Fu Honggang

Field emission properties of capped carbon nanotubes doped by alkali metals: a theoretical investigation

The electronic structures and field emission properties of capped CNT55 systems with or without alkali metal atom adsorption were systematically investigated by density functional theory calculation. The results indicate that the adsorption of alkali metal on the center site of a CNT tip is energetically favorable. In addition, the adsorption energies increase with the introduction of the electric field. The excessive negative charges on CNT tips make electron emittance much easier and result in a decrease in work function. Furthermore, the inducing effect by positively charged alkali metal atoms can be reasonably considered as the dominant reason for the improvement in field emission properties.

FT-RAMAN SPECTROSCOPIC STUDY OF Pb1−x Ca x TiO3 NANOCRYSTALS

FT-Raman Spectra of Pb1−x Ca x TiO3 nanocrystals with different lanthanum amounts were measured at 288 K and 378 K. Several nanocrystals of Pb0.85Ca0.15TiO3 with different grain size were also prepared at 288 K. The effects of the amount of lanthanum, grain size and temperature on phonon frequency were discussed in details. Furthermore, the conclusion that lattice expansions presentation in PCT nanocrystals can be obtained by the frequency comparison of PCT nanocrystal of x ≥ 0.2 with ceramic doped with the same amount of calcium.

Preparation of ferroelectric lead titanate ceramics by a modified sol-gel method

Abstract The usual sol-gel method for the preparation of nanocrystalline lead titanate has been improved in this research. The hydrolytic process of lead acetate [Pb(Ac)2] and titanium butoxide [Ti(O(CH2)3CH3)4] sol precursor was promoted by the addition of methyl alcohol (CH3OH) solution containing a certain amount of water. The fresh gel was directly sintered to transform the gel into PbTiO3 polycrystals, which were quite easily ground into fine powders for ceramics pellets. The modified sol-gel method has reduced the preparation period from a few days to several hours. X-ray diffraction and electrical measurements have indicated that the PbTiO3 thus obtained exhibits the same structure as that derived from ordinary sol-gel method and shows excellent dielectric and ferroelectric properties

Adsorption of Thiophene and the Mixture of Thiophene and Iso-octane on MCM-22 Zeolite by Monte Carlo Simulation

A grand canonical ensemble Monte Carlo simulation was performed to investigate the adsorption and distribution of thiophene, as well as the mixture of thiophene and iso-octane on MCM-22 zeolite. The adsorption isotherms and the isosteric heat of thiophene on MCM-22 zeolite were obtained at different temperatures (298, 363 and 393 K). The simulated results showed that the adsorptive capacity of pure thiophene on MCM-22 could be affected by temperature and pressure. The isosteric heats were similar at different temperatures. For the mixture of thiophene and iso-octane, competitive adsorption of thiophene and iso-octane occurred on MCM-22 zeolite at 298 K. Thiophene can distribute throughout two independent channels of MCM-22 but iso-octane mainly adsorbs within the supercage of MCM-22. Thus, thiophene and iso-octane can be separated effectively by MCM-22 zeolite.