Neue Kohlenstoffnanomaterialien aus massenselektierten molekularen Fragmenten

This work presents the results of various investigations regarding novel carbon nanomaterials. The general strategy to generate these materials was the use of the Low Energy Cluster Beam Deposition method which consists of the ionization and fragmentation of sublimable molecules in the gas phase followed by mass selection and soft-landing of the generated fragment ions on conducting or semiconducting surfaces. Also, the properties of already existing materials were modified by thermal treatment, doping with alkali metals and oxidation with atomic and molecular oxygen. This work contains studies concerning the following issues: - a series of measurements in which the binding energies between polyaromatic hydrocarbons (PAHs) and HOPG were measured by temperature programmed desorption in order to determine the graphite interlayer cohesion energy - the generation of PAH oligomers by deposition of dehydrogenated PAH fragments - a comparative study on the reactivity of various PAHs with atomic oxygen and also oxidized HOPG surfaces in order to explore the mediating role of these surfaces - an investigation of the efficiency and side reactions of the HF limination from fluorinated PAHs which are designed as precursors to generate curved nanostructures from planar molecules - attempts to purify single-walled carbon nanotubes by removing tensides or polymer coatings using thermal treatment and oxidation with atomic and molecular oxygen - the direct confirmation of covalent bonds between non-IPR fullerene cages by observing the sublimation of dimers - measurements on the properties of Cs doped non-IPR fullerene solids The properties of the generated materials were characterized using standard UHV methods of surface science: photoelectron spectroscopy, temperature programmed desorption, Raman spectroscopy as well as various microscopic methods

High‐Purity Er3_{3}N@C80_{80} Films: Morphology, Spectroscopic Characterization, and Thermal Stability

Films comprising the endohedral fullerene Er3N@C80 are deposited onto highly oriented pyrolytic graphite (HOPG) substrates in high purity enabled by performing mass-selected low-energy deposition from a cation beam. In the initial stage, the growth on HOPG is dominated by spontaneous nucleation of small 2D islands both on intact terraces as well as the step edges. The island growth exhibits strong differences from lms comprising other fullerenes grown by the same method. This behavior can be explained by the surface-diffusion-mediated nucleation model presented in previous work: Dominant components in the behavioural differences are a high intercage dispersion interaction and a lower kinetic energy of cages migrating on the surface in comparison with previously deposited materials. When annealed, the lms undergo several competing processes: A small fraction desorbs in the temperature range 700–800 K, another fraction forms covalent intercage bonds instead of the previous purely dispersive bonding mode, and a third fraction probably decomposes to small fragments

Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG

A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases

Influence of Dispersion Interactions on the Thermal Desorption of Nonplanar Polycyclic Aromatic Hydrocarbons on HOPG

A combination of low energy ion beam deposition and mass resolved thermal desorption spectroscopy is applied to analyze the binding behavior of two nonplanar polycyclic aromatic hydrocarbons (PAHs) to highly oriented pyrolytic graphite (HOPG) surfaces—also concerning their lateral dispersion interactions. In particular, the fullerene precursor C60H30 (FPC) and rubrene C42H28 are studied. Due to their smaller contact areas, both molecules exhibit significantly weaker binding energies to the HOPG surface compared to planar PAHs of similar size: C60H30 is bound to the surface by 3.04 eV, which is 0.6 eV lower than for a fully planar homologue. For rubrene, an isolated molecule–substrate binding energy of 1.59 eV is found, which is about 1 eV less than that of the corresponding planar homologue hexabenzocoronene C42H18. In contrast to FPC, rubrene shows a significant (intermolecular) lateral dispersion contribution to the binding energy as the submonolayer coverage increases

Microstructural and optical emission properties of diamond multiply twinned particles

Multiply twinned particles (MTPs) are fascinating crystallographic entities with a number of controllable properties originating from their symmetry and cyclic structure. In the focus of our studies are diamond MTPs hosting optically active defects—objects demonstrating high application potential for emerging optoelectronic and quantum devices. In this work, we discuss the growth mechanisms along with the microstructural and optical properties of the MTPs aggregating a high-density of “silicon-vacancy” complexes on the specific crystal irregularities. It is demonstrated that the silicon impurities incite a rapid growth of MTPs via intensive formation of penetration twins on {100} facets of regular octahedral grains. We also show that the zero-phonon-line emission from the Si color centers embedded in the twin boundaries dominates in photo- and electroluminescence spectra of the MTP-based light-emitting devices defining their steady-state optical properties

Pseudovertical Schottky Diodes on Heteroepitaxially Grown Diamond

Substrates comprising heteroepitaxially grown single-crystalline diamond epilayers were used to fabricate pseudovertical Schottky diodes. These consisted of Ti/Pt/Au contacts on p− Boron-doped diamond (BDD) layers (1015–1016 cm−3) with varying thicknesses countered by ohmic contacts on underlying p+ layers (1019–1020 cm−3) on the quasi-intrinsic diamond starting substrate. Whereas the forward current exhibited a low-voltage shunt conductance and, for higher voltages, thermionic emission behavior with systematic dependence on the p− film thickness, the reverse leakage current appeared to be space-charge-limited depending on the existence of local channels and thus local defects, and depending less on the thickness. For the Schottky barriers ϕSB, a systematic correlation to the ideality factors n was observed, with an “ideal” n = 1 Schottky barrier of ϕSB = 1.43 eV. For the best diodes, the breakdown field reached 1.5 MV/cm

Pseudovertical Schottky Diodes on Heteroepitaxially Grown Diamond

Substrates comprising heteroepitaxially grown single-crystalline diamond epilayers were used to fabricate pseudovertical Schottky diodes. These consisted of Ti/Pt/Au contacts on p− Boron-doped diamond (BDD) layers (1015–1016 cm−3) with varying thicknesses countered by ohmic contacts on underlying p+ layers (1019–1020 cm−3) on the quasi-intrinsic diamond starting substrate. Whereas the forward current exhibited a low-voltage shunt conductance and, for higher voltages, thermionic emission behavior with systematic dependence on the p− film thickness, the reverse leakage current appeared to be space-charge-limited depending on the existence of local channels and thus local defects, and depending less on the thickness. For the Schottky barriers ϕSB, a systematic correlation to the ideality factors n was observed, with an “ideal” n = 1 Schottky barrier of ϕSB = 1.43 eV. For the best diodes, the breakdown field reached 1.5 MV/cm