SIMS popularity,

Secondary ion mass spectrometry (SIMS) is by far the most sensitive surface teclmique, 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. For a more extensive treatment of SIMS the reader is referred to [3] and [14. 15 and 16]. The principle of SIMS is conceptually simple When a surface is exposed to a beam of ions... 

As in Auger spectroscopy, SIMS can be used to make concentration depth profiles and, by rastering the ion beam over the surface, to make chemical maps of certain elements. More recently, SIMS has become very popular in the characterization of polymer surfaces [14,15 and 16]. 

There are now several different types of machines that are all capable of microanalysis. All have advantages and disadvantages, but the choice of which to use is often governed by expense and availability to a particular institution. Electron probe microanalysis is by far the most popular, but here particle-induced X-ray emission (PIXE), the laser microprobe mass analyzer (LAMMA), electron energy loss spectroscopy (EELS), and secondary ion mass spectrometry (SIMS) are also considered. 

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]. 

GC/MS(/MS) is also popular for quantifying DBFs. Selected ion monitoring (SIM) or multiple reaction monitoring (MRM) mode are used with GC/MS and GC/ MS/MS, respectively, to maximize the sensitivity and provide low detection limits. Some EFA Methods utilize GC/MS, including EFA Method 524.2, which uses GC/ EI-MS for THM analysis [155], and EFA Method 521, which uses for GC/CI-MS/ MS for nitrosamine analysis [55]. In addition, many priority unregulated DBFs have been measured using GC/MS in a U.S. Nationwide Occurrence Study [11,12]. 

Owing to their unique and delicate flavour, species of the genus Passiflora have been the subject of intensive research on their volatile constituents [13]. The purple passion fruit (Passiflora edulis Sims) is a tropical fruit native to Brazil but is now grown in most tropical and subtropical countries [50]. Purple passion fruit is cultivated in Australia, India, Sri Lanka, New Zealand, and South Africa [48]. Yellow passion fruit (Passiflora edulis t flavicarpa) is one of the most popular and best known tropical fruits, having a floral, estery aroma with an exotic tropical sulfury note [62]. Yellow passion fruit is cultivated in Brazil, Hawaii, Fiji, and Taiwan [48]. Because of its more desirable flavour, the purple passion fruit is preferred for consumption as fresh fruit, whereas the yellow passion fruit is considered more suitable for processing [28]. 

The method of defining RSFs described is traditional in analytical chemistry, generates RSFs without units, results in larger numbers for elements for which the SIMS instrument is more sensitive, and is essentially the same as Wittmaack s proposed use of scaled sensitivity ratios [100]. However, an alternative definition of sensitivity factors that has gained much popularity with semiconductor specialists is that of Wilson [69,101] ... 

The most common species used with SIMS sources are Ar+, 02+, 0 , and N2+. These ions and other permanent gas ions are formed easily with high brightness and stability with the hollow cathode duoplasmatron. Ar+ does not enhance the formation of secondary ions but is popular in static SIMS, in which analysis of the undisturbed surface is the goal and no enhancement is necessary. 02+ and 0 both enhance positive secondary ion count rates by formation of surface oxides that serve to increase and control the work function of the surface. 02+ forms a more intense beam than 0 and thus is used preferentially, except in the case of analyzing insulators (see Chapter 11). In some cases the sample surface is flooded with 02 gas for surface control and secondary ion enhancement. An N2+ beam enhances secondary ion formation, but not as well as 02+. It is very useful for profiling and analysis of oxide films on metals, however. It also is less damaging to duoplasmatron hollow cathodes and extends their life by a factor of 5 or more compared to oxygen. 

SIMS instruments are generally grouped by type of secondary analyzer as well as by imaging type. Three general types enjoy wide popularity, and each has its distinct advantages. They are the magnetic sector, the quadrupole, and the time-of-flight (TOF). 

The most popular of these are secondary ion mass spectroscopy (SIMS), ion scattering spectroscopy (ISS), and Auger electron spectroscopy (AES) which have been developed by investigators such as Baun, McDevitt, and Solomon.16-20 These tools have proved practical even when the surface films are only on the order of atomic dimensions or when the failure occurred near the original interface and included parts of both the adhesive and the adherend. 

In the first place there is a host of surface spectroscopies. Some important ones have been discussed in sec. 1.7.II. Adamson gives a list of several tens of approaches and variants ). Most widely used are X-ray photoelectron spectroscopy (XPS), also called electron spectroscopy for chemical analysis (ESCA), Auger electron spectroscopy (AES), and secondary ion mass spectroscopy (SIMS) and. to a lesser extent, ion scattering spectroscopy (ISS). The main characteristics of these techniques have been collected in table 1.7.4. Other techniques may be more widely used in certain areas. For example, XPS is very popular in heterogeneous catalysis. 

The CCSD results of Salek et al (2005) and the MCSCF results of Luo et al (1993) compute the frequency dependence as an intrinsic part of the correlated calculation. The work of Sim et alP (1993) and Reiss et al. (2005) takes the static value obtained at the MP2 level and scales it using the RPA method to get the frequency dependence. Luo et alP (1993) also report the result of an RHF/RPA calculation where the frequency dependence is the natural extension of the RHF method. The plotted points are at the four readily available laser frequencies that have been used in almost all experimental work. The most popular of these has been the YAG frequency corresponding to 1.17 eV or 1064 nm. At this frequency the spread of results ranges from about 1550 to 2600 au. If only the two fully frequency-dependent correlated calculations are considered the range is from about 1700 to 2600 au. Salek et al, using the CCSD method find that as the frequency is increased from zero to 1.17 eV, increases from 1736 to 2667 au and Luo et al, using MCSCF, from 1373 to 1898 au. 

Let the basis set still be the BO states starting points. Sim we wish to focus upon all the diverse molecular phenomena which are classify as involving radiationless processes, it is necessary to center attention upon th molecule. This focus is best obtained by considering the effective Hamiltoniar Hett, for the molecule which accounts for all relaxation mechanisms other tha the intramolecular nonradiative decay. (The use of effective Hamiltonians is popular in considering the relaxation processes associated with studies of magnetic resonance 37L) For the present case, the effective Hamiltonian is 16>17)... 

Table 8.2 compares the main parameters of three mass analyzers. From Table 8.2 we can understand the reasons that the ToF analyzer has become so popular for static SIMS it provides high resolution, high transmission and high sensitivity. The major shortcoming of the ToF analyzer is its use of pulse primary ions. The ratio of primary beam on- to off-time is only about 10-4. Thus, it is not efficient for analysis such as depth profiling of chemical elements. 

ToF SIMS separated ion beams are used for etching and analysis purposes. A depth profile is obtained by periodically switching between etching and analysis. In addition, the pulse mode operation in ToF SIMS further slows down the process. ToF SIMS, however, can be used to obtain more accurate depth profiles if time is not a concern. The next section introduces depth profiling based on the dynamic SIMS technique, which is very popular in analyzing electronic materials. 

All methods have their different strengths and limitations, which are summarized in Table 2. When compared to SIMS and DESI, MALDI-MSI provides a good tradeoff between spatial resolution and sensitivity for equally small and higher mass molecules. In addition, as the MALDI instrumentation is commercially available at an affordable cost, this is the most popular MSI method. Consequently, the focus of this chapter is on the MALDI-MSI technique. 

Various techniques are used for these measurements. The most popular are capacitance-voltage (C-V) profiling, spreading resistance and secondary ion mass spectroscopy (SIMS). SIMS is not a strictly electrical characterization technique, but is included here because it is routinely used to measure the dopant atom distribution. The basis for these three techniques are very different and I will briefly describe them. 

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