Advanced Materials Characterization Chapter 10 Secondary Ion Mass Spectrometry

Advanced Materials Characterization Chapter 10 - by Igor Bello

The fundamental principle of secondary ion mass spectrometry (SIMS) is based on the emission of secondary ions, neutral atoms, atomic clusters, and molecular fragments at the interaction of energetic ions with solids. This emission phenomenon is known as sputtering. Said sputtering is the process at which high-energy ions impinging on solids transfer their momenta to surface atoms/molecules and cause their elastic and inelastic displacement and collision cascades. The structure of solid is compressed and stressed to such extent that at subsequent relaxation some atoms or molecular fragments of solids are emitted to vacuum. Mostly the emitted particles are electrically neutral.

Sputtering is quantitatively expressed by sputtering yield and the ion-sputtering yield. The sputtering yield depends on the energy of impinging ions, incident angle, individual properties of ions and a solid and chemical environment as described later.

SIMS is a surface analytical technique with a superior sensitivity. The high sensitivity for all elements of the periodic table enables us to detect elements at very low atomic densities. However, the sensitivity significantly varies with the surface environment, so called matrix effect. The matrix effect causes substantial changes in ion sputtering yield which is behind the extreme sensitivity of SIMS instruments. However, the same matrix effect causes difficulties in quantitative analysis that in fact is possible only with the preparation of special standards.