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Research Article Issue
Electrochemically stable lithium-ion and electron insulators (LEIs) for solid-state batteries
Nano Research 2022, 15 (2): 1213-1220
Published: 17 August 2021
Downloads:25

Rechargeable solid-state Li metal batteries demand ordered flows of Li-ions and electrons in and out of solid structures, with repeated waxing and waning of LiBCC phase near contact interfaces which gives rise to various electro-chemo-mechanical challenges. There have been approaches that adopt three-dimensional (3D) nanoporous architectures consisting of mixed ion-electron conductors (MIECs) to combat these challenges. However, there has remained an issue of LiBCC nucleation at the interfaces between different solid components (e.g., solid electrolyte/MIEC interface), which could undermine the interfacial bonding, thereby leading to the evolution of mechanical instability and the loss of ionic/electronic percolation. In this regard, the present work shows that the Li-ion and electron insulators (LEIs) that are thermodynamically stable against LiBCC could combat such challenges by blocking transportation of charge carriers on the interfaces, analogous to dielectric layers in transistors. We searched the ab initio database and have identified 48 crystalline compounds to be LEI candidates (46 experimentally reported compounds and 2 hypothetical compounds predicted to be stable) with a band gap greater than 3 eV and vanishing Li solubility. Among these compounds, those with good adhesion to solid electrolyte and mixed ion-electron conductor of interest, but are lithiophobic, are expected to be the most useful. We also extended the search to Na or K metal compatible alkali-ion and electron insulators, and identified some crystalline compounds with a property to resist corresponding alkali-ions and electrons.

Research Article Issue
Achieving room-temperature M2-phase VO2 nanowires for superior thermal actuation
Nano Research 2021, 14 (11): 4146-4153
Published: 24 March 2021
Downloads:20

Vanadium dioxide (VO2) has emerged as a promising micro-actuator material for its large amplitude and high work density across the transition between the insulating (M1 and M2) and metallic (R) phase. Even though M2–R transition offers about 70% higher transformation stress than M1–R structural phase transition, the application of the M2 phase in the micro-actuators is hindered by the fact that previously, M2 phase can only stay stable under tensile stress. In this work, we propose and verify that by synthesizing the VO2 nanowires under optimized oxygen-rich conditions, stoichiometry change can be introduced into the nanowires (NWs) which in turn yield a large number free-standing single-crystalline M2-phase NWs stable at room temperature. In addition, we demonstrate that the output stress of the M2-phase NWs is about 65% higher than that of the M1-phase NWs during their transition to R phase, quite close to the theoretical prediction. Our findings open new avenues towards enhancing the performance of VO2-based actuators by using M2–R transition.

Research Article Issue
Optomechanical control of stacking patterns of h-BN bilayer
Nano Research 2019, 12 (10): 2634-2639
Published: 20 August 2019
Downloads:24

Few-layer two-dimensional (2D) materials usually have different (meta)-stable stacking patterns, which have distinct electronic and optical properties. Inspired by optical tweezers, we show that a laser with selected frequency can modify the generalized stacking-fault energy landscape of bilayer hexagonal boron nitride (BBN), by coupling to the slip-dependent dielectric response. Consequently, BBN can be reversibly and barrier-freely switched between its stacking patterns in a controllable way. We simulate the dynamics of the stacking transition with a simplified equation of motion and demonstrate that it happens at picosecond timescale. When one layer of BBN has a nearly-free surface boundary condition, BBN can be locked in its metastable stacking modes for a long time. Such a fast, reversible and non-volatile transition makes BBN a potential media for data storage and optical phase mask.

Research Article Issue
Piezoelectricity in two-dimensional group-Ⅲ monochalcogenides
Nano Research 2015, 8 (12): 3796-3802
Published: 10 November 2015
Downloads:52

It is found that several layer-phase group-Ⅲ monochalcogenides, including GaS, GaSe, and InSe, are piezoelectric in their monolayer form. First-principles calculations reveal that the piezoelectric coefficients of monolayer GaS, GaSe, and InSe (2.06, 2.30, and 1.46 pm·V-1) are of the same order of magnitude as previously discovered two-dimensional (2D) piezoelectric materials such as boron nitride (BN) and MoS2 monolayers. This study therefore indicates that a strong piezoelectric response can be obtained in a wide range of two-dimensional materials with broken inversion symmetry. The co-existence of piezoelectricity and superior photo-sensitivity in these monochalcogenide monolayer semiconductors means they have the potential to allow for the integration of electromechanical and optical sensors on the same material platform.

Research Article Issue
Ultrafast shape change and joining of small-volume materials using nanoscale electrical discharge
Nano Research 2015, 8 (7): 2143-2151
Published: 17 July 2015
Downloads:8

Using nanoscale electrical-discharge-induced rapid Joule heating, we developed a method for ultrafast shape change and joining of small-volume materials. Shape change is dominated by surface-tension-driven convection in the transient liquid melt, giving an extremely high strain rate of ~106 s–1. In addition, the heat can be dissipated in small volumes within a few microseconds through thermal conduction, quenching the melt back to the solid state with cooling rates up to 108 K·s-1. We demonstrate that this approach can be utilized for the ultrafast welding of small-volume crystalline Mo (a refractory metal) and amorphous Cu49Zr51 without introducing obvious microstructural changes, distinguishing the process from bulk welding.

Research Article Issue
Topological crystalline insulator nanomembrane with strain-tunable band gap
Nano Research 2015, 8 (3): 967-979
Published: 17 October 2014
Downloads:16

The ability to fine-tune band gap and band inversion in topological materials is highly desirable for the development of novel functional devices. Here we propose that the electronic properties of free-standing nanomembranes of the topological crystalline insulators (TCI) SnTe and Pb1-xSnx(Se, Te) are highly tunable by engineering elastic strain and membrane thickness, resulting in tunable band gap and giant piezoconductivity. Membrane thickness governs the hybridization of topological electronic states on opposite surfaces, while elastic strain can further modulate the hybridization strength by controlling the penetration length of surface states. We propose a frequency-resolved infrared photodetector using force-concentration induced inhomogeneous elastic strain in TCI nanomembranes with spatially varying width. The predicted tunable band gap accompanied by strong spin-textured electronic states will open new avenues for fabricating piezoresistive devices, infrared detectors and energy-efficient electronic and spintronic devices based on TCI nanomembrane.

Research Article Issue
A nanoporous oxide interlayer makes a better Pt catalyst on a metallic substrate: Nanoflowers on a nanotube bed
Nano Research 2014, 7 (7): 1007-1017
Published: 04 June 2014
Downloads:11

To improve the contact between platinum catalyst and titanium substrate, a layer of TiO2 nanotube arrays has been synthesized before depositing Pt nanoflowers by pulse electrodeposition. Dramatic improvements in electrocatalytic activity (3×) and stability (60×) for methanol oxidation were found, suggesting promising applications in direct methanol fuel cells. The 3× and 60× improvements persist for Pt/Pd catalysts used to overcome the CO poisoning problem.

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