A Study On Fabrication Of PbS And Its Composite Nanofibers By Electrospinning And Their Optoelectric Properties

Lead sulphide is a typical narrow band gap semiconducting compound composedof IV-VI elements with gap energy about0.41eV and has important application in thearea of infrared optical and electronic devices. The previous research about PbS ismainly on the preparation and optoelectric properties of particles, thin films, andorganic composites while the preparation and properties of PbS nanofibers have notbeen reported yet. This research is aiming at the application of infrared nanodevices. Inthis thesis, organic composite nanofibers containing PbS particles were prepared byelectrospinning and PbS nanofibers were prepared by heat treatment and chemicalreaction from the electrospun precursor fibers. The structure, composition, andcrystallinity of the PbS and its composite nanofibers were characterized by SEM andXRD and their optoelectric properties were measured by semiconductor parametertester.The PbS composite nanofibers were prepared by using polyacrylonitrile （PAN）,polyvinylpyrrolidone （PVP）, or their hybrids as the matrices, dimethyl formamide（DMF） as the solvent, Pb（NO₃）₂and Pb（CH₃COO）₂as the lead sources. Polymernanofibers containing Pb²⁺were prepared by electrospinning, where the effects ofpolymer concentration, lead salt concentration, and the addition of PVP on the fiberstructure were investigated. These Pb2+contained polymer nanofibers were convertedinto PbS particle contained polymer nanofibers by reacting with H2S. SEM observationindicates that no obvious change in the fiber morphology occurred after the chemicalconversion. The fiber diameter increases with increasing the concentrations of polymerand Pb（NO₃）₂. The fibers with good morphology can still be obtained when addingPb（NO₃）₂with a mass ratio to PAN of150%at the PAN concentration of8%. Thesolubility of Pb（NO₃）₂in PAN/DMF solution is larger than Pb（CH₃COO）₂. Thecomposite nanofibers obtained from Pb（NO₃）₂is smoother and more uniform indiameter. When adding PVP to the electrospinning solutions the fiber diameter deceasesand the particles on the fiber surface increases.Based on the preparation of PbS composite nanofibers, PbO nanofibers wereproduced after preoxidation and high temperature heat treatment. After the sulfidationprocess in H2S atmosphere PbS nanofibers were obtained. The PbO nanofibers withoptimal morphology were obtained when the concentrations of PAN and PVP are equal.With the increase of Pb（NO₃）₂concentration the PbO nanofibers become more compactand more continuous. Heating mode influences the fiber morphology. The nanofiberswith uniform diameter without conglutination can be obtained by rapid heating. SEMobservation indicates that the fiber morphology remain unchanged after room temperature sulphureting in H₂S atmosphere.The optoelectric properties of the above PbS and its composite fibers weremeasured. Obvious photo and dark current were observed for the above nanofibers. Theratios of photo current to dark current are2.3and7.0for the PbS/PAN and PbS/PVPcomposite nanofibers, respectively. Comparing with the composite nanofibers the photoand dark current for the PbS nanofibers increase two orders of magnitude and the phototo dark current ratio is about15.5at5V. The electric resistance of the PbS nanofibers isabout5×10⁵Ω and decreases to3×10⁴Ω under light irradiation.In short, PbS and its composite nanofibers were obtained and their preparingprocess was established. In particular, the preparation of the PbS nanofibers has notbeen reported previously and represents an innovation. The obtained materials exhibitobvious photo detecting effects and are of high promise in application.