Abstract: Diffusion barrier layers are typically introduced in solid oxide fuel cells (SOFCs) to avoid reaction between state-of-the-art cathode and electrolyte materials, La1–xSrxCo1–yFeyO3-δ and yttria-stabilized zirconia (YSZ), respectively. However, commonly used layers of gadolinia-doped ceria (CGO) introduce overpotentials that significantly reduce the cell performance. This performance decrease is mainly due to the low density achievable with traditional deposition techniques, such as screen printing, at acceptable fabrication temperatures. In this work, perfectly dense and reproducible barrier layers for state-of-the-art cells (∼80 cm2) were implemented, for the first time, using large-area pulsed laser deposition (LA-PLD). In order to minimize cation interdiffusion, the low-temperature deposited barrier layers were thermally stabilized in the range between 1100 and 1400 °C. Significant enhanced performance is reported for cells stabilized at 1150 °C showing excellent power densities of 1.25 W·cm–2 at 0.7 V...

Abstract: For high temperature applications nickel base superalloys with aluminide coatings are reaching the service limit. Alternate materials such as refractory metal silicide alloys can extend high temperature capability, but the silica surfaces require coatings for enhanced environmental resistance. We present a review of an effective strategy to achieve the environmental resistance through the use of an integrated Mo-Si-B based coating that is applied by a co-deposition of Si and B by pack cementation. During oxidation of the (Si + B)-pack alloys, the initial MoSi2 outer layer is consumed by formation of the Mo5Si3 (T1) phase and the development of the underlying Mo5SiB2, T2 borosilicide and/or MoB boride phase layer. The T1 phase with B has excellent oxidation resistance and the loss of Si to the substrate is blocked by the underlying diffusion barrier (T2). Any damage to the outer T1 layer can be recovered from the T2 + MoB layer to yield a self-healing characteristic. The Mo-Si-B based coating on Mo based alloys exhibits robust performance up to at least 1700 °C not only to high temperature oxidation, but also to water vapor and corrosive deposit attack. Some of the applications are discussed for use of the coating strategy on ceramic materials.

Abstract: Combining high-performance (La0.58Sr0.4)(Co0.2Fe0.8)O3-δ (LSCF) cathodes with Y-doped ZrO2(YDZ) electrolytes in solid oxide fuel cells leads to the formation of SrZrO3 (SZO) as secondary phase with exceedingly low oxygen ion conductivity and poor catalytic capability. A promising prevention strategy is the insertion of Gd-doped CeO2 (GDC) as a reaction barrier. In this work, screen-printed GDC layers were sintered on YDZ substrates at temperatures varying from 1100 to 1400 °C. Subsequently, screen-printed LSCF was sintered on top at 1080 °C. The goal of this work was to understand microstructure formation during the two subsequent sintering processes by the analysis of nanometer-scale elemental distributions, crystal structures, and grain sizes of this extended cathode/electrolyte interface as a function of the GDC sintering temperature. Various representative regions on all samples were analyzed by transmission electron microscopy combined with energy dispersive X-ray spectroscopy with high spatial resol...

Abstract: Liquid metals (LMs) are a special case of metals that exist in a liquid at room temperature, making them one of the most attractive conductive materials in stretchable electronics. In many cases, however, the LM attacks other metals in contact with the LM through penetration, embrittlement, and alloying. To address these critical issues, there have been efforts to introduce robust barriers, which can preserve the underlying metals without degradation. For example, graphene is employed as a flexible barrier owing to its chemical inertness and impermeability. Nevertheless, this material is difficult to utilize in stretchable electronics because its defects result in inevitable fracture, even at a low strain (< 6%). In addition, it is a challenge to pattern the graphene layer on the point‐of‐interest area in a facile manner. Herein, it is shown that the insertion of single‐walled carbon nanotubes (SWCNTs) at the liquid metal–solid metal interface provides a proper barrier for LM under large deformation conditions. A tangled 1D structure of the SWCNTs formed from a solution process greatly suppresses the crack generation/propagation and maintains conductivity even under large strains, which facilitates the use of SWCNTs as stretchable barriers with long‐term reliability through the introduction of a corrugated structure.

Abstract: The duplex coating system consisted of electroplated Re-Ni as the diffusion barrier layer and the thermally sprayed NiCoCrAlY coating deposited. The adhesion strength and thermal shock resistance of the NiCoCrAlY coatings with and without the diffusion barrier were evaluated. Thermal shock resistance was investigated by quenching the coated samples in cold water from the temperature of 1100 °C. Also, the capability of Re-Ni as the diffusion barrier layer was investigated by isothermal oxidation at 1100 °C. The results showed that application of the thin interlayer of Re-Ni as a diffusion barrier beneath the NiCoCrAlY coating could slightly decrease the thermal shock and the adhesion strength of the NiCoCrAlY coating. The thermal expansion coefficient mismatch between the Re-Ni diffusion barrier and the NiCoCrAlY coating and the reduction of the substrate surface roughness due to Re-Ni deposition were the two main mechanisms limiting the lifetime of the NiCoCrAlY coating. But with significant improvement in oxidation resistance, these limitations could be compensated.

Abstract: Carbon diffusion is a critical process to the manufacture of many industry products, such as iron carbides, stainless steels, and carbon materials. Here we investigate carbon diffusion induced by tensile, screw dislocation, edge dislocation, and polycrystal boundary through reactive molecular dynamics simulations with ReaxFF potentials. The temperature enhances the dynamics and therefore the carbon diffusion. The pre-existing defects promote the carbon diffusion with a linear relationship between carbon diffusion barrier and strain as well as line defect concentrations. Furthermore, we also observed a linear relationship between the carbon diffusion barrier and the volume fractions of the polycrystalline boundary, indicating that the grain boundary mechanism is prominent in carbon diffusion in the carbon iron.

Abstract: Intercalation of metal ions in the van der Waals gap of layered materials forms the basis for large-scale electrochemical energy storage. In this work, by means of periodic density functional theory calculations, transition-metal dichalcogenide Mo1–xWxS2 alloys have been explored as efficient materials for lithium storage. Our study reveals that lithium prefers to bind efficiently to the monolayer alloy and diffuses easily with short diffusion distances. All bare phases of alloys are semiconducting, and a semiconducting to metallic phase transition occurs after lithiation, which ensures good electrical conductivity and is crucial for electrode material. We find negligible average open-circuit voltage at different chemical stoichiometries of 0.67, 1.33, and 2. Effects of both strain and concentration on adsorption energy and diffusion barriers are calculated. The effect of strain has manifested significant rise in adsorption energy, whereas in the case of diffusion barrier, this effect is almost negligible...

Abstract: Corrosion of alloy 625 was investigated in three supercritical CO2 (sCO2) environments: research-grade (RG) (99.999 pct pure), RG + 100 ppm O2 (at.), and RG + 1 pct CO (at.). Samples were exposed to each condition for a total of 1000 hours at 750 °C and 20 MPa. Each sample was analyzed using mass change, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), time-of-flight-secondary ion mass spectroscopy (TOF-SIMS), and Raman spectroscopy. Samples exposed to RG CO2 produced a compact uniform chromia layer. The samples exposed to oxygen-rich CO2 showed a less-uniform oxide with nodules characterized by Ni- and Fe-rich oxides on the surface with enhanced chromia formation beneath. The oxide grown in 1 pct CO exhibited the least protective oxide consisting of a duplex chromia scale with inner equiaxed grain structure and an outer porous layer. RG + 1 pct CO was the only environment in which carbon was observed throughout the oxide, although carbon enrichment was observed at the M-O interface of the oxides produced in RG and RG + 1 pct CO environments. A model for explaining carburization of chromium in sCO2 environments was produced by treating the oxide as a diffusion barrier and considering the chemical equilibrium of CO2 through the Cr2O3 phase.

Abstract: The diffusion of species in icy dust grain mantles is a fundamental process that shapes the chemistry of interstellar regions; yet, measurements of diffusion in interstellar ice analogs are scarce. Here we present measurements of CO diffusion into CO2 ice at low temperatures (T = 11–23 K) using CO2 longitudinal optical phonon modes to monitor the level of mixing of initially layered ices. We model the diffusion kinetics using Fick's second law and find that the temperature-dependent diffusion coefficients are well fit by an Arrhenius equation, giving a diffusion barrier of 300 ± 40 K. The low barrier along with the diffusion kinetics through isotopically labeled layers suggest that CO diffuses through CO2 along pore surfaces rather than through bulk diffusion. In complementary experiments, we measure the desorption energy of CO from CO2 ices deposited at 11–50 K by temperature programmed desorption and find that the desorption barrier ranges from 1240 ± 90 K to 1410 ± 70 K depending on the CO2 deposition temperature and resultant ice porosity. The measured CO–CO2 desorption barriers demonstrate that CO binds equally well to CO2 and H2O ices when both are compact. The CO–CO2 diffusion–desorption barrier ratio ranges from 0.21 to 0.24 dependent on the binding environment during diffusion. The diffusion–desorption ratio is consistent with the above hypothesis that the observed diffusion is a surface process and adds to previous experimental evidence on diffusion in water ice that suggests surface diffusion is important to the mobility of molecules within interstellar ices.

Abstract: The scaling limit of conventional Cu diffusion barriers has become the bottleneck for interconnect technology, which in turn limits the IC performance. Sub-nm diffusion barrier is urgently demanded to maintain the interconnect resistivity for ultra-scaled Cu interconnects. However, with this thickness, the blocking capabilities of conventional Cu diffusion barriers are lost. In this letter, sub-nm Cu diffusion barrier is realized by single-layer molybdenum disulfide (MoS2) grown at 400 °C using metal-organic chemical vapor deposition. MoS2 is directly grown on dielectrics without transfer processes and the continuous coverage in a large area (>1 cm2) is achieved. Its resistance to Cu diffusion is investigated by time-dependent dielectric breakdown (TDDB) measurements. Our results indicate that the MoS2 barrier can efficiently suppress Cu diffusion and enhance dielectric lifetime significantly. Although a few challenges, including Cu adhesion to the MoS2 surface and integration with the Damascene structure, have to be assessed before introducing this novel material to the back-end-of-line technology, our work lays the groundwork for further investigation.

Abstract: (M = Fe, Cr and Co) doped CaZrO3, CaZr0.7M0.3O3 (M = Fe, Cr and Co), was synthesized by solid state reaction method. Crystalline structure, microstructures, electronic conductivity, total conductivity and sensing performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Hebb-Wagner, DC van der Pauw and voltammetry method, respectively. XRD measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples belong to an orthorhombic perovskite structure. SEM measurements show that the CaZr0.7M0.3O3 (M = Fe, Cr and Co) samples have fine grains with average grain size of 0.5–2 μm. Electrical property measurements show that the CaZr0.7Fe0.3O3 and CaZr0.7Cr0.3O3 samples have the highest electronic conductivity and total conductivity in air, respectively. Sensing performance measurements show that limiting current-type oxygen sensors with 9YSZ solid electrolyte and CaZr0.7M0.3O3 dense diffusion barrier exhibit good limiting current (IL) plateau. Log IL depends linearly on 1000/T. IL depends linearly on oxygen partial pressure.

Abstract: This work investigates the problematic diffusion of metal atoms into phase change chalcogenides, which can destroy resonances in photonic devices. Interfaces between Ge2Sb2Te5 and metal layers were studied using X-ray reflectivity (XRR) and reflectometry of metal-Ge2Sb2Te5 layered stacks. The diffusion of metal atoms influences the crystallisation temperature and optical properties of phase change materials. When Au, Ag, Al, W structures are directly deposited on Ge2Sb2Te5 inter-diffusion occurs. Indeed, Au forms AuTe2 layers at the interface. Diffusion barrier layers, such as Si3N4 or stable diffusionless plasmonic materials, such as TiN, can prevent the interfacial damage. This work shows that the interfacial diffusion must be considered when designing phase change material tuned photonic devices, and that TiN is the most suitable plasmonic material to interface directly with Ge2Sb2Te5.

Abstract: Actually, MgB2 is the lightest superconducting compound. Its connection with lightweight metals like Ti (as barrier) and Al (as outer sheath) would result in a superconducting wire with the minimal mass. However, pure Al is mechanically soft metal to be used in drawn or rolled composite wires, especially if applied for the outer sheath, where it cannot provide the required densification of the boron powder inside. This study reports on a lightweight MgB2 wire sheathed with aluminum stabilized by nano-sized γ-Al2O3 particles (named HITEMAL) and protected against the reaction with magnesium by Ti diffusion barrier. Electrical and mechanical properties of single-core MgB2/Ti/HITEMAL wire made by internal magnesium diffusion (IMD) into boron were studied at low temperatures. It was found that the ultra-lightweight MgB2 wire exhibited high critical current densities and also tolerances to mechanical stress. This predetermines the potential use of such lightweight superconducting wires for aviation and space applications, and for powerful offshore wind generators, where reducing the mass of the system is required.

Abstract: The optimization of the interface between back contact and absorber is one of the main challenges to improve the electrical behavior and further enhance the efficiencies of Cu2ZnSn(S,Se)4 (CZTS(e)) solar cell devices. In this work, Mo/SixNy thin films with various film thicknesses were introduced as an interfacial layer to explore its influence on optoelectronic properties of the pure sulfide CZTS thin film solar cells. The SixNy was deposited through plasma enhanced chemical vapor deposition (PECVD). The film thickness and stress of the Mo/SixNy films were controlled to improve the adhesion of the CZTS layer and reduce the chances of cracking the deposited films. Energy dispersive X-ray spectroscopy (EDS) mapping measurements performed directly on the cross-section of Mo/SixNy/CZTS/Mo films indicate that the SixNy intermediate layer can effectively inhibit the formation of a highly resistive MoS2 layer and decomposition of CZTS at the CZTS/molybdenum (Mo) interface region. A reduced efficiency was obtain...

Abstract: La0.8Sr0.2Ga0.8Mg0.2O3–δ (LSGM) and La0.8Sr0.2(Ga0.8Mg0.2)1–xCrxO3–δ (LSGMC, 0.1 ≤ x ≤ 0.9) were synthesized by a solid-state reaction and characterized by X-ray powder diffraction (XRD), thermal expansion, and DC four-probe method. A limiting current oxygen sensor using LSGM solid electrolyte and LSGMC (x = 0.7) dense diffusion barrier was prepared by a co-pressing and co-sintering technique and the sensing performances were evaluated. XRD shows the presence of a crystal structure in the series belonging to Pm-3m (No. 221) for x = 0–0.9. Electrical conductivity and thermal expansion coefficients first decrease and then increase with increasing x. LSGMC (x = 0.7) is the most suitable ceramic material and is selected as dense diffusion barrier. There is a directly proportional relationship between limiting current and oxygen concentration, and the equation i L ( mA ) = 3.65 C O 2 ( % ) is established from the measured data by simple regression analysis. The Arrhenius model for limiting current is log i L ( mA ) = 3.11 − 2.16 / T ( K ) , and the activation energy for oxygen diffusion is 0.43 eV.