Visible improvements: Owing to the plasmon resonance of silver nanoparticles deposited on the surface of AgBr, the newly-prepared plasmonic photocatalyst Ag section signAgBr has a strong absorption in the visible region (see picture) and shows high efficiency in the photodegradation of organic pollutants under visible light.

Disorder-engineered nanophase anatase TiO(2) through hydrogenation has been demonstrated to exhibit substantial solar-driven photocatalytic activities [X. Chen, L. Liu, P. Y. Yu, S. S. Mao, Science, 2011, 331, 746], while the detailed image of the disorder is unclear, and the role of the hydrogenation as well as the mechanism of high photoactivity is still ambiguous. Based on first-principles calculations, we find by taking into account the synergic effect of Ti-H and O-H bonds that hydrogen atoms can be chemically absorbed both on Ti(5c) and O(2c) atoms for (101), (001), and (100) surfaces, while previous studies predicted that chemical absorption of H on both Ti(5c) and O(2c) only takes place on the (001) surface due to overlooking the synergic effect. The hydrogenation induces obvious lattice distortions on (101) and (100) surfaces of nanoparticles enhancing the intraband coupling within the valence band, while the (001) surface is not largely affected. Different from the previous understanding that the lattice disorder accounts for the induced mid-gap states while the hydrogen only stabilizes the lattice disorders by passivating their dangling bonds, we find that the adatoms not only induce the lattice disorders but also interact strongly with the Ti 3d and O 2p states, resulting in a considerable contribution to the mid-gap states. The optical absorption is dramatically red shifted due to the mid-gap states and the photogenerated electron-hole separation is substantially promoted as a result of electron-hole flow between different facets of hydrogenated nanoparticles, which may account for the exceptional high energy conversion efficiency under solar irradiation. Even more interestingly, we find that hydrogenation reverses the redox behavior of different surfaces of nanoparticles, which provides new hints that one can tune the photoexcited electron-hole flow between different surfaces of nanoparticles in accordance to one's request by appropriate chemical surface treatment. We believe that band-offset-engineering between different facets of nanocrystals can be an effective way to facilitate energy conversion efficiency and should be applicable to other nanophase materials.

Room-temperature ferromagnetism occurs in GaN nanoparticles even without any doped magnetic ions. The cause for this finding was examined by performing density functional calculations for the bulk GaN and the nonpolar surface of GaN with Ga- and N-vacancies. Our work indicates that the room-temperature ferromagnetism of undoped GaN nanoparticles originates from the nitrogen dangling bonds associated with the surface Ga-vacancies. The spins of the nitrogen dangling bonds couple ferromagnetically by through-bond spin polarization, and this ferromagnetic coupling is effective even when the vacancy separation is as long as ∼8 Å.

The electron-hole separation efficiency is a key factor that determines the performance of two-dimensional (2D) transition metal dichalcogenides (TMDs) and devices. Therefore, searching for novel 2D TMD materials with a long timescale of carrier lifetime has become one of the most important topics. Here, based on time-domain density functional theory (TD-DFT), we propose a brand new TMD material, namely Janus-MoSTe, which exhibits a strong built-in electric field. Our results show that in the Janus-MoSTe monolayer, the exciton consisting of an electron and hole has a relatively wide spatial extension and low binding energy. In addition, a slow electron-hole recombination process is observed, with a timescale on the order of 1.31 ns, which is even comparable to those of van der Waals (vdW) heterostructures. Further analysis reveals that the extremely long timescale for electron-hole recombination could be ascribed to the strong Coulomb screening effect as well as the small overlap of wavefunctions between electrons and holes. Our findings establish the built-in electric field as an effective factor to control the electron-hole recombination dynamics in TMD monolayers and facilitate their future applications in light detection and harvesting.

The photoexcitation dynamics plays a key role in determining the properties of van der Waals heterostructures (vdWHs). Based on the time-dependent density functional theory combined with nonadiabatic molecular dynamics, we investigate the charge transfer in Janus-MoSSe/WS vdWHs. Ultrafast charge separation is observed, arising from the large overlapping between the donor and acceptor states. While the electron-hole recombination is 2 orders of magnitude slower than the charge separation, this can be understood by the fact that the initial and final states are strictly confined to different materials. Additionally, photoresponsivity performance of the vdWHs is also evaluated using density functional theory combined with the nonequilibrium Green's functions. Simulated results of high photoresponsivity in a broad range of the spectrum endows proposed systems powerful potential in optoelectronic and photovoltaic applications. The atomistic picture revealed in our work provides chemical guidelines and facilitates the design of next-generation devices for light detecting and harvesting.