Using in situ electrical biasing transmission electron microscopy, structural and chemical modification to n–i–p‐type MAPbI3 solar cells are examined with a TiO2 electron‐transporting layer caused by ...bias in the absence of other stimuli known to affect the physical integrity of MAPbI3 such as moisture, oxygen, light, and thermal stress. Electron energy loss spectroscopy (EELS) measurements reveal that oxygen ions are released from the TiO2 and migrate into the MAPbI3 under a forward bias. The injection of oxygen is accompanied by significant structural transformation; a single‐crystalline MAPbI3 grain becomes amorphous with the appearance of PbI2. Withdrawal of oxygen back to the TiO2, and some restoration of the crystallinity of the MAPbI3, is observed after the storage in dark under no bias. A subsequent application of a reverse bias further removes more oxygen ions from the MAPbI3. Light current–voltage measurements of perovskite solar cells exhibit poorer performance after elongated forward biasing; recovery of the performance, though not complete, is achieved by subsequently applying a negative bias. The results indicate negative impacts on the device performance caused by the oxygen migration to the MAPbI3 under a forward bias. This study identifies a new degradation mechanism intrinsic to n–i–p MAPbI3 devices with TiO2.
Using an in situ biasing TEM experiment, a new intrinsic degradation mechanism of methylammonium lead triiodide (MAPbI3) solar cells with a titanium dioxide (TiO2) electron‐transporting layer is identified: oxygen migration from the TiO2 layer to the MAPbI3 under forward biasing, which leads to severe structural modification of the MAPbI3 and the process is pseudo‐reversible.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Black phosphorus (BP) with unique 2D structure enables the intercalation of foreign elements or molecules, which makes BP directly relevant to high‐capacity rechargeable batteries and also opens a ...promising strategy for tunable electronic transport and superconductivity. However, the underlying intercalation mechanism is not fully understood. Here, a comparative investigation on the electrochemically driven intercalation of lithium and sodium using in situ transmission electron microscopy is presented. Despite the same preferable intercalation channels along 100 (zigzag) direction, distinct anisotropic intercalation behaviors are observed, i.e., Li ions activate lateral intercalation along 010 (armchair) direction to form an overall uniform propagation, whereas Na diffusion is limited in the zigzag channels to cause the columnar intercalation. First‐principles calculations indicate that the diffusion of both Li and Na ions along the zigzag direction is energetically favorable, while Li/Na diffusion long the armchair direction encounters an increased energy barrier, but that of Na is significantly larger and insurmountable, which accounts for the orientation‐dependent intercalation channels. The evolution of chemical states during phase transformations (from LixP/NaxP to Li3P/Na3P) is identified by analytical electron diffraction and energy‐loss spectroscopy. The findings elucidate atomistic Li/Na intercalation mechanisms in BP and show potential implications for other similar 2D materials.
The intercalation of lithium and sodium in black phosphorus with orientation‐dependent channels and distinct anisotropic pathways is discovered using in situ transmission electron microscopy combined with density functional theory calculations. The atomic structure evolution along zigzag and armchair directions and the relevant changes in chemical states are elucidated, which offers a fundamental understanding of intercalation mechanisms.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this paper, a novel resonant reactive shield using a double-shield coil and phase-shift circuit is proposed to reduce magnetic field leakage in electric vehicle wireless charging applications. The ...double-reactive shield with a four-capacitor phase shifter generates a canceling magnetic field, the phase of which is perfectly opposite to that of the incident magnetic field, effectively reducing the leakage magnetic field as a result. The concept and structure, and an equivalent-circuit model analysis of the double-reactive shield are explained and discussed. The shielding effectiveness of the double-reactive shield is compared with that of a conventional reactive shield with a single-shield coil by a simulation and is verified by experiments.
Deep learning-based emotion recognition using EEG has received increasing attention in recent years. The existing studies on emotion recognition show great variability in their employed methods ...including the choice of deep learning approaches and the type of input features. Although deep learning models for EEG-based emotion recognition can deliver superior accuracy, it comes at the cost of high computational complexity. Here, we propose a novel 3D convolutional neural network with a channel bottleneck module (CNN-BN) model for EEG-based emotion recognition, with the aim of accelerating the CNN computation without a significant loss in classification accuracy. To this end, we constructed a 3D spatiotemporal representation of EEG signals as the input of our proposed model. Our CNN-BN model extracts spatiotemporal EEG features, which effectively utilize the spatial and temporal information in EEG. We evaluated the performance of the CNN-BN model in the valence and arousal classification tasks. Our proposed CNN-BN model achieved an average accuracy of 99.1% and 99.5% for valence and arousal, respectively, on the DEAP dataset, while significantly reducing the number of parameters by 93.08% and FLOPs by 94.94%. The CNN-BN model with fewer parameters based on 3D EEG spatiotemporal representation outperforms the state-of-the-art models. Our proposed CNN-BN model with a better parameter efficiency has excellent potential for accelerating CNN-based emotion recognition without losing classification performance.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Electronic skins (e-skins)-electronic sensors mechanically compliant to human skin-have long been developed as an ideal electronic platform for noninvasive human health monitoring. For reliable ...physical health monitoring, the interface between the e-skin and human skin must be conformal and intact consistently. However, conventional e-skins cannot perfectly permeate sweat in normal day-to-day activities, resulting in degradation of the intimate interface over time and impeding stable physical sensing. Here, we present a sweat pore-inspired perforated e-skin that can effectively suppress sweat accumulation and allow inorganic sensors to obtain physical health information without malfunctioning. The auxetic dumbbell through-hole patterns in perforated e-skins lead to synergistic effects on physical properties including mechanical reliability, conformability, areal mass density, and adhesion to the skin. The perforated e-skin allows one to laminate onto the skin with consistent homeostasis, enabling multiple inorganic sensors on the skin to reliably monitor the wearer's health over a period of weeks.
Epitaxial lift-off techniques, which aim to separate ultrathin single-crystalline epitaxial layers off of the substrate, are becoming increasingly important due to the need of lightweight and ...flexible devices for heterogeneously integrated ultracompact semiconductor platforms and bioelectronics. Remote epitaxy is a relatively newly discovered epitaxial lift-off technique that allows substrate-seeded epitaxial growth of ultrathin films through few layers of graphene. This universal epitaxial lift-off technique allows freestanding single-crystal membrane fabrication very quickly at low cost. However, the conventional method of remote epitaxy requires transfer of graphene grown on another substrate to the target single-crystalline substrate, which results in organic and metallic residues as well as macroscopic defects such as cracks and wrinkles, significantly reducing the yield of remote epitaxy. Here, we show that direct growth of thick graphene on the target single-crystalline substrate (SrTiO3 for this study) followed by atomic layer etching (ALE) of the graphene layers create a defect- and residue-free graphene surface for high yield remote epitaxy. We find that the ALE efficiently removes one atomic layer of graphene per cycle, while also clearing multi-dots (clumps of carbon atoms) that form during nucleation of the graphene layers. Our results show that direct-grown graphene on the desired substrate accompanied by ALE might potentially be an ideal pathway toward commercialization of remote epitaxy.
High manganese twinning induced plasticity (TWIP) steel is an attractive material for automotive applications as its use could result in an improved vehicle fuel efficiency and a superior passenger ...safety. Due to the limited research on the hot deformation behaviour of High Mn steel, the selection of suitable operating conditions for the hot rolling process is challenging. The present contribution focusses on the hot deformation behaviour and the dynamic recrystallization kinetics of V micro-alloyed high manganese TWIP steel, by means of single-hit compression test in the temperature range of 850–1000 °C and the strain rate range of 0.1–10 s
−1
. The activation energy for hot deformation and the processing map of a V-free TWIP steel and a V-added TWIP steel were compared by analysing their stress–strain curves. The V-added TWIP steel exhibited a higher activation energy than the V-free TWIP steel, i.e. 383.4 kJ/mol versus 372.5 kJ/mol. Processing maps based on a dynamic material model indicated that the hot workability of TWIP steel was decreased by micro-alloying with V. The effect of V on the hot deformation behaviour of TWIP steels was also analysed by means of its effect on the microstructure using the SEM-EBSD technique. The V-added TWIP steel was characterized by a higher peak stress at a lower peak strain as compared to the V-free TWIP steel, indicating that the onset of dynamic recrystallization was accelerated by the addition of V. The rapid dynamic recrystallization kinetics resulted in a smaller recrystallized grain size in the hot deformed microstructure of the V-added TWIP steel.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Remote epitaxy, which was discovered and reported in 2017, has seen a surge of interest in recent years. Although the technology seemed to be difficult to reproduce by other labs at first, remote ...epitaxy has come a long way and many groups are able to consistently reproduce the results with a wide range of material systems including III-V, III-N, wide band-gap semiconductors, complex-oxides, and even elementary semiconductors such as Ge. As with any nascent technology, there are critical parameters which must be carefully studied and understood to allow wide-spread adoption of the new technology. For remote epitaxy, the critical parameters are the (1) quality of two-dimensional (2D) materials, (2) transfer or growth of 2D materials on the substrate, (3) epitaxial growth method and condition. In this review, we will give an in-depth overview of the different types of 2D materials used for remote epitaxy reported thus far, and the importance of the growth and transfer method used for the 2D materials. Then, we will introduce the various growth methods for remote epitaxy and highlight the important points in growth condition for each growth method that enables successful epitaxial growth on 2D-coated single-crystalline substrates. We hope this review will give a focused overview of the 2D-material and substrate interaction at the sample preparation stage for remote epitaxy and during growth, which have not been covered in any other review to date.
Graphical Abstract
Electrolyte‐gated synaptic transistors (EGSTs) have attracted considerable attention as synaptic devices owing to their adjustable conductance, low power consumption, and multi‐state storage ...capabilities. To demonstrate high‐density EGST arrays, 2D materials are recommended owing to their excellent electrical properties and ultrathin profile. However, widespread implementation of 2D‐based EGSTs has challenges in achieving large‐area channel growth and finding compatible nanoscale solid electrolytes. This study demonstrates large‐scale process‐compatible, all‐solid‐state EGSTs utilizing molybdenum disulfide (MoS2) channels grown through chemical vapor deposition (CVD) and sub‐30 nm organic‐inorganic hybrid electrolyte polymers synthesized via initiated chemical vapor deposition (iCVD). The iCVD technique enables precise modulation of the hydroxyl group density in the hybrid matrix, allowing the modulation of proton conduction, resulting in adjustable synaptic performance. By leveraging the tunable iCVD‐based hybrid electrolyte, the fabricated EGSTs achieve remarkable attributes: a wide on/off ratio of 109, state retention exceeding 103, and linear conductance updates. Additionally, the device exhibits endurance surpassing 5 × 104 cycles, while maintaining a low energy consumption of 200 fJ/spike. To evaluate the practicality of these EGSTs, a subset of devices is employed in system‐level simulations of MNIST handwritten digit recognition, yielding a recognition rate of 93.2%.
This study explores ultrathin all solid‐state electrolyte‐gated synaptic transistors (EGSTs) with chemical vapor deposition (CVD) grown molybdenum disulfide (MoS2) channel and initiated chemical vapor deposition (iCVD) grown organic–inorganic hybrid electrolyte. The fabricated MoS2‐based EGST achieves outstanding synaptics properties, benefitting from sub‐30 nm ultrathin electrolyte and atomically thin channel. The approach provides a guide for EGSTs to overcome scaling challenge.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Abstract
Heterogeneous integration of dissimilar crystalline materials has recently attracted considerable attention due to its potential for high-performance multifunctional electronic and photonic ...devices. The conventional method for fabricating heterostructures is by heteroepitaxy, in which epitaxy is performed on crystallographically different materials. However, epitaxial limitations in monolithic growth of dissimilar materials prevent implementation of high quality heterostructures, such as complex-oxides on conventional semiconductor platforms (Si, III-V and III-N). In this work, we demonstrate gallium nitride (GaN) high-electron-mobility transistors with crystalline complex-oxide material enabled by heterogeneous integration through epitaxial lift-off and direct stacking. We successfully integrate high-κ complex-oxide SrTiO
3
in freestanding membrane form with GaN heterostructure via a simple transfer process as the gate oxide. The fabricated device shows steep subthreshold swing close to the Boltzmann limit, along with negligible hysteresis and low dynamic on-resistance, indicating very low defect density between the SrTiO
3
gate oxide and GaN heterostructure. Our results show that heterogeneous integration through direct material stacking is a promising route towards fabricating functional heterostructures not possible by conventional epitaxy.
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