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The exciton properties play a crucial role in controlling the optical properties of molybdenum disulfide (MoS2). In this work, horizontally oriented MoS2 (H-MoS2), horizontally and vertically oriented MoS2 (HV-MoS2), and vertically oriented MoS2 (V-MoS2) on the same SiO2/Si substrate have been synthesized and investigated using temperature-dependent photoluminescence spectroscopy from 7 to 300 K. Except for direct excitons called as A and B peaks, indirect exciton named as I peak is discovered with the splitting of three peaks. Compared with direct excitons, indirect excitons appear to be more susceptible to the orientation of MoS2. The exciton activation energies are larger, and the exciton–phonon coupling is stronger in V-MoS2 than in H-MoS2. The exciton properties of HV-MoS2 are more similar to those of V-MoS2, but there are some unusual phenomena. Our work provides a reference for optoelectronic applications based on transition-metal dichalcogenides represented by MoS2 grown with horizontal and vertical orientations. [ABSTRACT FROM AUTHOR]

The linear molybdenum disulfide (MoS2) with different nanostructures due to atomic arrangements is expected to show promising prospects in the next generation electronics and optoelectronic devices. In this work, three typical linear MoS2 nanostructures were grown on the SiO2/Si (285 nm, 500 μm) substrate by a modified chemical vapor deposition (CVD) method and were systematically analyzed by using angle-resolved polarized (ARP) Raman spectra. The results are as follows. The first and the second linear MoS2 are identified as nanoribbon-like structures with a tiled layered arrangement similar with the sheet MoS2, where the first linear MoS2 is grown directly on the substrate and the second linear MoS2 is coated on the upper surface of the cylindrical-shaped molybdenum oxide (MoO3). The third linear MoS2 is a nanotube-like structure, and its atomic structure includes vertical layered arrangement in addition. All three linear MoS2 produce a small-size effect, and the second linear MoS2 is more like an intermediate material between the first linear MoS2 and the third linear MoS2 during the growth of CVD. This study provides an effective approach to detect the optical anisotropy of linear nanostructures of two-dimensional materials which has potential applications in ARP optoelectronics devices. [ABSTRACT FROM AUTHOR]

Abstract Background Various expansions or contractions of inverted repeats (IRs) in chloroplast genomes led to fluxes in the IR-LSC (large single copy) junctions. Previous studies revealed that some monocot IRs contain a trnH-rps19 gene cluster, and it has been speculated that this may be an evidence of a duplication event prior to the divergence of monocot lineages. Therefore, we compared the organizations of genes flanking two IR-LSC junctions in 123 angiosperm representatives to uncover the evolutionary dynamics of IR-LSC junctions in basal angiosperms and monocots. Results The organizations of genes flanking IR-LSC junctions in angiosperms can be classified into three types. Generally each IR of monocots contains a trnH-rps19 gene cluster near the IR-LSC junctions, which differs from those in non-monocot angiosperms. Moreover, IRs expanded more progressively in monocots than in non-monocot angiosperms. IR-LSC junctions commonly occurred at polyA tract or A-rich regions in angiosperms. Our RT-PCR assays indicate that in monocot IRA the trnH-rps19 gene cluster is regulated by two opposing promoters, S10A and psbA. Conclusion Two hypotheses are proposed to account for the evolution of IR expansions in monocots. Based on our observations, the inclusion of a trnH-rps19 cluster in majority of monocot IRs could be reasonably explained by the hypothesis that a DSB event first occurred at IRB and led to the expansion of IRs to trnH, followed by a successive DSB event within IRA and lead to the expansion of IRs to rps19 or to rpl22 so far. This implies that the duplication of trnH-rps19 gene cluster was prior to the diversification of extant monocot lineages. The duplicated trnH genes in the IRB of most monocots and non-monocot angiosperms have distinct fates, which are likely regulated by different expression levels of S10A and S10B promoters. Further study is needed to unravel the evolutionary significance of IR expansion in more recently diverged monocots.

Self-assembled vertical heterostructure with a high interface-to-volume ratio offers tremendous opportunities to realize intriguing properties and advanced modulation of functionalities. Here, a heterostructure composed of two visible-light photocatalysts, BiFeO3 (BFO) and ε-Fe2O3 ( ε-FO), is designed to investigate its photoelectrochemical performance. The structural characterization of the BFO-FO heterostructures confirms the phase separation with BFO nanopillars embedded in the ε-FO matrix. The investigation of band structure of the heterojunction suggests the assistance of photoexcited carrier separation, leading to an enhanced photoelectrochemical performance. The insights into the charge separation are further revealed by means of ultrafast dynamics and electrochemical impedance spectroscopies. This work shows a delicate design of the self-assembled vertical heteroepitaxy by taking advantage of the intimate contact between two phases that can lead to a tunable charge interaction, providing a new configuration for the optimization of photoelectrochemical cell. [ABSTRACT FROM AUTHOR]