Surface penning ionization

Penning ionization is a dominant reaction when nitrogen or neon is used in the DART source. Nitrogen or neon ions are effectively removed by electrostatic lenses and are not observed in the background mass spectrum. When helium is used, the dominant positive-ion formation mechanism involves the formation of ionized water clusters followed by proton transfer reactions. Negative-ion formation occurs by production of electrons by Penning ionization or by surface Penning ionization ... 

Negative ions can be formed by electron capture due to the presence of thermalized electrons produced by Penning ionization or by surface Penning ionization. Negative ions can also be obtained by reactions of analyte molecules with negative ions formed from atmospheric water and oxygen to produce the deprotonated molecule. 

SPI Surface Penning Ionization Neutral atoms, usually He, in excited states are incident on a surface at thermal energies. A surface electron may tunnel into the unoccupied electronic level, causing the incident atom to become ionized and eject an electron, which is then detected. This technique measures the density of states near the Fermi-level, and is highly surface sensitive. 

Ultra-violet photoemission spectroscopy (UPS) probes the density of states, and ion neutralization spectroscopy (INS) and surface Penning ionization (SPI) provide similar information with probes of ions and metastable atoms, respectively. Angle-resolved UPS can determine the valence band structure. X-ray Photoelectron Spectroscopy (XPS) provides information on chemical shifts of the atomic core levels, and this can also help in understanding chemical bonding at the surface. 

SPiES Surface Penning ionization Eiectron Spectroscopy... 

SPIES Surface Penning ionization electron spectroscopy... 

Metastable helium atoms or nitrogen molecules are extracted from the plasma and directed to a sample surface, where Penning ionization makes product ions that can be analyzed by mass spectrometry or IMS. DART sources have been used to ionize a number of classes of compounds as solids or adsorbed directly onto a variety of surfaces. 

Whether the transition occurs adiabaticaily or nonadiabatically, the process can, in principle, be described analogously to chemiionization, namely in terms of approach of A and BC along a surface, with a probalnlity at each point of the tr ectory of transition to the A + BC surfaces. Unlike Penning ionization, however, the transition is reversible and, especially when the entrance channel is attractive, the (A-BC) intermediate may survive for several vibrations (complex formation) before redissociating. 

Among the possibilities available to postionize sputter-ejected neutral surface particles, electron impact ionization has been employed in a variety of experimental approaches. More recently, photoionization by resonant or nonresonant multiphoton absorption processes has been established as another very effective technique in SNMS. Other processes as Penning ionization or charge exchange play only a minor role in postionization for SNMS. 

This chapter describes fundamental aspects of the electronic structure of organic semiconductors (small molecules and polymers), and their interfaces, and the method to bridge the electronic structure and electrical property more directly using ultraviolet photoemission spectroscopy (UPS). Penning ionization electron spectroscopy (PIES), which is the most surface-sensitive method, is also introduced for study of electronic states at outermost surfaces of solids, which are responsible for charge exchange through the interfaces between different materials when they get contact to form a hybrid system. 

Soft erosion conditions were selected in order to minimize surface damage and signals were taken in the afterglow region—when the plasma is extinguished and corresponds to fragments ionized by Penning ionization from Ar metastables. 

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