Growth and characterizations of nanostructured tungsten oxides

Tungsten oxide (WO3) as nanostructured thin film is an attractive compound to be used for sensors applications. We report on WO3 nanostructured thin films deposited by radio-frequency plasma assisted laser ablation technique. A tungsten oxide ceramic target was irradiated at 193 nm wavelength; the depositions have been carried out in a gas mixture of oxygen and argon on heated substrates (corning glass and silicon) up to 600°C. The gas pressure varied between 1 Pa and 10 Pa. The influence of the substrate temperature, gas pressure and RF power on properties of the obtained nanostructures was investigated by Atomic Force Microscopy, Raman spectroscopy, Secondary Ion Mass Spectrometry and spectro-ellipsometry

Diamond detectors with electrodes graphitized by means of laser

In the last years there has been an increase of interest in diamond devices because of the promising applications in different field, such as high-energy physics, radiotherapy and biochemical applications. In particular, a new frontier is represented by the realization of full-carbon detectors characterized by graphite electrodes, which give to the devices considerable advantages like high radiation hardness, perfect mechanical adhesion and good charge collection properties. In this paper the manufacturing of full-carbon devices and their detection performances are illustrated and compared to a reference diamond detector characterized by traditional electrodes

PHASE STABILITY AND MARTENSITIC TRANSFORMATION ONSET IN TRANSITION METAL AND NOBLE METAL ß -PHASE ALLOYS

A unified approach, able to take into account the martensitic phase transition onset in transition metal and noble metal ß-phase alloys exhibiting shape-memory effect, is presented. The central concept of the interpretative model is the variation of a phenomenological parameter, the "Valence Electrons Localization Degree" (VELD), correlated with the changes of the electron density of states near the Fermi energy. The effects of the composition variation of the alloy allow for qualifying the substituent elements as electron donors or acceptors. Such a behaviour is tested by examining the transition temperature trends. The results are in very good agreement with the available experimental data

Control of cluster synthesis in nano-glassy carbon films

Carbon films were prepared by pulsed laser deposition (PLD), changing buffer gas nature and pressure and laser power density. Nanometer- sized cluster assembled (CA) films, resulting from direct aggregation of carbon clusters in the ablation plume, were obtained. Visible Raman spectroscopy shows that all films are trigonally co-ordinated and structurally disordered, with a dependence of the degree of disorder on the deposition parameters. The microstructure and morphology of the films were studied in a complementary way by scanning electron microscopy (SEM) both in plane and in cross-section, and by atomic force microscopy (AFM). Different growth modes are found in the deposited CA films, depending on the interplay of laser fluence and nature-pressure of the buffer gas. Threshold fluences of increasing value separate dense columnar growth from sponge like morphology, from an open dendritic structure. AFM pictures show that our glass-like carbon films consist of agglomerates of nanometer-sized clusters. Cluster formation in the plume is modeled, allowing to estimate the average number of carbon atoms per cluster. The calculated size of the clusters depends mainly on ambient gas pressure. Cluster sizes obtained by model predictions agree with those directly observed by transmission electron microscopy (TEM) imaging and with the deduced film coherence length from Raman spectroscopy conducted herein

Propagation of laser generated plasmas through inert gases

AbstractA fast photo imaging technique has been used to characterize the expansion dynamics of a laser generated silver plasma propagating through background inert gases (He and Ar) at different pressures. The time evolution of the expanding plasma was investigated in the framework of currently available phenomenological models. Mixed-propagation model gives an accurate description of the initial and late plasma expansion stages in Ar when proper input parameters are taken into account. In He, only the initial quasi-linear expansion and shock wave formation were observed along the space available to plasma motion