Continuous Composition Spread Research Articles

High-throughput synthesis and oxidation behavior of a continuous composition spread (Nb–Ti)1-x-ySixCry alloy thin film

High-throughput method of three targets magnetron sputter co-deposition was adopted to prepare (Nb–Ti)1-x-ySixCry composition spread alloy film (CSAF). Early oxidation behavior of the as-deposited alloy thin film was investigated in atmospheric conditions at 1250 °C for 10 min. A (Nb–Ti)1-x-ySixCry combinatorial material library covering (9.34–32.31) Si-(10.43–20.27) Cr (at. %) is obtained and as-deposited film was composed of amorphous phase. The oxidized film was separated into three regions having different oxidation products. The composition range for establishment of a protective scale (SiO2 and CrNbO4) and a small amount of Nb2O5 was ascertained efficiently across the entire alloy thin film.

Highly conductive Ag-SiNx composite thin film anode engineering for transparent battery

Silicon nitride-based electrodes (SiNx), have been proposed as promising candidates for high-capacity transparent anode electrodes in earlier studies. Unfortunately, they have low electrical conductivity, resulting in some disadvantages such as power density for application in thin film batteries. To improve electrical conductivity, bulk batteries use conductive carbon additives, which also impair transmittance. Thus, we conducted this research to enhance the electrochemical properties by improving the conductivity without compromising the transmittance by uniformly dispersed Ag nanoparticles in SiNx thin film. We obtained an Ag-SiNx composite thin-film anode via continuous composition spread sputtering and investigated the effect of the Ag concentration. The capacity of the thin-film battery raised to 242.8 μAh/cm2·μm with Ag0.236SiO0.7N anode compared to the SiO0.7N anode which had a capacity of 37.2 μAh/cm2·μm. In addition, while SiO0.7N was operated only up to 2 C, Ag0.236SiO0.7N has driven up to 5 C and 10 C, which are high C rates, was also possible. AgxSiO0.7N thin film with less than 0.236 mol content demonstrates an optical transmittance of over 60% in the visible area. These results indicate that improving the electrical conductivity by the addition of an Ag during the silicon nitride deposition can increase its electrochemical performance while maintaining its applicability to transparent batteries.

Multi-spray pyrolysis for combinatorial synthesis of materials libraries and their high-throughput screening: Application to Li-ion conducting electrolytes

We present a multi-head spray pyrolysis system and its application in high-throughput combinatorial synthesis for research of solid Li-ion conductors. Each spraying nozzle is fed with a separate precursor solution. The overlap of areas that are sprayed leads to unprecedented composition flexibility of the films obtained after pyrolysis. Thus, a library with a continuous composition spread of a Li-La-P-O model system is formed. The Li-ion conduction was determined on 169 cells of the library, using high throughput impedance measurements in a controlled environment. While the activation energies that were found were relatively small, Li-ion conduction was still low. This low mobility is hypothesized to originate from the sub-optimal occupation of Li sites in the non-stoichiometric materials' lattices, and/or porosity and tortuosity issues, which in turn, reduces their effective concentration and contribution to ion transport. In addition, porosity and tortuosity in sprayed electrolyte causes random orientation of the grains and grain boundaries in the solid followed by the random diffusion scattering of Li-ions and low Li-ions conductivity, despite low apparent activation energy of conduction.

Combinatorial synthesis of heteroepitaxial, multi-cation, thin-films via pulsed laser deposition coupled with in-situ, chemical and structural characterization

Combinatorial synthesis via a continuous composition spread is an excellent route to develop thin-film libraries as it is both time- and cost-efficient. Creating libraries of functional, multicomponent, complex oxide films requires excellent control over the synthesis parameters combined with high-throughput analytical feedback. A reliable, high-throughput, in-situ characterization analysis method is required to meet the crucial need to rapidly screen materials libraries. Here, we report on the combination of two in-situ techniques—(a) Reflection high-energy electron diffraction (RHEED) for heteroepitaxial characterization and a newly developed compositional analysis technique, low-angle x-ray spectroscopy (LAXS), to map the chemical composition profile of combinatorial heteroepitaxial complex oxide films deposited using a continuous composition spread method via pulsed laser deposition. This is accomplished using a unique state-of-the-art combinatorial growth system with a fully synchronized four-axis mechanical substrate stage without shadow masks, alternating acquisition of chemical compositional data using LAXS at various different positions on the sim 41 mm times 41 mm range and sequential deposition of multilayers of SrTiO_3 and hbox {SrTi}_{0.8}hbox {Ru}_{0.2}hbox {O}_3 on a 2-inch (50.8 mm) hbox {LaAlO}_3 wafer in a single growth run. Rutherford backscattering spectrometry (RBS) is used to calibrate and validate the compositions determined by LAXS. This study shows the feasibility of combinatorial synthesis of heteroepitaxial, functional complex oxide films at wafer-scale via two essential in-situ characterization tools—RHEED for structural analysis or heteroepitaxy and LAXS for compositional characterization. This is a powerful technique for development of new films with optimized heteroepitaxy and composition.

Electrical property modulation of Au/Ba0.6Sr0.4TiO3/La0.7Sr0.3MnO3 structure by continuous composition spread Mn doping

Composition spread Mn-doped Ba0.6Sr0.4Ti1-xMnxO3 (BSTMx, 0 ≤x ≤ 0.05) thin films were prepared on La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) layer by combinatorial pulsed laser deposition. When x is less than 3.3%, the BSTMx films are single phase according to X-ray diffraction data, and the Au/BSTMx/LSMO structure presents asymmetric transport properties. The asymmetry of the transport property gets weak with increasing Mn doping concentration. The reverse-bias current density of the Au/BSTMx/LSMO structure remains at a low value of 10−7 A/cm2, and the forward-bias current density reduces rapidly with the ascending doping content (x ≤ 1.8%). Further increasing the Mn content, the differences between the positive and reverse current densities become smaller, and almost vanish when the Mn content is greater than 3.8%, indicating the disappearance of the asymmetry of the transport property. The effects of the LSMO electrode, Au/BSTMx Schottky junction, BSTMx thin film, and BSTMx/LSMO interface on the whole electrical transport properties are discussed by virtue of the experimental and fitted impedance spectrums. Our results are helpful for insight into the doping mechanisms in perovskite oxides.

Al Composition Dependence of Band Offsets for SiO2 on α-(AlxGa1−x)2O3

Valence band offsets for SiO2 deposited by Atomic Layer Deposition on α-(AlxGa1-x)2O3 alloys with x = 0.26–0.74 were measured by X-ray Photoelectron Spectroscopy. The samples were grown with a continuous composition spread to enable investigations of the band alignment as a function of the alloy composition. From measurement of the core levels in the alloys, the bandgaps were determined to range from 5.8 eV (x = 0.26) to 7 eV (x = 0.74). These are consistent with previous measurements by transmission spectroscopy. The valence band offsets of SiO2 with these alloys of different composition were, respectively, were −1.2 eV for x = 0.26, −0.2 eV for x = 0.42, 0.2 eV for x = 0.58 and 0.4 eV for x = 0.74. All of these band offsets are too low for most device applications. Given the bandgap of the SiO2 was 8.7 eV, this led to conduction band offsets of 4.1 eV (x = 0.26) to 1.3 eV (x = 0.74). The band alignments were of the desired nested configuration for x > 0.5, but at lower Al contents the conduction band offsets were negative, with a staggered band alignment. This shows the challenge of finding appropriate dielectrics for this ultra-wide bandgap semiconductor system.

In situ compositional mapping of combinatorial materials libraries by scanning low-angle x-ray spectroscopy

A novel in situ diagnostic, scanning low-angle x-ray spectroscopy, has been introduced for compositional mapping of combinatorial thin film libraries. The technique uses high-energy electron beam-generated characteristic x rays from the films as they are deposited. The x-ray intensities are acquired dynamically, layer by layer at different film thicknesses, processed, and analyzed by Neocera-developed software using a unique algorithm. A fully automated four-axis mechanical stage facilitates data acquisition from a 2-in. diameter wafer providing a comprehensive compositional map across the wafer. A ternary materials library of Zn-Ti-Cr oxide has been deposited by continuous composition spread pulsed laser deposition to demonstrate the novel application of scanning low-angle x-ray spectroscopy for compositional mapping in situ. This in situ feedback on composition across the wafer significantly enhances the capability of any physical vapor deposition technique used for depositing combinatorial libraries, by providing compositional feedback during growth as well as the ability to monitor and control deposition processes for composition optimizations.

Tuning material properties of amorphous zinc oxynitride thin films by magnesium addition

The amorphous n-type multi-cation and multi-anion compound zinc magnesium oxynitride was fabricated by reactive long-throw magnetron co-sputtering from a metallic zinc and a metallic magnesium target. We achieved magnesium cation compositions in the thin films between 1 at. % and 7.5 at. % by varying the magnesium target power (variable-power approach) and compared this approach to a continuous composition spread. Both approaches lead to a reduction in Zn2+, an addition of Mg2+ cations, and a correlated increase in the oxygen content. Both these methods have the same effect on the optoelectrical properties: The increased magnesium content leads to a systematic decrease in the free charge carrier concentration regime from 1019 cm−3 to 1015 cm−3, a decrease in Hall mobility from 54 cm2 V−1 s−1 to 9 cm2 V−1 s−1, and a spectral shift of the absorption edge from 1.3 eV to 1.7 eV. The amorphous phase of zinc magnesium oxynitride is maintained until MgO crystallites form at a magnesium content ≥3 at. %. The electrical properties of the zinc magnesium oxynitride thin films show excellent long-term stability for at least 12 months.

Phase stabilization and oxidation of a continuous composition spread multi-principal element (AlFeNiTiVZr)1−xCrx alloy

Multi-Principal Element Alloys (MPEA) have been hypothesized to maintain a stable single alloy phase and resist corrosion at high temperatures, which are desirable in various functional applications, including material of turbine blades. However, studies into oxidation resistant alloys have been constrained to individual MPEA systems or a limited selection of compositions within those systems. Here, High-Throughput Experimental (HTE) techniques were utilized to rapidly assess phase stability and resistance to oxidation of an (AlFeNiTiVZr)1−xCrx continuous composition spread (CCS) thin-film alloy system. High-throughput synchrotron diffraction and Raman spectroscopy were used to identify phases, especially high symmetry structures and oxides, as a function of annealing time and composition. The formation of two distinct phase regions, R1 and R2, across the CCS was observed. One of these phase regions, R2, exhibited a stable high symmetry BCC-like phase at Cr concentrations greater than 25.4 at%, and grew a passivating mixed metal surface oxide; whereas, the R1 phase region, decomposed on oxidation to multiple oxides and reacted with the substrate to form silicides. The passivating mixed metal oxide layer appears to prevent destabilization of the (AlFeNiTiVZr)1−xCrx MPEA BCC solid solution. At longer annealing times the passivating phase was seen only above 29.2 at% Cr. High Cr-doped (AlFeNiTiVZr)1−xCrx appear to be a good candidate for high temperature, oxidation-resistant structural alloys.

Structural and Elastic Properties of α‐(AlxGa1−x)2O3 Thin Films on (11.0) Al2O3 Substrates for the Entire Composition Range

Structural properties of rhombohedral α‐(AlxGa1−x)2O3 thin films grown by two combinatorial pulsed laser deposition (PLD) techniques are investigated for the entire composition range. One α‐(AlxGa1−x)2O3 thin film is deposited on a 2 inch in diameter large a‐plane sapphire substrate using the continuous composition spread (CCS) PLD technique to fabricate a thin film with varying Al content ranging between x = 0.13 and x = 0.84. Laterally homogeneous α‐(AlxGa1−x)2O3 thin films exhibiting discrete Al contents are fabricated using radially segmented PLD targets on (11.0) Al2O3. Independent of the PLD technique, for x ≈ 0.55, a change from relaxed to pseudomorphic growth is observed as confirmed by the evolution of in‐ and out‐of‐plane lattice constants. The crystal structure is studied depending on the cation composition by X‐ray diffraction confirming the fabrication of epitaxial, corundum‐structured thin films.

Influences of Cr Content on the Phase Transformation Properties and Stress Change in V–Cr–O Thin-Film Libraries

VO2-based thin-film libraries with a continuous composition spread of Cr were obtained by reactive cosputtering. Gradual changes in the crystalline structures of VO2 were observed in the thin-film ...

Epitaxial stabilization of single phase κ-(InxGa1−x)2O3 thin films up to x = 0.28 on c-sapphire and κ-Ga2O3(001) templates by tin-assisted VCCS-PLD

High-quality (InxGa1−x)2O3 thin films in the orthorhombic κ-phase were grown by pulsed-laser deposition (PLD) on c-sapphire substrates as well as PLD-grown κ-Ga2O3 thin film templates. We varied the In-content 0 ≤ x ≤ 0.38 of the layers using a single, elliptically segmented, and tin-doped (In0.4Ga0.6)2O3/Ga2O3 target, employing the vertical continuous composition spread (VCCS) PLD-technique. A stoichiometric transfer of In and Ga from the target to the thin films has been confirmed, suggesting that the formation of volatile Ga2O and In2O suboxides is not a limiting factor in the tin-assisted growth mode. For all x, the thin films crystallized predominantly in the κ-modification as demonstrated by XRD 2θ-ω scans. However, for x > 0.28, phase separation of the cubic bixbyite and the κ-phase occurred. The κ-Ga2O3 template increased the crystalline quality of the κ-(InxGa1−x)2O3 thin film layers remarkably. Epitaxial, but relaxed growth with three in-plane rotational domains has been found for all thin films by XRD ϕ-scans or reciprocal space map measurements. Smooth surface morphologies (Rq < 3 nm) for all phase pure thin films were evidenced by atomic force microscopy measurements, making them suitable for multilayer heterostructures. The composition-dependent in- and out-of plane lattice constants follow a linear behavior according to Vegard’s law. A linear relationship can also be confirmed for the optical bandgaps that demonstrate the feasibility of bandgap engineering in the energy range of 4.1–4.9 eV. The results suggest κ-(InxGa1−x)2O3 as a promising material for heterostructure device applications or photodetectors.

Continuous Composition Spread and Electrochemical Studies of Low Cobalt Content Li(Ni,Mn,Co)O2 Cathode Materials

Many scientific efforts have been undertaken toward reducing the Co content in LiMn1/3Ni1/3Co1/3O2 cathode materials for thin-film batteries. In this study, we present cathodes with a wide range of Li(Ni, Mn, Co)O2 compositions to determine the material with the best electrochemical performance by changing the ratio of Ni to Mn at a fixed 0.1 at.% of Co by the continuous composition spread sputtering method. The cathode composition measurements by Rutherford backscattering spectroscopy show that the best electrochemical performance is obtained for a composition of Ni:Mn:Co = 19:71:10. The reasons for this improved electrochemical performance are further investigated by X-ray diffraction, electrochemical impedance spectroscopy, Fourier-transform infrared spectroscopy, and X-ray absorption near edge spectroscopy.

Band Alignment of Atomic Layer Deposited SiO2 and Al2O3 on (AlxGa1-x)2O3 for x = 0.2-0.65

(AlxGa1-x)2O3 is attracting attention for use in heterostructure devices grown on Ga2O3 substrates. The band alignments of amorphous, atomic layer deposited Al2O3 and SiO2 on (AlxGa1-x)2O3 for x = 0.2-0.65 have been determined using high resolution X-ray photoelectron spectroscopy. The (AlxGa1-x)2O3 was grown by continuous composition spread Pulsed Laser Deposition (CCS-PLD). The band alignments are type I (nested gap) in all cases, with conduction band offsets ranging from 1.57-0.67 eV for Al2O3 on (Al0.2Ga0.8)2O3 to (Al0.65Ga0.35)2O3 and 2.35-1.40 eV for SiO2 on these same compositions. Correspondingly, the valence band offsets are all >1.25 eV for SiO2 and 0.23-0.33eV for Al2O3 over this composition range. While these are the first reports for Al2O3 on (AlxGa1-x)2O3 over such a wide composition range, our results differ by up to 0.4 eV in conduction band offsets from past studies of SiO2 on (AlxGa1-x)2O3 of a more limited composition range, which themselves have shown variations of up to 0.5eV for conduction band offsets on nominally the same composition. These differences emphasize the influence of experimental conditions in determining band alignments.

Exploration of Si-doped SnO2 composition and properties of oxide/Ag/oxide multilayers prepared using continuous composition spread by sputtering

Si-doped SnO2/Ag/Si-doped SnO2 multilayer thin films were fabricated on flexible substrates at room temperature for indium free transparent conducting electrode. The optimal composition of Si-doped SnO2 was found by investigating electrical properties of various composition deposited by off-axis RF magnetron sputtering continuous composition spread method. Si-doped SnO2 thin films have low resistivity (0.07 Ω·cm) at doping content of Si (0.14 wt%). Si-doped SnO2/Ag/Si-doped SnO2 multilayer thin films were fabricated using optimized composition deposited by on-axis RF and DC sputtering. The optimized Si-doped SnO2/Ag/Si-doped SnO2 multilayer thin film has resistivity of 9.1 × 10−5 Ω·cm and 81% transmittance in the visible region (550 nm).

Effects of alloy composition and Si-doping on vacancy defect formation in (InxGa1–x)2O3 thin films

Various nominally undoped and Si-doped (InxGa1–x)2O3 thin films were grown by pulsed laser deposition in a continuous composition spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterisation technique in order to investigate the effect of alloy composition and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concentrations changing to In2O3-like behaviour along with the increase in the indium fraction. Increasing indium concentration is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron saturation trapping in VIn-like defects, suggesting a vacancy concentration of at least mid-1018 cm−3 independent of the indium content.

High‐throughput method to deposit continuous composition spread Sb2(SexS1 − x)3 thin film for photovoltaic application

AbstractSb2(SexS1 − x)3 alloy materials with tunable bandgaps combining the advantages of Sb2S3 and Sb2Se3 showed high potential in low cost, non‐toxicity, and high stability solar cells. The composition dependence of device performance becomes indispensable to study. However, traditional approaches often implement 1 composition at a time, which easily lead to long period and systematic errors. The present work developed a high‐throughput experimental method, close‐space dual‐plane‐source evaporation (CDE) method, to successfully deposit continuous composition spread Sb2(SexS1 − x)3 library at 1 time. On the surface of the obtained film, the x value of Se content evolved from 0.09 to 0.84 by a series of complementary characterizations. At depth direction, the alloy film kept high crystallinity and composition consistency. Solar cell arrays (19 × 6) were fabricated to investigate the relationship between compositions and performances. As the increase of Se content, the conversion efficiency first increased from 1.8% to 5.6% and then decreased to 5%. The Voc and Jsc demonstrated an opposite evolution trend. The champion device with the composition of Sb2(Se0.68S0.32)3 achieved the Voc and Jsc trade‐off exceeding the performances of Sb2S3 (2.43%) and Sb2Se3 (4.97%) devices. Cryogenic and transient characterizations were utilized to investigate the distinct performance evolution mechanism. There existed shallow defect levels in Se‐rich alloys and deep defects in sulfur‐rich ones. The widely tuned absorber compositions combined with distinct defect characters induced to the large variation of device performance. The present continuous composition spread Sb2(SexS1 − x)3 film and their CDE fabrication technique were expected to efficiently screen materials and promote the development of antimony chalcogenide solar cells.

Vital Role of Oxygen for the Formation of Highly Rectifying Schottky Barrier Diodes on Amorphous Zinc-Tin-Oxide with Various Cation Compositions.

We present electrical properties of Schottky barrier diodes on room-temperature deposited amorphous zinc-tin-oxide (ZTO) with Zn/(Zn + Sn) contents between 0.12 and 0.72. A combinatorial approach with continuous composition spread pulsed laser deposition is used to achieve the wide range of compositions with four samples each on 50 × 50 mm2 glass substrates. The Schottky barrier contacts were fabricated by the reactive direct-current sputtering of platinum. Best diode properties (rectification ratio SV = 2.7 × 107, ideality factor η = 1.05, and effective barrier height ϕB,eff = 1.25 eV) are obtained for a composition of 0.63 Zn/(Zn + Sn). Aging on the timescale of days and months is observed that leads to improved device properties (higher rectifications and lower ideality factors). In particular, the diodes with the lowest performance in the as-prepared state show the biggest improvements. The best diode properties after the aging process (SV = 3.9 × 107, η = 1.12, and ϕB,eff = 1.31 eV) were also observed for 0.63 Zn/(Zn + Sn).

Full range optical and electrical properties of Zn-doped SnO2 and oxide/metal/oxide multilayer thin films deposited on flexible PET substrate

As a potential replacement of indium-tin oxide (ITO), Zn-doped SnO2/Ag/Zn-doped SnO2 multilayer transparent conducting electrodes were prepared on the flexible poly ethylene terephthalate (PET) substrates by RF sputtering at room temperature. To find the optimized composition of Zn-doped SnO2 thin film, which will have higher conductivity and transmittance as compared to the undoped SnO2 thin film, an off-axis Continuous Composition Spread (CCS) sputtering method was used. Zn-doped SnO2 thin films have lower resistivity than undoped SnO2 thin films due to excess oxygen vacancies (Vo) and/or zin interstitials (Zni) in thin films. The minimum resistivity of thin film was 0.13 Ω cm at optimized 2.43 wt% Zn-doping. Zn-doped SnO2/Ag/Zn-doped SnO2 multilayer thin films were prepared using the optimized composition deposited by an on-axis RF sputter. The multilayer TCO film has the resistivity ∼5.33 × 10−5 Ω cm and the average transmittance >85% in the 550 nm wavelength region.

Wavelength-selective ultraviolet (Mg,Zn)O photodiodes: Tuning of parallel composition gradients with oxygen pressure

We report on ultraviolet photodiodes with integrated optical filter based on the wurtzite (Mg,Zn)O thin films. Tuning of the bandgap of filter and active layers was realized by employing a continuous composition spread approach relying on the ablation of a single segmented target in pulsed-laser deposition. Filter and active layers of the device were deposited on opposite sides of a sapphire substrate with nearly parallel compositional gradients. Ensure that for each sample position the bandgap of the filter layer blocking the high energy radiation is higher than that of the active layer. Different oxygen pressures during the two depositions runs. The absorption edge is tuned over 360 meV and the spectral bandwidth of photodiodes is typically 100 meV and as low as 50 meV.