Zhang Lide

Synthesis and structural and optical properties of mesoporous silica containing silver nanoparticles

Mesoporous silica with silver (Ag) nanoparticles within its pores was synthesized by thermal decomposition of silver nitrate. The structure of this new material was examined by x-ray diffraction, transmission electron microscope and Brunauer - Emmett - Teller techniques, and its optical absorption spectra were measured. It has been shown that Ag nanoparticles are isolated from each other and highly uniformly dispersed in pores which are less than 8 nm in diameter. The size of Ag particles follows a log-normal distribution function. Ag particle doping leads to a large red shift of the absorption edge and the edge position can be controlled across the whole visible region by varying the amount of Ag doping. There is no surface plasmon resonance peak other than an absorption edge on the absorption spectra. These facts are explained in terms of interband absorption and dipole interaction of Ag particles in silica, and interaction between pore walls and Ag particles.

Luminescence in nanostructured materials

Abstract Some new photoluminescence phenomena, which have not been observed for conventional coarse grain materials, are reported for nanostructured materials,such as nanostructured η,γ-Al 2 O 8 , boehmite, TiO 2 ( anatase), and amorphous silicon nitride. In this article we discussed the mechanisms of these new luminescence phenomena appearing in nanostructured materials in terms of quantum confinement effect, impurity and defect energy levels in the energy gap and destruction of selection rules of electronic transitions.

Characterization and the optical switching phenomenon of porous silica dispersed with silver nano-particles within its pores

Porous silica dispersed with silver nano-particles (about 3 nm) within its pores (cages) has been prepared by a new method. The microstructures, particle size distribution and optical absorption have been examined. We have found that in the process of alternating exposure to the ambient air and annealing, this new material assumes a optical switching and memory effect in the visible wave band or a reversible transition between transparency and opacity.

Anomalous Dielectric Behavior in Nanometer-Sized Amorphous Silicon Nitride

An anomalous dielectric behavior in nanometer-sized amorphous silicon nitride is reported. The dielectric constant of nanometer-sized amorphous silicon nitride has strong dependence on frequency at room temperature (RT), which is completely different from the conventional coarse-grain silicon nitride. The maximum of the dielectric constant of nanometer-sized amorphous silicon nitride at RT is about 40 times larger than that of the conventional silicon nitride. The anomalous dielectric behavior is explained by a kind of mechanism of polarization, that is, interfacial polarization.

Contribution of the R transformation to the two-way memory effect in TiNi alloys

Abstract Internal friction Q −1 , modulus M, shape change D and transformation peaks were studied as a function of increasing prestrain in the temperature range from 100 to −65°C for TiNi alloy samples exhibiting the two-way memory effect (TWME). The results show that the R transformation is beneficial to the TWME in TiNi alloys. The ratio of the TWME associated with the R transformation to that caused by both R and M transformations is not a constant but depends on many factors, such as alloy composition, applied load and thermomechanical history. With increasing prestrain the interaction of R interfaces with dislocations and martensitic interfaces is enhanced and causes the mobility of R interfaces to decrease. Thus the formation of favourable R variants becomes more difficult and the TWME caused by the R transformation decreases.

DIELECTRIC CHARACTERISTICS IN NANOSTRUCTURED γ-Fe2O3

Abstract The spectra of the dielectric constant and dielectric loss in nanostructured γ-Fe 2 O 3 have been measured by using the ac LRC method. The relaxation time of polarization and the conductance have also been calculated by means of the Debye mechanism, and two kinds of polarization processes with two different relaxation times have been proposed. ©1997 Acta Metallurgica Inc.

Aging damping associated with discontinuous transformation in Al-Zn and Al-Zn-Mg-Cu alloys

In this work, the aging damping associated with the discontinuous phase transformation was studied in two Al-Zn alloys using a forced-vibration pendulum. Correlating these results with an X-ray diffraction analysis and TEM observations the authors suggested that the aging damping was directly proportional to the total interface area which was related to the nucleation and growth during the discontinuous transformation.

Endothermic effects in porous silica doped with silver nanoparticles and the formation of by atmospheric oxygen via chemisorption

Porous silica dispersed with silver (Ag) nanoparticles (about 3 nm in diameter) within its pores has been prepared by a new method. The microstructures and the size distribution of particles within pores have been examined by transmission electron microscopy and the Brunauer - Emmett - Teller technique. The Ag nanoparticles are uniformly dispersed within the pores of silica; the particle size follows the log-normal distribution function. The thermal effect of this porous composite, exposed to ambient air for different times, has been investigated by differential scanning calorimetry and thermogravimetric analysis. An endothermic peak has been found for all the doped samples measured. At room temperature (298 K), a short exposure (2 d) to dry air leads to a wide endothermic peak at around 400 K; long exposure (1 month) results in a wider endothermic peak at around 450 K; when the sample was exposed to ambient air with relative humidity greater than 60%, a much higher endothermic peak exists at around 460 K. From the experimental results and discussions of adsorption and oxidation, the endothermic peaks for the samples exposed to dry air can be mainly attributed to the desorption of oxygen physisorbed and chemisorbed on the surface of the Ag particles within the pores, for lower- and higher-temperature peaks, respectively, and the corresponding desorption enthalpy values were estimated to be about 0.26 eV and 0.90 eV, respectively. For the sample exposed to humid air, the endothermic peak originates from the decomposition of silver oxide () formed on the surface layer of the Ag particles, and the bond energy of Ag - O in the film was estimated to be about 1.8 eV.

Effect of Substrates on CuInSe2 Nanoparticle Thin Films by Radio Frequency Reactive Sputtering

CuInSe2 (CIS) nanoparticle thin films have been prepared by radio frequency reactive magnetron sputtering from compound ternary fan-shaped targets on low-temperature substrates with pure argon gas as the atmosphere. The stoichiometry of the ternary compound semiconductor quantum dots can easily be controlled by the ratios of the ternary elements and sputtering parameters. CIS nanoparticle thin films regularly shaped and distributed reasonably uniform in size on substrates of 7059 glass etc can be grown in this way. The average particle diameter can be varied between 40-80 nm by an appropriate choice of the substrate temperature, power density and total CIS coverage. The optical and electrical properties of the CIS films have also been studied.

Effect of temperature on electrical resistivity of a hydrogenated LaNi5 thin film

The electrical resistivity of a hydrogenated LaNi5 thin film has been investigated as a function of temperature in vacuum and in hydrogen. While the film was heated in vacuum for the first time, the change in resistivity exhibited different characteristics during different ranges of temperatures due to the competition of two effects owing to the lattice scattering of conductive electrons and the number of them. The resistivity had a sharp drop near 600 K, which originates from the formation of high conducting lanthanum hydride and nickel due to a reaction between the dissolved hydrogen and LaNi5. The change in resistivity was not repeatable during the successive heating and cooling processes. When the film was heated under a hydrogen atmosphere, a drop in resistivity occurred near 700 K due to the reaction between LaNi5 and the hydrogen atmosphere. The film showed a linear temperature dependence of receptivity with completeness of the reaction. It was found that the reaction was irreversible. The film lost the ability of hydrogen absorption after the reaction, and it had a phase change from LaNi5 to LaH and Ni. This result was supported by x-ray diffraction patterns.