278 research outputs found
New multi stimuli-responsive organic semiconductors for smart materials
Tesis Doctoral inédita leÃda en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de QuÃmica Orgánica. Fecha de Lectura: 20-07-2021La financiación de este trabajo ha provenido del Ministerio de EconomÃa y Competitividad (CTQ2016-78557-R y PID2019-104125RB-I00
Strong interlayer coupling in van der Waals heterostructures built from single-layer chalcogenides
Semiconductor heterostructures are the fundamental platform for many
important device applications such as lasers, light-emitting diodes, solar
cells and high-electron-mobility transistors. Analogous to traditional
heterostructures, layered transition metal dichalcogenide (TMDC)
heterostructures can be designed and built by assembling individual
single-layers into functional multilayer structures, but in principle with
atomically sharp interfaces, no interdiffusion of atoms, digitally controlled
layered components and no lattice parameter constraints. Nonetheless, the
optoelectronic behavior of this new type of van der Waals (vdW) semiconductor
heterostructure is unknown at the single-layer limit. Specifically, it is
experimentally unknown whether the optical transitions will be spatially direct
or indirect in such hetero-bilayers. Here, we investigate artificial
semiconductor heterostructures built from single layer WSe2 and MoS2 building
blocks. We observe a large Stokes-like shift of ~100 meV between the
photoluminescence peak and the lowest absorption peak that is consistent with a
type II band alignment with spatially direct absorption but spatially indirect
emission. Notably, the photoluminescence intensity of this spatially indirect
transition is strong, suggesting strong interlayer coupling of charge carriers.
The coupling at the hetero-interface can be readily tuned by inserting
hexagonal BN (h-BN) dielectric layers into the vdW gap. The generic nature of
this interlayer coupling consequently provides a new degree of freedom in band
engineering and is expected to yield a new family of semiconductor
heterostructures having tunable optoelectronic properties with customized
composite layers.Comment: http://www.pnas.org/content/early/2014/04/10/1405435111.abstrac
Combating Global Warming: Modeling Enhanced Rock Weathering of Wollastonite Using Density Functional Theory
Negative emissions technologies target the removal of carbon dioxide from the atmosphere as a way of combating global warming. Enhanced rock weathering (ERW) is a vital negative emissions technology that applied globally could remove gigatons of carbon dioxide per year from the atmosphere. In ERW, silicate minerals exposed to the atmosphere trap CO2 via mineral carbonation as thermodynamically stable carbonates. To obtain an atomic scale understanding of the weathering process and to design more reactive silicates for enhanced rock weathering, carbon dioxide adsorption on low Miller index wollastonite (CaSiO3) surfaces was modeled using density functional theory. Atomic scale structure of (100), (010), and (001) surfaces of wollastonite was predicted and the thermodynamics of their interaction with carbon dioxide was modeled. Based on surface energy calculations, (001) and (010) surfaces of wollastonite exhibit similar stabilities, while (100) surface is found to be least stable. Depending on the surface structure and chemistry, different carbon dioxide adsorption geometries are possible. A common trend emerges, wherein carbon dioxide adsorbs molecularly and demonstrates proclivity to bond with surface layer calcium and oxygen binding sites. Mechanisms for electronic charge transfer between the adsorbate and the substrate were studied to shed light on the fundamental aspects of these interactions. The most favorable bent dioxide geometry was bridged between calcium atoms, revealing that the enhancement of the likelihood of this geometry and binding site could pave the way to designing reactive silicates for efficient carbon dioxide sequestration via ERW
Artificial Intelligence in Material Engineering: A review on applications of AI in Material Engineering
Recently, there has been extensive use of artificial Intelligence (AI) in the
field of material engineering. This can be attributed to the development of
high performance computing and thereby feasibility to test deep learning models
with large parameters. In this article we tried to review some of the latest
developments in the applications of AI in material engineering.Comment: V
NASA Thesaurus. Volume 2: Access vocabulary
The NASA Thesaurus -- Volume 2, Access Vocabulary -- contains an alphabetical listing of all Thesaurus terms (postable and nonpostable) and permutations of all multiword and pseudo-multiword terms. Also included are Other Words (non-Thesaurus terms) consisting of abbreviations, chemical symbols, etc. The permutations and Other Words provide 'access' to the appropriate postable entries in the Thesaurus
NASA Thesaurus. Volume 1: Hierarchical listing
There are 16,713 postable terms and 3,716 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary
NASA thesaurus. Volume 1: Hierarchical Listing
There are over 17,000 postable terms and nearly 4,000 nonpostable terms approved for use in the NASA scientific and technical information system in the Hierarchical Listing of the NASA Thesaurus. The generic structure is presented for many terms. The broader term and narrower term relationships are shown in an indented fashion that illustrates the generic structure better than the more widely used BT and NT listings. Related terms are generously applied, thus enhancing the usefulness of the Hierarchical Listing. Greater access to the Hierarchical Listing may be achieved with the collateral use of Volume 2 - Access Vocabulary and Volume 3 - Definitions
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