M. Rogala

Role of graphene defects in corrosion of graphene-coated Cu(111) surface

Protection of Cu(111) surface by chemical vapor deposition graphene coating is investigated. The X-ray photoemission spectroscopy results do not reveal any signs of corrosion on graphene-coated Cu(111), and suggest perfect protection of copper surface against interaction with atmospheric gases. However, the scanning tunneling spectroscopy results show that cracks in the graphene sheet open up windows for nanoscale corrosion. We have shown also that such local corrosions are not only limited to the discontinuities but may also progresses underneath the graphene cover.

The role of water in resistive switching in graphene oxide

The resistive switching processes are investigated at the nano-scale in graphene oxide. The modification of the material resistivity is driven by the electrical stimulation with the tip of atomic force microscope. The presence of water in the atmosphere surrounding graphene oxide is found to be a necessary condition for the occurrence of the switching effect. In consequence, the switching is related to an electrochemical reduction. Presented results suggest that by changing the humidity level the in-plane resolution of data storage process can be controlled. These findings are essential when discussing the concept of graphene based resistive random access memories.

Quasi-two-dimensional conducting layer on TiO2 (110) introduced by sputtering as a template for resistive switching

The insulator-to-metal transformation in the surface layer of TiO2 (110) induced by the Ar+ ion sputtering process is analyzed on the nanoscale. Local conductivity atomic force microscopy and photoelectron spectroscopy allow the changes in the valence of the Ti ions in the surface layer to be linked to the formation of its grain-like structure. The investigation of the cleavage plane of the crystal allowed us to estimate the thickness of the quasi-two-dimensional conducting layer generated by ion bombardment as 30 nm. The conducting layer is a template where the resistive switching of each single grain can be carried out.

The study of the interactions between graphene and Ge(001)/Si(001)

The interaction between graphene and germanium surfaces was investigated using a combination of microscopic and macroscopic experimental techniques and complementary theoretical calculations. Density functional theory (DFT) calculations for different reconstructions of the Ge(001) surface showed that the interactions between graphene and the Ge(001) surface introduce additional peaks in the density of states, superimposed on the graphene valence and conduction energy bands. The growth of graphene induces nanofaceting of the Ge(001) surface, which exhibits well-organized hill and valley structures. The graphene regions covered by hills are of high quality and exhibit an almost linear dispersion relation, which indicates weak graphene–germanium interactions. On the other hand, the graphene component occupying valley regions is significantly perturbed by the interaction with germanium. It was also found that the stronger graphene–germanium interaction observed in the valley regions is connected with a lower local electrical conductivity. Annealing of graphene/Ge(001)/Si(001) was performed to obtain a more uniform surface. This process results in a surface characterized by negligible hill and valley structures; however, the graphene properties unexpectedly deteriorated with increasing uniformity of the Ge(001) surface. To sum up, it was shown that the mechanism responsible for the formation of local conductivity inhomogeneities in graphene covering the Ge(001) surface is related to the different strength of graphene–germanium interactions. The present results indicate that, in order to obtain high-quality graphene, the experimental efforts should focus on limiting the interactions between germanium and graphene, which can be achieved by adjusting the growth conditions.

Ultra Highly Selective Synthesis of Double-Walled Carbon Nanotubes

Double-walled carbon nanotubes were synthesized by a carbon arc discharge using Fe catalyst. Electron microscopy revealed that the dominant fraction of nanotubes appears in bundles and has outer diameters between 2.5 and 4.0 nm. The by-products (catalyst particles and amorphous carbon) were readily removed using diluted nitric acid. The success of the purification was tracked by electron microscopy and X-ray photoelectron spectroscopy. The surface of purified nanotubes was found to be covalently functionalized with carbonyl-containing groups, which were subsequently removed by thermal annealing. The developed synthesis route has high selectivity for double-walled carbon nanotubes and uses simple starting materials.