(color online) Size effect on thermal conductivity of NWs. (a) Room temperature thermal conductivity of Si NWs (with fixed transverse boundary condition) versus longitudinal length with different heat baths. The inset is free (transverse) boundary condition case. (b) Diameter-dependent thermal conductivity of Si NWs calculated by Green–Kubo calculations with Tersoff potential. (c) Diameter-dependent thermal conductivity of Bi NWs with growth directions of [102] (pink hexagon) and [110] (blue circle) at 300 K. (d) Thermal conductivity of [100] Si NWs versus surface-to-volume ratio (SVR) for different geometries at 300 K. Panels adapted with permission from (a) Ref. [48], ©2010 Elsevier; (b) Ref. [76], ©2017 ACS; (c) Ref. [83], ©2011 ACS; (d) Ref. [67], ©2011 AIP.