Ag@Cu2O core-shell metal-semiconductor nanoparticles(NPs) were prepared by using solution phase strategy. It was found that Ag@Cu2O core-shell NPs were easily converted to Ag@Cu bimetallic core-shell NPs with the help of surfactant PVP and excessive reducer ascorbic acid in air at room temperature, which is a unique phenomenon. Varying volumes of Ag colloidal solutions were added into the reaction mixtures containing fixed initial concentrations of Cu2+ and PVP, Ag@Cu2O and Ag@Cu core-shell NPs with fixed core size but varying outer shell thicknesses could be obtained. The composites, structures, morphologies and extinction properties of Ag@Cu2O and Ag@Cu core-shell NPs were systematically characterized by XRD, TEM and extinction spectra. Both of these NPs show wide tunable optical properties. The extinction peaks could be shifted from 421 nm to 700 nm. FTIR results reveal that Cu+ ions on the surface of Cu2 O nanocrystalline coordinate with N and O atoms in PVP and further are reduced to metallic Cu by excessive ascorbic acid and then form a nucleation site on the surface of Cu2 O nanocrystalline. PVP binds onto a different site to proceed with the reduction until all the Cu sources in Cu2 O NPs are completely assumed. And the shell of Cu2 O is converted to Cu shell. The synthesis approach in this paper is simple and also a promising reference for synthesizing other core-shell NPs. Ag@Cu2O NPs can be easily converted to Ag@Cu NPs in air at room temperature, which is promising to be used in electronic devices.
YANG AiLingLI ShunPinWANG YuJinWANG LeLeBAO XiChangYANG RenQiang
Nano-ZnO thin films composed of nanoparticles with sizes of 10-16 nm on silicon substrates at low temperature were prepared by sol-gel method.By placing the nano-ZnO thin films at room temperature or annealing at 100°C in air for 10 h intermittently,within a total 70 h annealing time,the evolution of PL spectra of the nano-ZnO thin films were studied in detail.As the annealing time increases,the PL peaks shift from violet to blue and green bands.The PL peaks at violet and blue bands decrease with the annealing time,but the PL peaks at green band are opposite.The PL spectra are related to the defects in the nano-ZnO thin films.The PL peaks positioned at 430 nm are mainly related to defects of zinc interstatials(Zni),oxygen vacancies and(Vo);the ones at 420 nm to oxygen interstitials(Oi),Zinc vacancies(Vzn),Zni ;and the ones at 468 nm to Vzn,Zni,and charged oxygen interstatials(Vo+).The green luminescence is related to Oi,Vo and Zni.The evolutions of PL spectra and the defects are also related to the concentrations of Zn in the thin films,the thicknesses of the films and the annealing time.For the films with 0.5 M and 1.0 M Zn concentrations,after 20 h and 30 h annealing in air at 100°C,respectively,either placing them in air at room temperature or continuing anneal in air at 100°C,the PL spectra are stable.Under the low temperature annealing,Zni decreases with the annealing time,and Oi increases.Sufficient Oi favors to keep the nano-ZnO thin films stable.This result is important to nano-ZnO thin films as electron transport layers in inverted or tandem organic solar cells.
YANG AiLingYANG YunZHANG ZhenZhenBAO XiChangYANG RenQiangLI ShunPinSUN Liang
By stepwise adding of reducer N2H4.H2O, cuprous oxide （Cu2O） nanoparticles （NPs） with adjustable structures were synthe- sized. The features of Cu2O NPs were characterized by XRD, TEM and UV-Vis absorption spectra. When the reducer was added into the reactant system at one time, the sizes of the Cu2O NPs are in the range of 120-140 nm. Most Cu2O NPs are sol- id spheres. As the reducer was divided into two equal parts and stepwisely added, almost all the NPs are hollow spheres with good size （150-170 nm） distribution and dispersity. But when the reducer was divided into three or four equal parts and stepwisely added, the NPs are hollow spheres, core-shell structures or solid spheres, and the sizes distribution of the products is deteriorated. The effect of sodium hydrate （NaOH） was also probed. Addition of NaOH speeded up the nucleation and growth processes of Cu2O NPs. With the alkalinity increase, the shells of the hollow spheres become compact and the thicknesses of the shells increase, but the size distribution of the NPs is deteriorated. The absorption spectra of the CuzO NPs are tunable. With the shell thicknesses increase, the absorption peaks have red shifts. An inside-outside growth model of Cu2O NPs was proposed to explain the results. The Cu2O single crystalline grains grow not only in the reactant solution, but also inside of the hollow nanospheres. The new Cu2O nanocrystallines can not only aggregate onto the shells of the nano hollow spheres, but also inside and outside of the hollow spheres, which leads to increasing the shell thicknesses of the hollow spheres, forming core-shell structures or small solid spheres of Cu2O NPs, respectively.
YANG AiLingWANG YuJinLI ShunPinBAO XiChangYANG RenQiang
By adjusting pH values of reactant system,the mass ratio of stabilizer/water and aging temperature,size controllable spherical silver nanoparticles(NPs) were synthesized.The properties of silver NPs are characterized by X-ray diffraction(XRD),transmission electron microscope(TEM) and ultraviolet visible(UV-VIS) absorption spectra.Within the pH values of 7.0—11.0,the aging temperature of 80 °C is better to improve silver NPs in shape to nearly sphere,concentrate size distribution and reduce aggregation than the aging temperature of 25 °C.The shape and dispersibility of silver NPs are the best when the pH of the reactant system is within 7.0—8.0.With pH of 7.5,aging at 80 °C,and stabilizer/water mass ratio of 1%,the spherical silver NPs with sizes of 50—70 nm were synthesized.The results are promising to be used to synthesize core/shell NPs when silver NPs are as core.
The refractive indices of thin films based on Kramers-Kronig theory are corrected.And the correction theory is used to determine the optical indices of nano-ZnO thin films prepared by low temperature sol-gel method.The calculated results indicate that in the visible(Vis) range,the refractive indices of nano-ZnO thin films exhibit a slight abnormal dispersion,while in the ultraviolet(UV) region,the refractive indices increase with wavelengths increasing(normal dispersion).But the refractive indices show complex change near the absorption edge.The maximum refractive index(1.95) of nano-ZnO thin films within UV range at low temperature annealing is much lower than that of the films annealed at high temperature.The absorption and refractive indices are closely related to the defects in nano-ZnO thin films.
Cu2O@Cu2O core-shell nanoparticles (NPs) were prepared by using solution phase strategy. It was found that Cu2O@Cu2O NPs were easily converted to Cu2O@Cu NPs with the help of polyvinylpyrrolidine (PVP) and excessive ascorbic acid (AA) in air at room temperature, which was an interesting phenomenon. The features of the two kinds of NPs were characterized by XRD, TEM and extinction spectra. Cu2O@Cu NPs with different shell thicknesses showed wide tunable optical properties for the localized surface plasmon (LSP) in metallic Cu. But Cu2O@Cu2O NPs did not indicate this feature. FTIR results reveal that Cu+ ions on the surface of Cu2O shell coordinate with N and O atoms in PVP and are further reduced to metallic Cu by excessive AA and then form a nucleation site on the surface of Cu2O nanocrystalline. PVP binds onto different sites to proceed with the reduction utill all the Cu sources in Cu2O shell are completely assumed.
