Nanostructure of hydrogenated amorphous silicon (a-Si:H) films studied by nuclear magnetic resonance

The aim of this work is to investigate the nanostructures of nanoporous materials by studying the anisotropy of the nuclear spin-spin and spin-lattice relaxations of the guest molecules trapped in the pores. The nuclear magnetic resonance (NMR) data are analyzed in the framework of the theory of the nuclear relaxation dominated by the dipole-dipole interactions in gas or liquid species contained in nanopores. A distinctive feature of this theory is the establishment of a relationship between the degree of orientation ordering of nanopores in the host matrix and their characteristic volume and the anisotropy of the NMR relaxation times. In this work the complex experimental and theoretical approach was applied to study the nanostructure of hydrogenated amorphous silicon (a-Si:H) films. A feature of this study is the simultaneous investigation of the three (T₁, T_1ρ, and T₂) NMR relaxation times, for the same sample. This allows us to determine not only the degree of orientation ordering of nanopores but also to estimate their size (∼1 nm) and correlation times of the nanopore fluctuations. The obtained results demonstrate that the developed approach is effective in studying details of nanostructure of different nanoporous materials.