Please cite this article as: N. Hatsuta, D. Takemori, M. Takashiri, Effect of thermal annealing on the structural and thermoelectric properties of electrodeposited antimony telluride thin films, Journal of Alloys and Compounds (2016), ABSTRACTWe investigated the effect of thermal annealing on structural and thermoelectric properties of p-type antimony telluride (Sb 2 Te 3 ) thin films fabricated on a stainless steel (SUS304) substrate by electrodeposition. Antimony telluride thin films were annealed for 1 h at temperatures between 200 and 400°C. We observed that the as-deposited thin film and thin films annealed at temperatures less than 250°C possessed a stoichiometric atomic composition (Sb:Te = 40:60) with no impurities from the substrate. At the annealing temperature of 300°C, we observed a certain amount of impurities (Fe, Cr, Ni) in the thin film. The Seebeck coefficient was decreased but the electrical conductivity was increased for films treated at 300°C. As a result, the thin film exhibited a maximum power factor of 13.6 µW/(cm·K 2 ). On further increasing the annealing temperature to 400°C, the film structure and thermoelectric properties were drastically changed. The impurity concentration in the thin film reached approximately 50 at%. The crystal structure of Sb 2 Te 3 completely disappeared, and instead, other chemical compounds formed by alloying the elements of the thin film and the substrate were observed.

We investigated the effects of thermal annealing and homogeneous electron beam (EB) irradiation on the structural and thermoelectric properties of electrodeposited bismuth telluride (Bi2Te3) thin films. Bi2Te3 thin films were prepared by potentiostatic electrodeposition using a standard three-electrode cell. It was found that the thermal annealing contributed to enhance the crystallographic properties, leading to the increase of the thermoelectric properties. The maximum thermoelectric property (power factor) was 6.0 μW/(cm∙K2) by the thermal annealing. In addition, the Bi2Te3 thin films obtained relatively high (1 1 0) crystal orientation. On the other hand, the homogeneous EB irradiation treatment did not contribute to increase the crystallographic properties, so the thermoelectric properties of the EB irradiated thin films were mostly the same as that of the as-deposited thin films.

Effects of current pulse frequency and duty ratio [off-time/(on-time + off-time)] on thermoelectric properties of bismuth telluride (Bi2Te3) thin films were investigated. The crystal structure of the Bi2Te3 thin films was strongly affected by the duty ratio rather than the current pulse frequency. In particular, the Bi2Te3 thin films were highly oriented along (1 1 0) direction with smooth surface at the high current pulse frequency (5000 Hz) and the high duty ratio (80%). Overall, the electrical conductivities of the Bi2Te3 thin films with current pulse frequency of 5000 Hz were larger than that the thin films with 1000 Hz, whereas the Seebeck coefficients were mostly the same between the both frequencies. As a result, the highest power factor (1.1 μW/(cm·K2)) was observed at the Bi2Te3 thin films with a current pulse frequency of 5000 Hz and a duty ratio of 60%.

Purpose:Implantation of carmustine wafers (Gliadel) in vivo is accompanied by characteristic serial changes on MRI and CT, such as transient hyperintensity of the wafers on T1-weighted images (T1WIs) and considerable gas accumulation in surgical resection cavities. The purpose of this study was to evaluate intrinsic imaging changes to carmustine wafers in vitro.Methods:Three phantoms simulating a surgical resection cavity were constructed. Each contained either a carmustine wafer fixed with oxidized regenerated cellulose and fibrin sealant, an unfixed carmustine wafer, or a fixed polyethylene control disk, immersed in phosphate-buffered saline. Image acquisition of the phantoms was performed on MRI and CT until 182 days after construction. The radiological appearances of the object in each phantom were assessed by visual evaluation and quantification of the region of interest. The volume of gas around the objects at 24 h after constructing the phantoms was also measured.Results:The carmustine wafers showed low signal intensities on T1WIs and T2-weighted images (T2WIs), and high densities on CT images at 24 h. The signal intensities and CT densities gradually approximated those of saline over a period of months. However, the carmustine wafers never showed hyperintensity on T1WIs in vitro. The fixed carmustine wafer showed slower radiological changes, as compared to the unfixed wafer. The gas volume around the fixed carmustine wafer was greater than that around the fixed control disk.Conclusion:Changes to the carmustine wafers probably reflected penetration of fluid inside and degradation of the hydrophobic matrix. Reported transient hyperintensity of wafers on T1WIs in vivo is regarded as the result of biological reactions, whereas the initial production of gas is considered as an intrinsic characteristic of wafers.

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