The idea of fabricating artificial solids with band structures tailored to particular applications has long fascinated condensed matter physicists. Heterostructure (HS) construction is viewed as an effective and appealing approach to engineer novel electronic properties in two dimensional (2D) materials. Different from common 2D/2D heterojunctions where energy transfer is rarely observed, CsPbBr quantum dots (0D-QDs) interfaced with 2D materials have become attractive HSs for exploring the physics of charge transfer and energy transfer, due to their superior optical properties. In this paper, a new 0D/2D HS is proposed and experimentally studied, making it possible to investigate both light utilization and energy transfer. Specifically, this HS is constructed between monolayer WS and CsPbBr QDs, and exhibits a hybrid band alignment. The dynamics of energy transfer within the investigated 0D/2D HS is characterized by femtosecond transient absorption spectrum (TAS) measurements. The TAS results reveal that ultrafast energy transfer caused by optical excitation is observed from CsPbBr QDs to the WS layer, which can increase the exciton fluence within the WS layer up to 69% when compared with pristine ML WS under the same excitation fluence. Moreover, the formation and dynamics of interlayer excitons have also been investigated and confirmed in the HS, with a calculated recombination time of 36.6 ps. Finally, the overall phenomenological dynamical scenario for the 0D/2D HS is established within the 100 ps time region after excitation. The techniques introduced in this work can also be applied to versatile optoelectronic devices based on low dimensional materials.
The intact fruits of preclimacteric tomato (Lycopersicon escukntum Mill) or cantaloupe (Cucumis melo L.) produced very little ethylene and had low capability of converting 1-aminocyclopropane-l-carboxylic acid (ACC) to ethylene. When these unripe tomato or cantaloupe fruits were treated with ethylene for 16 hours there was no increase in ACC content or in ethylene production rate, but the tissue's capability to convert ACC to ethylene increased markedly. Such an effect was also observed in fruits of tomato mutants rin and nor, which do not undergo ripening and the climacteric increase in ethylene production during the senescence. The development of this ethylene-forming capability induced by ethylene increased with increasing ethylene concentration (from 0.1 to 100 microliters per liter) and duration (I to 24 hours), when ethylene was removed this capability remained high for sometime (more than 24 hours). Norbornadiene, a competitive inhibitor of ethylene action, effectively eliminated the promotive effect of ethylene in tomato fruit. These data indicate that the development of the capability to convert ACC to ethylene in preclimacteric tomato and cantaloupe fruits are sensitive to ethylene treatment and that when these fruits are exposed to exogenous ethylene, the increase in ethylene-forming enzyme precedes the increase in ACC synthase.Climacteric fruits are characterized by a surge in ethylene production at the onset of ripening and ethylene treatment is known to hasten such a process. This phenomenon is referred to as autocatalytic ethylene production (1). The pathway ofethylene biosynthesis has been demonstrated to be: Met4 --SAM -. ACC ethylene by Adams and Yang (2). Since preclimacteric (unripe) fruits lack both ACC synthase and EFE, a massive increase in ethylene production requires development of both enzymes (20). It has been shown that at the onset of ripening, ACC synthase activity increases which is accompanied by an increase in ACC content (3,8,10,18 from the field when the fruits weighing approximately 500 g were still green externally and internally, and the netting of the fruits was incompletely developed; they were stored overnight at 25°C before use. Only those fruits producing less than 0.2 nl g-' h-' ethylene were used in experiments. For ethylene treatments intact fruits (two or more) or discs, which were cut from pericarp tissue of tomato fruits with a cork borer (0.5 cm diameter) and placed on a moistened paper in a Petri dish, were enclosed in 8.6-L jars containing a cup of KOH solution for absorbing CO2 released from tissues. The appropriate amount of ethylene was introduced by syringe and the concentration of ethylene was verified by gas chromatography. In ethylene-free air treatments a cup of Hg(Cl04)2 solution was placed in the jar; this kept the ethylene concentration below 0.02 ul 1`during the treatment period. In NDE treatment, appropriate amount of NDE was injected with a syringe into a piece of paper hung in the jar to facilitate evaporation. The concentration of NDE ...
Graphical Abstract Highlights d The Chengjiang euarthropod Ercaicunia multinodosa preserves appendages in 3D d Head appendages include antennulae, differentiated antennae, mandibles, and maxillae d Trunk appendages are biramous with proximal epipodites d Ercaicunia represents the first stem-group pancrustacean known from macrofossils
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