Advantages of single-photon ionization over multiphoton ionization for mass-spectrometric surface analysis of bulk organic polymers

• Published in: Analytical chemistry (Washington) 1989-04, Vol.61 (8), p.805-811
• Main Authors: Pallix, Joan B, Schuhle, Udo, Becker, Christopher H, Huestis, David L
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Physicochemistry of polymers; Polymers and radiations; Properties and characterization
• ISSN: 0003-2700; 1520-6882
• DOI: 10.1021/ac00183a005

Several bulk organic polymers have been analyzed with surface analysis by laser ionization (SALI) employing pulsed ion beam sputtering or electron-stimulated desorption for material removal. Previously, nonresonant multiphoton ionization (MPI) of sputtered neutral species coupled with time-of-flight mass analysis has been shown to provide high sensitivity and reliable quantitation for the elemental analysis of inorganic materials. However, multiple photon absorption can cause excessive and nonspecific fragmentation of organic species to the detriment of molecular analysis. This fragmentation problem is alleviated through the use of single-photon ionization with pulsed coherent vacuum ultraviolet radiation at 118 nm (10.5 eV). To avoid sample damage due to the sputtering process itself, the primary ion beam dose was kept < 10 exp 13 ions/cm exp 2 during analysis. Electron-stimulated desorption can result in much less nonspecific fragmentation than ion-stimulated desorption. The characteristics of single-photon as opposed to multiphoton ionization are discussed, with an emphasis on the more representative mass spectra for single-photon ionization. Characteristic and readily interpretable mass spectra are shown for bulk samples of poly(methyl methacrylate), poly(ethylene glycol), and polystyrene. 32 ref.--AA