Kota Terai

In-plane lattice constant tuning of an oxide substrate with Ba1−xSrxTiO3 and BaTiO3 buffer layers

Oxide thin films are usually grown on substrates which offer the smallest mismatch with the desired structure of the film. The choice of high-quality substrates with suitable lattice constants is unfortunately very limited. Coherently grown films are therefore always under tensile or compressive in-plane strain. We report on the growth of a Ba1−xSrxTiO3/BaTiO3 bilayer buffer on a SrTiO3 substrate. Changing the Sr/Ba ratio in the Ba1−xSrxTiO3 layer can be used to select a desired in-plane lattice constant in the 3.9 to 4.0 A range. The thinner BaTiO3 film serves as a compliant layer while the thicker Ba1−xSrxTiO3 film determines the final surface lattice constant. This is achieved by a combination of low-temperature deposition and annealing at 1350 °C. X-ray diffraction and high-resolution transmission electron microscopy were used to show that the final buffer layer surface is fully relaxed, cubic, and essentially defect free, while all lattice mismatch between the substrate and the buffer is relieved by ...

Magnetic Properties of Strain-Controlled SrRuO3 Thin Films

Coherently-grown heteroepitaxial oxide thin films on single crystal substrates are always under elastic strain. This strain causes changes in the physical properties of thin films. We have studied the behavior of anisotropic magnetic properties of SrRuO3 films grown directly on SrTiO3 and on Ba1-xSrxTiO3/BaTiO3 bilayer buffer layers. The in-plane lattice constant of the buffer layer was adjusted between 3.91 and 3.99 A by changing the Ba/Sr ratio in the Ba1-xSrxTiO3 layer. It was found that the easy axis of magnetization is perpendicular to the surface in compressively strained films and rotates into the in-plane direction in strain-free films. Tensile strain was found to increase the ferromagnetic ordering temperature of SrRuO3 from 160 K to 164 K.

High-Mobility Organic Thin-Film Transistors Over 10 cm2 V-1 s-1 Fabricated Using Bis(benzothieno)naphthalene Polycrystalline Films

We have synthesized novel thieno-fused compounds, bis(benzothieno)naphthalenes (BBTNs), and studied their thin-film transistors characteristics and thin-film properties. It was found that BBTN derivatives showed high mobilities (up to 15.6 cm2 V-1 s-1). In order to elucidate the origin of high mobilities of BBTNs, X-ray single-crystal structure analysis, XRD measurements, and thermal measurements were carried out. The results suggest that both the herringbone crystal packing and strong CH–π interaction between the thieno-fused cores are the important factors for high mobilities.