Fig. 3.

Seebeck coefficient, σ/k and figure of merit (ZT) of the fibers of nanotubes. Seebeck coefficients S as a function of the temperature T (a). The blue circles represent the fabric of this work, with nanotube wall thickness of 65 ± 5 nm. Reported values at room temperature pSi thin films with different doping levels from Paul et al.¹⁷ and Van Herwaarden et al.¹⁸ are included. Lines represent the values expected for bulk/nanobulk pSi, from Hinsche et al.¹⁹, Ohishi et al.²⁰, and Kessler et al.²². Values in brackets indicate the boron doping concentration of the respective materials. b Geometry-independent figure σ/k as a function of temperature for the same pSi NT fabric (black squares). Values obtained from literature have been included in the graph for comparison: holey silicon nanostructures^21,30, etched silicon²², thin films^17,]31,32, pressed nanocristalline silicon²³. c Figure of merit of the samples with different wall thickness as a function of temperature. Dash lines from bulk crystalline Si^20,28 and polycristalline Si²⁸. Dot line represents the values obtained from the work of Kessler et al.²³. The main source of error reflected in the bars in the plot of ZT comes from the uncertainty in the  measurement of the effective section, required for   determining both σ and κ. It has been derived from the standard error of SEM cross sections obtained at different regions of the measured sample