Contributed talk

Synthesis and Characterization of Magnetic Aza-Triangulene Nanostructures
Francisco Romero-Lara¹, Alessio Vegliante¹, Manuel Vilas-Valera², Lorenz Meyer¹, Unai Uriarte¹, Héctor Briongos¹, Adrián Martínez², Niklas Friedrich², Dongfei Wang¹, Ricardo Ortiz³, Patrick Calupitan^3,4, Fabian Schulz¹, Natalia Koval¹, Martina Corso⁴, Emilio Artacho¹, Thomas Frederiksen³, Diego Peña², José Ignacio Pascual¹

1 CIC nanoGUNE BRTA, Donostia, Spain.
2 Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares, Santiago de Compostela, Spain.
3 Donostia International Physics Center, Donostia/San Sebastián, Spain
4 Centro de Física de Materiales CSIC-UPV/EHU, Donostia/San Sebastián, Spain

The emergence of spin states in triangular-shaped graphene fragments with zig-zag edges (triangulenes) is a conceptually attractive theoretical proposal from decades ago. Thanks to the recent development of on-surface synthesis strategies, triangulene nanostructures showing magnetic interactions can now be fabricated on metal substrates with atomic precision. In this work, we present the synthesis and characterization of aza-[5]-triangulene (A5T) and π-extended-aza-triangulene (ex-AT) on Au(111) surface. Theoretical models predict such structures to have more than two unpaired electrons, which could result in large spin states and/or magnetic interactions. Combined low temperature scanning tunnelling microscopy (LT-STM), and low temperature atomic force microscopy (LT-AFM) measurements using CO-functionalized tips confirm the precise structure of the triangular flakes. Scanning tunnelling spectroscopy (STS) was used to directly prove the magnetic character by measurements of the Kondo effect and spin excitations. Experimental findings are further corroborated by the predictions of advanced theoretical models based in density functional theory (DFT), Hubbard Hamiltonian models and the anisotropy of the current induced density (ACID). The N heteroatom substitution modifies the spin ground state of the molecules with respect to their undoped counterparts.

Figure 1: Bond-resolved images of A5T and ex-AT showing the chemical structures as insets. Shown STS spectra were recorded on the coloured dots. A5T shows a weak zero-bias resonance while ex-AT shows a sharp and intense zero-bias resonance and inelastic excitations at ±100mV.