We investigated the effects of surface treatments by aqua regia and (NH 4 ) 2 S x on the electrical and the microstructural changes of Pd contact on p-type GaN during annealing. The formation of a surface oxide was suppressed by the (NH 4 ) 2 S x treatment, and S-Ga and S-N bonds with binding energy of 162.1 eV and 163.6 eV were formed, degrading the structural ordering of Pd. After 300°C annealing, the contact resistivity in the aqua regia-treated sample increased significantly. This could be attributed to the outdiffusion of N atoms leaving N vacancies below the contact, as confirmed by the increase of the Pd (111) plane spacing probably due to the dissolution of N atoms in Pd interstitial sites. Meanwhile, the contact resistivity in the (NH 4 ) 2 S x -treated sample was not degraded and no change was observed in the Pd (111) plane spacing. These results suggest that S-Ga and S-N bonds formed on (NH 4 ) 2 S x -treated GaN could act as a diffusion barrier for the outdiffusion of N atoms. The contact resistivity for the aqua regia-treated sample decreased again, probably due to the outdiffusion of Ga as well as N atoms at 500°C.

We have studied the low-temperature crystallization of (Ba·Pb) hexa-ferrite thin films using real time synchrotron X-ray scattering, anomalous X-ray scattering, and vibrating sample magnetometer. The crystallization temperature of amorphous (Ba·Pb) hexa-ferrite film (300-Å-thick, ∼530 • C) was much lower than that of amorphous Ba hexa-ferrite film, ∼750 • C. The crystalline (Ba·Pb) hexaferrite phase was formed by solid phase transformation of the interfacial crystalline Fe 3 O 4 phase through the diffusion of Ba or Pb cations. The low crystallization temperature of the (Ba·Pb) hexa-ferrite phase was due to the lower diffusion activation barrier of Pb cations than that of Ba cations. The small grain size (∼40 nm in diamter) and comparable magnetic properties (Ms ⊥ : 337 emu/cm 3 , iHc ⊥ : 1.60 kOe) of the crystallized (Ba·Pb) hexa-ferrite film also demonstrate its potential possibility for high-density recording media.

We have studied the inhibition of abnormal acicular grain growth of the Ba–ferrite phase in the crystallization of Ba–ferrite films using real time synchrotron x-ray scattering, field emission scanning electron microscope, and vibrating sample magnetometer. Amorphous Ba–ferrite film on a SiO2 substrate is naturally crystallized into the abnormal acicular Ba–ferrite grains (major axis of ∼1000 nm in the in-plane direction). However, on α-Al2O3 substrate, fine grain sizes of the primary Ba–ferrite phase (∼70 nm) are obtained during crystallization. Nucleation of the α-Fe2O3 phase on the α-Al2O3 surface at an early stage induces the inhibition of the abnormal acicular grain growth of the Ba–ferrite phase. Because of the grain size refinement of the magnetic Ba–ferrite phase, the intrinsic coercivity of Ba–ferrite/α-Al2O3 film enhances 4.4 kOe, much larger than that of Ba–ferrite/SiO2 film (1.9 kOe). We suggest that the secondary α-Fe2O3 phase act as a useful inhibitor to abnormal grain growth in Ba–ferrite films for high-density recording media.

We found the correlation between microstructure and surface evolution in the crystallization of amorphous α-Fe2O3/α-Al2O3(0001) thin films using real-time synchrotron x-ray scattering and atomic force microscope. The amorphous precursor is crystallized to the epitaxial α-Fe2O3 grains in three steps; i) the growth of the well aligned α-Fe2O3 interfacial islands on α-Al2O3(0001), ii) the growth of the misaligned, homoepitaxial, α-Fe2O3 grains on the well aligned grains ( > 400 °C), and iii) the nucleation of the heteroepitaxial misaligned grains directly on the α-Al2O3substrate ( > 600 °C). The surface roughing is caused by the microstructure evolution during the crystallization of the amorphous precursor films.