Secondaryion

Secondaryion, in the context of mass spectrometry, refers to an ion ejected from a solid surface after bombardment by energetic primary ions. The term is often written as “secondary ion” in the literature, but some sources use the one-word form. Secondary ions are produced during techniques such as secondary ion mass spectrometry (SIMS), where a focused beam of primary ions (for example Ga+, Cs+, or O2+) strikes the sample surface. This impact causes sputtering of surface atoms and molecules, and a portion of these sputtered species are ionized and emitted into vacuum as secondary ions. These ions can be positive or negative and may be atomic, molecular, or cluster species.

The yield and identity of secondary ions depend on many factors, including the chemical state and matrix of the surface, as well as the energy and angle of the primary ion beam. Matrix effects can strongly influence ionization efficiency, complicating quantitative interpretation. Positive ions are common for many elements; negative ions can be enhanced by specific beam conditions or co-deposition of species such as cesium.

Analysis is performed by mass spectrometry to determine composition and structure. Time-of-flight SIMS (TOF-SIMS) offers broad mass range and high spatial resolution imaging, while other analyzers provide higher mass resolving power. Advances such as NanoSIMS enable nanoscale imaging and isotopic analysis, and depth profiling can be performed by incremental sputtering.

Applications span materials science, semiconductors, polymers, biology, geology, and catalysis, where secondary ions provide surface composition, chemical mapping, and depth information. Limitations include surface damage from sputtering, matrix-dependent ion yields, and challenges in quantitative accuracy.