Kenzo Hiraoka

Characteristic Energy Losses by Slow Electrons in Organic Molecular Thin Films at 77°K

Characteristic energy losses by slow electron impact have been measured for ⪖102 A films of several aromatic compounds as well as alkanes, alkenes, alcohols, acetone and ice at 77°K. Resonances are clearly indicated by the electron current I transmitted by the dielectric as a function of the modulated thermionic emitter voltage V, displayed as dI/dV vs V. Energy losses are measured directly by retarding potential analysis of backscattered electrons. Measurements at several incident electron energies provide the V‐dependence of the cross section. The method is particularly useful for measuring small losses (∼1 eV). There is no potential barrier for injecting electrons into the dielectrics examined, and the evidence indicates that they have positive bulk electron affinities. All systems show resonances at 0.5–1 eV which are attributed to transient negative ions. Acetone, n‐hexane and ice were examined in some detail for 0–4 eV losses by retarding potential analysis. The results indicate that electrons are a...

Characteristic energy losses by slow electron impact on thin‐film alkanes at 77 °K

Characteristic energy losses by slow electron impact have been measured on thin films of several alkanes at 77 °K. The cross section for the lowest loss at [inverted lazy s] 0.6 eV increases tenfold in the series n ‐pentane to n ‐nonane with increasing carbon number. For a given carbon number it decreases markedly with branching. Losses at [inverted lazy s] 3, [inverted lazy s] 6, [inverted lazy s] 9, and [inverted lazy s] 22 eV are common to all alkanes with no strong dependence on molecular size or configuration. The lowest losses may be due to temporary negative ion states or to pre‐existing trapping potentials. Losses at [inverted lazy s] 3 eV may be due to the highest temporary negative ions or to triplets. If the former is correct, then [inverted lazy s] 6 eV losses can be attributed to triplets. The [inverted lazy s] 9 eV losses are due to upper singlet states, and the [inverted lazy s] 22 eV losses may be due to collective excitations.

Characteristic Energy Losses by Slow Electrons in Thin Films of Alkali Halides

The potassium halides and the alkali iodides have been examined by electron impact in the range 0–50 eV. Both electron transmission and backscattering currents (It, Ib) have been measured while sweeping the modulated accelerating or retarding potentials (Vi, Vr). The characteristic energy loss spectra are presented as dIt/dVi vs Vi or dIb/dVr vs Vr. The principal events, in order of increasing Vi or decreasing Vr, are: electron trapping by cations to ns 2S and np 2P alkalis, and possibly higher; usually three resonances attributed to low‐lying states of halide ions, possibly 3P2, 1, 0 among others (triplet exciton); the fundamental singlet exciton; the vacuum level; the higher fundamental singlet exciton and vacuum level involving halogen ns 4P. The crystal electron affinities have been evaluated by two methods.