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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,729 records · Page 96
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Superabsorbing, Artificial Metal Films Constructed from Semiconductor Nanoantennas

In 1934, Wilhelm Woltersdorff demonstrated that the absorption of light in an ultrathin, freestanding film is fundamentally limited to 50%. He concluded that reaching this limit would require a film with a real-valued sheet resistance that is exactly equal to R = η/2 ≈ 188.5Ω/$\square$, where η=√μ 0 /ϵ 0 is the impedance of free space. This condition can be closely approximated over a wide frequency range in metals that feature a large imaginary relative permittivity ε r ", that is, a real-valued conductivity σ = ε 0 ε r "ω. A thin, continuous sheet of semiconductor material does not facilitate such strong absorption as its complex-valued permittivity with both large real and imaginary components preclude effective impedance matching. Here, we show how a semiconductor metafilm constructed from optically resonant semiconductor nanostructures can be created whose optical response mimics that of a metallic sheet. Because of this reason, the fundamental absorption limit mentioned above can also be reached with semiconductor materials, opening up new opportunities for the design of ultrathin optoelectronic and light harvesting devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Resilient Pathways to Atomic Attachment of Quantum Dot Dimers and Artificial Solids from Faceted CdSe Quantum Dot Building Blocks

Here, the goal of this work is to identify favored pathways for preparation of defect-resilient attached wurtzite CdX (X = S, Se, Te) nanocrystals. We seek guidelines for oriented attachment of faceted nanocrystals that are most likely to yield pairs of nanocrystals with either few or no electronic defects or electronic defects that are in and of themselves desirable and stable. Using a combination of in situ high-resolution transmission electron microscopy (HRTEM) and electronic structure calculations, we evaluate the relative merits of atomic attachment of wurtzite CdSe nanocrystals on the {1$\bar{10}$0} or {11$\bar{20}$} family of facets. Pairwise attachment on either facet can lead to perfect interfaces, provided the nanocrystal facets are perfectly flat and the angles between the nanocrystals can adjust during the assembly. Considering defective attachment, we observe for {1$\bar{10}$0} facet attachment that only one type of edge dislocation forms, creating deep hole traps. For {11$\bar{20}$} facet attachment, we observe that four distinct types of extended defects form, some of which lead to deep hole traps whereas others only to shallow hole traps. HRTEM movies of the dislocation dynamics show that dislocations at {1$\bar{10}$0} interfaces can be removed, albeit slowly. Whereas only some extended defects at {11$\bar{20}$} interfaces could be removed, others were trapped at the interface. Based on these insights, we identify the most resilient pathways to atomic attachment of pairs of wurtzite CdX nanocrystals and consider how these insights can translate to the creation of electronically useful materials from quantum dots with other crystal structures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Potential of nanocrystalline cellulose-fibrin nanocomposites for artificial vascular graft applications

Nanocrystalline cellulose, a new bio-nanomaterial is utilized as a reinforcing material for biocompatible fibrin matrix to form into a nanocomposite for small-diameter replacement vascular graft application (SDRVG). The periodate oxidation of NCC, which provided it with a reactive carbonyl group, allowed molecular interaction between NCC and fibrin. Such interaction resulted into an effective mechanical reinforcement indicated by the improvement of max. force, elongation at break and modulus when oxidized NCC (ONCC) was incorporated into fibrin. The nanocomposite’s mechanical properties can be manipulated to conform to the native blood vessel by varying the ONCC to fibrin ratio and/or by controlling the degree of oxidation of NCC. Using atomic force microscopy had provided fundamental information on the effects of molecular interactions to the nanolevel mechanical properties of NCC/fibrin nanocomposites. This fundamental information established the positive feasibility and commenced continuing investigation for the practical SDRVG application of NCC/fibrin nanocomposite.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2020

An Artificial Z-Scheme Constructed from Dye-Sensitized Metal Oxide Nanosheets for Visible Light-Driven Overall Water Splitting

Sensitization of a wide-gap oxide semiconductor with a visible-light-absorbing dye has been studied for decades as a means of producing H 2 from water. However, efficient overall water splitting using a dye-sensitized oxide photocatalyst has remained an unmet challenge. Here in this paper we demonstrate visible-light-driven overall water splitting into H 2 and O 2 using HCa 2 Nb 3 O 10 nanosheets sensitized by a Ru(II) tris-diimine type photosensitizer, in combination with a WO 3 -based water oxidation photocatalyst and a triiodide/iodide redox couple. With the use of Pt-intercalated HCa 2 Nb 3 O 10 nanosheets further modified with amorphous Al 2 O 3 clusters as the H 2 evolution component, the dye-based turnover number and frequency for H 2 evolution reached 4580 and 1960 h –1 , respectively. The apparent quantum yield for overall water splitting using 420 nm light was 2.4%, by far the highest among dye- sensitized overall water splitting systems reported to date. The present work clearly shows that a carefully designed dye/oxide hybrid has great potential for photocatalytic H 2 production, and represents a significant leap forward in the development of solar-driven water splitting systems.

14 SOLAR ENERGY↗