Catastrophic degradation of the interface of epitaxial silicon carbide on silicon at high temperatures

© 2016 Author(s). Epitaxial cubic silicon carbide on silicon is of high potential technological relevance for the integration of a wide range of applications and materials with silicon technologies, such as micro electro mechanical systems, wide-bandgap electronics, and graphene. The hetero-epitaxial system engenders mechanical stresses at least up to a GPa, pressures making it extremely challenging to maintain the integrity of the silicon carbide/silicon interface. In this work, we investigate the stability of said interface and we find that high temperature annealing leads to a loss of integrity. High-resolution transmission electron microscopy analysis shows a morphologically degraded SiC/Si interface, while mechanical stress measurements indicate considerable relaxation of the interfacial stress. From an electrical point of view, the diode behaviour of the initial p-Si/n-SiC junction is catastrophically lost due to considerable inter-diffusion of atoms and charges across the interface upon annealing. Temperature dependent transport measurements confirm a severe electrical shorting of the epitaxial silicon carbide to the underlying substrate, indicating vast predominance of the silicon carriers in lateral transport above 25 K. This finding has crucial consequences on the integration of epitaxial silicon carbide on silicon and its potential applications

Color Match of Composite Resin and Remaining Tooth Structure over a Period of 28 Days Using Spectrophotometer—A Randomized Clinical Trial

SUMMARY OBJECTIVES The tooth and the composite restoration can undergo a change in color after the restorative procedure over time. The purpose of this randomized clinical trial was to evaluate the color difference (ΔE) of two types of composite resins and remaining tooth structure over a period of 28 days. METHODS AND MATERIALS A total of 40 teeth in 30 patients with Class IV caries or EllisClass II fracture in maxillary incisors were randomized into two groups based on the type of composite resin used for restoration: IPS Empress (n=20 teeth) and Filtek Z250 (n=20 teeth). Shade selection was done using a spectrophotometer. Restorations were performed using an anatomical layering technique, and finishing and polishing was done after 48 hours. Baseline spectrophotometer color values for the remaining tooth structure were measured before isolation and for composite restorations, 10 minutes after light cure. Further color evaluations using a spectrophotometer for the remaining tooth structure and composite restorations were done at 48 hours (both before and immediately after finishing and polishing), 7days, 14 days, and 28 days, and color difference (ΔE) from baseline values for remaining tooth structure and restorations and ΔE between remaining tooth structure and restorations were calculated. Descriptive statistics including mean, standard deviation, and frequencies were computed. Mann–Whitney U test was done to compare spectrophotometer values. RESULTS There was a significant reduction in mean color difference (ΔE) from baseline values for both tooth (p&amp;lt;0.05) and composite restoration (p&amp;lt;0.05) at all evaluation periods in both groups. Filtek Z250 showed significantly lower mean ΔE between the tooth and the composite resin restoration than IPS Empress at 48 hours (before and after finishing and polishing), 7 days and 14 days (p&amp;lt;0.05). At the 28 day recall, mean ΔE value of IPS Empress restorations to tooth structure was 3.5, while the mean ΔE value of Filtek Z250 restorations to tooth structure was 3.6, which was not statistically different (p&amp;gt;0.05). CONCLUSION The remaining tooth structure as well as the composite restorations showed color changes at all evaluation periods, compared to baseline values in both the composite resin groups. Filtek Z250 exhibited less ΔE with remaining tooth structure at 48 hours, 7 days, and 14 days, when compared to IPS Empress. The composite restorations of both the groups reached clinically acceptable color match (mean ΔE&amp;lt;3.7) with the remaining tooth structure 28 days after the procedure. </jats:sec

Preexisting Dentinal Microcracks in Nonendodontically Treated Teeth: An Ex Vivo Micro–computed Tomographic Analysis

Introduction: This study evaluated the prevalence, location, and pattern of preexisting dentinal microcracks in roots of extracted teeth without endodontic treatment in patients from 2 age groups using micro-computed tomographic imaging. Methods: Six hundred thirty-three nonendodontically treated teeth extracted using an atraumatic procedure because of reasons unrelated to this study were collected and divided based on the patient age. Teeth were scanned with micro-computed tomographic imaging (resolution of 26.7 μm) to examine the presence of preexisting dentinal microcracks in roots. The characteristic features of preexisting dentinal microcracks determined were location, extent, length, and coronoapical distribution. Chi-square bivariate analysis was performed to assess the association between various parameters. Results: Forty-five of 633 nonendodontically treated teeth exhibited preexisting microcracks in roots with a prevalence of 7.1%. The prevalence of preexisting microcracks was found to be 8.3% in older patients (40-70 years) compared with 3.7% in younger patients (20-39 years) (P < .050). A significant association was found between the preexisting microcracks in mandibular teeth (10.3%) when compared with maxillary teeth (2.9%) (P < .001). All preexisting microcracks were located mesiodistally; 66% occurred in the cervical and middle thirds of root. Only 33% of the preexisting microcracks were complete in nature, showing canal involvement. Complete dentinal microcracks exhibited a mean length of 6.9 mm, whereas incomplete cracks had a mean length of 3.75 mm (P < .001). Conclusions: Preexisting dentinal microcracks in roots of nonendodontically treated teeth occurred more often in older patients (40-70 years) in the mesiodistal direction. They were predominantly found in the cervical and middle thirds of root and were more likely to be incomplete in nature

Deep Eutectic Solvents for Innovative Pharmaceutical Formulations

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