Chenlu Song

Band structures of TiO2 doped with N, C and B

This study on the band structures and charge densities of nitrogen (N)-, carbon (C)-and boron (B)-doped titanium dioxide (TiO2) by first-principles simulation with the CASTEP code (Segall et al., 2002) showed that the three 2p bands of impurity atom are located above the valence-band maximum and below the Ti 3d bands, and that along with the decreasing of impurity atomic number, the fluctuations become more intensive. We cannot observe obvious band-gap narrowing in our result. Therefore, the cause of absorption in visible light might be the isolated impurity atom 2p states in band-gap rather than the band-gap narrowing.

Ag nanoparticle dispersed PbTiO3 percolative composite thin film with high permittivity

Ag nanoparticle dispersed PbTiO3 percolative composite thin films were prepared in situ by sol-gel method using Pb(NO3)2, Ti(C4H9O)4, and AgNO3 as raw materials and lactic acid along with citric acid as complexing agent. The size of the Ag nanoparticles measured by ultraviolet-visible spectra is about 3nm. The percolation effect occurs in composite thin films. The composite exhibits relatively high dielectric constant which is about five times higher than that of PbTiO3 thin film and comparatively low dielectric loss comparable to pure PbTiO3 system. It is highly attractive in application of high quality dielectric devices and miniaturization.

Enhanced Luminescence of Eu-Doped TiO2Nanodots

Monodisperse and spherical Eu-doped TiO2nanodots were prepared on substrate by phase-separation-induced self-assembly. The average diameters of the nanodots can be 50 and 70 nm by changing the preparation condition. The calcined nanodots consist of an amorphous TiO2matrix with Eu3+ions highly dispersed in it. The Eu-doped TiO2nanodots exhibit intense luminescence due to effective energy transfer from amorphous TiO2matrix to Eu3+ions. The luminescence intensity is about 12.5 times of that of Eu-doped TiO2film and the luminescence lifetime can be as long as 960 μs.

Size- and density-controlled synthesis of TiO2 nanodots on a substrate by phase-separation-induced self-assembly

This work presents a facile way, i.e. phase-separation-induced self-assembly, to prepare TiO(2) nanodots on a substrate. This method induces convective flow in a spin-coated titanium tetrabutoxide (TBOT)/polyvinyl pyrrolidone (PVP)/ethanol liquid film through the Marangoni effect and turns TBOT into crystalline TiO(2) nanodots on a substrate after calcination. The size and density of the TiO(2) nanodots can be finely tailored by controlling the concentrations of TBOT and PVP in the precursor sol. The TiO(2) nanodot-deposited surface showed a hydrophilic characteristic and the wettability was obviously improved by increasing nanodot size.

Size-dependent ultraviolet luminescence and low-field electron emission of TiO2 nanodots formed by phase-separation-induced self-assembly

We present a study of phase-separation-induced self-assembled TiO2 nanodots. The Marangoni effect is utilized in the preparation of this TiO2 nanostructure. Unique and strong ultraviolet (UV) luminescence is observed from the TiO2 nanodots at room temperature. As the nanodot size reduces from 93 to 48 nm, the bandgap energy shifts from 3.43 to 3.76 eV and the luminescence peak energy increases from 3.38 to 3.58 eV. High electron emission at low electric field is also obtained from TiO2 nanodots. The turn-on field and threshold field for emission current densities of 1 µA cm−2 and 1 mA cm−2 are as low as 0.7 and 3.7 V µm−1, the lowest values ever reported for TiO2 materials.

Effect of PEG amount in amorphous calcium phosphate on its crystallized products.

Biphasic α-tricalcium phosphate/β-tricalcium phosphate (α/β-TCP) with a designed phase ratio is thought to have controllable dissolution–reprecipitation behavior that is significant in the repair and regeneration of bone. Amorphous calcium phosphate (ACP) was selected as a precursor to prepare biphasic α/β-TCP. The influence of polyethylene glycol (PEG) content in ACP on its crystallization, or on the phase ratio of the resulting biphasic TCP, was investigated. ACP was synthesized by the reaction of Ca(NO3)2 with (NH4)2HPO4 using PEG as an additive. Depending on the amount of PEG addition, resulting ACP could be crystallized to α-TCP, β-TCP or biphasic α/β-TCP after heat-treatment at 800°C, showing that PEG addition is a critical factor to tailor the phase ratio of biphasic α/β-TCP. One reason for the influence of PEG is that ACP with different PEG content could have two types of unit structures that tend to form α-TCP and β-TCP after crystallization.

Nucleation and growth of TiSi2 thin films deposited on glass by atmospheric pressure chemical vapor deposition

Titanium silicide (TiSi2) thin films were prepared on glass substrate by atmospheric pressure chemical vapor deposition using SiH4 and TiCl4 as the precursors. The phase structure of the thin films was identified by x-ray diffractometry. The surface morphology and thickness of the thin films were observed by field emission scannig electron microscopy and the sheet resistance of the thin films was measured using the four point probe method. The results show that the TiSi2 thin films are formed in a face-centered orthorhombic structure. Due to the influence of the amorphous glass substrate, an amorphous layer is initially formed on the substrate and the TiSi2 crystalline phase grows on top of it. As the thickness and content of TiSi2 crystalline phase increase with deposition time, the resistivity of the thin film decreases. Besides, the growth rate and thus the size of TiSi2 crystalline phase increase as the deposition temperature increases. The stack density decreases when the deposition temperature incre...

Room-temperature nonequilibrium growth of controllable ZnO nanorod arrays

In this study, controllable ZnO nanorod arrays were successfully synthesized on Si substrate at room temperature (approx. 25°C). The formation of controllable ZnO nanorod arrays has been investigated using growth media with different concentrations and molar ratios of Zn(NO3)2 to NaOH. Under such a nonequilibrium growth condition, the density and dimension of ZnO nanorod arrays were successfully adjusted through controlling the supersaturation degree, i.e., volume of growth medium. It was found that the wettability and electrowetting behaviors of ZnO nanorod arrays could be tuned through variations of nanorods density and length. Moreover, its field emission property was also optimized by changing the nanorods density and dimension.

Theoretical and experimental study of Raman spectra of pre-perovskite PbTiO3

The assignment of microscopic Raman spectra on powdered samples of pre-perovskite PbTiO3 (space group I4/m) has been established according to the correspondence between the experimental and theoretical frequency and relative intensity data. We find no giant longitudinal-optical (LO) and transverse-optical (TO) splittings in pre-perovskite PbTiO3. In contrast to conventional perovskite, the largest pre-perovskite LO-TO splitting comes from its stiffest Au mode instead of from its softest mode. The pre-perovskite’s Born effective charges, dielectric tensors, and infrared frequencies are also calculated to determine its lattice dynamics and optical properties, and compared with the conventional perovskite PbTiO3. The results provide invaluable information for use in further research on PbTiO3 phase transition.

Giant Dielectric Response up to High Frequency in SM1.75Sr0.25NiO4 Ceramics

The crystalline structure and dielectric properties of nominal Sm 1.75 Sr 0.25 NiO 4 ceramics are presented. Three phases, Sm 1.70 Sr 0.30 NiO 4 , Sm 2 O 3 and NiO, are found in the present ceramics, and the abundances are 77.7(1.1) wt%, 19.2(3) wt% and 6.1(2) wt%, respectively. The temperature-stable giant dielectric constant over 60 000 even up to 5 MHz is observed in a broad temperature range. The modulus plots show that the giant dielectric constant should be originated from the contribution of the grain interior instead of grain boundary. Compared with the other giant dielectric constant materials, the present materials have the great potentiality in the practical application, especially for the high frequency application.