Al Interlayer Research Articles

Influence of aluminum interlayer on optical properties of very thin silver thin film

Generally, Ag thin films on glass substrates grow three-dimensionally because of the high Ag/glass interface free energy. However, flatter growth has been reported to be achieved by introducing an appropriate interlayer between the substrate and Ag film. With flatter growth, enhanced optical properties are expected. In the present study, very thin Ag films were deposited on an Al interlayer and their optical properties over a wide wavelength range from the visible-light region to the infrared region were investigated. Ag/Al films and Ag films were formed on substrates via resistance-heating vacuum evaporation. The Al interlayer thickness was fixed at 1 nm, and the Ag thickness was varied from 6 to 15 nm. The surface morphology was observed by atomic force microscopy, and the sheet resistance was measured by the four-point-probe method. The visible-light transmittance was evaluated using a spectrophotometer, and the infrared reflectance was evaluated using Fourier transform infrared spectroscopy. The surface roughness of a 6 nm-thick Ag film was found to be reduced from 1.0 nm to 0.6 nm by the introduction of the interlayer. In the absence of the interlayer, the sheet resistance was too high to be measured; however a sheet resistance of 16.2 Ω/sq. was obtained when the interlayer was present. Similar effects were observed for a 10 nm-thick Ag film. Ag films with thicknesses of 6 and 10 nm showed improved visible-light transmittance and infrared reflectance upon introduction of the interlayer. However, when the thickness of the Ag film was 15 nm, no difference in the sheet resistance or optical properties was observed between samples with and without the interlayer. As a consequence, we found that introducing an Al interlayer is effective for two-dimensional-like growth of Ag films, leading to enhanced visible-light transmittance and infrared reflectance.

Effect of Equal Channel Angular Pressing on Mechanical and Tribological Properties of Sintered Al-Sn Composites

Evolution of structure of two-phase sintered Al-Sn composites during equal channel angular pressing (ECAP) without rotation of the sample between the passes (route A) was studied. The macrostructure with alternating thin Al and Sn interlayers was formed in the flow plane of the samples under the ECAP processing. It was found that the law of the changes in the parameters of the structure of the composites can be described using the geometry of ECAP. The greatest changes in the macrostructural parameters and increase in the strength of the composites were observed during the first two passes. The consequence of the thinning of aluminum interlayers is an increase in the depth of deformation of the subsurface layer and decrease in distance between tin interlayers which are sources of solid lubricant. As a result, the wear intensity of the sintered Al-Sn composites is additionally decreased under dry friction against steel if the sliding direction is perpendicular to the elongated phases interlayers. It was established that the composite containing about 40% Sn has the highest wear resistance.

Diffusion welding of stainless steel 304L/Monel K-500 composite materials produced with different methods

The stainless steel 304L (commercially supplied) and Monel K-500 that was prepared through cold pressing of metal matrix composite materials powder mixtures were joined by diffusion welding. Welding was performed under uniaxial compression using the 50 µm-thick nickel (Ni) and aluminum (Al) 2024 interlayers under 3 MPa at 950–980°C for 60 min in an argon gas atmosphere. After welding, the diffusion and intermediate zones of the samples were characterized using X-ray diffraction, optical microscopy, scanning electron microscopy, and energy-dispersive spectrometry analysis. As evaluating the diffusion zone with interlayer, it was determined that different interlayers expanded due to increasing temperature of the diffusion area. Interlayers expanded more on the K-500 side and relatively less on the 304L side. On the other hand, when samples with Ni interlayers were examined, high amount of Ni contained by both base material (304L) and interlayer led to the formation of rich Ni phases in the diffusion side. The brittle FeNi, Fe3Ni2, CuNi, Cu9Si, Cu0,81Ni0,19, Fe0,64Ni0,36, CrNi, Cr2Ni3, FeNi3, FeCu4, and Al0.71Cr0.3Fe17.65, which were identified to form irregularity in the diffusion zone. These intermetallic phases increased the hardness and significantly decreased the ductility of different material couples joined by diffusion welding. As a result, the microhardness and lap shear tests were applied to specimens to characterize the mechanical properties of the joint zones. The maximum hardness and maximum lap shear values were obtained at joint that made with the Al interlayer at 980°C as 432.8 HV and 165 MPa.

Magnetic impurities as the origin of the variability in spin relaxation rates in Cu-based spin transport devices

The Elliott-Yafet spin relaxation mechanism posits linear proportionality between spin and momentum lifetimes in low spin-orbit coupling nonmagnetic metals, and is widely accepted in spintronics. Accurate experimental determination of the Elliott-Yafet proportionality constants (${\ensuremath{\beta}}_{i}$) between the spin and momentum relaxation times for individual scattering sources is challenging, however. This is apparent from the literature on nonlocal spin transport in Cu, for example, where reported phonon (${\ensuremath{\beta}}_{\mathrm{ph}}$) and defect (${\ensuremath{\beta}}_{\mathrm{def}\phantom{\rule{4pt}{0ex}}}$) Elliott-Yafet constants vary by an order of magnitude. In recent work we discovered that even part-per-million-level magnetic impurity concentrations can substantially influence spin relaxation in Cu, via a spin transport analog of the Kondo effect. To clarify whether this could explain the reported variability in ${\ensuremath{\beta}}_{i}$, here we report on a comprehensive study of spin transport in Cu-based lateral nonlocal spin valves, varying the ferromagnetic contact material, interface structure, Cu thickness, and post-fabrication annealing conditions, resulting in widely varied microstructures and magnetic impurity concentrations. Quantifying the effects of magnetic impurities on charge and spin transport we demonstrate the dramatic, even dominant, effect these can have on spin relaxation rates, and thus extracted ${\ensuremath{\beta}}_{i}$. Minimization of magnetic impurity effects is achieved via Al interlayer insertion or moderate annealing, restoring the expected temperature dependence for phonon-mediated spin relaxation, and enabling more reliable determination of ${\ensuremath{\beta}}_{i}$ for phonons (740 \ifmmode\pm\else\textpm\fi{} 200), and nonmagnetic defects (240 \ifmmode\pm\else\textpm\fi{} 50). The latter contribution is shown to be dominated by grain boundaries in these polycrystalline Cu films. Cross-sectional transmission electron microscopy measurement of grain sizes in actual nonlocal spin valve devices then establishes a useful empirical relationship between average grain size and spin diffusion length. These measurements highlight the importance of magnetic impurities in metallic spin transport, explain the wide variability in reported ${\ensuremath{\beta}}_{\mathrm{ph}}$ and ${\ensuremath{\beta}}_{\mathrm{def}}$ in Cu, and elucidate the relationship between metallic spin transport and microstructure.

Formation of uniform and homogeneous ternary NiSi2−xAlx on Si(001) by an Al interlayer mediation

Ternary NiSi2−xAlx layer with uniform and smooth NiSi2−xAlx/Si interface has been achieved by Al interlayer mediated epitaxy. A 3 nm Al interlayer is introduced to the Nickel silicidation on Si(001) substrate. The morphology, composition, and micro-structure of the Ni silicide layers are analyzed for different annealing temperatures. It is found that under the assistance of Al atoms, the best quality Ni silicide layer is achieved by annealing at 700 °C. The reduced Ni diffusion and the modified energetics are conducive for the uniform reaction between Ni and Si, resulting in epitaxial ternary NiSi2−xAlx layer on Si(001) substrate.

Microstructure and mechanical properties of Al/steel dissimilar welds fabricated by friction surfacing assisted friction stir lap welding

Al/steel dissimilar welds were obtained by friction stir lap welding (FSLW) with an Al interlayer, which was fabricated by friction surfacing (FS). In present study, the tool pin was totally plunged into the Al plate and interlayer without stirring steel, which avoided the tool wear. The Al plate and interlayer were remarkably intermixed as pin length increased. A diffusion layer, instead of the intermetallic layer, was found at the Al/steel interface, indicating the enhanced atomic migration and related interfacial bonding. The maximum failure load of the joints of 2.8kN was reached when the 2.5mm pin tool was used. The heterogeneous microstructure, which was caused by the intermixing, was responsible for the fracture, according to the fracture profiles. Necking and dimples were depicted from the fractographies, indicating that the joints were failed by plastic fracture.

Effect of Al interlayer on resistance spot welding of MB3/Ti6Al4V

The aim of present study was to evaluate the effects of Al foil on microstructure and mechanical performances of Ti/Mg joint obtained by resistance spot welding. Experiment results reveal that a TiAl3 intermetallic compound layer was formed in the interface region of Ti/Mg joint with the addition of Al foil, which was the key to achieve joint strengthening. For Ti/Mg joint without Al foil, the maximum micro hardness value of 138 HV was measured in the interface region of spot weld. However, under the action of Al foil, the micro hardness of interface region increased to 152HV, attributed to the formation of TiAl3 layer. Besides, with optimal current of 9 kA and the aid of Al foil, the maximum tensile shear strength increased from 3.3 kN to 3.8 kN and the relevant fracture surface was characterized by plastic fracture features.

Interfacial microstructure of Ti/Ni joints with Ti–Al interlayer by rapid thermal explosion bonding in vacuum

The present study investigated the joining between Ti and Ni by rapid thermal explosion (TE) in vacuum of <10 Pa. The TE temperature of Ti–Al interlayer reaction was measured and the effects of hold time on microstructure and micro-hardness of Ti/Ti–Al/Ni joint were discussed. The TE temperature of Ti–Al interlayer reaction is about 940.3 °C and an obvious exothermic phenomenon lasting 13s during TE reaction process is observed. Obvious diffusion layers at both interfaces are observed due to the inter-diffusion of Ti, Ni and Al elements. With the increasing of hold time, thickness of diffusion layers was increased from 7.6 to 15 μm at the Ti/Ti–Al interface and from 16.7 to 23.7 μm at the Ti–Al/Ni interface. Furthermore, the micro-hardness of substrates and interlayer are not obviously changed with increasing of hold time ranging from 30 to 90 min.

Growth Mechanism and Properties of Self-Assembled InN Nanocolumns on Al Covered Si(111) Substrates by PA-MBE.

Self-assembled InN nanocolumns were grown at low temperatures by plasma-assisted molecular beam epitaxy with a high crystalline quality. The self-assembling procedure was carried out on AlN/Al layers on Si(111) substrates avoiding the masking process. The Al interlayer on the Si(111) substrate prevented the formation of amorphous SiN. We found that the growth mechanism at of InN nanocolumns started by a layer-layer (2D) nucleation, followed by the growth of 3D islands. This growth mechanism promoted the nanocolumn formation without strain. The nanocolumnar growth proceeded with cylindrical and conical shapes with heights between 250 and 380 nm. Detailed high-resolution transmission electron microscopy analysis showed that the InN nanocolumns have a hexagonal crystalline structure, free of dislocation and other defects. The analysis of the phonon modes also allowed us to identify the hexagonal structure of the nanocolumns. In addition, the photoluminescence spectrum showed an energy transition of at for the InN nanocolumns, confirmed by photoreflectance spectroscopy.

Long-lasting and efficient inverted pure blue organic light-emitting diodes by inserting an ultrathin aluminum interlayer

Blue organic light-emitting diodes (OLEDs) play an important role in OLED display and lighting applications, but short lifetime and low efficiency are still their two key issues in the commercialization. Here, we manage to address the two issues at the same time by simply inserting an ultrathin aluminum (Al) interlayer between the indium tin oxide (ITO) cathode and the electron injection layer of an inverted pure blue OLED. Current efficiency (CE) and external quantum efficiency were improved by optimizing the thickness of the Al interlayer. It has been approved from current-voltage characteristics, impedance spectra and an ultraviolet photoelectron spectrum that 1 nm thick Al interlayer is an effective work function modifier for the ITO cathode and can help to enhance electron injection from the ITO cathode to the electron transporting layer. The Al interlayer contributed also to extend dramatically the lifetime of the inverted pure blue OLED. A long operation lifetime (T80 > 83 h) with the maximum CE of 7.9 cd A−1 was achieved after adding 1 nm Al interlayer.

Friction Welding of Titanium to Stainless Steel Using Al Interlayer

Dissimilar friction welding between titanium and 304 austenitic stainless steel with aluminum as insert layer was examined to amend the joint properties and interface characteristics. To insert the interlayer into the joint, a two-step method was used. The resultant of the joint interfaces was characterized to reveal the reactions between interlayer and parent metals using scanning electron microscope, X-ray diffraction and electron probe micro-analyzer. Microhardness and tensile tests were used to evaluate the mechanical properties of the joints. It was observed that the development of brittle phases of FeTi and CrTi in the welded joint was successfully precluded using aluminum interlayer, whereas the presence of other phases which were in ductile nature compared to the FeTi- and CrTi-type phases of AlTi and FeAl was identified. The absence of reaction compounds and brittle phases ensued improvement in the mechanical and microstructural properties of the aluminum insert layer joints.

Microstructure and Mechanical Properties of Ultrasound-Assisted Soldered Al-50 wt.%Si/Al-27 wt.%Si Joints for Automotive Applications

Hypereutectic Al-27 wt.%Si alloy and hypereutectic Al-50 wt.%Si alloy have been soldered using a Zn-5 wt.%Al interlayer without flux at 420°C in air with ultrasound assistance. The influence of the ultrasound on the migration of Si particles and the microstructure of the solidified Zn-Al-based alloys was investigated. The effect of the distribution of Si particles and the microstructure of the solidified Zn-Al-based alloys on the shear strength is also discussed. As the duration of the ultrasound was increased, the distribution of Si particles became more uniform. The highest average shear strength of the joints reached 70.41 MPa, with fracture mainly occurring at the Si particulate-reinforced Zn-Al-based composite joint.

Interface characteristics of Mg/Al bimetal produced by a novel liquid-liquid compound casting process with an Al interlayer

Mg/Al bimetal was successfully prepared using a novel lost-foam casting (LFC) liquid-liquid compound process with an Al interlayer, and the interface characteristics including microstructure, mechanical properties, and fracture behavior of the Mg/Al bimetal were investigated in this paper. The results show that the mixing of AZ91D and A356 liquid metals was fully avoided by using the Al interlayer. A metallurgical bonding between the AZ91D alloy matrix and the A356 alloy matrix was achieved, obtaining a compact interface. The interface was constituted by the Al12Mg17 + δ (Mg) eutectic and the Al3Mg2 and Mg2Si reaction layers, which were respectively next to the AZ91D alloy matrix and the A356 alloy matrix. The reaction layers had much higher microhardnesses compared with the microhardnesses of the matrixes, and the highest microhardness up to 275–299 HV was obtained in the reaction layer next to the Al matrix. A brittle fracture morphology was observed in the fractured surface of the Mg/Al bimetal, and the fracture mainly initiated with the fracture of the reaction layer close to the Al matrix.

A Comparison of the Effects of Ambient Air Plasma Generated by Volume and by Coplanar DBDs on the Surfaces of PP/Al/PET Laminated Foil

This contribution presents a comparison of the effects of atmospheric-pressure plasma in ambient air on the surface properties of polypropylene/aluminum/polyethylene terephthalate (PP/Al/PET) laminated foil. Plasma treatment was applied by means of two types of ambient-air dielectric-barrier discharge (DBD): 1) coplanar DBD and 2) volume DBD. The surface energy levels of the PP and PET surfaces terms were measured. The morphology and surface chemistry of the PP and PET surfaces were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The differences in the effect of coplanar and volume DBDs on polymer surfaces are observed and explained in terms of the properties of microdischarges in coplanar and volume DBDs. The influence of the Al interlayer on plasma behavior is discussed.

Pulsed voltage breakdown of Al/CuO reactive multilayer films in metal-interlayer-metal structures

In this study, metal-interlayer-metal (MIM) structure samples are designed to investigate the breakdown properties of aluminum/cupric oxide (Al/CuO)-based reactive multilayer films (RMFs) and to evaluate the differences in the breakdown properties between the Al/CuO RMFs and the single-layer CuO film sample. The MIM structure samples use Al/CuO RMFs as the interlayers between the top and bottom aluminum electrodes, like a sandwich. The pulsed voltage is produced by a capacitor. The samples are not discharged until the external voltage exceeds the breakdown field strength (EB) of the Al/CuO RMFs. The results show that the EB of the Al/CuO RMFs can be improved by Al interlayers in the RMFs, but the destruction area caused by breakdown is smaller than that of the single-layer CuO film. A theoretical model indicates that the thermal conductivity and vaporization heat are crucial parameters for the breakdown of Al/CuO RMFs. The viewpoint from the breakdown of the Al/CuO RMFs proposed in this study might provide a new way for interpreting the electrical excitation process in RMFs.

Oxidation behavior of thermal barrier coating systems with Al interlayer under isothermal loading

In the present study, the phenomena related to the Thermally Grown Oxides (TGO) in atmospheric plasma sprayed Thermal Barrier Coatings (TBCs) are discussed. CoNiCrAlY bond coatings were sprayed on Inconel 600 substrates. Subsequently, thin Al layers were deposited by DC-Magnetron sputtering. Finally, yttria-stabilized zirconia (YSZ) top coatings were deposited to form a three-layered TBC system. The thus produced aluminum interlayer containing thermal barrier coatings (Al-TBC) were subjected to isothermal exposure with different holding times at 1150 °C and compared with reference TBCs of the same kind, but without Al interlayers (R-TBC). The oxide film formation in the interface between bond coating (BC) and top coating (TC) was investigated by scanning electron microscope (SEM) after 100 and 300 h of high temperature isothermal exposure. The growth of this oxide film as a function of the isothermal exposure time was studied. As a result, the designed Al-TBC system exhibited better oxidation resistance in the BC/TC interface than the two-layered R-TBC system. This was lead back to the Al enrichment, which slows down the formation rate of transition metal oxides during thermal loading.

Laser conduction welding characteristics of dissimilar metals Mg/Ti with Al interlayer

The immiscible and nonreactive characteristics of Mg/Ti dissimilar metals restrict the metallurgical bonding and reliable joining of them. To solve this problem, the Al interlayer between Mg/Ti was added. The Mg/Ti joint without addition of Al interlayer could not be welded, while relatively acceptable appearance was obtained when adding Al interlayer. The interfacial reaction was improved with the assistance of Al interlayer resulting in metallurgical bonding at the interface. The TiAl3 phase formed at the direct laser irradiation zone. Note that the interfacial reaction layer increased little with the increasing thickness of Al interlayer. The interfacial reaction layer was mainly restricted by dissolution of Ti element. Temperature field and thermodynamic calculation assisted to prove the interfacial reaction at the fusion zone/Ti interface and the formation of TiAl3. The tensile-shear testing indicated that the maximum tensile-shear force could reach 2230 N/cm (about 81% of that of AZ31B Mg alloy base metal) when the laser power was 2300 W and the thickness of added Al interlayer was 0.05 mm. The tensile-shear force decreased when network structure of Mg17Al12 precipitated in the weld zone. The fracture path changed from fusion zone/Ti to Mg fusion line when the thickness of Al interlayer exceeded 0.12 mm.

Microstructural, mechanical and metallurgical analysis of Al interlayer coating on Mg-Al alloy using diffusion bonding

Diffusion bonding process was adopted to bond the two dissimilar metals of aluminium coated AZ 80 magnesium alloy and AA 7075 aluminium alloy for different set of process parameters. The samples of AZ 80 magnesium alloy and AA 7075 aluminium alloy without interlayer were attempted with three trials of five different temperatures ranging from 325°C to 450 °C were taken in the present investigation. The other parameters such as bonding pressure of 10 MPa and bonding time of 15 min were kept constant. The mechanical properties of the samples showed improved mechanical properties at optimum temperature and that the surface properties were probed using optical micrsocopy and scanning electron microscope (SEM). The bonding quality with the effect of temperature on diffusion bonded specimen was investigated in detail.

Highly efficient tandem organic light-emitting devices adopting a nondoped charge-generation unit and ultrathin emitting layers

Abstract Highly efficient non-doped tandem phosphorescent organic light-emitting devices (PhOLEDs) have been demonstrated by employing LiF/AL/1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) as a charge generation unit (CGU) and ultrathin phosphorescent dyes as emitting layers (EMLs). It was found that the performance of the tandem PhOLEDs was significantly dependent on the Al thickness in CGU. Analyses regarding the current density-voltage characteristics of the CGU only devices indicate that the charge carriers are generated at the HAT-CN/NPB interface, and Al/LiF layers work as assistant electron injection layers to facilitate electron extraction from CGU and injection into the adjacent electron transport layer. From the capacitance-voltage and optical transparency characteristics of CGU with different thicknesses of Al interlayer, the thick Al layer is beneficial to charge separation, while it weakens the light output of the tandem device. Under the optimal Al thickness of 5 nm, more than twofold enhancement of current efficiency is achieved for the non-doped tandem blue device. Furthermore, the non-doped tandem white PhOLED was also developed showing a maximum current efficiency of 94.9 cd/A and maximum external quantum efficiency of 31.6%.

Shock-induced stacking fault pyramids in Ni/Al multilayers

The formations of stacking fault tetrahedra in {111}fcc/{111}fcc multilayers have been studied extensively, but the researches related to {001}fcc/{001}fcc interfaces can rarely be found in the literature. Using molecular dynamics (MD) simulations, the shock-induced dislocation structure in Ni/Al multilayers was studied in this article, the stacking fault pyramids (SFPs) initiated from Ni/Al interface was firstly observed, and the corresponding mechanism was explored. It was shown that the Shockley partial dislocations dissociated from the rectangular misfit dislocations along Ni/Al interface are first emitted into the Al interlayer and subsequently intersect with each other to form SFPs. With the propagation of the shock front in the multilayers, two adjacent SFPs interact with each other and form Lomer-Cottrell locks. The dislocation sheet composed of SFPs and Lomer-Cottrell locks can act as a barrier to dislocation transmission. The effect of shock piston velocity on the nucleation site of dislocation was also studied. It was shown that dislocations would originate from the interface at a low piston speed (<1.1km/s), and appear at the shock front if the piston speed exceeds 1.2km/s.