Katerina Soulantica

Cobalt Growth on the Tips of CdSe Nanorods

Best of both worlds: Reduction of an organometallic Co precursor on preformed CdSe nanorods yields two distinct semiconducting-magnetic heterostructures (see picture). The selective growth of Co on the tips of CdSe first gives nanosphere-nanorod dimers, which evolve into nanorod-nanorod structures. In the hybrid objects the magnetic properties of Co remain intact, while the luminescence properties of CdSe are affected but not completely quenched.

Synthesis and Self-Assembly of Monodisperse Indium Nanoparticles Prepared from the Organometallic Precursor [In(η5-C5H5)]

Spontaneous decomposition of [In(η5 -C5 H5 )] in the presence of poly(vinyl pyrrolidone) or trioctylphosphane oxide (TOPO) as a stabilizer gave monodisperse indium nanoparticles with a mean diameter of about 5-6 nm. In the case of TOPO, self-organization of the nanoparticles in two- and three-dimensional superlattices is observed.

Organometallic approach for the synthesis of nanostructures

Nanostructures are considered as chemical systems of high potential owing to their unusual properties at the interface of those of molecular species and bulk metals. Consequently, they are promising candidates for application in different domains such as catalysis, magnetism, medicine, opto-electronics or sensors. The control of the characteristics of nanostructures is a fundamental prerequisite if one envisages exploring their physical or chemical properties since they vary dramatically with size, shape and surface state. Thus, the development of efficient methods leading to reproducible nanostructures is presently one of the main objectives in the nanochemistry community. Although organometallic chemistry has been early involved, it arises only marginally in the field. Nevertheless, the concepts and techniques of organometallic chemistry appear to be well-adapted for the growth of well-controlled nanostructures. This will be discussed through recent advances in the synthesis of metal and metal oxide nanoparticles in terms of size dispersion, chemical composition, surface state, shape or organization, pointing out the role of ligands. Moreover their characterization at a molecular level and the development of their chemical/physical properties towards applications will be described. This review reflects more than 20 years of efforts of our team to achieve these goals.

Magnetism of single-crystalline Co nanorods

We report on the synthesis and preparation of oriented nanomaterials of single crystalline metallic Co nanorods of 6 nm in diameters and two different aspect ratios (7 and 15). They display optimized magnetic properties, with a spontaneous magnetization just below the bulk one, and large coercive fields (up to 6.5 kOe at 300 K) as a result of coherent switching (i.e., Stoner and Wohlfarth mechanism). We measured a strong effective anisotropy very close to the expected value resulting from the sum of shape and magnetocrystalline contributions.

The Big Impact of a Small Detail: Cobalt Nanocrystal Polymorphism as a Result of Precursor Addition Rate during Stock Solution Preparation

The control of nanocrystal structures at will is still a challenge, despite the recent progress of colloidal synthetic procedures. It is common knowledge that even small modifications of the reaction parameters during synthesis can alter the characteristics of the resulting nano-objects. In this work we report an unexpected factor which determines the structure of cobalt nanoparticles. Nanocrystals of distinctly different sizes and shapes have resulted from stock solutions containing exactly the same concentrations of [Co{N(SiMe(3))(2)}(2)(thf)], hexadecylamine, and lauric acid. The reduction reaction itself has been performed under identical conditions. In an effort to explain these differences and to analyze the reaction components and any molecular intermediates, we have discovered that the rate at which the cobalt precursor is added to the ligand solution during the stock solution preparation at room temperature becomes determinant by triggering off a nonanticipated side reaction which consumes part of the lauric acid, the main stabilizing ligand, transforming it to a silyl ester. Thus, an innocent mixing, apparently not related to the main reaction which produces the nanoparticles, becomes the parameter which in fine defines nanocrystal characteristics. This side reaction affects in a similar way the morphology of iron nanoparticles prepared from an analogous iron precursor and the same long chain stabilizing ligands. Side reactions are potentially operational in a great number of systems yielding nanocrystals, despite the fact that they are very rarely mentioned in the literature.

Solution Epitaxial Growth of Cobalt Nanowires on Crystalline Substrates for Data Storage Densities beyond 1 Tbit/in2

The implementation of nano-objects in numerous emerging applications often demands their integration in macroscopic devices. Here we present the bottom-up epitaxial solution growth of high-density arrays of vertical 5 nm diameter single-crystalline metallic cobalt nanowires on wafer-scale crystalline metal surfaces. The nanowires form regular hexagonal arrays on unpatterned metallic films. These hybrid heterostructures present an important perpendicular magnetic anisotropy and pave the way to a high density magnetic recording device, with capacities above 10 Terabits/in(2). This method bypasses the need of assembling and orientating free colloidal nanocrystals on surfaces. Its generalization to other materials opens new perspectives toward many applications.

Organometallic precursors of nano-objects, a critical view

The synthesis of nanoparticles has experienced a huge development over the past 20 years. However, this development has remained relatively limited to a few classes of nanomaterials such as iron oxides, semi-conducting oxides, plasmonic nanoparticles (essentially Au) and quantum dots. In these cases, a physical chemistry approach and standard recipes allow a good control of the size and shape of the resulting nano-objects. However, organometallic precursors have emerged as an important class allowing the preparation of a large variety of nano-objects, concerning a large number of elements and displaying a clean and controllable surface and therefore good physical and chemical properties. This perspective article is mostly devoted to the research efforts carried out by our group on the search for new classes of precursors and on the importance of knowing their exact structure and the molecular chemistry involved prior to the fabrication of the nano-objects.

Liquid crystalline magnetic materials

This work deals with the synthesis of a new magnetic liquid crystalline material: a side chain liquid crystal silicone, doped with magnetic cobalt nanorods. This new material presents very promising magnetic properties, discussed in terms of the influence of the lateral liquid crystal groups.

Indium and indium-oxide nanoparticle or nanorod formation within functionalised ordered mesoporous silica

Organized mesoporous silica materials containing phosphonate groups have been used for controlling the growth of indium(0) nanoparticles or nanorods, which are converted to indium-oxide without modification of their size and shape.

Homogeneous Biosensing Based on Magnetic Particle Labels.

The growing availability of biomarker panels for molecular diagnostics is leading to an increasing need for fast and sensitive biosensing technologies that are applicable to point-of-care testing. In that regard, homogeneous measurement principles are especially relevant as they usually do not require extensive sample preparation procedures, thus reducing the total analysis time and maximizing ease-of-use. In this review, we focus on homogeneous biosensors for the in vitro detection of biomarkers. Within this broad range of biosensors, we concentrate on methods that apply magnetic particle labels. The advantage of such methods lies in the added possibility to manipulate the particle labels by applied magnetic fields, which can be exploited, for example, to decrease incubation times or to enhance the signal-to-noise-ratio of the measurement signal by applying frequency-selective detection. In our review, we discriminate the corresponding methods based on the nature of the acquired measurement signal, which can either be based on magnetic or optical detection. The underlying measurement principles of the different techniques are discussed, and biosensing examples for all techniques are reported, thereby demonstrating the broad applicability of homogeneous in vitro biosensing based on magnetic particle label actuation.