Low temperature plasma as a means to transform nanoparticle atomic structure

Abstract

Low temperature plasma (LTP) is a highly nonequilibrium substance capable of increasing the specific free energy of mass that flows through it. Despite this attractive feature, there are few examples of the transformation of solid material with an equilibrium atomic structure into a material with a nonequilibrium atomic structure. As a proposed example of such a transformation, in this work, it is argued that the transformation of crystalline metal nanoparticles into amorphous metal nanoparticles is feasible using LTP. To inform the feasibility calculations, detailed characterization was performed to determine the electron temperature, ion density, and background gas temperature as a function of axial position in a typical flow-through, radiofrequency, capacitively-coupled plasma reactor. Measurements revealed the existence of an intense zone with sharply elevated ion density and gas temperature in the vicinity of the powered electrode. The high intensity zone, amidst an otherwise low-intensity plasma, provides a means by which to transform the atomic structure of nanoparticles while maintaining unipolar negative charge to suppress coagulation. Theory suggests that such an intense zone would provide intense heating of nanoparticles, and subsequent rapid cooling. Calculations for copper-zirconium (CuZr) alloy show that the temperature history of a nanoparticle depends primarily on the intensity of the zone in the vicinity of the powered electrode, and on particle size. If one considers melting CuZr nanoparticles in the intense zone and then rapidly cooling them in the low-intensity plasma downstream, then the quenching rates are found to be high, on the order of 10 5 K s −1 . Since quenching rates of this magnitude are sufficient to arrest an amorphous atomic structure, LTP reactors can be used to transform crystalline metal nanoparticles into amorphous metal nanoparticles via a highly nonequilibrium quenching process.

Superlocal chemical reaction equilibrium in low temperature plasma

“…The plasma was generated using excitation at 13.56 MHz through an impedance matching network (T&C Power Conversion, Rochester, NY). Nominal applied power read from the power supply was in the range from 20 to 200 W. Previous experiments have found that the efficiency of the impedance matching network and power delivery system was approximately 65% . For a given combination of independent variables, the RF power was adjusted to keep constant the ion density and electron temperature, as measured by double Langmuir probe (vide infra).…”

“…The FDTP method ameliorates deleterious effects of, for example, EMI or RF heating, when compared to other methods such as thermocouples and resistance temperature detectors . We have previously shown using a heat transfer model that FDTP measurements, in the type of reactor used here, provide accurate estimates of the background temperature . The FTDP was inserted into the reactor from the upstream side, through a small hole that was cut in the stainless steel mesh ground electrode.…”

Nonequilibrium Plasma Aerotaxy of InN Nanocrystals and Their Photonic Properties

“…Plasma power is also an important parameter for the NPA synthesis of InN NCs. Ion density increases proportionally with increasing power. , Higher ion density leads to higher particle temperatures in the plasma, ,, and accordingly, higher vaporization rates are achieved at higher particle temperatures . Increasing the plasma power from 50 to 80 W resulted in very high vaporization rates and a very low yield.…”

“…In I emission blends with the emission from atomic and molecular nitrogen species downstream of the powered electrode (Figure S2b). This zone, where both excited species are present, is the reaction zone of the NPA process, which is mediated by the nonthermal vaporization of the indium source aerosol inside the powered electrode. , In the reaction zone, growth and vaporization happen simultaneously . The indium vapor can lead to nucleation of indium clusters, and these clusters can react with excited nitrogen species.…”

Plasmonic Core–Shell Silicon Carbide–Graphene Nanoparticles

“…In this work, we demonstrate tunable infrared SPR in ceramic core, graphene shell nanoparticles. To achieve that, we leverage the capabilities of low-temperature (as referred to the gas temperature that remains close to room temperature 8 ), nonthermal plasmas to produce particles with a relatively narrow size distribution, 9 i.e., to avoid the formation of large particles that would compromise the optical performance of the sample. Nanoparticles are heated to temperatures considerably higher than the gas temperature in these reactors because of exothermic reactions with plasma-produced species (ions, radicals, metastables, etc.).…”