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We have investigated the electronic structure and carrier mobility of four types of phosphorous monolayer sheet (α-P, β-P,γ-P and δ-P) using density functional theory combined with Boltzmann transport method and relaxation time approximation. It is shown that α-P, β-P and γ-P are indirect gap semiconductors, while δ-P is a direct one. All four sheets have ultrahigh carrier mobility and show anisotropy in-plane. The highest mobility value is ~3 × 105 cm2V−1s−1, which is comparable to that of graphene. Because of the huge difference between the hole and electron mobilities, α-P, γ-P and δ-P sheets can be considered as n-type semiconductors, and β-P sheet can be considered as a p-type semiconductor. Our results suggest that phosphorous monolayer sheets can be considered as a new type of two dimensional materials for applications in optoelectronics and nanoelectronic devices.

Abstract.We studied the hygroscopic behavior of atmospheric aerosols by using a novel approach, the combination of atomic force microscopy (AFM) with transmission electron microscopy (TEM) imaging of the same individual particles. By comparing the dimensions of hydrated and dry ammonium sulfate particles collected above the North Atlantic Ocean, we determined that particle volumes are up to four times larger under ambient conditions (as determined by AFM) than in the vacuum of a transmission electron microscope. We interpret these changes as resulting from the loss of water. Organic films on the particles may be responsible for the relatively large water uptake at low relative humidities.