The local electrical properties of copper tetracyanoquinodimethane (CuTCNQ)/HfO2/Pt stacks were investigated thanks to conductive-atomic force microscopy (AFM) measurements. Local I-V and I-t spectroscopy evidenced repeatable and reversible bipolar electrical switching (SET and RESET operations) at the nanometer scale beneath the AFM tip. Experimental results suggest that resistive switching is due to the creation/dissolution of conductive filaments bridging the CuTCNQ surface to the AFM tip. A physical model based on the migration of Cu+ ions within a nanogap and the growth of a conductive filament shows an excellent agreement with the experimental results during SET operation achieved at nanoscale.

Purification of metallurgical grade silicon is one of the methods used to produce photovoltaic grade silicon. In our study, particles of metallurgical grade silicon were purified using a hydrogenated argon thermal plasma. During their residence time in the plasma, the particles were purified by partial evaporation and then sprayed into liquid droplets on the surface of a ceramic substrate. The in-flight purification of powder depends essentially on their evaporation rate, which is directly related to the temperature and chemical properties of the plasma zones crossed by the particles. It was, therefore, important to characterize the plasma parameters: electron density and temperature profiles. Excited states of atomic hydrogen, neutral and ionized silicon and impurity lines were detected in the plasma flow. Those lines were then used to estimate the electron density and temperature, which are around 2.4 × 1016 cm−3 and 10 500 K in the inductive zone. Finally, we estimate the silicon evaporated fraction X of the particles during their thermal treatment in the hydrogenated argon plasma. The results show that the loss of mass is weak (X = 2.5 × 10−4) but nevertheless sufficient for the elimination of the superficial impurities in the powders. This conclusion was confirmed by inductively coupled plasma analyses.

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