The Effects of Immobilization Stress on the Synthesis and the Catabolism of Dopamine and Norepinephrine in the Rat Hypothalamus

Immobilization stress was adopted as a prototype stress model for studying the effects of stress on dopaminergic and noradrenergic neuronal activity in the rat hypothalamus. Norepinephrine content was significantly increased after 4 hours of immobilization stress. Also, the turnover rates of both dopamine and norepinephrine were found to be significantly increased after the stress, providing the evidence of increased synthesis rates of both neurotransmitters. These findings were consistent with the increase in plasma corticosterone and catecholamine levels. The activities of tyrosine hydroxylase and dopamine-j1-hydroxylase, the synthesizing enzymes for catecholamines, were significantly increased after the stress, while that of monoamine oxidase, the catabolizing enzyme, did not change to a significant degree at all. Kinetic analysis of tyrosine hydroxylase, the rate-limiting step in catecholamine biosynthesis, revealed that Vmax was significantly increased after the stress without significant change of Km. These findings suggest that dopamine and norepinephrine may playa significant role in mediating stress responses by increasing their neuronal activities

Monolayer optical memory cells based on artificial trap-mediated charge storage and release.

Monolayer transition metal dichalcogenides are considered to be promising candidates for flexible and transparent optoelectronics applications due to their direct bandgap and strong light-matter interactions. Although several monolayer-based photodetectors have been demonstrated, single-layered optical memory devices suitable for high-quality image sensing have received little attention. Here we report a concept for monolayer MoS2 optoelectronic memory devices using artificially-structured charge trap layers through the functionalization of the monolayer/dielectric interfaces, leading to localized electronic states that serve as a basis for electrically-induced charge trapping and optically-mediated charge release. Our devices exhibit excellent photo-responsive memory characteristics with a large linear dynamic range of ∼4,700 (73.4 dB) coupled with a low OFF-state current (<4 pA), and a long storage lifetime of over 104 s. In addition, the multi-level detection of up to 8 optical states is successfully demonstrated. These results represent a significant step toward the development of future monolayer optoelectronic memory devices

Charge transport modulation of a flexible quantum dot solar cell using a piezoelectric effect

Colloidal quantum dots are promising materials for flexible solar cells, as they have a large absorption coefficient at visible and infrared wavelengths, a band gap that can be tuned across the solar spectrum, and compatibility with solution processing. However, the performance of flexible solar cells can be degraded by the loss of charge carriers due to recombination pathways that exist at a junction interface as well as the strained interface of the semiconducting layers. The modulation of the charge carrier transport by the piezoelectric effect is an effective way of resolving and improving the inherent material and structural defects. By inserting a porous piezoelectric poly(vinylidenefluoride‐trifluoroethylene) layer so as to generate a converging electric field, it is possible to modulate the junction properties and consequently enhance the charge carrier behavior at the junction. This study shows that due to a reduction in the recombination and an improvement in the carrier extraction, a 38% increase in the current density along with a concomitant increase of 37% in the power conversion efficiency of flexible quantum dots solar cells can be achieved by modulating the junction properties using the piezoelectric effect

Consecutive Junction-Induced Efficient Charge Separation Mechanisms for High-Performance MoS2/Quantum Dot Phototransistors.

Phototransistors that are based on a hybrid vertical heterojunction structure of two-dimensional (2D)/quantum dots (QDs) have recently attracted attention as a promising device architecture for enhancing the quantum efficiency of photodetectors. However, to optimize the device structure to allow for more efficient charge separation and transfer to the electrodes, a better understanding of the photophysical mechanisms that take place in these architectures is required. Here, we employ a novel concept involving the modulation of the built-in potential within the QD layers for creating a new hybrid MoS2/PbS QDs phototransistor with consecutive type II junctions. The effects of the built-in potential across the depletion region near the type II junction interface in the QD layers are found to improve the photoresponse as well as decrease the response times to 950 μs, which is the faster response time (by orders of magnitude) than that recorded for previously reported 2D/QD phototransistors. Also, by implementing an electric-field modulation of the MoS2 channel, our experimental results reveal that the detectivity can be as large as 1 × 1011 jones. This work demonstrates an important pathway toward designing hybrid phototransistors and mixed-dimensional van der Waals heterostructures.The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007−2013)/ERC Grant Agreement no. 340538. This work was also supported by the National Research Foundation of Korea (NRF) (2015M2A2A6A02045252) and Samsung Global Research Outreach (Samsung GRO) program. In addition, S.M.M. would like to thank The Royal Society for financial support

Balancing charge carriertransport in a quantum dot P-N junction toward hysteresis-free high-performance solar cells

In a quantum dot solar cell (QDSC) that has an inverted structure, the QD layers form two different junctions between the electron transport layer (ETL) and the other semiconducting QD layer. Recent work on an inverted-structure QDSC has revealed that the junction between the QD layers is the dominant junction, rather than the junction between the ETL and the QD layers, which is in contrast to the conventional wisdom. However, to date, there have been a lack of systematic studies on the role and importance of the QD heterojunction structure on the behavior of the solar cell and the resulting device performance. In this study, we have systematically controlled the structure of the QD junction to balance charge transport, which demonstrates that the position of the junction has a significant effect on the hysteresis effect, fill factor, and solar cell performance and is attributed to balanced charge transport

Balancing Charge Carrier Transport in a Quantum Dot P-N Junction toward Hysteresis-Free High-Performance Solar Cells.

In a quantum dot solar cell (QDSC) that has an inverted structure, the QD layers form two different junctions between the electron transport layer (ETL) and the other semiconducting QD layer. Recent work on an inverted-structure QDSC has revealed that the junction between the QD layers is the dominant junction, rather than the junction between the ETL and the QD layers, which is in contrast to the conventional wisdom. However, to date, there have been a lack of systematic studies on the role and importance of the QD heterojunction structure on the behavior of the solar cell and the resulting device performance. In this study, we have systematically controlled the structure of the QD junction to balance charge transport, which demonstrates that the position of the junction has a significant effect on the hysteresis effect, fill factor, and solar cell performance and is attributed to balanced charge transport

Strain-Mediated Interlayer Coupling Effects on the Excitonic Behaviors in an Epitaxially Grown MoS2/WS2 van der Waals Heterobilayer.

van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS2/WS2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS2 to MoS2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices

Evolution of local structural motifs in colloidal quantum dot semiconductor nanocrystals leading to nanofaceting

Colloidal nanocrystals (NCs) have shown remarkable promise for optoelectronics, energy harvesting, photonics, and biomedical imaging. In addition to optimizing quantum confinement, the current challenge is to obtain a better understanding of the critical processing steps and their influence on the evolution of structural motifs. Computational simulations and electron microscopy presented in this work show that nanofaceting can occur during nanocrystal synthesis from a Pb-poor environment in a polar solvent. This could explain the curved interfaces and the olivelike-shaped NCs observed experimentally when these conditions are employed. Furthermore, the wettability of the PbS NCs solid film can be further modified via stoichiometry control, which impacts the interface band bending and, therefore, processes such as multiple junction deposition and interparticle epitaxial growth. Our results suggest that nanofaceting in NCs can become an inherent advantage when used to modulate band structures beyond what is traditionally possible in bulk crystals