This paper reports the observation of bipolar, space-charge-perturbed transport in colloidal dispersions using an experimental technique that time-resolves electrophoresis in nonpolar colloidal systems. Unlike existing methods for studying electrophoresis, this technique can be applied to dispersions of diverse types and concentrations over a wide range of electric fields, including the space-charge-perturbed conditions often encountered in practical applications. The phenomenon is investigated as a special case of dielectric relaxation in a leaky capacitor connected in series to a perfect one. Using the first principle charge transport theory, such dielectric relaxation, occurring under the non-Ohmic supply and space-charge-perturbed transport conditions, is shown to differ from that expected by the conventional equivalent-circuit treatment. The combined theoretical analysis and the experimental technique provides a means for independently determining the densities and mobilities of charged species in such systems. Using a liquid developer for electrography as a prototype system, results are presented that illustrate the power of the technique as a new tool to provide new insights into the generic transport and generation mechanisms of charged species in colloidal systems.
The structural properties of silicon oxynitride films grown in a N 2 O environment at temperatures higher than 900°C and for use as gate dielectrics in vertically diffused power metal oxide semiconductor field effect transistor ͑PowerVDMOS͒ technologies have been studied by means of X-ray photoelectron spectroscopy. The progressive modifications of the bonding environments upon reaching the oxynitride-silicon interface have been analyzed as well as of the relation between these modifications and the selected oxynitridation process. The results show that the chemistry of the oxynitride layer is a rather complex one, and it significantly and progressively changes by moving toward the silicon interface, in a way strongly affected by the growth process. In particular, the medium thermal budget processes ͑950°C, 20-60 min͒ favor the formation of a relatively uniform distribution of the single oxidized O-N-Si 2 bonds both at the interface and throughout its immediate backstage. Such findings can help in assessing the role played by the nitridation process in the quality and reliability performances of the final device.In the last few years, silicon oxynitride thin films have been proposed as an alternative to SiO 2 as a thin gate dielectric for microelectronics applications. As the scale of integration increases and the thickness of the dielectric is reduced, the SiO 2 dielectric layer properties get less and less sufficient to reliably withstand the increasing electric field. As a consequence, the device degradation due to the high leakage currents and even gate rupture shows up at a higher rate. Silicon oxynitrides ͑SiO x N y ͒ are materials with a higher dielectric constant and, in thin layer form, exhibit reduced susceptibility to interface state generation with respect to SiO 2 , higher timeto-breakdown values and reliability, improved I-V and C-V characteristics. 1-3 Therefore, silicon oxynitride could eventually replace thin gate dielectrics characterized by a smaller thickness but an equal capacitance, thus assuring an improved robustness of the device. In this context, several analyses have been performed to characterize SiO x N y film quality in terms of both device performance and processing. 4,5 A clear understanding of the structure and chemical composition of the oxynitride film could be valuable help in assessing its quality as a gate layer in power devices. Nevertheless, in many works found in the literature, the only relevant parameter taken into account is the overall nitrogen content. In the attempt to disclose the role of the oxynitride structure in the electrical defectivity and reliability, it is of fundamental importance to know the nitrogen bonding configurations present at the silicon substrate interface and their relation with the selected oxynitridation process. In this respect, X-ray photoemission spectroscopy ͑XPS͒ is a powerful tool to perform a compositional analysis and also to investigate the relative bonding arrangements of silicon, oxygen, and nitrogen atoms. The aim of the present wo...
The presence of carbon nanostructures in evaporated carbon thin films has been evidenced by Raman spectroscopy measurements. The films were grown by means of a conventional electron beam evaporation equipment, used to sublimate a graphite target and by varying the substrate temperature T s from room temperature (RT) up to 830°C. The effect of predeposited very thin cobalt films was also investigated. The Raman spectra of the carbon thin films are characterized by two bands near 1550 and 1400 cm −1 due to E 2g stretching mode of graphite (G band) and to the double resonance Raman scattering, responsible for the observation of the defect induced-D mode in graphite (D band). In particular, at 830°C the characteristic features of a nanometric carbon structure are evident: the A 1g radial breathing mode (RBM) at 150-300 cm −1 and the first overtone of the D peak at 2450-2650 cm −1 . The formation, at a specific temperature, of Co particles of size below 100 nm has been identified as the main factor in determining the carbon nanostructures' growth.
The structural properties of silicon oxynitride films used at the gate dielectrics interface in Power vertically diffused metal oxide semiconductor technologies have been studied by means of X-ray photoelectron spectroscopy. An overall picture of the interface chemistry evolution as a function of the growth parameters in relation to the effects of the postgrowth reoxidation process is reported. The films were grown in an N 2 O environment at temperatures higher than 900°C and subsequently reoxidized at 1000°C in a dry oxygen environment. The results show that the chemistry of the oxynitride layer progressively changes by moving toward the silicon interface and, after the reoxidation process, the interface chemical configurations are strongly affected by the initial specific oxynitridation process. In particular, the application of the final reoxidation plays a significative role in determining the distribution of the oxidized O-N-Si 2 bonds near the interface.
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