Surface analysis 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. 

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... 

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. 

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. 

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). 

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. 

Ions Ion-induced X-ray spectroscopy (IIX) Proton-induced X-ray spectroscopy (PIX) Surface composition by analysis of neutral species and ion-impact radiation (SCANIIR) Glow-discharge optical spectroscopy (GDOS) Ion-neutralization spectroscopy (INS) Ion-induced Auger electron spectroscopy (lAES) Secondary-ion mass spectrometry (SIMS) Ion-scattering spectroscopy (ISS) Rutherford backscatter spectroscopy (RBS)... 

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