Depth Profiling of the Chemical Composition of Free-Standing Carbon Dots Using Xray Photoelectron Spectroscopy [component]

The chemical and geometrical structure of free-standing carbon dots (Cdots) prepared from the pyrolysis of N-hydroxysuccinimide (NHS) have been characterized using X-ray photoelectron spectroscopy (XPS). An aerodynamic lens system was used to generate a sufficient particle density of monodispersed Cdots for XPS studies at the PLEIADES beamline at the SOLEIL synchrotron facility. Varying the X-ray excitation energy between 315 and 755 eV allows probing of the Cdots from the surface toward their
more » ... ore, owing to the kinetic energy dependence of the photoelectron inelastic mean free path. The C1s, O1s and N1s core-levels were recorded with high spectral resolution to identify their main chemical components and branching ratios. While high-resolution transmission electron microscopy (HRTEM) reveals a defective graphitic core, the C1s spectrum evidences two main peaks similar to those measured from the solid NHS. Their relative abundance as a function of the probing depth is strongly related to the chemical composition of the ligand shell that does not vary substantially over the first 3.4 nm. Combining the depth-resolved XPS and HRTEM studies, it was concluded that the Cdots possess a graphitic core surrounded by a relatively homogeneous shell of at least 3.4 nm thickness with a composition similar to that of the solid NHS.
doi:10.1021/acs.jpcc.8b03800.s001 fatcat:gc2qna5rdjbpvczam4uyae4c4a