Rika Matsumoto

MoCl5 intercalation doping and oxygen passivation of submicrometer-sized multilayer graphene

We investigated doping material selection for multilayer graphene (MLG) interconnects and a passivation process to stabilize the doped state. Intercalation doping with Br2, FeCl3, and MoCl5 was compared in terms of doping ability and robustness against environmental effects, which are exacerbated by miniaturization. We found that MoCl5 was advantageous for miniaturization. We hypothesized that environmental stability would be enhanced by partially oxidizing MoCl5 and avoiding hydrolysis by water vapor in air. To test this, we examined a passivation process by dry oxygen exposure. We verified that the doping effect was improved and that intercalated material (MoCl5) was partially oxidized and confined in the MLG.

Highly Conductive and Transparent Large‐Area Bilayer Graphene Realized by MoCl5 Intercalation

Bilayer graphene (BLG) comprises a 2D nanospace sandwiched by two parallel graphene sheets that can be used to intercalate molecules or ions for attaining novel functionalities. However, intercalation is mostly demonstrated with small, exfoliated graphene flakes. This study demonstrates intercalation of molybdenum chloride (MoCl5 ) into a large-area, uniform BLG sheet, which is grown by chemical vapor deposition (CVD). This study reveals that the degree of MoCl5 intercalation strongly depends on the stacking order of the graphene; twist-stacked graphene shows a much higher degree of intercalation than AB-stacked. Density functional theory calculations suggest that weak interlayer coupling in the twist-stacked graphene contributes to the effective intercalation. By selectively synthesizing twist-rich BLG films through control of the CVD conditions, low sheet resistance (83 Ω ▫-1 ) is realized after MoCl5 intercalation, while maintaining high optical transmittance (≈95%). The low sheet resistance state is relatively stable in air for more than three months. Furthermore, the intercalated BLG film is applied to organic solar cells, realizing a high power conversion efficiency.

Intercalation doping of narrow multilayer graphene interconnects with sub-100 nm widths

An intercalation process for narrow graphene interconnects with linewidths of 5 µm size induced partial delamination of the graphene layers and insufficient intercalation in some graphene interconnects with linewidths of <500 nm. More moderate intercalation conditions such as lower temperature suppressed the delamination of the graphene layers and provided improved doping characteristics with a higher yield in narrow graphene interconnects with linewidths of <100 nm. The intercalation of MoCl5 into narrow graphene interconnects under suitable conditions was confirmed by Raman scattering spectroscopy. These results indicate that intercalation using MoCl5 is promising for the fabrication of narrow graphene interconnects.