phosphorene with a thickness varying from 2.1 to over 20 nm. Reduction of the total resistance with decreasing gate voltage is observed, indicating the p-type characteristic of phosphorene. Linear I-V relationship of transistor at low drain bias suggests good contact properties at the phosphorene/metal interface. Good current saturation at high drain bias values was observed. However, it was seen that the mobility is reduced in few-layer phosphorene when compared to bulk black phosphorus. Field-effect mobility of phosphorene-based transistor shows a strong thickness dependence, peaking at around 5 nm and decrease steadily with further increase of crystal thickness. Atomic layer deposition (ALD) dielectric layer and/or hydrophobic polymer is used as encapsulation layers in order to prevent device degradation and failure. Phosphorene devices are reported to maintain their function for weeks with encapsulation layer, whereas experience device failure within a week when exposed to ambient condition. Battery electrode Phosphorene is considered a promising anode material for rechargeable batteries, such as Lithium-ion batteries. The interlayer space allows lithium storage and transfer. The layer number and lateral size of phosphorene affect the stability and capacity of the anode. Inverter Researchers have also constructed the CMOS inverter (logic circuit) by combining a phosphorene PMOS transistor with a MoS2 NMOS transistor, achieving high heterogeneous integration of semiconducting phosphorene crystals as a new channel material for potential electronic applications. In the inverter, the power supply voltage is set to be 1 V. The output voltage shows a clear transition from VDD to 0 within the input voltage range from −10 to −2 V. A maximum gain of ~1.4 is attained. Solar-cell donor material (optoelectronics) The potential applications of mixed bilayer phosphorene in solar-cell material was examined as well. Flexible circuits Phosphorene is a promising candidate for flexible nano systems due to its ultra-thin nature with ideal electrostatic control and superior mechanical flexibility. Researchers have demonstrated the flexible transistors, circuits and AM demodulator based on few-layer phosphorus, showing enhanced am bipolar transport with high room temperature carrier mobility as high as ~310 cm2/Vs and strong current saturation. Fundamental circuit units including digital inverter, voltage amplifier and frequency doubler have been realized. Radio frequency (RF) transistors with highest intrinsic cutoff frequency of 20 GHz has been realized for potential applications in high frequency flexible smart nano systems. See also Borophene Germanene Graphene Silicene Stanene References Phosphorus Semiconductor materials Emerging technologies Monolayers