MIZUTANI Laboratory
<Major Research Areas>Properties of surfaces and interfaces, optical properties of solids, microscopy

Active Solid Surfaces and
Functional Interfaces Investigated
by Nonlinear Optical Effects

Research activity

　　If two incident photons coalesce into one photon with the sum frequency in a material, they cause a nonlinear optical effect. Through this optical process, we aim to observe, explain and utilize the characteristic phenomena on solid surfaces and interfaces. We are involved in determining the surface characteristics of active substances, and the nonlinear optical effects in nano-scale structures, as well as in searching for new related physical and natural phenomena. The research themes that have recently been of interest to our group are outlined below.

1Elucidation of surface phenomena through optical second harmonic (SH) spectroscopy

　　We develop optical SH spectroscopy techniques and use them as tools to monitor changes in surface electronic levels during the occurrence of important surface phenomena. We also establish precise methods of analyzing the electronic structure, as well as the orientation and order of the surface bonds of photo-catalyst TiO2 surfaces, surface adsorption systems, and semiconductor surfaces, using phenomenological calculation and ab-initio calculation.

2Research of surface adsorbates through vibrational spectroscopy using Raman scattering and sum frequency generation (SFG)

　　We investigate the microscopic mechanisms involved in phenomena on solid surfaces by analyzing the vibration of molecules. This analysis is done by means of vibrational spectroscopy, using a highly-sensitive Raman scattering spectrometer and a sum frequency generation system. We are interested in clarifying the adsorption states and reaction processes of adsorbate molecules on the surfaces of solids and catalysts, as well as the order of water molecules in the vicinity of bio-materials.

3Research on new properties of solids observed only on surfaces

　　The molecules, films and nano-structures on surfaces are expected to show properties that are dramatically different from those of bulk materials. We investigate the origin of this difference using metallic nanowires as an example, and develop new functional materials that take advantage of the surface-specific properties.

4Development and application of optical second harmonic microscopes and sum frequency microscopes

　　 We develop optical second harmonic microscopes and optical sum frequency microscopes to observe surface systems. The microscopes are designed to have high temporal and spatial resolutions for the observation of samples in an ultra-high vacuum state, and the excitation light wavelength can be tuned as necessary. We aim to discover interesting new physical phenomena by observing the nonlinear optical images of catalysts, semiconductors and living organisms.

　　Prof. Mizutani has a dream of being able to have adventures in his research world. He is searching for a way of raising the motivation of his group with regard to research by joining the JAIST-COE program, “Science emergence practice supported by research philosophies”.

Equipment

Surface SH/SF spectroscopy system, surface SH/SF microscopy system, visible IR OPO/OPG/OPA (Q switch/ mode locked Nd: YAG laser excitation), fs-OPA, high-sensitivity surface Raman spectroscopy system, surface preparation and analysis chamber, nanowire preparation chamber, XPS

The main research achievements in the past five years

1. A. B. El Basaty, Y. Miyauchi, G. Mizutani, T. Matsushima, and H. Murata, Optical second harmonic generation at heterojunction interfaces of a molybdenum trioxide layer and an organic layer, Applied Physics Letters 97, 193302 (2010).
2. Y. Miyauchi, H. Sano, J. Okada, H. Yamashita, and G. Mizutani, Simultaneous optical second harmonic and sum frequency intensity image observation of hydrogen deficiency on a H-Si(1 1 1) 1×1 surface after IR light pulse irradiation, Surf. Sci., 603(19), 2972 (2009).
3. Y. Maeda, T. Iwai, Y. Satake, K. Fujii, S. Miyatake, D. Miyazaki and G. Mizutani, Optical second-harmonic spectroscopy of Au(887) and Au(443) surfaces, Phys. Rev. B, 78(7), 075440 (2008).
4. H. Sano, J. Saito, J. Ikeda, and G. Mizutani, Electronic resonant images of an ion implanted Si(111) substrate observed by wavelength tunable optical second harmonic microscopy, J. Appl. Phys., 100(4), 043710 (2006).
5. Y. Miyauchi, H. Sano, and G. Mizutani, Selective observation of starch in a water plant by nonlinear optical microscopy, J. Opt. Soc. Am. A, 23(7), 1687-90 (2006).