Trimetallic nitride containing fullerenes are of potential use in the field of optoelectronics and quantum information processing. The great advantage is that there is no cage absorption at the frequencies where some clusters are optically active, allowing direct and selective optical interaction with an ion encapsulated within the fullerene cage [1, 2]. Direct optical excitation resulting in luminescence may provide a possible way for the realization of fullerene-based quantum computation schemes based on optical readout methods of endohedral spin qubits [3]. The practical implementation of such schemes requires the controlled fabrication of well-ordered one-dimensional or two-dimensional arrays of endohedral fullerenes on suitable substrates.
Here, we have studied the self-assembled formation of two-dimensional islands and molecular detail of Er3N@C80 and Sc3N@C80on a variety of substrates including Au(111) layers on mica, silver-terminated as well as clean Si(111) and Si(001). In-situ variable-voltage scanning tunnelling microscopy (STM) imaging at ambient and liquid nitrogen temperature as well as scanning tunnelling spectroscopy (STS) have been used to investigate the bias dependence of the fullerene contrast and to examine substrate-fullerene interactions.
The fullerenes were evaporated in-situ from K-cells attached to a variable-temperature UHV-STM system and subsequently imaged both at room temperature and liquid nitrogen temperature. At room temperature, the fullerenes self-assemble into monolayer-high hexagonal close-packed islands on Ag-passivated Si(111) whereas annealing at elevated temperatures (250-300°C) is necessary for the self-assembly of close-packed islands on Au(111). Intra-molecular resolution of the fullerenes has been achieved at liquid nitrogen temperature on Ag/Si(111) and already at room temperature on Si(001), when the rotation of the fullerenes is frozen. Electronic contrast effects and substrate-fullerene interactions have been investigated using STS and bias-dependent STM.
[1] M.A.G. Jones et al., Chem. Phys. Lett. 428 (2006) 303.
[2] R.M. Macfarlane et al., Chem. Phys. Lett. 343 (2001) 229.
[3] S.C. Benjamin, et al., J. Phys.: Cond. Matter 18 (2006) S867.
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