  We measure diffusion of organic molecules located a few nanometers from the
diamond surface. To study molecular diffusion, we perform local detection of
nuclear magnetic resonance, based on single shallow Nitrogen-Vacancy (NV)
centers in diamond. Specifically, we demonstrate measurements of translational
diffusion coefficient of phospholipids in an artificial cell membrane by
employing correlation spectroscopy. An analysis of correlation decay curves
using different diffusion models shows, that a simple 2D diffusion model gives
satisfactory diffusion coefficients, although the choice of the model affects
the extracted numbers. We find significant differences among the diffusion
coefficients measured by different single NV centers, which we attribute to
local heterogeneities of the lipid layers, likely caused by the supporting
diamond substrate.
