Composites sputtering damage

In secondary ion mass spectrometry (SIMS) the sample surface is sputtered by an ion beam and the emitted secondary ions are analyzed by a mass spectrometer (review Ref. [360]). Due to the sputtering process, SIMS is a destructive method. Depending on the sputtering rate we discriminate static and dynamic SIMS. In static SIMS the primary ion dosis is kept below 1012 ions/cm2 to ensure that, on average, every ion hits a fresh surface that has not yet been damaged by the impact of another ion. In dynamic SIMS, multiple layers of molecules are removed at typical sputter rates 0.5 to 5 nm/s. This implies a fast removal of the topmost layers of material but allows quantitative analysis of the elemental composition. 

In this review results from two surface science methods are presented. Electron Spectroscopy for Chemical Analysis (ESCA or XPS) is a widely used method for the study of organic and polymeric surfaces, metal corrosion and passivation studies and metallization of polymers (la). However, one major accent of our work has been the development of complementary ion beam methods for polymer surface analysis. Of the techniques deriving from ion beam interactions, Secondary Ion Mass Spectrometry (SIMS), used as a surface analytical method, has many advantages over electron spectroscopies. Such benefits include superior elemental sensitivity with a ppm to ppb detection limit, the ability to detect molecular secondary ions which are directly related to the molecular structure, surface compositional sensitivity due in part to the matrix sensitivity of secondary emission, and mass spectrometric isotopic sensitivity. The major difficulties which limit routine analysis with SIMS include sample damage due to sputtering, a poor understanding of the relationship between matrix dependent secondary emission and molecular surface composition, and difficulty in obtaining reproducible, accurate quantitative molecular information. Thus, we have worked to overcome the limitations for quantitation, and the present work will report the results of these studies. 

While a lot of work has been done with heavy-ion induced radiation damage in metals and semiconductors, very little has been done on compounds, especially on covalent ones. In the following section we shall try to cover the most important work on the radiation chemistry of compounds. In the section on metals only a few selected examples will be mentioned. In the last part of this chapter we shall deal with changes in the composition of surfaces due to sputtering of compounds. 

Ion beam sputtering is the primary process in SIMS, but as remarked earlier, it is also important in depth profihng, a method widely used in AES, XPS, SIMS, and many other techniques to study subsurface composition with quite fine depth resolution. When an ena-getic ion strikes a surface, it dissipates some of its energy into the surface. In the simplest case when the ion is scattCTed back out of the surface, the ena-gy transferred to a surface atom after a binary collision is sufficient to cause substantial local damage. Howeva-, when the incident ion is scattered into the solid, the result is a collision cascade leading to the emission of sputtered particles (ions, ionized clusters, atoms, and atomic clusters) from the... 

The third major limitation is that the analysis process itself can change the composition of the surfaces to be analyzed. The two most common t5 es of this problem are analysis beam-induced damage and inhomogeneities caused by the sputtering process, which is used often to probe past the topmost surface of the sample. 

The sputtering process is used deliberately in secondary ion mass spectrometry (SIMS) [48] not only to remove atoms from the surface and to identify them by measuring their mass but also to gradually erode the surface to probe the composition in depth (chemical depth-profiling). In LEIS, the goal is to make the measurement before damage or sputtering can alter the structure or composition of the surface. 

---