Emission of highly excited electronic states of potassium from cryptomelane nanorods

Cryptomelane (KMn8O16) nanorods were synthesized, characterized (XRD, Raman spectroscopy, TEM/SAED) and investigated by species resolved thermal desorption of potassium from the material in the range of 20-620 degrees C. The desorbing fluxes of ions, atoms and highly excited electronic states (field ionizable Rydberg states) were measured using an ion collector, surface ionization and field ionization detectors, respectively, in a vacuum apparatus. The non-equilibrium emission of potassium Rydberg species (principal quantum number > 30) strongly depends on the surface positive voltage bias with a broad maximum at 1-8 V. The stimulation of Rydberg species emission is discussed in terms of spatial and energetic overlapping between the electron cloud above the cryptomelane surface and the desorbing potassium ion.