报告题目：Nanocrystals and Small Clusters Investigated by Synchrotron Radiation and Microfluidics

报 告 人：Hiroyuki Oyanagi教授（Professor, Electronics and Photonics Research Institute, AIST, 1-1-1 Umezono, Tsukuba 305-8568, Japan）

报告时间：2013年7月25日（星期四）上午09:30

报告地点：张江园区综合办公楼101会议室

报告内容简介：

Recently, small clusters (SCs) formed by N atoms where N<50 attract keen attention, associated with recent demands on understanding microscopic mechanisms of initial growth (nucleation) of nanocrystals (NC’s) and state of “monomers”. Combining synchrotron radiation and x-ray absorption spectroscopy (XAS) with microfluidics allows us to study the initial process within a limited volume (v0<1 mm3) in-situ. Microfluidic cell1 is a microchannel device along which a chemical reaction occurs in a lamilar flow.2 For investigating time-dependent structures of NCs, “monomers” or SCs, a high-sensitivity is needed which is realized by high brilliance x-ray beam available from insertion devices at the 3rd generation facilities (ca. 1012 photons per sec) and modern x-ray detectors. Here, we describe in-situ XAS studies using microfluidics to illustrate the capability described above, demonstrated by a couple of applications, i.e., i) the structural and kinetics studies during the initial stage of CdSe NCs3 and ii) copper SCs (N=13-19) photo-induced by intense x-ray beam.

Colloidal semiconductor NCs, sometimes called quantum dots, became popular due to their size-tunable optical properties and a variety of industrial applications. We demonstrated that time-dependent EXAS (conventionally used as an average local probe) is informative on higher order structures, i.e., NC size and density if bond formation kinetics is analyzed.4 The second application is copper SCs formed by a reducing reaction in organic solvent under photo-irradiation. The local structure of SCs prepared in organic solution by reducing Cu(II) hexafluoroacetylacetonate [Cu(hfac)2] was studied as-grown by XANES and EXAFS. The Cu K-XANES spectra indicated the formation of copper SCs by ligand-exchange with oleylamine and a subsequent reducing by diphenylsilane. The multiple-scattering (MS) XANES calculation for various model clusters suggests that the SCs consist of 13-19 atoms, stabilized by ligand molecules in organic solution. Models with various symmetry structures and relaxations due to ligation were evaluated by DFT calculations and comparison with experiments, which revealed the inhomogeneous nature of intra- and inter-cluster electron density distribution that may characterize the unique properties of SCs.

报告人简介：

Hiroyuki Oyanagi 教授1980年毕业于东京大学物理系固体分光专业，获理学博士学位。1980年进入日本电子技术综合研究所工作。1992年起任该所基础物质研究室研究长。1992年《x射线吸收光谱研究》获日本科学技术厅长官奖。2000年4月起任日本京都大学教授。现为日本国立产业技术综合研究所主任研究员，国际x射线吸收学会主席，兼任中国科技大学国家同步辐射实验室客座教授，外专专家。Oyanagi教授在x射线吸收精细结构方面的研究共发表学术论文200余篇，论文被他引6000余次。