An Unbiased Peek At ZD6474

Nevertheless, 6:6-top C60, which prefer to be surrounded by unlike NN (unl-NN), and hex-vac C60, which prefer to be surrounded by like next neighbors (l-NN), form surface structures that remind of Ising-like systems (Fig. 2). This is even more astonishing, since in the standard Ising model either l-NN (interaction energy, J > 0) or unl-NN interactions (J ZD6474 In order to verify the visual impression of the STM images we performed a statistical analysis of the distribution of bright and dim C60 shown in Fig. 2. C60 molecules form a triangular surface lattice with six NN on Au(111)-substrates. In the case of a ratio x = 0.5 and J TRIB1 of l-NNrandom = 3 in the case of a random distribution of l-NN. In our case, the ratio of 6:6-top C60 amounts to x = 0.42 and the number of l-NNIsing for the bright C60 molecules, 2.25 �� 0.05, is derived from Fig. 2. This value has to be compared to a possible random distribution characterized by l-NNrandom = 2.52, which would be expected without NN interactions or at high temperatures. The obtained number of l-NNIsing from Fig. 2 shows a small, but statistically significant deviation from a random distribution and points to the fact, that the disordered (2��3 �� 2��3)R30�� superstructure of C60 on Au(111) can be described by an Ising-like model. This indicates that in the discussed superstructure small NN interactions exist and that the system does not adopt the lowest possible energy in the disordered (2��3 �� 2��3)R30�� superstructure. Influence of the deposition procedure on the C60 superstructure formation Starting from the usually observed disordered R30�� superstructure a lower energy state could be reached if the ratio of dim C60 molecules in a hex-vac position could be increased and thus, finally a pure domain of dim C60 molecules would result. This suggestion is supported by the superstructures selleck compound of dim C60 molecules observed on Pt(111) and Cu(111) surfaces after an annealing step at 1100 K [22] and 560 K [34], respectively. Moreover, a successive change from bright to dim C60-molecules on the Cu(111)-surface was monitored during annealing cycles and attributed to a reconstruction [32]. However, a domain of dim C60 molecules in hex-vac positions on the Au(111) surface can only be assembled, if enough vacancies are available. In order to create the required vacancies elevated temperatures can advantageously be applied during the C60 monolayer preparation process, as shown in [11] or [16].