Tuning fulleride electronic structure and molecular ordering via variable layer index

C60 fullerides are uniquely flexible molecular materials that exhibit a rich variety of behavior, including superconductivity and magnetism in bulk compounds, novel electronic and orientational phases in thin films, and quantum transport in a single-C60 transistor. The complexity of fulleride properties stems from the existence of many competing interactions, such as electron-electron correlations, electron-vibration coupling, and intermolecular hopping. The exact role of each interaction is controversial due to the difficulty of experimentally isolating the effects of a single interaction in the intricate fulleride materials. Here we report a unique level of control of the material properties of KxC60 ultra-thin films through well-controlled atomic layer indexing and accurate doping concentrations. Using STM techniques, we observe a series of electronic and structural phase transitions as the fullerides evolve from two-dimensional monolayers to quasi-threedimensional multilayers in the early stages of layer-by-layer growth. These results demonstrate the systematic evolution of fulleride electronic structure and molecular ordering with variable KxC60 film layer index, and shed new light on creating novel molecular structures and devices.Comment: 16 pages, 4 figures, to appear in Nature Material

ELECTRONIC-STRUCTURE OF MGO STUDIED BY ANGLE-RESOLVED ULTRAVIOLET PHOTOELECTRON-SPECTROSCOPY

We report on the electronic structure of MgO using angle-resolved ultraviolet photoelectron spectroscopy. The commonly catastrophic charging effects have been managed by means of an electron flood-gun. Features in the spectra, taken from the MgO(100) surface, can be assigned to a superposition of angle-integrated bulk transitions and direct bulk transitions. The results are in accordance with ab-initio bulk band-structure calculations

ANGLE OF INCIDENCE DEPENDENCE OF ELECTRON-BEAM INDUCED CRYSTAL CURRENT FROM AG(100) AND AG(111) SURFACES

We have examined the variation of medium energy ( ∼ 3 keV) electron beam induced crystal current from Ag(100) and Ag(111) surfaces, as a function of the polar and azimuthal angle of incidence. The results are interpreted in terms of a dynamical two-beam model, based on the variation of electron absorption as a function of the diffraction conditions. This model allows the determination of complex Fourier components of the one-electron potential in Ag, with which anisotropies in both elastic and inelastic scattering processes can be described. These anisotropies could be of importance in the interpretation of angle dependent X-ray photoelectron spectroscopy, angle dependent Auger electron spectroscopy, angle dependent inverse photoemission and various backscattered electron diffraction experiments

RELATIONSHIP BETWEEN ATOMIC AND ELECTRONIC-STRUCTURE OF CLEAN AND OXYGEN COVERED COPPER (110) SURFACE

We described the electronic band-structure of the clean and oxygen covered Cu(110) surface using a tight-binding method in a recursive layer by layer scheme. These are compared to angle-resolved ultraviolet photoelectron and angle-resolved inverse photoemission data. Good agreement for all (except image potential) surface states for the clean surface is obtained and also for the oxygen covered surface if the “ buckled-row” reconstruction is assumed, where alternate 〈001〉 copper rows are displaced outwardly by 0.6± 0.2 Å from the first layer and the oxygen atoms are located 0.1 ± 0.2 Å below these copper atoms. From this we conclude that the room temperature Cu(110)-p2 × 1-O superstructure is the result of a “buckled-row” reconstruction. The possibility of a “missing-row” reconstruction for the high temperature Cu(110)-p2 × 1-O superstructure is discussed