Fluorescence microscopy and spectroscopy of subsurface layer dynamics of polymers with nanometer resolution in the axial directionElectronic supplementary information (ESI) available: More details on the experimental procedure and accuracy of determining the depth of the performed diffusion; possible experimental artifacts that may be the real source of the observed effect; dependence of the number of detected molecules on the distance from the surface. See DOI: 10.1039/c5fd00055f

We studied the dynamics in ultrathin subsurface layers of an amorphous polymer by the spectra of single fluorescent molecules embedded into the layer by vapor deposition and subsequent controlled diffusion to the desired depth in 0.5 nm steps. The spectral trails of single molecules were recorded at 4.5 K as a function of diffusion depth. In depths shallower than 20 nm, the spectral dynamics deviate from those deep in the bulk. Less than 5 nm deep, the linewidths increase rapidly, whereas the number of detected molecules decreases. No zero-phonon lines were observed closer than 0.5 nm to the polymer surface. Possible physical reasons of the observed phenomena are discussed.