Composition Spread Thin Films Research Articles

Large anomalous Nernst conductivity of L10-ordered CoPt in CoPt composition-spread thin films

We demonstrate a high-throughput experimental characterization of anomalous Nernst conductivity ( αxyA ) of L10-ordered CoPt using Co1–x Pt x composition-spread thin films on MgO(100) substrates. The compositional dependence of the anomalous Nernst effect, anomalous Hall effect (AHE) and Seebeck effect is systematically measured. As increasing the Pt concentration, the crystal structure in the composition-spread film grown at 500 °C changes from face-centered cubic (fcc) Co, A1-disordered CoPt, L10-ordered CoPt, A1-CoPt to fcc Pt. The largest αxyA of 2.52 A m–1 K–1 is obtained in L10-CoPt for Pt-rich composition of x = 70%, which is larger than that for an additionally fabricated nearly stoichiometric L10-Co48Pt52 reference uniform film. The contribution from direct conversion of a temperature gradient to a transverse charge current through αxyA is dominant to the total anomalous Nernst coefficient compared to the AHE-related contribution. From a scaling analysis of the AHE, the intrinsic contribution is found to be dominant for x = 70%. A theoretical calculation for αxyA of L10-Co50Pt50 agrees with the experimental αxyA value for the nearly stoichiometric reference film by considering on-site Coulomb interaction for Co atoms. We also point out the possible electron doping effect by the addition of Pt in L10-CoPt, which could explain the larger αxyA for the off-stoichiometric Pt-rich composition than that for the nearly stoichiometric one. Our experimental and theoretical results suggest the potential of L10-CoPt with a large αxyA originating from the intrinsic mechanism for future thermoelectric applications.

Efficient thermodynamic model optimization and uncertainty quantification via integration of combinatorial materials chip and Bayesian approach

Combinatorial materials chips (CMC) are composition spread thin-films deposited on a substrate that can rapidly determine the compositional-temperature information of ternary phase diagrams by high-throughput characterization. In this study, phase boundary information determined by CMC from the recent studies was used as input to optimize the thermodynamic model parameters by ESPEI based on Bayesian approach. The uncertainties in the model were also quantified. Fe–Cr–Ni and Fe–Co–Ni systems were chosen as examples to demonstrate the effectiveness of process. The newly optimized phase diagrams are in good agreement with the experimental results. It is also verified that the model can be effectively optimized by the dense CMC phase boundary data only without including the scattered experimental data. Moreover, the uncertainty in the model is reduced with the addition of CMC data. Finally, probability distributions of various phase combinations in the phase diagram were calculated, providing confidence intervals for material design.

Combinatorial optimization for high spin polarization in Heusler alloy composition-spread thin films by anisotropic magnetoresistance effect

Half-metallic Heusler alloys are promising candidates for spintronic applications due to their high spin polarization. However, the spin polarization strongly depends on the atomic composition, which is time-consuming to optimize from various compositional combinations. Here, we demonstrate a high-throughput compositional optimization method for high spin polarization in Co2(Mn, Fe)Ge Heusler alloys by combining composition-spread films and anisotropic magnetoresistance (AMR) measurement. Two types of composition-spread films of polycrystalline Co2(Mn1−xFex)Ge and (Co2Mn0.5Fe0.5)1−yGey are fabricated on SiO2/Si substrates by combinatorial sputtering deposition, followed by post-annealing. The compositional dependence of AMR shows the largest negative AMR ratio of −0.13% and the smallest temperature dependence of the resistance change of AMR for y = 0.25 in the (Co2Mn0.5Fe0.5)1−yGey composition-spread film, suggesting the highest spin polarization and the closest nature to the ideal half-metal at this composition ratio. To verify this, we also develop a new technique to measure the compositional dependence of spin polarization by measuring the spin accumulation signals of nonlocal spin-valve devices fabricated on the composition-spread films and observe the highest spin polarization of 82% for y = 0.24. This confirms a clear qualitative correlation between the large negative AMR ratio and high spin polarization. Our combinatorial method using the composition-spread films and the AMR measurement proves to be a facile way for optimizing the fabrication conditions of half-metallic Heusler alloys with high spin polarization.

Optical properties study of high-throughput horizontal composition gradient FeSe1-xTex thin film based on ellipsometry

The high-throughput superconductivity research model can effectively accelerate the material synthesis and physical characterization process. It can rapidly form a database of materials and reveal the hidden key physical laws, which provides significant assistance to the research of superconducting materials, especially the exploration of superconductivity mechanism. In this work, FeSe1-xTex thin film with spread composition was grown by combined laser molecular beam epitaxy, the third generation combined thin film preparation technique. The film thickness and surface morphology were obtained by atomic force microscopy, which showed that the sample surface was relatively smooth. In addition, we measured the distribution of critical elements and c-axis lattice constants within the different microzones along the direction of composition variation on the surface of the film, by X-ray photoelectron spectroscopy and X-ray diffraction, respectively, which verified that the film was prepared in accordance with a continuous composition gradient. Based on this, nine microzones of the film were tested using the ellipsometer equipped with a focused light spot. The dispersion model of the FeSe1-xTex layer was established using the Drude-Lorentz oscillator, and the optical constants of the film with horizontal composition gradient were obtained by inversion and fitting of the data within each microzone. The results indicate that the FeSe1-xTex thin film shows an obvious composition-dependent optical property. Our work reports the optical constants of FeSe1-xTex composition-spread thin film by using a nondestructive and accurate method, spectroscopic ellipsometry, which enriches the database of this material. This work may provide a reference for establishing the correlation between the optical and superconducting properties of FeSe-based superconductors.

Magnetic phase diagram mapping in Fe1−xRhx composition-spread thin films

We have fabricated high-quality polycrystalline Fe1−xRhx composition-spread thin films by cosputtering Fe and Rh, and investigated their structural and magnetic transformations as a systematic function of composition. With increasing Rh concentration, Fe1−xRhx thin film undergoes from an α׳ phase to a disordered γ phase and also shows a magnetic transition from a ferromagnetic phase to a paramagnetic phase. Vibrating-sample magnetometry and x-ray magnetic circular dichroism measurements show an antiferromagnetic-ferromagnetic transition in the range of 0.52 < x < 0.58 in the Fe1−xRhx composition gradient at room temperature. Based on our structural and magnetic property mapping, we construct a thin-film phase diagram of Fe1-xRhx. Compared to reported results in bulk alloys, the antiferromagnetic-ferromagnetic transition in the Fe1−xRhx thin films was found to occur at slightly higher Rh concentrations, while the boundary between the pure γ phase and the α׳/γ mixed phase region is shifted to the lower concentration Rh.

Microscale Combinatorial Libraries for the Discovery of High-Entropy Materials.

Polyelemental material systems, specifically high-entropy alloys, promise unprecedented properties. Due to almost unlimited combinatorial possibilities, their exploration and exploitation is hard. This challenge is addressed by co-sputtering combined with shadow masking to produce a multitude of microscale combinatorial libraries in one deposition process. These thin-film composition spreads on the microscale cover unprecedented compositional ranges of high-entropy alloy systems and enable high-throughput characterization of thousands of compositions for electrocatalytic energy conversion reactions using nanoscale scanning electrochemical cell microscopy. The exemplary exploration of the composition space of two high-entropy alloy systems provides electrocatalytic activity maps for hydrogen evolution and oxygen evolution as well as oxygen reduction reactions. Activity optima in the system Ru-Rh-Pd-Ir-Pt are identified, and active noble-metal lean compositions in the system Co-Ni-Mo-Pd-Pt are discovered. This illustrates that the proposed microlibraries are a holistic discovery platform to master the multidimensionality challenge of polyelemental systems.

Broadband, High-Frequency Permittivity Characterization for Epitaxial Ba1−xSrxTiO3 Composition-Spread Thin Films

Next-generation millimeter-wave $(>30\phantom{\rule{0.1em}{0ex}}\mathrm{GHz})$ telecommunications electronics must be compact, energy efficient, and have good thermal management. Tunable materials may play a role in meeting these requirements for millimeter-wave front-end devices, but there are few models or even measurements of tunable dielectrics at these frequencies. Here, we report on the adaptation and development of high-frequency dielectric spectroscopy techniques for composition-spread thin films from 100 MHz to 110 GHz. Our comprehensive technique sequentially probes the composition, frequency, and electric field dependence of the complex permittivity in a combinatorial thin film library, which provides a platform to rapidly explore functional materials for emerging telecommunications electronics. This is achieved by modifying existing on-wafer transmission line permittivity measurement techniques to obtain a compact set of test devices that can be patterned to extract the complex permittivity in multiple regions of a thin film. We demonstrate this technique by applying it to composition-spread ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Ti}\mathrm{O}}_{3}$ thin films spanning compositions from $x=0$ to $x=1.$ The systematic approach to materials growth inherent in combinatorial synthesis allows for a comprehensive picture of the ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{Ti}\mathrm{O}}_{3}$ system. Our continuous, quantitative measurements provide an encompassing view of the composition- and voltage-dependent trends in the room temperature dielectric properties at millimeter-wave frequencies---from strong, few-picosecond relaxations to no relaxation, and from large relative tunability (${n}_{r}>50\mathrm{%}$ at $75\phantom{\rule{0.1em}{0ex}}\mathrm{k}{\mathrm{V}}_{}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$) to zero tunability. Our work underscores both the utility of our technique, and the need to discover lower-loss, highly tunable electronic materials for next-generation telecommunications.

High-Throughput Characterization of (FexCo1-x)3O4 Thin-Film Composition Spreads.

Thin-film continuous composition spreads of Fe-Co-O were fabricated by reactive cosputtering from elemental Fe and Co targets in reactive Ar/O2 atmosphere using deposition temperatures ranging from 300 to 700 °C. Fused silica and platinized Si/SiO2 strips were used as substrates. Ti and Ta were investigated as adhesion layer for Pt and the fabrication of the Fe-Co-O films. The thin-film composition spreads were characterized by high-throughput electron-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, and optical transmission spectroscopy. The Fe-content ranged from 28 to 72 at. %. The spinel phases Fe2CoO4 and FeCo2O4 could be synthesized and stabilized at all deposition temperatures with a continuous variation in spinel composition in between. The dependence of the film surface microstructure on the deposition temperature and the composition was mapped. Moreover, the band gap values, ranging from 2.41 eV for FeCo2O4 to 2.74 eV for Fe2CoO4, show a continuous variation with the composition.

Structural and Functional Properties of the Thin Film System Ti-Ni-Si.

The thin film system Ti-Ni-Si was investigated using methods of combinatorial materials science. A thin film composition spread library of the system was fabricated using combinatorial magnetron sputtering. The functional properties Seebeck coefficient, electrical resistivity, and luminance were determined using high-throughput characterization techniques. A thin-film phase diagram was established by the assessment of high-throughput X-ray diffraction results. Correlations between composition, phase constitution, and functional properties with focus on the binary composition space are discussed.

Application of High-Throughput Seebeck Microprobe Measurements on Thermoelectric Half-Heusler Thin Film Combinatorial Material Libraries.

In view of the variety and complexity of thermoelectric (TE) material systems, combinatorial approaches to materials development come to the fore for identifying new promising compounds. The success of this approach is related to the availability and reliability of high-throughput characterization methods for identifying interrelations between materials structures and properties within the composition spread libraries. A meaningful characterization starts with determination of the Seebeck coefficient as a major feature of TE materials. Its measurement, and hence the accuracy and detectability of promising material compositions, may be strongly affected by thermal and electrical measurement conditions. This work illustrates the interrelated effects of the substrate material, the layer thickness, and spatial property distributions of thin film composition spread libraries, which are studied experimentally by local thermopower scans by means of the Potential and Seebeck Microprobe (PSM). The study is complemented by numerical evaluation. Material libraries of the half-Heusler compound system Ti-Ni-Sn were deposited on selected substrates (Si, AlN, Al2O3) by magnetron sputtering. Assuming homogeneous properties of a film, significant decrease of the detected thermopower Sm can be expected on substrates with higher thermal conductivity, yielding an underestimation of materials thermopower between 15% and 50%, according to FEM (finite element methods) simulations. Thermally poor conducting substrates provide a better accuracy with thermopower underestimates lower than 8%, but suffer from a lower spatial resolution. According to FEM simulations, local scanning of sharp thermopower peaks on lowly conductive substrates is linked to an additional deviation of the measured thermopower of up to 70% compared to homogeneous films, which is 66% higher than for corresponding cases on substrates with higher thermal conductivity of this study.

Combinatorial Discovery of Lanthanum-Tantalum Oxynitride Solar Light Absorbers with Dilute Nitrogen for Solar Fuel Applications.

Oxynitrides with the photoelectrochemical stability of oxides and desirable band energetics of nitrides comprise a promising class of materials for solar photochemistry. Challenges in synthesizing a wide variety of oxynitride materials has limited exploration of this class of functional materials, which we address using a reactive cosputtering combined with rapid thermal processing method to synthesize multi-cation-multi-anion libraries. We demonstrate the synthesis of a LaxTa1-xOyNz thin film composition spread library and its characterization by both traditional thin film materials characterization and custom combinatorial optical spectroscopy and X-ray absorption near edge spectroscopy (XANES) techniques, ultimately establishing structure-chemistry-property relationships. We observe that over a substantial La-Ta composition range the thin films crystallize in the same perovskite LaTaON2 structure with significant variation of anion chemistry. The relative invariance in optical band gap demonstrates a remarkable decoupling of composition and band energetics so that the composition can be optimized while retaining the desirable 2 eV band gap energy. We also demonstrate the intercalation of diatomic nitrogen into the La3TaO7 structure, which gives rise to a direct-allowed optical transition at 2.2 eV, less than half the value of the oxide's band gap. These findings motivate further exploration of the visible light response of this material that is predicted to be stable over a wide range of electrochemical potential.

High-throughput study of binary thin film tungsten alloys

Combinatorial magnetron co-sputtering from elemental sources was applied to produce W-alloy thin film composition spread materials libraries with well-defined, continuous composition gradients (film thicknesses between 1 and 2.5μm). Three systems were studied: W-Fe (0–7at.%), W-Ti (0–15at.%) and W-Ir (0–12at.%). High-throughput characterization of the materials libraries comprised of chemical, morphological and microstructural analyses. Scanning electron microscope investigations revealed that the films have a columnar structure of inverted cone-like units separated by voided boundaries, with a strong correlation to the alloying element content. Significant morphological changes occurred with an increase in the amount of the added element; W films with lower at.% of the alloying element had higher density and tighter grain boundaries, altering towards an increased amount of voids as the concentration of the alloying element increased. Electron backscatter diffraction scanning was used to determine microstructural components (grain size, grain shape, texture evolution), in dependence on the concentration of the alloying element.

Automated Phase Segmentation for Large-Scale X-ray Diffraction Data Using a Graph-Based Phase Segmentation (GPhase) Algorithm.

The creation of composition-processing-structure relationships currently represents a key bottleneck for data analysis for high-throughput experimental (HTE) material studies. Here we propose an automated phase diagram attribution algorithm for HTE data analysis that uses a graph-based segmentation algorithm and Delaunay tessellation to create a crystal phase diagram from high throughput libraries of X-ray diffraction (XRD) patterns. We also propose the sample-pair based objective evaluation measures for the phase diagram prediction problem. Our approach was validated using 278 diffraction patterns from a Fe-Ga-Pd composition spread sample with a prediction precision of 0.934 and a Matthews Correlation Coefficient score of 0.823. The algorithm was then applied to the open Ni-Mn-Al thin-film composition spread sample to obtain the first predicted phase diagram mapping for that sample.

Electrical Properties of Al2O3 Incorporated CeO2 Thin Films Deposited by RF Magnetron Sputtering

High-k materials have been widely investigated as a new gate stack in metal-oxide-semiconductor (MOS) devices1,2) because leakage current through the conventional SiO2 gate increases as scaling down of MOS devices. Among them, CeO2 is one of the most noteworthy materials3) because of its high dielectric constant of 26, chemical stability and the promising interfacial properties owing to the compatibility with Si in terms of the crystal structure and the lattice constant: the cubic fluoric structure, lattice mismatch as small as 0.35%. Cerium dioxide is, however, likely to crystalize even just after RF magnetron sputtering deposition at room temperature, leading to the increase of the leakage current along with grain boundaries4). In our preliminary study, we found that the thin films of Al2O3 doped CeO2 (Al2O3 as 10% composition) was kept amorphous after annealing up to 500 °C in a N2 atmosphere. In this work, we will report the electrical properties of the Al2O3 incorporated CeO2 to suppress the poly-crystallization of the films as a function of the wide Al2O3 composition range. The oxide composite of CeO2 and Al2O3 was prepared by the RF magnetron sputtering equipped with the combinatorial mask system5). The deposition was carried out using 2 targets of CeO2 and Al2O3 with the applied RF powers of 150 and 200 W, respectively, in an Ar atmosphere with an O2 introduction (10%) at room temperature at a pressure of 0.5 Pa. We prepared the combinatorial composition spread thin films, with the total thickness of 32 nm, in which Al2O3 composition ratio was changed in the range of 0 ~ 60% against CeO2 in a sample. In the deposition process, we repeated the following procedures 80 times; first, 0.16 nm thick CeO2 layer deposition: second, a wedge shaped CeO2 layer deposition with a thickness of 0 to 0.24 nm by the moving mask: finally, a wedge shaped Al2O3 layer with a thickness of 0 to 0.24 nm by the mask moving to the counter direction. After the deposition, we prepared 2 kinds of samples; one was annealed in a N2 atmosphere, the other in an O2 atmosphere at 500­­ °C for 30 minutes. Then, Pt dot electrodes were formed using the metal mask with the 100 µm in diameter openings on the surface of the annealed samples by sputtering. The electrical properties were characterized by I-V and C-V measurements. For the sample annealed in a N2 atmosphere, the leakage current density obtained from I-V characteristics at the electric field of -1 MV/cm decreased from around 1.0 × 10-6 to the minimum value of 1.0 × 10-8 A/cm2 with increasing Al2O3 composition from 0 to 20%. When the Al2O3 composition increased above 20% up to 60%, however, the leakage current density approached back to the value without Al2O3 doping. For the O2 annealed sample, the annealing effect was limited; the minimum leakage current density was around 1.0 × 10-7 A/cm2 at the Al2O3 composition of 10%. The leakage current density was greater than that without Al2O3 doping at the doping level excess 20%. From the result of C-V measurement at 1 MHz, the estimated dielectric constant of the films, assuming the interfacial SiO2 layer with a thickness of 3.5 nm, was rapidly decreased from 18 to 8 with the increase of the Al2O3 composition from 0 to 15%. For the higher Al2O3 composition than 15%, the estimated dielectric constant represented a constant value of 8. Judging from both view points of the leakage current and the dielectric constant, the optimum Al2O3 composition was considered to lie around 8%. Compared with the annealing in N2, the O2 annealing was not effective in improving electrical properties. REFERENCES 1) Wei Wang, Ning Gu, J. P. Sun and P. Mazumder, Solid-State Electronics 50, 1489-1494 (2006). 2) Dedong Han, Jinfeng Kang, Changhai Lin and Ruqi Han, Microelectronic Engineering 66, 643-647 (2003). 3) D. G. Lim, G. S. Kang, J. H. Yi, K. J. Ynag and J. H. Lee, Journal of the Korean Physical Society 51, 1085-1088 (2007). 4) H. Y. Lee, S. I. Kim, Y. P. Hong, Y. C. Lee, Y. H. Park and K. H. Ko, Surface and Coatings Technology 173, 224 (2003). 5) M. L. Green, K.-S. Chang, S. DeGendt, T. Schram and J. Hattrick-Simpers, Microelectronic Engineering 84, 2209–2212 (2007).

Screening of material libraries for electrochemical CO2 reduction catalysts – Improving selectivity of Cu by mixing with Co

The efficiency of the direct electrochemical CO2 reduction can be improved by the development of new alloy catalysts, but to do so a highly resolved composition screening remains to be connected to complex sample preparation and time consuming analysis. We have developed a technique that allows a fast and easy initial catalyst composition screening by analyzing thin film composition spread samples, utilizing a scanning flow cell coupled to an online electrochemical mass spectrometer (SFC-OLEMS). As a first case example, the investigation of a Cu–Co thin film material library demonstrates the benefits and high potential of this approach. In particular, a shift in selectivity toward C2 species for low Co content (5–15at.%) has been found and is discussed as being related to changed adsorption energies of intermediate products and the consequent modification of reaction pathways.

Electrochemical CO2 Reduction: Screening of Material Libraries and Improving Selectivity of Cu By Mixing It with Co

Using CO2 and converting it into useful products or even fuels is considered as a “dream reaction”. However even after over 30 years of research in the field of electrochemical CO2 reduction the “dream” didn’t come true and still remains a scientific and technical challenge. Two main applications can be considered for the electrochemical CO2 reduction: (1) The operation as storage technology to compensate the unavoidable energy fluctuations produced by renewable energy source like wind or sun and (2) the syntheses of valuable products like ethylene. Whilst in gas-phase heterogeneous catalysis the conceptual understanding about converting CO2 into fuels and the applied processes are well developed, electrochemical CO2 reduction is still in a stage where fundamental research is inevitably necessary to prove feasibility before large-scale implementation. On the contrary distinct advantages are the direct use of electrical energy, a potential dependent and therefore customizable product distribution and operation at ambient pressure and temperature. Main reasons for a so far not realized commercial application are (1) the low selectivity for valuable products on hydrocarbon producing electrodes and thereby a costly product separation, (2) the low energy efficiency as a cause of high overpotential on the working electrode and (3) the oxygen evolution as counter reaction, that also shows high overpotential and in addition to that catalyst degradation by dissolution. In order to address the fundamental understanding of the reduction processes on various types of material combinations, we have developed an electrochemical technique that enables (1) screening of thin-film material libraries with different experimental parameters, (2) investigating catalyst activity and stability of electrodes in parallel by inductively coupled plasma mass spectrometry (ICP-MS) and (3) analyzing the selectivity of catalysts for certain products via online electrochemical mass spectrometry (OLEMS). First results utilizing this approach will be presented; the focus will be in particular on the shift in selectivity towards C2 products of the electrochemical CO2 reduction on Cu-Co thin film composition spread samples at ambient temperature and pressure. Due to a high resolution composition analysis we were able to find a composition where production of C1 species is suppressed, while in return C2 production is enhanced. Utilization of this technique deepens understanding of fundamental processes and shows its high potential for improving performance of electrochemical CO2 reduction.

Structure and dielectric characteristics of continuous composition spread Ba1−xSrxTiO3 thin films by combinatorial pulsed laser deposition

Ba1−xSrxTiO3 (0≤x≤1, BST-x) continuous composition spread thin films were grown on SrTiO3 substrates buffered by La0.9Sr1.1NiO4 (LSNO) electrodes using combinatorial pulsed laser deposition. The effects of Sr concentration on the structure and dielectric properties of the Au/BST-x/LSNO capacitors were investigated. X-ray diffraction patterns and reciprocal space maps revealed that both the in-plane and out-of-plane BST-x lattice parameters decreased with the increment of Sr content. Impedance measurements showed that the dielectric constant and tunability simultaneously changed with Sr concentration and reached the maximum at about x=0.5, which is comparable to that of BST-x individual thin films or bulks. Our results showed the large potential of combinatorial method in optimizing materials properties and even finding new materials.

Use of radiofrequency power to enable glow discharge optical emission spectroscopy ultrafast elemental mapping of combinatorial libraries with nonconductive components: nitrogen-based materials.

Combinatorial chemistry and high-throughput techniques are an efficient way of exploring optimal values of elemental composition. Optimal composition can result in high performance in a sequence of material synthesis and characterization. Materials combinatorial libraries are typically encountered in the form of a thin film composition gradient which is produced by simultaneous material deposition on a substrate from two or more sources that are spatially separated and chemically different. Fast spatially resolved techniques are needed to characterize structure, composition, and relevant properties of these combinatorial screening samples. In this work, the capability of a glow discharge optical emission spectroscopy (GD-OES) elemental mapping system is extended to nitrogen-based combinatorial libraries with nonconductive components through the use of pulsed radiofrequency power. The effects of operating parameters of the glow discharge and detection system on the achievable spatial resolution were investigated as it is the first time that an rf source is coupled to a setup featuring a push-broom hyperspectral imaging system and a restrictive anode tube GD source. Spatial-resolution optimized conditions were then used to characterize an aluminum nitride/chromium nitride thin-film composition spread. Qualitative elemental maps could be obtained within 16.8 s, orders of magnitude faster than typical techniques. The use of certified reference materials allowed quantitative elemental analysis maps to be extracted from the emission intensity images. Moreover, the quantitative procedure allowed correcting for the inherent emission intensity inhomogeneity in GD-OES. The results are compared to quantitative depth profiles obtained with a commercial GD-OES instrument.

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

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.

Combinatorial search of superconductivity in Fe-B composition spreads

We have fabricated Fe-B thin film composition spreads in search of possible superconducting phases following a theoretical prediction by Kolmogorov et al. [Phys. Rev. Lett. 105, 217003 (2010)]. Co-sputtering was used to deposit spreads covering a large compositional region of the Fe-B binary phase diagram. A trace of superconducting phase was found in the nanocrystalline part of the spread, where the film undergoes a metal to insulator transition as a function of composition in a region with the average composition of FeB2. The resistance drop occurs at 4 K, and a diamagnetic signal has also been detected at the same temperature. From the field-dependent resistive transition behavior, we estimate the upper critical field to be approximately 2 T.