| Popis: |
The possibility of surface layer analysis by measurement of secondary ions emitted after bombardment of a sample with energetic primary ions has been known for some time [3.1]. Secondary ion mass spectrometry (SIMS) has become a well-established tool in research on both solids and surfaces [3.2]. It is widely used for depth profiling the compositions near interfaces in metals, oxides, and semiconductors [3.3–6]. In 1973, BENNINGHOVEN opened a new avenue of application of SIMS by pointing out that experiments done at low primary ion currents and total doses can probe the uppermost surface layer [3.7]. He termed this mode of the experiment “static” SIMS. At 10−9 A/cm2 with an emission yield of secondary particles of 1 per incident ion, for example, it takes about 1/2 hour to remove 1% of a monolayer. Thus, although each ion impact damages a small region of the surface, the contribution of previously damaged regions to the observed spectrum can be made negligible. To determine the kinds of information that static SIMS can provide for surface science, one must focus on the collision process itself. The central issue is to establish the relations between measured SIMS parameters and the structure and chemistry of the original surface. Significant progress has been made in this area, but the issue is not yet fully resolved. The object of this paper is to examine the state of the art and discuss the promising directions for future development. |
