369 research outputs found
Data for "Tailoring Hot-Carrier Distributions of Plasmonic Nanostructures through Surface Alloying"
No full text<p>This upload includes the data presented and analyzed in the article "Tailoring Hot-Carrier Distributions of Plasmonic Nanostructures through Surface Alloying" by Jakub Fojt, Tuomas P. Rossi, Priyank V. Kumar, and Paul Erhart.</p>
<p>The codes for reproducing the data are provided at <a href="https://doi.org/10.5281/zenodo.10663218">doi:10.5281/zenodo.10663218</a>.</p>
<p>See <em>README.md</em> in <em>data.zip</em> for a detailed description.</p>
Graphene Oxide as a Promising Hole Injection Layer for MoS[subscript 2]-based Electronic Devices
No full textThe excellent physical and semiconducting properties of transition metal dichalcogenide (TMDC) monolayers make them promising materials for many applications. The TMDC monolayer MoS[subscript 2] has gained significant attention as a channel material for next-generation transistors. However, while n-type single-layer MoS2 devices can be made with relative ease, fabrication of p-type transistors remains a challenge as the Fermi-level of elemental metals used as contacts are pinned close to the conduction band leading to large p-type Schottky barrier heights (SBH). Here, we propose the utilization of graphene oxide (GO) as an efficient hole injection layer for single-layer MoS[subscript 2]-based electronic and optoelectronic devices. Using first-principles computations, we demonstrate that GO forms a p-type contact with monolayer MoS[subscript 2], and that the p-type SBH can be made smaller by increasing the oxygen concentration and the fraction of epoxy functional groups in GO. Our analysis shows that this is possible due to the high work function of GO and the relatively weak Fermi-level pinning at the MoS[subscript 2]/GO interfaces compared to traditional MoS[subscript 2]/metal systems (common metals are Ag, Al, Au, Ir, Pd, Pt). The combination of easy-to-fabricate and inexpensive GO with MoS[subscript 2] could be promising for the development of hybrid all-2D p-type electronic and optoelectronic devices on flexible substrates.Eni S.p.A. (Firm) (Eni-MIT Alliance Solar Frontiers Program
Nanocarbon-Based Photovoltaics
No full textCarbon materials are excellent candidates for photovoltaic solar cells: they are Earth-abundant, possess high optical absorption, and maintain superior thermal and photostability. Here we report on solar cells with active layers made solely of carbon nanomaterials that present the same advantages of conjugated polymer-based solar cells, namely, solution processable, potentially flexible, and chemically tunable, but with increased photostability and the possibility to revert photodegradation. The device active layer composition is optimized using ab initio density functional theory calculations to predict type-II band alignment and Schottky barrier formation. The best device fabricated is composed of PC[subscript 70]BM fullerene, semiconducting single-walled carbon nanotubes, and reduced graphene oxide. This active-layer composition achieves a power conversion efficiency of 1.3%—a record for solar cells based on carbon as the active material—and we calculate efficiency limits of up to 13% for the devices fabricated in this work, comparable to those predicted for polymer solar cells employing PCBM as the acceptor. There is great promise for improving carbon-based solar cells considering the novelty of this type of device, the high photostability, and the availability of a large number of carbon materials with yet untapped potential for photovoltaics. Our results indicate a new strategy for efficient carbon-based, solution-processable, thin film, photostable solar cells.MIT Energy Initiative Seed FundIntel Corporation (Intel Ph.D. Fellowship
Enhanced electrical, optical and chemical properties of graphene oxide through a novel phase transformation
No full textThesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2015.Cataloged from PDF version of thesis.Includes bibliographical references (pages 86-98).Graphene oxide (GO) is a versatile, solution-processable candidate material for next-generation, large-area, ultrathin electronics, optoelectronics, energy conversion and storage technologies. GO is an atom-thick sheet of carbon functionalized with several oxygen-containing groups dominated by the epoxy and hydroxyl functional groups on the basal plane, with carboxyls and lactols at the sheet edges. It is well known that reduction of GO at temperatures > 150°C leads to the removal of oxygen atoms from the carbon plane, leading to the formation of reduced GO (rGO) structures. Although GO has been utilized for multiple applications in the last decade, our understanding of the structure-property relationships at the atomic-level has still been lacking owing to the amorphous nature and chemical inhomogeneity of GO, which has in turn limited our ability to design and tailor GO nanostructures for high-performance applications. In particular, the material's structure and its structural evolution at mild annealing temperatures (< 1000°C) has been largely unexplored. In this thesis, we use a combination of first-principles computations, classical molecular dynamics simulations based on reactive force fields and experiments to model realistic GO structures and develop a detailed understanding of the relationship between the carbon-oxygen framework and the sheet properties, at the atomic level. Based on our understanding, we demonstrate a new phase transformation in GO sheets at mild annealing temperatures (50-80°C), where the oxygen content is preserved and as-synthesized GO structures undergo a phase separation into prominent oxidized and graphitic domains facilitated by oxygen diffusion. Consequently, as-synthesized GO that absorbs mainly in the ultraviolet region becomes strongly absorbing in the visible region, photoluminescence is blue shifted and electronic conductivity increases by up to four orders of magnitude. We then use this novel phase transformation to improve two sets of applications. 1) We demonstrate that cell capture devices making use of phase transformed-GO substrates have higher capture efficiencies compared to devices making use of as-synthesized GO substrates. 2) We show that the reduction of phase transformed-GO leads to better electrical properties of rGO thin films. Our results fill an important gap and establish a complete theory for structural evolution of GO over the entire range of temperatures, i.e. from room temperature to ~1000°C. Taken together, this structural transition in GO enables us to predict and control the sheet properties in new ways, as opposed to reduction, which is till date the only handle to control the structure of GO. This could potentially open the door for completely new applications or for enhancing the performance of existing applications based on GO.by Priyank Vijaya Kumar.Ph. D
Interface-Controlled Phase Separation of Liquid Metal-Based Eutectic Ternary Alloys
No full textLiquid metals (LMs) are immiscible in many common electrolytic
solutions and, when immersed in them, establish phase boundaries that
display intriguing interfacial characteristics. The application of
a cathodic potential to such interfaces may trigger phase separation
of solute elements out of the LMs. Here, we investigate this possibility
in two of the most researched and industrially used eutectic ternary
LMs of Galinstan (Ga-In-Sn) and Field’s metal (FM, In–Bi–Sn).
We observe that upon surface perturbation by an applied electric potential,
solute elements compete to segregate out of the LM alloys according
to their energy levels. The nature of the electrolytic solutions plays
a key role in the separation process as they dictate whether solute
metals are expelled selectively in their pure form or as binary compounds.
For example, in a phosphate-based aqueous electrolyte, nano-sized
Sn-based entities are selectively expelled from Galinstan, while only
Bi-based structures leave the surface of FM. In contrast, in a non-aqueous
electrolyte, nano-sized binary compounds of Sn–In and Bi–Sn
are separated from the surfaces of Galinstan and FM, respectively.
We show that selectivity in the surface separation process, achieved
by the alteration of the electrolytic solutions, is due to the interplay
between the electrodynamic interactions and the electrocapillary effect.
This study presents two key findings: (a) it is essential to carefully
consider the possibility of component separation in electrochemical
systems based on LMs and (b) it demonstrates interfacial metallurgical
pathways to process alloys for refining metals into specific purities,
component ratios, and dimensions
Oxygen Vacancies Engineering in Thick Semiconductor Films via Deep Ultraviolet Photoactivation for Selective and Sensitive Gas Sensing
No full textPublished April 2023Room-temperature detection of volatile organic compounds in particle-perbillion concentrations is critical for the development of wearable and distributed sensor networks. However, sensitivity and selectivity are limited at low operating temperatures. Here, a strategy is proposed to substantially improve the performance of semiconductor sensors. Tunable oxygen vacancies in thick 3D networks of metal oxide nanoparticles are engineered using deep ultraviolet photoactivation. High selectivity and sensitivity are achieved by optimizing the electronic structure and surface activity while preserving the 3D morphology. Cross-sectional depth analysis reveals oxygen vacancies present at various depths (≈24% at a depth of 1.13 μm), with a uniform distribution throughout the thick films. This results in ≈58% increase in the sensitivity of ZnO to 20-ppb ethanol at room temperature while ≈51% and 64% decrease in the response and recovery times, respectively. At an operating temperature of 150 °C, oxygenvacant nanostructures achieve a lower limit of detection of 2 ppb. Density functional theory analysis shows that inducing oxygen vacancies reduces activation energy for ethanol adsorption and dissociation, leading to improved sensing performance. This scalable approach has the potential for designing low-power wearable chemical and bio-sensors and tuning the activity and band structure of porous, thick oxide films for multiple applications.Zain Ul Abideen, Jun-Gyu Choi, Jodie A. Yuwono, Alexander Kiy, Priyank Vijaya Kumar, Krishnan Murugappan, Won-June Lee, Patrick Kluth, David R. Nisbet, Thanh Tran-Phu, Myung-Han Yoon, and Antonio Tricol
Rolling Moment of Slender Body at High Incidence for Air to Air Missile Rocket Applications
No full textMeasurements of moments were carried out on a slender body having a pointed forebody at lower velocities. The slender body had an ogive nose shape and an overall length to diameter ratio of 16. The angle of incidence was varied from low to moderate angles of attack in the pitch plane. The main objective of the present investigation was to measure the rolling moments on the slender body with and without the control technique. The side force was reduced using a rectangular cross-sectioned ringplaced suitably on the body, however, the slender body was found to experience rolling moments which may be catastrophic
Short-chain n-alkanes in benthic mats and mosses from the Larsemann Hills, East Antarctica
No full textVariation in leaf colour (green, red and grey) of mosses and lake benthic mats in Antarctica is often linked to water stress and ultraviolet light (UV-B) exposure. Changes in the abundance of organic compounds, such as pectin and phenols, are associated with mechanisms protecting against desiccation and UV radiation. However, the function of n-alkanes, especially against UV radiation, is rarely examined. Here, gas chromatography–mass spectrometry and Fourier-transform infrared spectroscopy analyses were performed to study the variation in n-alkanes in freshwater lake benthic mats and mosses collected from the Larsemann Hills in East Antarctica. Stable isotopes of organic carbon and nitrogen, environmental DNA characterisation and microscopy-based analyses are used to estimate the presence of cyanobacteria, algae and diatoms in moss and benthic mat consortia. Variation in the short-chain (n-C17 to n-C20) versus long-chain (n-C21 to n-C30) n-alkanes in the mosses and benthic mats with their colour were noted. The research links the relative abundance of short-chain n-alkanes to the UV-B exposure and proposes that Antarctic mosses and benthic mats synthesise short-chain n-alkanes for protection against UV-B.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Sanitary Engineerin
Journal of Undergraduate Materials Research
No full textThe effects of convective and unsteady inertia on the dynamics of periodically forced neutrally buoyant prolate spheroids in a quiescent Newtonian fluid medium, at low Reynolds numbers have been modeled. The resulting nonlinear equations have been solved using appropriate numerical methods. Several tests including a perturbation analysis are performed to validate results. A preferred direction, which is identified as the initial direction of motion, is observed that manifests itself in the properties of the solution. Results of the behavior of various parameters with respect to the Reynolds number, aspect ratio of the spheroid and the amplitude of the periodic force are presented. The results are technologically important as they may lead to insights in the development of active dampeners and smart fluids
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