P.J. Kowalczyk

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.

Graphene on gold: Electron density of states studies by scanning tunneling spectroscopy

Graphene devices require electric contacts with metals, particularly with gold. Scanning tunneling spectroscopy studies of electron local density of states performed on mono-, bi-, and trigraphene layer deposited on metallic Au/Cr/SiO2/Si substrate shows that gold substrate causes the Fermi level shift downwards which means that holes are donated by metal substrate to graphene which becomes p-type doped. These experimental results are in good accordance with recently published density function theory calculations.

Scanning tunneling microscopy and spectroscopy of Y-junction in carbon nanotubes

Scanning tunneling microscopy and spectroscopy were used to observe the variations of electronic structure on the carbon nanotube Y-junction. The electronic structure derived from tunneling conductance maps showed natural me- tallic-metallic and semiconducting-metallic transitions close to the Y-junction, and the occurrence of metallic character of the whole Y-junction with the presence of additional resonant state at energy of 0.2 eV below the Fermi level. It is suggested that the state originates from heptagons forming the junction. 2002 Elsevier Science B.V. All rights reserved.

Electronic size effects in three-dimensional nanostructures.

We show that bismuth nanostructures form three-dimensional patterns governed by two-dimensional electronic effects. Scanning tunneling microscopy reveals that both the vertical and the lateral dimensions of the structures strongly favor certain values and that the preferred widths are substantially different for each preferred height. First-principles calculations demonstrate that this vertical-lateral correlation is governed by the Fermi surface topology and that this is itself sensitively dependent on the dimensions of the structure.

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.

Anisotropic oxidation of bismuth nanostructures: Evidence for a thin film allotrope of bismuth

We present evidence that ultra-thin Bi(110) nanostructures oxidise from the edges, and that their top surfaces remain unoxidised. Even after prolonged oxidation, clean (unoxidised) bismuth is present in nanostructures that are less than 5 monolayers thick. Since the (110) surface of bulk bismuth is known to be readily oxidised, this is strong evidence for a thin film allotrope of bismuth. We present a comparison with calculated structures and the structures of polymeric nitrogen, which suggests that the allotrope is one of several complex or hybrid paired-layer structures.

The new high-temperature surface structure on reduced TiO2(001)

Scanning tunnelling microscopy, ultraviolet photoelectron spectroscopy and current imaging tunnelling spectroscopy (STM/UPS/CITS) were used to study the topographic and electronic structure of a high-temperature structure formed on the TiO(2)(001) surface after heating at 1173 K. The STM images revealed different domain-like ordering and periodicity on the surface in comparison to those observed previously. The UPS studies showed the presence of a surface state at energy about 1.1 eV below the Fermi level. This result was confirmed by the CITS data showing pronounced periodic maxima of the electron local density of states at energy around 1.1-1.2 eV below the Fermi level and located on top of every row of the new high-temperature structure. The CITS results recorded for small grains, which coexist with the observed structure, showed that their chemical composition is closer to the Ti(2)O(3) material than to TiO(2-x) for x << 1.

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.

Engineering multiple topological phases in nanoscale Van der Waals heterostructures: realisation of α-antimonene

Van der Waals heterostructures have recently been identified as providing many opportunities to create new two-dimensional materials, and in particular to produce materials with topologically-interesting states. Here we show that it is possible to create such heterostructures with multiple topological phases in a single nanoscale island. We discuss their growth within the framework of diffusion-limited aggregation, the formation of moire patterns due to the differing crystallographies of the materials comprising the heterostructure, and the potential to engineer both the electronic structure as well as local variations of topological order. In particular we show that it is possible to build islands which include both the hexagonal β- and rectangular α-forms of antimonene, on top of the topological insulator α-bismuthene. This is the first experimental realisation of α-antimonene, and we show that it is a topologically non-trivial material in the quantum spin Hall class.