The inherently low electrical conductivity of TiO₂-based electrodes as well as the high electrical resistance between an electrode and a current collector represents a major obstacle to their use as an anode for lithium ion batteries. In this study, we report on high-density TiO₂ nanotubes (NTs) branched onto a carbon nanofiber (CNF) "tree" that provide a low resistance current path between the current collector and the TiO₂ NTs. Compared to a TiO₂ NT array grown directly on the current collector, the branched TiO₂ NTs tree, coupled with the CNF electrode, exhibited ~10 times higher areal energy density and excellent rate capability (discharge capacity of ~150 mA·h·g^-1 at a current density of 1, 000 mA·g^-1). Based on the detailed experimental results and associated theoretical analysis, we demonstrate that the introduction of CNFs with direct electric contact with the current collector enables a significant increase in areal capacity (mA·h·cm^-2) as well as excellent rate capability.

We have investigated the optical properties of laterally aligned Si nanowire (SiNW) arrays in order to explore their potential applicability in transparent electronics. The SiNW array exhibited good optical transparency in the visible spectral range with a transmittance of ~90% for a NW density of ~20−25 per 10 μm. In addition, polarization-dependent measurements revealed a variation in transmittance in the range of 80%−95% depending on the angle between the polarization of incident light and the NW axis. Using the SiNWs, we demonstrated that transparent transistors exhibit good optical transparency (greater than 80%) and showed typical p-type SiNW transistor characteristics.