Auto-assemblage et propriétés magnétiques des nano-aimants moléculaires Mn12 et des clusters organo-bimétalliques sur la surface Au(111)
NAITABDI, Ahmed (2004) Auto-assemblage et propriétés magnétiques des nano-aimants moléculaires Mn12 et des clusters organo-bimétalliques sur la surface Au(111). Thèses de doctorat, Université Louis Pasteur.
Plein texte disponible en tant que :
My thesis work aimed to develop new materials with a view to potential applications in high density information storage. For this reason, two molecular systems possessing interesting physical properties were self-assembled on gold surfaces to obtain well-ordered magnetic structures. Single Molecule Magnets: In the field of molecular magnetism, recent advance in organometallic and coordination chemistry has allowed the synthesis of crystals of well-characterized molecular clusters. This approach leads to the emergence of a wide variety of molecule-based magnets with promising physical properties. In this topic, the high spin Single Molecule Magnets (SMMs) are much studied and attract continuous interest. The magnetic bistability of these systems at low temperature makes them very attractive as elementary units for high density data storage applications and in the design of quantum computers. Then, the main challenge consists in assembling monolayers of periodically arranged SMMs on a substrate. For this reason we have developed an approach leading to self-assembled monolayers of single molecule magnets Mn12Pivalates16, (Mn12Piv16), on functionalized gold surface. As a first step in this approach, the prefunctionalization of the Au(111) was achieved using an organosulfur acid which coordinates strongly to the gold. This self-assembled monolayer functionalized with carboxylic acid groups corresponds to a defect free (√3 × √3)R.30° organization of the sulfur head groups on Au(111). The second step of this grafting processes corresponds to a covalent anchoring of the Mn12Piv16 SMMs to the underlying organosulfur acid monolayer. This is achieved by exchange reactions between the pivalate ligands and the carboxylic terminal groups of the organosulfur acid. Then, the achieved SMMs film exhibits a self-organized assembly of molecules with coherence domains of 40 nm. Furthermore, the hysteresis loops obtained from the SQUID measurements confirm the magnetic behavior of the grafted film. A closer analysis however reveals that the quantum tunneling features of the magnetization are smeared out most probably due to the angular distribution of the magnetic anisotropy axes of the molecules. Hetero-organo-bimetallic clusters: One of the main objectives in the field of high-density recording media is the development of microscopically-controlled nanoparticles and nanostructured magnetic materials involving heterobimetallic or binary cluster-substrate interfaces. This approach is based on the combination of 3d element and 4d element (strong spin-orbit coupling) which is a promising way to achieve both a large magnetic moment and high anisotropy. These clusters should allow storage of bits on an always smaller number of particles until the ultimate goal of bit storage on a single cluster with the smallest possible size is achieved at room temperature. We developed a new strategy which exploits the ability of coordination chemistry to provide organo-metallic clusters with well defined proportion AxBy (x,y = 1…4) of transition metal atoms. A two step approach was used, first the molecules were grafted on the gold surface by means of sulfur ligands and second, the system was submitted to thermal annealing to strip off the ligands. For this purpose, we achieved the self-assembling of [HRuCo3(CO)11(PPh2C2H4SH)] clusters on Au(111) surface. The molecular arrangement in the self-assembled layer was characterised by STM which shows a locally ordered-structure. Subsequently, the thermal annealing is performed in UHV so as to recuperate the RuCo3 metallic monolayer. Thus, from XPS measurements, it is found that Co and Ru features converge towards metallicity and that the initial stoichiometry of the RuCo3 clusters is preserved.
Administrateurs de l'archive uniquement : éditer cet enregistrement