W. Bolse

Ion-beam induced atomic transport through bi-layer interfaces of low- and medium-Z metals and their nitrides

Abstract A detailed investigation of ion-beam induced atomic transport through bi-layer interfaces of low- and medium-Z metals and their nitrides as a function of the irradiation conditions and the materials combinations allowed us to distinguish between five different mixing mechanisms. In the strongly bound nitrides ballistic transport dominates the atomic intermixing, while for the metallic bi-layers diffusion in local (light- and medium-mass ions) and global thermal spikes (very heavy ions) seems to be the major mixing mechanism. Heavy ions were also found to initiate end-of-range spikes even in systems where mixing in the recoil cascade is of purely ballistic character. Besides these athermal processes, irradiaion at higher temperatures may result in thermally activated radiation-enhanced diffusion .

Ion beam mixing of ZnO/SiO2 and Sb/Ni/Si interfaces under swift heavy ion irradiation

We have investigated the irradiation induced interface mixing in ZnO/SiO2 (α-quartz) and Sb/Ni/Si thin layer systems under swift heavy ion irradiation in the electronic stopping power regime. The irradiations were carried out at 77 K using 100 MeV Ar, 260 MeV Kr, and 200 MeV Xe ions. For the ZnO/SiO2 system experiments were also carried out at lower ion energies (300, 600, and 900 keV, respectively) where nuclear stopping dominates. The alterations of the interface concentration profiles were determined by means of Rutherford backscattering spectrometry performed subsequently at the irradiated and the nonirradiated parts of the samples. While for the semimetal/metal Sb/Ni interface almost no mixing could be found after high-energy irradiation (mixing efficiency for Xe ions: k/Se<0.02 nm5/keV) the ceramic system ZnO/SiO2 strongly reacts upon high energy ion irradiation (Xe: k/Se=2.1 nm5/keV). The Ni/Si interface shows an intermediate effect (Xe: k/Se=0.2 nm5/keV). The mixing behavior found at high ion ener...

Amorphization and recrystallization of covalent tetrahedral networks

Abstract In the present paper recent studies on the amorphization and recrystallization of the light covalent ceramics SiC, Si3N4 and SiO2 (and in comparison Si) shall be reviewed. By combining long and short range order sensitive analysis techniques new insights into the disordering/reordering mechanisms and the structure of the disordered materials were gained. The results will be discussed in the light of a topological approach of the transition between periodic and aperiodic networks.

FORMATION AND DEVELOPMENT OF DISORDERED NETWORKS IN SI-BASED CERAMICS UNDER ION BOMBARDMENT

Abstract In the present paper the results of an extended study on the disordering of Si, SiC, Si 3 N 4 and SiO 2 by ion bombardment will be reviewed, with respect to both long and short range order. It was found that amorphization occurs by nucleation and growth of defect agglomerates in the still crystalline matrix, until a critical damage density is achieved and a transition between the ordered and the disordered networks occurs. In SiO 2 , Si 3 N 4 and Si the disordered phase consists of a random network of [SiX 4 ]-tetrahedrons (X = O, N, Si), which conserved the chemical short range order of the crystalline materials. In SiC first a highly disordered network of [SiC 4 ]-tetrahedra forms, which is however not as random as in the other materials, since a correlation between the orientation of neighboring tetrahedra exists. Further bombardment of this network then results in complete destruction of the initial chemical short range order and the formation of Si–Si and C–C bonds. The results are compared with theoretical predictions of the amorphizability of the different compounds and the microstructure of the disordered phases.

Mechanisms of ion beam induced atomic mixing in solids

Abstract In the present paper, selected typical studies on the ion-beam mixing of bi- and multi-layer systems are reviewed. It is shown that by proper variation of the materials (atomic number, chemical affinity between top and bottom layer) and of the irradiation conditions (ion species, energy, fluence, target temperature), significant conclusions can be drawn concerning the relevant mixing mechanisms. It is found that low temperature ion-beam mixing of light systems ( Z ≤18) is of pure ballistic character, without any influence of chemical driving forces. For higher atomic numbers and low or medium mass ions, mixing occurs by chemically biased diffusion in spatially separated local thermal-spikes. For very heavy ions mixing effects, which are non-linear with respect to the deposited energy density, point to the formation of coherent global spikes along the ion path by the overlapping of local spikes. Very heavy ions might also be able to initiate thermal-spikes in otherwise ballistic systems ( Z ≤18) at their end of range (end-of-range spikes) by a high density of subcascades. Chemically guided motion of residual defects from the collision cascade seems to play a role for ion beam induced mixing only at elevated temperatures.

Atomic mixing in thin film systems by swift heavy ions

Because of their sensitivity to the electronic energy loss of swift heavy ions, we have investigated the high energy ion beam mixing of oxide layer systems. In this paper we present a summary of the results and first steps towards interpretation and modelling of the observed phenomena. As was also observed in the case of track formation, mixing was found to occur only if the electronic energy loss exceeds a threshold value. The threshold is determined by the less sensitive material, which is a clear hint that both sides of the interface must have been molten, to enable for effective interdiffusion. This interpretation is supported by the estimated interdiffusion constants which indeed lie in the range known for liquid state diffusion.

Solid phase epitaxial regrowth of ion beam-amorphized α-quartz

Solid phase epitaxial growth of ion beam-amorphized α-quartz has been studied by means of Rutherford backscattering spectrometry in channeling geometry. α-quartz single crystals were irradiated with Cs+ and Xe+ ions and annealed in air or in vacuum at 500–900 °C. Complete epitaxial regrowth has been observed in the Cs-irradiated samples, after 875 °C annealing in air. On the other hand, vacuum annealing provided only incomplete regrowth of the amorphous layer, while Xe-irradiated α-quartz could not be regrown up to 900 °C. The behavior of Cs in the recrystallization process is discussed in terms of the SiO2-network topology.

Preparation of ion-implanted and sub-monolayer 111In-tracer layers for perturbed angular correlation analysis

Abstract Some 10 12 radioactive 111 In-tracer atoms are routinely implanted at 400 keV into different samples to perform Perturbed Angular Correlation (PAC) measurements. The experimental details and the tricks used during the preparation and implantation are summarized. As an alternative to ion-implantation, a method to deposit submonolayer 111 In-tracer films into metallic multilayers is described. The different applications and benefits of both techniques are compared.

Atomic transport in thin film systems under heavy ion bombardment

Abstract Besides the controlled doping of semiconductors by means of ion implantation, energetic ion beams offer a much broader range of possibilities to modify the structure and properties of materials, due to the very high local energy density deposited into the solid along the ion path. By reviewing selected experimental examples, the atomic transport processes initiated by energetic heavy ions at the interfaces of thin film systems will be summarized. The nature of the transport mechanisms and the reaction kinetics will be discussed, which strongly depend on the properties of the involved materials (atomic numbers, chemical affinities, electrical conductivity, …) and the irradiation conditions (ion species and energy, temperature, …). Special attention will be drawn to recent studies of the interface mixing due to the electronic energy loss of swift heavy ions.

Ion-beam induced amorphization and dynamic epitaxial recrystallization in α-quartz

We report on the evaluation of ion-beam induced damage in α-quartz and its dynamic annealing behavior in the temperature range between 80 and 1050 K using Rutherford backscattering spectrometry in channeling geometry. The results illustrate that the critical temperature for inhibiting amorphization during irradiation is about Tc≈940 K. The critical fluence φc for amorphization is independent of the temperature up to 550 K, but strongly increases at higher temperatures. The activation energy for the diffusion of defects in the collision cascade or at the amorphous/crystalline interface is found to be 0.28±0.02 eV. The dynamic annealing mechanism is explained by the vacancy out-diffusion model of Morehead and Crowder.