(Bi 2 Te 3 ) x (Sb 2 Te 3 ) 1- x thin films were synthesized using the pressure-gradient-sputtering (PGS) system, and the complex relationship between film thickness, composition, and multi-scale structure was systematically investigated. A hallmark of this study is the observation of a significant structural transition facilitated by the PGS process; while the system establishes a high-quality c -axis-oriented template at the early growth stage, Bi-rich films exhibit a dramatic degradation in orientation ( F -value from 0.97 to 0.17) as thickness increases. This orientation loss is attributed to the stress relaxation-induced grain tilting inherent to the Bi-rich lattice. Remarkably, despite this pronounced structural deterioration, the thermoelectric properties—Seebeck coefficient, electrical conductivity, and power factor—remain nearly invariant across a broad thickness range (0.5 to 4.2 μm). This suggests that the electronic transport is predominantly governed by the stable initial layer formed under the high-energy particle flux of the PGS process, effectively decoupling functional performance from bulk structural changes. Optimization of the composition yielded maximum power factors of 21 μW/(cm‧K 2 ) for p -type ( x = 0.24) and 6.7 μW/(cm‧K 2 ) for n -type ( x = 0.73). These findings demonstrate that the PGS system provides a unique growth kinetic that ensures thickness-tolerant performance even under significant structural instability, offering a robust platform for scalable micro-thermoelectric devices.
Takizawa et al. (Sun,) studied this question.