Field ionization enhancement

Okuyama, F. Hilt, E. Rollgen, F.W. Beckey, H.D. Enhancement of Field Ionization Efficiency of 10-pm Tungsten Filaments Caused by the Nucleation of... 

Fig. 2.7 Diagram showing how resonance field ionization occurs. When an image gas atom is field ionized, the tunneling electron may be reflected right back to the atom. Field ionization is enhanced if the atomic level lines up with an energy level formed between the metal surface and the potential barrier of the applied field, as shown in the figure. The potential barrier is approximately triangular in shape.

Field ionization can also be enhanced by photons. Tsong et al.43 searched for this effect and found that Ar field ion current near the threshold field of field ionization from an aluminum oxide tip could be enhanced by a factor of about 5 when the tip was irradiated with 4.16 eV photons from laser pulses of 2 p,s width at a pulse repetition rate of 25 Hz, or a duty cycle of only 0.005%. As the photon energy is much too small to... 

Photon enhanced field ionization was later also reported by Niu et a/.44... 

ADE = adiabatic detachment energies ESC A = electron spectroscopy for chemical analysis HOMO = highest occupied molecular orbitals MAES = metastable atom electron spectroscopy MIES = metastable ionization electron spectroscopy OAT = oxygen atom transfer PES = photoelectron spectra PEI = pulsed field ionization PIES = Penning ionization electron spectroscopy QM = quantum-mechanical REMPI = resonantly enhanced multiphoton ionization SC = semiclassical VDE = vertical detachment energies XPS = x-ray photoelectron spectroscopy ZEKE = zero electron kinetic energy Cp = cyclopentadienyl, Ph = phenyl, CeHs Tp =... 

In atomic laser spectroscopy, the laser radiation, which is tuned to a strong dipole transition of the atoms under investigation, penetrates the volume of species evaporated from the sample. The presence of analyte atoms can be measmed by means of the specific interaction between atoms and laser photons, such as by absorption techniques (laser atomic absorption spectrometry, LAAS), by fluorescence detection (laser-induced fluorescence spectroscopy, LIFS), or by means of ionization products (electrons or ions) of the selectively excited analyte atoms after an appropriate ionization process (Figures lA and IB). Ionization can be achieved in different ways (1) by interaction with an additional photon of the exciting laser or of a second laser (resonance ionization spectroscopy, RIS, or resonance ionization mass spectrometry, RIMS, respectively, if combined with a mass detection system) (2) by an electric field applied to the atomization volume (field-ionization laser spectroscopy, FILS) or (3) by collisional ionization by surrounding atoms (laser-enhanced ionization spectroscopy, LEIS). 

LEIS laser-enhanced ionization spectroscopy FILS field ionization laser spectroscopy RIS resonance ionization spectroscopy RIMS resonance ionization mass spectrometry... 

The formation of the starter cations M+ can occur at tips or wedges where the field enhancement promotes field ionization of the adjacent molecules (Schnabel and Schmidt, 1973 Wablat et al., 1975). In partial discharges occurring in transformer oil, similar polymerization processes are leading to the formation of wax (Fuhr and Schmidt, 1988). 

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