ABSTRACT
A method has been developed for the attachment of a dithiolane group to endohedral metallofullerenes via a 1,3-dipolar cycloaddition reaction. This sulfur-containing functional group serves as an anchor, enabling efficient immobilisation of endohedral fullerenes on Au(111) surfaces at room temperature, directly from the solution phase. The functionalised fullerenes form disordered monolayers that exhibit no long-range ordering, which is attributed to both the strong bonding of the dithiolane anchor to the surface and to the conformational flexibility of the functional group. Endohedral fullerenes Er(3)N@C(80) and Sc(3)N@C(80) have been used as models for functionalisation and subsequent surface deposition. Their chemical reactivity towards dithiolane functionalisation and their surface behaviour have been compared to that of C(60). The endohedral fullerenes appear to be significantly less reactive towards the functionalisation than C(60), however they bind in a similar manner to a gold surface as their dithiolane terminated C(60) counterparts. The optical activity of Er(3)N@C(80) molecules is preserved after attachment of the functional group. We report a splitting of the endohedral Er(3+) emission lines due to the reduction in symmetry of the functionalised fullerene cage, as compared to the highly symmetrical icosahedral C(80) cage of pristine Er(3)N@C(80).
ABSTRACT
We report on the use of interferometric autocorrelation measurements to investigate the non-linear absorption processes evident in single InGaN/GaN quantum dots. The near quadratic excitation intensity dependence of the photoluminescence signal in conjunction with the asymmetric collinear autocorrelation trace unambiguously confirms the process as being one involving two photons via an intermediate virtual state. These results highlight the inherently non-linear optical properties of these structures.
