Template Ordered Open-Grid Arrays of Paired Endohedral Fullerenes

Abstract

Developing useful molecular systems, such as planar networks of molecules for novel molecular-electronic architectures, 1-4 requires the ability to control the way molecules assemble at surfaces. Many techniques exploit non-covalent directional bonding interactions between molecules, such as hydrogen bonding, to facilitate the molecular assembly process. [5][6][7][8][9] However, if the molecules lack such directional bonding attributes then it becomes difficult to develop novel molecular architectures using this approach. Fullerenes 10 are molecules that do lack these directional bonds but are otherwise very attractive candidates for molecular based nanotechnologies. Endohedral fullerenes 11 are of particular interest in this area, because the atomic species bounded within the fullerenes could be manipulated for storing and processing bits of information. For example, the magneto-optical activity 12 of the Er 3 N@C 80 molecule 13 ( Figure 1a) may prove useful in solid-state quantum information processing systems. [2][3][4]14 Overcoming the challenge of coercing endohedral fullerenes to order into useful spatial configurations can be achieved through template-assisted assembly. A successful template requires the surface to be made up of patterned arrays of bonding sites for the fullerenes to adsorb onto. Impressive demonstrations of this have been achieved using pre-assembled molecular templates on metal or metal-terminated substrates. [15][16][17][18] Here we report how oxide crystal surfaces can be used as a template to controllably order endohedral fullerenes into two-dimensional (2D) open-grid arrays. This is compared to the ordinary close-packed ordering of endohedral fullerenes. The template is a nanostructured surface phase of (001) strontium titanate, 19 and the endohedral fullerenes are Er 3 N@C 80 molecules 13 (Figure 1a).The surfaces are prepared through an Ar + sputtering and annealing procedure, described in earlier work, 19 on 0.5%-weight Nb-doped SrTiO 3 (001) single crystals in ultrahigh vacuum (UHV) conditions. Er 3 N@C 80 molecules, or fullerenes, were deposited onto the surfaces from the vapor phase. Createc Knudsen cells, heated at 480°C, were used to evaporate Er 3 N@C 80 molecules for 20-30 min, allowing 0.15-0.20 monolayer coverage for each deposition. Er 3 N@C 80 has advantages over other endohedral fullerenes 3,4 (e.g. N@C 60 ) in that M 3 N@C 80 species (M ) metal forming a planar M 3 N species) are thermally stable 20,21 and can be readily evaporated onto heated substrates in UHV. The template patterns and molecular ordering are investigated through UHV scanning tunneling microscopy (STM) at room temperature. Etched W tips are used for imaging the sample surfaces at room temperature with a bias voltage applied to the sample.Close-packed surface ordering of fullerenes is achieved on a c(4 × 2) surface reconstruction, 22,23 as shown in the STM images of Figure 1b,c. The c(4 × 2) surface was formed by annealing at 1090°C for 30 min after sputtering. Er 3 N@C 80 is deposited on the c(4 × 2)...

Self-assembly of trimetallic nitride template fullerenes on surfaces studied by STM

“…The formation of planar hexagonal close-packed islands at elevated temperatures ($250°C) has also been observed for Er 3 N@C 80 on the non-stoichiometric SrTiO 3 (0 0 1)-c(4 · 2) surface [8]. However, on this surface the islands self-assemble on the terraces rather than on the step edges and do not exhibit an epitaxial relationship with the substrate.…”

“…Encapsulation of fullerenes in a carbon nanotube provides a means for producing one-dimensional arrays, whilst direct deposition onto a surface can create twodimensional networks. Custom-made two-dimensional networks with controlled spacings between fullerenes may be created using supramolecular [5][6][7] or structural [8,9] templates. Regular arrays of qubits open the door for global addressing schemes for quantum information processing, and two-dimensional networks have the advantage of being able to employ much more powerful error correction techniques [10].…”

Coexisting Chiral Two-Dimensional Self-Assembled Structures of 1,2,3,4-Tetrahydronaphthalene Molecules: Porous Pinwheel Nanoarchitecture and Close-Packed Herringbone Arrangement

“…One way to privilege the growth of one of the networks would be to change the supporting surface to tune the molecule−surface interaction. 70,71 ■ CONCLUSION…”

Direct CVD Growth of Graphene on Technologically Important Dielectric and Semiconducting Substrates

“…Therefore, direct growth of graphene on the surface of high‐k dielectric and scatter‐screening dielectric substrates becomes significant. SrTiO 3 (STO), a transparent, high‐k perovskite dielectric may have great thermal stabilities and potentials 60, 61, 62. Sun et al demonstrated the metal‐catalyst free direct CVD growth of graphene on STO (001) substrates using a simple APCVD technique (Ar/H 2 /CH 4 :100/50/2.5 sccm) 63.…”