Anna Herrmann | Searcharxiv

arXiv2024

Spectrally resolved far-field emission pattern of single photon emitters in MoS2

We explore the optical dipole orientation of single photon emitters in monolayer MoS2 as produced by a focused helium ion beam. The single photon emitters can be understood as single sulfur vacancies. The corresponding far-field luminescence spectra reveal several photoluminescence lines below the dominating luminescence of the exciton in MoS2. These sub-bandgap emission lines were predicted by ab initio theory, but they have never been resolved in luminescence experiments because of their small amplitude. We reveal the lines by their dependence as a function of the photon energy and momentum as measured in the back focal plane of the optical circuitry. The agreement between theory and experiment suggests that the defect states interact strongly within the Brillouin zone.

cond-mat.mes-hall↗

arXiv2020

Particle Diffusivity and Free-Energy Profiles in Inhomogeneous Hydrogel Systems from Time-Resolved Penetration Profiles

A combined experimental/theoretical method to simultaneously determine diffusivity and free-energy profiles of particles that penetrate into inhomogeneous hydrogel systems is presented. As the only input, arbitrarily normalized concentration profiles from fluorescence intensity data of labeled tracer particles for different penetration times are needed. The method is applied to dextran molecules of varying size which penetrate into hydrogels of polyethylene-glycol (PEG) chains with different lengths that are covalently cross-linked by hyperbranched polyglycerol (hPG) hubs. Extracted dextran bulk diffusivities agree well with fluorescence correlation spectroscopy data obtained separately. Scaling laws for dextran diffusivities and free energies inside the hydrogel are identified as a function of the dextran mass. An elastic free-volume model that includes dextran as well as PEG linker flexibility describes the repulsive dextran-hydrogel interaction free energy, which is of steric origin, quantitatively and furthermore suggests that the hydrogel mesh-size distribution is rather broad and particle penetration is dominated by large hydrogel pores. Particle penetration into hydrogels is for steric particle-hydrogel interactions thus suggested to be governed by an elastic size-filtering mechanism that involves the tail of the hydrogel pore-size distribution.

cond-mat.soft↗