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Graphene-based spintronics has attracted much attention owing to the weak spin–orbit interaction and long spin relaxation length in graphene. For implementation of practical and high-density graphene-based spintronic devices, we need to define nanoscale areas with room-temperature ferromagnetism on graphene. Here we report the room-temperature ferromagnetism observed in nanoscale functionalized (oxidized and hydrogenated) graphene using atomic force microscope lithography without involving potential surface contamination and chemical agents. By performing magnetic force microscope (MFM) measurements, we can clearly distinguish the local ferromagnetic signal of selectively functionalized graphene from that of surrounding non-magnetic pristine graphene. The nanoscale functionalized graphene shows experimental evidence of room-temperature ferromagnetism: (1) larger MFM signal than that of graphene; (2) repulsive and attractive interaction with an MFM tip the magnetization of which points into and out of the graphene, respectively; and (3) MFM signal reversal after applying a high magnetic field at an elevated temperature of 400 K. Our first-principles calculations reveal that unpaired spins are present at non-passivated dangling bonds of vacancies on functionalized graphene and the stable ferromagnetic exchange interactions between them are favored. Therefore, nanoscale functionalized graphene is a good candidate for use as the spin injector or detector of high-density graphene-based spintronic devices. [ABSTRACT FROM AUTHOR]

By means of theory and experiments, the application capability of nickel ditelluride (NiTe2) transition‐metal dichalcogenide in catalysis and nanoelectronics is assessed. The Te surface termination forms a TeO2 skin in an oxygen environment. In ambient atmosphere, passivation is achieved in less than 30 min with the TeO2 skin having a thickness of about 7 Å. NiTe2 shows outstanding tolerance to CO exposure and stability in water environment, with subsequent good performance in both hydrogen and oxygen evolution reactions. NiTe2‐based devices consistently demonstrate superb ambient stability over a timescale as long as one month. Specifically, NiTe2 has been implemented in a device that exhibits both superior performance and environmental stability at frequencies above 40 GHz, with possible applications as a receiver beyond the cutoff frequency of a nanotransistor. [ABSTRACT FROM AUTHOR]

By means of surface-science experiments, electrochemical tests and density functional theory, we unveil the mechanisms ruling the catalytic activity of PtSn4. Specifically, through an investigation of the surface chemical reactivity toward CO, H2O, and O2 molecules at room temperature and, moreover, of surface stability in air, we show that the catalytic activity of PtSn4 is determined by the atomic tin layer constituting its surface termination. The PtSn4 surface is not affected by CO poisoning, although it evolves into a tin-oxide skin in the ambient atmosphere. We demonstrate that the hydrogen evolution reaction on PtSn4 can be modelled by the combination of two steps, i.e. Volmer and Tafel reactions. Surprisingly, surface oxidation induces a reduction of the energy barrier for the Tafel reaction, so that oxidized PtSn4 behaves similarly to Pt(111), in spite of the reduced amount of Pt in the alloy and without available over-surface Pt sites. Correspondingly, we observe in electrochemical experiments a Tafel slope of 86 mV dec−1 and an onset potential similar to that of pure Pt. However, PtSn4 contains only 29% wt of Pt, with a reduction of the economic cost by 70%. Our results indicate PtSn4 as a promising novel material for electrocatalytic reactions, whose performance could be further tuned by surface treatments. [ABSTRACT FROM AUTHOR]

First principles calculations of the magnetic and electronic properties of VSe2 describing the transition between two structural phases (H,T) were performed. The results of the calculations evidence a rather low energy barrier (0.60 eV for the monolayer) for the transition between the phases. The energy required for the deviation of a Se atom or whole layer of selenium atoms by a small angle of up to 10° from their initial positions is also rather low, 0.32 and 0.19 eV/Se, respectively. The changes in the band structure of VSe2 caused by these motions of Se atoms should be taken into account for analysis of the experimental data. Simulations of the strain effects suggest that the experimentally observed T phase of the VSe2 monolayer is the ground state due to substrate-induced strain. Calculations of the difference in the total energies of the ferromagnetic and antiferromagnetic configurations evidence that the ferromagnetic configuration is the ground state of the system for all stable and intermediate atomic structures. Calculated phonon dispersions suggest a visible influence of the magnetic configurations on the vibrational properties. [ABSTRACT FROM AUTHOR]

Abstract: PtTe2 is a novel transition‐metal dichalcogenide hosting type‐II Dirac fermions that displays application capabilities in optoelectronics and hydrogen evolution reaction. Here it is shown, by combining surface science experiments and density functional theory, that the pristine surface of PtTe2 is chemically inert toward the most common ambient gases (oxygen and water) and even in air. It is demonstrated that the creation of Te vacancies leads to the appearance of tellurium‐oxide phases upon exposing defected PtTe2 surfaces to oxygen or ambient atmosphere, which is detrimental for the ambient stability of uncapped PtTe2‐based devices. On the contrary, in PtTe2 surfaces modified by the joint presence of Te vacancies and substitutional carbon atoms, the stable adsorption of hydroxyl groups is observed, an essential step for water splitting and the water–gas shift reaction. These results thus pave the way toward the exploitation of this class of Dirac materials in catalysis. [ABSTRACT FROM AUTHOR]

The investigation of the electronic structure of P‐ion implanted TiO2 thin films (E = 30 keV, D = 1 × 1017 cm−2) with anatase structure is performed by X‐ray photoelectron spectroscopy (XPS) measurements (core levels and valence bands) and first‐principles density functional theory (DFT) calculations. It is found that the XPS P 2p‐spectra reveal the presence of two signals at 134.2 and 130.3 eV which can be attributed to the formation of P–O (with P5+ ions) and P–Ti (with P3− ions) bonds, respectively. This means that both cationic (P → Ti) and anionic (P → O) substitution take place in P‐ion implanted anatase thin films. This conclusion is confirmed by DFT calculations which show that the XPS valence band structure of P:TiO2 can be reproduced only under mixed substitution. The presence of two kinds of phosphorus ions (P5+ and P3−) in ion‐implanted TiO2 can be useful for developing new multifunctional advanced materials with configurable properties for a wide range of applications. [ABSTRACT FROM AUTHOR]

The feasibility of highly water stable Zr-based metal organic frameworks (MOFs: UiO-66-NH 2 ) as a sensing probe material was explored for the detection of the electron deficient nitrobenzene (NB) molecule in an aqueous phase. The probe system was highly sensitive toward the NB molecule within the range of 10–100 ppm with a linear range of 0–30 ppm and a quenching efficiency of around 95% (at 100 ppm). The limit of detection (LOD) of the proposed probe was estimated to be 0.9 ppm. In contrast, this method was not affected sensitively by potential interferences such as other aromatic compounds. For instance, benzene (B), toluene (T), and chlorobenzene (CB) showed reduced quenching efficiencies (<40%). The specificity toward NB molecules for the proposed probe was appreciable in the presence of co-existing components (B, T, and CB). DFT calculations showed that the sensing mechanism was ascribable to electron transfer from the excited missed-linker induced sites of the Zr OH to the NB molecule. This interaction was confirmed by an FTIR analysis of the UiO-66-NH 2 -NB material. Therefore, the proposed UiO-66-NH 2 probe can be used as a potent sensing material for the NB even at low concentrations in an aqueous medium. [ABSTRACT FROM AUTHOR]

We demonstrate that isolated copper atoms can be bound to the four-coordinated surface nitrogen sites of a diamond lattice fully terminated by atomic hydrogen. This bonding is related to the ability of surface nitrogen sites to donate unpaired electrons (from an antibonding orbital) to third alien surface agents. [ABSTRACT FROM AUTHOR]

The electronic structure of hybrid perovskite MAPbI 3 (MA ​= ​CH 3 NH 3) doped with alkaline earth elements (Ca, Sr, Ba) has been studied. The calculation results show that partial substitution of Pb2+ centers by any of these impurities is an exothermic process at any concentration and distribution impurities. A gradual increase in the number of impurities corresponds to a decrease in the formation energy and an increase in the band gap. The simulation also shows that the segregation of impurities is less favorable than the uniform (quasi-random) distribution of impurities in the supercell. [Display omitted] • Doping of MAPbI 3 with alkaline earth elements (Ca, Sr, Ba) has been studied. • Increasing of the doping content provide widening of the bandgap. • Doping by considered elements provide stabilization of MAPbI 3 lattice. • Quasi–random distribution of impurities is more favorable then its segregation. [ABSTRACT FROM AUTHOR]