The formation of metal-free naphthalocyanine (H2Nc) self-assembled monolayers (SAMs) on reconstructed Au(100)hex is investigated by scanning tunneling microscopy (STM) at submonolayer coverage. The STM images show the aggregation of clusters, short stripes, and densely packed islands at the surface. These islands are orientated along two favored surface directions. The molecules’ orientation within these islands is determined. It is shown that the molecules’ axes are aligned parallel to the reconstruction lines along the [011̅] surface direction in both island orientations. When comparing the molecules’ position, the island types are identified as mirror domains. Subsequent thermal annealing induces a slight change in the densely packed island structure. The molecules’ axes are rotated by 5° compared to the reconstruction lines. The offset induces dislocations in the H2Nc structure increasing the unit-cell. A structure model is presented for the densely packed structures before and after annealing. The results are discussed within the context of phthalocyanine (Pc) findings in order to show the influence of the extended side-group system of the H2Nc molecule on the structural formation.

No abstract

No abstract

In order to understand the physical and chemical properties of advanced materials, functional molecular adsorbates, and protein structures, a detailed knowledge of the atomic arrangement is essential. Up to now, if subsurface structures are under investigation, only indirect methods revealed reliable results of the atoms' spatial arrangement. An alternative and direct method is three-dimensional imaging by means of holography. Holography was in fact proposed for electron waves, because of the electrons' short wavelength at easily accessible energies. Further, electron waves are ideal structure probes on an atomic length scale, because electrons have a high scattering probability even for light elements. However, holographic reconstructions of electron diffraction patterns have in the past contained severe image artifacts and were limited to at most a few tens of atoms. Here, we present a general reconstruction algorithm that leads to high-quality atomic images showing thousands of atoms. Additionally, we show that different elements can be identified by electron holography for the example of FeS2.

We report a combined high-resolution photoemission (XPS) and photoelectron diffraction (XPD) investigation of the three layer system MgO/Fe/GaAs(001). Each layer is investigated with regard to its structure. The two dimers model of the GaAs (4 × 2) reconstruction was confirmed by XPD patterns. We find the intermediate Fe layer in a crystalline structure. Further, the study clearly shows a well-ordered epitaxial MgO film on Fe. A careful analysis of the interface signals indicates an interdiffusion at the Fe/GaAs interface and partially shifted magnesium layers at the MgO/Fe interface.

No abstract

No abstract

No abstract