Amorphous Alloy Films Research Articles

Investigation of low temperature amorphous (InxGa1−x)2O3 films modulated by indium content for optimization in solar-blind photodetector

In this study, bandgap engineering of amorphous (InxGa1-x)2O3 alloy films fabricated at room temperature using pulsed laser deposition and alloy targets with different indium contents from 0 % to 50 % have been investigated. The effect of indium content on the characteristics of (InxGa1-x)2O3 films and the performance of metal–semiconductor-metal solar-blind photodetectors have been explored in detail. The moderate number of indium atoms introduced into Ga2O3 can obtain a flat surface morphology and adjusted bandgap to enhance the performance of solar-blind photodetector. When the excessive indium atoms were incorporated into the film, the obviously In enriched (InxGa1-x)2O3 alloy nano-clusters are observed on the film surface despite of the low growth temperature. It can be attributed to the segregation phenomenon because of the solid solubility limitation for indium in Ga2O3. Both of dark current and photocurrent of (InxGa1-x)2O3 photodetector increase with the incremental indium content mainly attributed to enhanced oxygen deficiency. As a result, the solar-blind photodetector can achieve an optimal performance using a balanced indium content of 20 % with an extremely low dark current of 4.4 × 10-12 A, a responsivity of 10.8 mA/W, a substantial on/off current ratio of 1.5 × 104 and a short rise/decay time of 0.33 s/0.54 s.

Coexistence of large anomalous Nernst effect and large coercive force in amorphous ferrimagnetic TbCo alloy films

The anomalous Nernst effect (ANE) has garnered significant interest for practical applications, particularly in energy harvesting and heat flux sensing. For these applications, it is crucial for the module to operate without an external magnetic field, necessitating a combination of a large ANE and a substantial coercive force. However, most materials exhibiting a large ANE typically have a relatively small coercive force. In our research, we have explored the ANE in amorphous ferrimagnetic TbCo alloy films, noting that the coercive force peaks at the magnetization compensation point (MCP). We observed that transverse Seebeck coefficients are amplified with Tb doping, reaching more than 1.0 μV/K over a wide composition range near the MCP, which is three times greater than that of pure Co. Our findings indicate that this enhancement is primarily due to direct conversion, a product of the transverse thermoelectric component and electrical resistivity. TbCo films present several significant advantages for practical use: a large ANE, the capability to exhibit both positive and negative ANE, the flexibility to be deposited on any substrate due to their amorphous nature, a low thermal conductivity, and a large coercive force. These attributes make TbCo films a promising material for advancing ANE-based technologies.

Tailoring the amorphous-nanocrystalline structures of TiNbZrNx films towards improving the anti-corrosion and mechanical properties by controlling nitrogen flow ratio

Multi-principal element alloy (MPEA) films demonstrate superior corrosion resistance and tribological properties, which have substantial potential for applications in marine engineering equipment. In this study, the TiNbZrNx MPEA nitride films were successfully deposited on 316 L austenitic stainless steel by direct current (DC) magnetron sputtering at various nitrogen flow ratio (RN2). The phase, composition, microstructure, corrosion and mechanical behaviors were investigated in detail. The results showed that the phase transitioned from amorphous to amorphous/nanocrystalline as RN2 increased. The TiNbZrNx films deposited at RN2 = 0.15–0.4 exhibited better corrosion performance in the electrochemical and salt spray tests. The RN2 = 0.4 film presented the optimal corrosion resistance, with the lowest self-corrosion current density (0.249 μA/cm2) and the largest passivation zone (from OCP to >1.2 VSCE). The amorphous/nanocrystalline film deposited at RN2 = 0.2 showed a remarkable nanohardness of 7.03 GPa and adhesion strength of 18.86 N. The strengthening effect can be attributed to the interstitial dissolution of nitrogen atoms among the metal atoms. The formation of nitride nanocrystalline phases and the existence of interfaces can effectively improve the plastic deformation ability of amorphous alloy films. This work provides theoretical guidance for the development of MPEA nitride films with tunable properties for key moving parts in marine equipment.

Solute atom mediated crystallization of amorphous alloys

We propose a new mechanism of crystallization of amorphous alloy which is mediated by additional solute atoms produced by electronic excitation. For a freestanding Pd-19at%Si amorphous alloy film, electron irradiation causes subtle structural change. By contrast, extensive crystallization of Pd-19at%Si amorphous alloy sandwiched by amorphous (a-) SiOx films, i.e., a-SiOx/a-Pd-Si/a-SiOx, occurred by 75 keV and 200 keV electron irradiation. This crystallization was induced by irradiation not only at room temperature but also even at 90 K. It should be emphasized that the crystallization can be realized by 75 keV irradiation at 90 K via the electronic excitation; where both knock-on damage and a possible thermal crystallization can be excluded. A resultant product of the crystallization after electronic excitation (i.e., electron irradiation), hexagonal Pd2Si, differs from that of thermal annealing (orthorhombic Pd3Si). Evidence for decomposition of a-SiOx by electronic excitation contributes essentially to the crystallization of the a-Pd-Si in the composite film has been obtained in this study. Supply of dissociated Si to the a-Pd-Si layer may cause instability of the amorphous phase, which serves as the trigger for the remarkable structural change; i.e., additional solute atom mediated crystallization.

Effect of Thermal Shock on Properties of a Strongly Amorphous AlCrTiZrMo High-Entropy Alloy Film.

AlCrTiZrMo high-entropy alloy (HEA) films with strong amorphization were obtained by co-filter cathode vacuum arc deposition, and the effect of thermal shock on the films was investigated in order to explore the protection mechanism of HEA films against mechanical components in extreme service environments. The results show that after annealing at 800 °C for 1 h, the formation of a dense ZrTiO4 composite oxide layer on the surface actively prevents the oxidation from continuing, so that the AlCrTiZrMo HEA film exhibits excellent oxidation resistance at 800 °C in air. In the friction-corrosion coupling environment, the AlCrTiZrMo HEA film annealed at 800 °C for 1 h shows the best tribocorrosion resistance due to the stable dense microstructure and excellent mechanical properties, and its ΔOCP, COF and wear rate possess the smallest values of 0.055, 0.04 and 1.34 × 10-6 mm-3·N-1·m-1.

Effect of interlayer and deposition temperature on the hydrogen storage properties of amorphous Mg-based thin films

In this work, the effect of different interlayers (including Mo, Nb, and Ti) and deposition temperatures (including 25 °C, 75 °C, 150 °C and 200 °C) on the hydrogen storage performance of MgNi amorphous alloy films are studied. On the one hand, the MgNi amorphous alloy films remain undestroyed after hydrogen absorption and desorption cycles with the help of Mo, Nb and Ti interlayers. However, the onset desorption temperature and peak desorption temperature of the MgNi amorphous alloy films are almost unchanged after inserting the interlayers. On the other hand, as the deposition temperature increases from 25 °C to 200 °C, there are nanocrystalline Mg2Ni and Mg phases formed in the amorphous MgNi alloy matrix. The crystalline-amorphous structure provides abundant nucleation sites for hydride formation, and accelerate the diffusion and dissociation of hydrogen.

Comparison of the in-plane coercive field and anomalous Nernst effect between a co-sputtered Sm–Co amorphous film and Sm/Co multilayer amorphous films with various layer thicknesses

Recent research revealed that Sm–Co-based amorphous films prepared by stacking many ultrathin Sm/Co pairs exhibit large in-plane coercivity and realize the zero-field operation of the anomalous Nernst effect (ANE). Here, we investigate the effect of the Sm/Co-pair thickness on the magnetic anisotropy and ANE in Sm–Co-based amorphous films and compare them with a co-sputtered Sm–Co-based amorphous alloy film. We find that the magnetic (magneto-thermoelectric) properties of the co-sputtered film are almost the same as that of the multilayer films with the Sm/Co-pair thickness of ≤1.0 nm (≤3.0 nm). This finding will serve as a guideline for investigating amorphous magneto-thermoelectric materials.

Extraordinary Hall effect of sputtered amorphous ferrimagnetic GdFeCo alloy films

We investigate extraordinary Hall effect of sputtered amorphous ferrimagnetic GdFeCo alloy films using a composite target method. The composite target consists of a FeCo alloy disk and several Gd chips. The alloy film changing from FeCo-rich to Gd-rich phase is realized by manipulating sputtering power during the growth, confirmed by the shift of the compensation point. The sign of the extraordinary Hall resistance is observed to change from positive for FeCo-rich films to negative for Gd-rich films. The reversed sign at magnetic compensation can be ascribed to the combined effect of FeCo and Gd sublattices with opposite sign. A large extraordinary Hall coefficient of 1–2 × 10-8 Ω cm/emu is derived, which is one order in magnitude larger than that in ferromagnetic [Co,CoFe/Pt] multilayers. This sufficiently large extraordinary Hall coefficient indicates amorphous ferrimagnetic GdFeCo alloy films are promising for the applications in perpendicular magnetoelectronic devices.

Preparation of FeNi-based nanoporous amorphous alloy films and their electrocatalytic oxygen evolution properties

The progress of this research is the preparation of FeNi alloy thin films by magnetron sputtering. Each step of the experimental process is based on the electrocatalytic performance of the sample, and characterized by many characterizations means such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray energy spectrometry (EDS) and step gauge thickness test for morphology, structure and elemental composition, etc. The analysis of the characterization results is used as a support for the experimental process. Adjustment of various preparation process parameters for material growth and subsequent processing include doping of non-metallic elements and construction of nanostructures. Doping of C elements can make FeNi based alloy films further amorphous. Zn element is used as a pore-forming agent. The two processes of doping and high-temperature vacuum dealloying can make the film obtain a nanoporous structure, which greatly increases the specific surface area. These two strategies reduce the overpotential (η10) of oxygen evolution reaction (OER) of FeNi alloy thin films to 393 mV and 314 mV, which are reduced by 47 mV and 79 mV step by step. The electrochemical properties of the finally obtained alloy film are: overpotential of 314 mV, Tafel slope of 61.8 mV/dec and the stability of only 10% decay at a current density of 10 mA/cm2 for 12 h. In this study, low-cost transition metals were used as the main materials to design OER catalysts, and the catalytic efficiency was comparable to that of commercial noble metal catalysts. The physical preparation methods made each sample have good reproducibility. It provides the experimental basis and theoretical basis for the design and synthesis of new catalytic materials at a higher level.

Environmental Friendly Modification of the Superhydrophobic Surface for Iron-Based Amorphous Alloy Films and Their Magnetic Surface Effect.

It is challenging to convert the superhydrophobic surfaces of iron-based amorphous films into hydrophilic surfaces through surface treatment. In this study, a novel, environmentally friendly method is used to change the superhydrophobic surfaces of Fe78Si13B9 amorphous alloy films, which include their rougher and smoother surfaces. The boron element in the films reacted with the flavonoids and anthocyanins in the solution to create organic conversion membranes and organic boronizing naphthoquinone derivatives on the surfaces of the films when they were dipped in tea polyphenol aqueous solution at 80 °C for 60 min. On the rougher surface and the smoother surface, the organic conversion membranes had thicknesses of about 10 and 3 μm, respectively. When iron-based amorphous alloy films were employed as soft magnetic materials to create electronic and electrical devices, the packaging issue caused by low wettability with epoxy resin had been resolved because both the side surfaces of modified films had good wettability with epoxy resin. In addition, the magnetic surface effect of modified films was significant. After surface treatment, the inductance value of the film decreased by more than 25%. The magnetic surface effect of iron-based amorphous films can be applied to the preparation of tea sensors, and the sensor can achieve the "one to one" high precision test of "one tea curve". The magnetic surface effect of the film provides a quick, simple, lower cost, and strong anti-interference idea for the rapid detection of tea polyphenols.

A Lightweight AlTiVNb High-Entropy Alloy Film with High Strength-Ductility Synergy and Corrosion Resistance.

The simultaneous improvement of mechanical and corrosion resistance is of great significance for engineering applications. In this work, a novel lightweight amorphous structure AlTiVNb high-entropy alloy (HEA) film was fabricated by magnetron sputtering. The compression test of the AlTiVNb HEA film nanopillar exhibits a high compressive strength of up to 3.6 GPa and deformability approaching 58%. The high strength is affected by the disordered state, the nanostructure, and the lattice distortion effect, while the high ductility comes from the ductile shear band and the island structure. In addition, the AlTiVNb HEA film shows a current density of 4.90 × 10-8 A/cm2 and a potential of -0.234 V in the 3.5% NaCl solution, comparable to that of the 316L stainless steel. The chemical disorder state, cocktail effect, and homogeneous amorphous structure contribute to excellent corrosion resistance. This finding offers new insights into high-performance HEA films with robust mechanical and anticorrosion performances for microelectronic devices and mechanical metamaterials.

Sm-Co-based amorphous alloy films for zero-field operation of transverse thermoelectric generation

ABSTRACT Transverse thermoelectric generation using magnetic materials is essential to develop active thermal engineering technologies, for which the improvements of not only the thermoelectric output but also applicability and versatility are required. In this study, using combinatorial material science and lock-in thermography technique, we have systematically investigated the transverse thermoelectric performance of Sm-Co-based alloy films. The high-throughput material investigation revealed the best Sm-Co-based alloys with the large anomalous Nernst effect (ANE) as well as the anomalous Ettingshausen effect (AEE). In addition to ANE/AEE, we discovered unique and superior material properties in these alloys: the amorphous structure, low thermal conductivity, and large in-plane coercivity and remanent magnetization. These properties make it advantageous over conventional materials to realize heat flux sensing applications based on ANE, as our Sm-Co-based films can generate thermoelectric output without an external magnetic field. Importantly, the amorphous nature enables the fabrication of these films on various substrates including flexible sheets, making the large-scale and low-cost manufacturing easier. Our demonstration will provide a pathway to develop flexible transverse thermoelectric devices for smart thermal management.

Effects of phase transition on tribological properties of amorphous VAlTiCrSi high-entropy alloy film by magnetron sputtering

High-entropy alloy films have shown great potential in high-temperature antifriction and anti-wear applications . Magnetron sputtering high-entropy alloy films with uniform composition will have inevitable structural changes at high temperatures, which have an impact on their tribological behavior. In this work, amorphous VAlTiCrSi high-entropy alloy films prepared by magnetron sputtering show good thermal stability and high-temperature tribological properties. Especially at 700 °C, the structural change from an amorphous phase to a mixture consisting of body-centered cubic, Al 8 Cr 5 , (V, Ti, Cr) 5 Si 3 , and amorphous phases are responsible for the improved tribological properties. The hard body-centered cubic phase with solid-solution strengthening effect and intermetallic compounds significantly enhance the mechanical properties of VAlTiCrSi film, so as to improve the wear resistance performance of the films. The insight into the relationship between structural changes and friction properties will contribute to the design of novel high-performance high-entropy alloy films in high-temperature environments. • Amorphous VAlTiCrSi high-entropy alloy film prepared by magnetron sputtering. • Structure changes from amorphous to body-centered cubic, Al 8 Cr 5 , and (V, Ti, Cr) 5 Si 3 . • The hard phases at 700 °C improve the mechanical and tribological properties.

Tailoring degradation of MgZn alloy films with bioinert amorphous carbon

MgZn based amorphous alloy films were composited with diamond-like carbon (DLC) in sputter deposition to tailor their degradation and the related biological properties. Structural and compositional analyses indicate that all the films are amorphous, but the films with intermediate MgZn:C ratio exhibit nanoparticles at surface, cracks, peeling off and electric insulation. Metal carbides are possibly formed during film deposition, and the surface layer is then converted to oxides, hydroxides and carbonates during the ageing in air. After immersion in the simulated body fluid for 2 days, apatite and Mg compounds layer is formed on the alloy and the composite films. Although Cl- ions and microgavlanic coupling can accelerate dissolution of the alloy, the carbon phase effectively delays dissolution of the alloy. The films have good antibacterial activity against E. coli, which comes from the released Mg2+ and Zn2+ ions. The MC3T3-E1 cell test shows that the film with metal elements content of 22.6 at% has the highest alkaline phosphatase activity among the tested samples. The suppressed and lasting dissolution of alloy elements is beneficial for antibacterial activity and osteoblast cell behaviors of the MgZn alloy-DLC films.

Hardening and toughening effects of intermediate nanosized structures in a confined amorphous alloy film

• Intermediate nanosized structure (termed as “nano shear bands” (NSBs)) between microscopic shear transformation zones (STZs) and macroscopic shear bands (SBs) was observed in the crystalline-layer confined amorphous (CLCA) NiW alloy films. • NSBs promoted multiple and controlled shear banding deformation, hence leading to the enhanced crystallization. • NSBs possessed both hardening and toughening effects for the CLCA films. The plastic deformation of amorphous alloys is well known to be localized into shear bands (SBs), which are believed to stem from the atomic-scale flow defects, i.e., shear transformation zones (STZs). Yet, the bridge between the mesoscopic SBs and the atomic-scale STZs remains poorly understood. In this work, through thermally activating pronounced β relaxations in the well-designed crystalline-layer confined amorphous (CLCA) NiW alloy films, we experimentally captured and observed an intermediate nanosized structure termed as “nano shear bands” (NSBs) with a typical size of 1–2 nm in thickness and 5–10 nm in length. The influences of such NSB structures on the macroscale deformation behavior were systematically investigated. It was found that NSBs lead to both hardening and toughening effects for the CLCA films, as they promote multiple and controlled shear banding deformation, which results in enhanced crystallization. The intermediate NSB structure could connect the microstructural characteristics and macroscopic plasticity in amorphous alloys and may provide new insights for understanding the microscopic deformation mechanism of amorphous alloys as well as tuning/designing their properties.

Ultrathin, sputter-deposited, amorphous alloy films of ruthenium and molybdenum

Microscopy and diffraction measurements are presented of ultrathin binary alloy films of ruthenium and molybdenum that are obtained by standard sputter deposition. For compositions close to Ru50Mo50, we find the films to be amorphous. The amorphicity of the films is accompanied by a significant reduction of the roughness with respect to the roughness of equally thick films of either ruthenium or molybdenum. We ascribe this to the absence of the grain structure that is characteristic of the polycrystalline films of the separate elements.

Synthesis and characterization of amorphous NiCoP alloy films by magnetic assisted jet electrodeposition

Magnetic assisted jet electrodeposition was used to prepare NiCoP alloy thin films efficiently and rapidly, in comparison with the films prepared using traditional jet electrodeposition. The surface morphology, crystal structure, magnetic properties, film adhesion, and corrosion resistance of the NiCoP alloy films were studied. The experimental results show that the magnetic assisted jet electrodeposition effectively changed the microstructure and properties of NiCoP alloy films. Magnetic assisted jet electrodeposition inhibited the growth of pores and nodules on the surface of the film, and the adhesion between the film and the substrate was enhanced. Furthermore, magnetic assisted jet electrodeposition accelerated the refinement of nanocrystallines embedded in amorphous phase of the films, which results in an obvious increase of the saturation magnetization to 201.43 emu/g. Magnetic assisted jet electrodeposition can improve the comprehensive performance of NiCoP alloy thin films, which is expected to be used in modern magnetic materials development.

Deformation Mechanism of Depositing Amorphous Cu-Ta Alloy Film via Nanoindentation Test.

As a representative of immiscible alloy systems, the Cu-Ta system was the research topic because of its potential application in industry, military and defense fields. In this study, an amorphous Cu-Ta alloy film was manufactured through magnetron sputter deposition, which was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Mechanical properties of Cu-Ta film were detected by the nanoindentation method, which show that the elastic modulus of Cu3.5Ta96.5 is 156.7 GPa, and the hardness is 14.4 GPa. The nanoindentation process was also simulated by molecular dynamic simulation to indicate the deformation mechanism during the load-unload stage. The simulation results show that the structure <0,2,8,4> and <0,2,8,5> Voronoi cells decreased by 0.1% at 50 Ps and then remained at this value during the nanoindentation process. In addition, the number of dislocations vary rapidly with the depth between indenter and surface. Based on the experimental and simulation results, the Voronoi structural changes and dislocation motions are the key reasons for the crystallization of amorphous alloys when loads are applied.

The correlation between structural characteristics and plasticity mediated by shear transformation zone size in amorphous alloys

In this study, the correlations between structural characteristics, shear transformation zone (STZ) size and shear-band mediated plasticity were systematically investigated in crystalline-layer confined amorphous (CLCA) NiW alloy films. In these films, the structural states with or without distributed structural defects – the so-called nano shear bands (NSBs) – could be regulated by thermal treatment. It was found that NSBs positively impacted the STZ size obtained by strain rate sensitivity (SRS) method (known as engineering STZ size), which actually reflected the combined size of the connected STZs and was proportional to the plasticity of amorphous alloys. Whilst, NSBs were unprevailing in case of the statistically determined STZ size. This was owing to the fact that such a size was closer to the real STZ size that was independent of the structural state and plasticity of amorphous alloys. The findings of the present work enabled one to elucidate the underlying mechanism of the discrepancy of STZ size, as well as to establish its relationship with structural characteristics and plasticity of amorphous alloys.

The Environmental Friendly Modification of the Superhydrophobic Surface for Iron-Based Amorphous Alloy Films and Their Magnetic Surface Effect

The Environmental Friendly Modification of the Superhydrophobic Surface for Iron-Based Amorphous Alloy Films and Their Magnetic Surface Effect