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We deposit TEMPO and methane thiosulfonate spin label (MTSSL) molecules on Au(111) and study the structure and spin properties by scanning tunnelling microscopy (STM), electron paramagnetic resonance (EPR) and cyclic voltammetry (CV). Both species are stable and persistent radicals, providing the possibility to design a magnetic molecular monolayer. TEMPO is a stable radical with ferromagnetic derivatives and phases. It occurs in two conformations, boat and chair. We observe an ordered self assembly of TEMPO molecules on atomically flat Au(111) terraces by STM. The topography reveals a pattern with periodicities between 6 to 10 Angstrom, which we attribute to a crystalline molecular layer. The observed distances are in agreement with theoretical and other experimental data. The EPR spectra show TEMPO being reduced on the atomically flat Au(111) surface. Cyclic voltammograms confirm the order of magnitude of a 10-10 mol/cm2 coverage, and the TEMPO molecules forming a dense monolayer on the substrate. Structural models for the assembly are discussed. In order to prevent the unpaired electrons from binding with the Au(111) surface upon adsorption, we use another nitroxide spin label (methanethiolsulfonate spin label) exhibiting a spacer containing sulfur and therefore providing a high probability to bind directly to the Au(111) substrate. The STM topography of the MTSSL layer shows a disordered and mobile but dense layer of molecules on the Au(111) surface. The layer exhibits a high number of etching holes, characteristic for thiols, and additional smaller defects in the surface, probably due to two species present on the surface upon splitting of the disulfur. Cyclic voltammetry reveals a strong binding of the Mtssl to the surface. The EPR measurements indicate, that the MTSSL remains stable as a free radical on the surface, the unpaired electron is preserved. Interestingly, a surprisingly strong EPR signal is found for MTSSL on the surface. |