Kaike Yang, Roberto D’Agosta, Angel Rubio

Nano-bio spectroscopy group and ETSF Scientific Development Center, Departamento de Fisica de Materiales, Universidad del Pais Vasco UPV/EHU, San Sebastian, Spain

Abstract

We investigate via density functional theory, the thermoelectric properties of 2D (germanene) and 1D (Ge nano-ribbons)

germanium systems. We report the linear response results, as a function of the nano-ribbon width and edge termination. For the

nano-ribbons, we have also investigated the possibility of nano-structuring these systems by mixing Ge and Si. We find that the

figure of merit at room temperature of these systems is remarkably high, up to 2.5.

Introduction

2D-Germanene

1D-Germanene Nanoribbons

ConclusionsIn summary, we have performed first-principle calculations of the thermoelectric coefficients of both two-dimensional germanene and 1D nano-ribbons. We have also considered hetero-structures of Ge and Si stripes to form a nano-ribbon, in the attempt to quench the phonon dynamics and thus increasing the figure of merit. These systems can be good thermoelectric materials if they can be reliably produced. Also, being based on Si and Ge, we expect these devices to be easily interfaced with the modern electronic systems, a distinct advantage with respect to other materials which have shown poor integrability with the actual technology.

Reference

K. Yang, S. Cahangirov, A. Cantarero, A. Rubio and R. D’Agosta, arXiv: 1310.0971v1.

Thermoelectrics, converting waste heat into the electric current, plays a significant role in the current quest for developing alternative energy technology in engineering and device applications.

1 1

1 /h c

h c h

T T ZT

T ZT T Tη − + −= ×

+ +

For a given ∆T (Th-Tc), The higher ZT, the higher the heat-to-electric conversion efficiency

2

( )e p

SZT T

σκ κ

=+

ZT: Figure of Merit, S: Seebeck Coefficient, Sigma: Electric

conductance, Ke and Kp: Electron and Phonon thermal

conductances.

1D-Germanene/Silicene Hetero-Nanoribbons

(a) 3x3 Germanene on 4x4 Ag substrate, (b) 3x3 Ge by

removing Ag, (c) and (d) band structures and (e) and (f)

electronic figure of merit corresponding to the Ag-grown

and free-standing Ge, respectively.

(a) ZigZag and (b) Armchair germanene nanoribbons, (c) and (d) phonon dispersion, (e) and (f) band gap.

(a) and (b) Seebeck coefficient, (c) and (d) phonon thermal conductance, (e) logarithm of Kp Versus log(T),

(f) and (g) figure of merit for Z-GeNRs and A-GeNRs, respectively.

(A): (a) and (b) Zigzag and Armchair GeSi hetero-nanoribbons, (B): figure of merit, (C): figure of merit for A-GeNRs,

A-SiNRs, A-GeSiNRs and disordered A-GeSiNRs, respectively.

(e) (f)

(c) (d)

(a) (b)

(c) (d)(e)

(f)

(a)

(b)

(c)

(d)

(e)

(f)

(g)

(A) (B) (C)