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The carrier concentration in Bi2Te3-based alloys is a decisive factor in determining their thermoelectric performance. Herein, we propose a novel approach to modulate the carrier concentration via the encapsulation of the alloy precursor powders. Atomic layer deposition (ALD) of ZnO and SnO2 was performed over the Bi2Te2.7Se0.3 powders. After spark plasma sintering at 500 °C for 20 min, the carrier concentration in the ZnO-coated samples decreased, while the carrier concentration in the SnO2-coated samples increased. This trend was more pronounced as the number of ALD cycles increased. This was attributed to the intermixing of the metal ions at the interface. Zn2+ substituted for Bi3+ at the interface acted as an acceptor, while Sn4+ substituted for Bi3+ acted as a donor. This indicates that the carrier concentration can be adjusted depending on the materials deposited with ALD. The use of fine powders changes the carrier concentration more strongly, because the quantity of material deposited increases with the effective surface area. Therefore, the proposed approach would provide opportunities to precisely optimize the carrier concentration for high thermoelectric performance. [ABSTRACT FROM AUTHOR]

This study demonstrates atomic layer deposition (ALD) of an extremely thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 to alleviate the adverse effects of multiple boundaries on their thermoelectric performance. Multiple boundaries reduce thermal conductivity (κ), but generate electrons, deviating from the optimum carrier concentration. Only one Al 2 O 3 ALD cycle effectively suppresses Te volatilization at the grain boundaries, resulting in a decrease from 5.8 × 1019/cm3 to 3.6 × 1019/cm3 in the electron concentration. Concurrently, the one-cycle-Al 2 O 3 coating produces fine grains, thus inducing numerous boundaries, ultimately suppressing the lattice κ from 0.64 to 0.33 W/m·K. A further increase in the number of Al 2 O 3 cycles leads in a significant rise in the resistance, resulting in degradation of thermoelectric performance. Consequently, the ZT value is increased by 51 % as a result of Al 2 O 3 coating with a single ALD cycle. Our approach offers new insights into the simultaneous reduction of the κ and electron concentration in n-type Bi 2 Te 3 -based materials. • Boundary engineering strategy for thermoelectric materials. • Conformal and thin Al 2 O 3 layer over n-type Bi 2 Te 2.7 Se 0.3 thermoelectric materials. • Facile atomic layer deposition-based approach. • Suppression of Te volatilization at the grain boundaries. • Simultaneous reduction of lattice thermal conductivity and electron concentration. [ABSTRACT FROM AUTHOR]

The ease of Te sublimation from Bi 2 Te 3 -based alloys significantly deteriorates thermoelectric and mechanical properties via the formation of voids. We propose a novel strategy based on atomic layer deposition (ALD) to improve the thermal stability of Bi 2 Te 3 -based alloys via the encapsulation of grains with a ZnO layer. Only a few cycles of ZnO ALD over the Bi 2 Te 2.7 Se 0.3 powders resulted in significant suppression of the generation of pores in Bi 2 Te 2.7 Se 0.3 extrudates and increased the density even after post-annealing at 500 °C. This is attributed to the suppression of Te sublimation from the extrudates. The ALD coating also enhanced grain refinement in Bi 2 Te 2.7 Se 0.3 extrudates. Consequently, their mechanical properties were significantly improved by the encapsulation approach. Furthermore, the ALD approach yields a substantial improvement in the figure-of-merit after the post-annealing. Therefore, we believe the proposed approach using ALD will be useful for enhancing the mechanical properties of Bi 2 Te 3 -based alloys without sacrificing thermoelectric performance. [ABSTRACT FROM AUTHOR]

The atomic layer deposition (ALD) of SnO 2 films has drawn interest from many researchers as a way to enhance the performance of functional materials for emerging applications such as transistors, sensors, and transparent electrodes. Among the critical issues in the exploitation of SnO 2 ALD in industrial applications is the lack of commercially available Sn precursors. Here, we demonstrate an ALD process for SnO 2 films using commercially available tetraethyltin (TET) as a precursor. H 2 O 2 is used as the oxygen source to overcome the lack of reactivity between TET and H 2 O, consequently the reaction of TET and H 2 O 2 results in the growth of SnO 2 films. The ALD process has a wide ALD window of 250–400 °C. In the range of the growth temperature, the grown films show a high density of ~6.2 g/cm3 and an optical band gap of 3.7–3.9 eV, which is comparable to that of bulk SnO 2. Negligible impurities remained in the films grown over the entire temperature range. The crystallization behavior and electrical properties of the SnO 2 films were examined as well. The ability of this ALD process to produce high-quality SnO 2 films with a commercially available tin precursor will allow it to be exploited in various applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • Inclusion of Ru in Bi 2 Te 3 -based alloys was achieved by atomic layer deposition. • Oxidation of Bi 0.4 Sb 1.6 Te 3 powders occurred during the atomic layer deposition. • Ru atomic layer deposition rather increased the resistivity due to oxidation. Despite the success of heterogeneous coatings of thermoelectric materials by atomic layer deposition (ALD), ALD-grown materials have been limited to oxides with high resistance. In this study, we attempted the nanoinclusion of metals in thermoelectric materials by the deposition of Ru metal on Bi 0.4 Sb 1.6 Te 3 powders using an ALD with a Ru precursor and O 2. As the number of Ru ALD cycles increased, the quantity of deposited Ru increased, and the grain size of Bi 0.4 Sb 1.6 Te 3 in the sintered Bi 0.4 Sb 1.6 Te 3 decreased. However, ALD resulted in the oxidation of the Bi 0.4 Sb 1.6 Te 3 powders because of the high-temperature growth at 300 °C with O 2 injection. The thermoelectric properties of the Ru-coated Bi 0.4 Sb 1.6 Te 3 pellets were governed by oxidation rather than Ru inclusion. This study demonstrates that an oxidation-free ALD process is necessary for the nanoinclusion of Ru in Bi 2 Te 3 -based alloys using ALD. [ABSTRACT FROM AUTHOR]

SnO 2 thin films were grown by atomic layer deposition (ALD) with dimethylamino-2-methyl-2-propoxy-tin(II) (Sn(dmamp) 2 ) and O 3 in a temperature range of 100–230 °C. The ALD window was found to be in the range of 100–200 °C. The growth per cycle of the films in the ALD window increased with temperature in the range from 0.018 to 0.042 nm/cycle. Above 230 °C, the self-limiting behavior which is a unique characteristic of ALD, was not observed in the growth because of the thermal decomposition of the Sn(dmamp) 2 precursor. The SnO 2 films were amorphous in the ALD window and exhibited quite a smooth surface. Sn ions in all films had a single binding state corresponding to Sn 4+ in SnO 2 . The concentration of carbon and nitrogen in the all SnO 2 films was below the detection limit of the auger electron spectroscopy technique and a very small amount of carbon, nitrogen, and hydrogen was detected by secondary ions mass spectroscopy only. The impurity contents decreased with increasing the growth temperature. This is consistent with the increase in the density of the SnO 2 films with respect to the growth temperature. The ALD process with Sn(dmamp) 2 and O 3 shows excellent conformality on a hole structure with an aspect ratio of ∼9. This demonstrates that the ALD process with Sn(dmamp) 2 and O 3 is promising for growth of robust and highly pure SnO 2 films. [ABSTRACT FROM AUTHOR]

The initial growth behavior of ZnOfilms by atomic layer deposition(ALD) on layer-structured Bi2Te3was investigated.Despite the lack of adsorption sites on the basal plane of Bi2Te3, negligible incubation in the ALD of ZnO onBi2Te3was found in the temperature range from100 to 160 °C, and even the enhancement of the initial growthwas observed at 200 °C. We demonstrate that a ZnTe interfaciallayer was formed in the early growth stage by the interaction betweendiethylzinc and Bi2Te3, which improved the nucleationof ZnO on the basal plane of Bi2Te3. These resultsindicate that surface modification via the interaction between a precursorand layer-structured materials is an efficient way to achieve fluentand uniform nucleation on layer-structured materials such as Bi2Te3. [ABSTRACT FROM AUTHOR]

Highlights: [•] We developed a new ALD process for HfO2 films using H2O2 as an oxygen source. [•] The ALD process using H2O2 effectively reduces oxygen vacancies in HfO2 films. [•] The robust HfO2 films grown with H2O2 show excellent electrical properties. [•] The use of the ALD process with H2O2 also revealed the conformal growth of HfO2 films. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ALD process of TiO 2 films from (CpMe 5)Ti(OMe) 3 and O 3 is examined. • The high thermal stability of (CpMe 5)Ti(OMe) 3 enables the ALD window up to a high temperature of 345 °C. • Dense and high-purity TiO 2 films were grown at higher temperatures of >300 °C. • The morphology with patterns spreading radially from multiple points eventually disappears at high temperatures of >300 °C. Atomic layer deposition (ALD) of TiO 2 films from (CpMe 5)Ti(OMe) 3 as precursor and O 3 as co-reactant was examined. The high thermal stability of (CpMe 5)Ti(OMe) 3 enabled ALD reaction up to a high temperature of 345 °C. A wide temperature window from 182 to 345 °C was achieved in the ALD process, and the growth per cycle increased with increasing the temperature from 0.025 to 0.06 nm/cycle in the ALD window. The impurity content of the films decreased with increasing growth temperature. Above 291 °C, the carbon content in the films decreased to the level in a single crystalline Si substrate. The morphology with patterns spreading radially from the multiple points developed above 236 °C, and the size of the grains decreased as the growth temperature increased. Eventually, a uniform morphology with fine grains was obtained at temperatures > 300 °C. The films grown at the high temperatures exhibited superior dielectric properties. Other common metalorganic precursors of Ti usually restrict the use of high-temperature ALD because they are thermally unstable and decompose below 300 °C. Therefore, (CpMe 5)Ti(OMe) 3 is favorable for forming dense and high-purity TiO 2 films by ALD. [ABSTRACT FROM AUTHOR]

Atomic layer deposition (ALD) on Ta-doped SnO 2 thin films is proposed as a methodology for the fabrication of capacitor electrodes, for application in dynamic random-access memories (DRAMs). In ALD of doped materials, dopant concentration gradients inevitably occur due to the cyclic process-based characteristics of ALD. In this study, the dopant distribution improves drastically by the decrease in the growth per cycle of TaO x ALD. The modified ALD recipe exploits the low reactivity between Ta and Sn precursors to facilitate a reduction in the growth per cycle. The Ta-doped SnO 2 films grown based on this modified ALD recipe exhibit improved crystallinity and conductivity. The ALD process yields excellent conformality of the Ta-doped SnO 2 film over a hole structure with a high aspect ratio of ~10, both in terms of physical thickness and composition. Additionally, the Ta-doped SnO 2 films serve as a template for the overgrowing dielectric TiO 2 film, which induces the formation of a high-temperature phase with a high dielectric constant, rutile TiO 2 , and exhibit excellent thermal stability even after annealing at 400 °C in forming gas atmosphere. These findings demonstrate that the proposed methodology for the growth of Ta-doped SnO 2 can facilitate the fabrication of capacitor electrodes for application in DRAMs. Unlabelled Image • A new ALD process of Ta-doped SnO 2 films is demonstrated. • Potential applications include use as reduction-resistant capacitor electrode. • Dopant distribution improves by decrease in the growth per cycle of TaO x ALD. • Films reveal ease of formation of high-k rutile TiO 2 and excellent thermal stability. [ABSTRACT FROM AUTHOR]