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Self-intercalation of native metal atoms in two-dimensional (2D) transition metal dichalcogenides has received rapidly increasing interest, due to the generation of intriguing structures and exotic physical properties, however, only reported in limited materials systems. An emerging type-II Dirac semimetal, NiTe

Exploring new-type 2D magnetic materials with high magnetic transition temperature and robust air stability has attracted wide attention for developing innovative spintronic devices. Recently, intercalation of native metal atoms into the van der Waals gaps of 2D layered transition metal dichalcogenides (TMDs) has been developed to form 2D non-layered magnetic TMDs, while only succeeded in limited systems (e.g., Cr

Collecting water from fog flow has emerged as a promising strategy for the relief of water shortage problems. Herein, using a UV-induced (ultraviolet light induced) controllable diffusion method combined with technology of three-dimensional (3D) printing, we fabricate biomimetic materials incorporating beetle-like hydrophobic-hydrophilic character and cactus-like cone arrays with various structure parameters, and then systematically study their fog-harvesting performance. The UV-induced controllable diffusion method can break away from the photomask to regulate the hybrid wettability. Moreover, employing 3D printing technology can flexibly control the structure parameters to improve the water collection efficiency. It is found that the water collection rate (WCR) can be optimized by controlling the hybrid wettability of the sample surface and cone distance and using substrates with printed holes, which lead to a 109% increase of WCR.

Collecting water from fog flow is emerging as a promising solution to the water shortage problem. This work demonstrated a novel environmentally responsive water collector made from a self-prepared Janus polyvinyl alcohol sponge in combination with a two-way shape memory alloy spring, which transforms the traditional manner of static water collection into a dynamic one. The unidirectional water transport of the Janus structure together with the dynamic collection approach correspond to a 30.8% increase in the water-collection rate (WCR). The resultant WCR is up to 5.1 g/h, which ranks relatively high compared to similar studies. The light- and thermal-response capability, easy fabrication, and good cycling performance indicate that our devices could be utilized in a variety of applications. In this work, an efficient, intelligent adaptive, simple-preparation, precision-guided, and economical fog-collecting devices are recommended. Our work provides new insights on the design of high-efficient water collectors with practicability.

Molybdenum carbides show great potential to replace platinum for electrocatalytic hydrogen evolution reaction (HER) to resolve the problem of hydrogen production, due to their high reserves, stabil...

Layered platinum tellurium (PtTe2) was recently synthesized with controllable layer numbers down to a monolayer limit. Using ab initio calculations based on anisotropic Midgal-Eliashberg formalism, we show that by rubidium (Rb) intercalation, weak superconductivity in bilayer PtTe2 can be significantly boosted with superconducting Tc = 8 K in the presence of spin-orbit coupling (SOC). The intercalant on one hand mediates the interlayer coupling and serves as an electron donor, leading to large density of states at Fermi energy. On the other hand, it increases the mass-enhancement parameter with electron-phonon coupling strength comparable to that of Pt. The potassium intercalated bilayer PtTe2 has a comparable Tc to the case of Rb intercalation. The relatively high Tc with SOC combined with experimental accessible crystal structures suggest that these superconductors are promising platforms to study the novel quantum physics associated with two-dimensional superconductivity, such as the recently proposed type-II Ising superconductivity., Comment: 7 pafges, 4 figures. Accepted by PRB(2021)

Searching for none or less Pt-containing electrocatalytic materials for hydrogen evolution is a promising way to reduce the cost of hydrogen production. Thus, a computational screening of electrocatalytic materials for hydrogen evolution reaction (HER), Pt monolayer on transitional metals (Pt/TM), are carried out by DFT in this work. According to several prerequisites, including difficulty of synthesis, stability in electrochemical environment, HER activity, and economical cost, several stable, high activity, and low cost surfaces for HER are chosen. In detail, the Pt/TM(001)[TM = Fe, Mo, V, W or Nb], Pt/TM(111)[TM = Ag, Pd or Au], and Pt/Re(0001) moieties are found to have a predicted high activity comparable to pure Pt. In particular, the five Pt/TM(001) surfaces are economical and seldom reported. Even more, Pt/TM(001)[W, Nb, V, Fe] may be even much better than pure Pt, for both the suitable hydrogen adsorption ability and larger exchange current. Further DFT analysis indicates the HER activity on Pt/T...

Defect and substrate introduced into catalyst are two feasible routes toward design of heterogeneous catalysts. It is vital to identify and understand the relationships among atomic, electronic structures and adsorbate binding ability of the catalytic surfaces. Herein, hydrogen evolution on different defect graphene with and without two-dimensional (2D) Mo2C substrate are selected as examples to explore the relationships. Three feasible electronic structural descriptors, including p and pz band centers of local atoms, electron transfer to local atoms, and deformation charge densities of composite structures, are exacted from electronic properties of the defect and substrate-supported graphene. It is found that those descriptors could predict the hydrogen binding energy quantitatively, and the hydrogen adsorption order qualitatively. The descriptor of local p and pz band centers originate from hybridization between the site atom and adsorbate. It is believed that the relationship of atomic structure, electronic structure and binding energy may be applied to other surfaces, and shed light on the nature origin of the structure–activity on electrochemistry. By tuning the descriptors by atomic structure of defect or substrate, suitable hydrogen binding ability and superior hydrogen evolution performance of graphene could be achieved. Several structures based on graphene own superior hydrogen evolution activity: the exchange current densities of S3NV1-G, S2NV2-G@Mo2C, N1-G@Mo2C, and N2-G@Mo2C are predicted to be 0.811, 0.963, 0.712, and 1.860 mA/cm2, respectively. Especially the last two ones, their negative interfacial binding energies, and the energy favorability of forming N1 and N2 defects, ensure their stabilities and easy syntheses in experiment, and enhance their potential applications.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have a range of unique physics properties and could be used in the development of electronics, photonics, spintronics and quantum computing devices. The mechanical exfoliation technique of micro-size TMD flakes has attracted particular interest due to its simplicity and cost effectiveness. However, for most applications, large area and high quality films are preferred. Furthermore, when the thickness of crystalline films is down to the 2D limit (monolayer), exotic properties can be expected due to the quantum confinement and symmetry breaking. In this paper, we have successfully prepared macro-size atomically flat monolayer NbSe2 films on bilayer graphene terminated surface of 6H-SiC(0001) substrates by molecular beam epitaxy (MBE) method. The films exhibit an onset superconducting critical transition temperature above 6 K, 2 times higher than that of mechanical exfoliated NbSe2 flakes. Simultaneously, the transport measurements at high magnetic fields reveal that the parallel characteristic field Bc// is at least 4.5 times higher than the paramagnetic limiting field, consistent with Zeeman-protected Ising superconductivity mechanism. Besides, by ultralow temperature electrical transport measurements, the monolayer NbSe2 film shows the signature of quantum Griffiths singularity when approaching the zero-temperature quantum critical point.

Two-dimensional superconductors exfoliated from layered materials harbor novel superconductivity and exotic correlated phases, often concomitantly, but their discovery has been few and far between. Employing the anisotropic Migdal-Eliashberg formalism based on ab initio calculations, we find monolayer ${\mathrm{NiTe}}_{2}$ to be an intrinsic superconductor with a ${T}_{\text{c}}\ensuremath{\sim}5.7$ K, although the bulk crystal is not known to superconduct. Remarkably, bilayer ${\mathrm{NiTe}}_{2}$ intercalated with lithium is found to display two-gap superconductivity with a critical temperature ${T}_{\text{c}}\ensuremath{\sim}11.3$ K and a superconducting gap of $\ensuremath{\sim}3.1$ meV, arising from a synergy of electronic and phononic effects. As monolayer and bilayer ${\mathrm{NiTe}}_{2}$ have been recently isolated experimentally, and lithium can be inserted into the bilayer via ionic liquid gating, the comparatively high ${T}_{\text{c}}$, substrate independence, and proximity tunability will make these superconductors ideal platforms for exploring intriguing correlation effects and quantum criticality associated two-dimensional superconductivity.

In contrast to traditional rechargeable rock-chair metal-ion batteries, dual-ion batteries (DIBs) involve redox reactions with anions rather than cations in p-type cathodes. In principle, regulating the electrochemical performance of the DIB by different anion species is highly feasible. Herein, the anion effect on the electrochemical performance of a DIB, the aqueous Zn- organic radical battery (Zn-ORB), consisting of a poly(2,2,6,6tetramethylpiperidinyloxy-4-yl vinyl ether) cathode and a Zn anode, was investigated by DFT calculations. SO4 2- , CF3 SO3 - , and ClO4 - with different molecular electrostatic potential values were selected as anion models. DFT calculations revealed that a stronger electrostatic interaction of the anion with the organic radical resulted in a higher operating voltage of the Zn-ORB, which was consistent with experimental results. These results bring new insight into the redox chemistry of p-type organic radicals with anions and will promote the development of high-power aqueous Zn-ORBs as well as inspire more investigations into the anion effect towards novel battery designs.

Charge density waves (CDWs) in the cuprate high-temperature superconductors have evoked much interest, yet their typical short-range nature has raised questions regarding the role of disorder. Here we report a resonant X-ray diffraction study of ZrTe\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{3}$$\end{document}3, a model CDW system, with focus on the influence of disorder. Near the CDW transition temperature, we observe two independent signals that arise concomitantly, only to become clearly separated in momentum while developing very different correlation lengths in the well-ordered state that is reached at a distinctly lower temperature. Anomalously slow dynamics of mesoscopic charge domains are further found near the transition temperature, in spite of the expected strong thermal fluctuations. Our observations signify the presence of distinct experimental fingerprints of pristine and disorder-perturbed CDWs. We discuss the latter also in the context of Friedel oscillations, which we argue might promote CDW formation via a self-amplifying process., The role of disorder in the formation of charge density waves (CDWs) remains elusive in typical CDW materials. Here, the authors report coexisting diffraction signals and anomalous slow dynamics of charge domains near the CDW transition temperature in ZrTe\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${}_{3}$$\end{document}3, suggesting as fingerprints of pristine and disorder-perturbed CDWs.

Monolayer 2H-NbSe2 has recently been shown to be a 2-dimensional superconductor, with a coexisting charge-density wave (CDW). As both phenomena are intimately related to electron-lattice interaction, a natural question is how superconductivity and CDW are interrelated through electron-phonon coupling (EPC), which is important to the understanding of 2-dimensional superconductivity. This work investigates the superconductivity of monolayer NbSe2 in CDW phase using the anisotropic Migdal-Eliashberg formalism based on first principles calculations. The mechanism of the competition between and coexistence of the superconductivity and CDW is studied in detail by analyzing EPC. It is found that the intra-pocket scattering is related to superconductivity, leading to almost constant value of superconducting gaps on parts of the Fermi surface. The inter-pocket scattering is found to be responsible for CDW, leading to partial or full bandgap on the remaining Fermi surface. Recent experiment indicates that there is transitioning from regular superconductivity in thin-film NbSe2 to two-gap superconductivity in the bulk, which is shown here to have its origin in the extent of Fermi surface gapping of K and K' pockets induced by CDW. Overall blue shifts of the phonons and sharp decrease of Eliashberg spectrum are found when the CDW forms., 12 pages, 13 figures in total. Accepted, Physical Review B (Rapid Communication) (2019)

Monolayer ${\mathrm{NbSe}}_{2}$ has recently been shown to be a two-dimensional superconductor, with a competing charge-density wave (CDW) order. This work investigates the electronic structure of monolayer ${\mathrm{NbSe}}_{2}$ based on first-principles calculations, focusing on charge and magnetic orders. It is found that decreased screening in the monolayer ${\mathrm{NbSe}}_{2}$ with a perfect lattice exhibits magnetic instability, which is removed by the formation of CDW. Two energetically competitive but distinct $3\ifmmode\times\else\texttimes\fi{}3$ CDW structures are revealed computationally, which have a significant impact on the Fermi surface. The relations of the potential CDW phases with experimental structure and the coexisting superconductivity are discussed.

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have a range of unique physics properties and could be used in the development of electronics, photonics, spintronics, and quantum computing devices. The mechanical exfoliation technique of microsize TMD flakes has attracted particular interest due to its simplicity and cost effectiveness. However, for most applications, large-area and high-quality films are preferred. Furthermore, when the thickness of crystalline films is down to the 2D limit (monolayer), exotic properties can be expected due to the quantum confinement and symmetry breaking. In this paper, we have successfully prepared macro-size atomically flat monolayer NbSe

We report the determination of electron effective mass in InN by using cyclotron resonance (CR) spectroscopy. To avoid the influence of sapphire substrate on CR measurements, InN epilayer with low residual electron concentration of 5 × 1017 cm−3 was grown on silicon substrate. Together with analyzing the effect of non-parabolic band structure, we derive that the isotropy c-plane electron effective mass of InN epilayer is 0 . 0 50 ± 0.0 0 2 m0 and 0 . 0 58 ± 0.0 0 2 m0 at temperatures of 4.2 and 50 K, respectively, which is in good agreement with our theoretical predication of the effective mass near the Γ point.

Quantum spin Hall (QSH) materials are two-dimensional systems exhibiting insulating bulk and helical edge states simultaneously. A QSH insulator processes topologically non-trivial edge states protected by time-reversal symmetry, so that electrons can propagate unscattered. Realization of such topological phases enables promising applications in spintronics, dissipationless transport and quantum computations. Presently, realization of such QSH-based devices are limited to complicated heterostructures. Monolayer 1T'-WTe2 was predicted to be semimetallic QSH materials, though with a negative band gap. The quasi-particle spectrum obtained using hybrid functional approach shows directly that the quantum spin Hall gap is positive for monolayer 1T'-WTe2. Optical measurement shows a systematic increase in the interband relaxation time with decreasing number of layers, whereas transport measurement reveals Schottcky barrier in ultrathin samples, which is absent for thicker samples. These three independent pieces of evidence indicate that monolayer 1T'-WTe2 is likely a truly 2-dimensional quantum spin Hall insulator., 21 pages, 6 figures; Has been published online by Advanced Materials (2016)

Charge-density-wave (CDW) order has long been interpreted as arising from a Fermi-surface instability in an initiating metallic phase. While phonon-electron coupling has been recently suggested to influence the formation of CDW order in quasi-two-dimensional (quasi-2D) systems, the presumed dominant importance of Fermi-surface nesting remains largely unquestioned in quasi-1D systems. A key step toward this quest requires a close-knit synthesis of spectroscopic evidence and microscopic knowledge about the electronic structure and the lattice dynamics in a prototypical system. Here we take this approach to show that phonon-electron coupling is also important for the CDW formation in a model quasi-1D system ${\mathrm{ZrTe}}_{3}$, with joint experimental and computational investigation. It is revealed that singularly strong coupling between particular lattice-distortion patterns and conduction electrons gives rise to anomalously broad Raman phonon peaks, which exhibit a distinct anisotropy in both the measured and the computed linewidths. The dependence of the coupling strength on electron momentum further dictates the opening of (partial) electronic gaps in the CDW phase. Since lattice distortion and electronic gaps are defining signatures of CDW order, our results demonstrate that while Fermi-surface nesting determines the CDW periodicity in this quasi-1D system, the conventional wisdom needs to be substantially supplemented by phonon-electron coupling for a quantitative understanding of the CDW order.

Electrodes with three-dimensional (3D) nanostructure are expected to improve the energy and power densities per footprint area of lithium ion microbatteries. Herein, we report a large-scale synthesis of a SnO(2)/α-Fe(2)O(3) composite nanotube array on a stainless steel substrate via a ZnO nanowire array as an in situ sacrificial template without using any strong acid or alkali. Importantly, both SnO(2) and α-Fe(2)O(3) contribute to the lithium storage, and the hybridization of SnO(2) and α-Fe(2)O(3) into an integrated nanotube structure provides them with an elegant synergistic effect when participating in electrochemical reactions. Large areal capacities and good rate capability are demonstrated for such a composite nanotube array. Particularly noteworthy is that the areal capacities (e.g. 1.289 mAh cm(-2) at a current rate of 0.1 mA cm(-2)) are much larger than those of many previous thin-film/3D microbattery electrodes. Our work suggests the possibility of further improving the areal capacity/energy density of 3D microelectrodes by designing ordered hybrid nanostructure arrays.