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Multiexcitons generation is a process of generating electron-hole pairs in nanostructured semiconductors by absorbing a single high-energy photon. The multiexciton process is essential for the performance of optoelectronic devices based on perovskite nanomaterials. In this paper, ultrafast time-resolved transient absorption spectroscopy is used to study the ultrafast dynamics of CsPbBr3nanocrystals. It is found that the multiexcitons Auger recombination lifetime increases with the decrease of pump fluence, while it is on the contrary for the hot carrier cooling time. The increase in the number of photons absorbed by each nanocrystal under high pump fluence slows down the relaxation of hot carriers to the band edge. The hot carrier cooling lifetime increases from 0.25 to 0.85 ps when the pump fluence increases from 6 to 127μJ cm-2. Temperature-dependent transient absorption spectroscopy exhibits that the relaxation process of hot carriers slows down sharply when the lattice temperature decreases from 280 to 80 K. Moreover, the exciton binding energy 46 meV of CsPbBr3nanocrystals is obtained by temperature-dependent steady-state photoluminescence spectroscopy. These findings provide insights for applications such as solar cells and light-emitting devices based on CsPbBr3nanocrystals.

The structures and electronic properties of InTe/graphene van der Waals heterostructures are systematically investigated using the first-principles calculations. The electronic properties of InTe monolayer and graphene are well preserved respectively and the bandgap energy of graphene is opened to 36.5 meV in the InTe/graphene heterostructure. An n-type Schottky contact is formed in InTe/graphene heterostructure at the equilibrium state. There is a transformation between n-type and p-type Schottky contact when the interlayer distance is smaller than 3.56 A or the applied electric field is larger than -0.06 V A-1. In addition, the Schottky contact converts to Ohmic contact when the applied vertical electric field is larger than 0.11 V A-1 or smaller than -0.13 V A-1.

The structure, electronic properties, charge transfer, band edge alignments and optical properties of WS2/BSe heterostructures are investigated by using first-principle calculations. Results imply that WS2/BSe heterostructures are semiconductor with an indirect energy gap (Egap) of 1.73 eV. Additionally, it has a feature of type-II band alignment, which contributes to spatial separation of photo-generated electron-hole pairs in WS2/BSe heterostructures. Charge transfer takes place from BSe to WS2 monolayers, which extends lifetime of the separated photo-induced charge carriers. Most importantly, band edges of the heterostructure are found to meet hydrogen evolution reaction (HER) in acid solutions (0 < pH < 7). Moreover, compared with only one for WS2 and BSe monolayers, the optical-absorption strength of the heterostructure is significantly enhanced and WS2/BSe heterostructures larges the range of absorption to 717 nm in the visible light region, improving the potential photocatalytic efficiency. These results explain the underlying mechanism of the enhanced photocatalytic activity of WS2/BSe heterostructures. Thus WS2/BSe heterostructures can be applied to 2D heterostructured photocatalysts.

The irradiation damage in nickel-base alloy C-276 irradiated with 115 keV Ar ions from low to very high doses was investigated. Structural characterization was performed using transmission electron microscopy (TEM), grazing incident X-ray diffraction (GIXRD) and atomic force microscopy (AFM). High density of interstitial type dislocation loops could be observed at a dose level of around 2.75 displacements per atom (dpa). With the irradiation dose increased to 27.5 dpa, the average size of loops increased from 5 nm to 16 nm, while the density of the loops decreased from 1.4 × 1011/cm2 to 4.6 × 1010/cm2. When the irradiation dose reached 82.5 dpa, original grains were transformed into subgrains whose sizes observed from TEM were about 20~60 nm. The fragmentation of grains was confirmed by GIXRD. The mean subgrain size was 40 nm, which was obtained from the full width at half maximum (FWHM) of the X-ray diffraction lines using the Scherrer formula and Williamson formula. AFM micrographs showed that nanometer-sized hillocks formed at the dose of 82.5 dpa, which provided further evidence of grain fragmentation at a high irradiation dose.

Recent reports on the observation of room temperature ferromagnetism in Cu doped ZnO have been highly regarded by the scientific community. There are several contradicting reports where some authors have confirmed the occurrence of ferromagnetism in ZnO while others have ruled it out. Even in studies where room temperature ferromagnetism is reported, the effect of carrier type with the ferromagnetic properties is still unclear. To study this problem, the observation of room temperature ferromagnetism in Cu-doped (5%) single crystalline ZnO films grown on Si substrates was observed. ZnO films were prepared by pulsed laser deposition. Hall measurements showed that the Zn0.95Cu0.05O film was n-type with carrier density around 4.3×1017 cm-3. This film exhibits room-temperature ferromagnetism with a saturation magnetization of 0.31 µB/Cu atom. The predominant valence state of the doped Cu atoms is monovalent. When additional electrons were introduced into the films, the ferromagnetism was weaken and vanished. Our results confirm that the p-type nature of the film is not essential for realizing ferromagnetic characteristics, if only the concentration of n-type carriers were not very high.