Solid Solution Films Research Articles

Reliable and high-performance Ag-doped MoSi2 film with enhanced mechanical and tribological properties

The Mo-Ag-Si solid solution film was prepared using magnetron sputtering to enhance hardness and toughness while reducing friction and wear. Compared with the pure MoSi2 film, the Mo-Ag-Si solid solution film exhibited a 25.69% increase in hardness, a 5.17% increase in the H/E ratio, and a 33.33% boost in the H³/E² ratio. Tribological tests revealed that Ag atoms formed a self-lubricating AgMoxOy phase, reducing the friction coefficient to 0.09 and the wear rate to 3.89 × 10⁻⁷ mm³/N·m over 565m. First-principle calculations indicate that the Mo-Ag-Si solid solution film exhibited better mechanical and tribological properties than the pure MoSi2 film. These findings provide another approach for developing reliable MoSi2 films with high performance.

Morphology and spatial distribution of ordered domains in GaInP/GaAs(001) according to transmission electron microscopy

The structure of epitaxial films of the GaInP solid solution, in which ordering occurs, was studied using transmission electron microscopy. The films were grown by metalorganic vapor phase epitaxy on GaAs (001) substrates near the half-composition point. During the study, dark-field images obtained using superstructure reflections for cross-sectional and plan-view specimens of films were analyzed. The morphology and relative spatial arrangement of ordered domains have been determined. The phenomenon of spontaneous self-organization of regions with CuPt–B+ and CuPt–B– ordering near the surface was discovered, while in the bulk of the film the domains are uniformly located and mutually overlap each other. The effect of spatial separation of domains is associated with the lattice relaxation, leading to a change in the surface topology.

Osteoinductivity enhancement by tailoring the surface chemical bond status: A strategy to mobilize host bone growth factors for in situ bone regeneration

The incorporation of growth factors and biomaterials is a promising strategy for improving osseointegration. However, current strategies to develop biomaterials with exogenous growth factors present disadvantages like inefficiency, difficult deployment, and potential off-target activation, making their translation into clinical practice challenging. This study reveals a bioactive N-doped tantalum carbide (TaC) solid solution film that can be used to construct a TaCN film via bionic interface engineering to recruit host bone growth factors to the wounded site and improve bone regeneration. X-ray photoelectron spectroscopy (XPS) and protein absorption analysis reveal that the performance of TaCN is related to the surface chemical bonds of films. The introduction of N to TaC causes a cascade effect wherein negative charges enrich on the TaCN surface, and the recruitment of positively charged bone growth factors around the TaCN film is facilitated. Under these circumstances, the endogenous bone growth factors enhance bone healing. The TaCN film shows an outstanding performance for in vivo osteogenic differentiation along with a superior in vitro cytocompatibility. Incorporation of N atoms into TaC provides a new clinically translatable strategy to mobilize host bone growth factors for in situ bone regeneration without the need for incorporation of exogenous growth factors.

(Invited) Modification of Dielectric Properties of Film Dielectric Materials by Solid Solution System

Compound semiconductor based power devices such as SiC and GaN require high temperature operating passive devices such as a capacitor. SiC-based active devices can operate above 250 °C. The development of high-temperature operational passives is urgently needed to advance to the module and system level. In the case of capacitors, currently available capacitors can only operate efficiently up to 175 °C. Therefore, a thin film capacitor that can operate at high temperatures and be monolithically integrated near the active device should be developed. In this talk, I will present our achievements in the development of high-temperature operating dielectric film materials using the solid solution system. One topic is A2B2O7 pyrochlore ferroelectrics. The ferroelectric materials with the pyrochlore structure such as Sr2Nb2O7 exhibited the high dielectric constant above 100 at high and low temperature ranges. However, due to the crystallographic direction dependence of the Curie-Weiss temperature, the temperature stability of the dielectric constant from room temperature to 300 °C was not available. In order to obtain the high temperature stability of dielectric constant from room temperature to 300 °C with high dielectric constant over 100, the pyrochlore ferroelectric solid solution thin films were investigated by employing the combinatorial synthesis. Composition spread thin films of solid solution of two or three kinds of materials were deposited on substrates by physical vapor deposition technique, which provided the systematic physical properties. High-throughput combinatorial synthesis method is effective in the rapid optimization of the correlation between the crystallization and the dielectric property change behavior. For the composition spread solid solution film, the Sr- or La-containing A2B2O7 pyrochlore ferroelectrics were selected from the viewpoints of ion radios and crystallographic direction dependence of the Curie-Weiss temperature. The composition spread films were formed on a Pt/Ti/SiO2/Si substrate by combinatorial RF sputtering with stoichiometric composition targets. The X-ray fluorescence spectrum of the composition-spread film showed a linear variation of the metal composition. After deposition, the samples were annealed at different temperatures under oxygen atmosphere to reduce oxygen vacancies and improve crystallinity. The crystallization of the composition-spread solid solution thin film was confirmed by X-ray diffraction patterns, indicating the composition dependence of the crystallographic orientation. Some compositions showed high dielectric constant over 100 and high temperature stability from room temperature to 300 °C. In the presentation, the correlation between film composition, orientation and dielectric constant will be discussed in detail. In the presentation, we also introduce our achievement of the BaTiO3 based relaxor ferroelectrics and other dielectric materials development using the solid solution system. For the relaxor ferroelectrics, among the BaTiO3 based relaxor ferroelectrics, we have selected x[BaTiO3]-(1-x)[Bi(Mg2/3Nb1/3)O3] . The permittivity of 400 and the stability <8% from room temperature to 400 °C were obtained, which are promising as high-temperature dielectric medium.

Efficient Deep-Blue Light-Emitting Diodes Through Decoupling of Colloidal Perovskite Quantum Dots.

Metal halide perovskite light-emitting diodes (PeLEDs) have exceptional color purity but designs that emit deep-blue color with high efficiency have not been fully achieved and become more difficult in the thin film of confined perovskite colloidal quantum dots (PeQDs) due to particle interaction. Here it is demonstrated that electronic coupling and energy transfer in PeQDs induce redshift in the emission by PeQD film, and consequently hinder deep-blue emission. To achieve deep-blue emission by avoiding electronic coupling and energy transfer, a QD-in-organic solid solution is introduced to physically separate the QDs in the film. This physical separation of QDs reduces the interaction between them yielding a blueshift of ≈7nm in the emission spectrum. Moreover, using a hole-transporting organic molecule with a deep-lying highest occupied molecular orbital (≈6.0eV) as the organic matrix, the formation of exciplex emission is suppressed. As a result, an unprecedently high maximum external quantum efficiency of 6.2% at 462nm from QD-in-organic solid solution film in PeLEDs is achieved, which satisfies the deep-blue color coordinates of CIEy <0.06. This work suggests an important material strategy to deepen blue emission without reducing the particle size to <≈4nm.

Large ferroelectric polarization and high dielectric constant in HfO2-based thin films via Hf0.5Zr0.5O2/ZrO2 nanobilayer engineering

HfO2-based ferroelectric films have been extensively explored and utilized in the field of non-volatile memory and electrical programmability. However, the trade-off between ferroelectric polarization and dielectric constant in HfO2 has limited the overall performance improvement of devices in practical applications. Herein, a novel approach is proposed for the Hf0.5Zr0.5O2/ZrO2 (HZO/ZrO2) nanobilayer engineering, which can effectively regulate the phase structure evolution of HfO2 films to construct a suitable morphotropic phase boundary (MPB). The findings highlight that the top ZrO2 layer can regularly promote the formation of either the ferroelectric o-phase or the antiferroelectric t-phase. An ideal MPB is successfully established in HZO/ZrO2 (6/9 nm) nanobilayer film by carefully optimizing the HZO/ZrO2 thickness ratio, which presents a high dielectric constant of 52.7 and a large 2Pr value of up to 72.3 μC/cm2 without any wake-up operation. Moreover, the HZO/ZrO2 nanobilayer thin films demonstrate faster polarization switching speed (1.09 μs) and better fatigue performance (109 cycles) compared to the conventional HZO solid solution films. The relationship between ferroelectric and dielectric properties can be harmoniously balanced through the designation. The results indicate that the HZO/ZrO2 nanobilayer engineering strategy is quite potential to pave the way for the development of next-generation memory technologies with superior performance and reliability.

High-light-yield and fast-response β-Ga2O3–Al2O3 thick-film scintillators epitaxially grown via chemical vapor deposition

β-gallia (β-Ga2O3) has been investigated for adoption in power semiconductor wafers; however, it is a promising scintillating material for X-ray detection screens. Thus, the research on methods for growing β-gallia crystals has attracted considerable attention. Herein, 15-μm thick Ga2O3–Al2O3 solid solution films with β-gallia structure were synthesized using metal–organic chemical vapor deposition (CVD) at deposition rate of 15 μm h−1. A high scintillation light yield of 5400 photons per 5.5 MeV and a fast decay response of 5.1 ns of the produced films were observed, which were comparable or superior to those of the β-Ga2O3 single crystals. CVD method proved advantageous for the rapid synthesis of micrometer-thick Ga2O3-based scintillation screens.

Defect dipole engineering for regulating ferroelectric photovoltaic performances in BiFeO3–SrCoO2.5 solid solution films

Defect dipole engineering for regulating ferroelectric photovoltaic performances in BiFeO3–SrCoO2.5 solid solution films

Decomposition and dewetting of super-saturated Cu-15 at. % Co solid solution film

Nano-structured copper thin films present numerous applications for miniaturization of electronic devices. Their long term stability is key for reliable functionality. This work explores the thermal stability and solid state dewetting of a Cu-Co solid solution thin film and compares it to pure Cu. As according to the phase diagram Co is practically immiscible in Cu at room temperature, a metastable solid solution of Cu-15 at. % Co was deposited as thin film on a sapphire wafer. The microstructural evolution of the Co super-saturated film at temperatures ranging from 673 to 1073 K was evaluated using X-ray diffraction and high resolution microscopy techniques such as scanning electron and transmission electron microscopy. Interestingly, there is a competition between grain growth and phase separation. Co precipitates at grain boundaries acting as pinning sites preventing rapid grain growth during heat treatment at intermediate annealing temperature. However, grain growth occurs very quickly at higher temperatures, once the elemental phases of Cu and Co are formed. The competition between grain growth and phase separation and their consequence for dewetting are discussed.

Unveiling the optical, electrical, and thermodynamic properties of γ-(Cs, Rb)PbBr3

The all-inorganic perovskite CsPbBr3 has garnered significant attention in the fields of optoelectronic devices owing to its favorable bandgap. However, CsPbBr3 undergoes polymorphic phase transitions, existing in three light-active phases: Pbnm (γ), P4/mbm (β), and Pm-3m (α). Although extensive investigations have been conducted on the α-phase, the room-temperature γ-phase has received limited investigation. The present work explores the thermodynamic properties and optoelectronic characteristics of the (Cs, Rb)PbBr3 perovskite system by means of a combinatorial density-functional-theory (DFT) and CALPHAD method. An increase in Rb doping of CsPbBr3 induces structural distortion of γ-phase, resulting in a widened bandgap from 2.12 eV to 2.28 eV. The bandgap increase will eventually lead to changes in optical properties, such as poor absorptivity and energy consumption under high Rb doping. Moderate doping enables (Cs, Rb)PbBr3 to retain the excellent optical properties and energy consumption of CsPbBr3. Especially when Rb doping is 0.25, the solid solution has the lowest reflection coefficient. The thermodynamic phase diagram shows that the solid solution (Cs, Rb)PbBr3 maintains excellent thermodynamic stability. In addition, the phase diagram quantifies the temperature range of the γ-phase, α-phase, and coexistence of two phases, which provides the theoretical guidance for the preparation of (Cs, Rb)PbBr3 solid solution films in the future.

Optimization of energy storage characteristics of xBiInO3-(1-x)BiFeO3 solid-solution thin films by controlling BiInO3 concentration

We optimized the energy storage properties of xBiInO3-(1-x)BiFeO3 (BIO) solid solution thin films on Pt/TiO2/SiO2/Si substrates by controlling the BiInO3 concentration. The BIO thin films with BiInO3 concentrations ranging from 10 to 50 mol% deposited by pulsed laser deposition were preferentially grown as c-oriented polycrystalline thin films. As the BOI concentration increases, the BIO thin films change from the rhombohedral (R) phase to a mixed phase of the R-phase and orthorhombic (O)-phase with reduced ferroelectric polarization, and then to the O-phase. At the same time, the grains become smaller and the distribution of a-domains increases, resulting in the relaxor ferroelectric properties. Therefore, the change of the BIO thin films from ferroelectric properties to the relaxor ferroelectric properties is due to a combination of phase changes, grain size changes, and a-domain formation. These relaxor ferroelectric properties enable the BIO thin films to have improved energy storage efficiency by improving recoverable energy density and reducing loss energy density. In particular, the BIO thin film with a BiInO3 concentration of 40 mol% showed a high recoverable energy density of about 50.7 J/cm3 and a high energy storage efficiency of about 78.5 %.

High temperature decomposition and age hardening of single-phase wurtzite Ti1−xAlxN thin films grown by cathodic arc deposition

Wurtzite TmAlN (Tm=transition metal) themselves are of interest as semiconductors with tunable band gap, insulating motifs to superconductors, and piezoelectric crystals. Characterization of wurtzite TmAlN is challenging because of the difficulty to synthesize them as single-phase solid solution and such thermodynamic, elastic properties, and high temperature behavior of wurtzite Ti1−xAlxN is unknown. Here, we investigated the high temperature decomposition behavior of wurtzite Ti1−xAlxN films using experimental methods combined with first-principles calculations. We have developed a method to grow single-phase metastable wurtzite Ti1−xAlxN (x=0.65, 0.75, 085, and 0.95) solid-solution films by cathodic arc deposition using low duty-cycle pulsed substrate-bias voltage. We report the full elasticity tensor for wurtzite Ti1−xAlxN as a function of Al content and predict a phase diagram including a miscibility gap and spinodals for both cubic and wurtzite Ti1−xAlxN. Complementary high-resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950∘C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semicoherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1–2 GPa. Published by the American Physical Society 2024

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

Growth of nanotextured thin films of GaInAsP and GaInAsSbBi solid solutions on GaP substrates by pulsed laser deposition

Composition-dependent crystal structure, dielectric properties and temperature stability of the (1-x)CaZrO3-xSrTiO3 paraelectric thin films

The (1-x)CaZrO3-xSrTiO3 solid-solution thin films were prepared with different compositions from x = 0.05 to x = 0.45. The as-prepared thin films experienced such a crystal structure transition process from orthorhombic to pseudo cubic and then to cubic as the x increases. Among the as-prepared films, the smallest expansion ratio of lattice volume with temperatures, and the highest temperature stability of dielectric response and leakage current density at high voltage were found in the x = 0.3 thin films. The relationship between the tolerance factor and the temperature stability was analyzed from the crystal structure dependence of the absorbed thermal energy distribution. Finally, the x = 0.3 thin films were developed into thin-film capacitors, which showed high DC resistance and uniform capacitance properties. The result also shows that high temperature stability of the perovskite-type paraelectric thin films could be realized through the phase boundary design, and further improved by optimizing the temperature stability of the lattice structure.

Growth of Epitaxial Layers of the Si&lt;sub&gt;1-x-y&lt;/sub&gt;Ge&lt;sub&gt;x&lt;/sub&gt;Sn&lt;sub&gt;y&lt;/sub&gt; Solid Solution from a Tin Solution-Melt

Mono-crystal films of a graded-gap solid solution Si1-x-yGexSny on Si &lt;111&gt;substrates were grown by liquid-phase epitaxy from a limited tin solution-melt in the temperature range 500–1100 °C. The chemical composition of the grown epitaxial films was determined using a scanning electron microscope.

Exploring the potential for simultaneous enhancement of mechanical, wear and corrosion performance of the CrB2 protective film actuated by soluting Si

The moving parts in marine equipment have to face the high humidity and high salinity, improving the stability and durability in such harsh conditions is necessary. Developing the thin films with high hardness, wear resistance and corrosion resistance to protect the moving parts is an effective method. In this work, we introduce Si contents ranging from 0 to 14.5 at% in binary CrB2 film to enhance their comprehensive properties, and two structure Si contained sample with the CrSiB solid solution (3.5 at. %, 6.1 at. % and 7.3 at. % Si) and the CrSiB/Si nanocomposite (10.1 at. % and 14.5 at. % Si) are obtained. In comparison to the binary CrB2 and CrSiB/Si nanocomposite, the CrSiB solid solution film with 6.1 at. % Si exhibits the highest hardness of 23.23 ± 0.26 GPa, owing to the solid solution strengthening and grain boundary strengthening effects. Additionally, the CrSiB solid solution film with 6.1 at. % Si also exhibits the lowest wear rate with 5.18 × 10−8 mm3/Nm due to the highest H3/E2 value of 0.178. Moreover, the CrSiB solid solution film has the best corrosion resistance, this is because the thickest passivation layer with the minimal vacancy defects and the high-quality crystal structure of the film, which could effectively prevent Cl− from reaching the substrate through the film. This study highlights a promising structure for the protective thin film with comprehensive properties that meet stringent application conditions.

The effect of trace solute Au atoms on the phase structure, mechanical and self-lubricating properties of MoSi2 films

To overcome the high friction coefficient and low toughness bottleneck of MoSi2 used as protective films for moving parts, a novel strategy of doping and alloying through magnetron sputtering to build self-lubricating Mo-Si-Au solid solution film has been proposed. Herein, a series of MoSi2 films with different Au contents were prepared, and their phase structure, mechanical and tribological properties were investigated. The results indicate that when Au/Mo atomic ratio R = 0.10, Au atoms tend to replace Si atoms to form Mo-Si-Au solid solution film. Nevertheless, the Au atom would segregate to form a nanocomposite at R = 0.20. The nanoindentation test shows that the Mo-Si-Au solid solution film possesses the largest hardness, which is mainly attributed to the solid solution strengthening. The result of tribological testing exhibits that Au doping can significantly reduce the friction coefficient of MoSi2. More importantly, Mo-Si-Au solid solution film is realized with a lower coefficient of friction (∼0.08), which is ascribed to the formation of MoSiOx lubricating phase during the sliding induced solute Au atoms. Accordingly, the research would provide a considerable theoretical and technical foundation for the development of novel self-lubricating films with excellent mechanical properties.

Preparation of {100}-oriented (1−x)(Bi,K)TiO3−xCaTiO3 solid-solution epitaxial films by the hydrothermal method and their ferroelectric and piezoelectric properties

(1−x)(Bi,K)TiO3−xCaTiO3 epitaxial films with x = 0–1.0 were grown on (100) c SrRuO3//(100)SrTiO3 substrates by the hydrothermal method. The film composition region can be divided into three in view of its crystal structure. The films in the range of x = 0–0.12 (Region 1) and 0.60–1.0 (Region 3) consisted of a single phase and their lattice parameters changed with the x value. This suggests the formation of a solid solution. On the other hand, two phases coexisted in the intermediate range of x = 0.18–0.43 (Region 2). The ferroelectricity and the effective transverse piezoelectric coefficient, effective d 33, were observed for the films in Regions 1 and 2. The slope difference of P r and the effective d 33 against x can be explained by the change in the tetragonality of the films with x in Region 1 and the volume fraction of the ferroelectric phase in Region 2.

Evolution between ferroelectric photovoltaic effect and resistance switching behavior engineered by the polarization field and barrier characteristics.

The bandgap and polarization field play a key role in the ferroelectric photovoltaic effect. However, narrow bandgap induced electrical conductivity always brings out a depression of the photovoltaic performances. Based on the mechanisms of the photovoltaic effect and resistance switching behaviors in ferroelectric materials, this work realizes an evolution between the two effects by engineering the polarization field and barrier characteristics, which addresses the trade-off issues between the bandgap and polarization for ferroelectric photovoltaic effect. SrCoOx (SC, 2.5≤x≤3) with multivalent transition is introduced into Na0.5Bi0.5TiO3 (NBT) matrix material to engineered the polarization field and barrier characteristics. (1-x)NBT-xSC (x=0.03, 0.05, 0.07) solid solution films present an evolution of ferroelectric photovoltaic effect to grow out of nothing again to the disappearance of the photovoltaic effect and the appearance of resistance switching behavior. The 0.95NBT-0.05SC film achieve the open-circuit voltage of 0.81 V and the short-circuit current of 23.52 µA/cm2, and the 0.93NBT-0.07SC film obtains the resistive switching behavior with switch ratio of 100. This work provides a practicable strategy to achieve the fascinating evolution between photovoltaic effect and resistive switching.

Rapid synthesis of nickel–iron-oxide (NiFeOx) solid-solution nano-rods thin films on nickel foam as advanced electrocatalyst for sustained water oxidation

The development of earth-rich, noble-metal-free, and highly electroactive catalysts to accelerate the oxygen evolution reaction (OER) is a formidable challenge for the establishment of water-splitting technologies. Here, a solid-solution nickel-iron oxide (NiFeOx) electrocatalyst is readily grown on a Ni-foam (NF) substrate by a rapid and economical aerosol-assisted chemical vapor deposition process. In particular, the NiFeOx thin film fabricated in 40 min acquires a distinctive nanorod structure and proves to be stable and efficient for OER in alkaline solutions. It is shown that the catalyst needs a low over-potential of 226 mV to reach the typical current density of 10 mA/cm2, and it can approach a remarkable current density level of 1000 mA/cm2 by taking a slightly higher over-potential of 139 mV. The small Tafel slope of 64 mv.dec−1 and splendid electrochemical stability of 40 h at high current densities outperform many known FeNi-based anodes as well as commercial IrO2 and RuO2. The unique structure of the thin film offers many electroactive sites and a high surface area in combination with an improved electrical conductivity of NF, which is believed to play an imperative role in the excellent activity of the catalyst. The cost-effective and simple strategy to fabricate NiFeOx nano-fibrous is very attractive for the development of electrocatalysts for water splitting.