ISS spectra

Although the XPS technique is important for determining the composition and oxidation states, also is for the metal dispersion of supported catalysts. Indeed, the 

ISS and XPS techniques have been used in order to obtain a better measure of the distribution of an oxide or metallic phase onto a porous stmcture support and so also determine the degree of coverage. 

As example, Zr02/Al203 samples were prepared with different Zr02 contents [1, 5, 10, and 20% (W)] onto alumina support. On these samples 1 % Pt was impregnated and submitted for XPS and ISS analyses [8]. 

The relative intensities of lAl/ IZr, determined by XPS and ISS, are displayed in Fig. 11.7, as function of the atomic bulk ratio Zr/Al. The intensity ratio of lAl/IZr increased linearly with increasing concentration of zirconia on the alumina surface up to 10% (weight) and then decreases due to nucleation of zirconia crystallites. That suggests the formation of a zirconia monolayer on the alumina surface for concentrations between 10 and 20 % of zirconia. 

ISS and XPS results show the formation of monolayer of zirconia on alumina for Zr02 content between 10 and 20 % Zr02. That is, the maximum surface concentration of zirconia on the alumina is not related to how the zirconia is impregnated, but of formation of crystals which is strongly dependent on the preparation method. 

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When all of the ISS spectra are plotted in a three-dimensional manner, such as the z- plot shown in Figure 3, the changes in surface composition with depth are much more obvious. In this figure, each spectrum represents the composition at a different cross section of the total depth sputtered, hence the spectra are plotted at different depths. Note that the spectra are not recorded at identical incremental depths. 

An example of the non individualistic nature of ISS spectra from polymers is seen in Figure 7 where data are shown for a simple linear hydrocarbon, polyethylene, and compared to data obtained under identical conditions for graphite. As can be seen, one would be hard pressed to identify the polymer here. Naturally, it would be even more difficult to identify individual polymers. 

The single scattering peaks are superimposed on the tail of this low energy peak and their intensities are very weak. As expected, an increase of the ion dose used for the ISS spectra accumulation improves the signal/noise ratio for the... 

In this method a surface is bombarded with noble gas ions, and the kinetic energy of the ions is measured after impact with the surface [21, 31]. In simple terms, this can be regarded as playing billiards with the uppermost atoms of the surface. Since the mass and energy of the noble gas ions prior to impact are known, mechanical energy and impulse equations can be used to calculate the mass of the impacted surface atom. In this way a sort of elemental analysis of the uppermost atomic layer is obtained. A disadvantage is that the lines in ISS spectra are relatively broad, and information about bonding is not obtained. 

Comparing the ISS spectra of an unused and a used silver catalyst for ethylene oxide synthesis shows how the alkali metal promoter on the catalyst behaves during the process (Fig. 5-50). In time, the alkali metal promoter spreads across the surface of the catalyst [25]. 

In the case of Cu deposition, the initial persistence of the PET pealcs is believed to be related to Cu penetration into the polymer. A confirmation of the Cu atom incorporation underneath the PET surface has been obtained by Ion Scattering measurements. For Al deposited on PET, the ISS spectra show a well-defined single scattering peak due to collisions with Al surface atoms, whereas in the case of Cu deposition, only a broad distribution with a high energy edge at Che Cu kinematic factor is observed. This indicates that essentially no Cu atoms are present in the uppermost monolayer since mainly inelastic and multiple collisions sequences are detected. Diffusion of Cu into the polymer bulk has also been mentioned in the literature for polyimide B substrates. 

Figure 63. Curve synthesis method applied to the ISS spectra from the catalyst CoMoS - y-AUO3 after heat treatment at 800 °C [203]...

Figure 64. Sequence of ISS spectra from an Fe53 - Ni47 alloy passivated in I mol/L NaOH (rp = 5 min, p= 0.44 V), during depth profiling [211]...

Figure 65. ISS spectra from NijAl (001) after exposure to oxygen at 2x10 Pa and 700 °C [214] a) Clean b) 1-s Exposure c) 15-s Exposure d) 100-s Exposure...

Figure 66. ISS spectra from a tungsten surface containing oxygen and barium, using a mixture of He and Ne to analyze for oxygen as well as separate barium and tungsten 1215]...

FIGURE 26. ISS spectra (a) from the original surface and (b) from the surface after stripping the gold. Reprinted with permission from Reference 33. Copyright 1981 Gordon and Breach Science Publishers. 

FIGURE 27. ISS spectra of CRS after (a) 3 min and (b) 7 min of sputtering ISS spectra of DQSK after (c) 3 min and (d) 7 min of sputtering at a sputter rate of 1-2 A/min. Reprinted with permission from Reference 31. Copyright 1986 Gordon and Breach Science Publishers. 

The locus of failure of epoxy bonded aluminum wedge samples was investigated by both SIMS and ISS. Figure 30 shows a spectrum from each technique from a selected area of the wedge sample. The appearance of chromium in both the SIMS and ISS spectra from area C suggested interfacial failure at the original etched alloy surface. 

Figure 52. ISS spectra recorded from polycrystalline Al metal, and from an AI2O3 film of thickness 5 nm on Al metal. (From Ref. 135.)...

Figure 53. Calculated Mg ISS spectra as from a DPCMA for 2 keV He+ incident on a Mg surface, using a scattering angle width of ° and primary ion beam FWHM of (a) 10, (b) 20, (c) 50 and (d) 90 eV. (From Ref. 136.)...

Some types of spectral features are common to nearly all ISS spectra. For example, in the spectra recorded from the Ag/a-AFOj ethylene epoxidation catalysts shown in Fig. 47, there are elemental features due to elastic scattering from atoms in the outermost atomic layer and there is a background due to niul-tiply scattered ions which have penetrated beneath the surface. In addition there... 

Figure 57. Nonnalized ISS spectra of He+ scattered from Al at incident energies of 1 and 4 keV. (From Ref. 137.)...

Figure 58. ISS spectra recorded from a platinized tin oxide surface (a) after insertion into the vacuum system, and after annealing in vacuum at (b) 300°C and (c) 450 C. (From Ref. 147.)...

Figure 62, ISS spectra recorded from a polycrystalline Ni/Cr alloy surface using I keV Ne+ (a) after cleaning by sputtering and annealing, (b) after exposing the cleaned surface to 100 L of Oi at room temperature, (c) immediately after heating the O-exposed sample to 500°C, and after annealing the 0-exposed sample at, WC for (d) O.. h, (e) 1 h, (f) 2 h and (g) 4 h. (From Ref. 149.)...

Figure 63. ISS spectra recorded using 4 keV He. scattered from clean Pd (a) before and (b) after a 30 min treatment in 3 x 10- Pa of Hi. (From Ref. 150.)...

Figure 64. He+ ISS spectra recorded from an H/Si (lOO)-(l x 1) surface prepared by exposing Si(lOO) to atomic hydrogen at room temperature. The peaks labeled D and D are the. scattering peaks from surface hydrogen, A is from Si, B is from O or C and G is recoil from H or O. (From Ref. 131.)...

Figure 65. ISS spectra recorded from carbon at a scattering angle of 138 using 2 keV He and He. (From Ref. 152.)...

The experimental geometry al.so has a strong influence on the elemental sensitivities. ISS spectra obtained from polycrystalline Ag after numerous sputtering and annealing treatments [153] are shown in Fig. 68. Forward-scattered and backscattered ion spectra obtained from the same surface are compared. In-... 

Figure 68. Forward- and backscattered ISS spectra recorded from the same Ag surface using a DPCMA after numerous sputtering and annealing treatments of the sample. (From Ref. 153.)...

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