Combinatorial Thin Film Research Articles

A combinatorial properties study of thin film Al Fe alloys

The microstructure of an AlFe combinatorial thin film library with a compositional spread ranging from 5 to 23 at.% Fe was analysed. The local crystallographic properties were correlated to the film microstructure dynamic changes. The presence of a transitional region between two metastable phases in the AlFe alloys was identified and related to a percolation threshold near Al-12 at.% Fe. Anodic oxidation of the parent metals produced a mixed oxide on the surface of the AlFe library. XPS investigation of the mixed oxides suggested an intimate mixing of Al2O3 and Fe2O3.

Effect Of Annealing Temperature On Structural Properties Of nanocrystalline Tl3(PW12O40) Thin Films

Thallium (I) doped tungsten heteropolyoxometalate (HPOM) combinatorial thin films have been deposited on glass substrate using simple chemical bath deposition technique. The deposited films were annealed at 100 o C, 150 o C, 200 o C and 250 o C. These annealed thin films were characterized by using SEM, EDAX, AFM, FT-IR, XRD and TGA-DTA techniques for their structural properties. SEM and EDAX results shows that, tungsten HPOM material is polycrystalline in nature and Tl (I) is intercalated in phosphotungustate anion. AFM studies on the films annealed at different temperatures reveal that the surface roughness increases with the increase in annealing temperature, suggesting an increase of crystallization with temperature. FT-IR study confirms the well formation of heteropolyoxometalate material under investigation. Various structural parameters such as lattice constants, crystallite size and grain size have been calculated and they are found temperature dependent. The lattice constant, crystallite size and grain size of tungsten HPOM material increases with increase in temperature. XRD pattern of annealed thin films shows better crystanality of tungsten HPOM material having simple cubic spinel structure. The TGA-DTA study revealed that, Tl3 (PW12 O40) material is thermally stable up to 265.12 o C.

Elastic properties of face-centred cubic Fe–Mn–C studied by nanoindentation and ab initio calculations

We have studied experimentally and theoretically the influence of C and Mn content on the Young’s modulus of Fe–Mn–C alloys. Combinatorial thin film and bulk samples were characterized regarding their structure, texture and Young’s modulus. The following chemical composition range was investigated: 1.5–3.0at.% C, 28.0–37.5at.% Mn and 60.6–69.8at.% Fe. The experimental lattice parameters change marginally within 3.597–3.614Å with the addition of C and are consistent with ab initio calculations. The Young’s modulus data are in the range of 185±12–251±59GPa for the bulk samples and the thin film, respectively. C has no significant effect on the Young’s modulus of these alloys within the composition range studied here. The ab initio calculations are 15–22% larger than the average Young’s modulus values of the as-deposited and polished thin film at 3at.% C. The comparison of thin film and bulk samples results reveals similar elastic properties for equivalent compositions, indicating that the applied research strategy consisting of the combinatorial thin film approach in conjunction with ab initio calculations is useful to study the composition dependence of the structure and elastic properties of Fe–Mn–C alloys. The very good agreement between the presented calculations and the experimentally determined lattice parameters and Young’s modulus values implies that the here-adopted simulation strategy yields a reliable description of carbon in Fe–Mn alloys, important for future alloy design.

Combinatorial Atmospheric Pressure Chemical Vapor Deposition (cAPCVD): A Route to Functional Property Optimization

We demonstrate how combinatorial atmospheric pressure chemical vapor deposition (cAPCVD) can be used as a synthetic tool for rapidly optimizing the functional properties of thin-films, by analyzing the self-cleaning properties of tungsten doped anatase as an example. By introducing reagents at separate points inside the reactor, a tungsten/titanium compositional gradient was formed and a diverse range of film growth conditions were obtained. By partially mixing the metal sources, a combinatorial film with a compositional profile that varied primarily in the lateral plane was synthesized. A combinatorial thin-film of anatase TiO(2) doped with an array of tungsten levels as a solid solution ranging from 0.38-13.8 W/Ti atom % was formed on a single glass substrate. The compositional-functional relationships were understood through comprehensively analyzing combinatorial phase space, with 200 positions investigated by high-throughput methods in this study. Physical and functional properties, and their compositional dependencies, were intercorrelated. It was found that increases in photocatalytic activity and conductivity were most highly dependent on film crystallinity within the 0.38-13.8 atom % W/Ti doping regime. However, enhancements in photoinduced surface wetting were primarily dependent on increases in preferred growth in the (211) crystal plane.

In situ infrared thermographic screening of compositional spread Mg–Ti thin-film libraries

An infrared imaging set-up and our own data treatment methodology have been developed to investigate hydrogen storage properties of combinatorial metallic thin-film libraries in situ. The technique has been tested by analysing the kinetics of hydrogen sorption and desorption in pure metallic magnesium films and in compositional-spread Mg–Ti libraries. Thermography was used to screen the surface emissivity of the libraries, since hydrogenated and dehydrogenated phases present very different values of this property. The proposed data treatment allows for direct visualisation of onset reaction temperatures ( T hydrogenation and T dehydrogenation) in function of composition which, in the present case, clearly reveals the catalytic influence of titanium on the kinetic properties of magnesium film dehydrogenation.

High-throughput Analysis for Combinatorial Epitaxial Thin Films by Concurrent X-Ray Diffraction

In order to rapid structural characterization of combinatorial epitaxial thin films, we developed a new x-ray diffraction system. A convergent x-ray beam from a curved crystal monochromator is focused on sample surface about 0.1 mm x 10 mm in size. Diffraction patterns of this area are observed on the two-dimensional detector. Rocking curve profile for each irradiated position can be measured within a few tens seconds, concurrently. We applied the present method to characterization of combinatorial [(SrTiO3)n/(BaTiO3)n]30 (n=12 to 30) superlattice and composition spread SrxBa1−xTiO3 on SrTiO3 substrate grown by laser molecular beam epitaxy (laser MBE). We could see the film diffraction peaks together with substrate peaks. Changes in superlattice periods and in composition of each position for the samples (combinatorial library) are clearly characterized only at one time rapid measurement.

Combinatorial Thin Film Synthesis and its High Throughput Screening for Inorganic Functional Materials

Combinatorial approach toward discovery of new functional materials and properties is a powerful method in fields of material science, because such approach can considerably decrease the time consumption for the discovery. Here, we focus on the combinaotorial approach to inorganic functional materials such as oxides, and review various studies on combinatorial thin film synthesis and high throughput screening techniques of structural, electric, magnetic, and optical properties.

Combinatorial library designs for quantifying thin film adhesion via the edge delamination test

We have demonstrated a combinatorial thin film library design for investigating the adhesion between film and substrate as measured by the edge delamination test. This library design allows rapid screening of critical parameters that control thin film reliability and bond strength in films and coatings. Specifically, our library design was aimed at quantifying the effect of film thickness and composition on the interfacial integrity between the film and underlying substrate by applying thermal stress. To create the combinatorial library, a single specimen was fabricated having a thickness gradient of an epoxy film on glass or silicon substrates. After sectioning the film into individual squares, a temperature gradient was applied orthogonal to the thickness gradient to induce debonding events where the adhesion is below a critical value. In addition, another combinatorial library was carried out using the epoxy films with concentration gradient and constant thickness, and applying a constant temperature. The combined results clearly demonstrate that our combinatorial library design and approach provide a large parameter space for accurately and reproducibly mapping the interfacial integrity and bond strength of film/substrate systems.

Influence of chemical composition and magnetic effects on the elastic properties of fcc Fe–Mn alloys

The influence of the Mn content on the elastic properties of face centered cubic Fe–Mn alloys was studied using the combinatorial approach. Fe–Mn thin films with a graded chemical composition were synthesized. Nanoindentation experiments were carried out to investigate the elastic properties as a function of the Mn content. As the Mn content increases from ∼23 to ∼39at.%, the average bulk modulus varies from 143 to 105GPa. Ab initio calculations served to probe the impact of magnetic effects on the elastic properties. The magnetic state description with disordered local moments yields the best agreement with the experimental results, whereas with non-magnetic and antiferromagnetic configurations the bulk modulus is overestimated. The strong impact of the magnetic configuration may be understood based on the differences in the chemical bonding and the magnetovolume effect. It is suggested that, owing to minute energy differences of competing antiferromagnetic configurations, a mixture of these with a “notional magnetic disorder” is present, which is in fact well described by the disordered local moments model. These results show that the combinatorial thin film synthesis with subsequent nanoindentation is an appropriate tool for investigating the elastic properties of Fe–Mn alloys systematically as a function of the chemical composition, to validate theoretical models.

Microstructural and dielectric properties of Ba0.6Sr0.4Ti1−xZrxO3 based combinatorial thin film capacitors library

Epitaxial growth of Ba0.6Sr0.4Ti1−xZrxO3 (0≤x≤0.3) composition spread thin film library on SrRuO3/SrTiO3 layer by combinatorial pulsed laser deposition (PLD) is reported. X-ray diffraction and energy dispersive x-ray spectroscopy studies showed an accurate control of the film phase and composition by combinatorial PLD. A complex evolution of the microstructure and morphology with composition of the library is described, resulting from the interplay between epitaxial stress, increased chemical pressure, and reduced elastic energy upon Zr doping. Statistical and temperature-related capacitive measurements across the library showed unexpected variations in the dielectric properties. Doping windows with enhanced permittivity and tunability are identified, and correlated to microstructural properties.

Preparation and Characterization of Combinatorial Thin Films for Solid Oxide Fuel Cell Cathodes

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Stoichiometric analysis of compositionally graded combinatorial amorphous thin film oxides using laser-induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a recently developed locally destructive elemental analysis technique that can be used to analyze solid, liquid, and gaseous samples. In the system explored here, a neodymium-doped yttrium aluminum garnet laser ablates a small amount of the sample and spectral emission from the plume is analyzed using a set of synchronized spectrometers. We explore the use of LIBS to map the stoichiometry of compositionally graded amorphous indium zinc oxide thin-film libraries. After optimization of the experimental parameters (distance between lens and samples, spot size on the samples, etc.), the LIBS system was calibrated against inductively coupled plasma atomic emission spectroscopy which resulted in a very consistent LIBS-based elemental analysis. Various parameters that need to be watched closely in order to produce consistent results are discussed. We also compare LIBS and x-ray fluorescence as techniques for the compositional mapping of libraries.

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High Throughput X-ray Diffraction Analysis of Combinatorial Polycrystalline Thin Film Libraries

With the increasing demand for new materials, analytical techniques which are able to rapidly characterize a large number of samples are becoming indispensable. Thin film technology has the potential to improve the amount of information contained on as-deposited samples by creating compositionally graded libraries. Conventionally, raster scan methods are used to interrogate such libraries but, in this paper, a different approach is presented to provide a method of high-throughput data collection and analysis using an X-ray diffraction (XRD) probe. An extended X-ray beam was used to illuminate the libraries, and a large area detector was used to collect the data. A new algorithm "Bandit" has been employed to analyze the collected data and extract the crystallographic information. The results of the technique have been compared with the raster scans showing that the algorithm provides reliable data at a significantly increased data acquisition speed.

Combinatorial thin film sputtering investigation of cerium concentration in Lu 2SiO 5 scintillators

Lutetium oxyorthosilicate (LSO) thin films with a cerium thickness gradient were sputter deposited to investigate the optimum cerium concentration for emission intensity. Thin film cerium concentration ranged from 0.06 to 0.88 at%. To compare the thin film samples to single crystal LSO, a set of single crystal LSO samples were investigated with cerium concentrations of 0.0015, 0.0095 and 0.078 at%. The thin film samples showed peak photoluminescence emission intensity at a cerium concentration of 0.35 at%; however, the single crystal samples exhibited peak photoluminescence emission intensity at a lower cerium concentration of 0.0095 at%. The photoluminescence excitation and emission spectra as a function of concentration demonstrate the concentration quenching behavior and the mechanisms are speculated to be due to radiative (self-absorption) and non-radiative energy transfer, which may be phonon assisted.

Manipulation of the crystallinity boundary of pulsed laser deposited high-k HfO2–TiO2–Y2O3 combinatorial thin films

Combinatorial library films of HfO2–TiO2–Y2O3, a high-k dielectric system, grown by pulsed laser deposition, exhibit visible boundary lines separating amorphous and crystalline phases. By changing processing space parameters, specifically substrate temperature during deposition, as well as the composition of the library film, we are able to manipulate the boundary and hence, the microstructural properties of the film. High-throughput x-ray diffraction and spectroscopic reflectometry are effective tools for measuring the properties of the resulting library films altered via these changes in processing. Electrical measurements confirm that the dielectric constant of the library films is composition and microstructure dependent.

Synthesis and screening of thin films in the CeCl 3–CeBr 3 system for scintillator applications

Thin film samples of CeCl 3, CeBr 3, and combinatorial compositions along the CeCl 3–CeBr 3 join were produced using thermal evaporation, which is being evaluated as a method for rapid screening of scintillator materials. The combinatorial thin films were shown to be compositionally reproducible from run-to-run within reasonable limitations. Analytical results suggest a continuous variation in the combinatorial samples in terms of their compositions, crystal structures, and luminescence characteristics.

Combinatorial (Ba,Sr)TiO3 thin film growth: X-ray diffraction and Raman spectroscopy

We report the investigation of the (Ba,Sr)TiO3 (BST) system of technological importance for microwave applications. The development of the combinatorial method enabled us to grow and study a library of samples ranging from BaTiO3 to SrTiO3 (ST) deposited on MgO substrate. The spatial control of the stoichiometry and of the structure has been evidenced and probed using energy dispersive x-ray spectroscopy, high resolution x-ray diffraction, and Raman spectroscopy. A global and coherent picture emerged from the complex interplay between the epitaxial/thermal stress and stoichiometry changes. Taking into account elastic interactions with the substrate we present subtle symmetry changes in the BST library in comparison with the bulk phase diagram such as tetragonal distortion observed on the ST side. Finally underdamped soft mode hardening and polar modes are detected on the high barium and strontium compositions, respectively, highlighting fundamental dynamical/structural differences with their bulk counterparts.

Capability of focused Ar ion beam sputtering for combinatorial synthesis of metal films

The authors examined the use of focused Ar ion beam sputtering (FAIS) for combinatorial synthesis. A Langmuir probe revealed that the electron temperature and density for FAIS of metal film deposition was lower than that of other major combinatorial thin film growth techniques such as pulsed laser deposition. Combining FAIS with the combinatorial method allowed the compositional fraction of the Pt–Ru binary alloy to be systematically controlled. Pt–Ru alloy metal film grew epitaxially on ZnO substrates, and crystal structures changed from the Pt phase (cubic structure) to the Ru phase (hexagonal structure) in the Pt–Ru alloy phase diagram. The alloy film has a smooth surface, with the Ru phase, in particular, showing a clear step-and-terrace structure. The combination of FAIS and the combinatorial method has major potential for the fabrication of high quality composition-spread metal film.

An approach to high-throughput X-ray diffraction analysis of combinatorial polycrystalline thin film libraries

With the demand for higher rates of discovery in the materials field, characterization techniques that are capable of rapidly and reliably surveying the characteristics of large numbers of samples are essential. A chemical combinatorial approach using thin films can provide detailed phase diagrams without the need to produce multiple, individual samples. This is achieved with compositional gradients forming high-density libraries. Conventional raster scanning of chemical or structural probes is subsequently used to interrogate the libraries. A new, alternative approach to raster scanning is introduced to provide a method of high-throughput data collection and analysis using an X-ray diffraction probe. Libraries are interrogated with an extended X-ray source and the scattering data collected using an area detector. A simple technique of `partitioning' this scattering distribution enables determination of information comparable to conventional raster scanned results but in a dramatically reduced collection time. The technique has been tested using synthetic X-ray scattering distributions and those obtained from contrived samples. In all cases, the partitioning algorithm is shown to be robust and to provide reliable data; discrimination along the library principal axis is shown to be ∼500 µm and the lattice parameter resolution to be ∼10−3 Å mm−1. The limitations of the technique are discussed and future potential applications described.