Experimental Observation of van Hove Singularities in Quasi-1D MoO₂ Nanotubes

Currently, a major challenge of investigating nanostructured materials lies in demonstrating exotic properties and outstanding performance through control of the structure and morphology. In particular, the density of states of each sub-band diverges when solid semiconductors transit into 1D materials, which results in a special distribution know as a van Hove singularity (VH). However, there are no reports on the existence of VHs in 1D materials other than carbon nanotubes. Quasi-1D MoO₂ nanotubes with large aspect ratio are synthesized using a simple hydrothermal method. The VHs in the density of states are demonstrated by characterizing the multiple peaks in absorbance and fluorescence spectra, which is the first time that the existence of VHs in oxide nanotubes has been experimentally demonstrated. Detailed analysis indicates that the bandgap energies in the VH structure are strongly correlated with the nanotube diameter. It is believed that this work will be significant for further understanding of electronic structures in 1D materials, which will also promote their potential applications in related fields, particularly optoelectronics.