Beam sources neutral

In contrast to the d.c. or microwave plasma apparatus, the sample environment produced by these directed beam sources has been reasonably well characterized. Studies of Kaufman source operation (Sharp et al., 1979) have established that H beams are typically composed of mixtures of H+ and H2+ ions and a roughly equal mixture of energetic neutrals. The ion energy spectrum of such a source is fairly sharply peaked at the maximum energy at low acceleration voltages (150-500 eV) but spreads out considerably if the source is operated at voltages above 1000V. 

The emission of molecular ions in organic SIMS is discussed with respect to the method of ionization and the various sample preparation and matrix-assisted procedures used. The matrices include various solid-state and liquid matrices such as ammonium chloride, charcoal, glycerol, and galliun. A neutral beam source is described to analyze thick insulating films. Various chemical derivatization procedures have been developed to enhance the sensitivity of molecular SIMS and to selectively detect components in mixtures. 

In subsection 7.2.1, it was discussed that the neutral clusters generated from the beam source have a wide range of cluster sizes. Although there is no single, easily available technique which allows the size specific detection of neutral clusters, it is now well accepted that the cluster size distribution can be manipulated, to a certain extent, by careful control of the various experimental parameters. Mass spectrometric detection of clusters in general and tandem mass spectrometry in particular offer the inherent advantage of enabling size specific studies of the cluster ions. 

A quadrupole ion trap (Figure 12.7C) mass analyzer collects ions in stable trajectories using a radiofrequency oscillating voltage on a central ring electrode. A gated electron beam ionizes neutral molecules within the trap, or ions may be injected into the trap from external ion sources. A second radiofrequency field between the end caps causes ions of a particular m/z to go into an unstable trajectory and pass through the holes in one end cap to the ion detector. Several... 

The development of hyperthermal neutral beam sources, some eight years ago, has disclosed a new field of beam research on charge transfer processes between neutral particles in their electronic ground state. In particular, charge transfer with low endoergicity of the order of 1 eV turned out to be very efficient and therefore has been studied extensively between its threshold and, say, 50 eV. The special interest of this field lies in its close relationship with chemical reaction kinetics and, from a theoretical point of view, its suitability to tell us more about diabatic behaviour at the crossing of potential energy surfaces. 

The Bendix mass spectrometer must be considered a commercial success, since many of these instruments can still be found in industrial and academic laboratories throughout the United States. In later years, manufacture of these instruments was taken over by CVC Products (Rochester, NY), which continued to produce the model 2000 until a few years ago. An attractive feature of the Bendix instruments seems to have been the ease with which they could be modified for specific applications. In 1962, Lehrle et al. replaced the electron beam in the Bendix ion source with an ion beam source that could be used to generate either ions or neutrals with kinetic energies in the range of 0 to 2 keV. While used primarily for studies of gas-phase ion-molecule or neutral-molecule reactions, it was also further modified to enable sputtering of surfaces. Shortly after the introduction of chemical ionization by Field and Munson in 1966, Futrell et al. described a modified ion source for... 

The beam of neutral gaseous analyte molecules enters the ionization chamber or ion volume, i.e., the actual region of ionization within the ion source block, in a line vertical to the paper plane and crosses the electron beam in the center. In order to reduce loss of ions by neutralizing collisions with the walls, the ions are pushed out immediately after generation by action of a low voltage applied to the repeller electrode [3,4]. They are then accelerated and focused towards the mass analyzer. Efficient ionization and ion extraction are of key importance for the construction of ion sources producing focusable ion currents in the nanoampere range [5]. 

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