Abstract
This thesis work presents the development of the nano-scale textures of Pd films and coercivity enhancement of Fe/Pd multilayer thin films for hydrogen gas sensing and perpendicular magnetic recording, respectively. Firstly, the simple preparation of the self-assembled network of palladium islands on MgO(001) substrate and the exploration of the gap closing mechanism in these nanostructured hydrogen sensors are reported. Pd films of 100 nm in thickness, deposited at 550 ˚C using the DC magnetron sputtering technique, possess the (002) preferred orientation that it still retains while doping with rare-earth metals such as Gd or Tb. However, the grain size and surface morphology of the Pd films change markedly with the addition of dopants, offering a route for tailoring the film toward higher sensitivity and scalable responses to changes in H2 concentrations. All the sensors show the decreased resistance in the presence of H2, the behavior attributed to the physical gap closing mechanism. Sensing performances of the samples are also compared. Secondly, the research focus was also on the attainment of perpendicular coercivity higher than 900 Oe in an FePd alloy thin film for realization of the perpendicular magnetic recording media. The off-stoichiometric FePd films were prepared through the multilayer growth of [Fe(2 nm)/Pd(2 nm)]×30 on MgO(001) substrates by magnetron sputtering, followed by the post-annealing at 700 ˚C for 1 h and 10 h. The results show that, with increasing annealing time, the FePd thin films are predominantly (001)-oriented with progressive increase of the grain size and surface roughness, as well as the improved crystallinity and reduced micro-strain. Accordingly, the perpendicular coercivity is significantly increased to the value of 1.5 kOe, and Pd loses its 4d electrons upon alloying. Furthermore, analysis of X-ray absorption data elucidates some structural details of the Fe scattering phase in addition to the dominant tetragonal FePd phase. Additionally, the thesis also presents a way of determining the long-range order parameter for the FePd alloy thin film, using combined information of tetragonality ratio extracted from extended x-ray absorption fine-structure spectroscopy and the stoichiometric deviation of the thin film.