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Microsupercapacitors (MSCs) are of increasing interest for powering microelectronic systems, while their applications are still limited by insufficient energy densities due to relatively large sizes. To address this critical challenge, herein nanosupercapacitors (NSCs) with fractal structures in 15 μm × 15 μm area are designed and fabricated by focused ion beam processing. Compared with typical interdigital electrode MSCs, the fractal geometry-designed NSCs (FNSCs) exhibit significantly enhanced performances, with the capacitance exceeding 15.1 mF cm−2. It is proved by COMSOL Multiphysics simulations that the abundant sharp corners and narrow inter-electrode distances of the unique fractal designs produce stronger electric field intensity, tremendously increasing their charge storage abilities. Furthermore, a systematic mathematical model is built to evaluate the charge transfer difficulty, stability and performances of FNSCs with different structures and complexities. This study establishes a rational fractal design strategy to screen superior NSCs and push the limit of supercapacitors in future study.

From chemical vapor deposition grown film to nanoscale lithographic devices, etching is a critical procedure to define two-dimensional (2D) materials’ geometry and edge type. Many reported etching procedures could potentially damage the activity of the edge, while a living edge is capable to heal and regrow back. Here we successfully demonstrated a continuous growth-etching-regrowth procedure to achieve the precise lateral control of graphene basal plane. The etching process leaves graphene with dominant zigzag edges. Up to 85% of the new graphene domains can be regrown from the living edges, replicating the graphene’s crystallographic orientation before the etching. At 1050 °C, the etching and regrowth can be linearly controlled at a rate of −2.7 μm/min and 2.4 μm/min, respectively. This represents a promising technique for precisely tailoring the lateral structure of graphene with selective edge type.

Electrocatalytic reduction of N2 to NH3 under an ambient atmosphere is highly desirable and extremely critical for energy-efficient nitrogen utilization. Inspired by the natural MoFe protein-based ...

To reverse the ever-increasing trend of the CO2 concentration in the atmosphere, human needs to develop a killer “catalyst”, which could convert the anthropogenic CO2 back into high value-added or energy-storage molecules, not under the natural photosynthesis Calvin cycle, but through an artificial CO2 reduction pathway. In the race to this emergent technology, the electrochemical reduction of CO2 (CO2RR) with carbon based catalyst becomes one of the frontrunners. However, the carbon-based catalysts are genetically complex, with edge, strain, intrinsic topological defect, and doping effects, coexisting and affecting the catalysis behavior. Without a relative activity ranking system under the same metrics, unveiling the mechanism and improving the catalyst would become formidable. Here we assessed different carbon materials’ CO2RR performance under standard experimental conditions. The catalytic activities were evaluated and sequenced by their cathodic potential, characterized with the peak CO faradic efficiency. The doping effect is leading in the sequence, followed with the other three factors, all of which are superior to the pristine sp2 carbon material.

We demonstrate the fabrication and characterization of large-area van der Waals heterostructure array composed of chemical vapor deposition (CVD) grown multilayer (ML) 2H-MoTe 2 and single-layer (SL) 2H-MoS 2 , which exhibits excellent rectifier properties. The transfer characteristics of field-effect transistors (FETs) are also investigated. Our work acquires excellent homogeneity and device performance, which facilitates the application of two-dimensional (2D) materials in electronics.

The observation of electrically tunable and highly confined plasmons in graphene has stimulated the exploration of interesting properties of plasmons in other two-dimensional materials. Recently, hyperbolic plasmon resonance modes have been observed in exfoliated ${\mathrm{W}\mathrm{Te}}_{2}$ films, a type-II Weyl semimetal with layered structure, providing a platform for the assembly of plasmons with hyperbolicity and exotic topological properties. However, the plasmon modes were observed in relatively thick and small-area films, which restrict the tunability and application for plasmons. Here, large-area (approximately cm) ${\mathrm{W}\mathrm{Te}}_{2}$ films with different thicknesses are grown by the chemical vapor deposition method, in which plasmon resonance modes are observed in films with different thicknesses down to about 8 nm. Hybridization of plasmon and surface polar phonons of the substrate is revealed by mapping the plasmon dispersion. The plasmon frequency is demonstrated to be tunable by changing the temperature and film thickness. Our results facilitate the development of a tunable and scalable ${\mathrm{W}\mathrm{Te}}_{2}$ plasmonic system for revealing topological properties and towards various applications in sensing, imaging, and light modulation.

Recent advances in van der Waals heterostructures have extensively promoted the development of new-generation electronic devices. However, the normally utilized mechanical exfoliation method for preparing two-dimensional semiconductors is not scalable for circuit-level application. Herein, the fabrication and characterization of wafer-scale heterostructure arrays composed of multilayer 2H-MoTe2 and single-layer 2H-MoS2 are demonstrated. Owing to the type-II band alignment facilitating efficient electron–hole separation, the devices fabricated by the p-MoTe2/n-MoS2 heterostructure exhibit an excellent gate-tunable PN diode behavior, with a rectification ratio of over 103 and a self-powered photocurrent with a remarkable on–off ratio of ∼103 at a zero bias voltage. Complementary inverter arrays based on p-MoTe2/n-MoS2 are also demonstrated. The scalable production of p–n junction devices and complementary inverters paves the way for future integrated platforms in photoelectric detection and logic computation.

Catalyst doped with a single-atom noble metal displays distinctive catalytic behavior from the bulk counterparts, with tunable electronic structures and spatial versatilities, which excels in today’s heterogeneous catalysis. To deposit noble metals in a single atomic level requires a restricted chemical environment and precise thermodynamic control. Electroplating methods are commercially used to deposit uniform and conformal metal thin films on different hardware surfaces. Yet the atomic level electroplating has never been achieved. Herein we demonstrate a voltage gauged electrochemical deposition method to synthesize single-atom Pt, Au, and Pd on MoS2 and other two-dimensional (2D) materials. The surface atomic doping level for Pt, Au, and Pd can reach 1.1, 7.0, and 14%, respectively, and the doping sites are precisely positioned at Mo- and S-vacancies. The monodispersed noble atoms show enhanced hydrogen evolution activity and saturated CO tolerance, as explained by density functional theory calculatio...

Advances in microelectronic system technology have necessitated the development and miniaturization of energy storage devices. Supercapacitors are an important complement to batteries in microelectronic systems; and further reduction of the size of micro-supercapacitors is challenging. Here, a novel strategy is demonstrated to break through the resolution limit of micro-supercapacitors by preparing nano-supercapacitors (NSCs) with interdigital nanosized electrodes using focused ion beam technology. The minimization of the size of the NSCs leads to a large increase in capacitance, with a high areal capacitance of 9.52 mF cm-2 and a volumetric capacitance of 18 700 F cm-3 , far superior to those of other reported works. Size reduction and the narrowing of the physical separation between nanoelectrodes are proved to be the most crucial factors in the enhancement of capacitive performances. New charge-storage mechanisms are discovered with a remarkable nonfaradaic double-layer capacitance that exists due to the considerable inner electric field force at the nanoscale. The developed strategy and the first set of data provided here shed light on the design and fabrication of flexible interdigitated NSCs that rival state-of-the-art supercapacitors in performance.

Hexagonal boron nitride (h-BN) is an important member of two-dimensional (2D) materials with a large direct bandgap, and has attracted growing interest in ultraviolet optoelectronics and nanoelectronics. Compared with graphene and graphite, h-BN has weak Raman effect because of the far off-resonance excitation; hence, it is difficult to exploit Raman spectroscopy to characterize important properties of 2D h-BN, such as thickness, doping, and strain effects. Here, we applied stimulated Raman scattering (SRS) to enhance the sensitivity of the E2g Raman mode of h-BN. We showed that SRS microscopy achieves rapid high resolution imaging of h-BN with a pixel dwell time 4 orders of magnitude smaller than conventional spontaneous Raman microscopy. Moreover, the near-perfect linear dependence of signal intensity on h-BN thickness and isotropic polarization dependence allow convenient determination of the flake thickness with SRS imaging. Our results indicated that SRS microscopy provides a promising tool for high-speed quantification of h-BN and holds the potential for vibrational imaging of 2D materials.

The booming frontier of electrochemistry is radically transforming the landscape of global chemical and energy industry. Most recent advancements in electrocatalysts have been built on trial and error, lacking model experiments to illuminate the fundamental factors hidden behind, such as phase, conductivity, and surface coordination environment. Here, we use phase-controllable, highly oriented two-dimensional MoTe2 as the model catalysts. The 2H phase MoTe2's conductivity can be engineered both extrinsically and intrinsically by single-layer graphene and lithiation, bringing down the sheet resistance from 0.95 MΩ/□ to 0.8 kΩ/□ and 0.6 kΩ/□. The corresponding electrocatalytic performance was unlocked from a silent state, catching up to its 1T' counterpart, with a parallel Tafel slope of 141 mV/dec. A focused ion beam further exposed the edge atoms, which exhibited a hydrogen evolution turnover frequency 104 times superior to that of basal plane atoms.

Chemical vapor deposition synthesis of semiconducting transition metal dichalcogenides (TMDs) offers a new route to build next-generation semiconductor devices. But realization of continuous and uniform multilayer (ML) TMD films is still limited by their specific growth kinetics, such as the competition between surface and interfacial energy. In this work, a layer-by-layer vacuum stacking transfer method is applied to obtain uniform and non-destructive ML-MoS

Author(s): Xu, H; Zhang, H; Liu, Y; Zhang, S; Sun, Y; Guo, Z; Sheng, Y; Wang, X; Luo, C; Wu, X; Wang, J; Hu, W; Xu, Z; Sun, Q; Zhou, P; Shi, J; Sun, Z; Zhang, DW; Bao, W | Abstract: Semiconductive transition metal dichalcogenides (TMDs) have been considered as next generation semiconductors, but to date most device investigations are still based on microscale exfoliation with a low yield. Wafer scale growth of TMDs has been reported but effective doping approaches remain challenging due to their atomically thick nature. This work reports the synthesis of wafer-scale continuous few-layer PtSe2 films with effective doping in a controllable manner. Chemical component analyses confirm that both n-doping and p-doping can be effectively modulated through a controlled selenization process. The electrical properties of PtSe2 films have been systematically studied by fabricating top-gated field effect transistors (FETs). The device current on/off ratio is optimized in two-layer PtSe2 FETs, and four-terminal configuration displays a reasonably high effective field effect mobility (14 and 15 cm2 V−1 s−1 for p-type and n-type FETs, respectively) with a nearly symmetric p-type and n-type performance. Temperature dependent measurement reveals that the variable range hopping is dominant at low temperatures. To further establish feasible application based on controllable doping of PtSe2, a logic inverter and vertically stacked p–n junction arrays are demonstrated. These results validate that PtSe2 is a promising candidate among the family of TMDs for future functional electronic applications.