Metal Al Produced by H₂ Plasma Reduction of AlCl₃: A Thermodynamic and Kinetic Study on the Plasma Chemistry

Abstract

In this paper we reported that low temperature plasma may reverse the direction of a chemical reaction. The thermodynamically forbidden reaction between H 2 and AlCl 3 was able to take place with the assistance of low temperature plasma, yielding metal Al. The plasma chemistry of the reaction was investigated by optical emission spectroscopy, which suggested that the dissociation of H 2 and AlCl 3 molecules by plasma led the reaction to a thermodynamically favorable one by creating reaction channels with low Gibbs free energy change. The addition of Ar promoted the reaction kinetics dramatically, which was attributed to the enhanced dissociation of AlCl 3 molecules by excited Ar species.

Plasma‐Assisted Approaches in Inorganic Nanostructure Fabrication

“…[69,85,[104][105][106] New chemistry can be introduced by these excited species, leading to chemical reactions at lower temperature or even thermodynamically forbidden conditions. [57,87,89,142] The nucleation, growth, and crystallization behavior of the nanostructures can be tuned due to the new chemistry equilibrium induced by the excited species at the plasma/solid interface. [47,55,92,106,117,125] Moreover, radicals and ions exhibit a synergic effect, which has been verified in plasma etching processes.…”

“…[142] The reaction AlCl 3 þ 3/2 H 2 ¼ Al þ 3 HCl is thermodynamically highly forbidden, even above 1000 8C, with a DG value of 285 kJ mol À1 at 298 K. The near-100% yield of metallic Al near room temperature was a surprising result, providing convincing evidence for the significance of plasma on the thermodynamics. From the OES diagnostics, dissociated species including AlCl radicals, Al atoms, and H atoms were detected in the plasma.…”

Ultrahigh GaN:SiO2etch selectivity byin situsurface modification of SiO2in a Cl2-Ar plasma

“…Thus, the sapphire OES spectrum can be effectively taken as the background spectra of the Cl 2 -Ar plasma). The AlN wafer produces a strong AlCl signal at 261 nm [38][39][40] and strong Al signals at 308 and 396 nm [37] in the OES. The Al wafer has even stronger AlCl and Al peaks in the OES than the AlN indicating that it releases more Al species into the plasma.…”

Low temperature synthesis of α-Al2O3 films by high-power plasma-assisted chemical vapour deposition

“…Consequently, more Ar* would be available for 3 dissociating the precursor. Zheng et al reported that in an inductively coupled discharge, the 4 presence of Ar* leads to efficient AlCl 3 precursor dissociation [19]. Generally, these dissociation 5 processes can be described by the following reaction [19], 10 should not only be attributed to the electron temperature and density increase, but also to the 11 enhancement of the dissociation by impact of Ar*.…”

“…Zheng et al reported that in an inductively coupled discharge, the 4 presence of Ar* leads to efficient AlCl 3 precursor dissociation [19]. Generally, these dissociation 5 processes can be described by the following reaction [19], 10 should not only be attributed to the electron temperature and density increase, but also to the 11 enhancement of the dissociation by impact of Ar*. Enhanced dissociation of BCl 3 has also been 12 reported upon increasing the discharge power in a PACVD plasma [20].…”