The characteristics of photon and phonon standing waves in a periodic medium.

The main characteristics of the spatial variation of the photon and phonon wave fields at the band gap boundaries are analysed for a one-dimensional medium with periodic optical or acoustic parameters. The derivations are based on symmetry considerations and on analytical results derived from the basic differential equation for the wave field. A simple relation is derived between the band gap width and the derivative of the field intensity at the interface between the regions of high and low wave velocity. The general field characteristics are derived for some examples. Using the analysis a remarkable asymmetric behaviour of the wave absorption near the Brillouin zone boundaries can be explained in a straightforward way.

Investigation of the formation process of MCs+-molecular ions during sputtering

In secondary ion mass spectrometry, the detection of MCs+ clusters (with M an element of the specimen) under a Cs bombardment is frequently used for the quantification of major elements. Despite some very good results obtained by this method, some problems still remain. In order to gain some more insight into these problems, the formation mechanism of the MCs+ clusters is investigated using a Monte Carlo model. It is shown that the majority of the constituent particles of the formed clusters are initially first or second neighbor atoms at the surface and that the velocity distribution of the MCs+ clusters becomes broader and peaked at higher velocities with increasing surface binding energy of the M atom. In addition, it is demonstrated that the interaction potential between the M and Cs+ particle has no influence on the velocity distribution of the MCs+ clusters. On the other hand, the cluster formation probability, defined as the probability that a sputtered M and Cs+ particle will form a MCs+ cluster, is extremely sensitive to this interaction potential. It is also shown that the cluster formation probability decreases with increasing surface binding energy. Finally, a good correspondence is obtained between the calculated and experimental velocity distributions of MCs+ clusters sputtered from different monoatomic materials. As a consequence, the Monte Carlo model and the discussed results can be validated.