Analysis of Degradation in Graphene-based Spin Valves

The degradation mechanisms of multilayer graphene spin valves are investigated. The spin injection signals in graphene spin valves have been reported to be linearly dependent on the drain bias voltage, which indicates that the spin polarization of injected spins in graphene is robust against the bias voltage. We present that the disappearance of this robustness is due to two different degradation mechanisms of the spin valves. Our findings indicate that the disappearance of the robustness is due to degradation rather than an intrinsic characteristic of graphene. Thus, the robustness can be greatly enhanced if degradation can be prevented.Comment: 14 pages, 4 figures (To appear in Applied Physics Express

Photo-oxidation of Graphene in the Presence of Water

Oxygen molecules are found to exhibit nonnegligible reactivity with graphene under strong light irradiation in the presence of water. The reaction is triggered by the laser Raman spectroscopy measurement itself, and the D band (ca. 1340 cm^–1) becomes larger as the laser irradiation is prolonged. The electronic transport properties of the graphene derivative are also investigated and both the electron and hole mobility are found to be reduced. These results are attributed to oxidation of graphene. This primitive modification method can be exploited to manipulate the structural and electronic properties of graphene

Reduction of the interfacial trap density of indium-oxide thin film transistors by incorporation of hafnium and annealing process

The stable operation of transistors under a positive bias stress (PBS) is achieved using Hf incorporated into InOx-based thin films processed at relatively low temperatures (150 to 250 °C). The mobilities of the Hf-InOx thin-film transistors (TFTs) are higher than 8 cm2/Vs. The TFTs not only have negligible degradation in the mobility and a small shift in the threshold voltage under PBS for 60 h, but they are also thermally stable at 85 °C in air, without the need for a passivation layer. The Hf-InOx TFT can be stable even annealed at 150 °C for positive bias temperature stability (PBTS). A higher stability is achieved by annealing the TFTs at 250 °C, originating from a reduction in the trap density at the Hf-InOx/gate insulator interface. The knowledge obtained here will aid in the realization of stable TFTs processed at low temperatures

Double-Helix Supramolecular Nanofibers Assembled from Negatively Curved Nanographenes

The layered structures of graphite and related nanographene molecules play key roles in their physical and electronic functions. However, the stacking modes of negatively curved nanographenes remains unclear, owing to the lack of suitable nanographene molecules. Herein we report the synthesis and one-dimensional supramolecular self-assembly of negatively curved nanographenes without any assembly-assisting substituents. This curved nanographene self-assembles in various organic solvents and acts as an efficient gelator. The formation of nanofibers was confirmed by microscopic measurements, and an unprecedented double-helix assembly by continuous π-π stacking was uncovered by three-dimensional electron crystallography. This work not only reports the discovery of an all-sp2-carbon supramolecular π-organogelator with negative curvature, but also demonstrates the power of three-dimensional electron crystallography for the structural determination of submicrometer-sized molecular alignment