No description available.

No description available.

This thesis contains experimental studies on low dimensional systems by means of scanning tunneling microscopy (STM). These studies include investigations on dinickel molecular complexes and experiments on iron nanostructures used for the implementation of the spin-polarized scanning tunneling microscopy technique at the IFW-Dresden. Additionally, this work provides detailed information of the experimental technique (STM), from the theoretical background to the STM-construction, which was part of this doctoral work. Molecular anchoring and electronic properties of macrocyclic magnetic complexes on gold surfaces have been investigated by mainly scanning tunneling microscopy and complemented by X-rays photoelectron spectroscopy. Exchange–coupled macrocyclic complexes [Ni2L(Hmba)]+ were deposited via 4-mercaptobenzoate ligands on the surface of Au(111) single crystals. The results showed the success of gold surface-grafted magnetic macrocyclic complexes forming large monolayers. Based on the experimental data, a growth model containing two ionic granular structures was proposed. Spectroscopy measurements suggest a higher gap on the cationic structures than on the anionic ones. Furthermore, the film stability was probed by the STM tip with long-term measurements. This investigation contributes to a new promising direction in the anchoring of molecular magnets to metallic surfaces. Iron nanostructures of two atomic layers and iron-coated tungsten tips were used in order to implement the spin-polarized scanning tunneling microscopy technique at the IFW-Dresden. First of all, a systematic study of the iron growth, from sub-monolayers to multilayers on a W(110) crystal is presented. Subsequent to the well-understanding of the iron growth, the experiments were focused on revealing, for the first time at the IFW-Dresden, the magnetic inner structure of iron nanostructures. The results evidently showed the presence of magnetic domains of irregular shapes. Furthermore, SP-STM probed the bias voltage dependence of the magnetic contrast on the iron nanostructures. This technique opens up a new powerful research line at the IFW-Dresden which is promising for the study of quantum materials as molecular magnets and strongly correlated systems.

This thesis contains experimental studies on low dimensional systems by means of scanning tunneling microscopy (STM). These studies include investigations on dinickel molecular complexes and experiments on iron nanostructures used for the implementation of the spin-polarized scanning tunneling microscopy technique at the IFW-Dresden. Additionally, this work provides detailed information of the experimental technique (STM), from the theoretical background to the STM-construction, which was part of this doctoral work. Molecular anchoring and electronic properties of macrocyclic magnetic complexes on gold surfaces have been investigated by mainly scanning tunneling microscopy and complemented by X-rays photoelectron spectroscopy. Exchange–coupled macrocyclic complexes [Ni2L(Hmba)]+ were deposited via 4-mercaptobenzoate ligands on the surface of Au(111) single crystals. The results showed the success of gold surface-grafted magnetic macrocyclic complexes forming large monolayers. Based on the experimental data, a growth model containing two ionic granular structures was proposed. Spectroscopy measurements suggest a higher gap on the cationic structures than on the anionic ones. Furthermore, the film stability was probed by the STM tip with long-term measurements. This investigation contributes to a new promising direction in the anchoring of molecular magnets to metallic surfaces. Iron nanostructures of two atomic layers and iron-coated tungsten tips were used in order to implement the spin-polarized scanning tunneling microscopy technique at the IFW-Dresden. First of all, a systematic study of the iron growth, from sub-monolayers to multilayers on a W(110) crystal is presented. Subsequent to the well-understanding of the iron growth, the experiments were focused on revealing, for the first time at the IFW-Dresden, the magnetic inner structure of iron nanostructures. The results evidently showed the presence of magnetic domains of irregular shapes. Furthermore, SP-STM probed the bias voltage dependence of the magnetic contrast on the iron nanostructures. This technique opens up a new powerful research line at the IFW-Dresden which is promising for the study of quantum materials as molecular magnets and strongly correlated systems.

No description available.

La spintronique est une technique utilisant le spin des électrons dans des composants électroniques. Le principe est fondé sur des propriétés physiques telles que la magnétorésistance, (Prix Nobel 2007, Albert Fert), ce qui signifie que la conductivité électrique d'un système peut dépendre du champ magnétique appliqué au composant. Le microscope à effet tunnel polarisé en spin (SP-STM) en est un parfait exemple. Il implique l'utilisation d'une pointe et d'une surface magnétiques ; il est ainsi un outil essentiel à l'étude locale des propriétés électroniques et magnétiques des surfaces. L'objectif de notre étude est de modéliser des images de microscope à effet tunnel polarisé en spin d'une surface Cr(001) en allant au-delà de l'approximation classique de Tersoff-Hamann. Nous utilisons une approche combinant les méthodes ab initio avec le code PWSCF, couplées avec une méthode de liaisons fortes (TB) correctement ajustée. Premièrement, nous avons mené une étude approfondie des propriétés électroniques et magnétiques de la surface du chrome, en insistant sur les états de surface localisés autour du niveau de Fermi. En outre, il existe une controverse au sujet de l'interprétation de spectres obtenus en STS. Nous avons clairement identifié les états de surface impliqués, et relevé que le pic en question est de symétrie dz2 − pz . Nous avons analysé la décroissance dans le vide des fonctions d'onde au-dessus de la surface Cr(001) et constaté que spectre observé par SP- STS provient essentiellement d'états de surface de symétrie pz et dz2 . Après avoir présenté le formalisme du transport électronique nous avons simulé un système idéal correspondant à une configuration SP-STM, à savoir deux surfaces Fe(001)-Cr(001) en vis-à-vis séparées par une couche de vide. Enfin nous présentons des calculs sur un système plus réaliste formé d'une pointe de Fer en contact tunnel avec une surface Cr(001). Le comportement général et les ordres de grandeurs des effets de TMR sont en bon accord avec l'expérience.

No description available.

The diploma thesis is divided into two main parts. The first part describes the production of chrome and cobalt tips for SP-STM with subsequent testing of chrome tips on the Fe-Ir system (111). Furthermore, the first results from the growth studies of niobium on iridium(111) are presented. In the second part is described in detail the experimental LT-STM microscope of the Faculty of Physical Engineering. The chapter deals with the development of the microscope and its testing on a HOPG sample under atmospheric and vacuum conditions. The chapter describes the biggest problems which were solved when the microscope was puting into operation state. The second part also introduces the design of a new vacuum transport system, which consists of a tip and sample transport pallet. At the end of the second part is described the testing of cooling systems for LT-STM and the design of their modifications.