Orientation and constraints of endohedral lanthanum inLa@C82molecules adsorbed on Cu(111)

Abstract

The orientation of the endohedral La atom in La@C 82 adsorbed on Cu͑111͒ has been determined using the normal-incidence x-ray standing wave ͑NIXSW͒ technique. The NIXSW measurements were carried out using both the normal ͗111͘ and 70.5°off-normal ͗1 11͘ Bragg reflections. The La ͗1 11͘ profiles of the La@C 82 monolayer and submonolayers are found to be similar to the ͗111͘ profile of the multilayer, while the ͗111͘ profiles of the monolayer and submonolayers are distinctly different with much lower peak height. This indicates significant ordering of the La atoms in the monolayers with respect to height above the Cu surface but little lateral ordering. The results of curve fits to the monolayer profiles show that the La atoms are regionally located at 1.62 ͑Ϯ0.77͒ Å above an extended scattering plane from the crystal. Cooling the monolayers to a temperature of 170 K increases ordering of the La atoms with respect to height above the surface. The NIXSW results demonstrate that the endohedral molecules adopt a restricted orientation upon adsorbing on the surface and the La atom resides on either the upper or lower half of the cage. Theoretical calculations show that the most stable La positions are located in the top half of the fullerene cage, which supports the La upper configuration. The results are explained in terms of electrostatic interactions between the endohedral atom, the fullerene cage, and the substrate.

Does an Encapsulated Atom ‘feel' the Effects of Adsorption?: X-ray Standing Wave Spectroscopy of Ce@C82 on Ag(111)

“…The absence of any appreciable difference in the XSW profile for a Ce@C 82 monolayer measured at 293 K compared to that measured at 100 K suggests that static disorder associated with the distribution of the Ce intramolecular positions underlies the lack of any coherence in the XSW signal. In addition, there were no dramatic changes in peak height between bulk and monolayer films as reported very recently for La@C 82 on Cu(111), and interpreted in terms of an increase in coherent fraction. This may be due to differences in the monolayer preparation procedure; in our case the endohedral fullerenes were deposited onto a Ag(111) crystal held at room temperature and subsequently annealed, whereas in ref the sample was held at 280 °C during the evaporation.…”

“…In addition, there were no dramatic changes in peak height between bulk and monolayer films as reported very recently for La@C 82 on Cu(111), and interpreted in terms of an increase in coherent fraction. This may be due to differences in the monolayer preparation procedure; in our case the endohedral fullerenes were deposited onto a Ag(111) crystal held at room temperature and subsequently annealed, whereas in ref the sample was held at 280 °C during the evaporation. Isomeric variations in the Ce@C 82 film may also be responsible.…”

“…To date there has been just one study, performed by Ton-That et al . , to locate the encapsulated atom within an adsorbed endohedral fullerene. This group observed differences in the intensity of the XSW profiles for multilayer and monolayer films which were interpreted as arising from increased order in the La positions.…”

Molecular Electronics with Endohedral Metallofullerenes: The Test Case of La2@C80 Nanojunctions

“…The above results are in agreement with DFT calculations on La 2 @C 80 (Si 2 H 4 (CH 2 )) 2 13 and recent experimental evidence pointing at a restricted positioning of the La atom in La@C 82 molecules adsorbed on Cu(111) surfaces . The latter is explained as the combined effect of electrostatic interactions and the restricted orientation of the adsorbed molecules with respect to the copper surface …”

Scanning tunneling microscopy study of molecular growth structures of Gd@C82on Cu(111)

“…[1][2][3][4][5][6][7] Moreover, in fullerene-based electronic applications, the molecular orientation, adsorption geometry, and packing density of fullerene strongly influence the conductance, and the formation of well-ordered fullerene structures can greatly improve the performance of the device, which motivates a considerable amount of research on the adsorption, structures, and/or self-assembly of fullerene-based adlayers on metal surfaces. [8][9][10][11] For fullerenes absorbed on a metal substrate, the hybridization of molecular frontier orbitals with the wave functions of the underlying metal substrate results in an inhomogeneous charge distribution around the carbon cage, which further affects the orientations and nucleation behaviors as well as the electronic structures of the fullerenes. [10][11][12][13][14][15][16] Here, we present a scanning tunneling microscopy (STM) study of the molecular growth and nucleation behaviors of Gd@C 82 molecules on Cu(111).…”