The chemical reactivity of different surfaces of titanium dioxide (TiO2) has been the subject of extensive studies in recent decades. The anatase TiO2(001) and its (1 × 4) reconstructed surfaces were theoretically considered to be the most reactive and have been heavily pursued by synthetic chemists. However, the lack of direct experimental verification or determination of the active sites on these surfaces has caused controversy and debate. Here we report a systematic study on an anatase TiO2(001)-(1 × 4) surface by means of microscopic and spectroscopic techniques in combination with first-principles calculations. Two types of intrinsic point defects are identified, among which only the Ti3+ defect site on the reduced surface demonstrates considerable chemical activity. The perfect surface itself can be fully oxidized, but shows no obvious activity. Our findings suggest that the reactivity of the anatase TiO2(001) surface should depend on its reduction status, similar to that of rutile TiO2 surfaces.

We report our investigation on the intrinsic chemical activity of the anatase TiO 2 (001)-(1 × 4) reconstructed surface, using epitaxially grown anatase TiO 2 (001) thin films and using methanol molecules as a probe, characterized by combining scanning tunneling microscopy and temperature-programmed desorption. Our results provide direct evidence that the perfect (1 × 4) lattice sites of the surface are intrinsically quite inert for the reaction of methanol. We obtain that the activation energy for desorption of molecular methanol is about 0.55−0.64 eV, which is in good agreement with our first-principle calculations based on the structural model with 5-fold coordinated Ti atoms at the ridges of (1 × 4) reconstruction. We find that two types of defect sites, that is, reduced Ti pairs and partially oxidized Ti pairs, are responsible for the chemical activity of the surface, evidenced by the desorption of water due to the dehydrogenation of methanol at the defect sites. The methoxy left at the reduced Ti-pair sites further produced CH 3 radical, and the methoxy near the partially oxidized Ti-pair sites produced formaldehyde and methanol through disproportionation reaction. The determination of these intrinsic properties can be important to understanding the conflicting results from this surface in the literature and thus to reveal the actual reaction mechanisms.

High pressure has been demonstrated to be a powerful approach of producing novel condensed-matter states, particularly in tuning the superconducting transition temperature (T c) of the superconductivity in a clean fashion without involving the complexity of chemical doping. However, the challenge of high-pressure experiment hinders further in-depth research for underlying mechanisms. Here, we have successfully synthesized continuous layer-controllable SnSe2 films on SrTiO3 substrate using molecular beam epitaxy. By means of scanning tunneling microscopy/spectroscopy (STM/S) and Raman spectroscopy, we found that the strong compressive strain is intrinsically built in few-layers films, with a largest equivalent pressure up to 23 GPa in the monolayer. Upon this, unusual 2 × 2 charge ordering is induced at the occupied states in the monolayer, accompanied by prominent decrease in the density of states (DOS) near the Fermi energy (E F), resembling the gap states of CDW reported in transition metal dichalcogenide (TMD) materials. Subsequently, the coexistence of charge ordering and the interfacial superconductivity is observed in bilayer films as a result of releasing the compressive strain. In conjunction with spatially resolved spectroscopic study and first-principles calculation, we find that the enhanced interfacial superconductivity with an estimated T c of 8.3 K is observed only in the 1 × 1 region. Such superconductivity can be ascribed to a combined effect of interfacial charge transfer and compressive strain, which leads to a considerable downshift of the conduction band minimum and an increase in the DOS at E F. Our results provide an attractive platform for further in-depth investigation of compression-induced charge ordering (monolayer) and the interplay between charge ordering and superconductivity (bilayer). Meanwhile, it has opened up a pathway to prepare strongly compressed two-dimensional materials by growing onto a SrTiO3 substrate, which is promising to induce superconductivity with a higher T c.

Objectives Coronavirus disease 2019 (COVID-19) is a novel infectious disease, with significant morbidity and mortality. This meta-analysis is to evaluate the prevalence of disseminated intravascular coagulation (DIC) in COVID-19 patients and to determine the association of DIC with the severity and prognosis of COVID-19. Methods We searched the PubMed, EMBASE, and China National Knowledge Infrastructure (CNKI) database until August 12, 2020. The meta-analysis was performed using Stata 16.0 software. Results 14 studies were included in our meta-analysis. The pooled analysis revealed that the incidence of COVID-19 patients developing DIC was 3% (95%: 1%–5%, P < 0.001). In addition, deaths were more likely to be associated with DIC (Log OR = 2.46, 95% CI: 0.94–3.99, P < 0.001) with statistical significance. Conclusions DIC is associated with the severity and poor prognosis of COVID-19 patients. Therefore, attention should be paid to coagulation dysfunction in COVID-19 patients. Monitoring of coagulation indicators may improve the prognosis of COVID-19 inpatients.