Efficient Hydrogen Isotope Separation by Tunneling Effect Using Graphene-Based Heterogeneous Electrocatalysts in Electrochemical Hydrogen Isotope Pumping.

The fabrication of a hydrogen isotope enrichment system is essential for the development of industrial, medical, life science, and nuclear fusion fields, and therefore, efficient enrichment techniques with a high separation factor and economic feasibility are still being explored. Herein, we report a hydrogen/deuterium (H/D) separation ability with polymer electrolyte membrane electrochemical hydrogen pumping (PEM-ECHP) using a heterogeneous electrode consisting of palladium and graphene layers (PdGr). By mass spectroscopic analysis, we demonstrate significant bias voltage dependence of the H/D separation factor with a maximum of ∼25 at 0.15 V and room temperature, which is superior to those of conventional separation methods. Theoretical analysis demonstrated that the observed high H/D factor stems from tunneling of hydrogen isotopes through atomically thick graphene during the electrochemical reaction and that the bias dependence of H/D results from a transition from the quantum tunneling regime to the classical overbarrier regime for hydrogen isotopes transfer through the graphene. These findings will help us understand the origin of the isotope separation ability of graphene discussed so far and contribute to developing an economical hydrogen isotope enrichment system using two-dimensional materials.

Controlled growth of boron-doped epitaxial graphene by thermal decomposition of a B4C thin film.

We show that boron-doped epitaxial graphene can be successfully grown by thermal decomposition of a boron carbide thin film, which can also be epitaxially grown on a silicon carbide substrate. The interfaces of B4C on SiC and graphene on B4C had a fixed orientation relation, having a local stable structure with no dangling bonds. The first carbon layer on B4C acts as a buffer layer, and the overlaying carbon layers are graphene. Graphene on B4C was highly boron doped, and the hole concentration could be controlled over a wide range of 2 × 1013 to 2 × 1015 cm-2. Highly boron-doped graphene exhibited a spin-glass behavior, which suggests the presence of local antiferromagnetic ordering in the spin-frustration system. Thermal decomposition of carbides holds the promise of being a technique to obtain a new class of wafer-scale functional epitaxial graphene for various applications.

Surface Morphology Analysis of Zirconium Dioxide Nanoparticles at 1200 K by Transmission Electron Microscopy.

Zirconium dioxide (ZrO2) nanoparticles were heated at 1200 K in a transmission electron microscope, and their surfaces were observed in situ via lattice imaging. The nanoparticles exhibited well-defined crystal habits while fluctuating the surface terrace structures. The stable surfaces and ridges were inferred from the fluctuation of the terraces, leading to the construction of the three-dimensional surface structures at 1200 K. By contrast, after the specimen cooled to room temperature, the surface fluctuation of the nanoparticles stopped and the crystal habit disappeared, implying that the crystal habit was maintained because of atomic diffusion during the surface fluctuation.

Development of 2000 K Class High Temperature In Situ Transmission Electron Microscopy of Nanostructured Materials via Resistive Heating.

We report the development of a new type of a 2000 K class high temperature stage for transmission electron microscopy (TEM) of various shaped nanostructured materials, i.e., nanometer-sized isolated nanostructures, such as particles, fibers, and thin films, and nanocrystalline bulk materials. The maximum temperature of the heating stage was 300­700 K higher than that of prevailing heating stages. In addition, we found that since the structure of the developed heating stage is simple, the stage can be applied to most of transmission electron microscopes without any additional modification. The stability of the heating stage was confirmed by In Situ high-resolution observation of the lattice fringes of the zirconium dioxide nanoparticles heated at 1183 K. We observed In Situ the nanoscale structural variation of titanium plate surfaces around 900 K and the melting of nanocrystalline iron thin films around 1808 K by this method. It was demonstrated that the heating stage is useful for the analysis of high temperature structural dynamics of various shaped nanostructured materials.

Radiation-mode optical microscopy on the growth of graphene.

Chemical vapour deposition (CVD) growth of graphene has attracted much attention, aiming at the mass production of large-area and high-quality specimens. To optimize the growth condition, CVD grown graphene is conventionally characterized after synthesis. Real-time observation during graphene growth enables us to understand the growth mechanism and control the growth more easily. Here we report the optical microscope observation of the CVD growth of graphene in real time by focusing the radiation emitted from the growing graphene, which we call 'radiation-mode optical microscopy'. We observe the growth and shrinkage of graphene in response to the switching on and off of the methane supply. Analysis of the growth feature reveals that the attachment and detachment of carbon precursors are the rate-determining factor in the CVD growth of graphene. We expect radiation-mode optical microscopy to be applicable to the other crystal growth at high temperatures in various atmospheres.