Abstract: Heterogeneous single-site catalysts can combine the R precise active site design of organometallic complexes with the efficient recovery of solid catalysts. Based on recent progress on homogeneous thioether ligands for Pd-catalyzed C-H activation reactions, we here develop a scalable metal-organic framework-based heterogeneous single-site catalyst containing S,O-moieties that increase the catalytic activity of Pd(II) for the oxidative alkenylation of arenes. The structure of the Pd@MOF-808-L1 catalyst was characterized in detail via solid-state nuclear magnetic resonance spectroscopy, N-2 physisorption, and high-angle annular dark field scanning transmission electron microscopy, and the structure of the isolated palladium active sites could be identified by X-ray absorption spectroscopy. A turnover frequency (TOF) of 8.4 h(-1) was reached after 1 h of reaction time, which was 3 times higher than the TOF of standard Pd(OAc)(2), ranking Pd@MOF-808-L1 among the most active heterogeneous catalysts ever reported for the nondirected oxidative alkenylation of arenes. Finally, we showed that the single-site catalyst promotes the oxidative alkenylation of a broad range of electron-rich arenes, and the applicability of this heterogeneous system was demonstrated by the gram-scale synthesis of industrially relevant products.

Abstract: Using density functional theory based first-principles calculations, we predict the dynamically stable 1H phase of a Janus single layer composed of S-Mo-O atomic layers. It is an indirect band gap semiconductor exhibiting strong polarization arising from the charge difference on the two surfaces. In contrast to 1H phases of MoS2 and MoO2, Janus MoSO is found to possess four Raman active phonon modes and a large out-of-plane piezoelectric coefficient which is absent in fully symmetric single layers of MoS2 and MoO2. We investigated the electronic and phononic properties under applied biaxial strain and found an electronic phase transition with tensile strain while the conduction band edge displays a shift when under compressive strain. Furthermore, single-layer MoSO exhibits phononic stability up to 5% of compressive and 11% of tensile strain with significant phonon shifts. The phonon instability is shown to arise from the soft in-plane and out-of-plane acoustic modes at finite wave vector. The large strain tolerance of Janus MoSO is important for nanoelastic applications. In view of the dynamical stability even under moderate strain, we expect that Janus MoSO can be fabricated in the common 1H phase with a strong out-of-plane piezoelectric coefficient.

Abstract: Plastic pollution has become a worldwide concern. It was demonstrated that plastic breaks down to nanoscale particles in the environment, forming so-called nanoplastics. It is important to understand their ecological impact, but their structure is not elucidated. In this original work, we characterize the microstructure of oceanic polyethylene debris and compare it to the nonweathered objects. Cross sections are analyzed by several emergent mapping techniques. We highlight deep modifications of the debris within a layer a few hundred micrometers thick. The most intense modifications are macromolecule oxidation and a considerable decrease in the molecular weight. The adsorption of organic pollutants and trace metals is also confined to this outer layer. Fragmentation of the oxidized layer of the plastic debris is the most likely source of nanoplastics. Consequently the nanoplastic chemical nature differs greatly from plastics.

Abstract: Grain boundaries between 60 degrees rotated and twinned crystals constitute the dominant type of extended line defects in two-dimensional transition metal dichalcogenides (2D MX2) when grown on a single crystalline template through van der Waals epitaxy. The two most common 60 degrees grain boundaries in MX2 layers, i.e., beta- and gamma-boundaries, introduce distinct distortion and strain into the 2D lattice. They impart a localized tensile or compressive strain on the subsequent layer, respectively, due to van der Waals coupling in bilayer MX2 as determined by combining atomic resolution electron microscopy, geometric phase analysis, and density functional theory. Based on these observations, an alternate route to strain engineering through controlling intrinsic van der Waals forces in homobilayer MX2 is proposed. In contrast to the commonly used external means, this approach enables the localized application of strain to tune the electronic properties of the 2D semiconducting channel in ultra-scaled nanoelectronic applications.

Abstract: Understanding the electric dipole switching in multiferroic materials requires deep insight of the atomic-scale local structure evolution to reveal the ferroelectric mechanism, which remains unclear and lacks a solid experimental indicator in high-pressure prepared LiNbO3-type polar magnets. Here, we report the discovery of Zn-ion splitting in LiNbO3-type Zn2FeNbO6 established by multiple diffraction techniques. The coexistence of a high-temperature paraelectric-like phase in the polar Zn2FeNbO6 lattice motivated us to revisit other high-pressure prepared LiNbO3-type A(2)BB'O-6 compounds. The A-site atomic splitting (similar to 1.0-1.2 angstrom between the split-atom pair) in B/B'-mixed Zn2FeTaO6 and O/N-mixed ZnTaO2N is verified by both powder X-ray diffraction structural refinements and high angle annular dark field scanning transmission electron microscopy images, but is absent in single-B-site ZnSnO3. Theoretical calculations are in good agreement with experimental results and suggest that this kind of A-site splitting also exists in the B-site mixed Mn-analogues, Mn2FeMO6 (M = Nb, Ta) and anion-mixed MnTaO2N, where the smaller A-site splitting (similar to 0.2 angstrom atomic displacement) is attributed to magnetic interactions and bonding between A and B cations. These findings reveal universal A-site splitting in LiNbO3-type structures with mixed multivalent B/B', or anionic sites, and the splitting-atomic displacement can be strongly suppressed by magnetic interactions and/or hybridization of valence bands between d electrons of the A- and B-site cations.

Abstract: The chiral p-wave order parameter in Sr2RuO4 would make it a special case amongst the unconventional superconductors. A consequence of this symmetry is the possible existence of superconducting domains of opposite chirality. At the boundary of such domains, the locally suppressed condensate can produce an intrinsic Josephson junction. Here, we provide evidence of such junctions using mesoscopic rings, structured from Sr2RuO4 single crystals. Our order parameter simulations predict such rings to host stable domain walls across their arms. This is verified with transport experiments on loops, with a sharp transition at 1.5 K, which show distinct critical current oscillations with periodicity corresponding to the flux quantum. In contrast, loops with broadened transitions at around 3 K are void of such junctions and show standard Little-Parks oscillations. Our analysis demonstrates the junctions are of intrinsic origin and makes a compelling case for the existence of superconducting domains.

Abstract: The relationship between irrigation water availability and crop revenue is multifaceted. However, most of the previous studies focused only on the direct effect of irrigation water on crop revenue or considered that the indirect effect passes only through the farmers’ improved farm inputs usage. Nevertheless, unlike previous studies, this study argues that a one-sided argument that irrigation water directly causes high crop revenue or indirectly affects crop revenue only via the farmers’ improved farm inputs usage is incomplete, as irrigation water not only directly contributes to crop revenue but also indirectly conduces to crop revenue via both the type of crops produced and the farmers’ improved farm inputs usage. Considering the previous studies’ limitations, this study investigates pathways how small-scale irrigation water affects crop revenue and identifies challenges of small-scale irrigation farming in Fogera district, Ethiopia. Results endorsed that irrigation water has both direct and indirect effects on crop revenue. The indirect effect is 67 percent of the total effect and it is mediated by both the type of crops produced and farmers’ improved farm inputs usage. The result also indicated that irrigation user farmers have a higher income, more livestock assets and resources and better food, housing, and cloths than the non-users. Moreover, challenges related to agricultural output and input market were identified as the most severe problem followed by crop disease. The findings of our study suggest that to utilize the benefits of irrigation water properly, it is crucial to encourage farmers to use more improved farm inputs and to shift from staple to cash crop production. Moreover, farmers are frequently exposed to cheating by illegal brokers in the output market, therefore it is also important to increase farmers’ accessibility to output and input markets, the quality of improved farm inputs, and the bargaining power of farmers with market information.

Abstract: By using density functional theory (DFT) calculations, we predict a puckered, dynamically stable Janus single-layer black arsenic-phosphorus (b-AsP), which is composed of two different atomic sublayers, arsenic and phosphorus atoms. The calculated phonon spectrum reveals that Janus single-layer b-AsP is dynamically stable with either pure or coupled optical phonon branches arising from As and P atoms. The calculated Raman spectrum indicates that due to the relatively strong P-P bonds, As atoms have no contribution to the highfrequency optical vibrations. In addition, the orientation-dependent isovolume heat capacity reveals anisotropic contributions of LA and TA phonon branches to the low-temperature thermal properties. Unlike pristine single layers of b-As and b-P, Janus single-layer b-AsP exhibits additional out-of-plane asymmetry which leads to important consequences for its electronic, optical, and elastic properties. In contrast to single-layer b-As, Janus single-layer b-AsP is found to possess a direct band gap dominated by the P atoms. Moreover, real and imaginary parts of the dynamical dielectric function, including excitonic effects, reveal the highly anisotropic optical feature of the Janus single-layer. A tight-binding (TB) model is also presented for Janus single-layer b-AsP, and it is shown that, with up to seven nearest hoppings, the TB model reproduces well the DFT band structure in the low-energy region around the band gap. This TB model can be used in combination with the Green's function approach to study, e.g., quantum transport in finite systems based on Janus single-layer b-AsP. Furthermore, the linear-elastic properties of Janus single-layer b-AsP are investigated, and the orientation-dependent in-plane stiffness and Poisson ratio are calculated. It is found that the Janus single layer exhibits strong in-plane anisotropy in its Poisson ratio much larger than that of single-layer b-P. This Janus single layer is relevant for promising applications in optical dichroism and anisotropic nanoelasticity.

Abstract: Using first-principle calculations, we systematically study strain tuning of the electronic properties of two- dimensional graphitic carbon nitride nanosheets with empirical formula CnNm. We found the following: (i) the ferromagnetic ordered state in the metal-free systems (n, m) = (4,3), (10,9), and (14,12) remains stable in the presence of strain of about 6%. However, the system (9,7) loses its ferromagnetic ordering when increasing strain. This is due to the presence of topological defects in the (9,7) system, which eliminates the asymmetry between spin up and spin down of the p(z) orbitals when strain is applied. (ii) By applying uniaxial strain, a band gap opens in systems which are initially gapless. (iii) In semiconducting systems which have an initial gap of about 1 eV, the band gap is closed with applying uniaxial strain.

Abstract: Using first-principles calculations, we study the effect of embedding various atoms into the nanopore sites of both C6N6 and C6N8 monolayers. Our results indicate that the embedded atoms significantly affect the electronic and magnetic properties of C6N6 and C6N8 monolayers and lead to extraordinary and multifarious electronic properties, such as metallic, half-metallic, spin-glass semiconductor and dilute-magnetic semiconductor behaviour. Our results reveal that the H atom concentration dramatically affects the C6N6 monolayer. On increasing the H coverage, the impurity states also increase due to H atoms around the Fermi-level. C6N6 shows metallic character when the H atom concentration reaches 6.25%. Moreover, the effect of charge on the electronic properties of both Cr@C6N6 and C@C6N8 is also studied. Cr@C6N6 is a ferromagnetic metal with a magnetic moment of 2.40 mu(B), and when 0.2 electrons are added and removed, it remains a ferromagnetic metal with a magnetic moment of 2.57 and 2.77 mu(B), respectively. Interestingly, one can observe a semi-metal, in which the VBM and CBM in both spin channels touch each other near the Fermi-level. C@C6N8 is a semiconductor with a nontrivial band gap. When 0.2 electrons are removed, it remains metallic, and under excess electronic charge, it exhibits half-metallic behaviour.

Abstract: Understanding the folding and stability of membrane proteins is of great importance in protein science. Recently, osmolytes and ionic liquids (ILs) are increasingly being used as drug delivery systems in the biopharmaceutical industry. However, the stability of membrane proteins in the presence of osmolytes and ILs is not yet fully understood. Besides, the effect of oxidative stress on membrane proteins with osmolytes or ILs has not been investigated. Therefore, we studied the influence of osmolytes and ILs as co-solvents on the stability of a model membrane protein (i.e., Bacteriorhodopsin in purple membrane of Halobacterium salinarum), using UV–Vis spectroscopy and molecular dynamics (MD) simulations. The MD simulations allowed us to determine the flexibility and solvent accessible surface area (SASA) of Bacteriorhodopsin protein in the presence and/or absence of cosolvents, as well as to carry out principal component analysis (PCA) to identify the most important movements in this protein. In addition, by means of UV–Vis spectroscopy we studied the effect of oxidative stress generated by cold atmospheric plasma on the stability of Bacteriorhodopsin in the presence and/or absence of co-solvents. This study is important for a better understanding of the stability of proteins in the presence of oxidative stress.

Abstract: Polycrystalline samples of CaLa2FeCoSbO9 and ALa2FeNiSbO9 (A=Ca, Sr, Ba) have been prepared in solid-state reactions and studied by a combination of transmission electron microscopy, magnetometry, X-ray diffraction, neutron diffraction and Mössbauer spectroscopy. Diffraction and TEM showed that each shows 1:1 B-site ordering in which Co2+/Ni2+ and Sb5+ tend to occupy two distinct crystallographic sites while Fe3+ is distributed over both sites. While X-ray and neutron diffraction agreed that all four compositions are monophasic with space group P21/n, TEM revealed different levels of compositional inhomogeneity at the subcrystal scale, which, in the case of BaLa2FeNiSbO9, leads to the occurrence of both a P21/n and an I2/m phase. Magnetometry and neutron diffraction show that these perovskites are ferrimagnets with a G-type magnetic structure. Their relatively low magnetisation can be attributed to their inhomogeneity. This work demonstrates the importance of studying the microstructure of complex compositions.

Abstract: In the present work, kelvin probe force microscopy (KPFM) technique has been used to study the CZTSe/CuxSe bilayer interface prepared by multi-step deposition and selenization process of metal precursors. Transmission electron microscopy (TEM) confirmed the bilayer configuration of the CZTSe/CuxSe sample. Two configuration modes (surface mode and junction mode) in KPFM have been employed in order to measure the junction voltage under illumination conditions. The results show that CZTSe/CuxSe has small junction voltage of similar to 21 mV and the presence of CuxSe secondary phase in the CZTSe grain boundaries changes the workfunction of the local grain boundaries region. The negligible photovoltage difference between grain and grain boundaries in photovoltage image indicates that CuxSe phase deteriorates the higher photovoltage at grain boundaries normally observed in CZTSe based device. These results can be important for understanding the role of secondary phases in CZTSe based junction devices.

Abstract: In the Comment, the authors state that the separation of the relative and center of mass variables in our work is not correct. Here we point out that there is a typographical error, i.e., qi instead of -e, in two of our equations which, when corrected, makes the Comment redundant. Within the ansatzes mentioned in our paper all our results are correct, in contrast to the claims of the Comment.

Abstract: Two-dimensional (2D) Janus materials are a new class of materials with unique physical, chemical, and quantum properties. The name “Janus” originates from the ancient Roman god which has two faces, one looking to the future while the other facing the past. Janus has been used to describe special types of materials which have two faces at the nanoscale. This unique atomic arrangement has been shown to present rather exotic properties with applications in biology, chemistry, energy conversion, and quantum sciences. This review article aims to offer a comprehensive review of the emergent quantum properties of Janus materials. The review starts by introducing 0D Janus nanoparticles and 1D Janus nanotubes, and highlights their difference from classical ones. The design principles, synthesis, and the properties of graphene-based and chalcogenide-based Janus layers are then discussed. A particular emphasis is given to colossal built-in potential in 2D Janus layers and resulting quantum phenomena such as Rashba splitting, skyrmionics, excitonics, and 2D magnetic ordering. More recent theoretical predictions are discussed in 2D Janus superlattices when Janus layers are stacked onto each other. Finally, we discuss the tunable quantum properties and newly predicted 2D Janus layers waiting to be experimentally realized. The review serves as a complete summary of the 2D Janus library and predicted quantum properties in 2D Janus layers and their superlattices.