The control of the energy carriers flow direction is fundamental for many applications. While, the first step toward this control was achieved for electrons 100 years ago, the rectification of phonons is still under debate. Thermal diodes would be new device paradigms for efficient thermal management in modern nanotechnology, citing electronics, energy conversion, and cooling among others. Such devices could regulate heat flow, mitigate overheating, and optimize energy usage in nanoscale systems. Thermal rectification traditionally has been demonstrated using mainly bulk materials, with new trends to use 1D or 2D low dimensional materials. It arises from the asymmetric flow of phonons, when changing the direction of the thermal bias. Although there is so far no greater consensus in the literature concerning the exact generic mechanism of thermal rectification, it has been proven that there are at least two necessary conditions: asymmetry along the heat flux direction and non-linearity of the thermal properties with respect to the temperature bias ∆T. The different strategies used to get thermal rectification are either to join two materials with different thermal properties separated by an interface perpendicular to the heat flux, or to tailor the thermal properties through appropriate geometries at the nanoscale.

Here, we will show thermal rectification for two distinguish configurations: tapered crystalline-core/amorphous-shell nanowires and partial perforated graphene. Concerning the first group the interface parallel to the heat flux, with the variable thickness of amorphous shells along the growth direction is a new strategy. It induces a position-dependent phononic dynamics in the crystalline core of the nanowire, due to the amorphous shell’s thickness variation, to obtain variable axial and radial phonon propagation/confinement. The rectification estimated is of the order of 5% (90% when one selects the cross-section selection on the hottest thermostat), with a better heat flow from the smaller cross-section to the larger one; thicker shell increases phonon scattering [Phys. Rev. B 103, 014202 (2021)].

For the second configuration, the partially perforated graphene we will show the influence of geometric parameters on the thermal conductivity and thermal rectification ratio, revealing a maximum thermal rectification rate of ~20%. The analysis considers key geometric factors such as the length of the pristine region and the pore size, shape, alignment, and orientation. It is found that heat preferentially flows from the perforated graphene to the pristine region, indicating that the principal rectification mechanism is the difference in the temperature-dependence of κ(T) for the pristine and the porous graphene [arXiv:2504.16013].