Antiferromagnetic molecular Cr7Ni rings have been recently proposed as candidates qubits. We have obtained, for the first time, a two-dimensional distribution of individually accessible Cr7Ni heterometallic rings on gold surface exploiting the direct grafting of sulphur-functionalized Single Molecule Magnets (SMM) [1]. Two different functionalizations have been synthesized: the Cr7Ni-3tpc cluster which presents 16 isotropic thiophene-carboxylate ligands and the Cr7Ni-thiobutane cluster which presents a single ammine-thiol ligand fixed with an H-bond at the centre of the ring, which is devised to force the molecule to graft with its axis normal to the surface. Susceptibility (?? measurements on dried powders show a temperature dependence of the ?? product quite close to that of the original Cr7Ni with small deviations probably due to a slightly different exchange Cr-Cr(Ni) coupling. A sub-monolayer distribution of functionalized Cr7Ni clusters were deposited from liquid phase on Au(111) surface and characterized by means of scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) on campus, X-ray absorption spectroscopy (XAS), X-ray Magnetic Circular Dichroism (XMCD) and X-ray Linear Dichroism (XLD) at the ESRF-ID8 beam-line. Combined STM and XPS investigations show that, the highest packing-level is obtained for the Cr7Ni-3tpc system, where about 15-20% of the total surface is occupied by well-isolated clusters, while for the Cr7Ni-thiobutane system the coverage is 4-6%. We observe, in both cases, the formation of a first thiol SAM due to the competition between the chemisorption of the intact Cr7Ni clusters and that of the free thiophene/thiobutane broken ligands. We have recently characterized the magnetic properties of those SMM's grafted on gold by means of XMCD (T=10K, Hmax=5T), while the cluster orientation has been investigated by XLD. By comparing the XMCD spectra of the monolayers with those of the thick films, we proved that the interaction of the cluster with the gold substrate and the low dimensionality do not significantly affect the magnetic properties of the Cr7Ni rings.
Isolated heterometallic Cr7Ni rings grafted on Au(111)
V Corradini;R Biagi;V De Renzi;A Ghirri;M Affronte;
2006
Abstract
Antiferromagnetic molecular Cr7Ni rings have been recently proposed as candidates qubits. We have obtained, for the first time, a two-dimensional distribution of individually accessible Cr7Ni heterometallic rings on gold surface exploiting the direct grafting of sulphur-functionalized Single Molecule Magnets (SMM) [1]. Two different functionalizations have been synthesized: the Cr7Ni-3tpc cluster which presents 16 isotropic thiophene-carboxylate ligands and the Cr7Ni-thiobutane cluster which presents a single ammine-thiol ligand fixed with an H-bond at the centre of the ring, which is devised to force the molecule to graft with its axis normal to the surface. Susceptibility (?? measurements on dried powders show a temperature dependence of the ?? product quite close to that of the original Cr7Ni with small deviations probably due to a slightly different exchange Cr-Cr(Ni) coupling. A sub-monolayer distribution of functionalized Cr7Ni clusters were deposited from liquid phase on Au(111) surface and characterized by means of scanning tunneling microscopy (STM) and X-ray photoemission spectroscopy (XPS) on campus, X-ray absorption spectroscopy (XAS), X-ray Magnetic Circular Dichroism (XMCD) and X-ray Linear Dichroism (XLD) at the ESRF-ID8 beam-line. Combined STM and XPS investigations show that, the highest packing-level is obtained for the Cr7Ni-3tpc system, where about 15-20% of the total surface is occupied by well-isolated clusters, while for the Cr7Ni-thiobutane system the coverage is 4-6%. We observe, in both cases, the formation of a first thiol SAM due to the competition between the chemisorption of the intact Cr7Ni clusters and that of the free thiophene/thiobutane broken ligands. We have recently characterized the magnetic properties of those SMM's grafted on gold by means of XMCD (T=10K, Hmax=5T), while the cluster orientation has been investigated by XLD. By comparing the XMCD spectra of the monolayers with those of the thick films, we proved that the interaction of the cluster with the gold substrate and the low dimensionality do not significantly affect the magnetic properties of the Cr7Ni rings.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
