Optical And Electronic Materials: Preparation And Characterization

In this thesis, several typical optical and electronic materials including a-C:H, ZnO, [(BaTiO3)m/(SrTiO3)m]n and CeO2 were prepared by chemical vapor deposition (CVD), electrospinning, physical vapor deposition (PVD) or/and their combined techniques. Some doping mechods related to CVD, electrospinning, and PVD is developed. Influence of Fe-doping and rere eareth-doping on photoluminescence of amorphous and polycrystal semiconductor is investigated, respectively.Low content and high content Fe-doped hydrogenated amorphous carbon (a-C:H:Fe) films were experimentally developed by plasma enhanced metal organic chemical vapor deposition (PEMOCVD), a promising chemical vapor deposition (CVD) technique combined plasma enhanced chemical vapor deposition (PECVD) with metal organic chemical vapor deposition (MOCVD). Ni nanocrytals (NCs) were embedded in [(BaTiO3)m/(SrTiO3)m]n superlattice structures using laser molecular beam epitaxy (L-MBE). Cerium dioxide (CeO2) films were epitaxially grown on SrTiO3 (001) substrates by L-MBE using a metallic Ce target in oxygen ambient. ZnO and its rare earth (Eu, Er, and Tb)-doped nanofibers and hollow nanofibers were deposited by electrospinning technique and sputtering using electrospun PVP nanofibers as templates, respectively. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscope, X-ray photoelectron spectroscopy, in situ reflection high energy electron diffraction, X-ray diffraction, Fourier transform infrared spectra, Raman spectra, UV-visible spectroscopy and photoluminescence (PL) spectra were used to characterize and analyze the surface morphologies, compositions, microstructral and optical properties of the materials, respectively. Some results are listed as follows:(1) Fe atom in amorphous carbon matrix bonds with C; The C-Fe binding energy centered at around 280.7 eV is confirmed; The two types of films contain rich C-H. Compared with the a-C:H films, more ring orders other that six are obtained in the a-C:H:Fe films due to ferrocene as a catalyst of the growth of rings. The structural disorder of the a-C:H films seems to be dependent on the Fe-containing. The cluster diameter or in-plane correlation length La of the a-C:H:Fe films is less than that of the a-C:H films.sp3 fraction and olefinic sites and sp2 clustering increase for high content Fe-doping, and decrease for low content Fe-doping. H content at.% H decreases 5～6% relative to the value of the a-C:H films after Fe-doping. The narrowing of Tauc optical gap of the a-C:H films after Fe-doping is attributed to two reasons as follows:(1) The a-C:H films contain more six-fold rings and ring orders other that six, more shared electrons and lower transition energy ofπandπ* bond pairs after Fe-doping. (2) The narrowing of the optical gap after doping is attributed primarily to the extended state around the Fe deep level in the band gap, and especially for high conent Fe-doped a-C:H films. PL center is shifted from 2.35 eV of the a-C:H films to 1.95 eV of low conent Fe-doped a-C:H films, and PL intensity is greatly enhanced in the low conent Fe-doped a-C:H films. On the one hand, due to the moreπandπ* bond pairs and higher sp2 carbon content and sp2 clustering of the low conent Fe-doped a-C:H films, optical excitation of the low conent Fe-doped a-C:H films generates more electron-hole pairs and the probability of their recombination increases. Compared with the a-C:H films, more emission electrons are obtained in the low conent Fe-doped a-C:H films. As a result, the PL of the low conent Fe-doped a-C:H films is greatly enhanced. On the other hand, due to electronic localization around the Fe deep level, which contributes partly to radiative transition in PL, the shoulder peak at 2.04 eV of the a-C:H:Fe films is observed near main peak 1.95 eV. The Fe deep level of the low conent Fe-doped a-C:H films be sensitive to 250 nm light. The recombination ofπandπ* bond pairs decreases due to the increasing of sp3 fraction, olefinic sites and sp2 clustering after high content Fe-doping. The slight change of the center of gravity of the PL after Fe-doping is attributed to the extended state the Fe deep level, which could contribute to the weak emission. The results of Tauc optical gaps of the a-C:H films after Fe-doping are good agreement with their PL results.(2) ZnO and its rare earth (Eu, Er and Tb)-doped hollow nanofibers have a uniform intact morphology. Electrospun ZnO and its rare earth (Eu, Er and Tb)-doped nonafibers have hexagonal crystalline structures, and a reactive mechanism of the transformation from poor polycrystalline ZnO (Zn-rich) prepared by sputtering from a metallic Zn target to good polycrystalline ZnO after annealing is proposed. Due to removing PVP cores by annealing and rare earth (Eu, Er and Tb)-doping, oxygen vacancies, interstitial zinc and their complexes decrease. Owing to the size confinement effects and lattice distortion, there are the A1(LO) and E1(LO) modes as well as surface phonon mode absorption for ZnO hollow nanofibers. Besides, A1(LO) mode is greatly decreased after rare earth (Eu, Er and Tb)-doping due to the increasing of interstitial zinc. ZnO and its rare earth (Eu, Er and Tb)-doped nonafibers have hexagonal crystalline structures and contain oxygen vacancies, interstitial zinc and their complexes. The high intensity ultraviolet emissions of the ZnO and rare earth (Eu, Er and Tb)-doped ZnO nanofibers and hollow nanofibers are based on polycrystalline structures originated from the oxidation reactions and recrystallization annealing. Enhancement of ultraviolet emission of the ZnO (hollow) nanofibers is linked to lasing characteristics on a basis of polycrystalline structures, namely, as the random medium. The green light and orange light emissions of the ZnO nanofibers and hollow nanofibers are suppressed after rare earth-doping. Besides, among these emission bands, the peak at 613 nm and the band around 590 nm and 580 nm can be identified as 5D0→7F2,5D0→7F1 and 5D0→7F0 of the Eu-doped ZnO nanofibers and hollow nanofibers, respectively.(3) Ni nanocrystal embedded in [(BaTiO3)m/(SrTiO3)m]n superlattices is confirmed. Epitaxial oriented growth and single crystal characteristic of BaTiO3 and SrTiOs can be kept after Ni NCs-embedding. The epitaxial growth of such nanocomposite films via a L-MBE technique can be engineered controllably for the desired quality. Cerium dioxide (CeO2) films have been epitaxially grown on SrTiO3 (001) substrates by L-MBE using a metallic Ce target in oxygen ambient. Epitaxial growth of CeO2 films have a uniform and smooth surface with a single crystal characteristic.