Photoemission from Organic Crystal in Vacuum Ultraviolet Region. IV

Abstract

The quantum yield and the energy distribution of photoelectrons were measured for organic crystals in the vacuum ultraviolet region. A model was presented for the photoemission from organic crystals with a narrow valence band, and a semiempirical power law was derived for the yield near the threshold. The ionization potentials found from the spectral distribution of the quantum yield using this model were as follows: anthracene–5.68 eV, naphthacene—5.43, pentacene—5.04, perylene—5.33, indanthrone—5.17, and tetrathionaphthacene—4.42. The effect of electrons which escape after one inelastic scattering was observed. It was shown how the contribution of once-scattered electrons can be separated in the energy distribution. The threshold for “pair production” was estimated to be nearly equal to the band gap for perylene and a little higher than the band gap for quaterrylene. The fine structures observed both in the yield spectra and in the energy distribution can be accounted for by assuming the existence of additional valence bands.

Electronic Structures of a Well-Defined Organic Hetero-Interface: C₆₀on Pentacene Single Crystal

“…Because of higher sensitivity and longer probing depth of the PYS method in comparison to the conventional UPS [29], photoelectron yield from the Pen-SC was detected even beyond the C 60 thickness of completion of the overlayer (∼ 5 nm). It is empirically known that the photoelectron yield Y can be expressed by the following power law as a function of the photon energy hν [30]; Y (hν) = Y 0 (hν − I th ) n · S(hν − I th ), where I th is the threshold ionization energy of the sample, Y 0 is a constant corresponding to the total photoemission strength, S(x) is an adequate step function that switches from 0 to 1 when x becomes negative to positive, and n = 3 is often adopted empirically for organic materials [31]. Note that this formula is applicable only when (hν − I th ) is small.…”

Determination of the highest occupied molecular orbital energy of pentacene single crystals by ultraviolet photoelectron and photoelectron yield spectroscopies

“…Note that this formula is applicable only when (h¯¹ I s ) is small, and we use a cube law (n = 3) which is empirically proposed for organic materials. 26 …”

Challenges in Applying Photoemission Electron Microscopy to Biological Systems†

“…Following Kane’s theory for semiconductors, Kochi et al. (55) established a cubic power model to explain photoemission from organic crystals. These models, like the Fowler‐Nordheim model, do not include the effect of temperature and therefore do not account for the thermal tail of the threshold curve.…”