Abstract
Lateral heterostructures of two-dimensional (2D) materials, integrating different phases or materials into a single piece of nanosheet, have attracted intensive research interests for ...electronic devices. Extending the 2D lateral heterostructures to spintronics demands more diverse electromagnetic properties of 2D materials. In this paper, using density functional theory calculations, we survey all IV, V, and VI group transition metal dichalcogenides (TMDs) and discover that CrS
2
has the most diverse electronic and magnetic properties: antiferromagnetic (AFM) metallic 1T phase, non-magnetic (NM) semiconductor 2H phase, and ferromagnetic (FM) semiconductor 1T′ phase with a Curie temperature of ~1000 K. Interestingly, we find that a tensile or compressive strain can turn the 1T′ phase into a spin-up or spin-down half-metal. Such strain tunability can be attributed to the lattice deformation under tensile/compressive strain that selectively promotes the spin-up/spin-down VBM (valence band bottom) orbital interactions. The diverse electromagnetic properties and the strain tunability enable strain-controlled spintronic devices using a single piece of CrS
2
nanosheet with improved energy efficiency. As a demo, a prototypical design of the spin-valve logic device is presented. It offers a promising solution to address the challenge of high energy consumption in miniaturized spintronic devices.
Lead-based organic-inorganic hybrid perovskite materials are widely applied in solar cells due to their excellent optoelectronic properties. These materials usually appear ferroelectricity with the ...built-in electric field, which can be used to improve the power conversion efficiency (PCE) of solar cells. However, the toxicity of lead has severely hampered their applications. Hence, it is of utmost significance to explore novel organic-inorganic hybrid perovskite materials with non-toxicity, ferroelectricity, and narrow bandgap at room temperature to enhance the PCE for broad practical applications. Herein, we reported a lead-free hybrid molecular ferroelectric material, i.e. (C5N2H9)3Bi2I9, with zero-dimensional perovskite-like structure. (C5N2H9)3Bi2I9 undergoes first-order ferroelectric phase transition with a Curie temperature of 327 K. Moreover, the dielectric constants of (C5N2H9)3Bi2I9 exhibit a step-like anomaly varied between the high-temperature paraelectric phase and the low-temperature ferroelectric phase. Furthermore, (C5N2H9)3Bi2I9 demonstrates a narrow bandgap of 2.1 eV. Hence, the as-reported novel member of the organic-inorganic hybrid family renders great promise for optoelectronic devices.
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•Novel organic-inorganic hybrid perovskite (C5N2H9)3Bi2I9 was synthesized.•It was designed by selecting N-methylimidazole and non-toxic metal Bi.•The material has shown a paraelectric-to-ferroelectric phase transition at 327 K.•This designed molecular ferroelectric also exhibit a narrow bandgap of 2.1 eV.
The fundamental question of whether CO2 can react with steam at high temperatures in the absence of electrolysis or high pressures is answered. These two gases are commonly co‐present as industrial ...wastes. Herein, a simple experiment by flowing CO2 and steam through a CaCl2 matrix at 500–1000 °C and atmospheric pressure was designed. Comprehensive characterizations and density functional theory calculations were conducted. Meanwhile, this study aims to recover HCl from CaCl2 via a low‐emission oxy‐pyrohydrolysis process. As confirmed, CO2 and steam interact strongly on the CaCl2 surface, leading to an explicit formation of CaCO3/CaO and a nearly complete release of HCl. This is mainly contributed to a halved energy required for the splitting of H2O, resulting from the formation of a bicarbonate‐like structure to replace Cl− out of CaCl2, an otherwise industrial waste, whilst an important dopant for carbon capture, utilization and storage, and medium for electrochemical synthesis.
No electrolysis needed: CO2 can react with steam at high temperatures in the presence of CaCl2 without electrolysis. This finding can be used to deliver a brand‐new oxy‐pyrohydrolysis of CaCl2 or advanced CO2 capture, utilization, and storage (CCUS). It also applies to the electrolysis processes where CaCl2 is applied as a medium for the direct reduction of CO2 and metal oxides.
Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) is one of the most widely used powerful explosives. The direct and selective detection of HMX, without the requirement of specialized equipment, ...remains a great challenge due to its extremely low volatility, unfavorable reduction potential and lack of aromatic rings. Here, we report the first chemical probe of direct identification of HMX at ppb sensitivity based on a designed metal-organic cage (MOC). The cage features two unsaturated dicopper units and four electron donating amino groups inside the cavity, providing multiple binding sites to selectively enhance host-guest events. It was found that compared to other explosive molecules the capture of HMX inside the cavity would strongly modulate the emissive behavior of the host cage, resulting in highly induced fluorescence “turn-on” (160 folds). Based on the density functional theory (DFT) simulation, the mutual fit of both size and binding sites between host and guest leads to the synergistic effects that perturb the ligand-to-metal charge-transfer (LMCT) process, which is probably the origin of such selective HMX-induced turn-on behavior.
Direct identification of HMX at ppb sensitivity based on a designed metal-organic cage was developed. Capture of HMX inside the cavity strongly induced fluorescence “turn-on” (160 folds) due to mutual fit of both size and binding sites between host and guest, leading to synergistic effects that perturb ligand-to-metal charge-transfer process. Display omitted
Multilayered graphene-based membranes are promising for a variety of applications related to ion or molecule transport, such as energy storage and water treatment. However, the complex ...three-dimensional cascading nanoslit-like structure embedded in the membrane makes it difficult to interpret and rationalize experimental results, quantitatively compare with the traditional membrane systems, and quantitatively design new membrane structures. In this paper, systematic numerical simulations were performed to establish an equivalent one-dimensional (1D) nanochannel model to represent the structure of multilayered graphene membranes. We have established a quantitative relationship between effective diffusion length Leff and cross-section area Aeff of the 1D model and our recently developed two dimensional (2D) representative microstructure for graphene membranes. We find that only in the cases of a relatively large lateral size L (> ~100 nm) and a small slit size h (< 2 nm), the effective diffusion length Leff and Aeff can be calculated by an over-simplified but often used model. Otherwise, they show complex dependence on all three structural parameters of the 2D structural model. Our equivalent 1D nano-channel model can reproduce experimental results very well except for h < 0.5 nm. The discrepancy could be attributed to the anomalous behaviour of molecules under nano-confinement that is not considered in our simulations. This model can also be extended to multilayered membranes assembled by other 2D materials.
Mechanical exfoliation is a widely used method to isolate high quality graphene layers from bulk graphite. In our recent experiments, some ordered microstructures, consisting of a periodic ...alternation of kinks and stripes, were observed in thin graphite flakes that were mechanically peeled from highly oriented pyrolytic graphite. In this paper, a theoretical model is presented to attribute the formation of such ordered structures to the alternation of two mechanical processes during the exfoliation： （1） peeling of a graphite flake and （2） mechanical buckling of the flake being sub- jected to bending. In this model, the width of the stripes L is determined by thickness h of the flakes, surface energy Y, and critical buckling strain ecr. Using some appropriate values of y and ecr that are within the ranges determined by other inde- pendent experiments and simulations, the predicted relations between the stripe width and the flake thickness agree reason- ably well with our experimental measurements. Conversely, measuring the L-h relations of the periodic microstructures in thin graphite flakes could help determine the critical mechan- ical buckling strain εcr and the interface energy γ.
Two-dimensional porous coordination polymers are the perfect candidates as ultrathin membranes with superior gas separation performances. However, fundamental understanding on the crystal growth, ...which is vital for membrane applications, is very limited. Studies on the crystal morphologies could provide valuable clues. In this paper, we carried out an ab initio study to understand the crystal morphology of the two-dimensional ZIF-L. Several typical surfaces, such as (001), (100), (010), and (110) surface slabs, were generated by using our developed automated surface generation software package. The corresponding surface energies were calculated. Our results show that the surface relaxation is localized in the first Zn layer, but the magnitude of energy reduction is quite significant, about 60% of surface energy of the as-cut surfaces. We identified two important factors that determine the surface energetic orders of different crystal surfaces: number density and the types of dangling bonds. Particularly, we find that breaking the second coordination bond at one zinc center costs about 65% more energy than the first bond. Based on our surface energy results, the Wulff construction reproduces the smooth curvy leaf shape morphology very well. In the end, we show that our understanding could be extended to another well-known 2D ZIF crystal. Our study would provide valuable insights into the physical/chemical interactions inside such 2D crystals and the growth mechanisms.
Molecular dynamics simulations are performed to understand the characteristics of the one-dimensional Brownian motion of water columns inside carbon nanotubes (CNTs) at room temperature. It is found ...that the probability of 2–10-nm-long water columns sliding a distance larger than the energy barrier period inside 2–5-nm-diameter CNTs is greater than 50 %. Moreover, a conservative estimation gives that the thermal fluctuation-induced driving force exceeds the upper bound of the sliding energy barrier for a water column shorter than 117 nm. These findings imply that although water molecules form layered structures near the CNT inner walls, there is no critical interfacial shear stress to conquer, and water could slip inside CNTs under any given pressure drop due to the thermal activation at room temperature.
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