Papers by Author: X. Li

Abstract: The cubic-NbN/NbCN multilayers with modulation periodicity (Λ) ranging from 4.2 to 39.1 nm were deposited on Si (100) substrate by reactive magnetron sputtering in a mixture of Ar and N₂ gases. The Λ dependent structural, mechanical and tribological properties for resulting c-NbN/NbCN multilayers were explored. As Λ varied from 4.2 to 39.1 nm, all the films exhibited an obvious modulated structure. Increasing the Λ, the Nb (C,N)(111) peak in XRD gradually shifted to bigger angles and the peak intensity of NbN(111) became stronger. The stress for all multilayers was compressive ranging in between the stress for both NbN and NbCN single layers, and the stress value was stable with increasing Λ. The NbN layer was beneficial to relaxing the compressive stress which induced by NbCN layer. In addition, as Λ increases, the hardness (H) first increased, and then decreased after reaching a maximum value. The obvious enhancement in hardness for multilayers was observed, whose maximum value approaches 43.3 GPa when Λ = 8.4 nm, 37% larger than that obtained by the rule of mixture value. The friction coefficient values of NbN/NbCN multilayers ranging between 0.34 and 0.4 were much lower than that of NbN monolayer but higher than that of NbCN monolayer were.

Abstract: The effects of an organic solvent on the electrospinning of water-soluble polyacrylamide with ultrahigh molecular weight were investigated. An organic solvent, DMF, was introduced to the polyacrylamide aqueous solution and subsequently, transparent spinning solutions were obtained. The spinning solution was electrospun at the voltage of 10 kV and the electrospun products were examined by scanning electron microscopy (SEM). Results indicated that all the electrospinning products including colloidal particles, beaded fibers and smooth fibers were fabricated in the DMF/H2O bi-component solvent and the morphology of electrospun products changed from smooth fiber to beaded fiber with the increasing amount of DMF used.

Abstract: The CdS/PVP fibers have been successfully prepared by electrospinning. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-Vis absorption spectra were used to characterize the structure. Results showed that the concentration of polymer solutions and the CdS amount in the solvent influenced the morphology and the diameter of the electrospun fibers. The electrospinning from CdS/PVP in ethanol produced a structure having a combination of fibers, ribbons, beads and an unexpected half hollow sphere (HHS) structure. When the weight ratio of CdS:PVP was kept at 1:1000, the morphologies of electrospun products changed from HHS, to beaded fibers and ribbons, to beaded fibers, and to bead-free fibers with the increasing of the PVP concentration.