J. Hafiz

Hypersonic plasma particle deposition—A hybrid between plasma spraying and vapor deposition

In the hypersonic plasma particle deposition process, vapor phase reactants are injected into a plasma and rapidly quenched in a supersonic nozzle, leading to nucleation of nanosize particles. These particles impact a substrate at high velocity, forming a coating with grain sizes of 10 to 40 nm. As previously reported, coatings of a variety of materials have been obtained, including silicon, silicon carbide, titanium carbide and nitride, and composites of these, all deposited at very high rates. Recent studies have shown that slight modifications of the process can result in nanosize structures consisting of single crystal silicon nanowires covered with nanoparticles. These nanowires are believed to grow in a vapor deposition process, catalyzed by the presence of titanium in the underlying nanoparticle film. However, simultaneously nanoparticles are nucleated in the nozzle and deposited on the nanowires, leading to structures that are the result of a plasma chemical vapor deposition (CVD) process combined with a nanoparticle spray process. The combination of these two process paths opens new dimensions in the nanophase materials processing area.

Thermal plasma synthesis of nanostructured silicon carbide films

Two methods for the synthesis of nanostructured silicon carbide films are discussed and compared, thermal plasma chemical vapour deposition (TPCVD) and hypersonic plasma particle deposition (HPPD). Both methods produce ?-SiC films with high growth rates on the order of 10??m?min?1. In TPCVD the generation of nanoscale grain sizes is caused by the fact that the film growth rate is much higher than the rate of surface diffusion. In HPPD a nanostructured film is grown by direct nanoparticle impact. In general, the films grown by TPCVD are denser and harder than in HPPD. X-ray diffraction spectra show that ?-SiC is essentially the only crystalline phase in the TPCVD films, whereas in HPPD a silicon crystalline phase is also present, even for films that are overall carbon-rich. Evidence is presented to support the hypothesis that HPPD films actually grow by a combination of nanoparticle impact and CVD. If this parallel process can be controlled, it could potentially lead to the design and high-rate synthesis of new nanostructured materials.

Synthesis and Deposition of Nanoparticles Using a Hypersonically Expanded Plasma

Si‐Ti‐N nanostructured coatings were synthesized by inertial impaction of nanoparticles using a process called hypersonic plasma particle deposition (HPPD). Transmission electron microscopy on samples prepared by focused ion beam (FIB) milling show TiN nanocrystallites in an amorphous matrix. X‐ray photoelectron spectroscopy results indicate the presence of amorphous Si3N4 in similar films. In‐situ particle size distribution measurements show that particle size distributions peak around 14 nm under typical operating conditions.

Hypersonic plasma particle deposition of nanostructured coatings and micropatterns

Nanostructured materials are attractive candidates for advanced friction and wear-resistant coatings due to their potentially enhanced mechanical properties. We have developed a one-step method called hypersonic plasma particle deposition [1] to produce and deposit nanoparticles using a thermal plasma reactor. Particle synthesis is achieved by dissociating vapor phase reactants in the plasma, and quenching the hot gas in a supersonic nozzle expansion. Particles are deposited on a substrate by hypersonic impaction to form a film, or are deposited as micropatterns using a process called focused particle beam deposition [2]. In-situ particle size distribution measurements are performed using a sampling probe interfaced to an extraction/dilution system for measurement by a scanning electrical mobility spectrometer.Copyright