FI-STM Investigation of Fullerenes Adsorbed on the Semiconductor and Metal Surfaces(STM-C_<60>)

Our systematic investigation using field-ion scanning tunneling microscopy (FI-STM) is reviewed for the adsorption and film growth of fullerenes (C_, C_, C_, and C_) and metallofullerenes (Sc@C_/Sc_2@C_, Sc_2@C_, Y@C_, and Gd@C_) on the Si(100)-2x1, Si(111)-7x7, GaAs(001)-2x4-As, Cu(111)1x1, and Ag(111)1x1 surfaces. The fullerene molecules are stable on the Si(100)-2x1 and Si(111)-7x7 surfaces at room temperature because of the strong bonding to the substrate dangling bonds. As a result, unique intramolecular structures of C_ molecule are observed. The STM images of the C_, Sc@C_/Sc_2@C_, and Sc_2@C_ molecules are used to draw information on the molecular structures. In contrast to the Si surfaces, the fullerene molecules are mobile on the terrace of the metal surfaces and initially segregate to the step. A well-ordered two dimensional overlayer forms with a close-packed arrangement upon annealing the fullerene covered surfaces. On the Cu(111) surface, the commensurate (4x4) phase forms for the cases of the C_, C_ and C_C_ adsorption, indicating a strong interaction between the Cu substrate and fullerenes. Beautiful intramolecular structures of the C_ and C_ molecules are observed and are interpreted as the local mappings of the electron density of states. One-dimensional cluster formation of C_, Y@C_, and Gd@C_ on the step of the Cu(111)-1x1 surface is analyzed and the preferential dimer formation is only observed for the case of Y@C_, which is attributed to the interaction between the unpaired electrons of the Y@C_ molecules. On the Ag(111) surface, the C_ and Sc_2@C_ monolayer films show several phases that have an almost identical nearest neighbour distance but are rotated from each other. Among the systems studied, C_ on the GaAs(001)-2x4-As surface shows a unique highly-strained fcc(110)-oriented multi-layer film growth, while all other systems show the well-known fcc(111)-oriented multi-layer growth

Field Ion Microscopy of C_<60> Molecules(APFIM/FIM)

Field ion microscopy of C_ on the tungsten substrate showed that (1) the field ion image of the C_ adsorbate reflects the LUMO (lowest unoccupied molecular orbital)-induced local density of states of the C_, similar to the recent STM image of the C60 on the Cu(111)1 x 1 surface and that (2) the field evaporation occurs as a C_ molecule, in glaring contrast to the recent report by Ohmae et al

Stripe charge ordering in SrO-terminated SrTiO3(001) surfaces

The local electronic structure of the SrO-terminated SrTiO3(001) surface was explored using scanning tunneling microscopy. At low bias voltages in the empty states, a unidirectional structure with a periodicity of 3 unit cells, superimposed on a c(2 x 2) reconstructed structure, was found to develop along the crystallographic a axis. This structure indicates a charge-ordered stripe induced by carrier doping from oxygen vacancies in the SrO and the subsurface TiO2 planes. In the filled states, localized deep in-gap states were observed in addition to large energy gaps in the tunneling spectra. This result represents inelastic tunneling due to significant electron-lattice interaction associated with unidirectional lattice distortion in the SrO-terminated surface.Comment: 6 pages, 5 figures, accepted for publication in PR

Stability of Sb line structures on Si(001)

Structure and stability of Sb-dimer linear chains on the Si(001) surface are studied by means of ab initio quantum-mechanical molecular dynamics using pseudopotentials. It is confirmed that the model comprising a double core of seven-membered rings of silicon for Bi/Si(001) nanolines is indeed one of the most stable structures energetically, and it also explains Sb/Si nanolines. Moreover, it is clear that stability of the odd-membered-ring (5-7-5) structure will decrease as the group-V adatom changes from Bi to Sb, and disappear for As/Si due to the size effect

Orientational Ordering of C_<60> Adsorbed on the Cu(111)1x1 Surface Studied by the FI-STM

The adsorption of C_ molecules on the Cu(111)1x1 surface has been investigated by field ion-scanning tunneling microscopy (FI-STM). At the initial stage adsorption, C_ molecules are mobile on the terrace at room temperature and segregate to the steps to form linear chains. With increasing coverage, two-dimensional islands form with a close-packed configuration. Upon monolayer adsorption, highly ordered Cu(111)-(4x4)-C_ overlayer forms. Bias voltage-dependent STM images of the individual C_ molecule show unique intramolecular structures. The adsorption geometry is determined by analyzing the STM images and the intramolecular structures are interpreted as the local density of the states of C_ interacting with the substrate

Scanning Tunneling Microscopy of the GaAs(001) Surface Reconstructions(STM-GaAs)

The atomic structure of the GaAs(001) surface has been disputed since molecular beam epitaxy (MBE) technique was developed in the earlier nineteen sixties. The invention of scanning tunneling microscopy (STM) with its real-space atom-resolution capability, has revolutionized the situation. This paper reviews the STM investigations of the principal reconstructions found on the GaAs(001) surface, As-rich 2x4 and 2x6, Ga-rich 4x2 and 4x6. These studies, together with advanced theoretical analyses, have finally resulted in establishment of a unified structural model for various reconstructions, with which we can explain most of the observations and long-standing controversies about the atomic structures and surface stoichiometries

Initial Stage of Molecular Adsorption on Si(100) and H-terminated Si(100) Investigated by UHV-STM(STM-Si(001))

We have investigated the initial stage of adsorption of a conjugated aromatic compound, 1, 4-bis[β-pyridyl-(2)-vinyl]benzene (P2VB), on the clean Si(100)-2×1 surface and the hydrogen terminated Si(100)-2×1-H surface by ultra-high-vacuum (UHV) scanning tunneling microscopy (STM). We found adsorbed molecules cannot migrate on the chemically active Si(100)-2×1 surface, while they can migrate on the chemically inactive hydrogen terminated Si(100)-2×1-H surface until they are trapped to hydrogen-missing dangling bonds. On the clean Si(100)-2×1, we observed four different adsorption directions. An individual molecule appears as two or three bright spots, the brightness and distance between bright spots varying for different cases. Through structural analysis and bias-voltage-dependent STM images, we conclude that the electronic states of Si dimers modulated by the adsorbed molecules are observed instead of the molecules themselves. A simple estimation by considering only the molecular size and shape reproduces the distribution of four different kinds of adsorption structures we observed

Atomic-scale visualization of initial growth of homoepitaxial SrTiO3 thin film on an atomically ordered substrate

The initial homoepitaxial growth of SrTiO3 on a (\surd13\times\surd13) - R33.7{\deg}SrTiO3(001) substrate surface, which can be prepared under oxide growth conditions, is atomically resolved by scanning tunneling microscopy. The identical (\surd13\times\surd13) atomic structure is clearly visualized on the deposited SrTiO3 film surface as well as on the substrate. This result indicates the transfer of the topmost Ti-rich (\surd13\times\surd13) structure to the film surface and atomic-scale coherent epitaxy at the film/substrate interface. Such atomically ordered SrTiO3 substrates can be applied to the fabrication of atom-by-atom controlled oxide epitaxial films and heterostructures