Advances in Atomic Layer Deposition (ALD) Nanolaminate Synthesis of Thermoelectric Films in Porous Templates for Improved Seebeck Coefficient

Abstract

Thermoelectrics is a green renewable energy technology which can significantly contribute to power generation due to its potential in generating electricity out of waste heat. The main challenge for the development of thermoelectrics is its low conversion efficiency. One key strategy to improve conversion efficiency is reducing the thermal conductivity of thermoelectric materials. In this paper, the state-of-the-art progresses made in improving thermoelectric materials are reviewed and discussed, focusing on phononic engineering via applying porous templates and ALD deposited nanolaminates structure. The effect of nanolaminates structure and porous templates on Seebeck coefficient, electrical conductivity and thermal conductivity, and hence in figure of merit zT of different types of materials system, including PnCs, lead chalcogenide-based nanostructured films on planar and porous templates, ZnO-based superlattice, and hybrid organic-inorganic superlattices, will be reviewed and discussed.

Highly Thermoelectric ZnO@MXene (Ti3C2Tx) Composite Films Grown by Atomic Layer Deposition

“…This makes atomic layer deposition (ALD) an attractive low-temperature deposition method for growing MXene-based films. − As a vacuum deposition technique, gaseous precursors are introduced into a vacuum chamber throughout each cycle in order to produce a monolayer via surface saturation chemical reactions . Due to the ALD’s saturation growth characteristics and self-limitation reaction, uniform thin films can be produced on any complex three-dimensional structure precisely with both the thickness and composition for meeting the demand of thermoelectric materials . The ALD can accurately control the number of single atomic layers to achieve the desired structural composition, providing a general strategy for increasing the performance of composite thermoelectric materials. , …”

“…39 Due to the ALD's saturation growth characteristics and self-limitation reaction, uniform thin films can be produced on any complex threedimensional structure precisely with both the thickness and composition for meeting the demand of thermoelectric materials. 40 The ALD can accurately control the number of single atomic layers to achieve the desired structural composition, providing a general strategy for increasing the performance of composite thermoelectric materials. 41,42 In our work, we have grown ZnO layers with various cycles on the MXene films by ALD.…”

Synthesis and Properties of Bismuth Selenide Based Nanolaminates for Application in Thermoelectrics

“…[10][11][12] Regarding reduction of thermal conductivity of TE materials, it was predicted theoretically that a significant decrease of the thermal conductivity due to the phonon scattering at the boundaries/interfaces is expected when the thickness of the material is reduced down to few tens of nm, as well as when the material consists of periodic thin-film structures with in the direction parallel to the film plane. [13][14][15] Recently, it also has been shown on an example of Bi 2 Se 3 nanowires that downsizing of the Bi 2 Se 3 below 20 nm results in significant suppression of the bulk conductance of this material, [16] while further downsizing of the TE materials-TI below 10 nm was proposed to result in enhancement of ZT of TE materials due to the opening of hybridization gap between the surface states. [17][18][19] However, the experimental investigation of properties of ultrathin films of bismuth chalcogenide family did not show any significant improvement from the bulk values of ZT, but at the same time identified significant sensitivity of Seebeck coefficient and electrical conductivity of these thin films to thickness reduction and position of Fermi level.…”

“…[7,[20][21][22] Also, it has been shown recently on an example of PbX (X = Se, Te) nanolaminates deposited by atomic layer deposition method, such structures showed significant enhancement of ZT in comparison with the single films due to the enhancement of the Seebeck coefficient and reduction of thermal conductivity owing to the processes occurring at the interfaces between the nanolaminate layers. [15] To the best of our knowledge, the TE properties of multi-layered periodic structures fabricated by PVD and composed of ultrathin (≈10-12 nm) layers of TE materials (nanolaminates) have not been yet studied. Development of simple and economically affordable technique as PVD for fabrication of high-quality ultrathin films based nanolaminates would significantly contribute of the application of such structures at industrial scale.…”

Formation Mechanism and Bandgap Reduction of GaN–ZnO Solid‐Solution Thin Films Fabricated by Nanolamination of Atomic Layer Deposition

“…[27][28][29] Nanolaminates manufactured by ALD possess several advantages including excellent film conformity, stoichiometry flexibility, and thickness controllability. [30] Accordingly, in the present study, ALD nanolamination was employed to fabricate the GaN-ZnO solid-solution films by varying the cycle ratio of Ga and Zn precursors. For the growth of GaN, the ALD window of trimethyl gallium (TMG) is typically at above 450 °C, but it has been proven to be self-limiting at 185-385 °C using NH 3 plasma with a saturation time of 90 s. [31] The self-limiting growth of ZnO has been reported to occur at 200-260 °C using diethyl zinc (DEZ) and H 2 O as the precursors.…”