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At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Magnetic semiconductors from functionalized Cr 2 ⁢C MXenes

Here, we report an ab initio investigation of functionalized and 3⁢𝑑-electron-doped Cr 2 ⁢C MXenes. Upon functionalization, the Cr 2⁢ C becomes chemically, dynamically, and mechanically stable, and it exhibits magnetic semiconducting behavior. Cr 2 ⁢CF 2 stands out as a wide band gap semiconductor, possessing superexchange interaction mediated by F atoms within the layer; however, the applied strain transforms it from an indirect to a direct band gap semiconductor. Strong spin-phonon coupling found in Cr 2 ⁢CH 2 is supported by the distorted Cr spin density due to the hydrogen environment. Two magnon branches, associated with two sublattice spins, are found in the ferromagnetic Cr 2 ⁢CO 2 and antiferromagnetic Cr 2 ⁢CF 2 . Depending on the types of 3⁢𝑑-electron dopants and functionalization, Cr 2 ⁢C MXenes (except for Cr 2 ⁢CO 2 ) change from an indirect band gap magnetic semiconductor to different states of electronic and magnetic matter, including an exotic direct band gap magnetic bipolar semiconductor. In addition, we reveal a band inversion between the two highest valence bands in the Fe-doped Cr 2 ⁢CCl 2 .

2D materials↗
DOE OSTI2020

Busbar Design and Optimization for Voltage Overshoot Mitigation of a Silicon Carbide High-Power Three-Phase T-Type Inverter

The silicon carbide (SiC) devices have faster switching speed than that of the conventional silicon (Si) devices, which however may cause excessive device voltage overshoot. Larger gate resistance can help to restrain the overshoot, it however slows down the switching speed and increases switching losses. There are other methods that can mitigate the voltage overshoot, e.g., using low-inductance busbars, adding snubber circuits, etc. In this article, the busbar design for a 250-kW SiC three-level T-type inverter is investigated. The current commutation loops (CCLs) are first analyzed using a single-phase equivalent circuit. Then the detailed busbar design methods, especially a 3-D busbar design concept, are proposed to select the optimal stacking order for the multilayer laminated busbar and to address constraints posed by the physical terminal arrangements of SiC modules and dc-link capacitors. The stray inductance in each CCL is extracted via a finite element analysis and validated on the actual inverter busbar prototypes using an impedance analyzer. To further minimize the busbar stray inductance, a hybrid busbar structure with printed circuit board based buffer circuit using high-frequency decoupling capacitors is designed and evaluated in this article. Lastly, the effectiveness of the designed busbars as well as the buffer circuit are validated using experimental studies.

42 ENGINEERING↗
DOE OSTI2021

Impact of carrier wafer on etch rate, selectivity, morphology, and passivation during GaN plasma etching

The choice of carrier wafer was found to significantly influence etch rates, selectivity, and morphology in GaN micropillar etching in a Cl 2 -Ar high-density inductively coupled plasma. 7 × 7 mm 2 GaN on sapphire chips with a plasma-enhanced chemical vapor deposition SiO 2 hard mask was etched on top of 4-in. fused silica, silicon carbide, silicon, sapphire, aluminum nitride, and high purity aluminum carriers. Silicon and silicon carbide carriers reduced GaN:SiO 2 selectivity because incidental SiCl x and CCl x etch products from the carriers attack the SiO 2 mask. Aluminum nitride and high-purity aluminum carriers yielded the highest GaN:SiO 2 selectivities due to the deposition of Al-based etched by-products, while the highest GaN etch rate was achieved using the sapphire carrier since it was the most inert carrier and did not sink any Cl 2 . Overall, results indicate that SiO 2 and Al may be used as passivation materials during GaN etching, as vertical profiles were achieved when SiO 2 or Al is redeposited from the fused silica and aluminum carriers, respectively. Floor pitting, trenching, sidewall roughness, and faceting were all influenced by carrier wafer type and will be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Carbon Corrosion in Polymer Electrolyte Fuel Cells: A Complex Interplay between Morphological Changes and Electrochemical Performance

Due to the high gravimetric energy density of hydrogen, the focus of implementation of polymer electrolyte fuel cells (PEFCs) has shifted from light duty passenger vehicles to heavy duty vehicles such as buses, trucks, locomotives and marine vessels. A mechanistic understanding of degradation is therefore necessary to improve durability and efficiency. During start-up and shut-down (SUSD) of PEFC systems, the catalyst (Pt nanoparticles embedded on carbon support) undergoes local potentials ~ 1 - 1.5 V caused by a combination of fuel (H 2 ) starvation, mixed fuel region and cell reversal. This leads to a series of degradation phenomenon including reduction in cathode catalyst layer (cCL) thickness and porosity, loss in electrochemical surface area (ECSA), ionomer degradation and loss in electrical contact, therefore resulting in severe performance loss. The convoluted relationship between these individual degradation mechanisms, their chronology and their effects on electrochemical performance are yet unresolved. Here, the complex interplay between morphological changes due to carbon corrosion and its effects on the electrochemical performance were analyzed using a combination of detailed electrochemical characterization, spectroscopy, and electron microscopy techniques.

25 ENERGY STORAGE↗
DOE OSTI2024

Systemic immunological responses are dependent on sex and ovarian hormone presence following acute inhaled woodsmoke exposure

Background: Rural regions of the western United States have experienced a noticeable surge in both the frequency and severity of acute wildfire events, which brings significant challenges to both public safety and environmental conservation efforts, with impacts felt globally. Identifying factors contributing to immune dysfunction, including endocrinological phenotypes, is essential to understanding how hormones may influence toxicological susceptibility. Methods: This exploratory study utilized male and female C57BL/6 mice as in vivo models to investigate distinct responses to acute woodsmoke (WS) exposure with a focus on sex-based differences. In a second set of investigations, two groups were established within the female mouse cohort. In one group, mice experienced ovariectomy (OVX) to simulate an ovarian hormone-deficient state similar to surgical menopause, while the other group received Sham surgery as controls, to investigate the mechanistic role of ovarian hormone presence in driving immune dysregulation following acute WS exposure. Each experimental cohort followed a consecutive 2-day protocol with daily 4-h exposure intervals under two conditions: control HEPA-filtered air (FA) and acute WS to simulate an acute wildfire episode. Results: Metals analysis of WS particulate matter (PM) revealed significantly increased levels of 63 Cu, 182 W, 208 Pb, and 238 U, compared to filtered air (FA) controls, providing insights into the specific metal components most impacted by the changing dynamics of wildfire occurrences in the region. Male and female mice exhibited diverse patterns in lung mRNA cytokine expression following WS exposure, with males showing downregulation and females displaying upregulation, notably for IL-1β, TNF-α, CXCL-1, CCL-5, TGF-β, and IL-6. After acute WS exposure, there were notable differences in the responses of macrophages, neutrophils, and bronchoalveolar lavage (BAL) cytokines IL-10, IL-6, IL-1β, and TNF-α. Significant diverse alterations were observed in BAL cytokines, specifically IL-1β, IL-10, IL-6, and TNF-α, as well as in the populations of immune cells, such as macrophages and polymorphonuclear leukocytes, in both Sham and OVX mice, following acute WS exposure. These findings elucidated the profound influence of hormonal changes on inflammatory outcomes, delineating substantial sex-related differences in immune activation and revealing altered immune responses in OVX mice due to ovarian hormone deficiency. In addition, the flow cytometry analysis highlighted the complex interaction between OVX surgery, acute WS exposure, and their collective impact on immune cell populations within the hematopoietic bone marrow niche. Conclusions: In summary, both male and female mice, alongside females subjected to OVX and those who had sham surgery, exhibit significant variations in the expression of proinflammatory cytokines, chemokines, lung mRNA gene expression, and related functional networks linked to signaling pathways. These differences potentially act as mediators of sex-specific and hormonal influences in the systemic inflammatory response to acute WS exposure during a wildfire event. Understanding the regulatory roles of genes expressed differentially under environmental stressors holds considerable implications, aiding in identifying sex-specific therapeutic targets for addressing acute lung inflammation and injury.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2020

Materials Data on AsC4S2Cl2O2F13 by Materials Project

(CCl)2(CF3)2AsF6SO2SF1 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight chloromethane molecules, eight fluoroform molecules, four sulfur dioxide molecules, four thiohypofluorous acid molecules, and four AsF6 clusters. In each AsF6 cluster, As1- is bonded in an octahedral geometry to six F1- atoms. There are a spread of As–F bond distances ranging from 1.76–1.81 Å. There are six inequivalent F1- sites. In the first F1- site, F1- is bonded in a single-bond geometry to one As1- atom. In the second F1- site, F1- is bonded in a single-bond geometry to one As1- atom. In the third F1- site, F1- is bonded in a single-bond geometry to one As1- atom. In the fourth F1- site, F1- is bonded in a single-bond geometry to one As1- atom. In the fifth F1- site, F1- is bonded in a single-bond geometry to one As1- atom. In the sixth F1- site, F1- is bonded in a single-bond geometry to one As1- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C28Cl5 by Materials Project

(C)23(CCl)5 crystallizes in the orthorhombic Cmcm space group. The structure is zero-dimensional and consists of forty chloromethane molecules and one hundred and eighty-four methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on HgH2C6(NCl2)2 by Materials Project

HgCl2(HC2N)2(CCl)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight aziridine molecules, eight chloromethane molecules, and four mercuric chloride molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CaH6C6(ClO4)2 by Materials Project

CaC4H4O7(CCl)2H2O crystallizes in the monoclinic C2/m space group. The structure is zero-dimensional and consists of eight chloromethane molecules, four water molecules, and two CaC4H4O7 clusters. In each CaC4H4O7 cluster, Ca2+ is bonded in a 8-coordinate geometry to eight O2- atoms. There are a spread of Ca–O bond distances ranging from 2.41–2.57 Å. There are two inequivalent C+1.67+ sites. In the first C+1.67+ site, C+1.67+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. In the second C+1.67+ site, C+1.67+ is bonded in a single-bond geometry to one O2- atom. The C–O bond length is 1.26 Å. There are two inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.99 Å. In the second H1+ site, H1+ is bonded in a single-bond geometry to one O2- atom. The H–O bond length is 0.98 Å. There are five inequivalent O2- sites. In the first O2- site, O2- is bonded in a water-like geometry to two equivalent Ca2+ and two equivalent H1+ atoms. In the second O2- site, O2- is bonded in a distorted water-like geometry to one Ca2+ and two equivalent H1+ atoms. In the third O2- site, O2- is bonded in a single-bond geometry to one Ca2+ atom. In the fourth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+ and one C+1.67+ atom. In the fifth O2- site, O2- is bonded in a distorted bent 120 degrees geometry to one Ca2+ and one C+1.67+ atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C8Cl3F2 by Materials Project

(C)3(CCl)3(CF)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of twelve chloromethane molecules, eight fluoromethane molecules, and twelve methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C4NCl2 by Materials Project

CCN(CCl)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of sixteen chloromethane molecules, eight hydrogen cyanide molecules, and eight methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on H3C8N2Cl3O2 by Materials Project

(C)2CNC2NH3O2(CCl)3 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of six chloromethane molecules, two hydrogen cyanide molecules, four methane molecules, and two nh2cho meoh molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C4NCl2 by Materials Project

CCN(CCl)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of sixteen chloromethane molecules, eight hydrogen cyanide molecules, and eight methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C7Cl8 by Materials Project

C(CCl)5CCl3 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of four chloroform molecules, twenty chloromethane molecules, and four methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni2C5(Cl2O)2 by Materials Project

Ni2C2O2Cl(CCl)3 crystallizes in the triclinic P-1 space group. The structure is zero-dimensional and consists of twelve chloromethane molecules and four Ni2C2O2Cl clusters. In two of the Ni2C2O2Cl clusters, there are two inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded in a distorted L-shaped geometry to one C+0.80+ and one Cl1- atom. The Ni–C bond length is 1.79 Å. The Ni–Cl bond length is 2.25 Å. In the second Ni2+ site, Ni2+ is bonded in a distorted L-shaped geometry to one C+0.80+ and one Cl1- atom. The Ni–C bond length is 1.80 Å. The Ni–Cl bond length is 2.25 Å. There are two inequivalent C+0.80+ sites. In the first C+0.80+ site, C+0.80+ is bonded in a distorted single-bond geometry to one Ni2+ and one O2- atom. The C–O bond length is 1.15 Å. In the second C+0.80+ site, C+0.80+ is bonded in a distorted single-bond geometry to one Ni2+ and one O2- atom. The C–O bond length is 1.15 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+0.80+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+0.80+ atom. Cl1- is bonded in a bent 120 degrees geometry to two Ni2+ atoms. In two of the Ni2C2O2Cl clusters, there are two inequivalent Ni2+ sites. In the first Ni2+ site, Ni2+ is bonded in a distorted water-like geometry to one C+0.80+ and one Cl1- atom. The Ni–C bond length is 1.80 Å. The Ni–Cl bond length is 2.25 Å. In the second Ni2+ site, Ni2+ is bonded in a distorted L-shaped geometry to one C+0.80+ and one Cl1- atom. The Ni–C bond length is 1.80 Å. The Ni–Cl bond length is 2.25 Å. There are two inequivalent C+0.80+ sites. In the first C+0.80+ site, C+0.80+ is bonded in a distorted single-bond geometry to one Ni2+ and one O2- atom. The C–O bond length is 1.15 Å. In the second C+0.80+ site, C+0.80+ is bonded in a distorted single-bond geometry to one Ni2+ and one O2- atom. The C–O bond length is 1.15 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a single-bond geometry to one C+0.80+ atom. In the second O2- site, O2- is bonded in a single-bond geometry to one C+0.80+ atom. Cl1- is bonded in a bent 120 degrees geometry to two Ni2+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C4NCl3 by Materials Project

ClCCN(CCl)2 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of eight chloro(methylimino)methane molecules and sixteen chloromethane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C8Cl4O3 by Materials Project

(C)2COCO2(CCl)4 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of sixteen chloromethane molecules, four formic anhydride molecules, and eight methane molecules.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on C8Cl5 by Materials Project

(C)3(CCl)5 crystallizes in the monoclinic P2_1/c space group. The structure is zero-dimensional and consists of forty chloromethane molecules and twenty-four methane molecules.

36 MATERIALS SCIENCE↗