Publications

Abstract Due to the heavy reliance on computers and networks, security issues have become a major concern for individuals, companies, and nations. Traditional security measures such as personal identification numbers, tokens, or passwords only provide limited protection. With the development of intelligent keyboard (IKB), this paper proposes a deep‐learning‐based keystroke dynamics identification method for increased security. The IKB is a kind of self‐powered, nonmechanical‐punching keyboard, which converts mechanical stimuli applied to the keyboard into local electronic signals. Multilayer deep belief network (DBN) is established to mine the useful information from raw electronic signals and output the keystroke dynamics identification result. The contributions include development of a novel solution that does not rely on manual feature extraction, and provides promising recognition accuracy on large amount of typing samples. One significant advantage of the proposed method is that it extracts features adaptively from the raw current signals and automatically recognizes the typing pattern, which simplifies the design of verification and identification system. The experimental results on 104 typing samples demonstrate the effectiveness of the proposed method. The proposed method has extensive applications in keyboard‐based information security.

Abstract Graphene has attracted considerable interest for next‐generation electronics. However, the absence of natural bandgap has limited the current on/off ratio of graphene‐based transistors. Vertical integration of 2D heterostructures offers a promising approach to address this challenge, enabling high‐current‐density vertical field‐effect transistor (VFET) with large on/off ratio. Here, a triboelectric potential‐powered VFET with a vertical stacked graphene/MoS 2 heterostructure and a sliding‐mode triboelectric nanogenerator (TENG) coupled with gate dielectrics are proposed. The tribotronic VFET has an ultrashort channel length in vertical direction, exhibiting excellent current driving capability with an ultrahigh on‐state current density of 950 A cm −2 and a good current on/off ratio of 630. It also demonstrates reconfigurable diode behavior with a rectification ratio over 10 2 . Temperature‐dependent studies are applied to tribotronic devices for the first time, indicating an effective modulation on the Schottky barrier height of 150 meV by the triboelectric potential. A green LED pixel is driven by the tribotronic VFET as a demonstration to work as a tactile interactive light‐emitting device. The demonstrated tribotronic vertical device offers a promising strategy for integrating various 2D layered materials with TENG in vertical direction, enabling 3D integration of low‐power and interactive devices for next‐generation electronics.

Though the application of bimetallic nanoparticles is becoming increasingly important, the local atomistic structure of such alloyed particles, which is critical for tailoring their properties, is not yet very clearly understood. In this work, we present detailed study on the atomistic structure of Au-Cu nanoparticles so as to determine their most stable configurations and the conditions for obtaining clusters of different structural variants. The dynamic behavior of these nanoparticles upon local heating is investigated. AuCu nanoparticles are characterized by high resolution transmission electron microscopy (HRTEM) and energy filtering elemental composition mapping (EFECM), which allowed us to study the internal structure and the elemental distribution in the particles. Quantum mechanical approaches and classic molecular dynamics methods are applied to model the structure and to determine the lowest energy configurations, the corresponding electronic structures, and understand structural transition of clusters upon heating, supported by experimental evidences. Our theoretical results demonstrate only the core/shell bimetallic structure have negative heat of formation, both for decahedra and octahedral, and energetically favoring core/shell structure is with Au covering the core of Cu, whose reverse core/shell structure is not stable and may transform back at a certain temperature. Experimental evidences corroborate these structures and their structural changes upon heating, demonstrating the possibility to manipulate the structure of such bimetallic nanoparticles using extra stimulating energy, which is in accordance with the calculated coherence energy proportions between the different configurations.

Epigenetic modification plays a crucial role in establishing the transcriptional program that governs the differentiation of CD8+ effector T cells. However, the mechanisms by which this process is regulated at an early stage, prior to the expression of master transcription factors, are not yet fully understood. In this study, we have identified PDCD5 as an activation-induced molecule that is necessary for the proper differentiation and expansion of antigen-specific CD8+ effector T cells in a mouse model of chronic viral infection. The genetic deletion of Pdcd5 resulted in impaired differentiation and function of effector T cells, while T-cell activation, metabolic reprogramming, and the differentiation of memory/exhausted T cells were largely unaffected. At the molecular level, we observed reduced chromatin accessibility and transcriptional activity of Tbx21 and its regulated genes in Pdcd5-/- CD8+ T cells. We further identified that PRDM9 facilitates the H3K4me3 modification of genes associated with the effector phenotype in CD8+ T cells. The interaction between PDCD5 and PRDM9 promotes the nuclear translocation and lysine methyltransferase activity of PRDM9. Collectively, these findings highlight the crucial role of the PDCD5/PRDM9 axis in epigenetic reprogramming during the early stages of fate determination for effector CD8+ T cell fate.

Two-dimensional (2D) molybdenum disulfide (MoS2) is an exciting material due to its unique electrical, optical, and piezoelectric properties. Owing to an intrinsic band gap of 1.2–1.9 eV, monolayer or a-few-layer MoS2 is used for fabricating field effect transistors (FETs) with high electron mobility and on/off ratio. However, the traditional FETs are controlled by an externally supplied gate voltage, which may not be sensitive enough to directly interface with a mechanical stimulus for applications in electronic skin. Here we report a type of top-pressure/force-gated field effect transistors (PGFETs) based on a hybrid structure of a 2D MoS2 flake and 1D ZnO nanowire (NW) array. Once an external pressure is applied, the piezoelectric polarization charges created at the tips of ZnO NWs grown on MoS2 act as a gate voltage to tune/control the source–drain transport property in MoS2. At a 6.25 MPa applied stimulus on a packaged device, the source–drain current can be tuned for ∼25%, equivalent to the results of applying an extra −5 V back gate voltage. Another type of PGFET with a dielectric layer (Al2O3) sandwiched between MoS2 and ZnO also shows consistent results. A theoretical model is proposed to interpret the received data. This study sets the foundation for applying the 2D material-based FETs in the field of artificial intelligence.

An optical fiber-based 3D hybrid cell consisting of a coaxially structured dye-sensitized solar cell (DSSC) and a nanogenerator (NG) for simultaneously or independently harvesting solar and mechanical energy is demonstrated. The current output of the hybrid cell is dominated by the DSSC, and the voltage output is dominated by the NG; these can be utilized complementarily for different applications. The output of the hybrid cell is about 7.65 μA current and 3.3 V voltage, which is strong enough to power nanodevices and even commercial electronic components.

Triboelectric nanogenerator (TENG)-based display techniques are promising in converting kinetic energy into light signals for optical communications. However, the instantaneous TENG current usually generates transient light, leading to incomplete information. Hence, a self-powered phosphorescence display (SPD) system is proposed to realize complete information display. Ultralong organic phosphorescence (UOP) combined with an elastomer is applied to contrive a delayed luminescent array, and a TENG in a slant grating electrode of 45° is fabricated to generate electricity in latitudinal and longitudinal trajectories. The assembled SPD system can provide ultralong phosphorescence over 2.5 s, about 10 times longer than the original LED. A luminescent array is fabricated to demonstrate the delayed display of the SPD system, where the patterned trajectory of the TENG is reproduced as a delayed display that can avoid missing information. This SPD system is anticipated to improve applications of UOP materials in displays and to broaden applications of TENG in self-powered display and visualized tracking.

The monitoring of space debris assumes paramount significance to ensure the sustainability and security of space activities as well as underground bases in outer space. However, designing a wide range monitoring system with easy fabrication, low power, and high precision remains an urgent challenge under the scarcity of materials and extreme environment conditions of outer space. Here, we designed a one-piece, robust, but flexible, and repairable 3D metal-printed triboelectric nanogenerator (FR-TENG) by incorporating the advantages of standardization and customization of outer space 3D metal printing. Inspired by the structure of hexagonal and pangolin scales, a curved structure is ingeniously applied in the design of 3D printed metal to adapt different curved surfaces while maintaining superior compressive strength, providing excellent flexibility and shape adaptability. Benefiting from the unique structural design, the FR-TENG has a minimum length of 1 cm with a weight of only 3.5 g and the minimum weight resolution detected of 9.6 g, with a response time of 20 ms. Furthermore, a multichannel self-powered collision monitoring system has been developed to monitor minor collisions, providing warnings to determine potential impacts on the space station and bases surfaces. The system may contribute to ensuring the successful completion of space missions and providing a safer space environment for the exploration of extraterrestrial life and the establishment of underground protective bases.