Thickness-Dependent Interactions Between Helical Chains of 2D Tellurene

Tellurene is the two-dimensional (2D) form of tellurium consisting of helical Te chains. The unique crystal structure of tellurene brings about remarkable properties, such as high hole mobility, excellent thermoelectricity, and anisotropic optical nonlinearity. 2D tellurene is predicted to have different phases because of the interaction between helical Te chains. However, it is not clear yet how the bonding of the helical chain changes due to interactions between chains, especially for Te with different thicknesses. In this work, we directly measured the bonding of Te within one helical chain and between different chains using x-ray absorption spectroscopy (XAS). We further demonstrated that the interaction between chains was strengthened when the thickness of tellurene decreased. This dependence on thickness is also consistent with the increased phonon frequency for smaller thicknesses. This work reveals the atomic bonding of 2D tellurene and paves the way for investigating the phase change of nanoscale elemental semiconductors.