Zuliang Du

Morphological structure and physicochemical properties of nanotube TiO 2

Morphological structure and physicochemical properties of nanotube TiO2 were investigated. It was found that the TiO2 nanotube consisted of 2–5 monolayers of TiO2 molecules, and its inner diameter was between 4.2 and 5.9 nm. The nanotube TiO2 powder had high specific surface area and pore volume (379 m2/g and 1.431 cm3/g respectively) and its decolorization activity for Reactive Brilliant Red X-3B was 2 times higher than that of raw TiO2 (p-25). This new type of TiO2 was hopeful for application in photocatalysis and composite nanomaterial.

Bandgap tunable Zn1−xMgxO thin films as electron transport layers for high performance quantum dot light-emitting diodes

Since the introduction of inorganic ZnO nanoparticles as an electron transport layer (ETL) material, the device performance of colloidal quantum dot light-emitting diodes (QLEDs) has been rapidly improved. Although there have been rapid advances in luminance, efficiency and lifetime, device performance is still limited by balanced electron/hole injection into the quantum dot layer. In this study, solution-processed Zn1−xMgxO (ZMO) films with tunable bandgaps were designed as an ETL for high performance QLEDs. It was found that the band gap of ZMO broadened as the energy level varied with increasing Mg concentration. As a consequence, the energy barrier between the Al cathode and ZMO ETL was tuned to balance the electron/hole injection towards a better device performance. The luminance intensity increased from 20 229 to 36 685 cd m−2, while the current efficiencies increased from 3.74 to 13.73 cd A−1, and the power efficiencies increased from 4.65 to 12.94 lm W−1 with a 0.05% Mg doping ratio. Particularly, the optimized device based on ZMO exhibited an enhanced external quantum efficiency (EQE) of 9.46%, which was 3.67-fold compared with that of pure ZnO nanoparticles (2.58%). The proposed approach provides a new method for the design and fabrication of high performance QLEDs by incorporating multielement semiconductors with variable bandgaps as an ETL.

Synthesis and bandgap variation of molecular-size CdSe clusters via electroporation of vesicles

Molecular-size uncapped CdSe clusters are synthesized via the electroporation of synthetic dioleoylphosphatidylcholine vesicles of diameter 178?nm. Cd2+ ions, originally entrapped in the vesicles, are ejected through the transient pores of the vesicle membrane into the bulk where they can react with SeSO32? ions in basic condition to form CdSe clusters at room temperature. Growth and self-aggregation of CdSe clusters is slowed down to timescales of days by their adsorption at the exterior surface of the vesicle, which permits spectral monitoring of the continuous growth process over a long period of time. Growth in the molecular size regime is found to entail novel blue-shifts of the characteristic absorption band. The blue-shift of the transition energy is in agreement with an analogous oscillation of the HOMO?LUMO gap calculated by the use of density functional theory for (CdSe)n clusters. The reason for the blue-shift absorption spectra of molecular-size CdSe clusters is interpreted as the higher stability and bigger gaps of magic number. On the basis of the similarity between the experimental and theoretical trends, the characteristic absorption peaks of 256?nm, 215?nm can be assigned to the monomer or dimer, trimer clusters of CdSe, respectively. Any further growth beyond trimers is associated with the customary monotonic red-shift of the absorption band, due to quantum size effects.

Oscillation of absorption bands of Zn1-xmnxs clusters : an experimental and theoretical study

Electroporation of synthetic vesicles is utilized for the preparation of molecular size uncapped Zn(1-x)Mn(x)S clusters. The absence of caps permits (i) continued growth of the Zn(1-x)Mn(x)S clusters formed, (ii) the assessment of their true absorption spectra unaltered by stabilizing ligands, and (iii) the previously inaccessible live observation of the growth of the clusters in the molecular size regime. Upon cluster growth, the UV spectra exhibit novel, time-dependent, oscillation of red and blue shifts of the characteristic absorption band. The structure and electronic properties of Zn(N-1)MnS(N) clusters with N = 1-9 are calculated using the first-principles DMol(3) package. On the basis of similarities between the oscillating trend of the experimentally observed absorption spectra and that of the calculated highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gap of Zn(N-1)MnS(N) clusters with N = 1-9, the wavelengths of the sequential spectral peaks can be assigned to Zn(2)MnS(3), Zn(3)MnS(4), Zn(4)MnS(5), Zn(6)MnS(7), and Zn(8)MnS(9), respectively. Our results demonstrate that both the cluster size and the composition can be used to tune the optical properties.

Path-related unexpected injection charges in BaTiO3 ferroelectric thin films studied by Kelvin force microscopy

The collective effect of injection charges constructed in a dot array using scanning probe microscopy (SPM) in BaTiO3 ferroelectric thin films was investigated with Kelvin force microscopy (KFM). Unexpected charges were observed in the SPM tip paths where poling bias was zero. The analysis of the array with different poling biases shows that the collective effect of the injection charges in the dot array induced a potential difference between film and tip, which in turn injected unexpected charges. The calculated potential difference distribution along the tip’s paths correlates well with KFM images of the unexpected charges.

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S2- to St- (stearateion). Chnracterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i.e. CdS particle inserts in the CdSt2, molecular layers to form a sandwirh-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.