摘要:

We present a detailed STM study on the atomic structure and electronic properties of dysprosium‐silicide nanowires, which can be formed on Si(001) by self assembly. Under ideal circumstances, these nanowires cover the whole silicon surface with a well‐ordered 2×7 superstructure. Using voltage dependent STM we are able to develop an atomic structure model. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639791

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We have investigated the growth of Co on Ag/Cu one‐dimensional, periodic striped nanostructures. The latter are obtained by evaporation of submonolayer amounts of Ag on top of vicinal Cu(111) surfaces, which leads to periodic faceting with Ag‐covered stripes and stepped Cu bands. Ag stripe width and superlattice periodicity is tuned with substrate miscut and Ag coverage. Nucleation and growth of Co proceeds differently on Ag or Cu stripes, although both in a similar way as on flat Ag‐covered and bare Cu(111), respectively. We describe how, by tuning the Ag/Cu mask one could produce arrays of linear Co structures, which eventually could display uniaxial magnetic properties. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639792

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We carried out STM/STS studies of Ag structures grown on Bi2Te3surface at different temperatures. This kind of investigation had not been attempted by others. We got images of surface of the substrate in many scales from micrometers to nanometers, which showed a layered structure of Bi2Te3, with many monoatomic terraces. We found agreement between measured heights and corresponding bulk crystal structure derived from X‐ray data. Using STS we carried out examination of the electronic structure of the substrate and created nanostructures. We observed different I‐V characteristics and contrast on CITS maps on non‐equivalent terraces of Bi2Te3as well as between Ag structures and the substrate. The dI/dV (∼DOS) curves referring to different terraces of the substrate were compared with theoretically calculated by Larson et al. DOS of Bi p and Te‐1 p orbitals. The analysis of our results allowed us to distinguish bismuth and tellurium planes. The diameters and densities of Ag clusters deposited on the Bi2Te3substrate were dependent on the substrate temperature. The diameter was increasing with temperature, contrary to the clusters’ density (number of clusters per unit of area). © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639793

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Thin permalloy (Ni80Fe20) films of 7–20 nm thickness were grown on silicon (100) substrates within an ultra high vacuum (UHV) system. The films were subsequently characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). The STM images show a polycrystalline structure. The size of the randomly oriented crystallites was in the range of 5–25 nm. The STS data show on top of atomically flat terraces of the larger crystallites two distinct signatures. We attribute these signature to the presence of nickel and iron at the surface. The spectroscopy on top of the iron regions exhibits a distinct peak at an energy of 0.6 eV. The position of the peak shifts to 0.9 eV when moving the tip away from the iron position while it decays. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639794

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We present direct experimental evidence of the formation of a superstructure on the (111) surface of a magnetite, Fe3O4single crystal. The superstructure, which has a periodicity of 42 A and three‐fold symmetry has been observed by means of STM and LEED. Under the correct conditions of oxygen pressure and sample anneal temperature the superstructure is reproducibly formed throughout most of the sample surface. The characteristics of the superstructure, including its dependency on the tunnel bias voltage and its atomic scale periodicity, suggest that it is an electronic effect rather than a mosaic of several iron oxide phases. We explain the results in terms of the formation of giant static polarons, although we notice that other types of electron‐lattice instabilities such as charge density wave may offer possible explanations. We suggest two possible scenarios of instability linking the electron band structure and lattice distortions in magnetite: either resulting from reallocation of Fe2+and Fe3+valence states between octahedral sites or alternatively from reallocation between octahedral and tetrahedral sites. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639795

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

The (001) surface of magnetite has been studied using Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM). A clean, octahedrally terminated surface was obtained by a combination of in‐situ annealing in an O2atmosphere, Ar+ion etching and subsequent annealing in UHV. LEED exhibits a (&sqrt2; × &sqrt2;)R45° mesh. STM was carried out with probes made from antiferromagnetic MnNi. Atomically resolved images of the octahedrally terminated surface show rows, running along the [110] direction, separated by 6 Å. Along these rows two different atomic scale features are imaged, with a periodicity of 6 Å, as opposed to the 3 Å periodicity of the Fe ions expected for bulk terminated magnetite (001). A model explaining the observed symmetry in terms of charge ordering of the Fe2+and Fe3+cations, on the surface octahedral sites, is proposed. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639796

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

We report on the reconstructions induced by the segregation of contaminants at the (001) surface of Fe3O4(magnetite). Natural and artificial single crystals of magnetite were annealed in ultra high vacuum (UHV) at ∼ 1000 K for periods of time ranging from few hours to several days. This preparation procedure causes impurities to segregate to the surface. Analytical techniques such as Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and scanning tunneling microscopy (STM) were used to study this effect. From previous studies we have determined that a clean surface of magnetite exhibits a (&sqrt2; × &sqrt2;)R45° reconstruction and, following our preparation procedure, is terminated at the octahedral plane. As impurities (K and Ca) segregate to the surface, the onset of a p(1 × 3) reconstruction was observed by LEED. As the annealing time increased, it was determined by AES that only Ca contaminants were present on the surface leading to a p(1 × 4) surface reconstruction. We propose two models to explain the observed p(1 × 3) and p(1 ×4) reconstructions which are in agreement with our AES, LEED and STM results. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639797

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Cryogenic STM/STS experiments of heavily Pb‐doped Bi2Sr2Ca2CuOy(Bi2212) superconductors were performed at 4.3 K. We succeeded in observing various kinds of atomic impurities as well as nano‐scale inhomogeneity of energy gap widely seen in Bi‐based superconductors. Furthermore, we found that the distribution patterns of impurities are not correlated with the spatial map of gap values derived from STS spectra, implying that the electronic inhomogeneity is not a consequence of the randomly distributed impurity atoms. These results strongly suggest that the inhomogeneity originates from atomic‐scale disorder of excess oxygen which is invisible by STM. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639798

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

With UHV‐LT‐STM, we studied the tunneling spectroscopy of single crystals of Bi2Sr2CaCu2O8+&dgr;. We find that the inhomogeneity of electronic structure reported in the literature depends strongly on the thermal loop between different temperatures during the measurement. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639799

出版商:AIP    

年代:1903

数据来源: AIP

摘要:

Monolayers of ligand‐stabilized Au55clusters deposited on a mica substrate were investigated by non‐contact atomic force microscopy (NC‐AFM) and spectroscopy. NC‐AFM images exhibit disordered cluster monolayers with pores of varying size showing the bare substrate. Frequency‐shift and dissipation‐versus‐distance measurements on cluster layers and on a clean mica substrate were performed. Different behavior for the two samples was found. This is discussed based on specific properties presented by the two samples. © 2003 American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.1639800

出版商:AIP    

年代:1903

数据来源: AIP