The present study aims to elaborate particle in-flight behavior during plasma spraying and its significance in determining the microstructure and mechanical properties of plasma sprayed yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The as-sprayed YSZ coatings were characterized in terms of defects (such as pores, unmelted particles and cracks) and fracture toughness. The results showed that, due to the higher temperature and velocity of in-flight particles in a supersonic atmospheric plasma spraying (SAPS) compared to that of atmospheric plasma spraying (APS), denser coatings were formed leading to a better fracture toughness. The percentage of defects of the microstructure was similar to the temperature and velocity of particles in-flight during plasma spraying. Furthermore, the structural defects had a strong effect on its mechanical behavior. The total defect percentage and fracture toughness in SAPS-TBCs spanned 6.9 ± 0.17%–13.26 ± 0.22% and 2.52 ± 0.06 MPa m1/2–1.78 ± 0.19 MPa m1/2; and 11.11 ± 0.36%–17.15 ± 0.67% and 2.13 ± 0.08 MPa m1/2–1.4 ± 0.12 MPa m1/2 in APS-TBCs.
Fractal theory is widely used to analyze the topography of surfaces; however, the relationship and characteristics of fractal dimension and microstructures of β-SiC films have not been reported. Using scanning electron microscopy and computer analysis, the microstructures of β-SiC films were evaluated; the films were prepared on AlN substrates by laser chemical vapor deposition using a diode laser and hydrido polycarbosilane as the precursor at different vacuum levels. The effect of vacuum level on the microstructure of β-SiC films was evaluated. The results show that the microstructures of β-SiC films exhibit the characteristics of fractals. Using the box counting method, the fractal dimensions of β-SiC films were calculated to be about 1.94–2.14, providing more fractal identification in evaluating the performance of films.
Owing to their large band gaps and high dielectric constants, III-V nitrides are very attractive for high temperature electronics and optoelectronic device applications. Improved material properties have recently led to a variety of devices being demonstrated such as blue, green, and yellow light-emitting devices as well as laser diodes, metal-semiconductor GaN based fieldeffect transistors (MESFETs), and AlGaN/GaN based high electron mobility transistors (HEMTs). The presence of parasitic resistance can significantly limit performance such as lower speed for electronic devices and higher turn-on voltage for the optical devices. There is room for improvements for both n- and p- type ohmic contacts in order to lower parasitic resistance and improve reliability. W based contacts on GaN and InGaN have been demonstrated and show excellent thermal stability, however the contact resistivity still in the range of 10−5 Ω-cm2. By using InN and graded InGaN as the contact layers, the contact resistivity can be reduced to ∼ 10−6 Ω -cm2.Besides low resistance ohmic contacts, a low leakage current and high turn-on voltage gate contact is critical to high performance electronic devices. Nitride based materials are very inert to conventional wet chemical etching used for other III-V compound semiconductors. Currently, dry etching is widely used for the device fabrication, however, III-nitrides are sensitive to dry etching, especially in the step of the gate recess etching. In this talk, metal insulator semiconductor (MIS) gate contacts based on AIN and Ga2O3/Gd2O3 will be discussed.
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