tailieunhanh - Báo cáo hóa học: " Determining factors of thermoelectric properties of semiconductor nanowires"

Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Determining factors of thermoelectric properties of semiconductor nanowires | Demchenko et al. Nanoscale Research Letters 2011 6 502 http content 6 1 502 o Nanoscale Research Letters a SpringerOpen Journal NANO REVIEW Open Access Determining factors of thermoelectric properties of semiconductor nanowires Denis O Demchenko1 Peter D Heinz2 and Byounghak Lee2 Abstract It is widely accepted that low dimensionality of semiconductor heterostructures and nanostructures can significantly improve their thermoelectric efficiency. However what is less well understood is the precise role of electronic and lattice transport coefficients in the improvement. We differentiate and analyze the electronic and lattice contributions to the enhancement by using a nearly parameter-free theory of the thermoelectric properties of semiconductor nanowires. By combining molecular dynamics density functional theory and Boltzmann transport theory methods we provide a complete picture for the competing factors of thermoelectric figure of merit. As an example we study the thermoelectric properties of ZnO and Si nanowires. We find that the figure of merit can be increased as much as 30 times in 8-Ằ-diameter ZnO nanowires and 20 times in 12-Ằ-diameter Si nanowires compared with the bulk. Decoupling of thermoelectric contributions reveals that the reduction of lattice thermal conductivity is the predominant factor in the improvement of thermoelectric properties in nanowires. While the lattice contribution to the efficiency enhancement consistently becomes larger with decreasing size of nanowires the electronic contribution is relatively small in ZnO and disadvantageous in Si. Introduction Using nanostructures for thermoelectric TE materials is a promising prospect as it opens up a possibility of controlling the TE properties by modifying the size and shape in addition to the composition of the material. The TE properties of a material are characterized by a dimensionless figure of merit ZT TS2ơ kb Kl where T s s Ke and Kl are temperature Seebeck .