Stable antiferromagnetic property and tunable electronic structure of two-dimensional MnPX3(X = S and Se) from pristine structure to Janus phase.

Transition-metal phosphorus trichalcogenides have been considered as very promising two-dimensional (2D) magnetic candidates up-to-date. We performed a systematical first-principles study on the electronic structures and magnetic properties of pristine MnPX3(X = S and Se) and Janus Mn2P2S3Se3monolayers. All monolayers behave as a direct-band-gap semiconductor in antiferromagnetic ground state which is caused by strong direct and indirect exchange interactions. It is found that the electronic structures and magnetic properties can be manipulated by Janus phase. The calculated band gap is 2.44 eV, 1.80 eV and 1.86 eV for MnPS3, MnPSe3and Mn2P2S3Se3with a valley polarization with consideration of spin-orbital coupling (SOC), respectively. In particular, significant energy-splittings emerge in the SOC-band structures of Janus Mn2P2S3Se3due to its broken-inversion-symmetry. Estimated by Monte Carlo simulations, the Néel temperature is 96 K, 71 K and 79 K based on Ising model while halved down to 41 K, 33 K and 36 K on the basis ofXYmodel for MnPS3, MnPSe3and Mn2P2S3Se3, respectively, indicating theXYmodel should be more reliable to describe the spin dynamics. Our research offers an insight into the magnetic mechanism and paves a feasible path to modulate the magnetism for 2D magnets in realistic applications on spintronics.

Investigations on structural, electronic and optical properties of ZnO in two-dimensional configurations by first-principles calculations.

The electronic structures and optical properties of two-dimensional (2D) ZnO monolayers in a series of configurations were systematically investigated by first-principles calculations with HubbardUevaluated by the linear response approach. Three types of 2D ZnO monolayers, as planer hexagonal-honeycomb (Plan), double-layer honeycomb (Dlhc), and corrugated tetragonal (Tile) structures, show a mechanical and dynamical stability, while the Dlhc-ZnO is the most energetically stable configuration and Plan-ZnO is the second one. Each 2D ZnO monolayer behaves as a semiconductor with that Plan-, Dlhc-ZnO have a direct band gap of 1.81 eV and 1.85 eV at theΓpoint, respectively, while Tile-ZnO has an indirect band gap of 2.03 eV. Interestingly, the 2D ZnO monolayers all show a typical near-free-electron character for the bottom conduction band with a small effective mass, leading to a tremendous optical absorption in the whole visible and ultraviolet window, and this origination was further confirmed by the transition dipole moment. Our investigations suggest a potential candidate in the photoelectric field and provide a theoretical guidance for the exploration of wide-band-gap 2D semiconductors.

Effective nitrosamines trap derived from the in situ carbonized mesoporous silica MCM-41.

A new route to modify the mesoporous silica MCM-41 with carbon, using the inherent surfactant template in the as-synthesized sample as the carbon precursor, is reported in this article. Apart from the advantage of omitting energy and time required for removal of template, the resulting silica-carbon composites exhibit a high efficiency in adsorption and catalytic decomposition of N-nitrosopyrrolidine (NPYR), the typical carcinogenic pollutant in environment. The influence of carbonization temperature on the structure and performance of the resulting carbon-silica composite was investigated by use of XRD, N(2) adsorption-desorption, FTIR and TG-DSC techniques, and the instantaneous adsorption and the temperature-programmed surface reaction (TPSR) of NPYR as well as the reduction of nitrosamines level of cigarette smoke were also utilized to assess the actual function of these composites. The carbonization performed in the range of 773-973 K enabled the resulting composites to possess a higher activity than parent MCM-41 in eliminating volatile nitrosamines, which is beneficial for controlling carcinogenic pollutants in environment.

Clinical effect of removable partial denture prepared by Saddle-Lock hidden-clasp.

OBJECTIVE: To study the method for preparing removable partial denture using Saddle-Lock hidden-clasp and evaluate its clinical effect. METHOD: Casting process was adopted for the preparation of the clasp, which was fixed at the points on the mesial and distal surfaces of the abutment tooth. The clinical records of 305 patients treated with such removable partial dentures were reviewed. RESULTS: Within a follow-up period of 6 years, 295 of the 305 patients retained good abutment condition and were satisfied with the denture that was capable of easy wearing and removing. CONCLUSIONS: Removable partial denture made by Saddle-lock hidden-clasp exhibits good performance in fixation and stability. As an innovation of traditional design of partial denture clasp, it is simple to prepare and well received by the patients with good clinical effect.

[Restoration of molar residual roots and crowns with multiple canals by unparalleled posts: an evaluation].

OBJECTIVE: To repair the residual roots and crowns of the molars with multi-canals using unparalleled posts and cores and ceramic crowns. METHODS: Unparalleled insertion of the posts and cores was adopted in the casting of the ceramic crown to repair the residual roots and crowns of the molars. RESULTS AND CONCLUSION: Unparalleled insertion of the posts increased the retention strength of the cores, which provided a solid foundation for the restoration of the molars with ceramic crowns, therefore yielding better clinical effect in repairing the molars.