Mehdi Moussavi

The lithium phthalocyanine radical: A low-dimensional molecular band semiconductor

Abstract The lithium phthalocyanine neutral π-radical molecular compound is depicted as a low-dimensional intrinsic band semiconductor whose spins are submitted to strong exchange interactions. It is suggested that the charge/spin carriers of this system ought to be analyzed in the frame of itinerant magnetism.

Weak field NMR and EPR spectrometers and magnetometers

Weak field magnetic resonance is usually limited by the signal-to-noise ratio, which decreases drastically with the field. The authors present high-resolution NMR (nuclear magnetic resonance) and ESR (electron spin resonance) sensors developed for Earth field magnetometry and spectrometry. For some of them the resonance signal is amplified by the Overhauser effect or laser optical pumping. The spectrometers and magnetometers are described. The features of magnetometers and many application fields are summarized. The performance of the low field spectrometers and their potential use in spin dynamic studies are also presented. >

An absolute Earth field ESR vectorial magnetometer

A principle for the construction of a vectorial Earth-field magnetometer is described. The electron spin resonance (ESR) in an organic radical is obtained with a polarization field much higher than the field to be measured which thus acts by its projection on this field. The pulsation of the polarization field between two opposite values gives the access to two error quantities used first to lock the magnetometer at the resonance and to construct a control loop to cancel the field to be measured. These two loops can be used jointly with the knowledge of the resonant frequency to calculate the absolute value of the measured field, independently of environmental parameters. >

Sol-Gel Derived Silica Layers for Low- k Dielectrics Applications

Porous silica exhibits attractive dielectric properties, which make it a potential candidate for use as insulator into interconnect structures. A new way of preparation of highly porous silica layers by the sol-gel route was investigated and is presented. The synthesis strategy was based on the use of common and low toxicity reagents and on the development of a simple process without gaseous ammonia post-treatment or supercritical drying step. Defect free layers were deposited by spin coating on 200 mm silicon wafers and characterized. Thin layers with a total porosity larger than 70% and an average pore size of 5 nm were produced. The dielectric constant measured under nitrogen flow on these highly porous layers is equal to ∼ 2.5, which can be compared to the value calculated from the measured porosity, ∼ 1.9. This difference is explained by the presence of water adsorbed on the hydrophilic surface of the unmodified silica.

High resolution low field ESR spectrometer

Abstract Organic conductors and semi-conductors are extensively studied usually by high field ESR Spectrometry. Higher resolution and choice criteria for materials used in earth-field magnetometers can be provided by low-field ESR experiments. In the spectrometer described, the sample is placed in a Bloch configuration where the rf measurement axis, the rf excitation axis and the dc field (1,8 MHZ) axis are orthogonal. The minimum detectable field in the detection coil is 10−14T. All the spectrometer is automatized. Typical results concerning three classes of known organic radicals which are good candidates for magnetometry are presented.