Norbert Schell

Development of texture in TiN films by use of in situ synchrotron x-ray scattering

During growth, the microstructural development of TiN films was studied—especially the change in texture with film thickness. The films were deposited by use of a magnetron sputtering source in a vacuum chamber equipped with two magnetron sources and mounted on a goniometer located at a synchrotron radiation beam line. X-ray diffraction and reflectivity measurements were carried out in situ to follow the microstructure as a function of film thickness. With the deposition parameters that were chosen, a crossover was observed: grains with a (002) plane parallel to the film surface dominated at small thicknesses, while, at larger thicknesses, (111) grains dominated. Recrystallization was identified as a mechanism that controls this texture development. The driving force for change of orientation of the individual grains arose from minimalization of the sum of the surface energy and the strain energy of the individual grains.

The High Energy Materials Science Beamline (HEMS) at PETRA III

The HEMS beamline at PETRA III has a main energy of 120 keV, is tunable in the range 30-200 keV, and optimized for sub-micrometer focusing with Compound Refractive Lenses. Design, construction, and main funding was the responsibility of the Helmholtz-Zentrum Geesthacht, HZG. Approximately 70 % of the beamtime is dedicated to Materials Research, the rest reserved for “general physics” experiments covered by DESY, Hamburg. The beamline P07 in sector 5 consists of an undulator source optimized for high energies, a white beam optics hutch, an in-house test facility and three independent experimental hutches, plus additional set-up and storage space for long-term experiments. HEMS has partly been operational since summer 2010. First experiments are introduced coming from (a) fundamental research for the investigation of the relation between macroscopic and micro-structural properties of polycrystalline materials, grain-grain-interactions, recrystallisation processes, and the development of new & smart materials or processes; (b) applied research for manufacturing process optimization benefitting from the high flux in combination with ultra-fast detector systems allowing complex and highly dynamic in-situ studies of microstructural transformations, e.g. in-situ friction stir welding; (c) experiments targeting the industrial user community.

A two magnetron sputter deposition chamber for in situ observation of thin film growth by synchrotron radiation scattering

The design of a sputter deposition chamber for the in situ study of film growth by synchrotron x-ray diffraction and reflectivity is reported. Four x-ray windows, sealed with low cost, nonhazardous Kapton, enable scattering both in the horizontal as well as in the vertical scattering planes. The chamber fits into a standard six-circle goniometer from Huber which is relatively widespread in synchrotron laboratories. Two miniature magnetron and additional gas inlets allow for the deposition of compound films or multilayers. Substrate heating up to 650 °C and different substrate bias voltage are possible. The performance of the chamber was tested with the deposition of high quality TiN films of different thicknesses.

Phase stability of epitaxially grown Ti2AlN thin films

The phase stability of Mn+1AXn phase (M: early transition metal, A: A-group element, and X: C and∕or N) Ti2AlN thin films reactively sputtered onto MgO(111) and Al2O3(0001) substrates has been investigated by in situ x-ray diffraction and Rutherford backscattering. High substrate temperature deposition results in epitaxial Ti2AlN growth with basal planes parallel to the substrate surface. In contrast to reported high thermal stability for bulk Ti–Al–N Mn+1AXn phases in air, Ti2AlN thin films in vacuum decompose already at ∼800°C. The decomposition proceeds by outward Al diffusion and evaporation, followed by detwinning of the as-formed Ti2N atomic layers into cubic TiNx and intermediate phases.

Thermal stability of grain structure and defects in submicrocrystalline and nanocrystalline nickel

Abstract The grain and defect structure of submicrocrystalline and nanocrystalline nickel produced by equichannel angular pressing or by ball milling, respectively, has been studied by isochronal and isothermal annealing experiments, and X-ray investigations. A detailed analysis of the thermal stability of the different types of microstructures will be presented.

Microstructure and nonbasal-plane growth of epitaxial Ti2AlN thin films

Thin films of the Mn+1AXn (MAX) phase (M: early transition metal, A:A-group element, X: C and/or N, n=1-3) Ti2AlN were epitaxially grown onto single-crystal MgO(111) and MgO(100) substrates by dc r ...

Nucleation and growth of Ti2AlN thin films deposited by reactive magnetron sputtering onto MgO(111)

The nucleation and growth of Ti2AlN thin films on MgO(111) substrates during dual direct current reactive magnetron cosputtering from Ti and Al targets in an Ar∕N2 atmosphere at a substrate temperature of 690 °C have been investigated. Time and thickness dependent in situ specular x-ray reflectivity and x-ray diffraction in combination with cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy reveal the formation of competing phases for slight N superstoichiometry with respect to Ti2AlN. The stoichiometry deviations initiate the layer-by-layer growth of a ∼380 A thick epitaxial N-substoichiometric cubic (Ti1−xAlx)Ny layer. N-vacancy driven diffusion of Ti and Al leads to decomposition of this metastable solid solution into nanosized cubic TiNy′ and AlNy″ domains as well as to a solid-state reaction with the MgO(111) by formation of a Mg2(Al:Ti)O4 spinel, reducing the transformed (Ti1−xAlx)Ny layer thickness down to ∼60 A. Local AlNy″ domains serve as templates for Ti...

Topotaxial growth of Ti2AlN by solid state reaction in AlN∕Ti(0001) multilayer thin films

The formation of Ti2AlN by solid state reaction between layers of wurtzite-AlN and α-Ti was characterized by in situ x-ray scattering. The sequential deposition of these layers by dual magnetron sputtering onto Al2O3(0001) at 200°C yielded smooth, heteroepitaxial (0001) oriented films, with abrupt AlN∕Ti interfaces as shown by x-ray reflectivity and Rutherford backscattering spectroscopy. Annealing at 400°C led to AlN decomposition and diffusion of released Al and N into the Ti layers, with formation of Ti3AlN. Further annealing at 500°C resulted in a phase transformation into Ti2AlN(0001) after only 5min.

Phase transformation kinetics during continuous heating of a β-quenched Ti–10V–2Fe–3Al alloy

The effect of heating rate on the phase transformation kinetics of a Ti–10V–2Fe–3Al metastable β titanium alloy quenched from the β field is investigated by fast in situ high energy synchrotron X-ray diffraction and differential scanning calorimetry. The initial microstructure is formed by α″ martensite and fine ωath particles distributed in the retained β-phase matrix. The phase transformation sequence varies with the heating rate as revealed by analysis of the continuous evolution of crystallographic relationships between phases. At low temperatures an athermal reversion of α″ martensite into β takes place. This reversion occurs to a larger extent with increasing heating rate. On the other hand, diffusion–driven precipitation and growth of the ω phase is observed for lower heating rates accompanying the reverse martensitic transformation. Furthermore, the results show that the stable α phase can form through three different paths: (a) from the ω phase, (b) from α″ martensite, and (c) from the β phase.

Observation of the growth mode of TiN during magnetron sputtering using synchrotron radiation

The heteroepitaxial growth of TiN on MgO(001), deposited by reactive magnetron sputtering, has been studied in situ. Using real-time specular x-ray reflectivity, layer-by-layer growth was observed, with the surface roughening decreasing with an increase in the deposition temperature. Higher temperatures also resulted in lower growth rates. The film thickness was measured with specular x-ray reflectivity. Using off-plane Bragg–Brentano as well as grazing incidence in-plane wide angle scattering, the pseudomorphic growth of TiN to the underlying MgO(001) was established. Transmission electron microscopy reveals atomic planes passing through the MgO–TiN boundary, thus confirming heteroepitaxial growth.