Mixed Interlayers Research Articles

Fracture Resistance and Crack Growth Mechanisms in Functionally Graded Ti–TiB

This paper presents the results of fracture tests and crack path observations for a layered functionally graded material (FGM) consisting of Ti and TiB phases. The composition varied in a nearly linear manner from a TiB-rich layer at the bottom to commercially pure (CP) Ti at the top. Elastic properties of the mixed phase interlayers were measured using nanoindentation testing, demonstrating a linear variation with composition. These results differ significantly from approximations calculated in previous studies using a non-linear rule-of-mixtures approach. Fracture tests were conducted on single edge notch bend [SEN(B)] specimens with the notch aligned orthogonal to the direction of the composition gradient. For this crack orientation, "average" R-curve behavior based on the J-integral was investigated to understand the mechanics of crack growth. The value of J was found to be minimal (less than 1 N/mm) below 47 pct volume fraction of TiB compared to a reported value of approximately 150 N/mm for pure Ti. These results indicate that a steeper transition to high concentrations of the metallic phase is necessary to achieve adequate fracture resistance in this metal/ceramic FGM. Observations on the specimen surface indicate crack path toughening mechanisms of this functionally graded material include crack bridging, branching, and deflection.

Achieving Good Bonding Strength of the Cu Layer on PET Films by Pretreatment of a Mixed Plasma of Carbon and Copper.

Cu layers were fabricated on PET films with and without pretreatment by a mixed plasma composed of carbon and copper using a magnetron sputtering technique for potential application as the flexible copper-clad laminate (FCCL) in 5G technology. In order to evaluate the effect of carbon plasma on the composited layer, the graphite target current was adjusted from 0.5 to 2.0 A. The microstructures and properties of Cu layers on PET films with different treatments were measured by an X-ray powder diffractometer, X-ray photoelectron spectroscope, Raman spectroscope, scanning electron microscope, transmission electron microscope, scratching test, indentation test, and four-probe detector. The results showed that the organic polymer carbon structure on the surface of PET films was changed to inorganic amorphous carbon due to the effect of the carbon plasma. At the same time, the active free radicals formed in the transition process react with metal copper ions to form organometallic compounds. Under the treatment of a mixed plasma of carbon and copper, the C/Cu mixed layer was formed on the PET film at the top of the substrate. Due to the presence of C/Cu mixed interlayers, the bonding strengths between the final Cu layers and the PET film substrates were improved, and the strongest bonding strength appeared when the graphite target current was 1.0 A. In addition, the presence of the C/Cu mixed interlayer enhanced the toughness of the Cu layer on PET film. It was proposed that the good bonding strength in combination and the enhanced toughness for the Cu layer on a PET film was due to the formation of a C/Cu mixed interlayer induced by the pretreatment of a mixed plasma of carbon and copper.

Realizing the stable spectrum in four-chromatic white organic light-emitting diodes by controlling the positions of various emitters in the bipolar interlayer

Maintaining a stable spectrum in white organic light-emitting diodes (WOLEDs) with multi-emissive layers (EMLs) remains a challenge. Herein, four-chromatic (blue–green–red–orange) WOLED with stable spectrum based on ultrathin EMLs and mixed bipolar interlayers was fabricated. We discovered that the locations of various color EMLs in the bipolar interlayers are essential for achieving the stable spectrum. The direct carrier trapping effects which destabilize the spectrum can be suppressed by placing red and green EMLs with both hole and electron traps in the middle of the bipolar interlayer and placing blue and orange EMLs with single-carrier traps on the two sides of the bipolar interlayer respectively. The resulting device exhibited the negligible color coordinate shifts of (0.008, 0.010) during the wide brightness range from 1000 cd m−2 to 10 000 cd m−2. Moreover, a high color rendering index of approximately 90 was obtained simultaneously. Our work demonstrated a significant method to achieve stable spectra in multi-EML WOLEDs based on bipolar interlayer.

High Rate and Stable Solid-State Lithium Metal Batteries Enabled by Electronic and Ionic Mixed Conducting Network Interlayers.

All solid-state lithium (Li) metal batteries (SSLMBs) are attractive for prospective electrochemical energy storage systems on account of their high energy densities and good safeties. However, the incompatible interface between the solid-state electrolyte and Li metal anode limits the ability of SSLMBs. Here, a three-dimensional (3D) electronic and ionic mixed conducting interlayer is proposed to improve the interfacial affinity in SSLMBs. The 3D electronic and ionic mixed conducting interlayer is composed of a Sn/Ni alloy layer-coated Cu nanowire (Cu@SnNi) network. The Li plating demonstrates that the Cu@SnNi network can possess fast Li+ ion transport channels from the Li metal to LiFePO4, acting as a stable interlayer between the Li metal and solid polymer electrolyte. Noticeably, the solid-state LiFePO4/Li cell with a Cu@SnNi interlayer exhibits an excellent rate capability (133 mA h g-1, 2 C; 100 mA h g-1, 5 C) in comparison to the low rate performance of the cell without the interlayer (117 mA h g-1, 2 C; 60 mA h g-1, 5 C). This unique structure design of electronic and ionic mixed conducting interlayer provides an alternative strategy to improve the performance of SSLMBs.

White organic light emitting devices based on ultrathin emitting layer and bipolar hybrid interlayer

In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) with stable spectra are fabricated based on doping-free ultrathin emissive layers and mixed bipolar interlayers. To achieve WOLEDs, at least three kinds of light-emitting layers, i.e. blue, green and red, are needed. The traditional method to fabricate emissive layers is by co-evaporation, which can improve electroluminescent efficiency. However, the co-evaporation rate and dopant concentration are difficult to control, which leads to a bad reproducibility and thus goes against commercialization. In order to simplify the structures of WOLEDs and improve repeatability, several doping-free ultrathin emissive layers are used in this paper with 3 nm mixed bipolar interlayers separating them. The optimal ratio of bipolar hybrid material is determined by hole-only device, electron-only device and blue phosphorescent OLED. In addition, green, orange and red monochromatic OLED have also been fabricated separately, which are used to prove that mixed bipolar material is also suitable for the three phosphorescent emitting material. The WOLED with TCTA interlayers is fabricated to confirm that mixed bipolar material is beneficial to the characteristics of WOLEDs. The energy transfer process between different emitting materials is verified by studying the transient photoluminescence lifetime. The maximum efficiency of three-color and four-color doping-free WOLED are 52 cd/A (53.5 lm/W) and 13.8 cd/A (13.6 lm/W), respectively, and the maximum external quantum efficiency of three-color and four-color doping-free WOLED are 17.1% and 11.2%, respectively. Due to the sequential energy transfer structure between different emitting layers, the Commission Internationale de L'Eclairage coordinates shows a very slight variation of (0.005, 0.001) from 465 cd/m<sup>2</sup> to 15950 cd/m<sup>2</sup> for three-color WOLED. The Commission Internationale de L'Eclairage coordinates shows a variation of (0.023, 0.012) from 5077 cd/m<sup>2</sup> to 14390 cd/m<sup>2</sup> for four-color WOLED. The four-color WOLED shows a maximum color rendering index of 92.7 at 884 cd/m<sup>2</sup>, and it reaches 88.5 at 14390 cd/m<sup>2</sup>. In addition, the lifetime of phosphorescent OLED is usually poor due to the trap formed by triplet-polaron annihilation. The exciton distribution can be broadened and the exciton concentration can be reduced by using ultrathin light emitting layers (< 1 nm) and mixed bipolar interlayers. Therefore, triplet-polaron annihilation will be reduced, and the lifetime of OLEDs will be improved.

Efficient white phosphorescent organic light-emitting diodes using ultrathin emissive layers (

In this paper, efficient phosphorescent white organic light-emitting diodes (WOLEDs) were fabricated based on ultrathin doping-free emissive layers and mixed bipolar interlayers. The energy transfer processes were proved via the research of WOLEDs with different interlayer thicknesses and transient photoluminescence lifetime. WOLEDs with optimized thickness of doping-free emissive layers show maximum current efficiency of 47.8 cd/A and 44.9 cd/A for three-colors and four-colors WOLEDs, respectively. The Commission Internationale de L’Eclairage coordinates shows a very slight variation of ( ± 0.02, ± 0.02) from 5793 cd/m2 to 11370 cd/m2 for three-colors WOLEDs and from 3038 cd/m2 to 13720 cd/m2 for four-colors WOLEDs, respectively. The stability of the spectra is attributed to the stable and sequential energy transfer among the various dyes. The color temperature of four-colors WOLEDs can be obtained from 2659 to 6636 by adjusting the thickness of ultrathin emissive layer.

Toward Increasing Micropore Volume between Hybrid Layered Perovskites with Silsesquioxane Interlayers.

Hybrid organic-inorganic layered perovskites are typically nonporous solids. However, the incorporation of silsesquioxanes with a cubic cage structure as interlayer materials creates micropores between the perovskite layers. In this study, we increase in the micropore volume in layered perovskites by replacing a portion of the silsesquioxane interlayers with organic amines. In the proposed method, approximately 20% of the silsesquioxane interlayers can be replaced without changing the layer distance owing to the size of the silsesquioxane. When small amines (e.g., ethylamine) are used in this manner, the micropore volume of the obtained hybrid layered perovskites increases by as much as 44%; when large amines (e.g., phenethylamine) are used, their micropore volume decreases by as much as 43%. Through the variation of amine fraction, the micropore volume can be adjusted in the range. Finally, the magnetic moment measurements reveal that the layered perovskites with mixed interlayers exhibit ferromagnetic ordering at temperature below 20 K, thus indicating that the obtained perovskites maintain their functions as layered perovskites.

Microstructural evolution and mechanical properties of CuW/CuCr interface with mixed powder interlayers by liquid diffusion bonding technique

Cu-W composites and CuCr alloy were bonded with mixed Cu-Fe powder interlayers using the liquid diffusion bonding technique at 1380 °C for 1 h. Microstructures of the CuW/CuCr joints with Cu-Fe powder interlayers were investigated and compared via field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. Tensile tests were examined to evaluate the resulting joints. The results show that a diffusion solution layer about 2–3 μm width formed at the Cu/W interphase and the interfacial strength can reach up to 400 MPa when Cu-3wt%Fe interlayer is introduced into the interfacial region between Cu-W and CuCr alloy. Furthermore, the interfacial fracture morphology presents more transgranular cleavage fractures of W particles. However, when the content of Fe in the powder interlayers is above 3 wt%, the interfacial strength decreases gradually with the increasing of Fe content. After Cu-15 wt%Fe interlayer was applied, Fe7W6 phase is found in W skeletons and micro-cracks appear at the CuW/CuCr interface. Therefore, the interfacial strength declines to 263 MPa. The fraction of cleavage fracture decreases and the cracks propagate cross different areas of the CuW/CuCr interface.

Mixed interlayers at the interface between PEDOT:PSS and conjugated polymers provide charge transport control

An insoluble polymer interlayer has a great effect on the charge injection from the PEDOT:PSS interface.

Gradual Controlling the Work Function of Metal Electrodes by Solution‐Processed Mixed Interlayers for Ambipolar Polymer Field‐Effect Transistors and Circuits

In this paper, a technique using mixed transition‐metal oxides as contact interlayers to modulate both the electron‐ and hole‐injections in ambipolar organic field‐effect transistors (OFETs) is presented. The cesium carbonate (Cs2CO3) and vanadium pentoixide (V2O5) are found to greatly and independently improve the charge injection properties for electrons and holes in the ambipolar OFETs using organic semiconductor of diketopyrrolopyrrolethieno[3,2‐b]thiophene copolymer (DPPT‐TT) and contact electrodes of molybdenum (Mo). When Cs2CO3 and V2O5 are blended at various mixing ratios, they are observed to very finely and constantly regulate the Mo's work function from −4.2 eV to −4.8 eV, leading to high electron‐ and hole‐mobilities as high as 2.6 and 2.98 cm2 V−1 s−1, respectively. The most remarkable finding is that the device characteristics and device performance can be gradually controlled by adjusting the composition of mixed‐oxide interlayers, which is highly desired for such applications as complementary circuitry that requires well matched n‐channel and p‐channel device operations. Therefore, such simple interface engineering in conjunction with utilization of ambipolar semiconductors can truly enable the promising low‐cost and soft organic electronics for extensive applications.

Enhancing Charge Transfer Kinetics by Nanoscale Catalytic Cermet Interlayer

Enhancing the density of catalytic sites is crucial for improving the performance of energy conversion devices. This work demonstrates the kinetic role of 2 nm thin YSZ/Pt cermet layers on enhancing the oxygen reduction kinetics for low temperature solid oxide fuel cells. Cermet layers were deposited between the porous Pt cathode and the dense YSZ electrolyte wafer using atomic layer deposition (ALD). Not only the catalytic role of the cermet layer itself but the mixing effect in the cermet was explored. For cells with unmixed and fully mixed cermet interlayers, the maximum power density was enhanced by a factor of 1.5 and 1.8 at 400 °C, and by 2.3 and 2.7 at 450 °C, respectively, when compared to control cells with no cermet interlayer. The observed enhancement in cell performance is believed to be due to the increased triple phase boundary (TPB) density in the cermet interlayer. We also believe that the sustained kinetics for the fully mixed cermet layer sample stems from better thermal stability of Pt islands separated by the ALD YSZ matrix, which helped to maintain the high-density TPBs even at elevated temperature.

Improving efficiency of pentacene/C 60 based solar cells with mixed interlayers

This work presents a modified architecture for conventional pentacene/fullerene (C 60) solar cells by inserting alternately deposited C 60/pentacene interlayers (~ 1–2 nm per layer). The cell parameters, the incident photon-to-current efficiency spectra and the atomic force microscopy were used to characterize devices that had different numbers of inserting layers. The power conversion efficiency (PCE) increased markedly from 0.77 to 1.60% as the number of the inserted pairs increased from zero to three. The PCE further increased to 1.73% after post-annealing. The interlayers formed an interpenetrating network, enlarging the area over which excitons dissociate. When the number of interlayers and post-annealing conditions were optimized, the resistance and the surface roughness were minimized. When the number of pairs was increased to five, cell performance was degraded. The mechanism by which the properties of the solar cells are related to the inserted layers is presented.

Enhanced power conversion efficiency of p-i-n type organic solar cells by employing a p-layer of palladium phthalocyanine

We demonstrate an enhancement in the power conversion efficiency (PCE) of p-i-n type organic solar cells consisting of zinc phthalocyanine (ZnPc) and fullerene (C60) using a p-layer of palladium phthalocyanine (PdPc). Solar cells employing three different device structures such as ZnPc/ZnPc:C60/C60, PdPc/PdPc:C60/C60, and PdPc/ZnPc:C60/C60 with varying thickness of mixed interlayers were fabricated by thermal evaporation. The mixed i-layers were deposited by co-evaporation of MPc (M=Zn,Pd) and C60 by 1:1 ratio. PCE of 3.7% was obtained for optimized cells consisting of PdPc/ZnPc:C60/C60, while cells with device structure of ZnPc/ZnPc:C60/C60 showed PCE of 3.2%.

An investigation of co-fired varistor-ferrite materials

The purpose of this work was to co-fire crack-free varistor-ferrite ceramic multilayers fabricated via a dry pressing route. Multilayers were sintered using a standard industrial grade varistor sintering regime. Sinter shrinkages of both varistor and ferrite materials were measured using dilatometry and showed that the varistor shrunk significantly more than the ferrite material. X-ray diffraction analysis indicated that no significant phase changes occurred in the materials under investigation as a result of the sintering process. Scanning electron microscopy observations of the dry-pressed co-fired varistor-ferrite revealed vertical cracking in the ferrite due to thermal expansion mismatch between the materials. By pressing a mixed composition interlayer in the ratio 50:50, between the varistor and ferrite materials, a crack-free multilayer structure could be obtained. Energy dispersive X-ray analysis of the co-fired ferrite and varistor confirmed diffusion of Fe and Ni components from the ferrite into the varistor material. The degree of diffusion was reduced by using 50:50 ratio mixed composition interlayers.

Fracture Testing and Analysis of a Layered Functionally Graded Ti/TiB Beam in 3-Point Bending

This paper presents a methodology for testing and analyzing a layered functionally graded beam consisting of Ti and TiB phases. The test specimen is a single edge notch bending (SENB), with composition varying from a TiB-rich layer at the bottom to commercially pure (CP) Ti at the top. The crack front is aligned parallel to the material gradation and it grows along this direction (mode I). For this crack orientation, average R-curve behavior is investigated in order to understand the mechanics of crack growth. The beam is modeled using two-dimensional finite elements considering elastoplastic behavior. Properties of the mixed phase interlayers are approximated using a rule-of-mixtures approach, and the validity of this approach is discussed. Characteristic response quantities are investigated such as the mechanical fields, crack mouth opening displacement, and J integral.

Large gap joining of Ti–6Al–4V alloy with mixed powder interlayers

Titanium based brazing alloys containing chromium, iron, copper, and nickel as β stabilisers have been studied for joining the titanium alloy Ti–6Al–4V. Two of these alloys were selected for use in producing large gap joints. The first brazing alloy, Ti–12Zr–14Cr–12Cu–12Ni (type 1), can be used to braze Ti–6Al–4V below its β transus temperature. Joints of thickness up to 150 μm can be made in a normal brazing cycle without prolonged holding. The interlayer consists of a β titanium alloy with no precipitation of intermetallic compounds. The second brazing alloy, Ti–12Zr–14Cr–6Fe–5Cu–5Ni (type 2), has to be brazed above the β transus temperature of Ti–6Al–4V. Its powders were mixed with pure titanium and Ti–6Al–4V powders and the mixture was used as the joining interlayer. Interlayers 5 mm in thickness were used to produce joints for microstructural examination and mechanical testing. It was found that residual pores in the interlayers were related to the amount of the brazing alloy in the interlayer. A fully dense interlayer could be obtained with 60 wt-% brazing alloy in the interlayer. The as bonded joints revealed tensile strength equal to 50% of that of the base metal. Diffusional treatment of the joints improved the joint efficiency to about 70%, compared with the base metal.

Large gap joining of Ti–6Al–4V alloy with mixed powder interlayers

Titanium based brazing alloys containing chromium, iron, copper, and nickel as β stabilisers have been studied for joining the titanium alloy Ti–6Al–4V. Two of these alloys were selected for use in producing large gap joints. The first brazing alloy, Ti–12Zr–14Cr–12Cu–12Ni (type 1), can be used to braze Ti–6Al–4V below its β transus temperature. Joints of thickness up to 150 μm can be made in a normal brazing cycle without prolonged holding. The interlayer consists of a β titanium alloy with no precipitation of intermetallic compounds. The second brazing alloy, Ti–12Zr–14Cr–6Fe–5Cu–5Ni (type 2), has to be brazed above the β transus temperature of Ti–6Al–4V. Its powders were mixed with pure titanium and Ti–6Al–4V powders and the mixture was used as the joining interlayer. Interlayers 5 mm in thickness were used to produce joints for microstructural examination and mechanical testing. It was found that residual pores in the interlayers were related to the amount of the brazing alloy in the interlayer. A fully dense interlayer could be obtained with 60 wt-% brazing alloy in the interlayer. The as bonded joints revealed tensile strength equal to 50% of that of the base metal. Diffusional treatment of the joints improved the joint efficiency to about 70%, compared with the base metal.

Two‐point conductivity tensor of nonmultilayer magnetic systems

AbstractThe transport properties of nonmultilayer magnetic systems are described in terms of a semiclassical Boltzmann equation. Interfaces are modeled asthin mixed interlayers so that both bulk impurity scattering and interface scattering are included in a position‐dependent relaxation time. Theresulting expression for the two‐point conductivity tensor is in accordance with that derived from the real‐space Kubo formula, indicating a close connection between the semiclassical method and the quantum approach.

Quasi-classical approach to perpendicular transport through metallic magnetic superlattices

We present an extended quasi-classical theory of the perpendicular transport of electrons through magnetic multilayers. The two-point conductivity and the perpendicular resistivity are analytically studied by treating the spin-dependent scattering at interfaces as bulk asymmetric scattering within mixed interlayers. The results obtained are shown to be equivalent to those derived from the quantum method, indicating that there is a direct connection between the Boltzmann and the Kubo approaches.