| Compared to lead-based function films where lead is a poisonous and volatile material, Ba1-xSrxTiO3(x=0.1,0.35), Bi1-yCeyFeO3 (0≤y≤0.25) (BCFO) and Zn0.95-zCo0.05CuzO (ZCCO) thin films have attracted considerable attention for their friendly environment, relative stability and some special properties.Ba0.9Sr0.1TiO3 thin films were deposited on fused quartz and Pt/TiNx/Si3N4Si substrates by radio frequency magnetron sputtering technique. Effects of annealing temperatures on microstructure, surface element compositions and the corresponding chemical bonding states, optical and electrical properties of the Ba0.9Sr0.1TiO3 films were investigated. Fitted X-ray photoelectron spectroscopy (XPS) subpeaks located at lower binding energy regions donoted as Ba(1), Sr(1) and Ti(1), are assigned to A-sited (Ba, Sr)-cations and B-sited Ti cations in ABO3-type perovskite structure, which are identified as XPS signals coming from Ba-O, Sr-O and Ti-O bonds, respectively. The fitted subpeaks located at higher binding energy regions donoted as Ba(2), Sr(2) and Ti(2), are ascribed to the ralaxed surface phases, caused by oxygen vacancies, (Ba, Sr,Ti)-cation defects and interior stresses. Compared to refractive index (1.97) of the as-deposited Ba0.9Sr0.1TiO3 film, the corresponding refractive indices for the films annealed at 650,700 and 750℃are 1.99,2.15 and 2.11 at 632.8 nm, respectively. The extinction coefficient increases from 3.46×10-4 to 4.85×10-3 at 632.8 nm, while the bandgap decreases from 3.86 to 3.68 eV with increasing annealing temperature. Inequipotential J-V characteristics for the Ba0.9Sr0.1TiO3 films annealed at different temperatures are attributed to different thermal histories of Pt/Ba0.9Sr0.1TiO3/Pt film capacitors, interdiffusion of Ba0.9Sr0.1TiO3/Pt interfaces, interface states of Ba0.9Sr0.1TiO3/Pt, defect concentrations of oxygen vacancy, (Ba, Sr, Ti)-cation vacancies, relaxed stresses, and varied Schottky barrier heights in the Ba0.9Sr0.1TiO3/Pt and Pt/Ba0.9Sr0.1TiO3 interfaces.XPS depth profiling associated with Ar+ etching shows that relative atomic concentrations of Ba at.%, Sr at.%, Ti at.% and O at.% present homogeneous distributions among surface, subsurface and interior of Ba0.65Sr0.35TiO3 film. A Ti-rich phenomenon present in Ba0.65Sr0.35TiO3/Pt interface, and Ti4+cations induced by oxygen vacancies, are reduced to form amorphous oxide TiOx (O<x<2). Based on analysis of XPS valence band spectrum, valence band edge is 2.9 eV below Fermi level of the film. Schottky barrier height of Ba0.65Sr0.35TiO3/Pt interface is 1.2 eV within Schottky limit, and the band-bending is upward in magnitude of 0.8 eV.Sol-gel-derived BiFeO3 films are rhombohedral structure, while crystal lattices of BCFO films are distorted after Ce3+ and Ce4+ cations are partially substituted for Bi3+ ions in BiFeO3 matrix. Compared to BiFeO3 counterparts, Raman redshifts of 2-4 cm-1 and shorter phonon lifetimes are obtained in Bi0.8Ce0.2FeO3 film, and the fitted Bi 4f7/2, Bi 4f5/2, Fe 2p3/2, Fe 2p1/2 and O 1s photoelectron peaks of the film shift towards higher binding energy regions by amounts of 0.33,0.29,0.43,0.58 and 0.49 eV, respectively. Dielectric properties of Bi0.8Ce0.2FeO3 film are improved in comparison with the BiFeO3 counterparts, based on the decreased oxygen vacancies and reduced probability of Fe3+ to Fe2+ in Bi0.8Ce0.2FeO3 matrix after Ce doping. Ferroelectric properties of the Bi0.8Ce0.2FeO3 film are enhanced because 4f1 electron of Ce3+ hybridizes with the empty 5d0 and 6s0 orbits of Ce3+and 2p6 orbits of O2-, meanwhile 5p6 electrons of Ce4+ hybridize with the empty 4f0,5d0 and 6s0 orbits of Ce4+ and the 2p6 orbits of O2-, resulting in the further distorted shape of electron cloud and the increased relative displacements of Bi, Fe and O in BiFeO3 matrix. Room temperature ferromagnetisms (RTFMs) of the BCFO films are enhanced in comparison with that of BiFeO3 film for the following reasons. When Ce3+ is substituted for Bi3+, a 4f electron with spin moment of 1.73μB is offered, suggesting that the 4f1 electron hybridizes with the empty 5d0 and 6s0 orbits of Ce3+ and the 2p6 orbits of O2-, and the spin moment is also coupled with the 2p6 orbits of O2-.Ce4+ ion substituting Bi3+ion acts as a donor dopant in the oxygen octahedron, leading to the decreased concentration of oxygen vacancy and reduced probability of Fe3+ to Fe2+ in the BCFO film. Ce3+ and Ce4+ cations are substituted for Bi3+ ions, indicating the suppressed spiral spin structure and the increased spin canting angle of sublattice. When VBias ranges from 0 to 3.5 V, slopes of lgJ-lg V plots for Pt/BCFO/Pt film capacitors are approximately 1, which corresponds to Ohmic conduction mechanism. At 3.5<VBias<10 V and-10 V<VBias<-3.5 V regions, dominant conduction mechanism of the film capacitors is interface-controlled Schottky emission mechanism.(002)-oriented ZCCO thin films with hexagonal wurtzite structure, were deposited on Si (100) substrates by pulsed laser deposition technique. Co2+, Cu2+and Cu1+ cations are partially substituted for Zn2+ ions in ZnO matrix, resulting in the decreased grain size and distorted crystal lattice of the ZCCO film. When Cu content increases from 0 to 0.015, the fitted Zn 2p3/2, Co 2p3/2, Co 2p1/2, Cu 2p3/2 peaks of the ZCCO film shift towards higher binding energy regions due to combined effects of decreased average grain size, different electronegativities of Zn, Co, Cu and O, hybridizations among O 2p-Zn 3d, O 2p-Co 3d and O 2p-Cu 3d, relaxed Zn, Co and Cu phases, oxygen vacancy and (Zn, Co, Cu)-cation defects. Meanwhile, O 1s peak shifts towards lower binding energy for the increased oxygen-deficient states and oxygen vacancy concentration since the ZCCO film was annealed in Ar(90%)/H2(10%)-reduced ambience. Room temperature magnetic measurements reveal that in-plane and out-of-plane M-H hysteresis loops are saturated, implying that all the ZCCO films have RTFMs. Furthermore, Zn0.95Co0.05O film doped with appropriate Cu content (z=0.01) can improve the RTFM of the ZCCO film because the crystal lattices are distorted after Co2+, Cu2+ and Cu1+ cations are substituted for Zn2+ ions in ZnO matrix, ferromagnetic coupling actions between Co2+ and Cu2+ spin states, and the enhanced exchange interactions among the unpaired electron spins originating from lattice defects, such as Vo¨, Zni·and Vo·induced by Cu doping in Zn0.95Co0.05O matrx. |
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