Shoupeng Shi

Enhanced hydrogen evolution catalysis in MoS2 nanosheets by incorporation of a metal phase

Here, we propose a metal 1T-phase incorporation strategy to dramatically enhance the hydrogen evolution reaction (HER) catalysis in primitive 2H-MoS2 nanosheets. Electrochemical measurement results indicate the fabricated 1T@2H-MoS2/C nanosheets exhibit facile electrode kinetics, low-loss electrical transport and possess a proliferated density of catalytic active sites compared to that of 2H-MoS2. As an electrocatalyst operating at a current density of 10 mA cm−2, the fabricated 1T@2H-MoS2/C nanosheets exhibited overpotentials of 64 mV in 0.5 M H2SO4, as well as a Tafel slope of 49 mV per decade, which exceed by far the activity of previous MoS2 catalysts. This design opens up new possibilities for effective manipulation of HER catalysts in two-dimensional nanostructures.

Singly-charged oxygen vacancy-induced ferromagnetism in mechanically milled SnO2 powders

The possibility of inducing long-range ferromagnetic order with non-transition metal ions has become a very exciting challenge in recent years. In order to elucidate the room temperature ferromagnetism of SnO2 powders, the magnetic properties of SnO2 powders that have been mechanically milled and subsequently annealed have been investigated. The results indicate that saturation magnetization of the samples increases with milling time, where a high saturation magnetization of 0.0012 emu g−1 can be obtained for the sample milled for 20 h, and saturation magnetization for the sample decreases gradually after annealing in air. Electron spin resonance results show large numbers of singly-charged oxygen vacancies on the surfaces of the SnO2 powders. Combined with X-ray photoelectron spectroscopy and room temperature photoluminescence results, this suggests that the observed ferromagnetism is related to the singly-charged oxygen vacancies.

High temperature ferromagnetism in Cu-doped MoS2 nanosheets

The synthesis of 2D metal chalcogenide based on ferromagnetic nanosheets is in high demand for modern electronics and spintronics applications. Herein, Cu-doped MoS2 nanosheets were successfully prepared by a hydrothermal method. Magnetic measurement results indicate that the doping of Cu ions can introduce ferromagnetism into MoS2 nanosheets, where saturate magnetization increases with increased Cu concentration. Further, the hysteresis curves measured at different temperatures demonstrate a high Curie temperature of 930 K for the Cu-doped MoS2 nanosheets. This result opens a new path to exploring spintronics in pristine 2D nanostructures by non-magnetic atom doping.

A series of unexpected ferromagnetic behaviors based on the surface-vacancy state: an insight into NiO nanoparticles with a core–shell structure

Antiferromagnetic nanoparticles as ultimate low-dimensional materials potentially give novel magnetic properties that differ from their bulk form due to strong quantum and surface effects. Herein, we propose that the observed anomalous ferromagnetic behavior of NiO nanoparticles is due to the formation of a ferromagnetic particle shell that is oxygen-vacancy related. A novel self-consistent estimation of the saturation magnetization further confirmed our proposal. The samples, synthesized by a thermal decomposition method, exhibit diversely anomalous ferromagnetic behavior, such as hysteresis curves, large coercivities, exchange bias and spin-glass behavior. A large saturation magnetization of 0.536 emu g−1 exists in the 6 nm NiO sample and it is found to decrease with increasing crystal size. Neither impurity element nor change of valence state has been found in the samples, through X-ray photoelectron, X-ray diffraction or selected-area electron diffraction measurements. Remarkably, a large amount of oxygen vacancies exists, which was verified by X-ray photoelectron spectrum fitting results and Raman spectroscopy. A post-hydrogen-annealing process strongly elevates ferromagnetic ordering, as a result of surface defect enhancement. Moreover, our estimation of the saturation magnetization based on first principle calculation results is in agreement with the experimental conclusion, which reveals the significance of surface states in mediating anomalous magnetic properties in low-dimensional antiferromagnetic materials.

Porous tin disulfide nanosheets with room temperature ferromagnetic nature

Two-dimensional nanomaterials usually have abnormal physical properties due to surface effects and large edge states. In this communication, it is demonstrated that porous hexagonal disulfide nanosheets exhibit clear room temperature ferromagnetism, where the observed ferromagnetism can be tuned by changing the porosity of the nanosheets. The disordered grain boundary, or defects in the nanosheets, is considered to be responsible for the long-range magnetic order. This finding suggests a route to facilitate the design of nanoelectronic devices.

Manifestation of high-temperature ferromagnetism in fluorinated graphitic carbon nitride nanosheets

Two-dimensional ferromagnetic metal-free materials possessing only an s/p electronic configuration with weak spin–orbit coupling and a large spin relaxation time play a crucial role in constructing future spintronic devices. Here, we demonstrate a novel two-dimensional material, fluorinated graphitic carbon nitride (g-C3N4) nanosheets, with intrinsic ferromagnetism; its Curie temperature can reach as high as 700 K. More surprising is that such unusual ferromagnetism can be further tuned by changing the concentration of fluorine. The tuneable electronic spin polarization, as well as the ferromagnetism observed in the fluorinated g-C3N4 nanosheets is quite promising for future device applications in spintronics.

Hierarchical ultrathin Mo(SxSe1−x)2 nanosheets with tunable ferromagnetism and efficient hydrogen evolution reaction activity: towards defect site effect

Layered transition metal dichalcogenides (TMDs) are now playing important roles in both fundamental studies and technological applications due to their special structures and rich physical properties. Here, hierarchical ultrathin TMD nanosheets based on molybdenum sulphoselenides [Mo(SxSe1−x)2] with tunable ferromagnetism were synthesized by a one step hydrothermal method. In addition, the hierarchical ultrathin Mo(SxSe1−x)2 nanosheets exhibit excellent composition-dependent electrocatalytic properties for the hydrogen evolution reaction (HER). It is considered that the intrinsic ferromagnetism and the efficient HER activity are related to the defect sites in the samples. This finding opens up a way to alter the ferromagnetism and electroactivity of layered chalcogenides by fine tuning of the composition.

Cu vacancies modulated the room temperature ferromagnetism in Cu2O/Cu nanoparticle composites

The Cu2O/Cu nanoparticle composites have been fabricated by heating a mixture of copper nitrate and different amounts of glycine. Magnetic measurement results indicate that the Cu2O/Cu composites show clear ferromagnetism, while the pure Cu2O and Cu show diamagnetism only. Through analyzing the photoluminescence X-ray photoelectron spectroscopy results, we proposed that the observed tunable ferromagnetism for the samples is attributed to Cu vacancies, where the interface of Cu2O/Cu composites plays an important role in modulating the concentration of Cu vacancies.

Argon ion irradiation induced phase transition and room temperature ferromagnetism in the CuO thin film

We have deposited a copper oxide (CuO) thin film using a magnetron sputtering system by modulating rate of oxygen flow, and we found that the phase of cuprous oxide (Cu2O) appeared after irradiation by argon ions. Magnetic measurement results indicate that the thin film exhibits room temperature ferromagnetism after irradiation, while the virgin CuO thin film is diamagnetic. Vacancies and interstitial would appear in the lattice during irradiation and phase transition, which will originate in the local magnetic moment. In combination with the analyses of Raman spectra, we believe that the ferromagnetism of the film may originate from Cu vacancies, which provides an approach in investigating the mechanism of magnetism in the diluted magnetic semiconductor.