H.D. Carstanjen

Morphology and interdiffusion behavior of evaporated metal films on crystalline diindenoperylene thin films

We present a transmission electron microscopy (TEM)/Rutherford backscattering spectrometry (RBS)/x-ray-diffraction (XRD) study of Au evaporated on crystalline organic thin films of diindenoperylene (DIP). Cross-sectional TEM shows that the preparation conditions of the Au film (evaporation rate and substrate temperature) strongly determine the interfacial morphology. In situ XRD during annealing reveals that the organic layer is thermally stable up to about 150u2009°C, a temperature sufficient for most electronic applications. The x-ray measurements show that the “as-grown” Au layer exhibits a large mosaicity of around 10°. Upon annealing above ≈120u200a°C the Au film starts to reorder and shows sharp (111)-diffraction features. In addition, temperature dependent RBS measurements indicate that the Au/DIP interface is thermally essentially stable against diffusion of Au in the DIP layer up to ≈100u2009°C on the time scale of hours, dependent on the Au thickness.

Ion beam analysis with monolayer depth resolution

Abstract The paper is concerned with the analysis of surfaces and near-surface layers with monolayer depth resolution by means of high resolution Rutherford backscattering (HRBS) and elastic recoil detection (HERDA) of ions with an energy of a few MeV, in combination with an electrostatic spectrometer. With this instrument, which has recently been set up at the 6 MV Pelletron accelerator of the Max-Planck-Institut fur Metallforschung in Stuttgart, depth resolutions of 0.1 nm are obtained in HRBS and 0.3 nm in HERDA experiments. This paper gives a short outline of the design and performance of the spectrometer followed by various examples of applications. These comprise examples showing the analyzing power of the instrument, the analysis of an X-ray mirror by HRBS, the study of the initial oxidation of surfaces of aluminum single crystals by HERDA and recent results concerning charge exchange in ion backscattering.

The temperature and strain-rate dependence of the flow stress of icosahedral AlPdMn single-quasicrystals

Abstract To study the deformation characteristics of icosahedral Al 70.4 Pd 20.8 Mn 8.8 single-quasicrystals flow-stress measurements by compression tests have been performed in the temperature range 990–1105 K. Each test was combined with a stress relaxation experiment to determine the strain-rate sensitivity of the flow stress. The activation enthalpies Δ H calculated from these data are: (i) considerably smaller than the data known until now from the literature and (ii) exhibit a step at about 1050 K indicating different mechanisms for dislocation motion in AlPdMn with Δ H ≅ 3.7 eV below and Δ H ≅ 5.5 eV above 1050 K. In both regimes Δ H increases proportional to T suggesting different pre-exponential factors if an Arrhenius behaviour is assumed for the strain rate. From the slopes of the Δ H-T curves values for Δ S can be deduced which amount to 13 k below and 27 k above 1055 K. The results are interpreted on the basis of present models of dislocation motion in quasicrystals.

Subsurface enrichment of Co in Si (100) at initial stages of growth at room temperature: a study by high-resolution Rutherford backscattering

The Co distribution in the initial stages of growth of Co on Si (100) at room temperature has been probed in situ by high-resolution Rutherford backscattering spectrometry. Even at very low coverage (0.08 ML) extensive Co in-diffusion is found. The in-diffused Co forms a pronounced subsurface maximum which shifts into the Si bulk with increasing coverage and persists up to a coverage of 1.19 ML. The Co concentration at the surface saturates at the value of 0.5 for 1.19 ML of Co. Evidence of Si out-diffusion is seen for 2 and 2.93 ML which results in the formation of a CoSi phase.

Investigation of strain softening of icosahedral AlPdMn single quasicrystals

Icosahedral AlPdMn single quasicrystals were deformed in compression with constant plastic strain rate in order to study the strain-softening phenomenon which is observed in the strain regime following the upper yield stress and which characterizes the shape of the stress-strain curves of quasicrystals. Stress-relaxation experiments and temperature changes were performed along the stress-strain curves at selected strains. It is found that both the strain-rate sensitivity and the temperature sensitivity of the stress decrease in the above strain regime with increasing strain. Within the regime of constant stress following the strain softening regime at large strains both sensitivities remain constant. These results favour a model which assumes strain softening being caused by a change of the configuration of large cluster-like obstacles (e.g. the icosahedral clusters present in i-AlPdMn quasicrystals) by the moving dislocations thus reducing the stress needed to maintain the deformation.

The strain-softening phenomenon of icosahedral Al–Pd–Mn single quasicrystals

Abstract For studying the strain-softening phenomenon of icosahedral Al–Pd–Mn single quasicrystals, compression tests with constant plastic strain rate were performed in the strain regime following the upper yield stress and combined with stress-relaxation experiments and temperature changes along the stress–strain curves at selected strains. It is found that both the strain-rate sensitivity and the temperature sensitivity of the flow stress decrease in the above strain regime with increasing strain. These results favour a model which assumes strain softening being caused by a change of the configuration of large cluster-like obstacles (e.g., the icosahedral clusters present in i-Al–Pd–Mn quasicrystals) by the moving dislocations thus reducing the stress needed to maintain the deformation.

Is d-Al-Cu-Co a random tiling?

Abstract Channeling Monte Carlo simulations, in combination both with Rutherford backscattering (RBS) and particle-induced X-ray emission (PIXE), have been performed on model quasicrystals of decagonal Al–Cu–Co with different amount of phason disorder. Comparing our simulation results to experimental data we obtain the best agreement for those models with a large amount of phason disorder. This leads us to the conclusion that the sample of d-Al–Cu–Co used in the measurements is a random tiling. Besides the aspect of phason disorder we also examined the Cu and Co distribution given by the Burkov models (S.E. Burkov, Phys. Rev. B 47 (1993) 12325). We show that the chemical distribution is in contrast to the experimental PIXE yield profiles. By exchanging some of the Cu and Co positions it is possible to eliminate the discrepancy.

Ion Channeling in Quasicrystals

It is the aim of this chapter to outline the principles of ion chapter in quasicrystals and to give an overview of the potential applications of this technique. We will see that in quasicrystals there exist rows and planes of atoms which are the prerequisite for channeling in ordered structures. In contrast to periodic lattices in quasicrystals these rows and planes exhibit a wide distribution of densities. This causes problems, in part, but does not render channeling impossible.