Contrasting Cloud Radiative Feedbacks during Warm Pool and Cold Tongue El Ninos

The study presents the contrasting characteristics of cloud-radiative feedbacks to the cold tongue (CT) and warm pool (WP) El Niño (EN). The maximum sea surface temperature anomalies (SSTA) of the CT-EN are located in the far-eastern Pacific. However, the maximum responses of the shortwave- and longwave- cloud-radiative forcing (SWCRF and LWCRF) to the CT-EN warming are centered near the dateline, showing 70° westward shift relative to the maximum SSTA center of CT-WN. In contrast, the maximum responses of the SWCRF and LWCRF to the WP-EN warming show only slight westward shift relative to the maximum SSTA center. The contrasting cloud-radiative feedbacks to the two types of ENs can be traced back to the contrasting precipitation feedbacks, which is associated with the convection threshold. When the warm SSTA of CT-EN occurs in the relatively cold eastern Pacific, the total SST in-situ may not exceed the convection threshold. Therefore, the induced precipitation anomaly would occur towards the warm western Pacific, and the corresponding cloud cover and cloud-radiative feedbacks would exhibit an apparent westward shift. As the warm SSTA of WP-EN occurs in the relatively warm central Pacific, the corresponding responses of the anomalous fields to the WP-EN show only slight westward displacement

Single layer MoS2 on the Cu(111) surface: First-principles electronic structure calculations

First-principles calculations of the geometric and electronic structures of a single layer of molybdenum disulfide (MoS2) on Cu(111) utilizing the van der Waals density functional show three energetically equivalent stacking types and a Moire pattern whose periodicity is in agreement with experimental findings. The layer is found not to be purely physisorbed on the surface, rather there exists a chemical interaction between it and the Cu surface atoms. We also find that the MoS2 film is not appreciably buckled, while the top Cu layer gets reorganized and vertically disordered. The sizes of Moire patterns for a single layer of MoS2 adsorbed on other close-packed metal surfaces are also estimated by minimizing the lattice mismatch between the film and the substrate

Anisotropic Singlet Fission in Single Crystalline Hexacene

Singlet fission is known to improve solar energy utilization by circumventing the Shockley-Queisser limit. The two essential steps of singlet fission are the formation of a correlated triplet pair and its subsequent quantum decoherence. However, the mechanisms of the triplet pair formation and decoherence still remain elusive. Here we examined both essential steps in single crystalline hexacene and discovered remarkable anisotropy of the overall singlet fission rate along different crystal axes. Since the triplet pair formation emerges on the same timescale along both crystal axes, the quantum decoherence is likely responsible for the directional anisotropy. The distinct quantum decoherence rates are ascribed to the notable difference on their associated energy loss according to the Redfield quantum dissipation theory. Our hybrid experimental/theoretical framework will not only further our understanding of singlet fission, but also shed light on the systematic design of new materials for the third-generation solar cells

Effective elastic properties of a van der Waals molecular monolayer at a metal surface

Adsorbing anthracene on a Cu(111) surface results in a wide range of complex and intriguing superstructures spanning a coverage range from 1 per 17 to 1 per 15 substrate atoms. In accompanying first-principles density-functional theory calculations we show the essential role of van der Waals interactions in estimating the variation in anthracene adsorption energy and height across the sample. We can thereby evaluate the compression of the anthracene film in terms of continuum elastic properties, which results in an effective Young\u27s modulus of 1.5 GPa and a Poisson ratio approximate to 0.1. These values suggest interpretation of the molecular monolayer as a porous material-in marked congruence with our microscopic observations

Thin Film Morphology Control by Mechanical, Electronic and Chemical Interactions: a Scanning Tunneling Microscopy and Photoelectron Spectroscopy Study

Thin film growth technology develops rapidly with the requirement of understanding the mechanical and electronic interaction and how they will control the Morphology of the film. Self-assembly of the organic molecules on metal substrate provide a bottom-up path toward building up desires conformation for nanotechnology application. In this study, STM and Photoelectron Spectroscopy have been used to investigate monolayer or sub-monolayer thin film grown on Cu(111) substrate. To be more specific, The films I investigate are monolayer MoS2 formed by strong covalent bonding between Mo and S atoms, Anthracene thin film formed by weak van der Waals interaction and Anthraquinone (AQ) honeycomb network form by hydrogen bonding and other long range surface mediated interaction. My research interest is using STM, XPS and ARUPS to investigate what is the role of these interactions during the growth of the thin film and how to control the film morphology by controlling these interactions

Toward The Growth Of An Aligned Single-Layer Mos2 Film

Molybdenum disulfide (molybdenite) monolayer islands and flakes have been grown on a copper surface at comparatively low temperature and mild conditions through sulfur loading of the substrate using thiophenol (benzenethiol) followed by the evaporation of Mo atoms and annealing. The MoS2 islands show a regular Moiré pattern in scanning tunneling microscopy, attesting to their atomic ordering and high quality. They are all aligned with the substrate high-symmetry directions providing for rotational-domain-free monolayer growth. © 2011 American Chemical Society

An Mos X Structure With High Affinity For Adsorbate Interaction

An Mo 2S 3 monolayer grown on copper coexists with well-known MoS 2 patches and triangular islands. Imaging by scanning tunneling microscopy after exposure to anthraquinone shows the new structure to be far more active in adsorption, permitting even the formation of a compressed adsorbate layer before other surface areas, including the supposedly reactive brim areas of MoS 2 islands, capture this adsorbate. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim