Atomic Force and Scanning Tunneling Microscopy Studies of Single Walled Carbon Nanotubes

In this diploma work I present the first experimental investigations of carbon nanotubes at Karlstads University. Raw nanotube powder of single walled carbon nanotubes have been dispersed primarily in 1,2-dichloroethane. The solutions have been spincoated on Au(111) substrates. In order to determine the solubility of carbon nanotubes in the solution the samples have been investigated in an atomic force microscope. Single walled carbon nanotubes deposited on a Au(111) substrate have been investigated in a scanning tunneling microscope. Atomically resolved STM images of single walled carbon nanotubes were obtained. Scanning tunneling spectroscopy spectra was taken on a tube revealing its chirality. The measured data from the nanotubes was compared to calculations and confirmed their properties. Dry direct contact transfers of individual single walled carbon nanotubes have been done as a first step when trying to deposit carbon nanotubes on reactive surfaces in ultra-high vacuum. Individual nanotubes were found, confirming the success of dry direct contact transfer

Thin Mn silicide and germanide layers studied by photoemission and STM

The research presented in this thesis concerns experimental studies of thin manganese silicide and germanide layers, grown by solid phase epitaxy on the Si(111)7×7 and the Ge(111)c(2×8) surfaces, respectively. The atomic and electronic structures, as well as growth modes of the epitaxial Mn-Si and Mn-Ge layers, were investigated by low-energy electron diffraction (LEED), angle-resolved photoelectron spectroscopy (ARPES), core-level spectroscopy (CLS), and scanning tunneling microscopy and spectroscopy (STM and STS). The magnetic properties of the Mn-Ge films were investigated by X-ray magnetic circular dichroism (XMCD). The Mn-Si layers, annealed at 400 °C, showed a √3×√3 LEED pattern, consistent with the formation of the stoichiometric monosilicide MnSi. Up to 4 monolayers (ML) of Mn coverage, island formation was observed. For higher Mn coverages, uniform film growth was found. Our results concerning morphology and the atomic and electronic structure of the Mn/Si(111)-√3×√3 surface, are in good agreement with a recent theoretical model for a layered MnSi structure and the √3×√3 surface structure. Similar to the Mn-Si case, the grown Mn-Ge films, annealed at 330 °C and 450 °C, showed a √3×√3 LEED pattern. This indicated the formation of the ordered Mn5Ge3 germanide. A strong tendency to island formation was observed for the Mn5Ge3 films, and a Mn coverage of about 32 ML was needed to obtain a continuous film. Our STM and CLS results are in good agreement with the established model for the bulk Mn5Ge3 germanide, with a surface termination of Mn atoms arranged in a honeycomb pattern. Mn-Ge films grown at a lower annealing temperature, 260 °C, showed a continuous film at lower coverages, with a film structure that is different compared to the structure of the Mn5Ge3 film. XMCD studies showed that the low-temperature films are ferromagnetic for 16 ML Mn coverage and above, with a Curie temperature of ~250 K