Secondary neutral

Sputtered Neutrals Mass Spectrometry Secondary Neutrals Mass Spectrometry Direct Bombardment Electron Gas SNMS... 

Electron-impact (El) Secondary Neutral Mass Spectrometry (SNMS)... 

Ion beam spectrochemical analysis (IBSCA) is a sputtering-based surface analytical technique similar to SIMS/SNMS. In IBSCA the radiation emitted by excited sputtered secondary neutrals or ions is detected. IBSCA was developed parallel to SIMS in the nineteen-sixties and early nineteen-seventies [4.246, 4.247]. It is also known... 

An IBSCA-spectrum (Fig. 4.48) consists of many peaks in the visible range (250-900 nm). Every peak can be related to an process of electron de-excitation of a sputtered particle from a higher to a lower state, for the more dominant peaks to the ground state. There are, in principle, two major types of peak family type I - photons emitted from excited sputtered secondary neutrals and type II - photons emitted from excited sputtered secondary ions (single charged). 

From these results it can be postulated that for oxidic glasses a fixed proportion of sputtered secondary neutrals is emitted in an excited state. Such linearities can only be determined for similar matrices, which limits the use of D-factors to sample systems similar to the reference sample system used for the D-factor determination. 

Jones, F.R., Interfacial aspects of glass fibre reinforced plastics. In Jones, F.R. (Ed.), Interfacial Phenomena in Composite Materials. Butterworths, London, 1989, pp. 25-32. Chaudhury, M.K., Gentle, T.M. and Plueddemann, E., Adhesion mechanism of poly(vinyl chloride) to silane primed metal surfaces. J. Adhes. Sci. Technol, 1(1), 29-38 (1987). Gellman, A.J., Naasz, B.M., Schmidt, R.G., Chaudhury, M.K, and Gentle, T.M., Secondary neutral mass spectrometry studies of germanium-silane coupling agent-polymer interphases. J. Adhes. Sci. Technol., 4(7), 597-601 (1990). 

SNMS Sputtered and/or secondary neutral mass spectrometry... 

Figure 4.1 The principle of SIMS. Primary ions with an energy between 0.5 and 10 keV cause a collisional cascade below the surface of the sample. Some of the branches end at the surface and stimulate the emission of neutrals and ions. In SIMS, the secondary ions are detected directly with a mass spectrometer, whereas in SNMS the secondary neutrals are ionized before they enter the mass spectrometer.

Table 4.1 illustrates that sputtered particles from clean metal surfaces are predominantly neutral. As we have seen in the previous section, sputter yields fall in general in the range l-10, whereas the yields of secondary ions, the product of Y and R, are almost all below 0.01 for metallic samples. Hence, typically 99% of the sputtered particles from metals are neutral. The great advantage of SNMS is that the signal intensity of secondary neutrals is [compare (4-1)]... 

I" is the intensity of secondary neutrals (expressed as a rate in counts per second)... 

As extensive tables of reliable sputter yields are available, SNMS is much more suitable than SIMS for quantitative work. Interestingly, ionic solids also give significant yields of secondary neutrals, underlining the fact that neutralization processes at the surface are also important for non-metallic samples. 

Figure 4.12 Secondary neutral and ion mass spectra of a 1 1 Fe-Ni alloy in the mass regions of monomers lop) and dimers (bottom). The dimer distribution indicates that iron and nickel are atomically mixed, as expected in an Fe-Ni alloy. Note the higher sensitivity of SIMS for iron and the manganese impurity (from ter Veen [36]).

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

H. Oechsner. Secondary Neutral Mass Spectrometry (SNMS) Recent Methodical Progress and Applications to Fundamental Studies in Particle/Surface Interaction. Int. J. Mass Spectrom. Ion Proc., 143(1995) 271-282. 

It has been estimated that a single impact causes the eruption of about 10 secondary neutrals, but yields only 0.02-1.5 ions. [46,48,57,58] The ions are then heading away from the surface in a supersonic expansion at speeds of about 1000 m s". [22,46]... 

Goschnick, J., J. Schuricht, and H. J. Ache, Calibration of Depth Profiles of Microparticles Measured with Plasma-Based Secondary Neutral Mass Spectrometry, Fresenius J. Anal. Chem.,... 

Figure 2.30 a) Principles of a secondary ion source b) Schematic diagram of an ion source of a secondary neutral mass spectrometer (SNMS). (J. S. Becker and Id. J. Dietze, Int. J. Mass Spectrom. Ion. Proc. 197, 1-35. (2000). Reproduced by permission of Elsevier.)... 

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