We demonstrate our latest results on quantum transport in curved nanostructures. From a theoretical perspective, electrons whose motions are constrained to a thin curved layer (or thin twisted wire) experience an effective potential field that stems from geometric curvature (or torsion). This suggests a significant deviation of transport properties from planar systems, whereas quantifications of the effects in real nanomaterials are remained to be explored. Among many interesting geometry, we devote our attention to: i) deformed nanocylinders, ii) corrugated nanolayers, and iii) twisted quantum rings, to unveil a curvature-induced shift in the Tomonaga-Luttinger exponent, a corrugation-induced resistivity enhancement, and a torsion-induced quantum phase shift. All of these phenomena are attributed to the effective potential fields arising from geometric curvature and torsion inherent to the systems.
When a C60 film is irradiated with a 3 kV electron-beam (EB) gun in vacuum (base pressure: 10−7 Pa), we have found that EB-irradiation of a C60 film gives rise to formation of a peanut-shaped C60 polymer with metallic electron-transport properties in air at room temperature. The peanut-shaped polymer has both positive and negative Gaussian curvatures (K), which can be classified into a new π-electron conjugated carbon allotrope that is different from graphite (K = 0), fullerenes (K > 0), nanotubes (K = 0 at body, K > 0 at cap edge), and hypothetical Mackay crystal (K < 0). In the present review article, we will introduce our recent results of the electron-transport, electronic, and optical properties of the nanocarbon, and describe theoretical analysis of its novel electronic properties on the basis of quantum mechanics on Riemannian surfaces. To our best knowledge, the peanut-shaped C60 polymer is only an existed material with a negative Gaussian curvature, whose electronic and optical properties are known experimentally. Thus we believe that the present system will open a new science “quantum science of condensed matters in Riemannian space”.
Photo- or electron beam (EB) irradiation of C60 results in various cross-linkages with various dimensionalities. One characteristic example of such coalesced structures is the one-dimensional (1D) peanut-shaped C60 polymer reviewed by J.O. in another article. This EB-irradiated C60 polymer exhibits a Fermi-edge anomaly in the valence band spectrum, showing a similarity to those observed in quasi-1D conductors. In this article, we demonstrate the photo-induced carrier dynamics of EB-irradiated C60 polymer by utilizing an ultrafast optical spectroscopy. We first present an overview of the carrier dynamics in typical quasi-1D conductors, and then compare the properties with those of the EB-irradiated C60 polymer. We also compare the carrier dynamics in the C60 polymer and pristine samples, and show that the polymer sample exhibits an additional slow relaxation component below T∼60K. This component is similar to the interband relaxation observed in quasi-1D conductors below Peierls transition temperature, whereas the temperature dependence of the relaxation time exhibits no critical divergence that accounts for coherent gap formation. We will discuss the plausible origin.
In the ongoing global warming it is required for the world to develop the new energy systems for adapting or mitigating the impacts of climate change and sustaining our prosperous society. Innovation of material science would be a crucial path for realizing the new energy systems. For innovation, large-scale simulation becomes a hopeful way for finding novel materials, analyzing their properties and designing new functions. In this paper, we briefly introduce our simulation research on Mackay crystal of carbon. The simulations show unique aspects of synthesis process of the crystal, mechanical and electronic properties, as well as applicability for solar cell.
Waste fibers are produced by textile industry and colored wastewater is released, the people hope to development the useful reused methods of it. And the release of colored wastewater induced aesthetically unpleasant, produced the carcinogen from chlorination. In this study, we produced the carbonaceous materials produced from waste fibers, developed the amount adsorbed and the adsorption rate of dyes. As a results, the specific surface area of waste fibers is increasing with increasing the carbonized temperatures. Amount adsorbed of each dyes onto carbonaceous materials produced from waste fibers at 1000oC is highest. In waste fibers, amount adsorbed of each dyes onto 2 h heating-2 h maintaining carbonaceous materials produced from waste fibers is increasing colored wool < untreated wool < colored wool-polyester < polyester, it showed the waste fiber from polyester is more suitable for adsorption than that of wool. Carbonaceous materials produced from waste fibers at 1000oC could treat to adsorbed the Methylene blue and Orange II in 20 min from the adsorption beginning. The carbonaceous materials produced from waste fiber would be utilized for adsorbates to remove dyes.
The microwave power dependence of the inverse spin-Hall effect (ISHE) induced by the spin pumping has been investigated for Ni81Fe19/Au films with changing the thickness of the Au layer. The spin pumping driven by magnetization precession injects spin currents into the Au layer, which gives rise to an electric potential difference between the edges of the Au layer via ISHE. The ISHE signal increases linearly with the microwave power for the Ni81Fe19 (20 nm)/Au (5 nm) film, which is consistent with the prediction of the conventional direct-current spin pumping model. By increasing the thickness of the Au layer, the variation of the ISHE signal changes critically. This unconventional variation indicates the coexistence of the linear and the nonlinear components in the spin-pumping induced ISHE.
Changes of surface structure for the initial stage of oxidation in the Langmuir type adsorption range on Si(100)-(2×1) surfaces were observed using a scanning tunneling microscope (STM). On the Si(100)-(2×1) surfaces exposed to oxygen (O2) at room temperature, bright spots located on the center of a dimer row and dark sites appeared, and increased in number with increasing of O2 exposure. It is considered that the bright spots correspond to the isolated Si dimer emitted by the oxidation-induced strain at SiO2/Si interface. At 380oC, O2 exposure induced the formation of one-dimensional Si islands and an SB step flow growth due to the surface diffusion of the emitted Si atoms. These STM observation results clarify that the SB step flow growth causes the decrease of 1×2/2×1 domain ratio and the behavior of emitted Si atoms support the unified Si oxidation reaction model proposed by Takakuwa.