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Your search keyword '"Evans, Austin M."' showing total 137 results
Start Over Author "Evans, Austin M." Publication Type Academic Journals
137 results on '"Evans, Austin M."'

3. Thermally conductive ultra-low-k dielectric layers based on two-dimensional covalent organic frameworks

Author

Evans, Austin M, Giri, Ashutosh, Sangwan, Vinod K, Xun, Sangni, Bartnof, Matthew, Torres-Castanedo, Carlos G, Balch, Halleh B, Rahn, Matthew S, Bradshaw, Nathan P, Vitaku, Edon, Burke, David W, Li, Hong, Bedzyk, Michael J, Wang, Feng, Brédas, Jean-Luc, Malen, Jonathan A, McGaughey, Alan JH, Hersam, Mark C, Dichtel, William R, and Hopkins, Patrick E

Subjects
Engineering, Materials Engineering, Nanoscience & Nanotechnology
Abstract

As the features of microprocessors are miniaturized, low-dielectric-constant (low-k) materials are necessary to limit electronic crosstalk, charge build-up, and signal propagation delay. However, all known low-k dielectrics exhibit low thermal conductivities, which complicate heat dissipation in high-power-density chips. Two-dimensional (2D) covalent organic frameworks (COFs) combine immense permanent porosities, which lead to low dielectric permittivities, and periodic layered structures, which grant relatively high thermal conductivities. However, conventional synthetic routes produce 2D COFs that are unsuitable for the evaluation of these properties and integration into devices. Here, we report the fabrication of high-quality COF thin films, which enable thermoreflectance and impedance spectroscopy measurements. These measurements reveal that 2D COFs have high thermal conductivities (1 W m-1 K-1) with ultra-low dielectric permittivities (k = 1.6). These results show that oriented, layered 2D polymers are promising next-generation dielectric layers and that these molecularly precise materials offer tunable combinations of useful properties.

Published
2021

4. A few-layer covalent network of fullerenes

Author

Meirzadeh, Elena, Evans, Austin M., Rezaee, Mehdi, Milich, Milena, Dionne, Connor J., Darlington, Thomas P., Bao, Si Tong, Bartholomew, Amymarie K., Handa, Taketo, Rizzo, Daniel J., Wiscons, Ren A., Reza, Mahniz, Zangiabadi, Amirali, Fardian-Melamed, Natalie, Crowther, Andrew C., Schuck, P. James, Basov, D. N., Zhu, Xiaoyang, Giri, Ashutosh, Hopkins, Patrick E., Kim, Philip, Steigerwald, Michael L., Yang, Jingjing, Nuckolls, Colin, and Roy, Xavier

Published
2023
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5. Electronically Coupled 2D Polymer/MoS2 Heterostructures

Author

Balch, Halleh B, Evans, Austin M, Dasari, Raghunath R, Li, Hong, Li, Ruofan, Thomas, Simil, Wang, Danqing, Bisbey, Ryan P, Slicker, Kaitlin, Castano, Ioannina, Xun, Sangni, Jiang, Lili, Zhu, Chenhui, Gianneschi, Nathan, Ralph, Daniel C, Brédas, Jean-Luc, Marder, Seth R, Dichtel, William R, and Wang, Feng

Subjects
Engineering, Disulfides, Electrons, Models, Molecular, Molecular Conformation, Molybdenum, Polymers, Chemical Sciences, General Chemistry, Chemical sciences
Abstract

Emergent quantum phenomena in electronically coupled two-dimensional heterostructures are central to next-generation optical, electronic, and quantum information applications. Tailoring electronic band gaps in coupled heterostructures would permit control of such phenomena and is the subject of significant research interest. Two-dimensional polymers (2DPs) offer a compelling route to tailored band structures through the selection of molecular constituents. However, despite the promise of synthetic flexibility and electronic design, fabrication of 2DPs that form electronically coupled 2D heterostructures remains an outstanding challenge. Here, we report the rational design and optimized synthesis of electronically coupled semiconducting 2DP/2D transition metal dichalcogenide van der Waals heterostructures, demonstrate direct exfoliation of the highly crystalline and oriented 2DP films down to a few nanometers, and present the first thickness-dependent study of 2DP/MoS2 heterostructures. Control over the 2DP layers reveals enhancement of the 2DP photoluminescence by two orders of magnitude in ultrathin sheets and an unexpected thickness-dependent modulation of the ultrafast excited state dynamics in the 2DP/MoS2 heterostructure. These results provide fundamental insight into the electronic structure of 2DPs and present a route to tune emergent quantum phenomena in 2DP hybrid van der Waals heterostructures.

Published
2020

7. A Dinuclear Mechanism Implicated in Controlled Carbene Polymerization

Author

Zhukhovitskiy, Aleksandr V, Kobylianskii, Ilia J, Thomas, Andy A, Evans, Austin M, Delaney, Connor P, Flanders, Nathan C, Denmark, Scott E, Dichtel, William R, and Toste, F Dean

Subjects
Density Functional Theory, Methane, Molecular Structure, Polymerization, Chemical Sciences, General Chemistry
Abstract

Carbene polymerization provides polyolefins that cannot be readily prepared from olefin monomers; however, controlled and living carbene polymerization has been a long-standing challenge. Here we report a new class of initiators, (π-allyl)palladium carboxylate dimers, which polymerize ethyl diazoacetate, a carbene precursor in a controlled and quasi-living manner, with nearly quantitative yields, degrees of polymerization >100, molecular weight dispersities 1.2-1.4, and well-defined, diversifiable chain ends. This method also provides block copolycarbenes that undergo microphase segregation. Experimental and theoretical mechanistic analysis supports a new dinuclear mechanism for this process.

Published
2019

9. Discovery of spontaneous de-interpenetration through charged point-point repulsions

Author

Hanna, Sylvia L., Chheda, Saumil, Anderson, Ryther, Ray, Debmalya, Malliakas, Christos D., Knapp, Julia G., Otake, Ken-ichi, Li, Peng, Li, Penghao, Wang, Xingjie, Wasson, Megan C., Zosel, Katarina, Evans, Austin M., Robison, Lee, Islamoglu, Timur, Zhang, Xuan, Dichtel, William R., Stoddart, J. Fraser, Gomez-Gualdron, Diego A., Gagliardi, Laura, and Farha, Omar K.

Published
2022
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13. Selective Electrochemical Modification and Degradation of Polymers.

Author

Hughes, Rhys W., Marquez, Joshua D., Young, James B., Garrison, John B., Zastrow, Isabella S., Evans, Austin M., and Sumerlin, Brent S.

Subjects
POLYMER degradation, POLYACRYLATES, ALKYL radicals, ACRYLATES, COPOLYMERS, DECARBOXYLATION, PHTHALIMIDES
Abstract

We demonstrate that electrochemical‐induced decarboxylation enables reliable post‐polymerization modification and degradation of polymers. Polymers containing N‐(acryloxy)phthalimides were subjected to electrochemical decarboxylation under mild conditions, which led to the formation of transient alkyl radicals. By installing these redox‐active units, we systematically modified the pendent groups and chain ends of polyacrylates. This approach enabled the production of poly(ethylene‐co‐methyl acrylate) and poly(propylene‐co‐methyl acrylate) copolymers, which are difficult to synthesize by direct polymerization. Spectroscopic and chromatographic techniques reveal these transformations are near‐quantitative on several polymer systems. Electrochemical decarboxylation also enables the degradation of all‐methacrylate poly(N‐(methacryloxy)phthalimide‐co‐methyl methacrylate) copolymers with a degradation efficiency of >95 %. Chain cleavage is achieved through the decarboxylation of the N‐hydroxyphthalimide ester and subsequent β‐scission of the backbone radical. Electrochemistry is thus shown to be a powerful tool in selective polymer transformations and controlled macromolecular degradation. [ABSTRACT FROM AUTHOR]

Published
2024
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26. Controlled n‐Doping of Naphthalene‐Diimide‐Based 2D Polymers.

Author

Evans, Austin M., Collins, Kelsey A., Xun, Sangni, Allen, Taylor G., Jhulki, Samik, Castano, Ioannina, Smith, Hannah L., Strauss, Michael J., Oanta, Alexander K., Liu, Lujia, Sun, Lei, Reid, Obadiah G., Sini, Gjergji, Puggioni, Danilo, Rondinelli, James M., Rajh, Tijana, Gianneschi, Nathan C., Kahn, Antoine, Freedman, Danna E., and Li, Hong

Published
2022
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34. Anisotropic Transient Disordering of Colloidal, Two-Dimensional CdSe Nanoplatelets upon Optical Excitation.

Author

Brumberg, Alexandra, Kirschner, Matthew S., Diroll, Benjamin T., Williams, Kali R., Flanders, Nathan C., Harvey, Samantha M., Leonard, Ariel A., Watkins, Nicolas E., Liu, Cunming, Kinigstein, Eli D., Yu, Jin, Evans, Austin M., Liu, Yuzi, Cuthriell, Shelby A., Panuganti, Shobhana, Dichtel, William R., Kanatzidis, Mercouri G., Wasielewski, Michael R., Zhang, Xiaoyi, and Chen, Lin X.

Published
2021
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38. Materials breaking the rules: general discussion.

Author

Addicoat, Matthew, Bennett, Thomas D., Brammer, Lee, Craig, Gavin, Das, Chinmoy, Dichtel, William, Doan, Huan, Evans, Austin M., Evans, Jack, Goodwin, Andrew, Horike, Satoshi, Jiang, Jianwen, Kaskel, Stefan, Kato, Masako, Kitagawa, Susumu, Kobayashi, Atsushi, Krause, Simon, Lavenn, Christophe, Lee, Jet-Sing M., and Phillips, Anthony E.

Published
2021
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39. Trends in the thermal stability of two-dimensional covalent organic frameworks.

Author

Evans, Austin M., Ryder, Matthew R., Ji, Woojung, Strauss, Michael J., Corcos, Amanda R., Vitaku, Edon, Flanders, Nathan C., Bisbey, Ryan P., and Dichtel, William R.

Abstract

Two-dimensional covalent organic frameworks (2D COFs) are synthetically diverse, layered macromolecules. Their covalent lattices are thought to confer high thermal stability, which is typically evaluated with thermogravimetric analysis (TGA). However, TGA measures the temperature at which volatile degradation products are formed and is insensitive to changes of the periodic structure of the COF. Here, we study the thermal stability of ten 2D COFs using a combination of variable-temperature X-ray diffraction, TGA, diffuse reflectance infrared spectroscopy, and density functional theory calculations. We find that 2D COFs undergo a general two-step thermal degradation process. At the first degradation temperature, 2D COFs lose their crystallinity without chemical degradation. Then, at higher temperatures, they chemically degrade into volatile byproducts. Several trends emerge from this exploration of 2D COF stability. Boronate ester-linked COFs are generally more thermally stable than comparable imine-linked COFs. Smaller crystalline lattices are more robust to thermal degradation than chemically similar larger lattices. Finally, pore-functionalized COFs degrade at significantly lower temperatures than their unfunctionalized analogues. These trends offer design criteria for thermally resilient 2D COF materials. These findings will inform and encourage a broader exploration of mechanical deformation in 2D networks, providing a necessary step towards their practical use. [ABSTRACT FROM AUTHOR]

Published
2021
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41. Electronically Coupled 2D Polymer/MoS2 Heterostructures.

Author

Balch, Halleh B., Evans, Austin M., Dasari, Raghunath R., Li, Hong, Li, Ruofan, Thomas, Simil, Wang, Danqing, Bisbey, Ryan P., Slicker, Kaitlin, Castano, Ioannina, Xun, Sangni, Jiang, Lili, Zhu, Chenhui, Gianneschi, Nathan, Ralph, Daniel C., Brédas, Jean-Luc, Marder, Seth R., Dichtel, William R., and Wang, Feng

Published
2020
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45. Acid Exfoliation of Imine‐linked Covalent Organic Frameworks Enables Solution Processing into Crystalline Thin Films.

Author

Burke, David W., Sun, Chao, Castano, Ioannina, Flanders, Nathan C., Evans, Austin M., Vitaku, Edon, McLeod, David C., Lambeth, Robert H., Chen, Lin X., Gianneschi, Nathan C., and Dichtel, William R.

Subjects
THIN films, CRYSTALLINE polymers, POROUS polymers, CONTINUOUS casting, OPTOELECTRONIC devices, MICROCRYSTALLINE polymers, NANOFILTRATION, DEPOLYMERIZATION
Abstract

Covalent organic frameworks (COFs) are highly modular porous crystalline polymers that are of interest for applications such as charge‐storage devices, nanofiltration membranes, and optoelectronic devices. COFs are typically synthesized as microcrystalline powders, which limits their performance in these applications, and their limited solubility precludes large‐scale processing into more useful morphologies and devices. We report a general, scalable method to exfoliate two‐dimensional imine‐linked COF powders by temporarily protonating their linkages. The resulting suspensions were cast into continuous crystalline COF films up to 10 cm in diameter, with thicknesses ranging from 50 nm to 20 μm depending on the suspension composition, concentration, and casting protocol. Furthermore, we demonstrate that the film fabrication process proceeds through a partial depolymerization/repolymerization mechanism, providing mechanically robust films that can be easily separated from their substrates. [ABSTRACT FROM AUTHOR]

Published
2020
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