Secondary neutral mass spectroscopies

The control of materials purity and of environmental conditions requires to implement physico-chemical analysis tools like ESC A, RBS, AUGER, SEM, XTM, SIMS or others. The principle of SIMS (Secondary Ion Mass Spectroscopy) is shown in Eig. 31 an ion gun projects common ions (like 0+, Ar+, Cs+, Ga+,. ..) onto the sample to analyze. In the same time a flood gun projects an electron beam on the sample to neutralize the clusters. The sample surface ejects electrons, which are detected with a scintillator, and secondary ions which are detected by mass spectrometry with a magnetic quadrupole. 

We will first consider, however, Secondary Ion Mass Spectroscopy (SIMS) in which both neutral and charged species are sputtered from the surface, and detected by means of a mass spectrometer. This involves ion beams of lower energy than in the techniques described previously. 

Resonant and non-resonant laser post-ionization of sputtered uranium atoms using SIRIS (sputtered initited resonance ionization spectroscopy) and SNMS (secondary neutral mass spectrometry) in one instrument for the characterization of sub-pm sized single microparticles was suggested by Erdmann et al.94 Resonant ionization mass spectrometry allows a selective and sensitive isotope analysis without isobaric interferences as demonstrated for the ultratrace analysis of plutonium from bulk samples.94 Unfortunately, no instrumental equipment combining both techniques is commercially available. 

Secondary ion mass spectrometry (SIMS) Secondary neutral mass spectrometry (SNMS) Ion-scattering spectroscopy (ISS)... 

Hi) Methods based on mass spectrometry Spark-source mass spectrometry Glow-discharge mass spectrometry Inductively coupled-plasma mass spectrometry Electro-thermal vaporization-lCP-MS Thermal-ionization mass spectrometry Accelerator mass spectrometry Secondary-ion mass spectrometry Secondary neutral mass spectrometry Laser mass spectrometry Resonance-ionization mass spectrometry Sputter-initiated resonance-ionization spectroscopy Laser-ablation resonance-ionization spectroscopy... 

Ions have greater masses than electrons thus their transfer of energy to surface species is much more efficient. Ions incident on surfaces can break chemical bonds and eject atoms, molecules, or molecular clusters. Most of these species are neutral, but the ion impact may also ionize a fraction of these ejected particles. The detection of these ions, called secondary-ion mass spectroscopy (SIMS), is an important technique of surface-composition analysis. Ion bombardment is used frequently to remove unwanted molecular or atomic layers of impurities in order to clean a surface efficiently. Ion sputtering is also used to deposit thin films of the bombarded material... 

FIGURE 40.18 Depth profiles by laser secondary neutral mass spectrometry (laser SNMS), secondary ion mass spectrometry (SIMS) with Ar and 02 primary ions, and Auger electron spectroscopy (AES) of implanted boron. Reprinted from Higashi, Y., Quantitative depth profiling by laser-ionization sputtered neutral mass spectrometry (1999) Spectrochimica Acta Part B Atomic Spectroscopy, 54(1), 109-122. Copyright (1999), with permission from Elsevier Science. 

Oechsner, H., Muller, M. (1999) INA-X a novel instrn-ment for electron-gas secondary neutral mass spectrometry with optional in situ x-ray photoelectron spectroscopy. Journal of Vacuum Science Technology A Vacuum, Surfaces, and Films, 17,3401-3405. 

There are several MS-based techniques that can provide chemical information for thin and thick layers [12]. For very thin layers (sub to 1-2 monolayers), nondestructive techniques such as static SIMS [13], ion scattering MS [14], or MS of recoiled ions [15] are suitable. These techniques are also the best adapted for examining surface contamination. They are all based on surface interactions of an ion beam with the solid surface. For depth profiling of thin and thick layers, MS is associated with a destructive source of neutrals or ions dynamic SIMS, secondary neutron mass spectroscopy (SNMS), glow discharge mass spectroscopy (GD-MS), matrix-enhanced SIMS, laser desorption/ionization MS, and desorption electrospray ionization (DESI) MS [16]. Ions are either desorbed from the solid surface or generated by postionization of neutrals sputtered off the surface. 

Secondary ion mass spectrometry (SIMS), secondary neutral mass spectrometry (SNMS), Auger electron spectroscopy (AES) and x-ray photoelectron spectro.scopy (XPS) can provide depth-.selective elemental profiles, but the... 

Secondary ion mass spectroscopy is the third of the three most common surface analysis techniques. In SIMS, the sample is irradiated with a primary ion beam (normally argon), the impact of which sputters away the surface atoms, some as neutrals and others as ions. Those atoms which become ionized are then detected in a mass spectrometer, where their masses are measured. 

Based on the Al implantation studies of Schilling et al. [73], who observed an increase in the intensity of the 3.3605 eV (,) emission line with increased Al concentration in ZnO, the (, transition is attributed to the Al impurity. Secondary ion mass spectroscopy (SIMS) revealed that Al was the dominant impurity with a concentration of more than one order of magnitude higher than that for other group III and group VII elements for samples where only the 3.3605 eV neutral donor-bound exciton line was observed [65]. Al was suggested to be an omnipresent impurity in vapor-grown ZnO [67]. 

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. 

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. 

Another important characteristic is that ion beams can produce a variety of the secondary particles/photons such as secondary ions/atoms, electrons, positrons. X-rays, gamma rays, and so on, which enable us to use ion beams as analytical probes. Ion beam analyses are characterized by the respectively detected secondary species, such as secondary ion mass spectrometry (SIMS), sputtered neutral mass spectrometry (SNMS), electron spectroscopy, particle-induced X-ray emission (PIXE), nuclear reaction analyses (NRA), positron emission tomography (PET), and so on. 

There are several methods available to probe the actual interphase to demonstrate the existence of interpenetrating networks directly. Among these techniques are depth profiling by SIMS (secondary ion mass spectrometry) or SNMS (sputtered neutral mass spectrometry), and the use of X-ray photoelectron spectroscopy (XPS) depth profiling or Auger electron spectroscopy (AES) depth profiling. 

In the FIM the ions are generated at the surface from incident neutrals. In other ion-probe methods the incident beam is already ionized and three major features may be distinguished when it interacts with a surface sputtering and desorption, ion neutralization, and ion scattering. Detection of secondary ions forms the basis of secondary-ion mass spectrometry (SIMS) which is well established as a technique for surface analysis (see ref 208 for a previous review in this series) while ion-neutralization spectroscopy (INS) yields both structural and bonding information on surface species (see ref 209). 

Fig. 1. Experimental techniques available for surface studies. SEM = Scanning electron microscopy (all modes) AES = Auger electron spectroscopy LEED = low energy electron diffraction RHEED = reflection high energy electron diffraction ESD = electron stimulated desorption X(U)PS = X-ray (UV) photoelectron spectroscopy ELS = electron loss spectroscopy RBS = Rutherford back scattering LEIS = low energy ion scattering SIMS = secondary ion mass spectrometry INS = ion neutralization spectroscopy.

---