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Using non-equilibrium molecular dynamics simulations, we investigate thermal transport in organic/inorganic Au/molecular nanolayer (MNL) nanolaminate. We examine the tunability of thermal conductivity via interfacial bonding by (i) homogeneous change of bonding strength and heterogeneous change of (ii) bond density and (iii) molecular coverage at the interface. By comparing the thermal conductivity of the nanolaminates with the interfacial thermal conductance of corresponding individual interfaces, we conclude that phenomenologically the thermal conductivity can be predicted from independent interfacial resistors connected in a series model, particularly at higher temperatures. However, interfacial thermal conductance shows a moderate increase with temperature, whereas the thermal conductivity of Au/MNL nanolaminates shows the opposite effect. We elucidate this apparent contradiction via phonon wave packet simulations at individual and multiple interface structures. [ABSTRACT FROM AUTHOR]

In this work, we use molecular dynamics simulations to investigate the switching behavior of BaTiO3 ferroelectric under the application of a high-amplitude high-frequency oscillatory electric field. While at lower frequencies, we observe a standard square-shaped hysteresis loop behavior, at frequencies approaching 1 THz, the hysteresis loop has an ellipsoidal shape. As the frequency increases, the average polarization oscillates without switching direction. To elucidate the origin of the ∼1 THz limit for the polarization switching, we analyzed unit-cell-level polarization vector maps. In this context, the analysis of the low-frequency switching events revealed that in addition to the majority of the polarization vectors exhibiting rapid switching, some "metastable" aligned polarization vectors persist longer with an average lifetime of ∼1 ps. As the frequency increases to the THz range, several polarization vector lines remain unswitched, thus preventing the polarization switching at the simulation domain level. Furthermore, we observe that with the increase in the amplitude of the applied electric field, one can increase the frequency at which switching is observed. [ABSTRACT FROM AUTHOR]

In this work, we use molecular dynamics (MD) simulations to investigate factors affecting polarization switching dynamics in the single domain and 180° bidomain models of BaTiO3 (BTO) and KNbO3 (KNO). In a single domain study for both materials, we observed that the hysteresis loop, while present in low-temperature phases, is essentially non-existent in the highest temperature non-cubic phase. We attribute this behavior to large spontaneous local polarization fluctuations leading to the effective elimination of the nucleation barrier that we observe. Interestingly, in the case of the bidomain structure, while we observe domain migration driven by the electric field, new domain nucleation is severely suppressed at high fields compared with single domain simulations. This behavior is explained by the suppression of simulation cell fluctuations due to the presence of the two domains. We give further credence to this conjecture by demonstrating that the artificial suppression of simulation cell dimension fluctuations in the case of a single domain switching also suppresses new domain nucleation. In this context, we discuss the role of size effects on polarization switching and phase changes in MD simulations. [ABSTRACT FROM AUTHOR]

Incorporating molecular nanolayers (MNLs) at inorganic interfaces offers promise for reaping unusual enhancements in fracture energy, thermal and electrical transport. Here, we reveal that multilayering MNL-bonded inorganic interfaces can result in viscoelastic damping bandgaps. Molecular dynamics simulations of Au/octanedithiol MNL/Au multilayers reveal high-damping-loss frequency bands at 33 ≤ ν ≤ 77 GHz and 278 ≤ ν ≤ 833 GHz separated by a low-loss bandgap 77 ≤ ν ≤ 278 GHz region. The viscoelastic bandgap scales with the Au/MNL interface bonding strength and density, and MNL coverage. These results and the analyses of interfacial vibrations indicate that the viscoelastic bandgap is an interface effect that cannot be explained by weighted averages of bulk responses. These findings prognosticate a variety of possibilities for accessing and tuning novel dynamic mechanical responses in materials systems and devices with significant inorganic–organic interface fractions for many applications, e.g., smart composites and sensors with self-healing/-destructing mechanical responses. [ABSTRACT FROM AUTHOR]

Graphite anodes offer low volumetric capacity in lithium‐ion batteries. By contrast, tellurene is expected to alloy with alkali metals with high volumetric capacity (≈2620 mAh cm−3), but to date there is no detailed study on its alloying behavior. In this work, the alloying response of a range of alkali metals (A = Li, Na, or K) with few‐layer Te is investigated. In situ transmission electron microscopy and density functional theory both indicate that Te alloys with alkali metals forming A2Te. However, the crystalline order of alloyed products varies significantly from single‐crystal (for Li2Te) to polycrystalline (for Na2Te and K2Te). Typical alloying materials lose their crystallinity when reacted with Li—the ability of Te to retain its crystallinity is therefore surprising. Simulations reveal that compared to Na or K, the migration of Li is highly "isotropic" in Te, enabling its crystallinity to be preserved. Such isotropic Li transport is made possible by Te's peculiar structure comprising chiral‐chains bound by van der Waals forces. While alloying with Na and K show poor performance, with Li, Te exhibits a stable volumetric capacity of ≈700 mAh cm−3, which is about twice the practical capacity of commercial graphite. [ABSTRACT FROM AUTHOR]

Tellurene: Alloying of Alkali Metals with Tellurene (Adv. Keywords: alloying; crystallinity; tellurene; volumetric capacity EN alloying crystallinity tellurene volumetric capacity 1 1 1 02/20/21 20210218 NES 210218 In article number 2003248, Nikhil Koratkar and co-workers work to better understand the electrochemical performance of Tellurene, a process akin to climbing a mountain. While the mountaineer uses specialized equipment such as ropes, crampons and ice axes to perform the perilous ascent, the electrochemist uses a suite of advanced microscopy and spectroscopy tools including in-situ characterization to reveal the fundamental electrochemical behavior of new materials. [Extracted from the article]