Inductively coupled nonthermal plasma synthesis of aluminum nanoparticles.

Metallic nanoparticles of aluminum (Al), a nontoxic and earth-abundant element, are relevant to plasmonic and energetic applications. However, monodisperse Al nanoparticles are difficult to synthesize using all gas-phase approaches, especially in the 10 to 20 nm size range; yet, many applications require particles of this size due to their enhanced properties. Here, an inductive nonthermal plasma reactor fed with aluminum trichloride (AlCl3) and Ar is used to synthesize single-crystal aluminum nanoparticles. The particles can be produced with or without hydrogen. Several reactor conditions such as AlCl3vapor concentration, flow rates, and power are found to strongly influence particle properties such as the oxide shell thickness, particle mono-dispersity, and particle size. Significant quantities of Ar relative to AlCl3, short residence times of 10 s of ms, and pressures in excess of 4.7 Torr are required to form Al particles with geometric mean sizes of 10-20 nm and geometric standard deviations as low as 1.3. While the Al nanoparticles are covered with 2-4 nm thick oxide shells, the best synthesis conditions yield particle sizes determined by electron microscopy that are comparable to crystallite sizes determined from x-ray diffraction.

Nonthermal Plasma-Enhanced Chemical Vapor Deposition of Two-Dimensional Molybdenum Disulfide.

Molybdenum disulfide (MoS2) is being studied for a wide range of applications including lithium-ion batteries and hydrogen evolution reaction catalysts. In this paper, we present a single-step nonthermal plasma-enhanced chemical vapor deposition (PECVD) process for the production of two-dimensional MoS2. This method provides an alternative route to established CVD and plasma synthesis routes. The approach presented here synthesizes films in only a few minutes using elemental sulfur (S8) and molybdenum pentachloride (MoCl5) as precursors. Deposition utilizes a nonthermal inductively coupled plasma reactor and temperatures around 500 °C. Film growth characteristics and nucleation are studied as a function of precursor concentrations, argon flow rate, plasma power, and deposition time. Few-layer two-dimensional (MoS2) films were formed at low precursor concentrations. Films with nanoparticle-like features were formed when the precursor concentration was high. Noncontinuous nonstoichiometric films were found at low plasma power, while high plasma power led to continuous films with good stoichiometry. The vacancies and defects in these films may provide active sites for hydrogen evolution.