Crater edge

The sample was analysed with a primary ion beam of extracted from an oxygen cold cathode discharge type source. A well-focussed 200 nA spot was attained at 4keV per molecular ion. The beam was scanned over a square of side 400 pm to produce a uniform primary beam current density and thus a flat-bottomed crater. In order to eliminate crater-edge effects, the counting system was only enabled when the centre of deflection of the beam was in a central area 125 x 125 pm. 

In another review, Magee and Honig [24] discuss three important aspects of depth profiling by SIMS depth resolution, dynamic range and sensitivity. First, the depth resolution is a measure of the profile quality. They point out that the depth resolution is limited by atomic mixing effects and the flatness of the sputtered crater within the analyzed area. Second, the dynamic range of depth profiles is limited by crater edge... 

Fig. 8.17. (a) Cross-sectional TEM micrograph of an etched ZnO Al film covered with about 1 pm of a microcrystalline silicon p-i-n solar cell [119] (b) SEM image of an etched ZnO Al film showing cross-section and etched surface. The crater edge on the ZnO surface is indicated by a black line... 

An example for an incubation process is displayed in Fig. 16. The SEM pictures show results of a treatment of barium borosilicate glass at F0=2.5 Jem-2 with a dye laser (r=300 fs, 1=620 nm) for different numbers of pulses per spot N [46]. Three pulses generated only darkening at the surface (not shown here). Five pulses caused slight ablation below the depth resolution of the optical microscope (Fig. 16a). For a higher number of pulses per spot (AT=20), the crater edges are heavily splintered off (Fig. 16b). Above 60 pulses, circular craters with a satisfying quality are formed (Fig. 16d). 

Section 53.232, the analyzed region is made much smaller than the sputtered area to remove crater edge effects and thus to improve depth resolution. 

Even if all possible measures to improve depth resolution are applied, there still exist the effects of the primary ion beam-induced damage experienced by the substrate as a result of the sputtering process. These are discussed in Section 5.3.2.4.1. Crater edge effects and crater base effects can also result in the loss of depth resolution. These are discussed in Sections 5.3.2.4.2 and 5.3.2.4.3, respectively. Dynamic range pertains to the range of concentrations of a specific element or molecule that can be examined in a particular depth profile. As can be envisaged, this depends on the detection limit and on the detector type or combinations thereof (detectors are covered in Section 4.2.3.3). 

In the case of primary ion pulsed Time-of-Fhght-based SIMS instruments, crater edge effects can be removed by rastering the primary ion analysis beam over a smaller region centered within the middle of the primary ion sputter beam raster pattern. 

Electronic gating describes the ability to filter out secondary ion signals from regions close to the crater edge throngh synchronization of the raster with the collection electronics. This, however, requires the use of small spot size primary ion beams, i.e. those noted when nsing low primary ion currents... 

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