Secondary ionization mass spectrometry SIMS

Earlier DI techniques include fast atom bombardment (FAB), secondary ionization mass spectrometry (SIMS), plasma desorption, and field desorption. Since their applications are primarily qualitative, they will not be discussed here. 

Early in the history of mass spectrometry (MS), large biomolecules were not analyzed because efficient methods to transport these molecules into the gas phase were unknown. Degradation typically occurred during vaporization of these nonvolatile molecules so that electron ionization of the intact molecular ion was not possible. Ionization by fast atom bombardment (FAB), field desorption (FD), secondary ionization mass spectrometry (SIMS), and plasma desorption (PD)" from the radioactive decay of Cf finally made the ionization and analysis of peptides possible. These latter techniques, although still used today, are not as popular as electrospray... 

Secondary ionization mass spectrometry (SIMS) is yet another method to analyze solid samples directly. SIMS uses a focused beam of ions (called the primary ion beam) to sputter atoms from the surface of a sample. A small fraction of the sputtered atoms are ionized by the sputtering action, hence the term secondary ionization. The secondary ions are extracted, accelerated, and analyzed by a mass analyzer. Two main configurations exist conventional SIMS, which uses electric... 

Seaborg, Glenn, 339, 342-343, 351 secondary ionization mass spectrometry (SIMS),... 

To measure Pb concentrations in small particles such as aerosols, or to study the variation in Pb concentrations within sohds such as mineral grains, there is a range in available techniques such as micro-beam XRF (including synchrotron methods), proton induced X-ray emission spectrometry (PIXE), secondary ionization mass spectrometry (SIMS), and laser ablation ICP-MS (LA-ICP-MS). These methods have been used for high spatial resolution even in 3-D, as well as for rapid analyses of biological or geological structures growing incrementally [39-43] or small, specihc phases [44]. 

Chemical reactions at the gas-surface interface can be followed by monitoring gas-phase products with, for example, a mass spectrometer, or by directly analyzing the surface with a spectroscopic technique such as Auger electron spectroscopy (AES), photoelectron spectroscopy (PES), or electron energy loss spectroscopy (EELS), all of which involve energy analysis of electrons, or by secondary ionization mass spectrometry (SIMS), which examines the masses of ions ejected by ion bombardment. Another widely used surface probe is low-energy electron diffraction (LEED), which can provide structural information via electron diffraction patterns. At the gas-liquid interface, optical reflection elHpsometry and optical spectroscopies are employed, such as Eourier transform infrared (ET IK) and laser Raman spectroscopies. 

At the present time, the most up-to-date methods of ionization in TLC/MS are FAB and secondary ionization mass spectrometry (SIMS) in which organic molecules are sputtered from the surface by impact of a stream of high-energy molecules, and laser desorption (LD) in which sputtering of organic molecules from the surface of a support is due to the influence of high thermal energy produced by a laser beam onto a plate surface. The ions produced this way are usually even-electron (M + H) and appear by means of chemical ionization. The interpretation of the spectrum follows the same lines. 

The desorption/ablation aspect of MALDl has been the object of an excellent review by Dreisewerd. Among the most basic functions of the matrix is absorption of the laser energy and conversion of most of it to heat. Subsequent matrix vaporization is sufficiently forceful that it entrains and ejects analyte that has been cocrystaUized in or on the matrix. The time scale is not as short as in fast atom bombardment (FAB) or secondary ionization mass spectrometry (SIMS) because the typical MALDl lasers used emit pulses of a few to hundreds of nanoseconds duration (e.g., N2 337 nm, 3 ns or tripled Nd YAG, 355 nm, 4—7 ns, Er YAG, 2.98 pm, 200 ns, although a range of pulse lengths has been studied ). This is slow compared to intramolecular motions. In UV MALDl, the energy conversion step is... 

Static Secondary Ion Mass Spectrometry (SIMS) involves the bombardment of a sample with an energetic (typically 1-10 keV) beam of particles, which may be either ions or neutrals. As a result of the interaction of these primary particles with the sample, species are ejected that have become ionized. These ejected species, known as secondary ions, are the analytical signal in SIMS. 

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. 

In other articles in this section, a method of analysis is described called Secondary Ion Mass Spectrometry (SIMS), in which material is sputtered from a surface using an ion beam and the minor components that are ejected as positive or negative ions are analyzed by a mass spectrometer. Over the past few years, methods that post-ion-ize the major neutral components ejected from surfaces under ion-beam or laser bombardment have been introduced because of the improved quantitative aspects obtainable by analyzing the major ejected channel. These techniques include SALI, Sputter-Initiated Resonance Ionization Spectroscopy (SIRIS), and Sputtered Neutral Mass Spectrometry (SNMS) or electron-gas post-ionization. Post-ionization techniques for surface analysis have received widespread interest because of their increased sensitivity, compared to more traditional surface analysis techniques, such as X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES), and their more reliable quantitation, compared to SIMS. 

There is a branch of MS specially designed for dealing with the analysis of inorganic materials.[21,22] Different specific ionization techniques, such as inductively coupled plasma mass spectrometry (ICP-MS),[23] glow discharge mass spectrometry (GD-MS)[24] and secondary ion mass spectrometry (SIMS),[25] are available and they are widely used in cultural heritage applications. Their description is beyond the scope of this chapter. 

As for silicon, secondary ion mass spectrometry (SIMS) is the most widely used profiling analysis technique for deuterium diffusion studies in III-V compounds. Deuterium advantageously replaces hydrogen for lowering the detection limit. The investigations of donor and acceptor neutralization effects have been usually performed through electrical measurements, low temperature photoluminescence, photothermal ionization spectroscopy (PTIS) and infrared absorption spectroscopy. These spectroscopic investigations will be treated in a separated part of this chapter. 

Secondary ion (mass spectrometry) SIMS Particle induced desorption/ ionization Nonvolatile molecular ions Semiconductors Surface analysis Imaging... 

Mass spectrometry is traditionally a gas phase technique for the analysis of relatively volatile samples. Effluents from gas chromatographs are already in a suitable form and other readily vaporized samples could be fairly easily accommodated. However the coupling of mass spectrometry to liquid streams, e.g. HPLC and capillary electrophoresis, posed a new problem and several different methods are now in use. These include the spray methods mentioned below and bombarding with atoms (fast atom bombardment, FAB) or ions (secondary-ion mass spectrometry, SIMS). The part of the instrument in which ionization of the neutral molecules occurs is called the ion source. The commonest method of... 

The principle of FAB, less frequently referred to as liquid secondary ionization mass spectrometry (LSIMS), is very similar to secondary-ion mass spectrometry (SIMS). However, FAB utilizes a liquid matrix, such as glycerol, in which a sample is dissolved. The matrix is used to enhance sensitivity and ion current stability. 

A striking feature of the ILs is their low vapor pressure. This, on the other hand, is a factor hampering their investigation by MS. For example, a technique like electron impact (El) MS, based on thermal evaporation of the sample prior to ionization of the vaporized analyte by collision with an electron beam, has only rarely been applied for the analysis of this class of compounds. In contrast, nonthermal ionization methods, like fast atom bombardment (FAB), secondary ion mass spectrometry (SIMS), atmospheric pressure chemical ionization (APCI), ESI, and MALDI suit better for this purpose. Measurement on the atomic level after burning the sample in a hot plasma (up to 8000°C), as realized in inductively coupled plasma (ICP) MS, has up to now only rarely been applied in the field of IE (characterization of gold particles dissolved in IE [1]). This method will potentially attract more interest in the future, especially, when the coupling of this method with chromatographic separations becomes a routine method. 

---