We investigated the structure of the interfacial water layers between graphene sheets and a sapphire substrate by observing them through graphene sheets at room temperature using atomic force microscopy. When graphene sheets were deposited at low relative humidity, the interfacial water layers appeared as small islands. They grew in layer-by-layer stacking with an increase in the relative humidity. We also investigated effects of the interfacial water layers on Raman spectra from the graphene sheets that cover the water layers. The correlation between G-peak position (intensity) and 2D-peak position (intensity) shows that the interfacial water induces hole-doping in graphene sheets. The doping density increases with increasing the amount of interfacial water. This study shows that the electrical properties of graphene sheets are tunable by controlling the hydrophilicity of substrate surfaces.

We investigated the effects of surface chemistry of substrates on the Raman spectra of graphene flakes that come into contact with various insulating substrates, such as quartz and sapphire, under ambient conditions at room temperature. The Gpeak positions of graphene flakes on such substrates were investigated, and significant blue-shifts of the G-band were observed on a chemically single-phased sapphire (0001) substrate. On a phase-separated sapphire (0001) substrate with Al-terminated (hydrophilic) and O-terminated (hydrophobic) domains, the G-band of graphene flakes was composed of two peaks centered at 1587 cm −1 (G 1 -peak) and 1593 cm −1 (G 2peak). The G 1 -peak originated from the O-terminated domain and the G 2 -peak from the Al-terminated one. Since the 2D-peak shifts were small, the Raman shifts in the G-band were attributed to chemical doping from environmental conditions, especially water layers at the graphene/substrate interface that cause hole-doping. The blue-shift in the G-band increased with the increase in the amount of water molecules subject to the surface chemistry of the substrate. Even though Raman spectroscopy is an excellent tool for characterizing the physical properties of graphene, this study indicates that preparation of the substrate surface is important for determining Raman spectroscopy of graphene because its peak positions are easily shifted due to the surface chemistry.

We attached single-layer graphene or few-layer graphene (FLG) on a sapphire (1-102) surface with well-ordered step/terrace structures and then etched them using catalytic nanoparticles. In the etching of FLG flakes, atomic steps can be utilized as guides or reflectors. In the case of single-layer graphene, the etching proceeds in a particular direction of a surface phase pattern on the terrace, and graphene nanoribbons are self-formed. The surface structures of the supporting substrate are good templates for graphene processing.

Graphene attached on a sapphire surface with regularly ordered step-terrace structure was observed using atomic force microscopy (AFM). We found that graphene tightly adheres to a sapphire surface and the buried step structure on the sapphire surface was clearly observed on the graphene surface. Height of a single-layer graphene was estimated to be approximately 0.36 nm on sapphire surface, which is in good agreement with the theoretical height. These results indicate that sapphire is suitable for the substrate that supports graphene because we can obtain undistorted graphene that is tightly fixed on a substrate surface. #

The mechanism of Sn surface segregation during the epitaxial growth of GeSn on Si (001) substrates was investigated by Auger electron spectroscopy and energy dispersive X-ray spectroscopy. Sn surface segregation depends on the growth temperature and Sn content of GeSn layers. During Sn surface segregation, Sn-rich nanoparticles form and move on the surface during the deposition, which results in a rough surface owing to facet formation. The Sn-rich nanoparticles moving on the surface during the deposition absorb Sn from the periphery and yield a lower Sn content, not on the surface but within the layer, because the Sn surface segregation and the GeSn deposition occur simultaneously. Sn surface segregation can occur at a lower temperature during the deposition compared with that during postannealing. This suggests that the Sn surface segregation during the deposition is strongly promoted by the migration of deposited Ge and Sn adatoms on the surface originating from the thermal effect of substrate temperature, which also suggests that limiting the migration of deposited Ge and Sn adatoms can reduce the Sn surface segregation and improve the crystallinity of GeSn layers.