Alon Research Articles

Preparation of transparent AlON from powders synthesized by novel CRN method

Aluminum oxynitride (AlON) powders were synthesized by a novel carbothermal reduction and nitridation (CRN) method. Homogenous and fluffy AlOOH/C core-shell nanoparticle precursor was hydrothermally synthesized with aluminum nitrate hydrate, sucrose and urea as starting materials. Then single-phase AlON powders were synthesized by CRN method at 1700 °C for 2 h. The phase transition and growth of Al2O3 particles was effectively retarded by the amorphous carbon nano-layers on the surface of precursor, resulting in significantly lower reaction temperature and further smaller particle size. Based on above fine AlON raw material, transparent AlON ceramic was prepared by pressureless sintering at 1880 ℃ with the in-line transmittance above 80 %.

Optical properties of powder and ceramics of aluminium oxynitride obtained by self-propagating high-temperature synthesis

The synthesis method of aluminium oxynitride (AlON) powders by nitriding of Al/Al2O3 mixture under highpressure nitrogen is proposed. The novelty of this method consists in adding KClO4 or Mg(ClO4)2 and extra Al into the starting mixture (Al+Al2O3) to cause the exothermal aluminium oxidation reaction, which therefore initiates the aluminium nitriding reaction. The microstructure and phase composition of the AlON powders obtained by self-propagating high-temperature synthesis are demonstrated by means of SEM and XRD analysis. Diffuse reflection spectra of AlON powders have been measured and the values of band-gap energy have been calculated. Optical transmission and reflection characteristics of the AlON ceramic samples sintered from AlON powders at 1930°C have been studied. The influence of the technological parameters of ceramics production on their transparency is revealed – the most transparent sample is obtained from the powders synthesized with the Mg(ClO4)2 additive and sintered for 6 h.

High-Quality-Factor AlON Transparent Ceramics for 5 GHz Wi-Fi Aesthetically Decorative Antennas.

Transparent material has been widely used in product design and has seen a large increase in its use. In this paper, a kind of aesthetically decorative 5 GHz Wi-Fi dielectric resonator antenna (DRA) of aluminum oxynitride (AlON) transparent ceramic has been designed. High-quality-factor AlON transparent dielectric ceramics were fabricated by presintering at 1780 °C and further cold isostatic pressing (CIP) under a 200 MPa argon atmosphere. For a 9.0 mm thick specimen, the in-line light transmittance reached 83%. Optimum dielectric constant (εr = 9.32), quality factor (Qf = 47 960) and temperature coefficient (TCF = -51.7 ppm/°C) was achieved in the AlON transparent ceramic by cold isostatic pressing. As a result, the proposed aesthetically decorative DRA can achieve an impedance bandwidth of 32% (4.48-6.19 GHz), a high radiation efficiency of 85%, and a low cross-polarization discrimination (XPD) of -30 dB. To achieve a broad bandwidth, the proposed antenna was excited in its dominant TE111x mode and higher-order TE113x mode. The proposed antenna is thus an excellent candidate for an indoor decoration Wi-Fi antenna.

Study of interface trap density of AlOxNy/GaN MOS structures

GaN metal–oxide–semiconductor structures were fabricated by atomic layer deposition of aluminum oxynitride thin films on bulk GaN substrates with c-, a-, and m-plane surfaces. Capacitance–voltage measurements ranging from 5 kHz to 1 MHz were conducted at room temperature. The interface trap number density (Nit) and interface trap level density (Dit) of the devices were extracted. A Nit of less than 2 × 1011 cm−2 and a Dit of less than 2 × 1011 cm−2 eV−1 were obtained on the a-plane and m-plane samples. Nit and Dit values were larger for c-plane samples, with the largest interface trap density observed on the c-plane sample with the highest dislocation density. The different Nit and Dit values can be attributed to different dislocation densities and dangling bond densities among different samples.

Aluminum Nitride to Silicon Direct Bonding for an Alternative Silicon-On-Insulator Platform.

The next generation of microelectromechanical systems (MEMS) requires new materials and platforms that can exploit the intrinsic properties of advanced materials and structures, such as materials with high thermal conductivity, broad optical transmission spectra, piezoelectric properties, and miniaturization potential. Therefore, we need to look beyond standard SiO2-based silicon-on-insulator (SOI) structures to realize ubiquitous MEMS. This work proposes using AlN as an alternative SOI structure due to several inherent material property advantages as well as functional advantages. This work presents the results of reactively sputtered AlN films on a Si handle wafer bonded with a mirror-polished Si device wafer. Wafer bonding was achieved by using hydrophilic wafer bonding processes, which was realized by appropriate polymerization of the prebonding surfaces. Plasma activation of the AlN surface included O2, Ar, SF6, SF6 + Ar, and/or SF6 + O2, which resulted in a change in the chemical and topography state of the surface. Changes in the AlN surface properties included enhanced hydrophilicity, reduced surface roughness, and low nanotopography, components essential for successful hydrophilic direct wafer bonding. Wafer bonding experiments were carried out using promising surface activation methods. The results showed a multilayered bonding interface of Si(Device)/SiO2/ALON/AlN/Si(Handle) with fluorine in the aluminum oxynitride layer from the proceeding AlN surface activation process. More notably, this work provided wafer bonding tensile strength results of the AlN alternative SOI structure that compares with the traditional SiO2 SOI counterpart, making AlN to Si direct bonding an attractive alternative SOI platform.

Synthesis and luminescence properties of Eu2+/Ce3+, Ce3+/Tb3+ and Eu2+/Tb3+ co-doped AlONs

Series of Eu2+/Ce3+, Ce3+/Tb3+ and Eu2+/Tb3+ co-doped aluminum oxynitrides Al5O6N were prepared using the standard sol-gel technique with following annealing in the flow of N2. In all the samples Al5O6N is a major phase, just traces of α-Al2O3 and AlN were found for some particular samples with high loading of rare-earth ions. According to pulsed cathodoluminescence and photoluminescence data a non-radiative energy transfer occurs from Ce3+ to Eu2+, from Ce3+ to Tb3+ and from Eu2+ to Tb3+. Also, it was shown that for Eu2+/Ce3+ co-doped Al5O6N the optimal contents of both REE ions are different compared to those for single doped Al5O6N (0.25 at% of Eu2+ and 0.04 at% of Ce3+). In case of Al5O6N:0.4%Tb3+,yCe3+ (y = 0.01…0.08%) the PCL and PL intensities increase in the whole range of Ce3+ content. Finally, for Al5O6N:0.4%Tb3+,yEu2+ (y = 0.1…0.8%) no pronounced dependence of luminescence caused by Tb3+ ions on the Eu2+ content is observed. Concentration quenching of Eu2+ caused luminescence is given at Eu2+ content above 0.3%. The chromaticity coordinates of prepared co-doped AlONs were calculated and three samples were found to give close to white emission.

Combustion Synthesis of Aluminum Oxynitride in Loose Powder Beds.

This paper describes combusting loose powder beds of mixtures of aluminum metal powders and aluminum oxide powders with various grain sizes under various nitrogen pressure. The synthesis conditions required at least 20/80 weight ratio of aluminum metal powder to alumina powder in the mix to reach approximately 80 wt% of γ-AlON in the products. Finely ground fused white alumina with a mean grain size of 5 μm was sufficient to achieve results similar to very fine alumina with 0.3 μm grains. A lower nitrogen pressure of 1 MPa provided good results, allowing a less robust apparatus to be used. The salt-assisted combustion synthesis upon addition of 10 wt% of ammonium nitrite resulted in a slight increase in product yield and allowed lower aluminum metal powder content in mixes to be ignited. Increasing the charge mass five times resulted in a very similar γ-AlON yield, providing a promising technology for scaling up. Synthesis in loose powder beds could be utilized for effective production of relatively cheap and uniform AlON powder, which could be easily prepared for forming and sintering without intensive grounding and milling, which usually introduce serious contamination.

Chemically activated combustion synthesis of AlON under high nitrogen pressure

This work explores the synthesis of aluminum oxynitride (AlON) by combustion of Al/Al2O3 mixtures under a high-pressure nitrogen atmosphere. The effect of nitrogen pressure and addition of Mg(ClO4)2 and excess Al on the exothermicity of the mixture, kinetics of the combustion process, and phase composition of combustion products is studied. In particular, we reveal the dependence of the AlON lattice parameter on nitrogen pressure (and, correspondingly, nitrogen content in the combustion products). Finally, we demonstrate the possibility of the fabrication of transparent Y2O3-doped AlON ceramics from the combustion products.

Rapid synthesis of AlON powders by nitriding combustion synthesis precursor

Polycrystalline aluminum oxynitride (AlON) powders have been prepared by the carbothermal reduction nitridation of amorphous precursor obtained by solution combustion synthesis (SCS). Firstly, a mixed precursor of amorphous transition alumina and incompletely combusted organic matter has been combustion synthesized of a mixed solution of aluminum nitrate, urea and glucose. Then the pure phase AlON powders with D50 = 0.846 μm can be prepared by calcining the SCS precursor at 1700 °C for only 10 min. The influences of different urea/aluminum nitrate nonahydrate ratio, calcining temperature and holding time on the properties of products have been discussed in detail. The research can provide a valuable reference for the efficient synthesis of AlON powders.

Structure of Aluminum Oxynitride Powders Produced by Plasma-Chemical Synthesis

Structure of Aluminum Oxynitride Powders Produced by Plasma-Chemical Synthesis

Efficient vortex beam generation using gradient refractive-index microphase plates.

Vortex beams were theoretically demonstrated by patterning a fiber facet with $N$-segment microphase plates. By changing the aluminum oxynitride material composition of each segment, gradient refractive-index phase plates (GRPs) were designed and introduced a ${{2}}\pi l$ azimuthal optical phase difference. The gradient index profile was able to convert a fiber Gaussian mode to a Laguerre-Gaussian mode with varieties of topological charge $l$. A three-dimensional finite-difference time-domain method was applied to calculate the near-field optical phase maps and the far-field beam profiles projected from the micro-GRPs. A uniform vortex beam with a symmetrical doughnut shape was obtained by optimizing the GRPs' radii and the number of segments. The micro-GRPs enabled flat optical components for efficient vortex beam generation.

Calculation of Transparent Armor Resistance to a High-Speed Impact by a Spherical Projectile

Using the computer-based simulation method within the scope of continuous mechanics, impact interaction with a speed of 3000 m/s between a steel ball and a transparent armor target is calculated (the target has three layers). The face layer of the transparent armor is made of aluminum oxynitride; the middle layer, of hardened glass; and the lower layer, of polycarbonate. The influence of the angle of the projectile approach to the target and thickness of the hardened glass layer on the process of target penetration is studied.

The Post-treatments of Aluminum Oxynitride(AlON) Powders Synthesized by the Carbothermal Reduction and Nitriding Process

The Post-treatments of Aluminum Oxynitride(AlON) Powders Synthesized by the Carbothermal Reduction and Nitriding Process

Синтез прекерамического прекурсора на основе органических солей алюминия для стереолитографической 3D-печати корундовой керамики

Various options for the synthesis of aluminum acrylates, including substituted hydroxoacrylates, as well as an adduct of aluminum isopropylate with allylamine, have been tested in order to develop a mixture that can be formed by photopolymerization, followed by annealing while maintaining the shape of the ceramics, meaning further molding using stereolithographic 3D printing. By photopolymerization of a polymer precursor based on an acrylate suspension of in situ synthesized alumoxane of the Al(OH)2(ООСН2СН=СН2), corundum ceramics of a given shape were prepared. The inhomogeneity of the polymer precursor is not an obstacle to its use in technology. A significant percentage of weight loss during heat treatment of a polymer precursor suggests its possible use as a binder when filled with dispersed aluminum oxide powder. The strongest shrinkage of a ceramic product occurs in the range of 200 – 400 °C; it is necessary to develop a special program for heating the product to the sintering temperature in order to minimize the consequences of severe shrinkage. When a molded product is heat treated in an inert atmosphere, the shrinkage is less than when annealed in air, since a large amount of amorphous carbon remains during pyrolysis. Annealing such ceramics with amorphous carbon in a nitrogen atmosphere is promising for carrying out the carbonitridization process in the preparation of aluminum nitride and oxynitride.

Design of electrotunable all-weather smart windows

Smart windows, capable of selective filtering of solar spectral radiation can help to significantly reduce the energy consumption by heating and cooling systems. However, robust and industry-standard designs of such windows, tunable for all-weather conditions, have been a challenge to date. In this work, we report on the design of ultra-thin electrotunable smart window ‘glasses’ using noble metals as well as their relatively-inexpensive alternatives. We adopt a lithography-free design approach using multilayer metallo-dielectric structure, that can dynamically control the intensity of transmitted solar radiation, depending upon the weather/climate condition. We make use of an electro-optic polymer as dielectric, which on applying voltage, changes the effective refractive index by virtue of electro-optic effect, allowing tunable filtering of visible and infrared radiation over a voltage range of −15 V to +15 V. Our theoretical results are in excellent agreement with those of full-wave simulations. Our design is robust, ultra-thin (60–100 nm thick), large-area compatible, polarization-independent, and angle-insensitive (up to 75 degrees). Aluminium oxynitride based glasses are suitable for designing military-grade, bulletproof, portable, and blast-resistant windows. The figure-of-merit calculations reveal that our relatively-inexpensive metals can outperform industry-standard commercial glasses as well as infrared-blocking plasmonic glasses, reported in the literature.

Fabry–Perot resonance assisted dual-layer coating with enhanced wavelength-selective refection and emission for daytime radiative cooling

Radiative cooling has significant potential for application in the cooling of buildings, thermoelectric and photovoltaic owing to its no energy consumption and emission of harmful gases. In this paper, a daytime radiative cooling emitter (DRCE) consists of a dual-layer coating made of aluminum oxynitride (ALON) and silicon dioxide (SiO2) on an aluminum (Al) substrate is proposed to achieve daytime radiative cooling. The thicknesses of the ALON and SiO2 are respectively optimized to 10.23 and 7.40 μ m by variable metric method and genetic algorithm, and the transfer matrix method is used to calculate the radiative properties of the optimized DRCE. At a temperature of 30°C, the optimized DRCE achieves a high average total hemispherical emissivity (about 70%) in the wavelength band of atmospheric window, owing to the combining of the emissivities of the ALON and SiO2 in this wavelength band and the help of the Fabry–Perot (F–P) resonance. Owing to the high spectral directional transmissivity of only the dual-layer coating and high spectral directional reflectivity of bulk Al in the wavelength band of solar radiation, a high average total hemispherical reflectivity (about 98%) can be achieved in the wavelength band of solar radiation. When the power of solar radiation is about 900 W/m2, the cooling power of the optimized DRCE is about 110 W/m2 at the ambient air temperature (Tamb=30°C), and the steady-state temperature of the optimized DRCE can be about 7°C lower than the ambient air temperature. This study shows that by selecting suitable materials and utilizing the F–P resonance, even a simple dual-layer structure can achieve high-performance daytime radiative cooling. Furthermore, it is also demonstrated that ALON may be a good candidate material for the DRCE, providing more material choices for improving its performance.

Oxidation behavior and mechanism of aluminum oxynitride (AlON) at elevated temperatures

AbstractThe oxidation behavior and mechanism of aluminum oxynitride (AlON) powder exposed to air at elevated temperatures between 800°C and 1300°C was investigated by X‐ray diffractometry (XRD), scanning electron microscope (SEM), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and simultaneous thermogravimetry, differential thermal analysis, and mass spectrometry techniques (TG‐DTA‐MS). The weight of AlON gradually increases to a maximum value at 1150°C and then decreases with further heating. Meanwhile, AlON powder undergoes chemical changes, as evidenced by lattice expansion, and turns eventually into alumina. ESR spectra reveal the occurrence of lone pair electrons in the oxidized products and the intensity of corresponding resonance signal increases before disappearing with the increase in temperature. Combined with the results of NMR and TG‐DTA‐MS, the measured data suggest that Al‐N in [AlO3N] tetrahedron and [AlO5N] octahedron are gradually oxidized into Al‐O‐N group with lone pair electrons, which causes continuous weight gain and lattice expansion. Further oxidation at higher temperatures results in alumina and N2.

Improved Understanding of Atomic Ordering in Y4SixAl2–xO9–xNx Materials Using a Combined Solid-State NMR and Computational Approach

Ceramics based around silicon aluminum oxynitrides are of both fundamental structural chemistry and technological interest. Certain oxynitride crystal structures allow very significant compositional variation through extensive Si/N exchange for Al/O, which implies a degree of atomic ordering. In this study, solid-state 29Si MAS NMR and variable field 1D and 2D 27Al MAS NMR measurements are combined with density functional theory calculations of both the structural and NMR interaction parameters for various points across the Y4Si2O7N2-Y4Al2O9 compositional range. This series provides numerous possibilities for significant variation of atomic ordering in the local ditetrahedral (Si,Al)2O7-xNx units. The two slightly structurally inequivalent aluminum sites in Y4Al2O9 are unambiguously assigned to the observed resonances. Computational findings on Y4Si2O7N2 demonstrate that the single observed 29Si NMR resonance covers a range of local inequivalent silicon environments. For the first time, the MAS NMR and neutron diffraction data from the Y4SiAlO8N structure have been directly reconciled, thus establishing aspects of atomic order and disorder that characterize this system. This comparison suggests that, although the diffraction data indicates long-range structural order supporting a highly crystalline character, the short-range information afforded by the solid-state NMR measurements indicates significant atomic disorder throughout the (Si,Al)2O7-xNx units.

Preparation of aluminum oxy-nitride (AlON) through investigating the rheological behavior and gel-casting parameters of alumina/aluminum nitride

In this research, the mixture of alumina powders and nanoparticle of aluminum nitride was used with the alumina stoichiometric ratio in order to characterize the gel casting parameters. The milling method and three-dimensional mixer were used for agglomeration and slurry, respectively. The surface of the powders was modified by phosphoric acid to prevent the hydrolysis of aluminum nitride in water. The results of analysis such as the pH test, FT-IR, XRD and FE-SEM reveal that the effect of phosphoric acid was activated after 17 h. The characterization of rheological properties was performed by the optimization of slurry parameters with a rotary viscometer. Dolapic CE-64 was used as a dispersant to disperse slurry. Acrylamide and methacrylamide, methylene bisacrylamide, ammonium sulfate and tetraethyl ethylene di-amine were used as the monomer, transverse coupler, initiators, and catalysts, respectively. In order to determine the optimal density of samples and achieve the aluminum oxy-nitride phase (AlON), the sintering of the samples was carried out by the sintering method without pressure. The highest relative density of the crude body (55%) and sintered body (96%) was obtained for a sample containing 75% by weight of solids and 5% by weight of monomer with a ratio of 3:1. The differential thermal analysis of the crude body shows that the existing monomers were removed from the body at a temperature of 250–450 °C. The porosity test showed that the appropriate time for the de-agglomeration of the slurry is 5 h.

Low temperature and pressureless synthesis of MgAlON: qualitative analysis and formation evolution

Abstract By calculating the Gibbs free energy of a magnesium aluminium oxynitride (MgAlON) system, pure MgAlON was obtained by pressureless sintering at 1 570 °C in a nitrogen atmosphere using Al, Al2O3, and MgO as raw materials. The formation mechanism of MgAlON and phase evolution of the Al-Al2O3-MgO-N2 system were investigated. The aluminium was melted at approximately 660 °C and formed AlN in the range 740- 1 250 °C. The reaction of AlN, Al2O3, and MgO started to form a primary crystalline MgAlON phase at 950 °C, and as the temperature increased, the minerals continuously dissolved in the primary crystalline phase.