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Results for “single nanowire”

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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206 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

n-Type doping of a solution processed p-type semiconductor using isoelectronic surface dopants for homojunction fabrication

The p-n junction is one of the fundamental requirements for a practical semiconductor-based electronic device. Designing a heterojunction comprising of dissimilar p-type and n-type semiconductors calls for careful energy level considerations, both when selecting the semiconductor materials as well as the metal contacts. A homojunction based on a single semiconductor simplifies this task, as energy levels of the p-type and n-type materials are already fairly similar, allowing for easier selection of contacts. Traditionally, homojunctions rely on doping of a bulk semiconductor to achieve p- and n-type transport through controlled addition of aliovalent dopants via energy-intensive processes such as ion implantation or thermal annealing. Exact control of doping in nanocrystalline semiconductors is significantly more challenging, due to self-purification effects. However, owing to their large surface areas, surface moieties can be utilized to both dope the nanostructures as well as tune their energy levels. Here, we present a facile technique based on an isoelectronic surface dopant in order to achieve p- and n-type materials based on the same semiconductor. We show that thin p-type colloidal Bi 2 Te 3 nanowires can be switched to n-type through surface functionalization, thus increasing the availability of new nanocrystalline solution-processable p-n homojunctions.

42 ENGINEERING↗
DOE OSTI2024

Measuring the Electronic Bandgap of Carbon Nanotube Networks in Non-Ideal p-n Diodes

The measurement of the electronic bandgap and exciton binding energy in quasi-one-dimensional materials such as carbon nanotubes is challenging due to many-body effects and strong electron–electron interactions. Unlike bulk semiconductors, where the electronic bandgap is well known, the optical resonance in low-dimensional semiconductors is dominated by excitons, making their electronic bandgap more difficult to measure. In this work, we measure the electronic bandgap of networks of polymer-wrapped semiconducting single-walled carbon nanotubes (s-SWCNTs) using non-ideal p-n diodes. We show that our s-SWCNT networks have a short minority carrier lifetime due to the presence of interface trap states, making the diodes non-ideal. We use the generation and recombination leakage currents from these non-ideal diodes to measure the electronic bandgap and excitonic levels of different polymer-wrapped s-SWCNTs with varying diameters: arc discharge (~1.55 nm), (7,5) (0.83 nm), and (6,5) (0.76 nm). Our values are consistent with theoretical predictions, providing insight into the fundamental properties of networks of s-SWCNTs. The techniques outlined here demonstrate a robust strategy that can be applied to measuring the electronic bandgaps and exciton binding energies of a broad variety of nanoscale and quantum-confined semiconductors, including the most modern nanoscale transistors that rely on nanowire geometries.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Corrosion of Commercial Mg–Al Alloys: AZ31B, AM60, and AZ91D

Aqueous corrosion, atmospheric corrosion, and ionic liquid dissolution studies were performed on commercial alloys AZ31B, AM60, and AZ91D and compared with previously reported results for single-phase binary Mg–Al alloys containing similar Al concentrations (αMg-2 at% Al, αMg-5 at% Al, and Mg-8 at% Al). Polarization studies in 0.6 M NaCl were used to characterize the aqueous free corrosion behavior during 20-h free immersion. Accelerated corrosion testing was performed using a rotating-disk electrode which revealed the evolution of an Al-rich mud-cracking and platelet morphology. Atmospheric droplet testing showed rapid pH increases that depended on the Al concentration in the alloy. Time-dependent contact angle measurements showed that the degree of droplet wetting increased during free corrosion by ~50° over 20 h in 0.6 M NaCl. Ionic liquid dissolution studies in 1:2 M choline chloride:urea deep eutectic solvent were performed in order to examine the current-voltage behavior of these alloys in the absence of water and hydrogen reduction. The results of these studies revealed the formation of nanowire corrosion morphologies within a honeycomb lattice structure which we attribute to selective dissolution of Mg via a two-dimensional stepflow process

25 ENERGY STORAGE↗
DOE OSTI2022

3ω techniques for measurement of volumetric heat capacity and anisotropic thermal conductivity of a solution processable, hybrid organic/inorganic film, Te-PEDOT:PSS

We report that measuring the thermal properties of anisotropic films of hybrid materials poses a challenge to existing metrology techniques. We have developed a new approach for measuring the volumetric heat capacity and anisotropic thermal conductivity of these systems using the 3ω method. While there exist many avenues for measuring the thermal properties of thin films, most carry with them difficult requirements such as smooth surfaces or advanced lithography. Here, we present measurements of a film's in-plane and cross-plane conductance and its volumetric heat capacity using relatively simple sample configurations, each requiring a single heater. For the measurement of volumetric heat capacity, we present a new model fitting method, relying on a standard film-on-substrate configuration. For the measurement of in-plane thermal conductance by 3ω, we have developed the use of an embedded micro-wire heater in suspended drop cast films, allowing for a 12 μm wide heater without the need for advanced lithography. We also expose the surprisingly significant effect of thermal radiation in the suspended film measurement and its associated error. Our measurements reveal a large anisotropy in the thermal conductivity of our test material, Te-PEDOT:PSS, of k in-plane / k cross-plane = 19, consistent with the nanoscale morphology of the material.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Three-dimensional super line-localization in low signal-to-noise microscope images via prior-apprised unsupervised learning (PAUL)

Biological processes such as processive enzyme turnover and intracellular cargo tracking involve the dynamic motion of a small "article" along a curvilinear biopolymer track. To understand these processes that occur across multiple length and time scales, one must acquire both the trajectory of the particle and the position of the track along which it moves, possibly by combining high-resolution single-particle tracking with conventional microscopy. Yet, usually there is a significant resolution mismatch between these modalities: while the tracked particle is localized with a precision of 10 nm, the image of the surroundings is limited by optical difraction, with 200 nm lateral and 500 nm axial resolutions. Compared to the particle's trajectory, the surrounding curvilinear structure appears as a blurred and noisy image. This disparity in the spatial resolutions of the particle trajectory and the surrounding curvilinear structure image makes data reconstruction, as well as interpretation, particularly challenging. Analysis is further complicated when the curvilinear structures are oriented arbitrarily in 3D space. Here, we present a prior-apprised unsupervised learning (PAUL) approach to extract information from 3D images where the underlying features resemble a curved line such as a filament or microtubule. This three-stage framework starts with a Hessian-based feature enhancement, which is followed by feature registration, where local line segments are detected on repetitively sampled subimage tiles. In the final stage, statistical learning, segments are clustered based on their geometric relationships. Principal curves are then approximated from each segment group via statistical tools including principal component analysis, bootstrap and kernel transformation. This procedure is characterized on simulated images, where sub-voxel medium deviations from true curves have been achieved. The 3D PAUL approach has also been implemented for successful line localization in experimental 3D images of gold nanowires obtained using a multifocal microscope. Lastly, this work not only bridges the resolution gap between two microscopy modalities, but also allows us to conduct 3D super line-localization imaging experiments, without using super-resolution techniques.

42 ENGINEERING↗
DOE OSTI2021

The Surface Chemistry and Structure of Colloidal Lead Halide Perovskite Nanocrystals

Since the initial discovery of colloidal lead halide perovskite nanocrystals, there has been significant interest placed on these semiconductors because of their remarkable optoelectronic properties, including very high photoluminescence quantum yields, narrow size- and composition-tunable emission over a wide color gamut, defect tolerance, and suppressed blinking. These material attributes have made them attractive components for next-generation solar cells, light emitting diodes, low-threshold lasers, single photon emitters, and X-ray scintillators. While a great deal of research has gone into the various applications of colloidal lead halide perovskite nanocrystals, comparatively little work has focused on the fundamental surface chemistry of these materials. While the surface chemistry of colloidal semiconductor nanocrystals is generally affected by their particle morphology, surface stoichiometry, and organic ligands that contribute to the first coordination sphere of their surface atoms, these attributes are markedly different in lead halide perovskite nanocrystals because of their ionicity. Herein, emerging work on the surface chemistry of lead halide perovskite nanocrystals is highlighted, with a particular focus placed on the most-studied composition of CsPbBr 3 . We begin with an in-depth exploration of the native surface chemistry of as-prepared, 0-D cuboidal CsPbBr 3 nanocrystals, including an atomistic description of their surface termini, vacancies, and ionic bonding with ligands. We then proceed to discuss various post-synthetic surface treatments that have been developed to increase the photoluminescence quantum yields and stability of CsPbBr 3 nanocrystals, including the use of tetraalkylammonium bromides, metal bromides, zwitterions, and phosphonic acids, and how these various ligands are known to bind to the nanocrystal surface. To underscore the effect of post-synthetic surface treatments on the application of these materials, we focus on lead halide perovskite nanocrystal-based light emitting diodes, and the positive effect of various surface treatments on external quantum efficiencies. We also discuss the current state-of-the-art in the surface chemistry of 1-D nanowires and 2-D nanoplatelets of CsPbBr 3 , which are more quantum confined than the corresponding cuboidal nanocrystals but also generally possess a higher defect density because of their increased surface area-to-volume ratios.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Entangled two-plasmon generation in carbon nanotubes and graphene-coated wires

Here, we investigate the two-plasmon spontaneous decay of a quantum emitter near single-walled carbon nanotubes (SWCNTs) and graphene-coated wires (GCWs). We demonstrate efficient, enhanced generation of two-plasmon entangled states in SWCNTs due to the strong coupling between tunable guided plasmons and the quantum emitter. We predict two-plasmon emission rates more than twelve orders of magnitude higher than in free space, with average lifetimes of a few dozen nanoseconds. Given their low dimensionality, these systems could be more efficient for generating and detecting entangled plasmons in comparison to extended graphene. Indeed, we achieve a tunable spectrum of emission in GCWs, where sharp resonances occur precisely at the plasmons' minimum excitation frequencies. We show that by changing the material properties of the GCW's dielectric core, one could tailor the dominant modes and frequencies of the emitted entangled plasmons while keeping the decay rate ten orders of magnitude higher than in free space. By unveiling the unique properties of two-plasmon spontaneous emission processes in the presence of low-dimensional carbon-based nanomaterials, our findings set the basis for a novel material platform with applications to on-chip quantum information technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Orientation-dependent mutual crystalline and amorphous order in a single phase solid

Amorphous materials distinguish themselves from crystalline materials by lacking long-range order while retaining structural order at the local scale (2–5 Å). However, the complexity in topological and chemical order prevents current characterization tools from fully unveiling the structure in disordered materials. Consequently, the nature of medium-range order in amorphous materials has remained elusive. The Zachariasen and crystal competing models have been proposed to describe disordered phases and have both been verified through synthesis and characterization. The main difference between them is thought to be whether the amorphous phase shows medium-range order. Here we demonstrate a form of organized inorganic matter that is amorphous in two dimensions, while exhibiting long-range order and a high degree of crystallinity in the third. The structure consists of periodically stacked 2-dimensional amorphous Nb-W-O monolayers without long-range in-plane order. The unique periodic and therefore crystalline stacking along one principal axis enables direct imaging and revealed that the amorphous Nb-W-O monolayers formed in agreement with the Zachariasen model for 2 dimensions. Our findings show that the gap between crystalline and amorphous materials does not only depend on medium-range order but can also apply to principal dimensions within the same solid.

Nanowires↗