The optical nonlinearity of the nonstoichiometric silicon carbide with a variable C/Si composition ratio is studied. The significantly enhanced optical nonlinearity and the mechanism related to the bonding structures and the composition ratio in the nonstoichiometric silicon carbide are elucidated.

Microparticles produced by high current vacuum arcs significantly reduce the insulation performance of vacuum interrupters. The objective of this paper is to observe the generation and dynamics of microparticles during the arcing and post-arcing period, and to further reveal the possible effects of particles during interruption of a high current vacuum arc. A plasma diagnosis system based on a laser-shadow technique was used to measure the particles in a demountable vacuum chamber. The results show that contact materials affect particle generation patterns. For a CuCr contact with a higher proportion of chromium, the formation of a melting pool is much more difficult and the flow of liquid metal on the surface can be suppressed, which also impedes the formation of particles. Moreover, reignition after arc extinction was found to be triggered by some incandescent particles. These hot particles have two effects on breakdown events during the post-arcing phase: they trigger a micro-discharge between a particle and the electrode, and new weak points are left on the surface that enhance the local field. More crucially, the lifetime of spontaneous particles spans up to hundreds of milliseconds after current zero, which indicates that long-delayed breakdown is correlated with the existence of particles. In addition, some particles could remain suspended near the electrode or oscillate between the contacts. The dynamic behavior of these particles can significantly lower the breakdown threshold and increase the possibility of breakdown.

A highly selective gas sensor based on the WO3/WS2 van der Waals heterojunction for 2-chloroethyl ethyl sulfide (2-CEES) was successfully realized.

Spark gas switches (SGS) are widely used in various pulsed power applications where sulfur hexafluoride (SF6) is still dominant because of its excellent insulating performance. However, particle contamination generated by SF6 possesses some special properties that can greatly reduce the effectiveness of the gas switches. The objective of this paper is to study the effects of particles generated spontaneously by consecutive breakdowns of high-pulse-power SGS on the insulating performance in compressed SF6. A double electrode/double pulse method, coupled with laser scattering and laser shadow photography, is adopted to detect the particles and examine their specific roles in the breakdown process. Many large particles in SF6, of approximately 150 μm in diameter, are observed at about 80 milliseconds after a single breakdown. Furthermore, numerous particles gradually suspend and accumulate in the gap after consecutive breakdowns. Particles generated by SF6 can reach tens of micrometers in size. They have rough microtopography covered by abundant floccules, and contain rich electronegative elements: fluorine and sulfur. Moreover, particle-involved abnormal breakdowns in SF6 usually occur with nearly equal threshold and probability in spite of the increasing consecutive breakdowns, and conversely, the abnormal breakdowns in N2 appear more frequently and unsteadily with a high dispersibility. The analysis of field enhancement caused by these large metal-fluoride/sulfide particles shows that they can directly cause significant field emission (FE) due to their properties of surface-field enhancement and causticity. Such FE further triggers micro-discharge. Subsequently, this behavior eventually leads to abnormal breakdowns at a lower threshold.

Sensitive detection of toxic and harmful gases is essential in the field of environmental monitoring and human health. Among the detection strategies, gas sensors based on metal oxides are widely...