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In this paper, we use three-dimensional kinetic Monte Carlo simulations on superlattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC step-bunched substrates with miscuts towards the <11-20> and <1-100> directions. We find that the preferential 3C conversion observed on <1-100> misoriented substrates could be due to a different step-to-island interaction which enhances island stability and expansion in this specific direction. For this reason 3-4 degrees off step-bunched 6H substrates with miscut towards the <1-100> direction should be the best choice for the stable and reproducible hetero-polytypical growth of high quality cubic epitaxial films. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Micro- and nano-electromechanical systems (MEMS and NEMS) fabricated in 3 C-SiC are receiving particular attention thanks to the material physical properties: its wide band gap (2.3 eV), its ability to operate at high temperatures, its mechanical strength and its inertness to the exposure in corrosive environments. However, high residual stress (which is normally generated during the hetero-epitaxial growth process) makes the use of 3 C-SiC in Si-based MEMS fabrication techniques very limited leading to a failure of micro-machined/sensor structures. In this paper, micro-Raman characterizations and finite-element modeling (FEM) of microstructures realized on poly and single-crystal (100) 3 C-SiC/Si films are performed. Transverse optical (TO) Raman mode analysis reveals the stress relaxation on the free standing structure (796.5 cm−1) respect to the stressed unreleased region (795.7 cm−1). Also, microstructures as cantilever, bridge and planar rotating probe show an intense stress field located around the undercut region. Here, the TO Raman mode undergoes an intense shift, up to 2 cm−1, ascribed to the modification of the Raman stress tensor. Indeed, the generalized axial regime, described by diagonal components of the Raman stress tensor, cannot be applied in this region. Raman maps analysis and FEM simulations show the 'activation' of the shear stress, i.e. non-diagonal components of the stress tensor. The stress-Raman modes shift correlation, in the case of fully non-diagonal stress tensors, has been investigated. The aim of future works will be to minimize the stress field generation and the defects density within the epitaxial layer. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Chemical vapor deposition in the low pressure regime of a high quality 3C-SiC film on silicon (100)-oriented substrates was carried out using silane (SiH4), propane (C3 H8), and hydrogen (H2) as the silicon supply, carbon supply, and gas carrier, respectively. The resulting bow in the freestanding cantilever structures was evaluated by an optical profilometer, and the residual gradient stress (σ1) in the films was calculated to be approximately between 15 and 20 MPa, which is significantly lower than the previously reported 3C-S1C on Si films. Finite element simulations of the stress field in the cantilever have been carried out to separate the uniform contribution (σ1), related to the SiC/Si interface, from the gradient one (σ0), related to the defects present in the SiC epilayer. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic accumulation chamber methods have been extensively used to estimate the total output of CO2 released from active volcanic area. In order to asses the performance and reliability of a closed dynamic system several tests were carried out with different soil permeabilities and soil CO2 fluxes. A special device was used to create a constant one-dimensional CO2 flux through a soil column with a known permeability. Three permeabilities were investigated, ranging between 3.6×10−2 and 3.5×10 μm2, as were several CO2 fluxes (ranging between 1.1×10−6 and 6.3×10−5 kg m−2 s−1). The results highlight that the accuracy of soil CO2 flux measurements strictly depends on the soil gas permeability and the soil CO2 flux regimen. Generally chamber measurements underestimate CO2 fluxes at low soil permeability and low soil CO2 fluxes, whereas appreciable overestimations occur for high permeability soil, especially for high soil CO2 fluxes. Other tests carried out with different settings for the measurement device, such as the chamber volume and the flux of the pump used to recirculate air through the chamber and the gas analyzer (recirculation flux), revealed a strong dependence of the closed dynamic chamber measurements on the recirculation flux. Low recirculation fluxes (0.2–0.4 l min−1) decreased the performance of the measurement system, causing underestimations of the actual soil CO2 flux, whereas higher values (0.6–1.0 l min−1) resulted in overestimations, especially for elevated soil CO2 fluxes. An empirical equation was deduced to allow accumulation chamber fluxes to be calculated very accurately based on soil gas permeabilities measured in the field. [Copyright &y& Elsevier]

Abstract: A physical model based on the advective–diffusion theory was developed in order to describe the mixing between a deep gas source and the atmosphere. The model was used to predict the isotopic fractionation of carbon in soil CO2. Gas samples were collected at different depths in areas characterized by different geological settings and CO2 fluxes. The relative theoretical and experimental isotopic profiles were compared and a good agreement was found. These profiles show how the isotopic composition of CO2 changes through the upper few decimeters of soil and how the amount of the isotopic fractionation is strongly influenced by soil CO2 flux. Finally, the model was used to derive the carbon isotopic composition of unfractioned deep CO2 source for all the investigated sites. [Copyright &y& Elsevier]

Abstract Purpose Field-in-Field (FIF) is an advanced radiation therapy planning technique [1]. We studied the effectiveness of this technique for breast radiotherapy, with respect to 3D standard technique, in terms of dosimetric benefits and treatment reproducibility. PTV volume dependence on both techniques was also investigated. Methods Two endpoints were analysed. For the first endpoint, dosimetric benefits were studied on 230 breast cancer patients from Macerata hospital who received whole breast radiotherapy with either 3D standard or FIF technique. The second endpoint was a reproducibility study: 28 patients from Macerata and Rieti hospitals were included. For each patient, a 3D standard plan and a FIF plan were prepared on the first simulation CT. All patients underwent other two CT scans on which the original plans were recalculated. Comparisons between techniques were made using V95%, D95%, Dmean, Dmax, HI and CI. Results The FIF technique significantly reduced the PTV Dmax, increased Dmean, allowed better dose coverage and more homogenous dose distribution (Fig. 1). When the irradiated OAR values were compared, the results were slightly higher for the FIF technique, but still within the tolerance limits (p < 0.05). Dosimetric parameters are not influenced by PTV size, for both techniques. Differences between plans calculated on the repeated CT scans (Δ 1/2 and Δ 1/3) were not statistically significant between the two techniques (p < 0.05), also for large breasted patients ( V PTV > 1000 cc) (Table 1). Conclusions The FIF technique provided better dose distribution in terms of coverage and homogeneity, also for larger PTVs, both techniques respected OAR dose-volume limits and FIF reproducibility was equivalent to 3D standard technique reproducibility. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a tomograph for single photon emission imaging (SPECT) of the breast for the detection of small size tumors. The SPECT is mounted on a ring that is rotating around the breast with the patient in prone position. The breast will be imaged by two opposing detector heads of approximately each, with a field of view about 13cm wide. Each head is made up of one pixilated NaI crystal matrix coupled to three Hamamatsu H8500 PMTs. A “general purpose” lead collimator is positioned in front of the crystal. Detailed simulations have been made for the optimization and the evaluation of the detector performances. Monte Carlo results indicate that tumors of 8mm diameter are detectable with a tumor/background uptake ratio of 5:1. The experimental characterization of the detector head is presented. The rotating ring is now being assembled. [Copyright &y& Elsevier]