SURFACE CHARACTERIZATION WITH KEV CLUSTERS AND MEV IONS Conference Paper uri icon

abstract

  • Desorption of atomic and molecular species from solids can be achieved by bombardment with keV and MeV projectiles. In the studies described here, the secondary ions (SIs) are identified by time-of-flight mass spectrometry (TOF-MS) in an event-by-event counting mode. In this paper, desorption induced by two types of projectiles, viz. particle desorption mass spectrometry (PDMS) and secondary-ion mass spectrometry with keV clusters as projectiles (cluster-SIMS), is discussed. PDMS uses fast heavy ions as projectiles (i.e., ions of E 0.1 MeV/amu and m 40 amu fission fragments are well suited for PDMS). The features of PDMS can be summarized as follows: it is suitable for isotopic and molecular analysis by virtue of the TOF-MS procedure; the desorption yield (ratio [%] of ions desorbed vs primary projectiles) can reach and even exceed 100%; thus mass spectra are obtained with a very low total primary-ion dose of 106 ions. PDMS has a shallow sampling depth (5-100 monolayers, depending on the target), i.e. the technique is suitable for outermost-surface analysis without interference from the substrate. Cluster-SIMS opens new perspectives for surface characterization. Clusters are attractive as projectiles because they are quasineutral, yet they can be accelerated, steered and focused. Their size, mass velocity and chemical composition can be selected to yield maximum SI emission. A new experimental approach has been devised to implement cluster-SIMS. We have observed up to 30-fold enhancement in the SI yield for cluster- vs monoatomic projectiles of equal velocities. Generally, the SI yields increase with the mass of the projectile and its velocity. The technique has particular promise for the surface mapping of organics. Event-by-event coincidence counting can be combined with TOF-MS. This allows one to determine which masses are desorbed together from a primary impact size. Surface homogeneity is thus revealed with high planar resolution. 1990.

published proceedings

  • NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS

author list (cited authors)

  • SCHWEIKERT, E. A., BLAIN, M. G., PARK, M. A., & DASILVEIRA, E. F.

citation count

  • 23

complete list of authors

  • SCHWEIKERT, EA||BLAIN, MG||PARK, MA||DASILVEIRA, EF

publication date

  • April 1990