Observation of a Metastable Honeycomb Arrangement of C₆₀ on Ni(111) with (7 × 7) Periodicity: Tailoring an Interface for Organic Spintronics

Abstract

Hybrid nanostructures in which organic molecules are interfaced with metal surfaces hold promise for the discovery of intriguing physical and chemical phenomena, as well as for the development of innovative devices. In this frame, it is crucial to understand the interplay between the structural details of the interface and the electronic properties of the system. Here, an experimental investigation of the C 60 /Ni(111) interface is performed by means of scanning tunneling microscopy/spectroscopy (STM/STS) and low-energy electron diffraction (LEED). The deposition of C 60 at room temperature, followed by high-temperature annealing, promotes the stabilization of two different phases. A hitherto unreported phase forming a (7 × 7) honeycomb overlayer coexists with the well-known (4 × 4) reconstruction. Highly resolved STM images disclose the adsorption geometry of the molecules for both phases. STS reveals that the electronic properties of C 60 /Ni(111) are strongly influenced by the morphology of the interface, suggesting the possibility of tuning the electronic properties of the organic/inorganic heterostructures by adjusting the structural coupling with the substrate. This achievement can be important for hybrid magnetic interfaces, where the harmonization between the molecular and the magnetic orders can enhance the development of hybrid magnetic states.

C60 Adsorbed on Ni(111) and Co(0001) Surfaces

“…For this reason, we did not try annealing at higher temperatures. Therefore, in this study, did not observe the recently reported (7 × 7) overlayer structure obtained by annealing at 670 K. 17 This structure is remarkably similar to the (7 × 7) phase we report above for C 60 /Co(0001). The identified adsorption sites are identical, with 2 of the C 60 in the unit cell in alternate 3-fold sites and the remaining C 60 in a 2-fold degenerate atop site.…”

“…We describe in detail a (7 × 7) phase for unannealed C 60 /Co(0001), finding that the three C 60 molecules in the unit cell occupy three distinct adsorption sites: two hollow sites with 3-fold symmetry and one atop site with 6-fold symmetry. This is similar to the (7 × 7) C 60 / Ni(111) phase observed by Picone et al 17 In our measurements of C 60 /Ni(111), identification of the molecular orientations was not possible. Due to the similar lattice parameters of Co(0001) and Ni(111), we conclude that the perpendicular orientation is (7 × 7) on both substrates.…”

“…We did not observe the metastable (7 × 7) C 60 /Ni(111) structure observed by Picone et al 17 with STM; we attribute this to the metastability of the phase combined with differences in experimental conditions. Postannealing, both systems exhibit B and D (bright and dim) molecules.…”

“…12 More recently, a metastable (7 × 7) superstructure of C 60 /Ni(111) was observed. 17 Previous work on Co(0001) has been on a thin film of Co(0001) atop Au(111), in an effort to circumvent the martensitic transformation that occurs in bulk Co. 18 Molecular growth systems on simple metals generally form domains with several degrees of freedom. These include translational degeneracy, due to molecular superstructure unit cells covering multiples of the substrate unit cell, and rotational degeneracy, which occurs when the orders of rotational symmetry differ between substrate and adsorbate, and is the product of these orders of rotational symmetry.…”

Self-assembly of C60 on a ZnTPP/Fe(001)–p(1 × 1)O substrate: observation of a quasi-freestanding C60 monolayer

“…Chemisorption is the typical scenario for molecules stabilized on metallic substrates. Here, the hybridization between the molecular orbitals and the electronic states of the substrate generally modifies the intrinsic properties of the molecules, inducing the broadening of the molecular resonances, the narrowing of the band gap, and the development of interface states [ 15 – 16 ]. The ability to tailor the degree of electronic coupling between the molecules and the substrate is of utmost importance when it comes to embedding the interface in a specific application.…”