Search for: All records

III-Nitride materials such as gallium nitride (GaN) and indium nitride (InN) are critical for applications in electronics and optoelectronics due to their exceptional properties. However, their high-temperature stability is often limited by decomposition into constituent elements at low nitrogen pressures near or below ambient. This work investigates the use of nonequilibrium nitrogen plasma to stabilize GaN and InN at elevated temperatures and low pressures. Bulk nitride synthesis was demonstrated via plasma-assisted nitridation of Ga and In metals. Following synthesis, the suppression of nitride decomposition at temperatures exceeding the predicted equilibrium limits was accomplished by means of a nonequilibrium nitrogen plasma. Experimental results revealed that the nonequilibrium plasma imparted an additional chemical potential onto the ground state nitrogen by electron impact excitation, stabilizing GaN at 1000 °C and InN at 600 °C for nitrogen partial pressures as low as 10 Pa. With this experimental approach, the chemical potential of excited nitrogen species in the plasma was estimated to be 1.8 eV higher than the ground state value. These findings highlight the potential for plasma-based processing to enable scalable synthesis and stabilization of III-nitrides at high temperatures for advanced material applications. 

Abstract In this work, we demonstrate plasma‐catalytic synthesis of hydrogen and acrylonitrile (AN) from CH₄and N₂. The process involves two steps: (1) plasma synthesis of C₂H₂and HCN in a nominally 1:1 stoichiometric ratio with high yield up to 90% and (2) downstream thermocatalytic reaction of these intermediates to make AN. The effect of process parameters on product distributions and specific energy requirements are reported. If the catalytic conversion of C₂H₂and HCN in the downstream thermocatalytic step to AN were perfect, which will require further improvements in the thermocatalytic reactor, then at the maximum output of our 1 kW radiofrequency 13.56 MHz transformer, a specific energy requirement of 73 kWh kg_AN⁻¹was determined. The expectation is that scaling up the process to higher throughputs would result in decreases in specific energy requirement into the predicted economically viable range less than 10 kWh kg_AN⁻¹. 

Nonthermal plasmas in contact with liquids have been shown to generate a variety of reactive species capable of initiating reduction–oxidation (redox) reactions at the electrochemically active plasma–liquid interface. In conventional electrochemical cells, selective redox chemistry is achieved by controlling the reduction potential at the solid electrode–electrolyte interface by applying a bias via an external circuit. In the case of plasma–liquid systems, an analogous means of tuning the reduction potential near the interface has not clearly been identified. When treated as a floating surface, the liquid is expected to adopt a net negative charge to balance the flux of hot electrons and relatively cold positive ions. The reduction potential near the plasma–liquid interface is hypothesized to be proportional to the floating potential, which can be approximated using an analytical model provided the plasma parameters are known. Herein, we present a framework for correlating the electron density and electron temperature of a noble gas plasma jet to the reduction potential near the plasma–liquid interface. The plasma parameters were acquired for an argon atmospheric plasma jet in contact with an aqueous solution by means of laser Thomson scattering. The reduction potential was determined using identical reference electrodes to measure the potential difference between the plasma–liquid interface and bulk solution. Interestingly, the measured reduction potentials near the plasma–liquid interface were found to be in good agreement with the model-predicted values determined using the plasma parameters obtained from the Thomson scattering experiments. 

In this work, methods based upon nonequilibrium thermodynamics are elucidated to predict stationary states of chemical reactions in nonequilibrium plasma, and limits for energy conversion efficiency. CO2 splitting is used as an example reaction. Expectations from the theoretical framework are compared to experimental results, and reasonable agreement is obtained. The key conclusion is that the probability of observing either reactants or products increases with the amount of energy dissipated by that side of the reaction as heat through collisions with hot electrons. The side of the reaction that dissipates more energy as heat has a higher probability of occurrence. Furthermore, endergonic chemical reactions in nonequilibrium plasma, such as CO2 splitting at low temperature, require an intrinsic energy dissipation to satisfy the 2nd law of thermodynamics – a sufficient and necessary waste. This intrinsic dissipation limits the maximum theoretical energy conversion efficiency.