TAKAMURA (Yukiko) Laboratory
<Major Research Areas>thin film growth, surface interface engineering

Development of nanomaterials based on the understanding of surface and interface

Research activity

　　Modern industry is founded on thin film materials technologies, ranging from protective coatings to electronic devices, and in order to improve their performance, controlling film-substrate interfaces would be critical. The surfaces and interfaces become even more important in the growth of nanomaterials and their properties, since the bulk part is reduced and the surfaces and interfaces become dominant. Our aim is to develop new nanomaterials based on the understanding of surfaces and interfaces.
　　Ordered interfaces formed between very different materials such as semimetal and semiconductor, normal conductor and superconductor, organic and inorganic, are very attractive, but sometimes very difficult to realize. We should understand the growth process together with the interface structures, and effectively control the film growth process to achieve the goal.

　　In order to understand the growth process, we have an ultra-high vacuum film growth system with a capability of monitoring the film growth in-situ using light and/or electron as a probe. By combining the results of the in-situ monitoring of the film growth process and the ex-situ analysis of the interface, we would like to understand and control the surface and the interface, and develop new materials.

　　One of the main research projects in our group is the hetero-epitaxial growth of zirconium diboride (ZrB2), which has a very good lattice matching to a wide-gap semiconductor, hexagonal gallium nitride (GaN). ZrB2 is a promising buffer layer for GaN growth when it is grown on a low cost, large diameter substrate such as Si wafers, and it is also a promising heat-resistant electrode material for high power device when it is grown on wide band gap semiconductors such as GaN. Semiconductor-semimetal superlattice of GaN and ZrB2 would also be an interesting material, if alternating epitaxial growth were to be realized.

　　Another hot research topic in our group is the study of Si-version graphene, “silicene”, which is an ultimate nanomaterial with single-atom thickness. We found this new two-dimensional material while trying to understand the surface structure of diboride thin films grown on Si wafers. “Silicene” is a fruit of successful collaboration with the photoelectron spectroscopy group and the first-principles calculation group in JAIST. Our findings attracted lots of interests among scientists and general public, and now the collaboration is expanding to universities and institutions in Japan and overseas.

　　We will not limit our research to the above studies. There are numerous surface and interface problems waiting to be solved. We would like to help you find, understand, and solve these interesting and challenging problems.

Equipment

Ultra-high vacuum thin film growth system, ultra-high vacuum scanning probe microscopy, transmission electron microscopy, thin film X-ray diffraction

The main research achievements in the past five years

1. A. Fleurence and Y. Yamada-Takamura, Scanning tunneling microscopy investigations of the epitaxial growth of ZrB₂ on Si (111), Phys. Status Solidi (c) 8 (2011), in press. (To be featured on the front cover of March issue).
2. Y. Yamada-Takamura, F. Bussolotti, A. Fleurence, S. Bera, and R. Friedlein, Surface electronic structure of ZrB₂ buffer layers for GaN growth on Si wafers, Appl. Phys. Lett. 97, 073109 (2010). (Selected for the August 30, 2010 issue of Virtual Journal of Nanoscale Science and Technology)
3. S. Bera, Y. Sumiyoshi, and Y. Yamada-Takamura, Growth of single-crystalline zirconium diboride thin film on sapphire, J. Appl. Phys. 106, 063531 (2009).
4. “Scientists study graphene sibling: Single-layer‘ silicene’ sheets might have electronic uses”, Science News, 179, p. 14 (2011).
5. “Silicon’s Next Wave”, Discover, Jan-Feb, p. 82 (2011). Selected as one of the Top 100 stories of 2011