G. Schrieder

Bio: G. Schrieder is an academic researcher from Ruhr University Bochum. The author has contributed to research in topics: Small-angle neutron scattering & Scattering. The author has an hindex of 3, co-authored 3 publications receiving 75 citations.

Tridyn — A TRIM simulation code including dynamic composition changes

Abstract: Based on the sputtering version of the TRIM program for multicomponent targets, a Monte Carlo code has been developed which computes range profiles of implanted ions, composition profiles of the target and sputtering rates for a dynamically varying target composition. It takes into account compositional changes both due to the spatial distribution of target atoms deposited in collision cascades, and due to the presence of the implanted ions. The local density of the target is allowed to relax according to a given function of the densities of the individual components. The applications of the program cover a wide range of problems like the collisional atomic mixing of multilayered targets, dynamic implantation profiles at large fluences, and the fluence-dependent preferential sputtering of multicomponent materials. The present paper provides a description of the program and a critical comparison to similar Monte Carlo codes. As an application, the behaviour of the Ta-C system under He bombardment is studied with respect to sputtering yields, surface composition and composition profiles. Satisfactory agreement is obtained with experimental results given in the literature.

The4He(12C, γ)16O reaction at stellar energies

Abstract: The capture reaction4He(12C, γ)16O (E cm= 134–338 MeV) as well as the elastic scattering process4He(12C,12C)4He (E cm=144–338 MeV) have been investigated with the use of an intense12C beam and a windowless and4He recirculating gas target system The measurements involved two large NaI(T1) crystals in close geometry to an extended gas target, whereby angle-integrated γ-ray yields were obtained A large area plastic detector was used for the suppression of time-independent background A search for cascade γ-ray transitions was carried out by coincidence techniques The measurement of absolute cross sections is also reported Theoretical fits of the excitation function for the groundstate γ-ray transition requireE1 as well asE2 capture amplitudes, which are of equal importance at stellar energies This result increases significantly the stellar burning rate of4He(12C, γ)16O and leads to16O as the dominant product at the end of helium burning in massive stars The observed capture yield to the 692 MeV state is dominated by the direct capture mechanism and plays a small role at stellar energies

TRI3DYN – Collisional computer simulation of the dynamic evolution of 3-dimensional nanostructures under ion irradiation

Abstract: A computer program is described which allows fully three-dimensional dynamic collisional simulations of ion irradiation effects in particular in nanosystems. The program is based on the well-known TRIDYN code which describes dynamic modifications along one dimension. In a computational volume composed of fixed and equisized voxels, local atomic density changes due to ion implantation or recoil relocation are relaxed to constant predefined atomic volumes. This is accomplished by interaction with neighboring voxels and by material transport towards and away from the surface. Arbitrary initial system shapes and elemental distributions can be defined as well as a wide range of irradiation conditions including non-uniform beam profiles. The paper addresses details of the involved algorithms and discusses potential artifacts with respect to surface sputtering, broadening of compositional profiles, and surface contours. It demonstrates the capabilities of the program by examples of focused ion beam erosion, self-organized surface pattering, and ion implantation and sputter-shaping of nanostructures.