Neutral primary beam-SIMS

SIMS Analysis. The equipment and instrumental conditions have been described in detail (7.121. Mostly, a model 6300 Perkin Elmer spectrometer was used which was equipped with a 0-255 amu quadrupole mass analyzer. The primary beam of 4.5 keV Xe+ and 60 pA current was rastered in a 2x2 mm2 area. The total ion dose was not more than 3xl012 ions per cm2, which is considered a practical limit for static conditions (5rZ)- Charge neutralization was done by means of 500 eV electrons. Spectral optimization has been described (7.121. 

To analyze material absorbed on a surface required a less energetic primary beam that would not disrupt the crystalline structure of the substrate. This technique was described as static SIMS. Problems arose inasmuch poorly conducting substrates would become charged, disrupting the primary beam and the emission of secondary ions. Vickerman and co-workers showed in 1979 that the use of a fast atom beam, a stream of energetic neutrals, reduced the charging problem and improved the stability of the secondary ion beam. They called their technique fast atom bombardment SIMS or FAB SIMS. The technique was taken up by Barber and co-workers for the analysis of... 

The high voltages used to generate the primary beam and hence the secondary beam plus the high concentration of sputtered neutral molecules made magnetic sector instruments the most ideal mass analyzer to use with liquid SIMS sources. Linear... 

The principle of operation of secondary ion mass spectrometry (SIMS) devices was described in Chapter 1 an energetic ion beam (primary beam) impinges on the sample causing secondary ions and neutrals to be desorbed from the surface and enter a mass spectrometer where these ions are analyzed. A schematic of a SIMS device is shown in Figure 5.2 (Betti 2005). This device includes two ion sources (Duoplasmatron and cesium), a sample chamber with a transfer rod. 

Static Secondary Ion Mass Spectrometry (SIMS) involves the bombardment of a sample with an energetic (typically 1-10 keV) beam of particles, which may be either ions or neutrals. As a result of the interaction of these primary particles with the sample, species are ejected that have become ionized. These ejected species, known as secondary ions, are the analytical signal in SIMS. 

Figure 2 Relationship of SIMS, separate bombardment SNMSs and direct bombardment SNMSd. (a) Materials for SIMS analysis are those ions formed In the sputtering with a focused primary ion beam. The largest fraction of the particles sputtered from the surface are neutral atoms, (b) Ions for SNMS analysis are formed by ionization of the sputtered neutrals, (c) When the plasma is used as an ionizer, plasma ions can also be used to sputter the sample surface at low energies.

In secondary ion mass spectrometry (SIMS), a beam of energetic primary ions is focused onto the surface of a solid. Some of the ions are reflected but most of the energy of the primary ions is dissipated in the surface by binary collisions that cause neutrals, excited neutrals, and ions (positive and negative) to be ejected or sputtered from the surface. The secondary ions can be analyzed by a mass spectrometer to provide information about the surface composition of the solid. 

In SIMSLAB from VG Scientific, both surface analytical techniques - SIMS and SNMS - have been applied (see Figure 5.34). In this mass spectrometer different types of primary ion sources are available. Ar+, Cs+, Ga+ or O) primary ions are accelerated in the secondary ion source on the solid sample surface. Similar to the CAMECA IMS-7f, with this experimental arrangement, besides depth profiling, a microlocal analysis can also be performed. The sputtered secondary ions (for SIMS) or the post-ionized sputtered neutrals (for SNMS) - the post-ionization is carried out by an electron beam in an ionizer box (right-hand schematic in Figure 5.34) - are separated... 

In the SIMS a primary noble gas atom or ion (e.g. Ar°, Ar+, Xe°, Xe+) beam is bombarded on the sample in ultra-high vacuum, penetrating to a depth of 30-100 A. The kinetic energy of the particle is assumed to dissipate via a collision cascade process, which causes the emission of electrons, neutral species and secondary ions, the yields of which vary with polymer surface composition and obviates the possibility of quantitative SIMS informa-... 

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