Synthesis of Te and Sb Doped Black Phosphorus Single Crystals, Oxidation-Resistance and Room-Temperature Gas Sensing Applications

Black phosphorus (BP) is another highly potential semiconducting two-dimensional (2D) material after graphene and transition metal dichalcogenides (TMDCs). Its optoelectronic properties depend on the number of layers and the in-plane directions of the BP 2D structure. The optoelectronic properties range from monolayer Phosphorene to bulk BP can just link those of graphene and TMDCs, enabling 2D materials to cover a wide range of optoelectronic properties. Besides, coupled with its unique armchair wrinkled crystal structure, BP has irreplaceable advantages and can be widely used in sensing, optics, electronics, thermoelectrics, and other fields. However, since each phosphorus atom in the BP structure has a lone electron pair, it is easy to spontaneously degrade in the atmospheric environment, which significantly limits its practical application in various fields. So far, many studies have shown that the environmental stability of BP or the performance of BP components can be effectively improved by surface coating, nanostructure modification, or element doping. However, different protection strategies are often accompanied by changes in the essential characteristics of BP, and the causal relationship is still, up to now, not fully clear yet.<br/>In this study, BP crystals were prepared by chemical vapor transport (CVT), and tellurium and antimony were respectively doped in the synthesis process to potentially change the energy band structure of BP and improve its environmental stability. The obtained BP crystals were further exfoliated by ultrasonic liquid phase exfoliation (LPE). A series of BP nanosheets, tellurium-doped BP nanosheets, and antimony-doped BP nanosheets were prepared in the organic solvent N-methylpyrrolidone (NMP) with a 900-watt ultrasonic wave. Then, BP nanosheets with a specific size distribution are screened by centrifugal rotation speed. Then, various techniques were applied to analyze the degradation degree of these three types of BP nanosheets exposed to a specific atmospheric environment (relative humidity: 75%~90%, temperature: 23~30°C). Finally, these three types of BP nanosheets were respectively placed on the interdigitated substrate for gas sensing. It was found that the highest conversion rate of pure BP, tellurium-doped BP, and antimony-doped BP crystals can reach ~98%. According to x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, optical microscopy (OM), atomic force probe microscopy (AFM), and transmission electron microscopy (TEM) analysis, it was confirmed that the doping of tellurium or antimony is an effective strategy to improve the environmental stability of BP nanosheets. Finally, the gas sensing results show that among eleven kinds of gases (CH₄, C₂H₆, C₃H₈, NO₂, NO, NH₃, C₂H₅OH, CO, acetone, HCOH, H₂), all the prepared BP nanosheets, tellurium or antimony doped BP nanosheets exhibited highly selective responses to NO₂ and NO at room temperature. In addition, doping of tellurium and antimony could also reduce the response/recovery time to NO₂ and NO.<br/><br/>Keywords: black phosphorus, phosphorene, dope, anti-degradation, gas sensor