Bonding-Guided Anisotropic Growth of Quasi-1D M₂X₃Se₈ Thermoelectric Nanowires

Quasi-1D van der Waals materials have emerged as promising candidates for flexible electronic and thermoelectric applications due to their intrinsic anisotropy, narrow band gaps, and mechanical flexibility. Herein, M₂X₃Se₈ (M = Nb, Ta, X = Pd, Pt) nanowires are studied to understand the bonding-directed growth mechanism. Bond valence sums and binding energy analyses reveal that weak X2-Se2 interactions perpendicular to the c-axis facilitate anisotropic growth. Integrated Crystal Orbital Hamilton Population calculations show that the Ta─Se bonds in Ta₂Pd₃Se₈ possess greater bonding strength along the growth direction compared to the Nb─Se bonds in Nb₂Pd₃Se₈ and Nb₂Pt₃Se₈, predicting longer nanowires for Ta₂Pd₃Se₈. Experimental synthesis and SEM length statistics confirm this trend. Thermoelectric measurements confirm n-type behavior with enhanced power factor in Ta₂Pd₃Se₈. Ta₂Pd₃Se₈ also forms centimeter-long, flexible nanowires via chemical vapor transport. This work demonstrates bond-guided growth for quasi-1D M₂X₃Se₈ and identifies Ta₂Pd₃Se₈ as a leading candidate for flexible thermoelectric devices.