We have employed two-photon photoemission (2PPE) spectroscopy to investigate the dynamics of photo-excited electron on alkanethiolate self-assembled monolayers (SAMs) formed on Au(111) surface. The photo-excited electron in image potential states on standing-up structure of SAM is detected with its two-dimensional freeelectron- like nature. The lifetime of the excited electron elongates with the alkyl chain length ranging from sub- to 100 ps, showing that the standing-up structure of SAM works as a well-designable insulating organic monolayer. The change in the lifetime with the insulator thickness is dramatic at < 10 Å, whereas it becomes milder at > 10 Å. The result suggests that dominant electron decay pass switches at ~10 Å; (1) coupling with the electronic state locating at gold-sulfur linkage (< 10 Å), and (2) simple tunneling decay process (> 10 Å). Furthermore, from the photon energy dependence of 2PPE measurement, it is realized that the interfacial resonance formed in the alkyl layer plays a role of efficient electron excitation pass to the surface.
Thiolate (SR)-protected gold clusters (Aun(SR)m) have attracted much attention as building blocks of functional nanomaterials. Our group has been studying the high-resolution separation of Aun(SR)m clusters using reversedphase high-performance liquid chromatography. In this article, we summarize our recent results on the separation of Aun(SR)m clusters and their doped clusters according to the core size, charge state, ligand composition, and coordination isomer. Additionally, this article describes new findings obtained by using such high-resolution separations. We believe that the techniques and knowledge gained in these studies would contribute to the creation of Aun(SR)m clusters with the desired functions and associated functional nanomaterials.
Ionic crystals are normally non-porous because of the isotropic and long-range Coulomb interactions. However, the use of molecular ions with appropriate elements, charges, sizes, shapes, or ligands enables the formation of pores. Polyoxometalates (POMs) are nano-sized metal-oxide macroanions, and have stimulated research in broad fields of science. Since POMs bear negative charges, they are potentially useful as building blocks of porous crystals in combination with appropriate macrocations. Recent studies on the design and syntheses of functional ionic crystals, and their selective gas adsorption, catalysis, and ion-exchange and diffusion properties will be described.
Metal-Organic Frameworks (MOFs) composed of transition metal ions and bridging organic ligands have been extensively studied. The characteristics of MOFs are highly regular channel structures, controllable channel sizes approximating molecular dimensions, designable surface potentials and functionality, and flexible frameworks responsive to guest molecules. Owing to these advantages, successful applications of MOFs range from molecular storage/separation to heterogeneous catalysts. In particular, use of their regulated and tunable nanochannels for a field of polymerization allows multi-level controls of polymerization. This account focuses on recent progress in polymerization using the nanochannels of MOFs, and demonstrates that this methodology for polymer synthesis is a promising strategy for the controlling polymer primary structures, creation of precision polymer assembly, and the design of well-defined nanohybrid materials.
Electrostatic interactions in nano space play an important role in materials properties. Here I describe how electrostatic interactions are extracted based on X-ray diffraction data and how its method works in some functional materials such manganites and cyanides. Taking account of local structural information, the method will become a robust tool for nano materials science.
Astronomical observations have revealed the presence of organic molecules in the early stage of planetary formation. It is a prevalent hypothesis that mineral particles work as catalysts to form the organic molecules from CO, H2, H2O, N2 and other interstellar gases. The surface of mineral particles irradiated by intense cosmic ray in the interstellar environment produces free radicals consisting of Si, Al, O, Mg, and Fe. To study chemical processes in such an environment, size-selected gas-phase clusters provide good models of free radicals with mineral compositions. In this regard, we are working on formation and reaction of clusters with mineral composition. In this review, we describe formation of hydrated alumina clusters through reactions of aluminum cluster cations, AlN + (N = 1−14), with a mixture of H2O and O2. Furthermore, we present reactions of size-selected free silicon oxide cluster anions, SinOm − (n = 3−7, 2n − 1 ≤ m ≤ 2n + 2) with a CO gas. Adsorption of CO on SinOm − is observed as a major reaction channel, and experimental and theoretical results suggest that a pair of dangling O atoms appearing in SinOm − with m = 2n + 1 is the reaction site. The present findings give molecular-level insights into adsorption of CO molecules on silicates in the interstellar environment.