on the occasion of his 80th birthdayThe energy loss of protons in the energy region from 40 to 350 keV is measured for (110), (loo), and (1 11) planar channeling, for ( l l O > , (11 l}, (1 12> axial channeling, and for random directions in silicon. The investigations are carried out by means of the transmission experiment using silicon targets of several thicknesses. Stopping power values are derrved from the peak and the leading edge of energy spectra for channeled particles. Special procedures are applied to correct the obtained stopping power data with respect to the target thickness. In the case of leading edge the stopping power data depend strongly on the target thickness. It is shown that only the extrapolation to zero thickness leads to correct stopping power values for best channeled particles. It is found that the ratio of channeled to random stopping power shows a maximum in the energy region a t about 70 keV. Here the stopping power for channeling and random directions reach their largest value, too. I n der vorliegenden Arbeit werden die Energieverluste von Protonen im Energiebereich von

A detailed theoretical analysis of experimental energy spectra of axial-channeled protons transmitted through thin silicon targets is performed by Monte Carlo calculations. Energy spectra are calculated for (1 lo), (1 1 l), and (1 12) channels in the energy region from 50 to 300 keV. The Monte Carlo program is based on the continuum string model. The energy loss on valence electrons is calculated on the basis of a modified Lindhard model for channeling energy loss and the stopping number is taken from the local density approximation of the Lindhard-Winther formalism. The anisotropic distribution of the valence electron density in a semiconductor is taken into account. Stopping due to core electrons is considered by a semiclassical approximation. Multiple scattering and energy straggling are included in the simulation program. The calculated energy spectra and channeling stopping powers are in good agreement with experimental ones. Mit

The theory of resonance dechanneling under axial-to-planar transition conditions is further developed. For describing the structure of the atomic planes a n analytical potential expression is used in the Thomas-Fermi-MoliBre approximation on the basis of Lindhards string of strings model. As a result of the investigation of the nonlinear equation of ion motion along the planar channel an expression is derived to calculate the 'tilt angle amin required for planar channeling to be effective. This angle increases with increasing transversal coordinate in the planar channel.I n this way the angular interval amin < a < amax is obtained which separates the axial channeling from the "pure" planar one. In a linear approximation of increasing transversal oscillation amplitude the initial amplitude is calculated, for particles which take part in the resonance of given order. The theoretical results are in sufficient agreement with numerical calculations and experimental values.Die Theorie der Resonanzdekanalisierung unter den Bedingungen des Axial-Flachen-ubergangs wird weiterentwickelt. Zur Beschreibung der Struktur der Atomflachen wird ein analytischer Ausdruclr in der Thomas-Fermi-MoliL;re-N&herong im Rahmen des Lindhardschen ,,Ketten von Ketten"-Modells verwendet. I m Ergebnis der Untersuchiingen der nichtlinearen Gleichungen der Ionenbewegung im Flachenkanal wird ein Ansdruck fur den Einfallswinkel amin gefunden. von dem a b planare Kanalleitung realisiert ist. Dieser Winkel wachst mit der Transversalkoordinate im Flachenkanal an. Somit wird das Winkelintervall a,in < a < amax erhalten, welches die axiale und die ,,reine" Fliichenkanalleitung trennt. Weiterhin werden allgemeine Resonanzbedingungen und ein Ausdrnck fur die Amplitudenabhiingigkeit der Schwingungsfrequenz der kanalisierten Ionen abgeleitet. In einer linearen Niiherung des Anwachsens der Schwingungsamplitude wird die Anfangsamplitude filr die Teilchen berechnet, die a n der Resonanz der gegebenen Ordnnng teilnehmen. Die theoretischen Ergebnisse stinimen befriedigend mit Computerrechnungen und experimentellen Werten iiberein.

Short Note we present transmission and backscattering measurements for the determination of the proton stopping power in silicon. The significant differenc e s between an amorphous and a crystalline target a r e discussed,The experimental set-up was described in /2/. For the transmission experiments thin amorphous Si foils of various thicknesses from 47 nm to 250 nm were used. The layer thicknesses were determined by an analysis of backscattering signals what is possible without knowledge of the stopping power. The energy of the protons before and after passing the foils was measured by an electrostatic analyzer with an accuracy better than 0.5 %. Fig. 1 shows the energy loss of the protons AE in dependence on the target thickness Ax for several primary energies E In the used interval a linear function between AE and Ax exists.From the slope of the functions the stopping power can be determined. 0' Rutherford backscattering (PBS) experiments were carried out with amorphous and crystalline (Ill)-oriented Si targets. The crystalline specimens were rotated around an angle of 120 O, 15 for obtaining a random value of the RBS signal. The backscattering yield H for the primary ener 0 away from the -aXiS gy E w a s measured for several emerging 0 t 3R 20 L 41 10 Fig. 1, The dependence of energy loss on the layer thickness for various primary energies in the transmission experiment; + 50 keV, A 70keV, 0 150keV, o 300keV 0 SR 100 I . ZRR 2.50 dx (nm) -1) Invalidenstr. 42, DDR-1040 Berlin, DDR.

Recently it has been shown/l/ that combination of ionbackscattering andX-ray diffraction canbe successfully used to study composition, crystalline quality, and tetragonal distortion in strained layer superlattices (SLSs) . F o r large-mismatched systems P i c r a w et al. /2/ f i r s t demonstrated the direct determination of strainby 1) LinnBstr. 5, DDR-7010 Leipzig, GDR.2) Invalidenstr. 110, DDR-1040 Berlin, GDR. 111 cIIG Laac UI uuu 6 LIIC lull-sLrallleu pseuuomorpnic growcn((oa/a,,)= 0) was proved by X-ray rocking curves recorded in (400) and (422) reflections. The angular separations between the satellite peaks (Fig. 2) a r e related to the average period