Takako Konoike has expertise in Evaluation and her passion in improving the various measurements under pressure and crystal growth of organic conductors, especially organic Dirac fermion system α-(BEDT-TTF) 2I3. We have measured the specific heat and thermo power of organic Dirac fermion System under high pressure. We have succeeded in obtaining the first experimental results of the specific heat of Dirac fermions and observing the giant Nernst effect reflecting the intrinsic nature of the zero-mode Landau level, which is characteristic of the Dirac fermion system. From these results, we can conclude that the high-purity organic crystal can provide an ideal testing ground for experimental studies of Dirac fermions.
Statement of the Problem: Since the discovery of graphene, it attracted a great interest because the electrons in graphene behave like massless Dirac fermions. It shows anomalous behaviors resulting from the peculiar liner dispersion. It has been recognized that Dirac fermion system is also realized in organic conductor α-(BEDT-TTF)2I3 under high pressure. This system is composed of organic molecule BEDT-TTF and inorganic anions I3. These molecules are stacked alternatively and forming a multi-layered structure of conducting and insulating layer, respectively. By taking advantage of its bulk nature, we have experimentally studied the physical properties of Dirac fermions in this compound. In high magnetic field, the characteristic edge state with spin current at the sample edges is theoretically predicted. By using the micro/nano crystals, which contains large amount of edges, we aimed to observe the evidence of the edge state of this system. Methodology: Micro/nano crystal growth of α-(BEDT-TTF)2I3 is based on nano-scale electrocrystallization was carried out by using Nano-Wire Fabrication Kit, Iwata Glass Industrial Co., Ltd., The electrodes used in the crystal growth were made on a silicon substrate with 300 nm SiO2. Platinum electrode was deposited on a masked substrate and 5 m gap was made by photolithography. The substrate was set into a saturated THF solution of above two molecules. DC current was applied between the electrodes at 20C in incubator during 24 h. Findings: The typical crystal obtained by this method is shown in Figure 2. The shape of the grown micro-crystal resembles with that grown by usual electrocrystallization. The surface of the crystal is almost flat and specularly reflected suggesting that the crystal is high purity. Conclusion: By using the nano-scale electro-crystallization, we could obtain high purity micro-crystals. We will study this micro-crystal to detect the evidence of the edge state and spin current.
Metals alloys are of great technological interest which may even increase if they are nanostructured. Also, it can be found in the literature, same proposed chemical synthesis methodologies obtain different kind of materials with nanocrystal particles content. Then, the main objective of this work was to obtain a CuNiCo alloy, by an alternative procedure capable of generating nanostructured grains, followed by its preliminary characterization. It has been done by dividing the process into two steps the first one is the thermal decomposition of a nitrate solution [Cu(NO3)2, Ni(NO3)2 and Co(NO3)3] aiming to obtain a homogeneous co-formed metal oxide. In the second step, these oxides are heated up to a desired temperature and kept in a reductive flow of hydrogen, leaving the CuNiCo alloy as final product. The applied reduction temperatures were 300 °C and 900 °C. The materials obtained after each step were characterized by scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDS). As result of the first step, it was found that oxygen, Cu, Ni and Co were, as desired, homogeneously distributed, as shown in the SEM elemental mapping (Figure-1). The after reduction obtained material present different shape and particle size, depending on the applied reducing temperatures (Figure-2). The more circular and greater size observed at 900 °C confirms an increased sintering occurrence at higher temperature and the EDS results indicate the expected composition for Co, Ni and Cu (Figure-3). The initial results given by transmission electron microscopy (TEM) have shown the presence of particles with spherical morphology and a homogeneous distribution of the elements, which are sharing the same crystal structure. Also, it was noted the presence of particles smaller than 100 nm in the CuNiCo alloy, as show in Figure-4 (bright and dark fields).