P. Oberschachtsiek

Trace-impurity detection by Rutherford backscattering and nuclear resonance reactions

Abstract The use of a multisegment annular Si detector together with a multiline electronic processing system has led to an improvement of the detection limit in Rutherford backscattering spectrometry by about two orders of magnitude as compared to the standard single-line arrangement. With regard to nuclear reaction analysis, using particle/γ-ray resonance processes, similar large enhancements have been realized by an effective background-suppression system eliminating environmental and cosmic radiation. The present state of both experimental facilities will be demonstrated and compared with other trace-element detection techniques.

A four-moments analysis of 1H range profiles IN Si

Abstract 1 H implants, with energies ranging from 25–300 keV, were profiled by the 15 N nuclear reaction using an in-line low-level-background facility. The numerical analysis shows that all four moments, projected range, range straggling, skewness, and kurtosis agree with TRIM calculations to within 2%, 8%, 12% and 15%, respectively.

Energy loss and straggling of MeV 4He ions in a Si/Sb multilayer target

Abstract In a novel approach to energy loss and straggling measurements a multi-σ-layer target of Sb in amorphous Si, grown in a molecular epitaxy facility, has been used for Rutherford backscattering experiments with 4He ions. Within the measured energy range of 0.1–4 MeV our stopping power data differ from the values published by Ziegler by up to −10% around the stopping power maximum at about 0.5 MeV, but tend to merge at lower and higher energies. The precision is 1% or better. The energy straggling shows an energy dependence from about −20% to +15% with respect to the Bohr prediction.

Experimental evidence for 15N charge-change processes at a low energy regime

Abstract We have measured the linewidths of the 15N resonant nuclear reaction at 6.38 MeV on H bearing 1 to 10 nm thin films. By comparing the full width at half maximum values of the same film obtained by incident nitrogen ions of charge states 2 + and 3 + we have found evidence that the charge equilibration process takes place in less than 10 nm. This feature should be taken into account whenever films thinner than 10 nm are analyzed using the above mentioned reaction.

Experimental and calculated range moments of deep implants

Abstract The first four range moments of deep implants, ranging to micrometre depths, have been determined by nuclear reaction and Rutherford backscattering analysis for a few selected ion species in amorphous semiconductors. In order to achieve reasonable accuracy for the higher moments, considerable efforts have been undertaken to obtain sufficient statistical precision over the total range distribution. In the nuclear reaction analysis, we have made use of efficient background suppression by using an in-line low level system. In the Rutherford backscattering measurements, a multisegment annular silicon detector system has been used to fulfil the statistical requirements. The experimental results are compared with TRIM calculations, and the degree of agreement for the different moments has been evaluated. In general, some systems show an overall agreement of better than 10% even for the higher moments; other systems, however, show deviations up to 30%, especially for the first moment. These results will be discussed in terms of basic ion-solid interaction mechanisms.

15N Doppier spectroscopy of 1H on diamond

Diamond single crystals of 〈100〉, 〈110〉 and 〈111〉 orientation have been chemically treated in order to prepare monolayer (ML) coverages of 1H. Subsequently, sample surface areas of about 0.1 cm2 have been exposed to a 15N beam of 30 nA at the resonant-reaction energy of 6.385 MeV. The resulting 4.4 MeV gamma rays have been detected by a 10 in × 10 in NaI(Tl) crystal inside a low-level system. The results can be summarized as follows: The initial H coverage of a few ML equivalent quickly desorbs under ionizing radiation, until at about 1 ML a slow desorption stage prevails. In general, the different crystal surfaces, characterized by strong topological irregularities, do not exhibit ideal ML coverage. Similarly, the corresponding Doppler widths do not show the expected dependence on crystal orientation, but are the same within experimental error.

Range parameters of deep ion implants in group IV semiconductors

Abstract Ions of selected elements of the periodic system were implanted into amorphous layers of C, Si and Ge with specific energies of up to 1 MeV/amu. The resulting profiles were measured with specific nuclear reactions ( A 1 A 2 ) and Rutherford backscattering ( A 1 > A 2 ) up to depths of 10 μm. In all cases, the first and second range moments of the concentration profiles were determined as a function of implantation energy, whereas both the next two higher moments could be derived only in those cases where the complete ion distribution was measurable down to the surface position. Here, for a few typical examples, also lateral distributions, by measuring implants with varied angle of incidence, were obtained and analyzed with respect to the first two even lateral moments. The results of a detailed comparison of the range parameters are discussed in terms of scaling properties within the framework of LSS theory. As regards the projected ranges predicted by TRIM calculations, significant deviations from our experimental values occur within the interval of + 20% and − 60%. These discrepancies are attributed to the electronic stopping powers used by the TRIM program.

A 3-MV Pelletron for materials research at Heidelberg

Abstract We describe an accelerator laboratory under construction for materials research. A 3-MV tandem of the Pelletron type, obtained recently, is planned to feed three beam lines for materials analysis and modification. The purpose of the experimental arrangements will be explained and the performance of the accelerator described.

Deep range profiling by Rutherford backscattering and nuclear reaction analysis

Abstract The experimental requirements for nuclear process analysis of ion ranges at depths of 1–10 μm have been studied for both Rutherford backscattering and nuclear reactions analysis. The consequences of higher analyzing energies are discussed.

Range parameters of 13C implants in semiconductor and metal targets

Abstract Silicon, gallium arsenide and stainless steel samples were implanted with 150 keV 13 C ions at room and liquid-nitrogen temperatures. The depth distributions were analyzed by making use of the narrow 13 C(p,γ)-resonance at 1.75 MeV. The experimentally determined moments of the depth distributions for gallium arsenide and stainless steel are in reasonable agreement with theoretical predictions. In the case of silicon the agreement is less satisfactory, especially as far as the third and fourth moments are concerned. The experimental results indicate a symmetrical implantation profile in silicon, whilst from theoretical calculations a strongly skewed distribution is expected.