We report here details of steady-state and time-resolved spectroscopy of excitonic dynamics for Janus transition metal dichalcogenide monolayers, including MoSSe and WSSe, which were synthesized by low-energy implantation of Se into transition metal disulfides. Absorbance and photoluminescence spectroscopic measurements determined the room-temperature exciton resonances for MoSSe and WSSe monolayers. Transient absorption measurements revealed that the excitons in Janus structures form faster than those in pristine transition metal dichalcogenides by about 30% due to their enhanced electron−phonon interaction by the built-in dipole moment. By combining steady-state photoluminescence quantum yield and time-resolved transient absorption measurements, we find that the exciton radiative recombination lifetime in Janus structures is significantly longer than in their pristine samples, supporting the predicted spatial separation of the electron and hole wave functions due to the built-in dipole moment. These results provide fundamental insight in the optical properties of Janus transition metal dichalcogenides.

Defects in transition metal dichalcogenides (TMDs) play an important role in tailoring electrical and optical properties.Here we employ Ar + plasma to controllably generate active defects in WSe 2 monolayers to tune their optical properties. Two defect-activated PL emission peaks are emerging in the low temperature PL spectra of WSe 2 monolayer treated with Ar + plasma. These emissions are attributed to the recombination of excitons bound to different types of structural defects. The shallow level emission originates from the recombination of excitons at chalcogen vacancies, while the deep level emission might arise from other types of defects, such as transition metal vacancies, cluster of vacancies, rotational defects, or antisite defects. Our results demonstrate that Ar + plasma treatment is an effective approach to induce desirable defects in TMDs monolayers and PL spectroscopy is an efficient method to investigate these defects.

Abstract. Surface roughness has been considered as an important influencing factor for cell response. The aim of this study was to find out whether MC3T3-E1 cells, a mouse osteoblast-like cell line, can sense the amplitudes of surface topography of titanium alloy (Ti6Al4V), and if surface-dependent cell morphology would be presented on the substrata with varied roughness. A series of polished samples (R a : 0.30~1.80 µm) were prepared to produce macroscopically parallel grooves using different grades of silicon carbide sandpaper (#100, #320, #600, #1000 and #2000). The experimental results indicated that the behavior and morphology of cells largely depended on the substrata where they were cultured. More efficient proliferation of MC3T3-E1 cells was shown on the surfaces with R a of 0.50~1.00 µm, with respect to either the rougher or the smoother specimens. Furthermore, MC3T3-E1 cells seeded on the Ti6Al4V surfaces within this narrow range responded to the increasing surface roughness with increased proliferation. Contact guidance of cells could be observed on the rougher specimens (R a : 0.80~1.00 µm), whereas more random orientations were exhibited for the adsorbed cells on the smoother surfaces (R a : 0.50~0.60 µm).

Birefringent materials with large optical anisotropy, which can be used to modulate the polarization of light, play a key role in laser techniques and science. However, the exploration studies of new, superior birefringent materials develop extremely slowly due to the lack of effective guidelines for rational design. Herein, three antimony(III) fluoride oxalates, namely, Na 2 Sb 2 (C 2 O 4 )F 6 , K 2 Sb 2 (C 2 O 4 )F 6 , and Cs 2 Sb 2 -(C 2 O 4 ) 2 F 4 •H 2 O, were successfully synthesized through a rational combination of π-conjugated C 2 O 4 2− anions and Sb 3+ cations with stereochemically active lone pairs. These oxalates feature unique quasi-one-dimensional chain structures that induce large optical anisotropy. Remarkably, Cs 2 Sb 2 (C 2 O 4 ) 2 -F 4 •H 2 O exhibits the largest birefringence (0.325@546 nm) among all reported antimony(III)-based oxysalts. Detailed structural analysis and theoretical calculations confirmed that the optical anisotropy of these oxalates could be tuned through the synergetic interactions of templated cations and anionic functional groups. This work may open the door to efficiently designing excellent birefringent materials and guide the further discovery of other novel structure-driven functional materials.