ABSTRACT
We report a combined reflectance difference spectroscopy and scanning tunneling microscopy study of ultrathin α-sexithiophene (6T) films deposited on the Cu(110)-(2×1)O surface. The correlation between the layer resolved crystalline structure and the corresponding optical spectra data reveals a highly sensitive dependence of the excitonic optical properties on the layer thickness and crystalline structure of the 6T film.
Subject(s)
Copper/chemistry , Heterocyclic Compounds, 4 or More Rings/chemistry , Thiophenes/chemistry , Microscopy, Scanning Tunneling , Molecular Structure , Optical Phenomena , Surface PropertiesABSTRACT
Reflectance difference spectroscopy (RDS) is applied to follow in situ the preparation of clean and carburized W(1 1 0) surfaces and to study the temperature-induced transition between the R(15 × 3) and R(15 × 12) carbon/tungsten surface phases. RDS data for this transition are compared to data obtained from Auger-electron spectroscopy and low-energy electron diffraction. All techniques reveal that this transition, occurring around 1870 K, is reversible with a small hysteresis, indicating a first-order-like behaviour. The present results also prove a high surface sensitivity of RDS, which is attributed to the excitation of electronic p-like surface resonances of W(1 1 0).
ABSTRACT
We have studied the growth of para-sexiphenyl (p-6P) on the Cu(110)-(2×1)O surface using reflectance difference spectroscopy (RDS) in combination with scanning tunneling microscopy (STM). The evolution of the optical anisotropy reveals that the growth of p-6P on the Cu(110)-(2×1)O surface at room temperature follows the Stranski-Krastanov growth mode with a two monolayer thick wetting layer. During all stages of growth, the p-6P molecules are well orientated with their long molecular axis aligned parallel to the Cu-O rows along the [001] direction of the Cu(110) substrate. The high packing density of the p-6P molecules in the first and second monolayer evidenced by RDS and STM is believed to be responsible for the switch from layer-by-layer to three-dimensional island growth.