-
[show abstract]
[hide abstract]
ABSTRACT: Adsorption and electronic structure of octithiophene (8T) molecules on Cu(III) and Au(III) surfaces are investigated using scanning tunneling microscopy (STM) and spectroscopy (STS) at room temperature. We find a large difference in adsorption behavior of 8T molecules on the two surfaces. At the initial stage of adsorption, 8T molecules are stabilized in the form of molecular chain on a terrace of Cu(III), whereas neither such chain structure nor isolated 8T molecules have been observed on a terrace of Au(III). By increasing the amount of adsorbed molecules, a disordered monolayer film is formed on Cu(III) while a well-ordered monolayer film is formed on Au(III). From the spectroscopic investigations using bias-dependent STM images and STS spectra and by comparing the data with theoretical calculations, it is found that the electronic property of 8T molecules in the molecular chain on Cu(III) is different from that of a free-standing 8T molecule while that in the monolayer film on Au(III) keeps original character of the free-standing 8T molecule. The present study shows that adsorption of 8T molecules on Cu(III) results in a formation of adsorption-induced states near the Fermi level.
Journal of Nanoscience and Nanotechnology 05/2012; 12(5):4007-11. · 1.56 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The creation of a molecular-scale covalently bound assembly of fullerene C(60) molecules has been precisely controlled in ultrathin multilayer films of C(60) molecules. When a negative sample bias voltage is applied to a tunneling junction between the C(60) film and the tip of a scanning tunneling microscope (STM), a C(60) molecule beneath the tip covalently bonds to an adjacent molecule in the underneath layer. We show that such a chemical reaction is not necessarily limited to the top and second layers of the C(60) film and that the resulting C(60) oligomer can be tuned to form a dimer, trimer, tetramer, or pentamer; the number of interconnected C(60) molecules increases one by one upon increasing the magnitude of the local electric field under the STM tip. The created oligomers are linear chains of C(60) molecules starting from the top layer and aligned toward the interface layer in the multilayer C(60) films. We consider that the electrostatic negative ionization of C(60) molecules and its spatial distribution in the multilayer C(60) film are critical factors in achieving size-tunable oligomerization.
ACS Nano 09/2011; 5(10):7830-7. · 10.77 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The initial stage of the adsorption of octithiophene (8T) molecules on a Cu(111) surface is investigated using a scanning tunneling microscope at room temperature. We find a characteristic molecular chain structure of 8T molecules on a terrace of the Cu(111) surface, which has not been reported so far for adsorption of oligothiophene molecules on metal surfaces. Up to the adsorption of 0.26 monolayer (ML), 8T molecules in the molecular chain align with their long axis parallel to the Cu<11-2> direction. With increasing coverage, there appear 8T molecules that align with their long axis parallel to the Cu<110> direction. The appearance of different molecular orientations is understood by the decrease of the number of the adsorption sites for extending the molecular chains. Fragments of 8T molecules, such as single thiophene molecules, are also observed in this work. They are trapped only at the step edges of the Cu(111) surface at the beginning and later trapped in a small Cu(111) region surrounded by 8T molecules.Research Highlights► A characteristic molecular chain structure of 8T molecules on a Cu(111) is found. ► The molecular orientation of 8T is found to be dependent on the coverage of 8T. ► 8T molecules in the molecular chain align along the Cu<11-2> direction. ► With increasing coverage, 8T molecules aligning along the Cu<110> direction appear. ► Fragments of 8T, such as single thiophene molecules, are also observed.
Surface Science 06/2011; 605(11-12):1021-1026. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The nanoscale control of reversible chemical reactions, the polymerization and depolymerization between C60 molecules, has been investigated. Using a scanning tunneling microscope (STM), the polymerization and depolymerization can be controlled at designated positions in ultrathin films of C60 molecules. One of the two chemical reactions can be selectively induced by controlling the sample bias voltage (V(s)); the application of negative and positive values of V(s) results in polymerization and depolymerization, respectively. The selectivity between the two chemical reactions becomes extremely high when the thickness of the C60 film increases to more than three molecular layers. We conclude that STM-induced negative and positive electrostatic ionization are responsible for the control of the polymerization and depolymerization, respectively.
Journal of Nanoscience and Nanotechnology 04/2011; 11(4):2829-35. · 1.56 Impact Factor
-
Advanced Materials 04/2010; 22(14):1622-5. · 13.88 Impact Factor
-
Small 06/2008; 4(5):538-41. · 8.35 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Using two types of selective growth, selective C60 growth and selective Si growth, on a common Si(1 1 1) substrate, an array of C60 nanoribbons with controlled values of width and thickness is fabricated. On a surface that has Si(1 1 1)√3 × √3R30°–Ag (referred to as Si(1 1 1)√3–Ag hereafter) and bare Si(1 1 1) regions at the same time, the preferential growth of C60 multilayered film is recognized on the Si(1 1 1)√3–Ag region. The growth of Si selectively occurs on a bare Si(1 1 1) region if the substrate surface has C60-adsorbed and bare Si(1 1 1) regions at the same time. As a demonstration of the use of these selective growths, we fabricate an array of well-isolated C60 nanoribbons, which show a well-ordered molecular arrangement and have sizes of about 40 nm in widths and 3–4 nm in thicknesses.
Surface Science 07/2006; 600(13):2810-2816. · 1.99 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have presented a method of fabricating an array of C60 nanoribbons on a Si(111) surface and have investigated the electron-beam-induced polymerization of C60 nanoribbons using scanning tunneling microscopy (STM) and spectroscopy (STS). By selective growth of C60 multilayers on the terrace of a misoriented Si(111)√3×√3R30°-Ag surface, a uniformly oriented array of C60 nanoribbons having the dimensions of 40 nm×4–5 nm (width×thickness) has been fabricated. The length of these nanoribbons exceeds several micrometers. The cluster-shaped C60 oligomer has been created on the nanoribbons after electron beam irradiation. In the case of the oligomer, we have observed a higher electron density near the Fermi level than in the case of the nonpolymerized C60 molecules.
Thin Solid Films · 1.89 Impact Factor
