Carbon nanotubes (CNTs) have been explored as a material for vertical interconnects since they can handle higher current densities than copper and offer ballistic transport. This paper from IMEC demonstrates a 5x improvement in electron mean free path for CNTs compared to previous work. The CNT mean free path of 24-74nm approaches copper. Contact resistance is improved significantly compared to previous work as well.
[4.3. M. van der Veen, et al., “Electron Mean Free Path for CNT in Vertical Interconnects Approaches Copper”, imec]