Recent progress in terahertz modulation using photonic structures based on two-dimensional materials

Terahertz(THz)technology has attracted great attention in the past few decades for its unique applications in various fields,including spectroscopy,noninvasive detection,wireless communications,and imaging.In parallel to this,the practical,fast,and broadband modulation of THz waves is becoming indispensable.Two-dimensional(2D)materials exhibit unusual optical and electrical properties,which has prompted tremendous interest and significant advances in THz modulation.This review provides the recent progress in 2D materials-based THz modulators,outlining the operating principles,including all-optical,electro-optic,magneto-optic,and other exotic mechanisms.We focus on the recent advances in THz modulation by the designed photonic structures,such as heterostructure,metamaterial,capacitor,optical cavity,and waveguide integration.Lastly,we discussed the challenges and opportunities for 2D materials-based THz modulators and presented our prospects for the future development.

Surface energy-driven solution epitaxial growth of anatase TiO2 homostructures for overall water splitting

Titanium dioxide(TiO2)has been extensively investigated as a photocatalyst for water splitting to produce H2.However,an overall water splitting by using anatase TiO2 is extremely difficult due to the short lifetime of holes.In this work,we propose that a surface energy decrease from{001}to{101}of anatase TiO2 is able to drive an epitaxial growth.A novel anatase TiO2 homostructure has been successfully synthesized via a facile hydrothermal route,where{101}semi-pyramid nanoparticles epitaxially grew on the both sides of the{001}nanosheets.The epitaxial relationship between the nanoparticles and the nanosheets has been characterized to be{001}//{001}of anatase TiO2.For the first time,it is interesting to find that the homostructure with 12 wt%of{101}semi-pyramid can significantly improve the H2 evolution rate by nearly 5 times compared to the pure nanosheets under the ultraviolet irradiation.More importantly,such homostructure enables 10.78μmol g-1h-1 of O2 production whereas the pure nanosheets cannot evolve detectable O2 gas.Meanwhile,the time-resolved photoluminescence analysis indicates that the mean lifetime of the holes is increased from 2.20 ns of the nanosheets to 3.59 ns of the homostructure,accounting for the observed overall water splitting.The findings suggest that constructing a homostructure by a surface energy strategy could be promising towards overall water splitting,which may be applicable to other photocatalytic materials.