Strain evolution during spinodal decomposition of TiAlN thin films

We use a combination of in-situ X-ray scattering experiments during annealing and phase-field simulations to study the strain and microstructure evolution during decomposition of TiAlN thin films. The evolved microstructure is observed to depend on the initial alloy composition, where the microstructure is finer and the TiN and AlN domains formed are more interconnected and aligned in the [100] directions in the higher Al content film. The simulations show strain formation in the evolving cubic AlN and TiN domains, which is a combined effect of increasing lattice mismatch and elastic incompatibility between the domains. The experimental results show that the strain of the film is a result of defect density, thermal strains, and the phase evolution during decomposition of the cubic TiAlN. The compressive strain increases at temperatures above ~ 850 °C for Ti_0.35Al_0.65N and above ~ 930 °C for Ti_0.53Al_0.47N due to the onset of transformation to hexagonal-AlN, which is similar to the temperature where the maximum hardness of similar TiAlN films has been found. The higher driving force for decomposition in the higher Al content film results in a higher decomposition rate revealed by the simulations and earlier formation of hexagonal-AlN in this film.     

Microstructure and magnetic properties of zinc ferrite thin films produced by pulsed laser deposition

Zinc ferrite thin films were deposited from a target of zinc ferrite onto a MgO substrate using XeCl excimer laser operating at 308 nm and frequency of 30 Hz. The crystallographic characterizations of the films were performed using X-ray diffraction (XRD). Microstructure, surface morphology, chemical composition and grain size, as well as surface roughness were obtained from scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and atomic force microscopy (AFM). The magnetic properties of the thin films were studied in the temperature range 5–300 K and in fields of up to 5 T using SQUID magnetometry. Data on temperature and field dependence of magnetization provide a strong evidence for superparamagnetism. Paper presented at 8 AGM of MRSI, BARC, Mumbai, 1997.     

Preparation and characterization of TiO2 anode film with spinodal phase separation structure in dye-sensitized solar cells

Low electronic transmission efficiency and high charge recombination are the existing problems of photoanode film in traditional dye sensitized solar cells (DSSCs). This paper put forward the photoanode TiO₂ films with spinodal phase separation structure (SPSS) and continuous TiO₂ skeleton which were triggered by the photopolymerization of organic monomers in a photomonomer-inorganic precursor system. The photoanode TiO₂ films fabricated by different precursor solution compositions and different coating layers were characterized mainly by scanning electron microscopy (SEM), photocatalysis and photoelectric performance test. The results indicated that, the as-prepared TiO₂ anode film with seven coating layers and heat treated at 500 °C showed higher photoelectric conversion efficiency at about 2% than that of other samples with less coating layers and lower heat treatment temperature. The film also showed excellent photocatalytic activity by using methylene blue (MB) dye as a model organic substrate under fluorescent lamp irradiation. It is suggested that the film with SPSS structure has the potential to improve the electronic transmission efficiency and reduce the carrier recombination due to its particular structure, higher surface area, and lack of bottleneck in electronic transmission. It is worth noting that the SPSS structure provides new ideas to develop new photoanode films and further improve the photoelectric conversion performance of the DSSC in future.     

Mössbauer spectrometry study of early stage spinodal decomposition in Fe-Cr-Co alloy under high magnetic field

Local structure in a low-cobalt-type Fe-25Cr-12Co-1Si ferromagnetic alloy spinodal decomposed under an external magnetic field up to 120 kOe was investigated by Mössbauer spectrometry. The high magnetic field was found to significantly affect the local structure in the alloy formed at the early stage of phase decomposition. It was found that high magnetic field favors the acceleration of phase decomposition of ferromagnetic alloy at the early stage, resulting in the enhancement of average hyperfine field. The effect of high magnetic field on spinodal decomposition in ferromagnetic alloy was initially interpreted based on the free energy analyses.     

Kinetic process of phase separation in Co-SiO2 thin films and preparation of mesoporous SiO2 thin films with mesopore channels aligned perpendicularly to substrate surfaces

A physical co-sputter deposition process under a relevant working gas pressure condition was used to produce a multi-component thin film with a longitudinally self-organized microstructure. In this paper, Co-Si-O thin films were prepared by radio frequency (RF) magnetron sputtering, and their growth structures were studied by means of SEM, TEM, XRD and XPS. The microstructural changes in the Co-Si-O thin film and their dependence on Ar working gas pressure were investigated; the formation of Co-Si-O thin films, having a regular array of needle-like Co columns aligned perpendicularly to the substrate surfaces, was observed with appropriate Ar working gas pressure, and the diameter of the columns increased with increasing Ar pressure. Mesoporous silica thin films having perpendicular mesopore channels were obtained by chemical etching of the columnar Co parts in the Co-Si-O thin films. Through experimental observations, we propose that the phase separation and resultant microstructures in the thin films are determined by the surface mobility of the two components (Co and silica) on the film surface. A simple model, incorporating a diffusion process in the simultaneous deposition of two components, is presented. The model demonstrates the general trends of a kinetically self-organized microstructure in a two-component thin film.     

Advances in piezoelectric thin films for acoustic biosensors,acoustofluidics and lab-on-chip applications

Recently, piezoelectric thin films including zinc oxide (ZnO) and aluminium nitride (AlN) have found a broad range of lab-on-chip applications such as biosensing, particle/cell concentrating, sorting/patterning, pumping, mixing, nebulisation and jetting. Integrated acoustic wave sensing/microfluidic devices have been fabricated by depositing these piezoelectric films onto a number of substrates such as silicon, ceramics, diamond, quartz, glass, and more recently also polymer, metallic foils and bendable glass/silicon for making flexible devices. Such thin film acoustic wave devices have great potential for implementing integrated, disposable, or bendable/flexible lab-on-a-chip devices into various sensing and actuating applications. This paper discusses the recent development in engineering high performance piezoelectric thin films, and highlights the critical issues such as film deposition, MEMS processing techniques, control of deposition/processing parametres, film texture, doping, dispersion effects, film stress, multilayer design, electrode materials/designs and substrate selections. Finally, advances in using thin film devices for lab-on-chip applications are summarised and future development trends are identified.