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.
Abstract:Recently, the rapid emergence of antibiotic-resistant pathogens has caused a serious health problem. Scientists respond to the threat by developing new antimicrobial materials to prevent or control infections caused by these pathogens. Polymer-based nanocomposite hydrogels are versatile materials as an alternative to conventional antimicrobial agents. Cross-linking of polymeric materials by metal ions or the combination of polymeric hydrogels with nanoparticles (metals and metal oxide) is a simple and effective approach for obtaining a multicomponent system with diverse functionalities. Several metals and metal oxides such as silver (Ag), gold (Au), zinc oxide (ZnO), copper oxide (CuO), titanium dioxide (TiO 2 ) and magnesium oxide (MgO) have been loaded into hydrogels for antimicrobial applications. The incorporation of metals and metal oxide nanoparticles into hydrogels not only enhances the antimicrobial activity of hydrogels, but also improve their mechanical characteristics. Herein, we summarize recent advances in hydrogels containing metal ions, metals and metal oxide nanoparticles with potential antimicrobial properties.
Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using firstprinciples calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the dshell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials. G raphene 1 and single sheets of hexagonal boron nitride 2 are novel two-dimensional (2D) materials with a similar atomic structure but drastically different electronic properties: while the former is a semimetal with zero bandgap, the latter is a wide gap insulator. Both materials can be grown by chemical vapor deposition (CVD) methods on various transition metal (TM) 3,4 and alloy 5 substrates. As graphene-BN lateral and vertical heterostructures and hybrid BCN systems have been predicted 6−9 to exhibit unique electronic and optical properties, several attempts to synthesize such systems have been made. 10−15 However, precise control over the atomic structure of the mixed material has not yet been achieved, which may be related to the choice of the substrate metal used and nonoptimal growth parameters. In the context of the CVD growth of BCN systems, one of the key issues is the solubility and diffusivity of B/C/N atoms in the metal. When solubility is high (as e.g., C in Ni), the metal can take up a considerable amount of the species, and growth can proceed via supersaturation and segregation. The species dissolved in the metal can give rise to precipitation of undesirable extra layers of the material upon cooling the system. Even for metals with low solubility (e.g., Au or Cu), the behavior of interstitials in the bulk is important in the context of ion-irradiation-mediated growth of graphene 16,17 and potentially other 2D materials: successive implantation of different atoms in the metal substrate well above the solubility limit followed by annealing of the sample can give rise to nucleation of new 2D mixed systems on metal surfaces. 16,17 At the same time, relatively little is known about the solubility and mobility of B/C/N atoms in ...
The direct band gap of monolayer semiconducting transition-metal dichalcogenides (STMDs) enables a host of new optical and electrical properties. However, bilayer STMDs are indirect band gap semiconductors, which limits its applicability for high-efficiency optoelectronic devices. Here, we report that the direct band gap can be achieved in bilayer Compared with gapless graphene 1,2 , two-dimensional (2D) STMDs have attracted great interest because of its sizeable band gap [3][4][5][6][7] . Monolayer STMDs (MX 2 ; M = Mo, W and X = S, Se, Te) is composed of three atomic layers, a transition-metal layer sandwiched between two chalcogen layers. Within monolayer the metals and chalcogens form strong covalent bonds, whereas in bulk STMDs, the layers are bonded by the weak van der Waals (vdW) interaction. Because of the strong intralayer interaction and the weak interlayer interaction, the ultrathin sheets of STMDs can be isolated from the bulk by the micromechanical cleavage technique 8 . The direct band gap of monolayer STMDs enables a host of new optical and electrical properties, such as strong photoluminescence 9,10 and electroluminescence 11 . Novel electronic and optoelectronic devices with improved performance have also been demonstrated, such as ambipolar and high-quality field-effect transistors 12,13 , electric double-layer transistors 14 , integrated circuits 15 and phototransistors with high responsivity 16,17 . However, experimentally it is still a challenge to precisely control layer number of STMDs, the synthesized samples are usually several layer thickness. The multilayer STMDs are indirect band gap semiconductors 9,10 , which limits its applicability for high-performing optoelectronic devices. If the electronic properties can be tuned from the indirect band gap to the direct band gap, they will be quite promising for practical application.Bilayer STMDs have received much attention because they possess extra and distinct degrees of freedom, such as heterostructures and stacking orders, which makes bilayer STMDs exhibiting richer properties. Heterostructures have been the essential elements in modern semiconductor industry due to its electronic properties beyond those offered by individual constituent parts. Creating heterostructures between 2D STMDs would enable band engineering and provide new strategy to tune the electronic properties of semiconductors. Advances in 2D layered materials have allowed STMDs-based vertical and lateral heterostructures to be fabricated [18][19][20][21][22]
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