Towards Unveiling the Exact Molecular Structure of Amorphous Red Phosphorus by Single-molecule Studies.

Since the discovery of amorphous red phosphorus (a-red P) in 1847, a number of possible structures of a-red P have been proposed. However, the exact molecular structure of a-red P is not determined yet due to the amorphous nature. Here in this study, we utilize several methods to investigate some basic properties of a-red P, which are helpful to determine the structure. The experimental results from scanning tunneling microscopy (STM) and gel permeation chromatography (GPC) confirm that a-red P is a linear inorganic polymer with a broad molecular weight distribution. The theoretical single-molecule elasticities of the possible a-red P structures are obtained by quantum mechanical (QM) calculations. It is found that the experimental single-molecule elasticity of a-red P measured by single-molecule AFM matches with the theoretical result of the zig-zag ladder structure, indicating that a-red P may adopt this structure. Although this conclusion needs further validation in the future, this fundamental study represents a helpful attempt to solve the long-lasting riddle of phosphorus. It is expected that the strategy utilized in this work can be applied to study other inorganic polymers.