchi, S. Daimon, E. Saitoh, M. Goto, Combinatorial investigation of spin-orbit materials using spin Peltier effect, Scientific Reports, 8 (2018). [48] Y.J. Wu, M. Sasaki, M. Goto, L. Fang, Y.B. Xu, Electrically Conductive Thermally Insulating Bi-Si Nanocomposites by Interface Design for Thermal Management, Acs Appl Nano Mater, 1 (2018) 3355-3363. [49] Y.X. Liao, S. Iwamoto, M. Sasaki, M. Goto, J. Shiomi, Heat conduction below diffusive limit in amorphous superlattice structures, Nano Energy, 84 (2021). [50] Y.J. Wu, K. Akagi, M. Goto, Y.B. Xu, Topological data analysis of TEM-based structural features affecting the thermal conductivity of amorphous Ge, Int J Heat Mass Tran, 221 (2024). [51] M. Goto, A. Kasahara, M. Tosa, Frictional property with preferred crystal orientation of platinum oxide and palladium oxide coatings synthesized by combinatorial sputter coating system, Vacuum, 80 (2006) 740-743. [52] M. Goto, A. Kasahara, M. Tosa, Low frictional property of copper oxide thin films optimised using a combinatorial sputter coating system, Appl Surf Sci, 252 (2006) 2482-2487. [53] M. Goto, A. Kasahara, M. Tosa, Reduction in Frictional Force of ZnO Coatings in a Vacuum, Jpn J Appl Phys, 47 (2008) 8914-8916. [54] M. Goto, A. Kasahara, M. Tosa, Low-Friction Coatings of Zinc Oxide Synthesized by Optimization of Crystal Preferred Orientation, Tribol Lett, 43 (2011) 155-162. [55] M. Goto, M. Sasaki, A. Kasahara, M. Tosa, Frictional Property Depended on Crystal Preferred Orientation Analyzed by a Combinatorial Technique, Tribol Lett, 55 (2014) 289-293. [56] M. Sasaki, M. Goto, Development of ZnO-coated bearings with the preferred crystal orientation for micro gas turbines, Thin Solid Films, 761 (2022). [57] M. Sasaki, M. Goto, Piezoelectric effect of crystal nanodomains on the friction force, J Vac Sci Technol B, 40 (2022). [58] V. Linseis, F. Völklein, H. Reith, P. Woias, K. Nielsch, Platform for in-plane measurement and Hall coefficient determination of thin films in a temperature range from 120 K up to 450 K, J Mater Res, 31 (2016) 3196-3204. [59] S. Heinz, E.C. Angel, M. Trapp, H.J. Kleebe, G. Jakob, Phonon Bridge Effect in Superlattices of Thermoelectric TiNiSn/HfNiSn With Controlled Interface Intermixing, Nanomaterials-Basel, 10 (2020). [60] B.H. Liu, J. Zhou, X.F. Xu, B.W. Li, Thermal conductivity of one-dimensional organic nanowires: effect of mass difference phonon scattering, Nanotechnology, 31 (2020).  26 [61] Y. Zhao, Y. Li, J.X. Qiao, S. Jiang, P.Y. Mao, J.H. Qiu, S.Q. Kang, J. Tan, K.P. Tai, C. Liu, Decoupling phonon and carrier scattering at carbon nanotube/BiTe interfaces for improved thermoelectric performance, Carbon, 170 (2020) 191-198. [62] Y.C. Zhao, Z.J. Li, Y.Q. Su, C.Z. Wu, Y. Xie, Ultralow In-Plane Thermal Conductivity in 2D Magnetic Mosaic Superlattices for Enhanced Thermoelectric Performance, Acs Nano, (2022). [63] Y.N. Bai, X. Wang, X.D. Jiang, T.Y. Ouyang, W.Y. Wang, X.R. Li, Y.W. Yan, W. Gao, J.M. Cai, X.M. Cai, H.L. Tan, Compositing effects for high thermoelectric properties of n-type Bi2S3 via doping C60 nanoparticles, Mater Today Chem, 42 (2024). [64] H.W. Hu, Y.Y. Liao, S.S. Tan, C. Li, J. Tang, K. Zheng, L. Yang, Decoupled electron-phonon transport in AgSe thermoelectric materials through constructing TiO/MoS co-decorated cell-membrane-mimic grain boundaries, Nanoscale, 16 (2024) 21031-21038. [65] K.Y. Luo, H.W. Chen, W.Y. Hu, P.P. Qian, J.B. Guo, Y.X. Deng, L. Yang, Q. Sun, L. Liu, L. Cao, W.B. Qiu, J. Tang, Tailoring interfacial states for improved n-type bismuth telluride thermoelectrics, Nano Energy, 128 (2024). [66] D.Y. Wang, J.M. Ding, Y.Q. Mal, C.L. Xu, Z.Y. Li, X. Zhang, Y. Zhao, Y. Zhao, Y.Q. Di, L.Y. Liu, X.J. Dai, Y. Zou, B. Kim, F.J. Zhang, Z.T. Liu, I. McCulloch, M. Lee, C. Chang, X. Yang, D. Wang, D.Q. Zhang, L.D. Zhao, C.A. Di, D.B. Zhu, Multi-heterojunctioned plastics with high thermoelectric figure of merit, Nature, 632 (2024) 528-+. [67] Y.E. Luo, J.L. Zhu, X.R. Rao, Y. Xie, W.X. Ou, R.H. Li, R. Ang, Optimized Interface Engineering Enhances Carrier and Phonon Scattering for Superior Thermoelectric Performance in Yb-Filled Skutterudites, Acs Appl Mater Inter, 17 (2025) 8047-8054. [68] S. Radha, J. Mani, A.B.S.S. Andrew, R. Rajkumar, M. Arivanandhan, G. Anbalagan, Inclusion of 2D nanosheets on ZnSb matrix as a unique approach to improve its thermoelectric performance, Mat Sci Semicon Proc, 186 (2025). [69] Y. Yao, H. Chen, Z.K. Ding, W.H. Xiao, N.N. Luo, J. Zeng, L.M. Tang, K.Q. Chen, Interface phonon transport in nanomaterials: numerical methods and modulation strategies, J Phys-Condens Mat, 37 (2025). [70] W.Y. Zhao, Z.Y. Liu, Z.G. Sun, Q.J. Zhang, P. Wei, X. Mu, H.Y. Zhou, C.C. Li, S.F. Ma, D.Q. He, P.X. Ji, W.T. Zhu, X.L. Nie, X.L. Su, X.F. Tang, B.G. Shen, X.L. Dong, J.H. Yang, Y. Liu, J. Shi, Superparamagnetic enhancement of thermoelectric performance, Nature, 549 (2017) 247-+. [71] J.U. Rahman, N.V. Du, W.H. Nam, W.H. Shin, K.H. Lee, W.S. Seo, M.H. Kim, S. Lee, Grain Boundary Interfaces Controlled by Reduced Graphene Oxide in Nonstoichiometric SrTiO Thermoelectrics, Scientific Reports, 9 (2019). [72] Y.Y. Li, M.N. Ren, Z.S. Sun, Z. Yao, Nanoarchitectonics of p-type BiSbTe with improved figure of merit introducing PbTe nanoparticles, Rsc Adv, 11 (2021) 36636-36643. [73] M. Choi, J.Y. An, H.Y.J. Lee, H. Jang, J.H. Park, D.H. Cho, J.Y. Song, S.M. Kim, M.W. Oh, H. Shin, S. Jeon, High figure-of-merit for ZnO nanostructures by interfacing lowly-oxidized graphene quantum dots, Nature Communications, 15 (2024). [74] J.J. Kang, Q. Ma, Y. Li, S. Fu, X.Y. Yi, J.X. Wang, J.M. Li, M. Liang, L. Wang, Z.Q. Liu, Thermoelectric properties of InGaN/GaN superlattices structure with high indium composition quantum dots, Appl Phys Lett, 125 (2024). [75] M. Liu, W.D. Ma, Enhanced Thermoelectric Performance of PbTe Nanocomposites with Ag Nanoinclusions, J Comput Theor Trans, 53 (2024) 451-462. [76] T.H. Zou, X.Y. Qin, Y.S. Zhang, X.G. Li, Z. Zeng, D. Li, J. Zhang, H.X. Xin, W.J. Xie, A. Weidenkaff, Enhanced thermoelectric performance of β-ZnSb based nanocomposites through  27 combined effects of density of states resonance and carrier energy filtering, Scientific Reports, 5 (2015). [77] M. Thesberg, H. Kosina, N. Neophytou, On the effectiveness of the thermoelectric energy filtering mechanism in low-dimensional superlattices and nano-composites, J Appl Phys, 120 (2016). [78] M. Sabarinathan, M. Omprakash, S. Harish, M. Navaneethan, J. Archana, S. Ponnusamy, H. Ikeda, T. Takeuchi, C. Muthamizhchelvan, Y. Hayakawa, Enhancement of power factor by energy filtering effect in hierarchical BiSbTe nanostructures for thermoelectric applications, Appl Surf Sci, 418 (2017) 246-251. [79] C. Gayner, Y. Amouyal, Energy Filtering of Charge Carriers: Current Trends, Challenges, and Prospects for Thermoelectric Materials, Advanced Functional Materials, 30 (2020). [80] S. Ghosh, G. Shankar, A. Karati, G. Rogl, P. Rogl, E. Bauer, B.S. Murty, S. Suwas, R.C. Mallik, Preferential phonon scattering and low energy carrier filtering by interfaces of formed InSb nanoprecipitates and GaSb nanoinclusions for enhanced thermoelectric performance of InCoSb, Dalton T, 49 (2020) 15883-15894. [81] Z. Ma, C. Wang, J.D. Lei, D. Zhang, Y.Q. Chen, Y.X. Wang, J.L. Wang, Z.X. Cheng, Core-shell nanostructures introduce multiple potential barriers to enhance energy filtering for the improvement of the thermoelectric properties of SnTe, Nanoscale, 12 (2020) 1904-1911. [82] A.T.T. Pham, P.T.N. Vo, H.K.T. Ta, H.T. Lai, V.C. Tran, T.L.H. Doan, A.T. Duong, C.T. Lee, P.K. Nair, Y.A. Zulueta, T.B. Phan, S.D.N. Luu, Improved thermoelectric power factor achieved by energy filtering in ZnO: Mg/ZnO hetero-structures, Thin Solid Films, 721 (2021). [83] C. Archana, S. Harish, R. Abinaya, J. Archana, M. Navaneethan, Interface modified MoS2/CNT with enhanced power factor via energy filtering effect for flexible thermoelectric applications, Sensor Actuat a-Phys, 348 (2022). [84] T. Hong, C.R. Guo, D.Y. Wang, B.C. Qin, C. Chang, X. Gao, L.D. Zhao, Enhanced thermoelectric performance in SnTe due to the energy filtering effect introduced by BiO, Mater Today Energy, 25 (2022). [85] C. Kim, D.H. Lopez, Energy filtering and phonon scattering effects in BiTe-PEDOT:PSS composite resulting in enhanced n-type thermoelectric performance, Appl Phys Lett, 120 (2022). [86] H.T. Liu, Q. Sun, Y. Zhong, Q. Deng, L. Gan, F.L. Lv, X.L. Shi, Z.G. Chen, R. Ang, High-performance in n-type PbTe-based thermoelectric materials achieved by synergistically dynamic doping and energy filtering, Nano Energy, 91 (2022). [87] S.T. Wei, B.Y. Wang, Z.P. Zhang, W.H. Li, L. Yu, S.K. Wei, Z. Ji, W.Y. Song, S.Q. Zheng, Achieving high thermoelectric performance through carrier concentration optimization and energy filtering in CuSbSe-based materials, J Materiomics, 8 (2022) 929-936. [88] R.S. Almufarij, W. Raza, A. Ashfaq, E.A. Shokralla, H.A. Alsalmah, U.U. Rehman, A. Ali, R.J.r. Macadangdang, R.Y. Capangpangan, A.C. Alguno, S. Akhtar, Enhanced the thermoelectric power factor of n-type Bi2Te3 thin film via energy filtering effect, Inorg Chem Commun, 157 (2023). [89] A. Ashfaq, R.S. Almufarij, M.Y. Ali, A. Ali, S. Tahir, M.M. Sabugaa, M.A. Fahmy, E.A. Shokralla, A.H. Ragab, D.E. El-Refaey, K. Mehmood, High thermoelectric power factor of n-type Bi2(Se,S)3 via synergetic influence on the charge carrier concentration and energy filtering effect, Int Commun Heat Mass, 146 (2023). [90] A. Ashfaq, M.M. Sabugaa, M. Ben Moussa, N. Almousa, E.A. Shokralla, R.Y. Capangpangan, A.C. Alguno, M.A. Hossain, A.M. Alanazi, M. Abboud, High thermoelectric  28 power factor of Sr doped BiTe thin film through energy filtering effect, Int Commun Heat Mass, 143 (2023). [91] R.C. Chen, Y.X. Wang, L.F. Jiang, R.A. Min, H.J. Kang, Z.N. Chen, E.Y. Guo, X. Yang, X. Jiang, T.M. Wang, Enhancing thermoelectric properties of MCoSb-based alloys by entropy-driven energy-filtering effects and band engineering, Mater Today Phys, 30 (2023). [92] T. Manimozhi, S. Kavirajan, M. Navaneethan, Synergistic effect of energy filtering, modulation doping and boundary scattering of multiphase Cu-Sb-Bi-S system for enhanced thermoelectric performance, Surf Interfaces, 41 (2023). [93] I. Vareli, A. Gkaravela, S. Polyviou, N.M. Barkoula, A.S. Paipetis, Structural Carbon-Enhanced Cementitious Thermoelectric Generators (TEGs): Optimal Energy Filtering and TEG Design for Outstanding Energy Harvesting, Acs Appl Electron Ma, 6 (2023) 2851-2861. [94] S.A. Yamini, R. Santos, R. Fortulan, A.A. Gazder, A. Malhotra, D. Vashaee, I. Serhiienko, T. Mori, Room-Temperature Thermoelectric Performance of n-Type Multiphase Pseudobinary Bi2Te3-Bi2S3 Compounds: Synergic Effects of Phonon Scattering and Energy Filtering, Acs Appl Mater Inter, (2023). [95] D. Kim, J. Kim, S. Chung, K. Cho, Quantum-Dot-Induced Energy Filtering Effect in Organic Thermoelectric Nanocomposites, Adv Electron Mater, 10 (2024). [96] J. Mani, S. Radha, T.R.S. Devi, R. Rajkumar, M. Arivanandhan, G. Anbalagan, Effect of energy filtering on CuNiSnS/CuO composites for thermoelectric applications, J Mater Sci, 59 (2024) 8911-8929. [97] J. Mani, S. Radha, F.J. Prita, R. Rajkumar, M. Arivanandhan, G. Anbalagan, Enhancing the Thermoelectric Performance of CuS/CuO Nanocomposites Through Energy-Filtering effect and Phonon Scattering, J Inorg Organomet P, 34 (2024) 1548-1563. [98] T. Meng, X.W. Zhang, J.S. Yao, W.W. Zhang, H.M. Zhong, H.D. Zhu, Y.Y. Zhang, H. Zhang, P. Zhang, H. Lu, Y. Zhao, Quantum confinement and energy filtering effect enhancing the thermoelectric power factor of InGaAs with buried ErAs nanoparticles, Appl Phys Lett, 125 (2024). [99] C.S. Prasanna, S. Harish, S.K. Eswaran, H. Ikeda, M. Navaneethan, Tuning the thermoelectric properties of ZnO/MoS/carbon fabric via interface-induced energy filtering effect for wearable thermoelectric application, J Mater Sci-Mater El, 35 (2024). [100] M.M. Timm, H. Bouteiller, B. Konrad, E. Oliviero, J.F. Barbot, D. Troadec, P.F.P. Fichtner, N. Fréty, Enhancing Thermoelectric Efficiency in CrSi Films through Al Ion Implantation-Induced Energy Filtering, Acs Appl Electron Ma, 7 (2024) 246-252. [101] V. Vijay, S. Ponnusamy, M. Navaneethan, Synergistic effect of energy filtering effect and secondary phase formation in Cu substituted SnS for enhanced thermoelectric applications, J Mater Sci-Mater El, 35 (2024). [102] J. Vinodhini, S. Harish, H. Ikeda, M. Navaneethan, Flexible AgSe/AgS nanocomposite on carbon fabric optimized via interfaced engineered energy filtering effect for a textile based wearable thermoelectric generator, Surf Interfaces, 54 (2024). [103] L.X. Xu, Q.J. Zhang, L.D. Zhao, H.L. Zhang, Z. Su, Q. Wang, J.L. Wang, Q. Cao, Z.H. Ding, S.F. Wang, Z.L. Li, Exploiting synergies for high thermoelectric performance in higher manganese silicide-based semiconductors through element Co-doping, energy filtering, and phonon scattering, Ceram Int, 50 (2024) 17604-17612. [104] M.Z. Du, Y. Wen, Z.J. Chen, Y.C. Xu, J. Qin, H.L. Cheng, Y. Du, K. Zhang, S. Shin, J.Y. Ouyang, A Polymer Film with Very High Seebeck Coefficient and Overall Thermoelectric  29 Properties by Secondary Doping, Dedoping Engineering and Ionic Energy Filtering, Advanced Functional Materials, 35 (2025).