Monoclinic Thin Films Research Articles

On the influence of local oxygen addition on the growth of sputter deposited yttrium oxide thin films

Yttrium oxide thin films are grown by reactive magnetron sputtering. To achieve a high deposition rate, target poisoning is avoided by local oxygen addition at the substrate. In all deposited thin films only the monoclinic Y2O3 phase is observed. A strong variation in the film texture across the sample for experiments with a stationary sample stage is noticed. This inhomogeneity can be partially traced back to an uneven oxygen gas distribution. Sample rotation resolves this problem, but still the gas distribution influences both the texture and the Bragg peak positions. Several configurations for the gas supply are tested with a different number of gas distribution pipes. An overview of all experiments shows an interesting correlation between the texture coefficient and the peak position of the monoclinic (111) Bragg reflection. When the peak shifts towards higher diffraction angles, the texture coefficient drops as a higher contribution of the 402¯ orientation is observed. This trend however is further complicated by the exact geometrical configuration on the deposition rate, and the energy/momentum of the species arriving at the substrate. As previously reported, an increasing energy/momentum per deposited atom results in monoclinic thin films with a preferential (111) out-of-plane orientation.

Cu, Mo-doped and pristine-BiVO4 thin films prepared by rf sputtering process for photocatalytic applications

Cu, Mo-doped and pristine BiVO4 thin films were realized by coupling rf sputtering and mechanochemical synthesis technique. These monoclinic thin films were deposited over silicon substrate under the pure argon atmosphere (Ar: 72 sccm). The sputtering targets were prepared by the respective ball-milled powders hydraulically pressed at optimal conditions. XRD analysis shows that the as-deposited thin films are amorphous and the monoclinic structure is obtained with a post-annealing process in the air at 450 °C for 2 h. Compositional, morphological and optical studies were thoroughly investigated by using FE-SEM, AFM and UV–Vis absorption spectroscopies respectively and discussed as a function of photocatalytic degradation of methyl orange organic dyes in solution. The pseudo first-order degradation rate constant values were estimated as 0.028, 0.031 and 0.022 min−1 for Cu, Mo-doped and pristine BiVO4 thin films respectively. Degradation performances are correlated as a function of their structural, surface morphological and film thickness aspects as well as the role of doping agent. Mo-doped high crystalline BiVO4 thin films with thickness 130 nm and morphology of small nano-sized islands on the surface (RMS = 5.08 nm) contributed well to the amplification of photocatalytic performance and followed by Cu doped and pristine BiVO4 thin films.

A rigorous investigation of BiMnO3 ferroelectricity through a development of a novel way to stabilize twin free and monoclinic thin film

Bulk BiMnO3 has a monoclinic structure and exhibits ferromagnetic properties below Tc∼105 K. The existence of ferroelectricity was one of the hottest issues in this compound. To investigate the ferroelectricity in BiMnO3, a good film with low-enough leakage is highly required. However the reported quality of BiMnO3 thin films has shown critical dependence on stoichiometry. Previously, we reported that a BiMnO3 thin film grown on top of a SrTiO3 (001) substrate has good stoichiometry, as well as bulk-quality ferromagnetic properties, but our results did not demonstrate the Q-E hysteresis curves. However, we could not exclude the possibility that non-ferroelectricity observed in the BiMnO3 film is partly due to the tetragonal symmetry enforced by the strong epitaxial strain of the substrate since the ferroicity in most oxides accompanies with or equivalently originates from crystal symmetry breaking and/or lowering. In the present work, we used a SrTiO3 (110) substrate with an anisotropic in-plane atomic arrangement to stabilize the BiMnO3 thin film having the symmetry lower than tetragonal symmetry. After observing the stabilization of twined monoclinic phase in the BiMnO3 film, we solved the twin problem by trying a novel substrate; i.e., miscut SrTiO3 (110) substrate. The physical properties for the stoichiometric, twin-free, monoclinic BiMnO3 thin film were notably similar to those reported for the stoichiometric BiMnO3 bulk with monoclinic symmetry. We believe this new data more rigorously demonstrates the absence of ferroelectricity in stoichiometric monoclinic BiMnO3.

The infrared response of lead phthalocyanine thin films to chlorine and iodine doping

Abstract Monoclinic thin films of PbPc were deposited on KBr disc substrates by a high-vacuum thermal-evaporation technique. The infrared response of the films was studied with respect to chlorine and iodine exposure in the range 400–4000 cm −1 . Doping with chlorine and iodine led to a generation of acceptor levels within the band gap and led to a splitting of the valence band. The data was analysed to estimate the intraband transition energy between the valence subbands. The ionization energy of the acceptor levels was estimated.