Investigation of Ag and Cu Filament Formation Inside the Metal Sulfide Layer of an Atomic Switch Based on Point-Contact Spectroscopy

The atomic switches have attracted wide attention owing to their applications in nonvolatile electric devices. The atomic switch is operated by the formation and dissipation of a metallic filament inside a metal sulfide film, which is controlled by a solid electrochemical reaction. Although the metallic filament is considered to consist of metal atoms, the chemical species of the metallic filament are difficult to be identified due to challenges in observing the metallic filament inside the solid. In this study, we report the investigation on the metallic filament in the atomic switch with metal sulfide based on point-contact spectroscopy (PCS). By cooling the atomic switch, the switch voltage increased to 1 V, which allowed for the PCS measurement. The PCS revealed that the metallic filament was composed of Ag atoms in the case of the Pt/Ag₂S/Ag atomic switch. We applied this technique to the Pt/Cu₂S/Ag and Pt/Ag₂S/Cu atomic switches to uncover the formation process of the metallic filament. In both atomic switches, the chemical species of the metallic filament were Ag. The metal atoms were supplied from both the metal electrode and the sulfide layer.

Measuring Number of Free Radicals and Evaluating the Purity of Di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium [DPPH] Reagents by Effective Magnetic Moment Method

Di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium [DPPH] is widely used as a standard for measuring the number of free radicals. Here, we evaluated the number of free radicals of "DPPH" reagents from three manufacturers by effective magnetic moment method. Interestingly, the reagents from different manufacturers had varying temperature dependencies for both magnetic moment and g-value at low temperatures. As a result, the maximum relative difference among the three reagents on the number of free radicals per unit mass was 20%. Carbon hydrogen nitrogen (CHN) analyses, high-resolution EPR measurements, FT-IR measurement, and NMR measurement confirmed that a major component of only one among the three reagents was "pure" DPPH. The evaluated purity based on free radical content was 0.998 kg kg^-1 with expanded uncertainty of 0.036 kg kg^-1. The other two reagents were found to be contaminated by several % of benzene in the DPPH crystal structure.