Angular distribution, secondary ions

The angular dependence of the secondary ion intensity is expected to follow a simple cosine law, in particular for randomly oriented polycrystalline surfaces. The explanation for this is that upon impact the collision cascade takes care of an isotropic distribution of the energy through the sample. Hence the intensity of collision... 

Angular Distributions of Secondary Ions From Adsorbate Covered Surfaces... 

Most experimental studies aimed toward determining the angular distributions of secondary particles have focussed on the measurement of the secondary ions. The reason for this emphasis is that there have been no techniques available for detecting the neutral species with monolayer sensitivity. It would be extremely valuable to be able to perform these experiments to be able to obtain data that was directly comparable to the classical dynamics calculations and to get some... 

Angular distribution of neutral atoms angular distributions, 94,95f energy distributions, 93-9 1 schematic of detector, 93,94f Angular distribution of secondary Ions adsorbate-covered... 

Further evidence for secondary processes during the sq>aration of the He-H intermediate arises from the observation of translationally hot H ions, containing possibly up to 0.5 eV energy, even in the thermal reaction . >. however, it should be noted that analysis of the angular distribution of the ions is consistent with E < Eat E = 100 meV. ... 

Secondary ion angular distributions tend to peak around the sample normal with a generally noted Cosine function. Exceptions are seen when crystallographic surfaces are present. 

Fig. 2.25 Model proposed to explain the data shown in Fig. 2.24. A4HeRh2+ ion, in its as-desorbed orientation, cannot field dissociate as explained in Fig. 2.23. It can dissociate only when it is rotated by an angle greater than 90° from its as-desorbed orientation. The maximum dissociation rate occurs when the rotation angle is 180°. If it is not dissociated during the angular rotation between 90 and 270° then it has to wait for the right orientation again. By that time, the ion is too far away from the surface and the field is too low for field dissociation to be possible. Thus a well-defined field dissociation zone exists. From the additional energy deficit of the secondary Rh2+ peaks and the field distribution above the surface, the dissociation time and the 180° rotation time of the compound ion is calculated to be 790 21 fs.

Associative ionization allows a very simple kinematical analysis of the differential cross section, even if unselected beams have been used, because the product ion carries away essentially all CM-kinetic energy. Thus the angular ion distribution is determined by the energy distribution of primary and secondary beams and the angular beam width. If these factors are known, a complete analysis is possible. From the maximum angle at which the process is observed the threshold energy can be determined. 

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