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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.

Superconducting niobium (Nb) thin films have recently attracted significant attention due to their utility for quantum information technologies. In the processing of Nb thin films, fluoride‐based chemical etchants are commonly used to remove surface oxides that are known to affect superconducting quantum devices adversely. However, these same etchants can also introduce hydrogen to form Nb hydrides, potentially negatively impacting microwave loss performance. Here, comprehensive materials characterization of Nb hydrides formed in Nb thin films as a function of fluoride chemical treatments is presented. In particular, secondary‐ion mass spectrometry, X‐ray scattering, and transmission electron microscopy reveal the spatial distribution and phase transformation of Nb hydrides. The rate of hydride formation is determined by the fluoride solution acidity and the etch rate of Nb2O5, which acts as a diffusion barrier for hydrogen into Nb. The resulting Nb hydrides are detrimental to Nb superconducting properties and lead to increased power‐independent microwave loss in coplanar waveguide resonators. However, Nb hydrides do not correlate with two‐level system loss or device aging mechanisms. Overall, this work provides insight into the formation of Nb hydrides and their role in microwave loss, thus guiding ongoing efforts to maximize coherence time in superconducting quantum devices. [ABSTRACT FROM AUTHOR]

High-temperature operation of metal–semiconductor–metal (MSM) UV photodetectors fabricated on pulsed laser deposited β-Ga2O3 thin films has been investigated. These photodetectors were operated up to 250 °C temperature under 255 nm illumination. The photo to dark current ratio of about 7100 was observed at room temperature and 2.3 at a high temperature of 250 °C with 10 V applied bias. A decline in photocurrent was observed until a temperature of 150 °C beyond which it increased with temperature up to 250 °C. The suppression of the UV and blue band was also observed in the normalized spectral response curve above 150 °C temperature. Temperature-dependent rise and decay times of temporal response were analyzed to understand the associated photocurrent mechanism at high temperatures. Electron–phonon interaction and self-trapped holes were found to influence the photoresponse in the devices. The obtained results are encouraging and significant for high-temperature applications of β-Ga2O3 MSM deep UV photodetectors. [ABSTRACT FROM AUTHOR]

Because of the relatively low electron mobility of Ga2O3, it is important to identify suitable current spreading materials. Fluorine-doped SnO2 (FTO) offers superior properties to those of indium tin oxide (ITO), including higher thermal stability, a larger bandgap, and lower cost. However, the Ga2O3:Si/FTO heterojunction, including the important band offsets and the I–V characteristics, have not previously been reported. In this work, we have grown a Ga2O3:Si/FTO heterojunction and performed x-ray photoelectron spectroscopy measurements. The conduction and valence band offsets were determined to be 0.11 and 0.42 eV, indicating a minor barrier for electron transport and a type-I heterojunction. The subsequent I–V measurement of the Ga2O3:Si/FTO heterojunction exhibited pseudo-ohmic behavior. The results of this work support the potential of FTO for the current spreading layers of Ga2O3 devices for high temperature and ultraviolet applications. [ABSTRACT FROM AUTHOR]

Implantable polymeric biodegradable devices, such as biodegradable vascular scaffolds, cannot be fully visualized using standard X-ray-based techniques, compromising their performance due to malposition after deployment. To address this challenge, we describe a new radiopaque and photocurable liquid polymer-ceramic composite (mPDC-MoS 2 ) consisting of methacrylated poly(1,12 dodecamethylene citrate) (mPDC) and molybdenum disulfide (MoS 2 ) nanosheets. The composite was used as an ink with microcontinuous liquid interface production (μCLIP) to fabricate bioresorbable vascular scaffolds (BVS). Prints exhibited excellent crimping and expansion mechanics without strut failures and, importantly, with X-ray visibility in air and muscle tissue. Notably, MoS 2 nanosheets displayed physical degradation over time in phosphate-buffered saline solution, suggesting the potential for producing radiopaque, fully bioresorbable devices. mPDC-MoS 2 is a promising bioresorbable X-ray-visible composite material suitable for 3D printing medical devices, such as vascular scaffolds, that require noninvasive X-ray-based monitoring techniques for implantation and evaluation. This innovative biomaterial composite system holds significant promise for the development of biocompatible, fluoroscopically visible medical implants, potentially enhancing patient outcomes and reducing medical complications.

Spinel-type lithium manganese oxide (LiMn 2 O 4 ) cathodes suffer from severe manganese dissolution in the electrolyte, compromising the cyclic stability of LMO-based Li-ion batteries (LIBs). In addition to causing structural and morphological deterioration to the cathode, dissolved Mn ions can migrate through the electrolyte to deposit on the anode, accelerating capacity fade. Here, we examine single-crystal epitaxial LiMn 2 O 4 (111) thin-films using synchrotron in situ X-ray diffraction and reflectivity to study the structural and interfacial evolution during cycling. Cyclic voltammetry is performed in a wide range (2.5-4.3 V vs Li/Li + ) to promote Mn 3+ formation, which enhances dissolution, for two different electrolyte systems: an imidazolium ionic liquid containing lithium bis-(trifluoromethylsulfonyl)imide (LiTFSI) and a conventional carbonate liquid electrolyte containing lithium hexafluorophosphate (LiPF 6 ). We find exceptional stability in this voltage range for the ionic liquid electrolyte compared to the conventional electrolyte, which is attributed to the absence of Mn dissolution in the ionic liquid. X-ray reflectivity shows a negligible loss of cathode material for the films cycled in the ionic liquid electrolyte, further confirmed by inductively coupled plasma mass spectrometry and transmission electron microscopy. Conversely, a substantial loss of Mn is found when the film is cycled in the conventional electrolyte. These findings show the significant advantages of ionic liquids in suppressing Mn dissolution in LiMn 2 O 4 LIB cathodes.

LiNiO 2 (LNO) is a promising cathode material for next-generation Li-ion batteries due to its exceptionally high capacity and cobalt-free composition that enables more sustainable and ethical large-scale manufacturing. However, its poor cycle life at high operating voltages over 4.1 V impedes its practical use, thus motivating efforts to elucidate and mitigate LiNiO 2 degradation mechanisms at high states of charge. Here, a multiscale exploration of high-voltage degradation cascades associated with oxygen stacking chemistry in cobalt-free LiNiO 2 , is presented. Lattice oxygen loss is found to play a critical role in the local O3-O1 stacking transition at high states of charge, which subsequently leads to Ni-ion migration and irreversible stacking faults during cycling. This undesirable atomic-scale structural evolution accelerates microscale electrochemical creep, cracking, and even bending of layers, ultimately resulting in macroscopic mechanical degradation of LNO particles. By employing a graphene-based hermetic surface coating, oxygen loss is attenuated in LNO at high states of charge, which suppresses the initiation of the degradation cascade and thus substantially improves the high-voltage capacity retention of LNO. Overall, this study provides mechanistic insight into the high-voltage degradation of LNO, which will inform ongoing efforts to employ cobalt-free cathodes in Li-ion battery technology., (© 2021 Wiley-VCH GmbH.)