Near-ultraviolet inverse photoemission spectroscopy using ultra-low energy electrons

In previous inverse photoemission spectroscopy (IPES) experiments, either X-ray (hν > 1 keV) or vacuum ultraviolet (hν ≈ 10 eV) photons were detected following the injection of electrons with energies of 10–1000 eV into solid materials. Here, we demonstrate IPES in the near-ultraviolet range (hν < 5 eV) using electrons with kinetic energies less than 4 eV. The energy resolution of the instrument is attained to be 0.27 eV. From the spectra of copper phthalocyanine films, it is found that damage to the organic sample is significantly reduced, demonstrating that this method is especially suitable for organic semiconducting materials.