We report on transport and capacitance measurements of graphene devices in magnetic fields up to 30 T. In both techniques, we observe the full splitting of Landau levels and we employ tilted field experiments to address the origin of the observed broken symmetry states. In the lowest energy level, the spin degeneracy is removed at filling factors $\nu=\pm1$ and we observe an enhanced energy gap. In the higher levels, the valley degeneracy is removed at odd filling factors while spin polarized states are formed at even $\nu$. Although the observation of odd filling factors in the higher levels points towards the spontaneous origin of the splitting, we find that the main contribution to the gap at $\nu= -4,-8$, and $-12$ is due to the Zeeman energy.
The movement of a micron-size section of an individual domain wall in a uniaxial garnet film was studied using ballistic Hall micromagnetometry. The wall propagated in characteristic Barkhausen jumps, with the distribution in jump size $S$, following the power-law relation, $D(S)\ensuremath{\propto}{S}^{\ensuremath{-}\ensuremath{\tau}}$. In addition to reporting on the suitability of employing this alternative technique, we discuss the measurements taken of the scaling exponent $\ensuremath{\tau}$, for a single domain wall in a two-dimensional sample with magnetization perpendicular to the surface, and low pinning center concentration. This exponent was found to be $1.14\ifmmode\pm\else\textpm\fi{}0.05$ at both liquid helium and liquid nitrogen temperatures.
Pyrolysis is one of the most common methods of end-of-life tires (ELTs) recycling. This study considered the use of carbon black from pyrolysis of ELTs as a carbon carrier for metals (Co, Ni, Cu, Fe) and their oxides to produce catalytic systems. The synchronous thermal analysis showed the positive effect of metal oxides/recovered carbon black (MOs/rCB) on ammonium perchlorate thermolysis. It was selected as a model catalytic reaction. Metal oxides/recovered carbon black (MOs/rCB) catalysts facilitated a reduction in the thermal decomposition phases of ammonium perchlorate, resulting in a significant narrowing of the decomposition interval. The greatest narrowing (22.7°C) was observed at 103.5°C for non-catalytic process. All tri-metallic catalytic systems showed high catalytic efficiency, providing a narrowing of the decomposition interval on average 2.5 times more in comparison with mono-metallic catalysts. Trioxide catalyst CuO/CoO/FeO/rCB showed the most significant shift in the high-temperature decomposition stage by 13 % (from 334.0°C to 293.2°C). The activity of di-, tri-, and tetra-metallic catalytic systems was further enhanced by the synergistic effect induced by the addition of a second (or more) metal to the system. Efficient use of rCB for impregnated catalyst systems production could improve the economic efficiency of ELTs pyrolysis.
We report a room temperature tunneling anisotropic magnetoresistance in Co/Al2O3/NiFe junctions containing magnetic electrodes oxidized prior to forming the Al2O3 layer. A significant change in a tunnel magnetoresistance is observed when the layer magnetizations are rotated collinearly in the junction plane by an applied external field. The angular dependence of the tunneling anisotropic magnetoresistance could be explained by the presence of an antiferromagnetic oxide layer formed within the barrier.
A full understanding of how the electrochemical properties of two-dimensional (2D) materials depend on their structure and surrounding environment is critical for their successful implementation in electrochemistry-related technologies. Although this understanding is currently limited, the complex and tunable electronic structure of 2D materials suggests that a large landscape of possibilities exists in optoelectronics, energy storage/conversion, and photocatalysis. 1 Here we show that modification of conductive electrodes with sub-nanometer thick 2D materials leads to a reciprocal interaction between the electrode and the 2D material. This interaction can be viewed as a chemical passivation of the electrode surface by the 2D material, alongside the endowment of the 2D material with the electronic properties of the conductive substrate. We will present two examples of this approach in the context of electrochemistry. First, we will discuss hexagonal boron nitride (hBN) on graphite, which represents a wide-gap tunneling barrier on a semimetallic substrate (Figure). We will examine the dependence of the electrochemical tunneling current and the electron transfer kinetics on the number of hBN layers. Second, we will discuss molybdenum disulfide (MoS 2 ) on gold, which represents a semiconducting (1.9 eV bandgap) barrier on a metallic substrate. We will show that a single layer of MoS 2 effectively passivates the surface chemistry of the underlying Au substrate, and that in turn, the Au increases the density of the electronic state of the MoS 2 , rendering it metallic. 2 These findings show that a tunable electrochemical response can be achieved by modification of conductive substrates with 2D materials, either through the nature or thickness of the 2D material. Our results can be exploited in future research and applications in areas such as electrode modification, electrochemical switching or surface passivation. Velický M. and Toth P. S., Appl. Mater. Today 8, 2017 ,68-103. Velický M. et al. , ACS Nano 12, 2018 , 10463-10472. Figure 1
