Alan Savan

Development of multifunctional thin films using high-throughput experimentation methods

Abstract This paper describes the use of thin film high-throughput experimentation methods for the efficient development of multifunctional materials, using Ni – Ti – X and ferromagnetic shape memory alloys as examples. The thin films were fabricated in the form of binary, ternary, and quaternary materials libraries by special magnetron sputter deposition processes. These materials libraries were subsequently processed and characterized by high-throughput experimentation methods in order to relate compositional information with structural and functional properties. For this, appropriate visualization of the data is necessary. Results show that the martensitically transforming regions in ternary thin films are generally larger than was known from literature. Within these regions, the variation of the functional properties can be mapped with respect to the composition and microstructure, and thus the most suitable materials for applications can be effectively selected.

Thermally Oxidized Mn–Co Thin Films as Protective Coatings for SOFC Interconnects

Thin metallic Mn 50 Co 50 coatings (0.3 and 1 μm) were deposited by magnetron cosputtering on bare and on 100 h preoxidized ZMG232L stainless steel substrates for application as protective coatings for solid oxide fuel cells (SOFCs) interconnects. The coatings on bare steel were oxidized for different times of up to 101 h at 800°C in ambient air. After 1 h heat-treatment, the metallic films had already converted to (Mn,Co) 3 O 4 oxide with a spinel structure. With increasing oxidation time, a Mn 2 O 3 phase was also detected, independent of the thickness of the coatings. This phase formation was attributed to Mn ion enrichment in the coating. Cr diffusion and stresses in the thin coatings were also observed. Bare steel samples were also preoxidized for different durations to determine a suitable oxidation time to form a stable (Mn,Cr) 3 O 4 /Cr 2 O 3 oxide scale on their surface. Steel samples preoxidized for 100 h and coated with Mn 50 Co 50 were subjected to time-dependent area specific resistance (ASR) measurements for 500 h. The ASR values obtained were 15 and 17 mΩ cm 2 for the substrate coated with 0.3 and 1 μm Mn 50 Co 50 , respectively. Also, no Mn 2 O 3 phase was present, and no Cr diffusion was detected in the thicker coating.

Interdiffusion in Fe-Pt multilayers

Fe∕Pt multilayers with modulation periods Λ=24.1±0.2 and 37.2±0.1A and [110]‖[111] bcc-fcc texture were fabricated by magnetron sputtering on thermally oxidized Si wafers. The structural evolution of the multilayers with annealing temperature in the range of 300–600K was studied by in situ x-ray diffraction (XRD) and x-ray reflectivity. Two temperature regimes were found from the XRD data. Below 534±4K slow, short-range diffusion is observed without significant broadening of the satellite peaks or changes in the texture. Above 534K fast, long-range diffusion is observed accompanied by significant broadening of the satellites and rapid increase of the misorientations of the grains. The multilayers crystallize at about 583K into the tetragonal FePt phase with a small degree of ordering and strong [111] texture. The transition resembles a first-order phase transition with a critical exponent β=0.48±0.01 which practically does not depend on Λ. The bulk interdiffusion coefficient, determined from the decay of ...

High-Throughput Characterization of Pt Supported on Thin Film Oxide Material Libraries Applied in the Oxygen Reduction Reaction

Thin film metal oxide material libraries were prepared by sputter deposition of nanoscale Ti/Nb precursor multilayers followed by ex situ oxidation. The metal composition was varied from 6 at.% Nb to 27 at.% Nb. Additionally, thin wedge-type layers of Pt with a nominal thickness gradient from 0 to 5 nm were sputter-deposited on top of the oxides. The materials libraries were characterized with respect to metallic film composition, oxide thickness, phases, electrical conductivity, Pt thickness, and electrochemical activity for the oxygen reduction reaction (ORR). Electrochemical investigations were carried out by cyclic voltammetry using an automated scanning droplet cell. For a nominal Pt thickness >1 nm, no significant dependence of the ORR activity on the Pt thickness or the substrate composition was observed. However, below that critical thickness, a strong decrease of the surface-normalized activity in terms of reduction currents and potentials was observed. For such thin Pt layers, the conductivity of the substrate seems to have a substantial impact on the catalytic activity. Results from X-ray photoelectron spectroscopy (XPS) measurements suggest that the critical Pt thickness coincides with the transition from a continuous Pt film into isolated particles at decreasing nominal Pt thickness. In the case of isolated Pt particles, the activity of Pt decisively depends on its ability to exchange electrons with the oxide layer, and hence, a dependence on the substrate conductivity is rationalized.

Properties of anodic oxides grown on a hafnium–tantalum–titanium thin film library

Abstract A ternary thin film combinatorial materials library of the valve metal system Hf–Ta–Ti obtained by co-sputtering was studied. The microstructural and crystallographic analysis of the obtained compositions revealed a crystalline and textured surface, with the exception of compositions with Ta concentration above 48 at.% which are amorphous and show a flat surface. Electrochemical anodization of the composition spread thin films was used for analysing the growth of the mixed surface oxides. Oxide formation factors, obtained from the potentiodynamic anodization curves, as well as the dielectric constants and electrical resistances, obtained from electrochemical impedance spectroscopy, were mapped along two dimensions of the library using a scanning droplet cell microscope. The semiconducting properties of the anodic oxides were mapped using Mott–Schottky analysis. The degree of oxide mixing was analysed qualitatively using x-ray photoelectron spectroscopy depth profiling. A quantitative analysis of the surface oxides was performed and correlated to the as-deposited metal thin film compositions. In the concurrent transport of the three metal cations during oxide growth a clear speed order of Ti > Hf > Ta was proven.

High-Throughput Compositional and Structural Evaluation of a Li a (Ni x Mn y Co z )O r Thin Film Battery Materials Library

A Lia(NixMnyCoz)Or cathode materials library was fabricated by combinatorial magnetron sputtering. The compositional analysis of the library was performed by a new high-throughput approach for Li-content measurement in thin films, which combines automated energy-dispersive X-ray spectroscopy, Deuteron-induced gamma emission, and Rutherford backscattering measurements. Furthermore, combining this approach with thickness measurements allows the mapping of density values of samples from the materials library. By correlating the obtained compositional data with structural data from high-throughput X-ray diffraction measurements, those compositions which show a layered (R3̅m) structure and are therefore most interesting for Li-battery applications (for cathode (positive) electrodes) can be rapidly identified. This structure was identified as being most pronounced in the compositions Li0.6(Ni0.16Mn0.35Co0.48)O2, Li0.7(Ni0.10Mn0.37Co0.51)O2, Li0.6(Ni0.23Mn0.33Co0.43)O2, Li0.3(Ni0.65Mn0.08Co0.26)O2, Li0.3(Ni0.63Mn0.08Co0.29)O2, Li0.4(Ni0.56Mn0.09Co0.34)O2, Li0.5(Ni0.45Mn0.13Co0.42)O2, and Li0.6(Ni0.34Mn0.14Co0.52)O2.

Combinatorial investigation of Fe-B thin-film nanocomposites.

Abstract Combinatorial magnetron sputter deposition from elemental targets was used to create Fe–B composition spread type thin film materials libraries on thermally oxidized 4-in. Si wafers. The materials libraries consisting of wedge-type multilayer thin films were annealed at 500 or 700 °C to transform the multilayers into multiphase alloys. The libraries were characterized by nuclear reaction analysis, Rutherford backscattering, nanoindentation, vibrating sample magnetometry, x-ray diffraction (XRD) and transmission electron microscopy (TEM). Youngs modulus and hardness values were related to the annealing parameters, structure and composition of the films. The magnetic properties of the films were improved by annealing in a H2 atmosphere, showing a more than tenfold decrease in the coercive field values in comparison to those of the vacuum-annealed films. The hardness values increased from 8 to 18 GPa when the annealing temperature was increased from 500 to 700 °C. The appearance of Fe2B phases, as revealed by XRD and TEM, had a significant effect on the mechanical properties of the films.

High-throughput characterization of film thickness in thin film materials libraries by digital holographic microscopy

Abstract A high-throughput characterization technique based on digital holography for mapping film thickness in thin-film materials libraries was developed. Digital holographic microscopy is used for fully automatic measurements of the thickness of patterned films with nanometer resolution. The method has several significant advantages over conventional stylus profilometry: it is contactless and fast, substrate bending is compensated, and the experimental setup is simple. Patterned films prepared by different combinatorial thin-film approaches were characterized to investigate and demonstrate this method. The results show that this technique is valuable for the quick, reliable and high-throughput determination of the film thickness distribution in combinatorial materials research. Importantly, it can also be applied to thin films that have been structured by shadow masking.

Preparation of 24 ternary thin film materials libraries on a single substrate in one experiment for irreversible high-throughput studies.

For different areas of combinatorial materials science, it is desirable to have multiple materials libraries: especially for irreversible high-throughput studies, like, for example, corrosion resistance testing in different media or annealing of complete materials libraries at different temperatures. Therefore a new combinatorial sputter-deposition process was developed which yields 24 materials libraries in one experiment on a single substrate. It is discussed with the example of 24 Ti-Ni-Ag materials libraries. They are divided based on the composition coverage and orientation of composition gradient into two sets of 12 nearly identical materials libraries. Each materials library covers at least 30-40% of the complete ternary composition range. An acid etch test in buffered-HF solution was performed, illustrating the feasibility of our approach for destructive materials characterization. The results revealed that within the composition range of Ni < 30 at.%, the films were severely etched. The composition range which shows reversible martensitic transformations was confirmed to be outside this region. The high output of the present method makes it attractive for combinatorial studies requiring multiple materials libraries.

Accelerated atomic-scale exploration of phase evolution in compositionally complex materials

Combining nanoscale-tip arrays with combinatorial thin film deposition and processing as well as direct atomic-scale characterization (APT and TEM) enables accelerated exploration of the temperature- and environment-dependent phase evolution in multinary materials systems. Results from nanocrystalline CrMnFeCoNi show that this alloy is unstable and already decomposes after 1 h at low temperatures of around 300 °C. The combinatorial processing platform approach is extendible to explore oxidation and corrosion in complex structural and functional materials on the atomic scale.