Time-of-Flight Secondary Ion Mass Spectrometry ToF SIMS

Static Secondary Ion Mass Spectrometry (S-SIMS) is a more sensitive (sensitivity of 10 atoms/cm ) surface analysis technique than X ray Photoelectron Spectroscopy (10 atoms/cm ) [6,18]. Under primary bombardment with a focused ion beam the solid surface emits secondary particles. As illustrated in Fig. 5, the bom bardment with primary ions such as Ga, Ar, or other molecular ion sources like SF5 [19-21] or C0O [22], which should enhance molecular ion formation at high masses vs fragmentation, provokes the emission of neutral, positively, or negatively charged fragments and clusters. 

In SIMS, one distinguishes between the static and the dynamic modes. In static SIMS only a fraction of the first monolayer of the surface layer Is perturbed. This depends on the flux of the primary Ion beam, which Is kept well below 10 par-ticles/cm. This number corresponds to l%o of the number of particles of the first monolayer, which is approximately 10 particles. Past this limit, degradation signatures can be detected. During further bombardment the top-surface will then be completely destroyed, leading to a depth profile type of Information (dynamic mode). 

The intensity 1 for emitted positively or negatively charged secondary ions measured for a given target is described by the following equation  

Here Ip is the primary Ion current, the total neutral sputter yield of species A in the matrix M, (M) the Ionization probability of species A in the matrix M, the isotopic abundance of element A, cy the atomic concentration, andqs an in strumental constant. ly may vary over several orders of magnitude. Due to its high sensitivity, surface contamination may influence it strongly. Furthermore, is very dependent upon matrix effects that influence strongly the number of emitted ions compared to emitted neutrals. Their ratio is typically 10 or smaller for polymers and biomaterials [23]. The influence of the matrix on the ionization represents the severest limitation of this technique for quantitative analysis of both inorganic and organic materials. 

The relation between acceleration voltage, Vg, , and kinetic energy, Ei i, of the secondary Ions Is developed into 

1 Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) 

Instrumentation for carrying out this mass spectrometric technique is discussed in Appendix 1. 

SIMS is the most commonly used of the surface mass spectrometry techniques. SIMS analyses the secondary ions ejected from a sample following bomhardment with a primary ion beam, usually argon ions. The impact of the primary ion causes an atomic-scale collision cascade within the surface layers of the sample and, at points remote from impact, secondary ions are ejected from the surface. These ions are then determined by MS. 

There are two modes of operating SIMS static and dynamic. 

Static SIMS (SSIMS). This operates under non-damaging conditions. It gives good information on molecular content and, like Auger spectroscopy, can be used for surface micro-analysis at high spatial resolution. 

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The use of separation techniques, such as gel permeation and high pressure Hquid chromatography interfaced with sensitive, silicon-specific aas or ICP detectors, has been particularly advantageous for the analysis of siUcones in environmental extracts (469,483—486). Supercritical fluid chromatography coupled with various detection devices is effective for the separation of siUcone oligomers that have molecular weights less than 3000 Da. Time-of-flight secondary ion mass spectrometry (TOF-sims) is appHcable up to 10,000 Da (487). 

J. Batcheller, A. M. Hacke, R. Mitchell and C. M. Carr, Investigation into the nature of historical tapestries using time of flight secondary ion mass spectrometry (ToF SIMS), Applied Surface Science, 252, 7113 7116(2006). 

R. N. S. Sodhi. Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) Versatility in Chemical and Imaging Surface Analysis. Analyst, 129(2004) 483-487. 

A sample of a composition, nominally containing 22 ppm silver in water, was analyzed by time-of-flight secondary ion mass spectrometry (TOF-SIMS) in order to determine the form of silver in the composition. The conclusion is that the bulk of the silver exists as silver (0) [that is, metallic silver] and that there is a surface coating which as on average a composition of silver (II) oxide [AgO]. As mentioned above silver (II) oxide is usually a stoichiometric combination of silver (I) and silver (III). 

Time Of Flight Secondary Ion Mass Spectrometry (TOF SIMS) analyses of Ecat and RV4+ from a commercial trial. Show that while the vanadium concentration may be higher on the surface of the particles, vanadium is found throughout the RV4+ particle, not only on the outer surface. The SIMS scan also shows that vanadium is found throughout the catalyst particle as well. This shows that over time, there is intraparticle mobility of vanadium in both catalyst and RV4+ particles[5]. 

Suitable methods to reveal the surface chemistry of modified materials include X-ray photoelearon spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). XPS speara are obtained by irradiating materials with X-ray beams, while simultaneously measuring the kinetic energy and number of electrons escaping from the top 1 to lOnm of the material s surface being analyzed. Qualitative information from the measured chemical shifts allows the identification of surface functionality, quantitative analysis... 

Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) is a surface analysis technique used to analyze mass and image constituents that are present on the surface of materials. The equipment (Figure 12.47) uses a pulsed primary ion beam to desorb and ionize species from the sample surface. The resulting secondary ions are accelerated into a mass spectrometer and analyzed by measuring the ToF from the sample surface to the deteetor. The location and distribution of the species on the surface can be identified and an image shown at the detector. The composition is determined from the mass spectrum. Many different primary sources can be used for ionization ... 

For environmental reasons, direct examination of polymers by spectroscopy and/or by non-destructive methods is preferred over solvent-consuming techniques.Poleunis et al. " reported the use of time-of-flight secondary ion mass spectrometry (ToF-SIMS) to analyze additive migration toward polymer surface in thin films of amorphous polyester containing variable quantities of an antioxidant (Irgafos 168) and a UV stabilizer (Hostavin N30). The results obtained were promising, but authors stated that ToF-SlMS data can be compared quantitatively only if the surfaces have undergone identical treatments. 

Zeng and Bruckenstein [383] have studied UPD of Cu at polycrystalline gold in 0.1 M NH3 + 0.1 M NaCl04 electrolyte using the rotating disk electrode, electrochemical quartz crystal microbalance, and time-of-flight secondary ion mass spectrometry (TOF-SIMS). The experiments have revealed that Cu(0) UPD occurs in the potential range —0.4 V <... 

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