Atomic concentration depth

AES atomic concentration depth profile for an untreated PBTMSS film on Au/Si (1 min. sputtering = 140 A). 

Figure 12. Atomic concentration depth profile in F8G sample the values are related to the calcium concentration...

Figure 11. Carbon, oxygen and nitrogen atomic concentration depth profile for C-PA (open symbols) and PAO (solid ones) membranes...

Sputtered Neutral Mass Spectrometry (SNMS) is the mass spectrometric analysis of sputtered atoms ejected from a solid surface by energetic ion bombardment. The sputtered atoms are ionized for mass spectrometric analysis by a mechanism separate from the sputtering atomization. As such, SNMS is complementary to Secondary Ion Mass Spectrometry (SIMS), which is the mass spectrometric analysis of sputtered ions, as distinct from sputtered atoms. The forte of SNMS analysis, compared to SIMS, is the accurate measurement of concentration depth profiles through chemically complex thin-film structures, including interfaces, with excellent depth resolution and to trace concentration levels. Genetically both SALI and GDMS are specific examples of SNMS. In this article we concentrate on post ionization only by electron impact. 

As in RBS analysis, ERS can provide information on the atomic concentration of hydrogen as a function of depth (measured in atoms/cm ). This is derived from the height Aobs°f ERS spectrum (counts per channel), at energies corresponding to particular depths within the sample (see Figure 3c). For a sample consisting of H and another material X, with composition the spectrum height... 

Several features of ISS quantitative analysis should be noted. First of all, the relative sensitivities for the elements increase monotonically with mass. Essentially none of the other surface spectroscopies exhibit this simplicity. Because of this simple relationship, it is possible to mathematically manipulate the entire ISS spectrum such that the signal intensity is a direct quantitative representation of the surface. This is illustrated in Figure 5, which shows a depth profile of clean electrical connector pins. Atomic concentration can be read roughly as atomic percent direcdy from the approximate scale at the left. 

SIMS is by far the most sensitive surface technique, but also the most difficult one to quantify. SIMS is very popular in materials research for making concentration depth profiles and chemical maps of the surface. The principle of SIMS is conceptually simple A primary ion beam (Ar+, 0.5-5 keV) is used to sputter atoms, ions and molecular fragments from the surface which are consequently analyzed with a mass spectrometer. It is as if one scratches some material from the surface and puts it in a mass spectrometer to see what elements are present. However, the theory behind SIMS is far from simple. In particular the formation of ions upon sputtering in or near the surface is hardly understood. The interested reader will find a wealth of information on SIMS in the books by Benninghoven et al. [2J and Vickerman el al. [4], while many applications have been described by Briggs et al. [5]. 

For calculating atomic concentration ratios of the elements, photoionization cross-section by Scofield (4) and apparatus function by VuUi (5) were adopted. Electron escape depth (a) is determined by an experimental equation A =e0 7 (where E is kinetic energy of the electron) proposed by Hirokawa, et. al. (6). 

Depth profiles are usually presented as atomic concentrations versus sputter time, assuming we know the rate at which the sample sputters. A typical depth profile is shown in Figure 25. It is interesting to see that at the surface there is carbon, silicon dioxide and some molybdenum. As soon as the surface layer is sputtered off (300 A), the oxygen and carbon impurities drop to constant and small values. For this CVD film, the molybdenum silicide came out to be very silicon rich. We can also see that the stoichiometry of the silicide changed with position (depth) in the film. 

Fig. 12.58. XPS atomic concentration profile of the passive film of Al alloys as a function of sputtering depth (a)...

The formation of a rare earth metal oxide on the metal surface, impedes the cathodic reduction of oxygen and thus cathodic inhibition is achieved by the addition of a rare earth metal salt to a system. The surface atom concentration ratio, [Ce/Ce + M], where M is Fe, Al or Zn, is a function of cerium oxide film thickness determined by AES depth profiles as shown in Fig. 12.2. 

Ion etching). They are utilized to determine the composition of specimens as a function of depth. The units along the abscissa are normally sputter time. Sputter time can be converted to depth If the sputter rate of the material Is known. The units along the ordinate are normally Auger signal Intensities or calculated atomic concentrations. 

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