Black arsenic phosphorus–based photodetectors sense detect long-wave mid-infrared light with high detectivity at room temperature.

The utilization of black phosphorus and its monolayer (phosphorene) and few-layers in field-effect transistors has attracted a lot of attention to this elemental two-dimensional material. Various studies on optimization of black phosphorus field-effect transistors, PN junctions, photodetectors, and other applications have been demonstrated. Although chemical sensing based on black phosphorus devices was theoretically predicted, there is still no experimental verification of such an important study of this material. In this article, we report on chemical sensing of nitrogen dioxide (NO2) using field-effect transistors based on multilayer black phosphorus. Black phosphorus sensors exhibited increased conduction upon NO2 exposure and excellent sensitivity for detection of NO2 down to 5 ppb. Moreover, when the multilayer black phosphorus field-effect transistor was exposed to NO2 concentrations of 5, 10, 20, and 40 ppb, its relative conduction change followed the Langmuir isotherm for molecules adsorbed on a surface. Additionally, on the basis of an exponential conductance change, the rate constants for adsorption and desorption of NO2 on black phosphorus were extracted for different NO2 concentrations, and they were in the range of 130-840 s. These results shed light on important electronic and sensing characteristics of black phosphorus, which can be utilized in future studies and applications.

New layered anisotropic infrared semiconductors, black arsenic-phosphorus (b-AsP), with highly tunable chemical compositions and electronic and optical properties are introduced. Transport and infrared absorption studies demonstrate the semiconducting nature of b-AsP with tunable bandgaps, ranging from 0.3 to 0.15 eV. These bandgaps fall into the long-wavelength infrared regime and cannot be readily reached by other layered materials.

Black phosphorus can be prepared under low-pressure conditions at 873 K from red phosphorus via the addition of small quantities of gold, tin, and tin(IV) iodide. Au3SnP7, AuSn, and Sn4P3 were observed as additional phases. Tin(IV) iodide remains unreacted during the preparation process. The crystal structure of black phosphorus was redetermined from single crystals. P (295 K): a = 3.316(1) A, b = 10.484(2) A, c = 4.379(1) A, V = 152.24(6) A3, space group Cmce (No. 64). Solid-state 31P MAS NMR spectroscopy and X-ray powder diffraction were performed to substantiate the high crystal quality of black phosphorus. A possible mechanism for the formation is discussed in terms of the comparable structural features of black phosphorus and Au3SnP7. Thermodynamic calculations showed that the only relevant gas-phase species, P4, and the transport reactions are not suitable for the preparation of orthorhombic black phosphorus at temperatures above 773 K. A kinetically controlled mechanism must be favored instead of a thermodynamically controlled formation. The new preparation method of black phosphorus represents an easy and effective way to avoid complicated preparative setups, toxic catalysts, or "dirty" flux methods and is of general interest in elemental chemistry.