Xueying Chu

Influence of Exciton Localization on the Emission and Ultraviolet Photoresponse of ZnO/ZnS Core-Shell Nanowires.

The structural and optical properties of ZnO and ZnO/ZnS core-shell nanowires grown by a wet chemical method are investigated. The near-bandgap ultraviolet (UV) emission of the ZnO nanowires was enhanced by four times after coating with ZnS. The enhanced emission was attributed to surface passivation of the ZnO nanowires and localized states introduced during ZnS growth. The emission of the ZnO and ZnO/ZnS core-shell nanowires was attributed to neutral donor-bound excitons and localized excitons, respectively. Localized states prevented excitons from diffusing to nonradiative recombination centers, so therefore contributed to the enhanced emission. Emission from the localized exciton was not sensitive to temperature, so emission from the ZnO/ZnS core-shell nanowires was more stable at higher temperature. UV photodetectors based on the ZnO and ZnO/ZnS core-shell nanowires were fabricated. Under UV excitation, the device based on the ZnO/ZnS core-shell nanowires exhibited a photocurrent approximately 40 times higher than that of the device based on the ZnO nanowires. The differing photoresponse of the detectors was consistent with the existence of surface passivation and localized states. This study provides a means for modifying the optical properties of ZnO materials, and demonstrates the potential of ZnO/ZnS core-shell nanowires in UV excitonic emission and detection.

Pressure and temperature-dependent Raman spectra of MoS2 film

Molybdenum disulfide (MoS2), a relatively new and exciting two-dimensional graphene-like material, has been attracting more and more attentions from the researchers due to its unique structural and fascinating properties. The potential application of MoS2 under high-pressure and low-temperature is expected, while the related research is few at present. In this paper, quadrilayer MoS2 was synthesized by chemical vapor deposition, and its structural properties under different pressures (0–20.7 GPa) and temperatures (10–300 K) were investigated via the Raman spectra. We find that the lattice of quadrilayer MoS2 is not damaged and the quadrilayer MoS2 exhibits good semiconductive properties under large variable pressures from atmospheric to 20.7 GPa, which is much different to its bulk and single crystalline phases. In addition, the lattice structures of the quadrilayer MoS2 are stable in 10–300 K, and the Gruneisen parameters of E12g and A1g modes are smaller than that of bulk. This study indicates that quad...

Fabrication and Visible Light Photocatalytic Activity of Co-doped ZnO Nanorods

Co-doped ZnO nanorods were prepared by electrochemical deposition method in aqueous solution. To study the as-grown samples, several characterizations were carried out. The scanning electron microscopy(SEM) images show that the samples present a rod-like shape with hexagonal cross sections and roughened surface. There is a slight shift for (002) diffraction peak of Co-doped ZnO nanorods in XRD because Co2+ ions entered into the ZnO lattice. Energy-dispersive X-ray spectroscopy(EDS) and X-ray photoelectron spectroscopy(XPS) results also show the exist of Co in the sample. Photoluminescence(PL) spectra of the samples were observed at room temperature, the UV emission of Co-doped ZnO shows a slight red shift compared with that of undoped ZnO. Thus, we can reach the conclusion that Zn2+ ions have been substituted by Co2+ ions in the ZnO samples. In addition, photocatalysis property of Co-doped ZnO nanorods was investigated under the irradiation of visible light. It was found that the degradation rate of methyl orange is increased greatly by Co-doped ZnO nanorods in comparison to undoped ZnO nanorods.

Preparation, Applications of Two-Dimensional Graphene-like Molybdenum Disulfide

Two-dimensional graphene-like molybdenum disulfide, a relatively new and exciting transition metal dichalcogenides, has a number of unique properties which have been widely studied. The structure, property and preparation methods of molybdenum disulfide are introduced in this paper in detail. In order to improve performance of molybdenum disulfide, some researchers start paying close attention to composite and decorating about molybdenum disulfide, such as graphene-MoS2, metal-MoS2, which is not mentioned in other review papers. In addition, we systematically review the application of molybdenum disulfide, which included field effect transistor, phototransistors, gas detector, digital logic transistors and biosensor. At last, we prospect for future advances in methods for preparing atomically thin layers and devices.

Enhanced Mn2+ emission in ZnS:Mn nanoparticles by surface plasmon resonance of gold nanoparticles

The Mn2+ emission of ZnS:Mn nanoparticles was enhanced by a simple procedure. 3-Mercaptopropionic acid was used as a complexing agent in the synthesis of ZnS:Mn nanoparticles. Sulfydryl groups of 3-mercaptopropionic acid acted as bridging groups, to form composites of ZnS:Mn and Au nanoparticles. The peak wavelength of Au surface plasmons was red-shifted by 5 nm upon compositing. The intensity of Mn2+ emission at 590 nm because of the 4T1-6A1 transition was enhanced by 469% from the effects of the surface plasmon resonance. The enhancement was greatly influenced by the ratio of ZnS:Mn and Au. Enhancement was primarily attributed to localized surface plasmon resonance on the Au nanoparticle surface.

Enhanced Photocatalytic Activity of Mg-Doped ZnO Nanorods Prepared by Electrodeposition

Mg-doped ZnO nanorods were prepared by electrochemical deposition method in aqueous solution. To test the sample, the results show that the sample presents a rod-like shape with hexagonal cross sections and typical morphology of wurtzite ZnO, and (002) diffraction peak of Mg-doped ZnO nanorods move to large-angle direction in XRD. The peak of Mg element has appeared in EDS. XPS shows that there is Mg-O binding in the sample. PL spectrums of the samples are observed at room temperature, the UV emission of Mg-doped ZnO presents blue shift compared with undoped ZnO, absorption spectrum shows that band gap of Mg-doped ZnO is larger. We can reach the conclusion that the Zn2+ ions are successfully substituted by Mg2+ ions in the ZnO lattice. In addition, photocatalysis property of Mg-doped ZnO nanorods is investigated. It is found that the degradation efficiency of methyl orange raise twice by Mg-doped ZnO nanorods in comparison to undoped ZnO nanorods. The result indicates that the photocatalysis activity of ZnO nanorods can enhance after Mg2+ ions are doped into ZnO lattice.

High sensitivity glucose detection at extremely low concentrations using a MoS2-based field-effect transistor

In recent years, molybdenum disulfide (MoS2) based field-effect transistors (FETs) have attracted much attention because of the unique properties of MoS2 nano-materials as an ideal channel material. Using a MoS2 FET as a glucose solution biosensor has the advantages of high sensitivity and rapid response. This paper is concerned with the fabrication of a bilayer MoS2-based FET and the study of its application in the high sensitivity detection of an extremely low concentration glucose solution. It was found that the source-drain current (Ids) increases as the concentration of the glucose solution increases at the same gate voltage (Vgs) and drain voltage (Vds). The sensitivity of the biosensor as high as 260.75 mA mM−1 has been calculated and the detection limit of 300 nM was measured. The unknown concentration of a glucose solution was also detected using data based on the relationship between Ids and glucose solution concentration. In addition, many significant advantages of the biosensor were observed, such as short response time (<1 s), good stability, wide linear detection range (300 nM to 30 mM) and the micro-detection of glucose solutions. These unique properties make the bilayer MoS2-based FET a great potential candidate for next generation biosensors.

Photocatalytic Performance in Oxide Nanomaterials

As a result of the cumulatively environmental pollution and the worldwide fossil fuel reserves shortage, nanostructrued photocatalysts have attracted much attention as a potential solution due to their unique performance advantages. Over the past decades, different strategies for synthesis and modification of oxide materials on the nanometer scale have been developing rapidly. Therefore, it is of significance to highlight recent approaches in the development of oxide nanomaterials as activity-enhanced photocatalysts. This report presents recent research progress of the high photocatalytic activity of nanostructured photocatalysts for expansion of solar spectrum response and enhancement of charge separation efficiency. Significantly, all the researchers and their achievements in this field are making contributions to the development of catalytic industry and environment purification.

Controllable Growth of Functional Gradient ZnO Material Using Chemical Vapor Deposition

As a kind of semiconductor material, the morphology of zinc oxide directly affects its physical properties. By adjusting the ratio of the reaction source and the rate of the incoming gas flow, we obtained one-dimensional nanowire and two-dimensional nanoflag-like functional gradient material (FGM) using chemical vapor deposition (CVD) method. Compared with the one-dimensional nanowires, the growth of the two-dimensional ZnO FGM not only c-oriented, but other directions are also appeared. Photoluminescence results show that the FGM has a higher visible/UV emission intensity ratio than the nanowires for several orders of magnitudes. Meanwhile, the growth mechanism of these nanostructures were discussed in details.

Effect of rapid thermal annealing on the optical properties of GaAsSb alloys

GaAsSb ternary alloys are fundamental components of advanced electronic and optoelectronic devices in the future. The presence of localized states could greatly affect the optical properties in GaAsSb alloy, which depend on the fluctuation of alloy composition. In order to optimize the optical properties, GaAsSb alloys were treated by rapid thermal annealing (RTA) at different temperatures, and the optical behaviors of the annealed samples were investigated in detail. During RTA, a significant reduction of the localized states was observed by photoluminescence (PL) spectral analysis. Furthermore, the RTA process also altered the distribution of the components of the GaAsSb alloy, which caused a slight red-shift of the maximum PL peak at 150 K. The relationship between the localized states and the temperature of the RTA process was also investigated. The process involving the conversion of localized carriers to free carriers was proposed. Under the suitable RTA conditions, the Sb component was homogenized and the depth of carrier localization was decreased.