Stoichiometric Aluminum Nitride Research Articles

Synthesis and characterization of nanoparticles of wurtzite aluminum nitride from various nut shells

Nanoparticles of Aluminum Nitride (AlN) were synthesized from a thermal treatment of mixtures of aluminum oxide (Al2O3) and either shells of almond, cashew, coconuts, pistachio, or walnuts in a nitrogen atmosphere at temperatures in excess of 1450 °C. By selecting the appropriate ratios of each nutshell powder to Al2O3, it is demonstrated that stoichiometric aluminum nitride is produced via carbo-thermal reduction in nitrogen atmosphere. In addition, results show the formation of Al from Al2O3 before transformation to AlN. On the other hand, when Al was mixed with nutshell powder first, mixed phases of AlN and Al4C3 were formed before complete transformation to AlN. X-ray diffraction analysis, Raman scattering and Fourier Transform Infrared spectroscopy confirmed the wurtzite phase of aluminum nitride. Transmission electron microscopy indicated the formation of AlN nanoparticles. The formation of AlN from nutshells offers a simple route and avoids multiple-step processes involving carbon rich agents at elevated temperatures.

Nanoparticles of wurtzite aluminum nitride from the nut shells

Nanoparticles of aluminum nitride were produced from a thermal treatment of a mixture of aluminum oxide (Al2O3) and shells of almond, cashew, coconuts, pistachio, and walnuts in a nitrogen atmosphere at temperatures in excess of 1450 °C. By selecting the appropriate ratios of each nut powder to Al2O3, it is shown that stoichiometric aluminum nitride can be produced by carbo-thermal reduction in nitrogen atmosphere. Using x-ray diffraction analysis, Raman scattering and Fourier Transform Infrared spectroscopy, it is demonstrated that aluminum nitride consists of pure wurtzite phase. Transmission electron microscopy showed the formation of nanoparticles and in some cases nanotubes of AlN.

Low-temperature growth of stoichiometric aluminum nitride films prepared by magnetic-filtered cathodic arc ion plating

AlN films were prepared on Si(100) and quartz glass substrates with high deposition rate of 30 nm·min−1 at the temperature of below 85 °C by the magnetic-filtered cathodic arc ion plating (FCAIP) method. The as-deposited AlN films show very smooth surface and almost no macrodroplets. The films are in amorphous state, and the formation of AlN is confirmed by N1s and Al2p X-ray photoelectron spectroscopy (XPS). The XPS depth profile analysis shows that oxygen is mainly absorbed on the AlN surface. The AlN film has Al and N concentrations close to the stoichiometric ratio with a small amount of Al2O3. The prepared AlN films are highly transparent over the wavelength range of 210–990 nm. The optical transmission spectrum reveals the bandgap of 6.1 eV. The present technique provides a good approach to prepare large-scale AlN films with controlled structure and good optical properties at low temperature.

AlN thin film growth using electron cyclotron resonance reactive sputtering

In this report, we investigated conditions to deposit stoichiometric aluminium nitride (AlN) thin films grown on (100)-oriented Si substrates under various Ar/N2 gas flow rates at a wide range of temperature from room temperature (RT) to 350°C using electron cyclotron resonance (ECR) reactive sputtering. This study revealed that stoichiometric of thin film can be controlled by N2/Ar flow rate and that stoichiometric N/Al = 1 was archived at N2/Ar = 2. This study also revealed that crystallinity can be controlled by substrate temperature. From RT to 200°C, thin films were amorphous or poly-crystal, at 350°C however, thin film was mainly [110] and [100] AlN. Obtained thin films are densely packed and have very low root mean square (RMS) roughness of 0.41 nm which is much less than other sputtering methods.

Wear and corrosion performance of two different tempers (T6 and T73) of AA7075 aluminium alloy after nitrogen implantation

The present work reports the improvements in corrosion resistance and tribological properties achieved after Nitrogen ion implantation into aluminium alloy AA7075 subjected to two different tempers, T6 and T73.Nitrogen implantation at a nominal dose of 2×1017ions/cm2 and at an accelerating voltage of 50keV produced an increase of the surface hardness of the alloys up to a 130% in T6 samples and to 190% in T73 samples.The increase in hardness has a very positive effect on wear resistance as indicate the significant reduction of specific wear rate on both tempers (about −75% for T6 and −90% for T73 samples).Similarly, an improvement in corrosion properties of both tempers is confirmed by DC techniques, showing a decrease of the registered current density on potentiodynamic curves, and by the increase of impedance shown by AC techniques.This overall improvement in the alloy performance has been mainly attributed to the formation of a stoichiometric aluminium nitride layer (AlN), identified by XPS and GIXRD.The combination of EXCO immersion tests and electrochemical measurements allowed explaining the effect of AlN layer, which behave as a barrier delaying the onset of corrosion and slowing its progress. However, the implantation do not modified the corrosion morphology which seems to be determined mainly by the heat treating conditions. Thereby, in both tempers the localized attack starts at the intermetallic/matrix interface, but in T6 type specimens the progress of corrosion is clearly intergranular, while T73 specimens show the formation of clusters of small geometrical pits, probably related to the biggest MgZn2 strengthening precipitates.

Defining the surface binding energy in dynamic Monte Carlo simulation for reactive sputtering of compounds

In Monte Carlo simulations of reactive sputtering, it is commonly assumed that the surface binding energy (SBE) for the different phases in the target exhibits a linear behaviour in the transition between the metal mode and the compound mode. In this work we study how the transition between the two modes takes place, and more specifically attempt to experimentally identify how the SBE for the different phases behaves in the transition between the two modes. In essence, this is done by comparing XPS measurements of the aluminium 2p binding energy on samples comprising pure aluminium, stoichiometric aluminium nitride and aluminium oxide with the corresponding measurements on understoichiometric aluminium nitride samples. In this work, it is assumed that the binding energy of the core level is directly correlated to the SBE of the phase in question. That is to say, if the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration, the SBE for the compound exhibits a constant and discrete value independent of the surface concentration of nitrogen. It was found by the XPS measurement that the aluminium 2p binding energy in aluminium nitride exhibits a constant and discrete value independent of the nitrogen concentration in the samples and it was, therefore, concluded that the SBE for the different phases exhibits constant and discrete values independent of the surface concentration of nitrogen. The discrete behaviour of the SBE was implemented in the TRIDYN program and the results from these simulations were compared with simulations in which it is assumed that the SBE of the different phases exhibits a linear behaviour in the transition between the metal mode and the compound mode.

Structural, optical and mechanical properties of aluminium nitride films prepared by reactive DC magnetron sputtering

Aluminium nitride (AlN) is a wide band gap III–V semiconductor material which is often used for optical applications. We have deposited aluminium nitride films by reactive DC magnetron sputtering in an Ar–N 2 atmosphere on Si (100) and glass substrates. The total pressure was kept constant at 0.8 Pa. For thin film preparation the N 2 flow was varied from 0 to 8 sccm, while the Ar flow has been adjusted to maintain a constant total pressure. The corresponding films have been characterized by a variety of techniques including Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), X-ray reflectometry (XRR), optical spectroscopy, spectroscopic ellipsometry and wafer curvature measurements to determine the deposition stress in the films. The stoichiometry of the films has been determined by RBS, which shows that stoichiometric AlN can be prepared for N 2 flows above 4.75 sccm. The structure of the films has been determined by XRD, which shows that crystalline aluminium nitride can be formed above 4.75 sccm N 2. XRR was used to determine the thickness, density and surface roughness of the films. The sputter rate decreases upon increasing N 2 flow, while at the same time the density of the films increases from 2.7 g/cm 3 for metallic films to 3.1 g/cm 3 for the stoichiometric and transparent films. Optical spectroscopy and spectroscopic ellipsometry measurements determine that the stoichiometric AlN films prepared above 4.75 sccm possess a refractive index of n ≈ 1.9 at 533 nm (2.3 eV). Wafer curvature measurements reveal that stoichiometric AlN films are characterized by high tensile stresses.

Argon ion beam voltage in a dual ion beam sputtering system influence on the aluminum nitride films microstructure

The aluminum nitride (AlN) film has been successfully prepared at argon ion beam voltages ranging from 600 to 1200 V in the dual ion beam sputtering system. The AlN film had the (0 0 2) preferred orientation at 800 V and then changed to AlN (1 0 0) above 1000 V. Moreover, the nano-grain size presented in AlN film was observed using TEM. The Al-2p 3/2 and N-1s spectra were, respectively, centered at 74.2±0.2 eV and 397.4±0.2 eV at all voltages, which indicated the formation of Al–N bond. Furthermore, the Al concentration decreased monotonically with argon ion beam voltages. The stoichiometric AlN films can be synthesized around 960 V in the present study. The microstructure changes associated with argon ion beam voltages are also discussed.

Improving the corrosion protection of aluminium alloys using reactive magnetron sputtering

Most high strength aluminium alloys used in the aircraft industries are susceptible to corrosion. Up to now hexavalent chromium is the conventional corrosion inhibitor. Because chromium in hexavalent state is carcinogenic, it is necessary to develop effective alternative inhibitor systems. We investigated magnetron sputtered substoichiometric and stoichiometric aluminium nitride (AlN x with x ⩽ 1) coatings for corrosion protection of aluminium alloys 2024-T3, 6061-T4 and 7075-T6. The corrosion behaviour of the treated surfaces was tested by anodic polarization scanning and salt spray testing. From the polarization curves it can be concluded that magnetron sputter coating with AlN x leads to a higher pitting potential of the three aluminium alloys investigated. The salt spray tested samples also confirm the protective effect of the coatings. In addition we found that AlN x layers with high nitrogen content lead to a stronger shifting in pitting potential than those with low nitrogen content. Anyway, the results of the salt spray testing show that particularly nitrogen-rich AlN x layers are less stable towards NaCl electrolyte.

Electrochemical Behaviour of AIN Films Prepared by Reactive Cathodic Sputtering

Aluminium nitride films were deposited on glass and steel substrates, by reactive sputtering. Because stoichiometric aluminium nitride film deposited on glass substrates presents the highest electrochemical corrosion resistance, such a stoichiometric film was deposited on reactive substrates (steels). The porosity of the samples was determined using an electrochemical method, and corrosion tests were carried out in different solutions, using classic electrochemical techniques with direct and alternating currents. The porosity of aluminium nitride on metallic substrates was found to be inferior to 0.018 / 100. Despite the low thickness of the films (∼ 1 μm), an effective improvement of the corrosion resistance of stainless and mild steels was established, in H 2 SO 4 and NaCl solutions.

A study of the physical properties and electrochemical behaviour of aluminium nitride films

Thin films of aluminium nitride (AlN) were deposited onto glass substrates by reactive sputtering. Various N 2 partial pressures were used to produce films the composition of which ranged from pure aluminium to stoichiometric aluminium nitride. X-ray diffractometry, electrical resistance measurements and electrochemical tests were carried out to characterize these films. The XRD patterns show that the films are stoichiometric (N/Al=1) for a nitrogen partial pressure PN 2=1.33 × 10 −2 Pa. From XRD patterns and electrical resistance values of the films, we have demonstrated that for under-stoichiometric films PN 2 <1.33 × 10 −2 Pa, N/Al<1)), the structure goes through an intermediary state where both metallic (Al) and ceramic (AlN) phases take place. The electrochemical behaviour of the films was studied in H 2SO 4 and HCl solutions using classical electrochemical techniques as impedance diagrams and polarization curves. The results allow the proposition of a model for the under-stoichiometric films, which describes a contact between the metallic phase of Al and ceramic phases of AlN. When N 2 partial pressure is increased, the corrosion resistance of the films is also increased. The stoichiometric AlN films PN 2 = 1.33 × 10 −2 Pa)) show a corrosion resistance superior by several orders of magnitude to those of the under stoichiometric ones.

Ion bombardment of AlN films deposited in a reactive sputtering process with accurate control of the mass flow of the reactive gas

Aluminum nitride (AlN) films can be used as tribological coatings in aggressive media to reduce wear and corrosion owing to its remarkable chemical stability and high decomposition temperature. In the present investigations AlN films were produced by r.f. sputtering under different conditions and then post bombarded by light ions to tailor the surface properties for low coefficient of friction and long wear life. AlN films deposited with varying sputtering conditions differ considerably in deposition rates, crystallinity, and stoichiometry. As-deposited and ion bombarded metal-rich AlN films exhibit a much lower coefficient of friction (less than 0.2) than stoichiometric AlN films (around 0.6). Metal-rich and stoichiometric AlN films exhibit an enormous improvement in wear life when bombarded with B + ions or a mixture of B + and C + ions. The improvement factor due to ion bombardment is higher for metal-rich AlN films. Ionic bombardment of metal-rich AlN film results in improved crystallinity and increased grain size as a function of ion dose.

Nitrogen solubility and aluminum nitride precipitation in liquid iron, Fe-Cr, Fe-Cr-Ni, and Fe-Cr-Ni-Mo alloys

The nitrogen solubility and aluminum nitride formation in liquid Fe-Al, Fe-Cr-Al, Fe-18 pct Cr-8 pct Ni-Al and Fe-18 pct Cr-8 pct Ni-Mo-Al alloys were measured by the Sieverts' method. The temperature range extended from 1823 to 2073 K, and the aluminum contents from 1.01 to 3.85 wt pct Al. Increasing aluminum content increases the nitrogen solubility. The effect of molybdenum additions was determined for 2, 4 and 8 wt pct Mo levels. The first and second order effects of chromium, nickel, molybdenum and aluminum on the activity coefficient of nitrogen in iron were determined. The first and second order effects of chromium, nickel and molybdenum on the activity coefficient of aluminum also were determined. The nitride precipitates were identified as stoichiometric aluminum nitride, AIN, by X-ray diffraction analysis. The lattice spacing was in good agreement with the ASTM standard patterns for AIN in both higher and lower Al content solutions. The solubility product of AIN increases with increasing aluminum concentration and with temperature in liquid iron and the iron alloys studied. However, the magnitudes of the solubility products of AIN in those alloys are different because of the effects of chromium and nickel additions. Additions of molybdenum show little effect on the solubility product of AIN. The standard free energy of formation of AIN in liquid iron is: δG‡ = -245,990 + 107.59 \T J/g-molAIN, based on the standard state of the infinitely dilute solution in liquid iron for aluminum and nitrogen, referred to a hypothetical one wt pct solution, and on the pure compound for A1N.