Electron energy loss spectroscopy with parallel readout of energy and momentum

We introduce a high energy resolution electron source that matches the requirements for parallel readout of energy and momentum of modern hemispherical electron energy analyzers. The system is designed as an add-on device to typical photoemission chambers. Due to the multiplex gain, a complete phonon dispersion of a Cu(111) surface was measured in seven minutes with 4 meV energy resolution

The influence of the substrate on the structure and electronic properties of carbon-based 2D materials

The exploration of two-dimensional materials, such as graphene, has become the hottest research of interest in recent years. In this dissertation, we examine two classes of materials considered of importance for both fundamentals studies and devices applications, namely graphene on 6H-SiC(0001) and palladium-/platinum- phthalocyanine on Ag(111), with the aim of assessing the interactions at the interface. Using different surface science techniques, we are able to study the modification of their electronic and structural properties in relation to the supporting substrate. At first, we present a new approach used to gauge the strength of the interactions at the interface in graphene/substrate systems which is based on the determination of the adsorption height of the graphene layer. From the comparison of different graphene/SiC interfaces, i.e.,~carbon buffer layer, hydrogen intercalation and germanium intercalation, we find that the graphene layer is best decoupled from the underlying substrate when the hydrogen intercalation is present at the interface. The effect of the supporting substrate (and interface) on the graphene properties is further investigated upon doping. We find that depending on the type of interface, i.e.,~carbon buffer layer or hydrogen intercalation, the quantity as well as the variety of nitrogen dopants substituted into the graphene lattice varies but not the n-type carrier increase. This leads to the conclusion that the effective doping of graphene depends on the supporting material. In fact for hydrogen intercalated graphene, the nitrogen dopants partially replace hydrogen at the intercalation, contributing to the doping ('proximity doping') but leading to an increment of the interaction at the interface. In contrast, the carbon buffer layer is found inert against the nitrogen doping, but active against the boron doping; a behavior most likely dependent on the preparation method. Finally, the molecular symmetry reduction (from the $\mathrm{D_{4h}}$ symmetry group) via degeneracy lifting of the platinum- and palladium-phthalocyanine/Ag(111) complexes is investigated using vibrational spectroscopy. Because of the presence of an interfacial dynamical charge transfer, some vibrational peaks show a Fano-type line shape. Their assignment to vibrational modes which are infrared active only in the $\mathrm{C_{2v}}$ symmetry group proves that a preferential charge transfer from the Ag surface into one of the originally doubly degenerate lowest unoccupied molecular orbitals takes place, i.e. the electronic degeneracy is lifted and the molecule-surface complex acquires the twofold symmetry

Adsorption-induced symmetry reduction of metal-phthalocyanines studied by vibrational spectroscopy

We investigate the vibrational properties of Pt- and Pd-phthalocyanine (PtPc and PdPc) molecules on Ag(111) with high-resolution electron energy loss spectroscopy (HREELS). In the monolayer regime, both molecules exhibit long-range order. The vibrational spectra prove a flat adsorption geometry. The redshift of specific vibrational modes suggests a moderate interaction of the molecules with the substrate. The presence of asymmetric vibrational peaks indicates an interfacial dynamical charge transfer (IDCT). The molecular orbital that is involved in IDCT is the former Eg lowest unoccupied molecular orbital (LUMO) of the molecules that becomes partially occupied upon adsorption. A group-theoretical analysis of the IDCT modes, based on calculated vibrational frequencies and line shape fits, provides proof for the reduction of the symmetry of the molecule-substrate complex from fourfold D4h to C2v(σv), Cs(σv), or C2 and the ensuing lifting of the degeneracy of the former LUMO of the molecule. The vibration-based analysis of orbital degeneracies, as carried out here for PtPc/Ag(111) and PdPc/Ag(111), is particularly useful whenever the presence of multiple molecular in-plane orientations at the interface makes the analysis of orbital degeneracies with angle-resolved photoemission spectroscopy difficult

Electronic and Chemical Properties of Donor, Acceptor Centers in Graphene

Chemical doping is one of the most suitable ways of tuning the electronic properties of graphene and a promising candidate for a band gap opening. In this work we report a reliable and tunable method for preparation of high-quality boron and nitrogen co-doped graphene on silicon carbide substrate. We combine experimental (dAFM, STM, XPS, NEXAFS) and theoretical (total energy DFT and simulated STM) studies to analyze the structural, chemical, and electronic properties of the single-atom substitutional dopants in graphene. We show that chemical identification of boron and nitrogen substitutional defects can be achieved in the STM channel due to the quantum interference effect, arising due to the specific electronic structure of nitrogen dopant sites. Chemical reactivity of single boron and nitrogen dopants is analyzed using force–distance spectroscopy by means of dAFM

Silicon Pore Optics Mirror Module Production and Testing

Silicon Pore Optics (SPO) has been established as a new type of x-ray optics that enables future x-ray observatories such as Athena. SPO is being developed at cosine with the European Space Agency (ESA) and academic and industrial partners. The optics modules are lightweight, yet stiff, high-resolution x-ray optics, that shall allow missions to reach an unprecedentedly large effective area of several square meters, operating in the 0.2 - 12 keV band with an angular resolution better than 5 arc seconds. In this paper we are going to discuss the latest generation production facilities and we are going to present results of the production of mirror modules for a focal length of 12 m, including x-ray test results