Nitrophosphorene: A 2D Semiconductor with Both Large Direct Gap and Superior Mobility

A new two-dimensional phosphorus nitride monolayer (<i>P</i>2₁/<i>c</i>-PN) with distinct structural and electronic properties is predicted based on first-principle calculations. Unlike pristine single-atom group V monolayers such as nitrogene, phosphorene, arsenene, and antimonene, <i>P</i>2₁/<i>c</i>-PN has an intrinsic direct band gap of 2.77 eV that is very robust against the strains. Strikingly, <i>P</i>2₁/<i>c</i>-PN shows excellent anisotropic carrier mobility up to 290 829.81 cm² V^–1 s^–1 along the <i>a</i> direction, which is about 18 times that in monolayer black phosphorus. This put <i>P</i>2₁/<i>c</i>-PN way above the general relation that carrier mobility is inversely proportional to bandgap, making it a very unique two-dimensional material for nanoelectronics devices

Hydrolysis of Sulfur Dioxide in Small Clusters of Sulfuric Acid: Mechanistic and Kinetic Study

The deposition and hydrolysis reaction of SO₂ + H₂O in small clusters of sulfuric acid and water are studied by theoretical calculations of the molecular clusters SO₂–(H₂SO₄)_<i>n</i>–(H₂O)_<i>m</i> (<i>m</i> = 1,2; <i>n</i> = 1,2). Sulfuric acid exhibits a dramatic catalytic effect on the hydrolysis reaction of SO₂ as it lowers the energy barrier by over 20 kcal/mol. The reaction with monohydrated sulfuric acid (SO₂ + H₂O + H₂SO₄ – H₂O) has the lowest energy barrier of 3.83 kcal/mol, in which the cluster H₂SO₄–(H₂O)₂ forms initially at the entrance channel. The energy barriers for the three hydrolysis reactions are in the order SO₂ + (H₂SO₄)–H₂O > SO₂ + (H₂SO₄)₂–H₂O > SO₂ + H₂SO₄–H₂O. Furthermore, sulfurous acid is more strongly bonded to the hydrated sulfuric acid (or dimer) clusters than the corresponding reactant (monohydrated SO₂). Consequently, sulfuric acid promotes the hydrolysis of SO₂ both kinetically and thermodynamically. Kinetics simulations have been performed to study the importance of these reactions in the reduction of atmospheric SO₂. The results will give a new insight on how the pre-existing aerosols catalyze the hydrolysis of SO₂, leading to the formation and growth of new particles

Plasmonic MoO₂ Nanospheres as a Highly Sensitive and Stable Non-Noble Metal Substrate for Multicomponent Surface-Enhanced Raman Analysis

Semiconductor-based surface-enhanced Raman spectroscopy is getting more and more attention because of its great price advantage. One of the biggest obstacles to the large-scale application of it is the poor stability. Here, we report that plasmonic MoO₂ nanospheres can be used as a highly sensitive and stable semiconducting-substrate material for surface-enhanced Raman scattering (SERS). By using the MoO₂ nanospheres as Raman substrates, a series of typical compounds with high attention can be accurately detected. This new non-noble metal substrate material shows a very high detection limit of 10^–8 M, and exhibits great near-field enhancement with one of the highest enhancement factor of 4.8 × 10⁶ reported to date. More importantly, the oxide with intermediate valence displays unexpected ultrahigh stability, which can withstand the corrosion of strong acid and strong alkali as well as 150 °C high temperature oxidation in air. Moreover, the accurate detection of multicomponent samples was also successful on this substrate. These results show that some simple metal oxides with intermediate valence may become sensitive and stable SERS substrate materials due to their abundant free electrons and structure that easily causes hot spots