Researchers at Japan's National Institute for Materials Science (NIMS) and Advanced Institute for Materials Research (AIMR) have achieved the first successful atomic-level observation of growing strontium titanate thin films.
Led by Assistant Professor Takeo Ohsawa of NIMS and Associate Professor Taro Hitosugi of Tohoku University's AIMR, a research team has developed a new advanced system, combining a super-resolution microscope and a deposition chamber for growing oxide thin films. With this system, they successfully observed for the first time the growing metal-oxide thin films at an atomic level on the surface of single-crystal strontium titanate (SrTiO3). Based on these observations, they identified the mechanism involved in the growth of the thin films in which titanium atoms rose to the surface of the film.
Metal oxides, including perovskite-type oxides such as SrTiO3, are commonly used due to their diverse properties, which include superconductivity, ferromagnetism, ferroelectricity and catalytic effect. In recent years, novel properties generated at the interface between two dissimilar oxides have been vigorously investigated. However, little is known about the mechanism involved in the formation of such interfaces. Understanding this mechanism is key to further research advances in this field.
The NIMS/AIMR research group developed an innovative system that combines a scanning tunneling microscope capable of identifying individual atoms with a pulsed laser deposition method that enables the growth of high-quality thin films. In addition, they also established a method for preparing a single-crystal SrTiO3 substrate on which atoms are arranged in a periodic pattern. Epitaxial thin films were grown on the surface of the substrates and the growth was observed with atomic-scale spatial resolution. In their observations, they found there was a great difference in the growth process when SrTiO3 and SrOx thin films were deposited on the surface of the substrates.
Furthermore, the team identified a phenomenon in which excess titanium atoms present on the surface of the SrTiO3 substrate rose to the surface of the thin film. These observations facilitated a clear atomic-scale understanding of the growth process regarding how oxide thin films are formed. These results may not only contribute to the understanding of the origin of interfacial properties but also lead to the creation of new electronics devices through the development of new functional materials.
This research was carried out as part of the Japan Science and Technology Agency's Strategic Basic Research Programs. The research will be published in the U.S.-based scientific journal ACS Nano in the near future.
- Ryota Shimizu, Katsuya Iwaya, Takeo Ohsawa, Susumu Shiraki, Tetsuya Hasegawa, Tomihiro Hashizume, Taro Hitosugi. Atomic-Scale Visualization of Initial Growth of Homoepitaxial SrTiO3 Thin Film on an Atomically Ordered Substrate. ACS Nano, 2011; 5 (10): 7967 DOI: 10.1021/nn202477n
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