Varying Aluminum Content Research Articles

Design of high-entropy films as ultra-violet light reflector

This study proposes the design and implementation of high-entropy alloy (HEA) thin films as materials for the reflector of deep ultraviolet light-emitting devices and marks the first application of HEA in optical field. In the material design phase, an Al-Co-Zn-Ni alloy is designed by considering the reflectivity, phase stability and binary formation energy. Reverse Monte Carlo calculation is employed to establish stable atomic structure. Frequency-dependent dielectric equations are derived from first principles calculations, with dielectric constants incorporating contributions from ions and electrons and combining classical Drude and Lorentz models. The dielectric equations yield optical constants that are used to calculate the reflectance. In the experimental phase, we systematically vary the aluminum content and prepare Al-Co-Zn-Ni thin films ranging from pure aluminum to equimolar compositions. In the deep ultraviolet region, the reflectance of thermally treated Al65Zn12Co12Ni11 and Al50Zn16Co17Ni17 thin films is found superior to that of gold by three times. Structural and crystalline changes with varying aluminum content are found, as well as intriguing phase separation and superlattice formation that persist until equimolar compositions. This unique nanoscale structural variation causes the Young's modulus and hardness of Al-Co-Zn-Ni thin films to initially increase and then decrease with decreasing aluminum content. There is a significant increase in the corrosion potential difference when reducing Al contents in Al-Co-Zn-Ni, indicating improved passivation effects as the equimolar composition is approached. By modulating the aluminum content, the nanoscale structure of Al-Co-Zn-Ni can be adjusted, thereby improving its optical, mechanical, corrosion resistance, and thermal stability properties. This demonstrates the high versatility of this material for practical optical applications.

High-temperature terahertz quantum-cascade lasers: design optimization and experimental results

Objectives. Terahertz quantum-cascade lasers (THz QCLs) are compact solid-state lasers pumped by electrical injection to generate radiation in the range from 1.2 to 5.4 THz. The THz QCL operating frequency band contains absorption lines for a number of substances that are suitable for biomedical and environmental applications. In order to reduce the size and cost of THz QCLs and simplify the use of THz sources in these applications, it is necessary to increase the operating temperature of lasers.Methods. To calculate electron transport in THz QCLs, we used a system of balance equations based on wave functions with reduced dipole moments of tunnel-bound states.Results. As a result of the calculations, an original band design with a period based on three GaAs/Al0.18Ga0.82As quantum wells (QWs) and a gain maximum at about 3.3 THz was proposed. Based on the developed design, a THz QCL was fabricated, including the growth of a laser structure by molecular beam epitaxy, postgrowth processing to form strip lasers with a double metal waveguide, as well as an assembly of lasers mounted on a heat sink. The developed THz QCLs was capable of lasing at temperatures of up to 125 K as predicted by the performed calculations. We also studied band designs based on two GaAs/AlxGa1–xAs QWs having varying aluminum contents in the barrier layers (x = 0.20, 0.25, and 0.30).Conclusions. The calculated temperature dependences of the peak gain for two-QW designs with x > 0.2 confirm the possibility of creating THz QCLs operating at temperatures above 200 K. Thus, we have proposed two-QW band designs that outperform existing high-temperature designs in terms of maximum operating temperature.

Investigation of wurtzite formation in MOVPE-grown zincblende GaN epilayers on AlxGa1−xN nucleation layers

The influence of AlGaN nucleation layers on zincblende GaN epilayers was studied to investigate the formation of wurtzite phase inclusions in the epilayer. GaN epilayers grown on AlGaN nucleation layers with varying aluminum contents suffer from the increasing presence of wurtzite inclusions as the aluminum content of the nucleation layer increases. High-resolution transmission electron microscopy along with four-dimensional scanning transmission electron microscopy is used to investigate the origin of the wurtzite inclusions in the nucleation layer and at the GaN/AlGaN interface. It was observed that a GaN nucleation layer and an Al0.95Ga0.05N nucleation layer grew in the zincblende and wurtzite phase, respectively. These phases were then adopted by the overgrown GaN epilayers. For a GaN epilayer on an Al0.29Ga0.71N nucleation layer, wurtzite inclusions tend to form at the GaN/ Al0.29Ga0.71N interface due to strong {111}-type faceting observed in the zincblende nucleation layer. This strong faceting is correlated with an enrichment of aluminum in the upper part of the nucleation layer, as observed in energy dispersive x-ray spectroscopy, which may influence the kinetics or thermodynamics controlling the surface morphology.

Electrochemical behaviour of lead-free Sn-In-Al solders alloys in 3.5 wt.% NaCl solution

The corrosion properties of lead-free solder alloy can not be ignored in the field of the electronic industry. However, there is no literature on the effect of aluminium on Sn-In binary solder alloys. This study looked at the corrosion of a lead-free solder alloy in a 3.5 wt.% NaCl simulated seawater environment. Three isopleths were created with varying aluminium content in the Sn-In-Al system while maintaining Sn and In radio constant (1:1). The vacuum sealing process was used to create the samples. The corrosion resistance of this lead-free solder ware was investigated at room temperature in a 3.5 wt.% NaCl solution. Corrosion resistance improves with Al content, according to the potentiodynamic polarization test. By lowering the current density (Icorr), the inclusion of aluminium refines the microstructure. It enhances the corrosion resistance of Sn-In-Al solder alloys, resulting in high resistance of the passive layer produced by lowering the current density (Icorr). Scanning electron microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDS) was used to analyze of surface morphology of the non-corroded and corroded Sn-In-Al solder alloys. Intermetallic compound (IMC) of non-corroded and corrosion products on the surface corroded solder alloys were studied using X-ray diffraction (XRD). According to XRD analysis, the composition of corrosion products altered as the aluminium content changed, forming phases such as Sn3O(OH)2Cl2, oxides, and chlorides of Sn.

Investigation on oxidation stability of V2AlC MAX phase

Nanolaminated V2AlC MAX phase has been synthesized through pressureless sintering by varying aluminum content. The oxidation stability of the V2AlC is studied under non-isothermal conditions through a TGA/DTA technique at multiple heating rates in the air atmosphere. It is observed that the oxidation of V2AlC occurred in two different stages. Thermodynamic calculations are also performed to predict the oxidation reaction pathway of V2AlC MAX phase. The kinetic triplets (activation energy, pre-exponential factor and reaction mechanism) are determined for both stages of oxidation. The Kissinger-Akahira-Sunose (KAS) and the Flynn-Wall-Ozawa (FWO) isoconversional kinetic methods are used to calculate the activation energy. The reaction mechanism is identified by employing the integral master plot method. The results indicated that the nucleation mechanism dominated the oxidation process in the V2AlC MAX phase. P4 and A4 nucleation reaction mechanisms are identified in stage I and stage II of oxidation, respectively.

Effect of Al additions on the microstructures and tensile properties of AlxCoCr3Fe5Ni high entropy alloys

AlxCoCr3Fe5Ni high entropy alloys with varying aluminum contents (x = 0, 0.1, 0.2 and 0.3) were synthesized by induction melting and casting method. The microstructures and tensile properties of the new HEAs were investigated. Different regions of CoCr3Fe5Ni matrix HEA have different microstructures. With the increase of Al content, the microstructure changes from dendrite to lamellar eutectic and dual-phase structure comprising FCC and BCC phases was found in all four samples with different ratios. The volume fraction of BCC phase increased. The ultimate tensile strength (UTS) of the alloy increased, with the highest UTS (1018.9 MPa) achieved at x = 0.3 in this work. On the other hand, increasing Al content further induced distortion of the crystalline lattice and enhanced the alloy strength.

Microstructure of spheroidal graphite aluminum-alloyed cast irons (SGAACI) containing up to 7.5 wt% produced via in-mold process

In the present research work, the effect of various aluminum contents on the microstructure of spheroidal graphite cast irons produced via the in-mold process was investigated. Samples containing 0, 3.7, 5.5, 6.4 and 7.5 wt% aluminum were cast and characterized by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction analysis (XRD) and hardness test. It was observed that by increasing the Al content from 0 to 7.5 wt%, the micro-hardness of pearlite and ferrite phases increases by 228 and 254 Vickers, respectively. Moreover, the addition of aluminum led to an increase in the nodule count from 168 to 668 per mm2, reduction in the nodule diameter from 21.4 to 8.8 µm and also reduction in the sphericity from 65 to 48%. The obtained results revealed that varying aluminum content affects the precipitated pearlite morphology. This seems to be the result of aluminum reaction with carbon and the change in both carbon activity and rate of diffusion and also the aluminum atom behavior in the solid solution of Fe–Al–C alloys.

Highly selective hydrogenation of diesters to ethylene glycol and ethanol on aluminum-promoted CuAl/SiO2 catalysts

A highly selective CuAl/SiO2 catalyst was prepared for the hydrogenation of dimethyl oxalate (DMO) and ethylene carbonate (EC) to ethanol and ethylene glycol (EG), respectively. Aluminum modified silica sol was used to prepare CuAl/SiO2 catalysts by a hydrothermal method. The catalytic performance of the CuAl/SiO2 catalysts with varying aluminum content was investigated at the conditions of 553 K and 2.5 MPa for DMO hydrogenation, while 453 K and 3 MPa for EC hydrogenation. The results showed that the Cu1.0Al/SiO2 catalyst exhibited the highest selectivity of ethanol (∼94 %) in the DMO hydrogenation, while the Cu0.5Al/SiO2 catalyst exhibited the highest selectivity of EG (∼95 %) and methanol (65 %) in the EC hydrogenation. Characterizations (e.g., TPD, TPR and XANES) indicated that the moderate aluminum modification on SiO2 in the form of SiOHAl bond could not only tune the support acidity to polarize the CO bond of esters, but also intrinsically facilitate the dispersion of Cu active species to activate H2, which thus facilitated the selective hydrogenation reaction to EG, ethanol and methanol.

Catalytic cracking of triglycerides over micro/mesoporous zeolitic composites prepared from ZSM-5 precursors with varying aluminum contents

A series of micro/mesoporous nano-ZSM-5/SBA-15 analog composites (ZSC) was prepared from ZSM-5 precursors with variable aluminum contents (Si/Al ratio = 10–50) and their catalytic performance was evaluated in the cracking of waste vegetable oil under the fluid catalytic cracking conditions using a Single-Receiver Short-Contact-Time Microactivity Test unit (SR-SCT-MAT, Grace Davison). It was found that the preparation of the ZSC catalyst by properly tuning the initial aluminum content enables to improve its catalytic performance in terms of selectivity toward light olefins and quality of gasoline. Compared to single materials, i.e. microporous H-ZSM-5 and mesoporous Al-SBA-15, the ZSC catalyst shows the enhanced concentration of C3 and C4 olefins in the gaseous hydrocarbon fraction (ca. 85%) while lowering that of aromatic hydrocarbons in the gasoline fraction (ca. 40%). Furthermore, the reduced aromatic hydrocarbons are offset by the more environment-friendly components for boosting the octane rating of gasoline, i.e. iso-paraffins and iso-olefins. The superior catalytic performance of the ZSC catalyst can be attributed to the bimodal pore system coupled to the medium acid amount, which effectively suppresses hydrogen transfer reactions of primary light olefins while facilitating the cracking and isomerization transformations of hydrocarbon intermediates, leading to the improved formation of C3 and C4 olefins and branched gasoline hydrocarbons.

Microstructure and high temperature mechanical properties of as-cast FeCrAl alloys

The microstructure and high temperature mechanical properties of as-cast FeCrAl alloys with varying aluminum contents were experimentally investigated. Crystal phases were identified using X-ray diffractometry and the solidified structures were analyzed, taking into account the freezing range, AlN precipitation and the aluminum addition. A series of tensile tests were conducted at temperatures from 700 °C to 1200 °C and the effects of aluminum content on the stress-strain behavior including peak stress, yield stress and Young's modulus were investigated. The solid-solution strengthening of aluminum is reflected by the increase of peak stress and yield stress with increasing aluminum content at all temperatures, particularly below 1000 °C. Hot ductility is discussed in terms of the variations of the reduction in area value with temperature. Decreased ductility between 800 °C and 900 °C is attributed to ferritic grain coarsening and the precipitation of carbides within the grain boundaries. The occurrence of continuous dynamic recrystallization under the conditions of this study, can play an important role in grain refinement thus increasing the hot ductility of FeCrAl alloys.

Characteristic of martensite–austenite constituents in coarse grained heat affected zone of HSLA steel with varying Al contents

The fine microstructure of martensite–austenite (M–A) constituents in simulated coarse grained heat affected zone (HAZ) of high strength low alloy steel with varying aluminium content (0·038 and 0·070 wt-%) at 100 kJ cm−1 heat input welding was investigated. The result shows that M–A constituents with 0·038%Al consisted of lath martensite and retained austenite. The retained austenite was distributed along the martensite lath. Whereas, the M–A constituents with 0·070%Al consisted of lath martensite and retained austenite, as well as a small amount of twinned martensite. The amount of retained austenite in M–A constituents with 0·070%Al was becoming higher slightly than that with 0·038%Al. Accordingly, the volume fraction of M–A constituents was reduced with 0·070%Al. Appropriate aluminium addition could decrease not only the area fraction but also the size of M–A constituents, which are beneficial for improving the toughness of HAZ.

Radiative recombination mechanism of carriers in InGaN/AlInGaN multiple quantum wells with varying aluminum content

The structural and optical properties of In0.20Ga0.80N/AlxInyGa1−x−yN multiple quantum wells samples with varying Al content in barrier layers grown on sapphire substrates by metalorganic chemical vapor deposition have been investigated by means of high-resolution X-ray diffraction, Raman scattering measurements and temperature-dependent photoluminescence. Raman measurements verified the existence of In-rich clusters in ternary and quaternary layers. At 10K and 300K, the PL spectrum of each sample is dominated by a sharp emission peak arising from In0.20Ga0.80N well layers. The anomalous temperature-dependent S-shaped behaviors of emission energies have been observed, indicating the presence of localized states induced by the potential fluctuations in the quantum wells due to the inhomogeneous distribution of In-rich clusters. The degree of the localization effect and the transition temperatures between different temperature regions can be enhanced by increasing Al content in barrier layers. The improvement of the localized states emission has been observed at the lower energy side of band gap emission of quantum wells with increasing Al content. The origin of the deep localized states could be attributed to the larger quantum-confined Stark effect in the quantum wells with higher Al content. The recombination mechanism of carriers between band edge and localized states was proposed for interpreting of the emission characteristics.

Low-temperature FTIR Investigation of Aluminum Doped Solar-grade Silicon

Low-temperature FTIR spectroscopy is further developed to be applicable to measure the aluminum concentration in solar-grade silicon in concentrations up to 4 × 1016 atoms/cm3. Absorption spectra of multicrystalline silicon samples doped with varying aluminum content are measured at 10 K and correlated to the dopant density obtained by four point probe resistivity measurements. Calibration factors for absorption peaks of unpaired substitutional aluminum at 443, 472, 516+524 and 867 cm-1 as well as for a Fano anti-resonance at 962 cm-1 are reported.

Microstructural modelling solution for complex Co based alloys and coatings

Microstructural changes following oxidation at high temperatures of a complex coating or alloy can significantly influence its properties. This paper investigates possible solutions that can accurately model alloy microstructures that result from such a process in a cobalt-rich CoNiCrAlReY bond coat alloy system. Four different alloys with varying aluminum content were studied after heat treatments at 1000°C or 1150°C. SEM, EPMA and XRD were used to characterize the alloy microstructure, and hardness testing was performed to determine the role of microstructure on mechanical properties. Experimental microstructures were modeled using two databases of Thermo-Calc, namely TTNI8 and SSOL5. Effects of Al content on phase changes and materials properties were quantitatively investigated. Data showed that a 1 wt. % increase of Al in the alloy caused an 8% increase in the beta phase, and a Cr and Re rich sigma phase precipitated preferentially at high Al concentrations. In addition, alloy hardness was found to increase by 4 and 81%, respectively, with a 10% increase in the beta and sigma phases. Modeled results using the TTNI8 database showed excellent agreement with experimental observations, but the SSOL5 database produced erroneous information.

Cyclic oxidation behavior of β-NiAlDy alloys containing varying aluminum content at 1200 °C

β-NiAlDy cast alloys containing varying aluminum content were prepared by arc-melting. The microstructures and cyclic oxidation behavior of the alloys at 1200°C were investigated. Grain refinement was achieved by increasing aluminum content in the alloy, which is beneficial to selective oxidation. The Ni–55Al–0.1Dy alloy showed excellent cyclic oxidation resistance due to the formation of a continuous, dense and slow-growing oxide scale. In contrast to this, severe internal oxidation as well as large void formation at the scale/alloy interface occurred in the Ni–45Al–0.1Dy alloy. The aluminum content dependence of the reactive element effects in β-NiAlDy was established that Dy doping strengthened the scale/alloy interface by pegging mechanism in high-aluminum alloys but accelerated internal oxidation in low-aluminum alloys during high-temperature exposure.

AlGaInAs quantum dot solar cells: tailoring quantum dots for intermediate band formation

We report on the realization of quantum dot (QD) solar cells comprising a spectrally large absorption range. The QD absorption band is designed by integrating quaternary AlGaInAs QDs with varying aluminum contents in combination with conventional InAs/GaAs QDs in the intrinsic region of an AlGaAs p-i-n structure. By adjusting the material composition in the different QD layers, we can cover a spectral range from 680 to 1150 nm by QD absorption. Based on our results we discuss a newly proposed solar cell design employable to facilitate intermediate band absorption for an increased efficiency.

Continuous multi cycle nanoindentation studies on compositionally graded Ti1−xAlxN multilayer thin films

Abstract Two types of Compositionally Graded Multilayer (CGM) films of Ti 1− x Al x N consisting of 21 layers were synthesized by reactive magnetron co-sputtering technique. The first one begins with a layer of Ti 0.4 Al 0.6 N from substrate and ends with TiN, whereas exactly a reverse order has been followed in the second one. As deposited CGM films are poly-crystalline with rocksalt structure similar to stoichiometric TiN. Secondary Ion Mass Spectrometry (SIMS) depth profile of the films showed the presence of 21 layers of equal thickness (50 nm) with varying aluminum content in steps. Continuous Multi Cycle (CMC) nanoindentation technique was used to analyze the failure modes of these films. Topographic examination of the indented zone revealed the presence of edge cracks inside and outside the indentation area when the load exceeds beyond 90 mN. The load–displacement profiles of CMC and single indentations exhibited the onset of pop-ins at a depth of ∼200 nm.

Electrochemical Synthesis of Zn−Al Layered Double Hydroxide (LDH) Films

A new electrodeposition condition to produce Zn-Al LDH films was developed using nitrate solutions containing Zn (2+) and Al (3+) ions. Deposition was achieved by reducing nitrate ions to generate hydroxide ions on the working electrode. This elevates the local pH on the working electrode, resulting in precipitation of Zn-Al LDH films. The effect of deposition potential, pH of the plating solution, and the Zn (2+) to Al (3+) ratio in the plating solution on the purity and crystallinity of the LDH films deposited was systematically studied using X-ray diffraction and energy dispersive spectroscopy (EDS). The optimum deposition potential to deposit pure and well-ordered Zn-Al LDH films was E = -1.65V versus a Ag/AgCl in 4 M KCl reference electrode at room temperature using a solution containing 12.5 mM Zn(NO 3) 2.6H 2O and 7.5 mM Al(NO 3) 3.9H 2O with pH adjusted to 3.8. The resulting film contained 39 atomic %Al (3+) ions replacing Zn (2+) ions, leading to a composition of Zn 0.61Al 0.39(OH) 2(NO 3) 0.39. xH 2O. Increasing or decreasing the aluminum concentration in the plating solution resulted in the formation of aluminum- or zinc-containing impurities, respectively, instead of varying aluminum content incorporated into the LDH phase. Choosing an optimum deposition potential was important to obtain LDH as a pure phase in the film. When the potential more negative than the optimum potential is used, zinc metal or zinc hydroxide was deposited as a side product, whereas making the potential less negative than the optimum potential resulted in the formation of zinc oxide as the major phase. The pH condition of the plating solution was also critical, as increasing pH destabilizes the formation of the LDH phase while decreasing pH promoted deposition of other impurities.

Bound-to-bound and bound-to-free transitions in surface photovoltage spectra: Determination of the band offsets forInxGa1−xAsandInxGa1−xAs1−yNyquantum wells

We present an extensive study leading to a general understanding about the optical transitions involved in the surface photovoltage (SPV) spectra of type-I quantum well (QW) structures. SPV measurements were carried out on ${\mathrm{In}}_{0.3}{\mathrm{Ga}}_{0.7}\mathrm{As}∕\mathrm{GaAs}$ QW samples with varying QW width and on ${\mathrm{In}}_{0.15}{\mathrm{GaAs}}_{0.85}∕{\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{As}$ QW samples with varying aluminum content. The results are compared with experimental electroreflectance spectra, absorption spectra simulated with multiband $\mathbf{k}∙\mathbf{p}$ computations, and theoretical calculations of the electronic states in the QWs. Thus, the transitions which induce steps in the SPV spectra are unambiguously identified. Most remarkably, the bound electron-to-free hole transition is detected by SPV measurements. This distinguishes the SPV method from many other optical techniques like photoluminescence and photoreflectance spectroscopy that allow only the observation of bound-to-bound and free-to-free transitions. The analogous free electron-to-bound hole transition does not give rise to a feature in the SPV spectra. In addition, the bound-to-bound transitions ${e}_{1}\text{\ensuremath{-}}h{h}_{1}$, ${e}_{1}\text{\ensuremath{-}}l{h}_{1}$, and ${e}_{2}\text{\ensuremath{-}}h{h}_{2}$ are observed, if the respective states are confined. Also, the free-to-free transition $ce\text{\ensuremath{-}}ch$ is measured. We demonstrate how these transitions can typically be identified in the spectra without any further measurements or calculations. With this knowledge, the practical band offsets of the QW structure, i.e., the energy difference between the lowest confined states in the QW and the extended states in the barrier, can be extracted directly from the spectra. An advantage over conventional techniques for the determination of band offsets is that neither any additional knowledge of other QW parameters nor simulations are necessary. As an example for the application of the SPV technique, the electronic states and band offsets of a series of ${\mathrm{In}}_{0.3}{\mathrm{Ga}}_{0.7}{\mathrm{As}}_{0.98}{\mathrm{N}}_{0.02}∕\mathrm{GaAs}$ QWs with varying QW width are characterized. These experiments directly show that nitrogen affects only the conduction band states.

The kinetics and mechanism of cathodic oxygen reduction on zinc and zinc–aluminium alloy galvanized coatings

A rotating disk electrode technique is used to investigate the kinetics and mechanism of O 2 reduction as it occurs at the surface of various hot-dip Al–Zn alloy coatings (on steel) immersed in weakly alkaline (pH 9.6) aqueous sodium chloride. The zinc component of coatings behaves electrochemically as though it were free zinc and the O 2 reduction pathway is determined by the potential dependent state of zinc. A 2e − reduction to H 2O 2 predominates at potentials near the free corrosion potential, where zinc is (hydr)oxide covered. A 4e − reduction to OH − predominates at potentials where zinc is bare. Tafel slopes (∂ E/∂log i) of 0.058 V dec −1 and 0.132 V dec −1 are determined for 2e − and 4e − O 2 reduction on pure zinc, respectively. Aluminium is virtually inert and varying aluminium content between 0.1% and 55% exerts little influence on O 2 reduction kinetics. However, all the Zn–Al alloy surfaces give very much higher O 2 reduction currents at low polarization than does pure zinc and it is proposed that this arises through an electrocatalysis of 2e − O 2 reduction by traces of substrate derived iron.