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A consensus view in catalysis is that a higher density of catalytically active sites indicates a higher reaction rate. Using molecular dynamics simulations capable of mimicking the electrochemical formation of gas molecules, we herein demonstrate that this view is problematic for electrocatalytic gas production. Our simulation results show that a higher density of catalytic active sites does not necessarily indicate a higher reaction rate─a high density of active sites could lead to a reduction in the rate of reaction. Further analysis reveals that this abnormal phenomenon is ascribed to aggregation of the produced gas molecules near catalytic sites. This work challenges the consensus view and lays the groundwork for better developing gas-producing reaction electrocatalysts.

Two-dimensional (2D) semiconductors are promising channel materials for next-generation field-effect transistors (FETs). However, it remains challenging to integrate ultrathin and uniform high-κdielectrics on 2D semiconductors to fabricate FETs with large gate capacitance. We report a versatile two-step approach to integrating high-quality dielectric film with sub-1 nm equivalent oxide thickness (EOT) on 2D semiconductors. Inorganic molecular crystal Sb2O3is homogeneously deposited on 2D semiconductors as a buffer layer, which forms a high-quality oxide-to-semiconductor interface and offers a highly hydrophilic surface, enabling the integration of high-κdielectrics via atomic layer deposition. Using this approach, we can fabricate monolayer molybdenum disulfide-based FETs with the thinnest EOT (0.67 nm). The transistors exhibit an on/off ratio of over 106using an ultra-low operating voltage of 0.4 V, achieving unprecedently high gating efficiency. Our results may pave the way for the application of 2D materials in low-power ultrascaling electronics.

The low NH3yield rate is a grand challenge for electrocatalytic N2reduction to NH3. Herein, we report the first uranium single-atom catalyst (SAC) capable of catalyzing the electrochemical N2reduction reaction (NRR). The uranium SAC features a low limiting potential (<0.5 V) and near-zero free energy changes for N2adsorption and NH3desorption. The integration of these merits enables the uranium SAC to afford an unprecedentedly high NH3yield rate, 3–4 orders of magnitude higher than that of the Ru(0001) surface, which is widely recognized as an excellent NRR electrocatalyst. Further theoretical analysis reveals that the N2reduction catalyzed by the uranium SAC is synergistically regulated by the dand felectrons of atomic uranium. This work proposes a promising solution (that is, atomically dispersed uranium) to the daunting challenge associated with the low NH3yield rate, thus enabling the scalable production of NH3via electrochemical N2reduction.

Two-dimensional (2D) semiconductors have opened opportunities for the development of next-generation semiconductor devices and the continuation of Moore’s law. The absence of qualified dielectrics hinders the scalable application of 2D semiconductors. Herein, we present a joint theory-experiment study shedding light on the exciting prospect of zeolite-like molecules (ZLMs) as the dielectrics for 2D semiconductors. Specifically, ZLMs possess bandgaps and dielectric constants comparable to those of SiO2(the commonly used dielectric in the Si-based semiconductor industry), and ZLMs and 2D semiconductors can form ideal interfaces, in which ZLMs are in van der Waals (vdW) contact with 2D semiconductors and preserve well the intrinsic semiconducting properties of 2D semiconductors. Furthermore, we demonstrated that molecules with a zeolite-like backbone can exhibit remarkable environmental stability. This work offers a promising new family of vdW dielectrics with important implications for the field of 2D semiconductors.

The high electrical conductivity of 1T′-WTe2deserves particular attention and may show a high potential for hydrogen evolution reaction (HER) catalysis. However, the actual activity certainly does not match expectations, and the inferior HER activity is actually still ambiguous at the atomic level. Unraveling the underlying HER behaviors of 1T′-WTe2will give rise to a new family of HER catalysts. Our structural analysis reveals that the inferior activity could result from insufficient charge density around the Te site and blocked adsorption channel at the W site, which cause too weak hydrogen adsorption. Herein, we fabricated a single WTe2sheet-based electrocatalytic microdevice for directly extracting enhanced HER activity of doped electronegative F atoms. The overpotential at –10 mA cm–2reduced to 0.27 V after F doping compared to 0.45 V for the original state. In situ electrochemical measurement and electrical tests on a single sheet indicate that doped F can regulate surface charge and hydrogen adsorption behavior. Furthermore, the theory simulation uncovers that the smaller atomic radius of F contributes to an empty coordination environment; meanwhile, strong electronegativity induces hydrogen adsorption. Thus, the ΔGH*at W sites around the doped F is as low as 0.18 eV. Synergistically modulating the charge properties and opening steric hindrance provides a new pathway to rationally construct electrocatalysts and beyond.

Recent discovery of intrinsic ferromagnetism in Fe3GeTe2(FGT) monolayer [Deng, Y.; Nature2018, 563, 94−99; Fei, Z.; Nat. Mater.2018, 17, 778–782] not only extended the family of two-dimensional (2D) magnetic materials but also stimulated further interest in the possibility to tune their magnetic properties without changing the chemical composition or introducing defects. By means of density functional theory computations, we explore strain effects on the magnetic properties of the FGT monolayer. We demonstrate that the ferromagnetism can be largely enhanced by the tensile strain in the FGT monolayer due to the competitive effects of direct exchange and superexchange interaction. The average magnetic moments of Fe atoms increase monotonically with an increase in biaxial strain from −5 to 5% in FGT monolayer. The intriguing variation of magnetic moments with strain in the FGT monolayer is related to the charge transfer induced by the changes in the bond lengths. Given the successful fabrication of the FGT monolayer, the strain-tunable ferromagnetism in the FGT monolayer can stimulate the experimental effort in this field. This work also suggests an effective route to control the magnetic properties of the FGT monolayer. The pronounced magnetic response toward the biaxial strain can be used to design the magnetomechanical coupling spintronics devices based on FGT.

Organic/inorganic interfaces play dominant roles in the formation of organic thin films and the performance of organic electronic devices. Preparing a high-quality and high-stability interfacial organic layer on the inorganic substrate is currently challenging, and understanding the self-assembly mechanism of the interfacial layer (IL) in depth at a molecular level is thus essential. In this work, by studying the self-assembly of perylene-3,4,9,10-tetracarboxylic dianhydride IL on graphene, we unveil that intermolecular H-bonds can considerably widen the nucleation area, heighten the stability–metastability critical temperature, promote the nucleation speed, and guide the nucleation direction. We further demonstrate that such positive effects on the IL self-assembly are of generality. Moreover, it is found that IL can transform into a well-ordered crystal from an amorphous state through suitable thermal treatment or molecule coverage control. Our work highlights that fabricating H-bond networks is desirable for the synthesis of robust and high-quality IL and points out feasible routes to improve the quality of poor IL.

In this paper, we present systematic studies on the B-, R- and Ks -band luminosity-metallicity (L-Z) relations for a set of metal-poor, blue compact dwarf galaxies (BCDs). Metallicity is derived by using both the empirical N2 and the direct Te methods. Our work reconciles contradictory results obtained by different authors and shows that the L-Z relationship does also hold for BCDs. The empirical N2-based slope of the L-Z relation, for each photometric band, is consistent with the Te -based one. We confirm that the slope of the L-Z relation is shallower in the near-infrared than that in the optical. Our investigations on the correlations between the LB -Z relation residuals and different galactic parameters show that the star formation activities could be a cause of the large scatter in the optical L-Z relationships, whereas the internal absorption might be another possible contributing factor.

A general layered 2D materials-derived atomic substitution conversion strategy is proposed to achieve the synthesis of large-size ultrathin nonlayered 2D materials.Using low-melting-point CdI2flakes via a simple hot plate assisted vertical vapor deposition method as precursor, large-size ultrathin CdS flakes were successfully converted from layered to nonlayered nanostructures through a facile low-temperature chemical sulfurization process.The size and thickness of CdS flakes can be controlled by the CdI2precursor. The growth mechanism is ascribed to the chemical substitution reaction from I to S atoms between CdI2and CdS, which has been evidenced by experiments and theoretical calculations.

We undertook a 4-day spectroscopic observation and conducted a 13-day photometric study of an SU UMa-type dwarf nova, ER Ursae Majoris. The mean $K$-amplitude for the emission lines is $54 \pm 8 \,\mathrm{km} \,\mathrm{s}^{-1}$and the $\gamma$velocity is $8 \pm 4 \,\mathrm{km} \,\mathrm{s}^{-1}$based on our spectroscopic results. A phase shift of 0.22 was also obtained. Our photometric observation confirms superhumps in normal outbursts of ER UMa, and reconciles contradictory observational results obtained by different authors. We find that superhumps possibly develop near each normal outburst maximum and fade out before the next outburst maximum. If the observed humps were not late superhumps, but ordinary superhumps, much more theoretical work should be done to explain the new phenomena.